design study of grain dryer

C.O.E.&T.,Akola

Design & Study of Grain Dryer

CHAPTER - I

INTRODUCTIONI) HISTORY & IMPORTANCE OF DRYING

India produces about 150 million tonnes of food grains per year. The major

components of production are 47 million tonnes of wheat, 64 million tonnes of rice, and 13

million tonnes of pulses (Anon. 1987). Due to technological advances in agriculture and the

introduction of high-yielding varieties, this may increase. From this production, an average

10% is lost during postharvest operations between the field and consume. This means that

about 15 million tonnes of food grain, valued at about $A240 million (Indian Rupees 10,800

million) goes to waste. The major share of the loss occurs during storage of surplus stock.

Among the various causes of losses, the most important one is improper drying before

storage.

The preservation of agricultural produce by drying is a long-established

technique. Sun drying in the open, on mud-plastered or concrete floors, is the conventional

method of drying grain and also cash crops like chillies, and plantation and horticultural

crops. The drying time required in the open sun for these crops ranges from 5 to 45 days

depending upon the crop to be dried. Unfavourable weather conditions are likely to occur

during the drying period and degradation in quality of the final produce therefore becomes

unavoidable.

It is well-known that deterioration in quality caused by improper drying cannot

be eliminated until improved drying systems based on mechanical dryers have been adopted.

However, for many reasons, these systems have not been adopted. The main reason that is

encountered is a lack of organizational or government incentive to the farmer to deliver a

quality product that might command a premium price. This results in not only a negative

attitude, but also leads to the overall quality of the product gathered at market points being

alarmingly poor.

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A second important reason for not using dryers is their high initial costs. Most

of the commercially available dryers are designed to suit the needs of the processing industry

and their output capacity is therefore far above the needs of individuals, or even of farmer

groups. An awareness of availability of dryers and of their use and advantages in drying food

grain for better storage and marketing is lacking among crop growers. The main reason for

this is inadequate extension programs. So far, extension agencies have concentrated on

increasing production. The time has now come to see that grain saved is equivalent to grain

produced. High technology has led to production targets being achieved, but much less

attention has been given to minimising losses, which have remained constant since the

beginning of the 'Green Revolution'. Annual postproduction losses by crop in India, expressed

as a percentage of total production, are estimated to be as follows: wheat, 8%; paddy, 11%;

pulses, 9.5%; and all food grains, 9.3%.

Commercial use of dryers

Dryers are used extensively in grain processing industries such as rice milling,

pulse milling, and oil extraction. Here the need for dryers has been realised not only for

proper storage of stock but also for timeliness of subsequent operations where wetting of

grain and redrying are involved.

In the case of the rice milling industry, parboiling of rice is a common practice.

The population of the coastal belt of the country consumes parboiled rice and about 70% of

production is processed in this manner. The paddy is soaked in water for variable lengths of

time depending on the process used and is then steaming.

High moisture content (m.c.) paddy is dried to 12-14% m.c. for milling. There

are about 100 000 rice mills with a total installed capacity of about 40 000 tonnes of paddy

per hour. About 30000 dryers of 1-2 t/h drying capacity are in use in the industry. The most

commonly used dryer is the LSU type in which air is heated for drying by burning rice hulls.

The steam requirement for drying is 21.3% of the total steam produced in the boiler, which

consumes about 4% of the total power required by the mill. In this type of dryer, the grain is

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tempered for 30 minutes after every hour of drying so to equilibrate the moisture and avoid

stress cracking in further milling operations.

Dryers are also used in the pulse milling industry. Here both LSU-type and

flat-bed perforated-floor dryers are well, ranging in capacity from 1-4 t/h. There are about

4000 pulse mills in India having an average processing capacity of 10-20 t/day. Dryers are

required in industry for the following reasons:

To dry the stock purchased from market before storing it; and

To dry the grain which has become wet during processing.

In the LSU-type dryer, steam is used as the heating source, while in the flat-

bed dryers, light diesel oil is used, fuel consumption being 7-12 lt/h One such commercial

dryer. It consists of a drying tray or platform, an oil-fired burner, and an air blower. The cost

of a 3 t/h dryer is about SA13 500.

Use of dryers at farmer level

About 70% of total grain production in India is retained at farmer level: only

30% is sold on the open market. This means that a sizeable quantity of about 105 million

tonnes is kept by farmers. The losses here, though perhaps not felt by individuals, on a

collective basis have a substantial impact on the country. It is therefore essential that drying

technology be disseminated to this group which is a major custodian of the nation's grain.

To promote the use of dryers in rural areas, the concept of a community drying-cum

storage system was put forward by T.P. Ojha in 1984. He suggested that changes in ecological

balances and the introduction of high- yielding varieties of field crops necessitated the use of

mechanical dryers and other devices to protect the food grains from spoilage due to untimely

rains. If rain-soaked food grains are not dried properly, farmers have to sell their excess stocks

at low prices to meet urgent financial needs. A community drying-cum-storage centre would

therefore serve them well by way of protecting the grain from spoilage and also by advancing

temporary loans on their grain deposits. As soon as grain prices stabilise, stocks can be sold

and payments can be made to the farmers after deducting dues such as rental and service

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charges, loans paid, and interest on advances. Such a system would no doubt benefit farmers.

They would not be required to make forced sales of their produce and, as a result, storage

losses would be minimised.

For such complexes, selection of a dryer of the correct design is very

important. The large capacity dryers used in grain-processing industries are not economical or

feasible for most farmer groups. In India, the average village has a population of about 1000

and the small amount of surplus grain available for drying at this level suits dryers of 2-4

t/day capacity operating for 60 days per year. In India, many research organizations have

developed, or are currently developing dryers for village groups, but so far with little success.

The main considerations for selection of a grain dryer suited to this level are:

The dryer should be of a size that matches the amount of grain available in a village or

a cluster of villages;

The dryer's cost should be within the reach of users;

It must be simple in construction and operation and easily understandable to users;

The dryer should be simple in design so that it is easy for local artisans to repair, and

The dryer should be suitable for drying a range of crops.

Specific Problems

Why there is a tremendous need of dryers ?

To Farmers :

In year 2002 near about 80% loss of crops like black gram, green gram etc. due to

heavy rain at the time of harvesting. If there is a facility of dryers in every village may be at

Grampanchayat level, this heavy loss may be eliminated.

Sorghum crop :- After total maturity period of sorghum crop. is not harvested for near about

one month due to presence of moisture. Normally the problem faced by farmer is that rain

comes during this period and sorghum is affected, which results in bad quality as it turns

black. Due to this reason, the cost in market is reduced. This loss can be recovered if the

dryers are used at this stage.

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After drying farmers can store the grains for a long period and it will send in

market at the highest rate.

To Dal Mill:

In the Dal mill the pulses are dried at different stages. The drying is done on the

platform by using solar energy, which is time consuming and large manpower required. So to

avoid this the dryers are used in the Dal mills.

To Food Corporation of India (FCI)

In foreign countries the grains are stored in Silos where there is on line drying of

grains but in India grains are stored in bags which is unhealthy. So, by applying dryers, the

problems of storage should be overcome.

To Industries

Different types of dryers are used in following industries

1) Textile industries, paper mills.

2) Plastic and polymer industry.

3) Chemical industries.

4) Food storage plants.

II) CHEMICAL COMPOSITION OF GRAIN:-

Grain is a living biological product, which germinates and respires also. The

grain is composed of both organic and inorganic substances, such as carbohydrates, proteins,

vitamins, fats, water, mineral salts and enzymes.

III) EFFECT OF TEMPERATURE ON QUALITY OF GRAIN.

Proteins: - At temperature above 500C denaturation and even coagulation of proteins takes

place. As a result, the water absorbing capacity of proteins and their capacity for swelling

decreases.

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Starch: - At temperature above 700C and especially in presence of high moisture in the grain,

gelatinisation and partial caramelisation of sugars with the formation of caramel may take

place which causes deterioration in colour of the product.

Fats: - At temperature above 700C, fats may also undergo a partial decomposition resulting in

an increase of acid numbers.

Vitamins: - The heat sensitive B - vitamins present in the germ and aleurone layer are

destroyed at high temperature.

IV) PHYSICAL PROPERTIES: -

The knowledge of physical properties such as shape, size, volume, surface

area, density, porosity, colour etc. of different grain is necessary for design of various storing

and drying systems.

Porosity: - It is the percentage of volume of inter grain space to the total volume of grain

bulk.

Sphericity: - Sphericity is the ratio of surface area of sphere having same volume as that of

particle to the surface area of particle.

Coefficient of friction: - The coefficient of friction between granular materials is equal to the

tangent of the angle of internal friction and depends upon grain shape, surface characteristics.

Angle of repose: - Angle of repose is the angle between base and slope of cone formed on a

free vertical fall of the grain mass to a horizontal plane.

V) THERMAL PROPERTIES: -

The raw foods are subjected to various types of thermal treatment namely,

heating, cooling, drying etc. for processing. The change of temperature depends on the

thermal properties of the product. Therefore, knowledge of thermal properties namely,

specific heat, thermal conductivity, thermal diffusivity is essential.

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Resistance of grain bed to air flow:

In the design of blowers for grain dryers, it is necessary to know resistance

exerted by grain bed to the air current blown through it. The resistance is dependent upon i)

bed thickness ii) air velocity iii) orientation of the grains and iv) type of grain.

VI) CHANGES IN STORED PRODUCTS -

There are many changes, which occurs to a product during transportation,

handling, storage and preserving.

Chemical Changes - The effect of canning upon the minerals, proteins and vitamins of

various food products is a large scientific field in itself. In stored hay and grains, changes

occur in fat acidity, enzymes, color and vitamins. These changes are influenced greatly by

moisture content and temperature, which are often used as a means of indicating the quality of

stored products.

Respiration and Heating: - In hay, grains, fruit and vegetable products respiration or

breathing continues after storage. Heat is produced by respiration process. The quantity of

heat produced is greatly influenced by moisture content and temperature of product. Loss of

viability or germination often occurs after heating. Movement of air through the products

helps to prevent excessive temperature by removing heat and excess moisture.

Microorganism: - Changes occurs in the amount of mold and yeast growth in stored product.

The changes largely depend upon temperature and moisture.

Insects and Rodents: - The population of insects is affected by moisture and temperature of

environment of stored product. Ventilation presents a method of controlling growth of insects,

but after they get out of control, chemical means are commonly used.

VII) LOSSES OF FARM CROPS: -

The losses of farm crops can be used to indicate the importance of proper

harvesting, storage and drying.

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Table 1.1 : Estimated loss of production during harvest and storage.

Product Harvesting % Storage %

Wheat, oat, rice, barley 5% 4.5%

Corn 4% 6%

Cotton 2.5% 0.25%

Potato 7% 8%

Soyabean 5% -

Prevention: _

Maximum loss occurs because of an accumulation of moisture in grain, even

though dry when placed in the storage. Two terms are used for preservation of grain through

moisture control, drying and aeration.

Drying is the procedure used to remove excess moisture from the grain to

reduce the moisture to a level acceptable for safe storage or for commercial sale. Drying may

be accomplished by using either heated or unheated air.

Aeration refers to moving a small amount of air through the grain to cool and

ventilate the grain at frequent intervals. The reverse operation, turning refers to moving the

grain through the air by transferring the grain from one bin to another.

* * *

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CHAPTER - II

THEORY OF GRAIN DRYINGGenerally the term refers to the removal of relatively small amount of moisture

from a solid or nearly solid material by evaporation. Therefore, drying involves both heat and

mass transfer operations simultaneously. In convective drying the heat required for

evaporating moisture from the drying product is supplied by the external drying medium,

usually air. Because of the basic difference in the characteristics of grains in thin layer and

deep bed, the whole grain drying process is divided in to thin layer drying and deep bed

drying.

I) MOISTURE CONTENT: -Usually the moisture content of a substance is expressed in percentage by

weight on wet basis. But the moisture content on dry basis is more simple to use in

calculation, as the quantity of moisture at any time is directly proportional to the moisture

content on dry basis.

The moisture content, m per, wet basis -

100WdWm

Wmm ×

+=

The moisture content, M, dry basis percent

100xm100

m100

Wd

WmM

−=×=

Where Wm = weight of moisture.

Wd = weight of bone dry material.

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TABLE 2.1 Approximate moisture content for safe storage % (w.b.)

CROPFOR SAFE STORAGE

FOR ONE YEAR FOR TWO YEARCorn 13 11

Wheat 13-14 11-12Barley 13 11

Sorghum 13 10-11Pea beans 17 -

Rice 13 -Soyabeans 13 10

II) EMC: - Most of agricultural products, specially the food grains absorb moisture from

environment or loose moisture. At a particular condition the moisture content of grain

depends upon the temperature and relative humidity of environment. If the vapour pressure of

water present in grains is more than the vapour pressure of water vapours in the air, the water

present in grain vaporises and diffuses in the atmosphere. Alternatively, if the vapour pressure

of water present in grain is less than the atmospheric vapour pressure, grain will absorb

moisture from atmosphere. This property of gaining or loosing of moisture as per the

atmosphere condition is known as hygroscopicity.

The moisture content attained by a grain with respect to a set of atmosphereic

temperature and relative humidity is called the EMC. In such condition, the grain moisture is

in equilibrium with surrounding air.

Methods for determination of EMC. There are two methods for determination

of EMC -

i) Static Method: -

In the static method, the grain is allowed to come to equilibrium with the

surrounding still air without any agitation. This method is time consuming; at high relative

humidities mould growth in the grain may take place before equilibrium is reached.

ii) Dynamic Method: -

In the dynamic method, the air is generally mechanically moved. The dynamic

method is faster and is thus preferred. The EMC is to be determined under constant relative

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humidity and temperature conditions of air. Generally, a thermostat is used to control the

temperature and aqueous acid or salt solution of different concentrations are used to control

the relative humidity of air.

TABLE 2.2 : Grain equilibrium moisture content, %, Wet basis, Relative humidity, %

GRAIN Humidity

Temp0C10 20 30 40 50 60 70 80 90 100

Paddy 23 4.9 7.3 8.7 9.81

0.912.4 13.5 15.9 19 -

Paddy 30 - 7.1 8.5 101

0.911.9 13.1 14.7 17.1 -

Paddy 44 - - - - - 10.3 12.3 14.3 16.5 -

Wheat white 25 5.2 7.5 8.6 9.41

0.511.8 13.7 16 19.7 26.3

Wheat 32 - 5.3 7 8.61

0.311.5 12.9 14.3 - -

Wheat 49 - - 6.2 7.4 9.6 10.4 11.9 13.6 - -Shelled corn

(WD)25 5.1 7.2 8.5 9.8 11.2 12.3 13.9 15.5 18.9 24.6

Shelled corn

(YD)32 - - 5.3 6.6 8.3 10.2 12.1 13.9 - -

Shelled corn

(YD)49 - - - 5.3 6.5 7.8 9.3 10.7 - -

Shelled corn

(YD)70 3.9 6.2 7.6 9.1

1

0.411.9 13.9 15.2 17.9 -

Sorghum 25 4.4 7.3 8.6 9.8 11 12 13.8 15.8 18.8 21.9

Sorghum 32 - 7 8.71

0.211.8 12.2 13.1 14.8 - -

Sorghum 70 - 6.6 8 9.41

0.711.6 12.7 14.3 - -

Oats 25 4.1 6.6 8.1 9.11

0.311.8 13 14.9 18.5 24.1

Barley 25 4.4 7 8.5 9.71

0.812.1 13.5 15.8 19.5 26.8

Rye 25 5.2 7.6 8.7 9.91

0.912.2 13.5 15.7 20.6 -

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III) DETERMINATION OF DRYING CONSTANT: -

There are two methods of determination of drying constant -

i) Graphical Method: -The drying constant, K can be worked out easily by finding out the slope of the

straight line. 1

.1

y .01

x

.001 20 40 60 80 100 120 140 160 180 200 210 220

Drying Time, MinGraph to calculate drying constant

ii) Half life period method: -

If the time of one - half response in a drying process be defined as the Number

of hours necessary to obtain a moisture content ratio of one-half, then drying equation.

MeMo

MeM

−−

= Exp [- Kθ] can be written as -

K

2In or ]Kexp[

2

12/12/1 =θθ−=

andK

4In or ] K[ exp

4

14/14/1 =θθ−=

Therefore, by knowing the values of θ1/2 or θ1/4, K can be found out.

12

Moi

stur

e R

atio

,M-M

e / M

0Me

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IV) DRYING EQUATION:-

Based on Newton’s equation for heating or cooling of solids, a simple drying

equation is derived as follows-

The Newton’s equation is- )tt(Kd

dte−−=

θ

If the temperature term t is replaced by the moisture term M, then

)MM(Kd

dMe−−=

θ......................... (1)

where M = Moisture content (d.b), %

θ = time, hr,

Me = EMC, (d.b), %

K = drying constant , 1/hr

Rearranging the equation (1)

θ−=−

KdMM

dM

e

Integrating the above equation within proper limits, we get

]Kexp[MM

MM

e0

e θ−=−−

or e

eo

MM

MMIn

K

1

−−=θ

e

eo

MM

MM

−−

is known as the moisture ratio, M.R.

V) THIN LAYER DRYING: -

Thin layer drying refers to the grain drying process in which all grains are fully

exposed to the drying air under constant drying conditions. i.e. at const air temperature and

humidity. Generally, up to 20 cm thickness of grain bed (with a recommended grain ratio) is

taken as thin layer. All commercial flow dryers are designed on thin layer drying principles.

i) Constant rate period: -

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Some crops including cereal grains at high moisture content are dried under

constant rate period at the initial period of drying. Falling rate period follows subsequently.

As for example, wheat is dried under constant rate period when its moisture content exceeds

72%.

In the constant rate period the rate of evaporation under any given set of air

condition is independent of the solid and is given set of air condition is essentially the same as

the rate of evaporation from a free liquid surface under the same condition. The rate of drying

during this period is dependent upon.

Difference between the temperature of air and temperature of the wetted surface at

constant air velocity and relative humidity.

Difference in humidity between air stream and wet surface at constant air velocity and

temperature.

Air velocity at construction air temperature and humidity.

Under adiabatic and controlled drying air conditions, the temperature of wetted

surface attains the wet bulb temperature. In the constant rate period drying takes place by

surface evaporation and moisture moves by vapour pressure difference. The moisture content

at which the drying rate ceases to be constant is known as the critical moisture content of the

solid. The average critical moisture content Xc for a given type of material depends upon the

surface moisture concentration, bed thickness, rate of drying and characteristics of solids such

as shape, size and the drying conditions.

ii) Falling - rate period: -

Cereal grains are usually dried entirely under falling - rate period. The falling -

rate period enters after the constant drying rate period and corresponds to the drying cycle

where all surface is no longer wetted and the wetted surface continually decreases until at the

end of this period the surface is dry.

The falling rate period is characterised by increasing temperature both at the

surface and within the solid. Further more, changes in air velocity have a much smaller effect

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than during the constant rate period. The falling rate period of drying is controlled largely by

the product and is dependent upon the movement of moisture within the material from the

center to the surface by liquid diffusion and the removal of moisture from the surface of the

product.

The falling rate period of drying can be divided into two stages -

(a) Unsaturated surface drying.

(b) Drying where the rate of water diffusion within the product is slow and is the controlling

factor.

Practically all cereal grains are dried under falling rate period if their moisture

content is not very high.

iii) Remarks on thin layer Drying: -

None of the theoretical equations represents the drying characteristics of grains

accurately over a wide range of moisture and temperature, on account of the following

limitations -

The theoretical drying equations are based on the concept that all grains in thin layer

are fully exposed to the drying air under constant drying conditions and dried

uniformly. Therefore, there is no gradient in thin layer of grain, which is not true for

finite mass depth.

The grain drying equation developed from diffusion equations are based on the in

correct assumptions that Dv and K are independent of moisture and temperature.

It is not possible to choose accurate boundry conditions and shape factors for drying of

biological materials.

Drying equation developed from Newton equation for heating or cooling does not take

into account of the shape of the material.

Therefore, the uses of theoretical drying equations are limited. However, if

accurate results are not desired and the values of Dv and K are known then the theoretical

drying equation can be used and give fairly good results within a limited range of moisture.

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Many empirical drying equation for different cereal grains are found to be

useful and frequently used as they give more accurate results in predicting drying

characteristics of a particular grain for a certain range of moisture, temperature, air flow rate

and relative humidity. A few empirical drying equation are presented below: -

Becker (1959) proposed the following equation for wheat: -

MR = 1 - 8.78 (Dv θ)1/2 + 13.22 (Dv θ )

For (Dv θ )1/2 < 0.0104

MR = 0.509 x exp [- 58.4 Dv θ]

For (Dv θ)1/2 ≥ 0.0104

where, Dv = 7.135 e-19944/T

Dv = m2/hr, θ = hr and T = 0K

Based on drying equation for planar symmetry Pabis and Henderson (1961)

developed the following expression for diffusivity for thin layer drying of corn

D v corn = 5.853 x 10-10 exp [-12502/T] on the basis of drying equation for

sphere, the following expression for drying constant K corn has been developed -

K corn = 5.4 x 10-1 exp [- 9041/T]

Where k = 1/sec, T = 0K

VI) DEEP BED DRYING: -

In deep bed drying all the grains in the dryer are not fully exposed to the same

condition of drying air. The condition of drying air at any point in the grain mass changes

with time and at any times it also changes with the depth of the grain bed. over and above the

rate of overflow per unit mass of grain is small compared to the thin layer drying of grain. All

on farm static bed batch dryers are designed on deep bed drying principle. The condition of

drying in deep bed is shown in figure.

16

Fig.2.1

Moi

stur

e co

nten

t of

padd

y (%

)

Drying time in hr.

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The drying of grain in deep bin can be taken as the sum of several thin layers.

The humidity and temperature of air entering and leaving each layer vary with time depending

upon the stage of drying, moisture removed from the dry layer until the equilibrium moisture

content is reached. Little moisture is removed, rather a small amount may be added to wet

zone until the drying zone reaches it. The volume of drying zone varies with the temperature

and humidity of entering air, the moisture content of grain and velocity of air movement.

Drying will cease as soon as the product comes in equilibrium with the air.

i) Time of advances of drying front

The time period taken by the drying front to reach the top of the bin is called

the max drying rate period.

The time taken by the drying front to reach the top of the bed can be calculated

by -

11sx1 )HH ( G A

100

)MM(Waθ−=

−

OR

100 )H(HG A

)MM( Wa

1S

x11 −

−=θ

Where - M1 = Initial moisture content of grain ( d.b) %

Mx = Ave moisture content (d/b) % at the end of the drying front advance at the top.

θ1 = Time of advance, hour.

A = C/s area of dryer, through which air passes, m2

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G = Mass flow rate of dry air, Kg/hr m2

Hs = Humidity of the saturated air leaving the dryer Kg./kg.

H1 = Humidity of the air entering in to the dryer, Kg/Kg.

wd = Weight of dry grain in the bin, Kg.

ii) Decreasing rate period: -

As soon as the drying front reaches the top of the bin, the rate of drying. Starts

decreasing and is termed as decreasing rate period. The time of drying for this decreasing rate

period can be expressed by -

−−=θMeM

MeMxIn

K

12

where, θ2 = Time of drying during decreasing rate period, hr.

Me = Equilibrium moisture content of grain (db)

K = Drying constant, 1/hr.

M = Average moisture content (db) at the end of decreasing rate period.

Mx = Average initial moisture content (db) at the beginning of decreasing period.

∴ The total drying time for grains in the bin is -

Total drying time , θ = θ1 + θ2

iii) Remark on deep bed drying: -

(1) If drying air at high relative humidity and relative low temperature is used, then the total

drying time will be very long due to slow rate of drying which may cause spoilage of grains.

(2) The correct choice of air flow rate is very imp.

(3) Drying air at high temperature cannot be used due to the development of moisture

gradients within the grain bed. It leads to non - uniform drying of grain. In general an air

temperature of 400C ( 150C rise) is recommended for deep bed drying.

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VII) EFFECTS OF DIFFERENT FACTORS ON THE DRYING PROCESS: -

The drying rate is depend upon many factors, namely air temperature, air flow

rate, relative humidity, exposure time, types, variety and size of grain, initial moisture content,

grain depth, etc. of them, first four factors are imp. They are -

i) Effect of air temperature: -

The rate of drying increases with the rise of air temperature. But the

equilibrium moisture content falls as air temperature increases.

ii) Effect of air velocity: -

Henderson and pabis found that air rate has no observable effect on thin layer

drying of wheat when air flow was turbulent. A/c to them, air flow rate varying from

10cm3/sec/cm2 to 68 cm3/sec/cm2 had no significant effect on the drying rate of wheat. But in

case of paddy and corn it has been found that air rate has some effect on rate of drying.

iii) Effect of air humidity: -

When the humidity of air increases the rate of drying decreases. The effect is

much smaller in comparison to the effect of temperature changes.

iv) Effect of air exposure Time: -

In the case of intermediate drying, drying rate of grain depends on its exposure

time to the drying air in each pass. Total drying time, which is the sum of all exposure times,

is dependent upon exposure time. Total drying time reduces as exposure time decreases.

* * *

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CHAPTER - III

METHODS OF GRAIN DRYINGSo far, drying systems have not been classified systematically. However,

drying methods can be broadly classified on the basis of heat transfer to the wet solid.

According to mode of heat transfer, drying methods can be divided in to :

(a) Conduction drying (b) Convection drying and (c) radiation drying. There are other

methods of drying also, namely dielectric drying, chemical or sorption drying, vaccum drying,

freeze drying.

Of them, convection drying is commonly used for drying of all types of grain.

Conduction Drying: - When the heat for drying is transferred to the wet solid mainly by

conduction through a solid surface (metallic) the phenomenon is known as conduction or

contact drying. In this method, conduction is the principal mode of heat transfer and the

vaporised moisture is removed independently of heating media. Conduction drying is

characterised by -

a) Heat transfer to the wet solid takes place by conduction through a solid surface, usually

metallic. The source of heat may be hot water, steam, flue gases, hot oil, etc;

b) Surface temperature may vary widely;

c) Dust and dusty materials can be removed very effectively. Conduction drying can be

carried out either continuously or batch wise.

Convection Drying :- In this drying, the drying agent ( hot gases ) in contact with wet solid

is used to supply heat and carry away the vaporised moisture and the heat is transferred to the

wet solid mainly by convection. The characteristics of convection drying are -

a) Drying is dependent upon the heat transfer from drying agent to wet material.

b) Steam heated air, direct flue gases of agricultural waste, etc. can be used as drying agent ;

c) Fuel consumption per kg of moisture evaporated is always higher than that of conduction

drying.

20

C.O.E.&T.,Akola


Convection drying is most popular in grain drying. It can be carried out either

continuously or batch wise.

Convection drying further classified as -

Natural air drying: - The unheated air as supplied by nature is utilised.

Supplemental heat drying: - drying with supplimental heat just sufficient amount of heat

(temperature rise 50 to 100 C) only is supplied to drying air.

Heated air drying:-

In heated air drying air is heated to a considerable extent. The natural air

drying and drying with supplemental heat method which may require one to four weeks or

even more, heated air drying is most useful when large quantity of grain is to be dried within a

short time.

Radiation drying :-

Radiation drying is based on the absorption of radiant energy of the sun and its

transformation in to heat energy by the grain, sun drying is an example of radiation drying.

The effectiveness of sun drying depends upon temperature and relative humidity of the

atmospheric air, speed of the wind, type and condition of the grain, etc.

Sun drying: -

Sun drying is the most popular traditional method of drying. A major quantity

of grain is still dried by the sun in most of the developing countries.

Infra - Red Drying: -

Infra-red rays can penetrate into the irradiated body to a certain depth and

transformed into heat energy, special infra red lamps used as generators in infra red radiation.

Radiation dryers have been used in many countries for drying the painted surfaces of

machinery, textile industry and food industries.

Dielectric drying :-

In dielectric drying, heat is generated within the solid by placing it in a fixed

high frequency current. In this method, substance is heated at the expense of dielectric loss

21

C.O.E.&T.,Akola


factor. The molecules of the substance, placed in a field of high frequency current are

polarized and begin to oscillate in accordance with the frequency. The oscillations are

accompanied by friction and thus a part of the electric energy is transformed into heat. The

main advantage of this method is that the substance is heated with extraordinary rapidity.

Chemical drying :-

Various chemicals such as sodium chloride, calcium propanate, copper

sulphate, ferrous sulphate, urea etc have been tried for the preservation of wet paddy of these,

common salt has been proved to be effective and convenient. The common salt absorbs

moisture from paddy but it cannot penetrate in to endosperm through husk layer. This is

unique property of paddy.

Sack drying: -

This method is particularly suitable for drying of small quantity of seed. The

grain bags are laid flat over holes cut on the floor of a tunnel system so that heated air can be

forced up through the grain from an air chamber underneath.

***

22

C.O.E.&T.,Akola


CHAPTER - IV

GRAIN DRYERSGrain dryers can be divided in to two broad categories, unheated air dryers and

heated air dryers. Different types of grain dryers of both groups have been discussed in this

chapter.

I) UNHEATED AIR DRYERS: -

Unheated or natural air-drying is usually performed in the grain storage bin.

Natural air-drying is commonly used for on farm drying for a relatively small

volume of grains. Either full bin or layer drying system is employed in natural air drying.

The period of drying for either system may be as long as several weeks depending on the

weather. In layer drying, the bin is filled with a layer of grain at a time and drying, is begun.

After the layer is partially dried, other layers of grain are added periodically, perhaps daily

with the continuation of drying until the bin is full and whole grain mass is dried. In full bin

drying a full bin of grain is dried as a single batch. Then the drying bin is used for storage

purposes. The air flow rate provided is relatively low. Though natural air is supposed to be

used, an air heating system should be kept so that supplemental heat may be supplied to

natural air during rainy seasons. Grain containing moisture more than 20 % should not be

dried with natural air. As in natural air drying the grain is aerated and stored in the same unit,

the complete installation simply consists of a storage unit equipped with ducts for air

distribution and devices for air exhaustion and a blower.

II) HEATED AIR DRYERS :-

Heated air dryers of different types are as follows.

i) Deep bed dryers :- These batch in bin dryers are of large capacities to several hundred

tonnes. The most common shapes are round or rectangular. To operate deep bed dryers

efficiently following rules may be followed :-

23

C.O.E.&T.,Akola


An air flow rate of 2.94 - 3.92 m3/minute per tonne is

recommended. Rates above 3.92 m3/minute per tonne may

result in uneven drying and is expensive in operation.

If the moisture content of grains is up to 18% the layer

depth of grain should be limited to 3 m and for above 18%

moisture depth recommended is 2.5m.

The net perforated are of the floor should be 15% of total

floor area. Air velocity of 300 m/minute through opening

is preferable.

ii) Flat bed dryer :-

In the flat bed batch type dryer

surface area of dryer is more and depth of drying

layer is less. These dryers are of usually 1 - 2 tonne

capacity. Grains are spread 0.6 to 1.2 m deep over

the perforated floor and dried. The main

advantages are

The whole batch is dried quickly.

There is less likehood of over drying.

Lower air pressure is required to force the drying air.

iii) Continues flow dryers :-

These dryers are columner type in which wet grains flow from

the top to bottom of the dryers. These dryers are of two types.

1) Mixing and 2) Non - mixing.

1) Mixing type continuous flow dryers :- When the grains are

diverted in the dryer, it is called a mixing type dryer. Drying is

accomplished by forcing heated air across the falling

layers of grains.

24

Fig. Deep bed dryers.1. Exit air 2.Wet grain 3. Drying

zone 4. Dry grain 5. Blower

Fig. Flat bed dryer1. Exit air 2. Plenum chamber 3. Blower

Fig. Continuous flow dryer (mixing)1.feed hopper2.exit air

3.plenum chamber 4.dry material outlet

C.O.E.&T.,Akola


In mixing dryers, baffles are provided to cause the grains to mix during their

downward flow. These dryers use low air flow rates of

50-95m3/min tonne and high drying temperature of

650C Zig-Zag columns enclosed by screens on both

sides are used primarily to achieve mixing action during

drying process.

2) Non-Mixing dryers :- Baffles are not provided in

the column and drying takes place between two parellel

screens, 15-25 cm apart. In these dryers high air flow

rates of 125-250 m3/min - tonne can be used. Drying

air temperature of 540C used in non mixing dryers.

iv) Recirculating dryers :-

In this type, a multipass

procedure is used to avoid excessive drying stress.

During each pass, the grain are exposed to the

heated air for short time ( 15-30 minutes ) and

about 1 - 3 % of moisture is removed. Drying

temperature is 60 - 800C is used. Drying is faster

and effective because of continuous movement of

grains during short drying times.

v) L. S. U. dryer :- The design of this continuous dryer was developed at the Lousiana State

University called LSU dryer. It is a mixing type continuous flow dryer. The layers alternate

between hot air intake and exhaust air outlets and are staggered to provide mixing. The LSU

dryer is of high capacity and being used in big commercial rice mills.

25

Fig. Continuous flow dryer (non mixing) 1.feed hopper2.plenum chamber 3.exit air 4. dry grain outlet 5.screened grain column

Fig. Recirculatory dryer's1.elevator 2.tempering bins 3.wet material

4.semidried material 5.conveyor

C.O.E.&T.,Akola

Fig. LSU dryerA' 1.garner 2. duct 3. dry material outlet 4. hopper 5.continuous flow 6.door 7.roof

B' 1. Cross section of drying chamber 1. air exhaust 2. air intake


vi) Fluidized bed dryer :-

It is mainly used for granular material, it also applicable in the drying of

solutions, pastes and liquids sprayed on to the fluidized inert bed. The principle of operation

of fluidized bed dryer is to be provide sufficient air pressure to fluidize a thin bed of

grain/product giving excellent air/grain contact. The drying method is based on ventilating

hot air through the bed of product kept on the support grid. When the air velocity becomes

higher than the critical fluidization velocity, the bed progressively expands until it reaches a

state that of boiling liquid. This

phenomenon is called fluidization.

vii) Rotary Dryer :-

In commercial rotary

dryers the diameter of drum is between

1 to 3 m and length is from 3 to 6 m.

It is operated at slight inclination. The

drum rotates on its axis. The grain

flows downward through the rotating

drum and is periodically lifted by

26

Fig. Continuous flow heated sand medium rotary dryer

C.O.E.&T.,Akola

Fig. Tray dryer1. exit air 2.blower 3.heater 4. inter space between trays 5.trays 6. plenum chamber

Fig. Direct dryer (natural convention)1.exit air2.chimney3.transferable

panel4.bamboo5.air intake 6.clear plastic sheet


inclined flights, then dropped, ensuring good air/grain contact. In small scale rotary dryers,

the walls are heated by direct contact with flue gases.

viii) Tray dryer :-

In a tray dryer, many shallow trays are

kept one above the other with a gap between in the

drying chamber. Try dryer is generally used for drying

vegetables. If the heated air is coming from the sides of

drying chamber, the trays may not have perforated

bottom. Products are kept in thin layers in the trays.

ix) Tunnel dryer :-

It is similar to tray dryer. When

the group of trays is moving in a tunnel, the

system becomes a tunnel dryer. The flow of

heated air in a tunnel dryer may be concurrent

or counter current.

x) Grain drying in bags :-

This method is useful to dry grains in

small quantities. Method requires large number of unskilled labours and more space is

needed. The heated air is forced through the racks and

bags. During drying, the bags are inverted at least once to

accomplish drying on both sides of the bags.

xi) Solar dryers :- Solar drying of agricultural products

can be advantageous to sun drying for the farmers of

developing nations. Two basic principles are inherent in the

operation of solar dryers, firstly solar heating of air

and secondly the removal of moisture from the wet

material by the heated air.

27

Fig. Tunnel dryer1.blower 2. heater 3.trays 4.exit air chimney

C.O.E.&T.,Akola


CHAPTER - V

SELECTION OF GRAIN DRYERSMany factors are to be considered before the final selection of the most

suitable type of dryer for a given application. The selection is little but made difficult by a

whole range of dryers in to days market.

The commercial dryers are not enough flexible enough to compensate design

factors and the problems associated with handling of different types of food materials, which

are not taken into consideration previously. For this reason, it is particularly important that all

pertinent points be considered and drying tests be conducted before the final selection for

particular operation.

I) PRELIMINARY DRYER SELECTION :

The important factors to be considered in the preliminary selection of a crop

dryer are as follows :-

i) Physico chemical properties of the crop being handled.

ii) Drying characters of crop.

(1) Type of moisture.

(2) Initial, final and equilibrium moisture content.

(3) Permissible drying temperature.

(4) Drying curves and drying times for different crops with different dryers.

iii) Flow of crop to and from the dryer.

Quantity to be handled per hour.

Continuous or batch generations.

Process during drying and subsequent to drying.

iv) Product Qualities

(a) Colour

(b) Flavour

(c) Shrinkage

28

C.O.E.&T.,Akola


(d) Contamination

(e) Uniformity of drying

(f) Decomposition or Conversion of product constituents.

(g) Overdrying

(h) State of subdivision.

(i) Product Temperature

(j) Bulk density.

(k) Case hardening and

(l) Cracking and other desirable qualities of the end products.

v) Dust recovery problems.

vi) Facilities available at the site of proposed installation.

a) Space

b) Temperature, humidity, cleanliness of air.

c) Availability of fuels.

d) Available electric power.

e) Permissible Norse, vibration dust or heat losses.

f) Source of wed feed

g) Exhaust gas outlets.

II) COMPARISON OF DRYERS :-

The dryers selected are to be evaluated on the basis of drying performance and

the cast data.

Various drying tests for various crops have to be carried out with the dryers

under consideration to determine product characteristics. An approximate cost analysis is also

useful for evaluation of dryers.

29

C.O.E.&T.,Akola


III) FINAL SELECTION OF DRYERS.

From the results of the drying tests and analysis the final selection of the must

suitable dryer can be made.

For successful introduction of any grain dryer at farm level, a few additional

parts are to be borne is mind in the section and design of grain drying system. They are as

follows :-

The dryer should be of proper size matching with the demand of a farmer ;

The price of the dryer should be reasonable.

The design of layer should be simple and made of different cheap and locally available

materials so that it can be manufactured locality.

It should be easy to operate.

It should be possible to make the dryer portable if necessary.

The operating cast should be minimum solar or furnance (i.e. fired with agricultural

waste like hustic shells etc.) air heating system should be introduced in grain drying to

minimise the cast of grain drying.

The repair and maintenance requirement should be minimum.

It should be possible to use the dryer for different grains and to be used as a storage bin

later for its maximum utilization.

* * *

30

C.O.E.&T.,Akola


CHAPTER - VI

DESIGN PROCEDURE OF GRAIN DRYERSThe heated air grain dryers can be divided into three major groups.

1) Static deep bed batch dryers.

2) Continuous - flow - batch dryers. (either mixing or non - mixing type) and

3) Continuous dryer.

Grain dryers mainly consist of

(a) Drying chamber.

(b) Air distribution system.

(c) Direct or indirect air heating system.

(d) Blower.

(e) Control system (if any) and

(f) Grain conveying system (for flow dryers)

The following important factors are taken into consideration in the design of

heated air grain dryers -

DRYER FACTORS: -

(a) Size, shape and type of dryer ;

(b) Grain feeding rate ;

(c) Total drying time ;

(d) Air flow pattern and air distribution system;

(e) Depth of grain bed in the dryer; and

(f) System of cooling grain (if any).

AIR FACTORS :-

(a) Velocity and air flow rate per unit mass of the grain.

(b) Temperature and relative humidity's of the heated air and exhaust air.

(c) Static pressure of the air at which it is blown and

(d) Average ambient conditions.

31

C.O.E.&T.,Akola


GRAIN FACTORS :-

(a) Type, variety and condition of grain.

(b) Initial and final moisture contents of grain.

(c) The usage of dried grain and

(d) Latent heat of evaporation of grain moisture.

HEATING SYSTEM: -

(a) Type of fuel and rate of fuel supply.

(b) Type of burner (for liquid fuel) or type of furnace (for solid fuel) and

(c) Type of heat exchanger (for indirect heating system)

IMP. DESIGN FACTORS: -

Following are some of the important design factors -

(1) Size, shape and type of dryer :-

Size or capacity of a dryer is decided by the amount and variety of grain to be

dried per day or for the whole season. The sizes of dryer are express either in terms of

holding capacity of amount of grain to be dried per unit time or the amount of grain passing

through the dryer per unit time.

Thickness of grain layer exposed to the heated air is generally restricted to

room for continuous flow dryers. The designs of the continuous flow dryer are based on thin

layer drying principles whereas static batch dryers are designed in deep bed drying principles.

Choice of a grain dryers largely depends on the situation. Continuous flow

dryers are normally used for commercial purpose whereas static deep bed batch dryers are

used for on farm drying. Farm level batch dryers can be made of locally available materials,

namely, wood, bamboo, etc. if necessary. But commercial big dryers are made of mild steel

sheet, angle iron, channel section supports.

32

C.O.E.&T.,Akola


(2) Calculation of air and heat for heated air dryers i.e. Mass and Heat Balance in grain

drying:-

The air flow rate required for heated air drying systems can be calculated as follows :

The rate of air flow required for drying may be calculated by making heat

balance. The heated air drying system is represented by :

where

G = air flow rate, m3/min.

H1, H2 = humidities of ambient and heated air, kg/kg.

H3 = humidity of exhaust air, kg/kg.

RH1, RH2 & RH3 = relative humidities of ambient, heated and exhaust air,

respectively, per cent.

t1, t2 & t3 = dry bulb temperatures of ambient, heated

and exhaust air respectively, 0C.

Wd = total weight of bone dry grain in the dryer, kg.

X1, X2 = initial and final moisture contents of grain, kg/kg.

21 GG t,t = initial and final grain temperatures, 0C.

v1 = initial humid volume, m3/kg.

Heat supplied by drying air, qa, kcals :

qa = (0.24+0.45 H1) G' (t2 - t3 ) θ

33

AMB. AIR

C1V1t1H1,RH1

HEATER AIR

t2H1,RH2

EXHAUST AIR

t3,H3,RH3

HEATER

X1.t.c1

DRYER W

d

X2,tG2

C.O.E.&T.,Akola


Where G' = rate of air supply, kg/min.

θ = total drying time, min.

Amount of heat required :

Heat required for evaporation of moisture from the grain, q1, kcals :

q1 = W d ( X1 - X2 ) λ

where,

λ = average value of latent heat of vaporisation of moisture from the grain

kcals/kg.

Sensible heat required to raise the temperature of the grain and its moisture, q, kcals :

1GGwdGGgd X)tt(CW)tt(CWq1112

−+−=

where

Cg, Cw = specific heats of grain and water respectively,

K cal/kg 0C

Thereforeqqq 1a +=

or G' = (0.24+0.45 H1) (t2 - t3 ) θ

= ]X)tt(C)tt(C)XX[(W 1GGwGGa21d 1222−+−+λ−−

or θ−+

−+−+λ−=

)t(t )H 45.024.0(

]X)tt(C)tt(C)XX[(WG

321

1GGwGGa21d' 1212

∴ G = G' x v1

where v1 = humid volume.

(3) Calculation of fuel requirement:-

Fuel consumption :

The rate of fuel consumption can be calculated as follows :

nexb

a

C...

'qf

ηηη−= −

34

C.O.E.&T.,Akola


where f = fuel rate, kg/hr.

q'a = total heat required to heat the drying air, kcal/hr.

Cn = Calorific value of fuel, kcal/kg of fuel.

η = efficiency of the heating system.

ηex = efficiency of the heat exchanger.

ηb = efficiency of the boiler, if any.

(4) Design of fan and blowers:-

Selection/Design of a centrifugal blower

For a given set of airflow rate and static pressure, the impeller diameter and

width of blower may be calculated as below,

1 Calculate the specific speed (Ns) for the specific static pressure, air flow rate and designed

motor speed.

rpm p

QNN

75.0S

s =

Where, N = speed of motor, rpm

Q = air flow rate, cfm

ps = static pressure, inches water gauge.

2. From Fig. 6.1 determine the type of air moving unit which would operate at high efficiency,

at or near peak efficiency at the calculated specific speed. If more than one type of air moving

unit has good efficiency, make the final selection on other factors involved in the application

such as relative cost, size and shape of space available and the characteristics of the air flow

path.

3. From Table 6.1 find the typical value of pressure coefficient Ψ by interpolation, for the type

of fan or blower selected and the value of Ns.

4. Calculate the diameter of the impeller.

35

C.O.E.&T.,Akola


22

S8

dN

p1035.2 ×=ψ

where Ψ = pressure coefficient

d = diameter of the impeller, inch

5. Find out the typical value of flow coefficient φ from table and then calculate the width.

2Nd

Q175W

φ=

Where, φ = flow coefficient

W= width of the impeller, inch

36

C.O.E.&T.,Akola


Table 6.1 Values of specific speeds, typical pressure co-efficient, typical flow co-efficient and dimensions of centrifugal blowers

Dimension Specific Speed

Typical pressure coeff.

Typical flow coeff.

A B C Ns Ψ φ13,000 1 0.15

1.7(D) 1.5(D) 1.25W+0.1D 20,000 2.0 0.540,000 1.0 0.75

4,000 1.4 0.002

1.4(D) 1.35(D) W+0.1D 8,000 1.0 0.0120,000 0.8 0.10

15,000 1.0 0.082.0(D) 1.6(D) W+0.16D 30,000 0.75 0.3

45,000 0.5 0.5

37

Fig.6.1 Specific speed vs. static efficiency of various impellers

C.O.E.&T.,Akola


A review of manufacturer's literature is done to see that whether blower wheel

of calculated dimensions is available. If it is not available, then slightly smaller or larger

wheel is selected and the performance requirement is revised.

Blower housing:-

The configuration of the housing considerably affects the performance of a

centrifugal blower and thus is as important as the blower wheel. The size of the housing must

be considered keeping in view the space available. The standard housing dimensions

recommended by the blower manufacturers may be followed to maximise performance of a

particular blower wheel. These dimensions are generally given as proportions of wheel

diameter and width and so can be determined after the selected procedure is completed.

The purpose of

centrifugal blower housing as shown in

Fig. 6.2, is to control the air flow from

intake to discharge, and in the process,

to convert the velocity head into the

static pressure head. Pressure conversion

is accomplished as the cross-section of

the air stream increases in the increasing

annular space on the periphery of the

blower wheel from cutoff to discharge.

Since the amount of pressure conversion is determined by the scroll configuration, the shape

of the housing considerably affects air performance. The cutoff eliminates almost all free

circulation of air within the housing.

Diffuser angle:-

The increase in annular cross-section in the scroll around a blower wheel is

proportional to the developed length of the wheel periphery (Fig 6.3). The angle between the

38

Fig. 6.2 Housing of centrifugal blower

C.O.E.&T.,Akola


developed scroll surface and blower wheel periphery is called the diffuser angle. Wheel

diameter and diffuser angle determines the shape and dimensions of the scroll.

The diffuser angle can be determined graphically and expressed in terms of

impeller diameter and either the maximum height or maximum width of the housing. Diffuser

angle may be given as,

−=α 1

d

H12 M

h .................................. (1)

−=α 1

d

W12 M

w .................................. (2)

As shown by above equations, the diffuser angle decreases if either dimensions

AE or CG decreases. However it is less sensitive to change in AE.

As the diffuser angle increases, the flow rate increases significantly at any

particular static pressure. Diffuser angle also affects performance of the blower in a particular

system.

The diffuser angle generally used as the basis for blower performance data is

10°. Although large diffuser angle improve performance, the relative amount of improvement

gradually diminishes and the size of the housing with respect to the diameter of the blower

wheel becomes too large.

39

Fig. 6.3 Scroll development of a centrifugal blower

C.O.E.&T.,Akola


The housing width may be determined by the following equation

M=1.25 W + 0.1 d .................................. (3)

where, M = housing width

W = impeller width

d = impeller diameter

The optimum diameter is based on a blower wheel mounted close to the inlet

ring and minimal clearance between the wheel back plate and side of the housing.

If the width of the housing recommended for the standard blower wheel is too

large, a narrower housing should be selected. If either dimension AE or CG of the

recommended housing is too large for the space available, a housing with a smaller diffuser

angle should be selected. The resulting reduction in air flow rate should then be determined

and compared to the original requirement.

Calculating diffuser angle:-

The diffuser angle, αh, equation (1) may be calculated with dimensions AE

equal to the maximum dimension Y of the space available (Fig. 6.3).

The diffuser angle, αw, equation (2) may be calculated with dimension CG

equal to the maximum dimension X of the space available.

The smaller of two diffuser angles corresponds to the housing that will fit into

the space available for blower. If the calculated diffuser angle is 4° or less, the housing is too

tight. If possible, a smaller blower wheel that produces the required air performance at a

higher operational speed should be selected.

(5) Drying air temperature :-

Correct choice of drying air temperature for a given type of grain is very imp.

as it has effects on the quality of dried product. The highest allowable air temperature for

drying of grain depends on the type and condition of grain and the usage of dried grain.

The upper limit of drying air temperature for different grain to be used for food, feed and seed

purpose are different and are given in following table.

40

C.O.E.&T.,Akola


(6) Grain parameters :-

The grain factors which affect the rate of drying are as follows :-

Type, variety and condition of grain.

Initial harvest moisture content, final moisture and equilibrium moisture content of

the grain.

Structure and chemical composition of the kernel, seed, coat, husk etc. and

Foreign materials present in the grain.

The above stated, factors are therefore to be considered in the design of grain

dryers.

Table 6.2 : Bulk densities of grain at different moisture contents

Grain Moisture content % (w.b.) Density Kg/m3

Paddy 14.0

18.0

587.9

615.2Wheat 11.0

14.1

789.8

756.1Corn (Shelled ) 13.0

16.2

736.9

720.9Barley 16.8

10.8

592.7

576.7Sorghum 12.0

14.3

752.9

752.9

Table 6.3 : Latent Heat of vaporization of grain moisture

Grain Moisture content Temperature 0C Heat of vaporisation

41

C.O.E.&T.,Akola


%(w.b.) Kcal/kgWheat 13 38 629.4

13 65 611.617 38 589.917 65 573.8

Corn 13 38 698.813 65 679.417 38 644.417 65 626.1

Sorghum 13 38 624.413 65 606.217 38 593.317 65 576.6

Water - 38 576.1- 65 560.0

Table 6.4 : Specific gravity of cereal grains

Grain Moisture content % (w.b.) Specific gravity of kernel

Rice 8.6 1.36

Wheat 8.5 1.41

Corn 6.7 1.29

Barley 7.5 1.42

Millets 9.4 1.11

Oats 10.33 0.99

Table 6.5 : Thermal properties of cereal grains.

Grain Moisture content %(w.b)

Temperature range 0C

Specific heat kcal/kg 0C

Thermal conductivity kcal/m hr 0C

Thermal diffusivity

m2/hrPaddy 12 - 0.3934 - -

15 - 0.4255 - -17 - 0.4469 - -

Wheat 9.2 - 0.370 0.1198 0.00041411.7 26.50 to 31.0 - 0.128 -

Wheat, hard 12 - 0.367 - -

42

C.O.E.&T.,Akola


white

15 - 0.391 - -Wheat, soft

white

14.4 9.0 to 23.0 0.5 0.116 0.000295

Corn, yellow

dent

9.8

13.2

8.3 - 23.2

26.6-31.1

0.438

-

0.1308

0.102

0.000338

-Oats 12 - 0.380 - -

15 - 0.415 - -17 - 0.439 - -

(7) Air flow pattern and air distribution :-

Any one of the three systems of airflow namely crosses flow; counter flow and

co-current flow can be adopted in flow type grain dryers. Generally cross flow of air is

preferred. Double screen and baffle type of columnar dryers have a plannum chamber and

L.S.U dryer has inverted V shaped air channels for uniform distribution of air throughout the

drying chamber. The deep bed batch dryer has the plenums at the bottom of the graindrying

chamber.

Aeration system

Both propeller and centrifugal types of blowers are used for aeration.

Centrifugal blowers may have cither forward-curved or backward-curved blades.

The airflow and static pressure requirements for different types of grains and

for different depths of grains are given in Table.

Air distribution system

Sufficient care should be taken in selecting and designing the air distribution

System so that .air is uniformly distributed throughout the grain bulk and void pockets are

avoided. There are five major systems of air distribution :

(a) Perforated floor,

(b) Central horizontal duct,

(c) Main duct and laterals, and

(d) Vertical slatted duct.

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C.O.E.&T.,Akola


(a) Perforated flow

The circular storage bin can be fitted with the perforated false floor through

which unheated air is blown. Though the system is suitable for small and medium sized round

bins and for small depths of grain, it is used for large rectangular bins and for higher grain

depths as well.

(b) Central horizontal duct

This system is used in the quonset type units. This type of duct with openings

in the wall can distribute air more uniformly through the grain bulk.

(c) Main duct and laterals

The system -of main duct and laterals is most commonly used and is adopted

in ground, square and rectangular bins. The laterals are open at the bottom and raised off the

floor of .the bin so that the air can flow through the mass. The literals are inverted V or U or

rectangular in shape and are made of wood or steel or concrete or ferro-cement. The laterals

are spaced in accordance with the size of the storage unit, quantity of grain to be aerated or

dried and depth of the grain (Figs. 6.4 to 6.6). In round bins the ducts can also be placed in the

form of a ring on the bin floor.

44

Fig 6.4

Fig 6.5

Fig. 6.6 Four common floor layouts for the main duct and lateral in bins

Fig. 6.7

Fig. 6.8

Fig 6.9

C.O.E.&T.,Akola


(d) Vertical ducts

This system consists of either a vertical slatted duct or a central vertical

perforated tube (Fig.6.7). The air is blown, through the slots or perforations and is spread

laterally through the grain mass.

(8) Conveying and Handling System :-

Bucket elevators, vertical screw lifts for feeding, hopper bottom with proper

inclination for grain discharging are commonly used. Forced discharge mechanism with

slowly rotating fluted rolls are used for better control of the feed rate and drying rate. Dried

grain from the dryer is usually conveyed to different place by belt conveyor or screw

conveyor and bucket elevator.

(9) Air Heating System :-

Generally direct firing system are used for gaseous and liquid fuels and

indirect heating system using heat exchangers is employed for solid fuels. But direct flue gas

from the husk fired furnace can also be efficiently used for the grain drying. The drying cost

can be further reduced by introducing solar - cum - husk fired grain drying system.

Table 6.6 : Approximate Net Heating Values of Various Fuels

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Fuel Density Heating Value

kg/m3 lb/ft3 Kcal/kg kJ/kg Btu/lb

Agricultural Crop residues

Bagasse, dry 4443 18,600 8,000

Corn stalks, dry 3965 16,600 7,150

Cotton batting 3953 16,550 7,114

Cottonseed hulls 4778 20,000 8,600

Newspaper 4378 18,330 7,880

Pecan shells 4940 20,680 8,890

Straw 3332 13,950 6,000

Wheat (Straw) 45 4167 17,445 7,500

Alcohol – gas

Ethyl (C2H5OH) 1.965 0.122 6625 27,750 11,930

Methyl (CH3OH) 1.363 0.085 5043 21,115 9,080

Alcohol - liquid (pure)

Ethyl (C2H5OH) 815.3 50.9 6268 26,240 11,280

Methyl (CH3OH) 796.1 49.7 4677 19,580 8,420

Coal

Anthracite 7112 29,772 12,800

Bituminous Specific Gravity=1.12-

1.35

7500 31.401 13,500

Semi-bituminous 8112 33,960 14,600

Manufactured briquets 7251 30,355 13,050

Fuel oil lb/gal

No.1 813.6 6.79 10384 43,473 18,690

No.2 863.9 7.21 10173 42,590 18,310

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No.4 932.2 778 9856 41,263 17,740

No.5 938.2 7.83 9800 41,030 17,640

No.6 964.2 8.05 9545 39,960 17,180

Gasoline 736.9 6.15 10500 43,960 18,910

Kerosene 817.2 6.82 10367 43,403 18,600

Gas ( CnH2n+2) lb/ft3

Natural, methane (CH4 ) 0.680 0.0424 11956 50,055 21,520

Ethane (C2H6) 1.287 0.0803 11343 47,488 20,416

Manufactured 0.769 0.048 5878 24,610 10,580

Propane (C3H8) 1.924 0.120 11081 46,390 19,944

Butane (C4H10) 2.532 0.158 10934 45,775 19,680

Wood dry 5000 20,934 9,000

10) Safety features

Safety Features of Burner

Farmers, insurance companies, equipment manufacturers, and equipment

dealers are interested in the safe operation of burners used for heated air drying systems.

Important considerations of an installation designed for safe operation include the following:

(1) a flame control to shut off the fuel supply in the case of ignition failure, (2) a high

temperature limit switch which will stop the burner but allow the fan to continue to operate,

(3) a temperature control on the bonnet of the burner to prevent overheating of heater, (4)

proper electrical wiring connecting the fan and burner to the electric circuit (Fig. 7.3). All

units should be designed to "fail safe."

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C.O.E.&T.,Akola


There is a tendency to overemphasize the danger of starting a fire from

particles of trash getting into the open flame of a heated air dryer operated outside. The

velocity of the air passing the flame is so great that straw, chaff, and even cotton lint carried

into the airstream do not remain in contact with the flame long enough to ignite, although

such a circumstance is not recommended.

Safety Features of Installation

A properly designed heater can be used in an unsafe manner. Safety features of

an installation should include the following: (1) fuel pump and piping located a safe distance

from the flame of the burner, (2) the fuel feed line from the tank to the fuel pump protected

from mechanical injury, (3) the fuel tank located at least 5 m (16 ft) from the bin and other

buildings, (4) oil drums refilled a safe distance from the drying unit or the drying unit shut

down when the drums are refilled, (5) separate drying and storage installations provided for

safe and efficient grain drying by heated air, (6) if the crop is dried in batches, on wagons, or

in a batch bin, drying equipment separated from the main building by 3 m (10 ft), (7) the

48

Fig. 6.10 Automatic control system for a portable dryer heater

C.O.E.&T.,Akola


drying unit connected to the bin by a duct of flameproofed canvas or other noncombustible

material. Insurance companies may require that a special permit be obtained to install and use

a heated air crop dryer. The insurance company representatives will determine if the

installation is reasonably safe, and if approved, a permit may be purchased.

CHAPTER - VII

DRYER PERFORMANCE & TESTINGDryer performance can be expressed in terms of various efficiency factors

which are given below :-

(a) Thermal efficiency :-

Thermal efficiency can be defined as the ratio of the latent heat of evaporation

credited to the heat energy of the fuel charged.

Thermal efficiency can be expressed mathematically as follows :-

q

d W d

dM

θ

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where

)hh(v

VA60q 01=

Kg hr/Kg,rate dryingd

dM =θ

Wd = weight of dry material, Kg.

τ = latent heat of evaporation, K cal/Kg

q = rate of heat flow, K cal /hr

V = air rate, m3/min m2

A = area, m2

v = humid volume of air ( at the point of rate measurement ) m3/Kg.

h1 and h0 = enthalpy of drying and ambient air K cal/Kg.

(b) Heat utilization factor :- (HUF)

HUF may be defined as the ratio of temperature decrease due to cooling of the

air during drying and the temperature increases due to heating of air.

01

21

tt

tt

applied Heat

utilised HeatHUF

−==

HUF may be more than unity under certain drying conditions.

(c) Coefficient of performance :- ( C.O.P.)

The COP of a grain dryer is express mathematically as follows :-

01

02

tt

ttCOP

−−

=

where :- t2 = dry bulb temperature of exhaust air, 0C

t0 = dry bulb temperature of ambient air, 0C

t1 = dry bulb temperature of drying air, 0C

(d) Relation Between HUF and COP :-

HUF = 1 - COP

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Testing of Grain Dryers

No generalized test procedure can be adopted for all types of grain dryers. The

testing method for static deep bed batch dryer cannot be same as that of continuous flow thin

layer dryers. It is always preferable that test procedure for each type of dryer be designed

separately.

However, for convenience, the dryer testing method can be broadly divided

into two major heads : simple method and rigorous method. Either of these two methods can

be adopted in accordance with the objectives of the test.

a) Simple Method

A simple test procedure is so designed as to determine the approximate

performance of the grain dryer.

The simple test procedure for a batch dryer is tabulated as follows :

Table 7.2 : Test Procedure for the Performance of the Static Deep Bed Batch dryerType and model No. of dryer :Type of grain and variety

Grain 1. Initial weight of wet grain (kg)2. Final weight of dried grain (kg)3. Initial moisture content (per cent)4. Final moisture content (per cent)5. Dryer loading time (hr)6. Dryer unloading time (hr)

Air 1. Air flow rate (maximum) (m3/min)2. Air flow rate (minimum) (m3/min)3. Max. static pressure (mm water)4. Min. static pressure (mm water)5. Average ambient d.b. temp. ( 0C )6. Average ambient w.b. temp. ( 0C)7. Average heated air d.b. temp. ( 0C )8. Average heated air w.b. temp. ( 0C )

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C.O.E.&T.,Akola


9. Average exhaust air d.b. temp. ( 0C )Drying capacity 1. Total drying time (hr)

2. Cooling time (if any) (hr)3. Total moisture evaporation (kg)4. Rate of moisture evaporation (kg/hr)5. Rate of dried grain productions (tonnes/hr)

Heater and Fuel 1. Air heating method (oil fired burner/husk fired furnace/steam heat

exchanger)2. Type of air heating (direct/indirect)3. When oil fired burner/husk fired furnance is used(a) type of fuel and cal. value (b) total fuel consumption (kg)(c) rate of fuel consumption (kg/hr)4. When steam heat exchanger is used(a) incoming steam pressure (kg/cm2)(b) rate of condensate outflow (kg/hr)(c) Temperature of condensate ( 0 C)

Power 1. Power consumption for blowing air to burner (KW)2. Power consumption for pumping oil to burner (KW)3. Power consumption for blowing heated air (KW)4. Power consumption for loading and unloading grain (KW)5. Power consumption for running feed rolls (KW)

Quality of dried grain

1. Germination of grain before drying (per cent)

2. Germination after drying (per cent)3. Head yield before drying (per cent-for paddy)4. Total yield before drying (per cent)5. Head yield after drying (per cent)6. Total yield after drying (per cent)7. Other quality factors

The simple test procedure for continuous flow dryer

Besides the test items tabulated in the above. Table, the following items are to

be taken into consideration for continuous flow dryers :

(1) Moisture content after each pass ( per cent )

(2) Residence time in the dryer for each circulation (hr) ;

(3) Number of passes ;

(4) Tempering time (hr) ;

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C.O.E.&T.,Akola


(5) Average rate of moisture reduction or rate of moisture evaporation in each circulation

(kg/hr) ;

(6) Rate of grain recirculation (tonnes/hr) ;

(7) Drying air temperature at each pass ( 0 C) ;

(8) Weight of remaining grain in the dryer, elevator, etc.(kg).

b) Rigorous method

Rigorous test procedures for some batch and continuous flow dryers are given

as follows. The whole test procedure can be grouped into the following major heads :

(1) Checking of construction ;

(2) Drying performance test ;

(3) Fan/blower performance test ;

(4) Control system performance test ;

(5) Handling equipments performance test ; and

(6) Checking of different dryer-parts after disassembling (after the drying tests).

(1) Checking of Construction

The purpose of this test is to ascertain the major dimensions, material of

construction and other necessary specifications of the dryer and its accessories.

Investigation items: Specifications of : (a) dryer as a whole, (b) drying chamber with air

distribution system, (c) blower, (d) heating system and (e) conveying units such as bucket

elevator, grain distributor, screw conveyor, belt conveyor, etc. The specifications of the above

items have already been discussed earlier.

(2) Drying Performance Test

The objectives of this test are to determine the drying performance of a dryer

on the basis of rate of drying, rate of consumption of fuel and electricity, heat utilisation,

quality of the dried grain and other operating conditions.

The investigation items have already been tabulated.

(3) Blower Performance Test

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The objective of this test is to determine the performance of the fan/blower

attached with the dryer.

Investigation items : Power input, kw, (b) air flow rate, m3/min., (c) static and total pressure,

mm water, (d) static pressure efficiency and (e) vibration, noise and other working conditions

of the blower.

CHAPTER VIII

SUGGESTED MODELS

DESIGN OF SUGGESTED MODELS FOR DAL MILLS:

Case:- Pulses

Design a rectangular bin batch dryer having hole capacity of 2.5 tonnes of pulses with 12%

w.b.

Solution :- Assume the following data.

Ambient air temperature = 300C

Relative humidity of ambient air = 70 %

Initial moisture content of pulses = 17% w.b.

Final moisture content of pulses = 12% w.b.

Grain inlet temperature = 300C = tG1

Grain Outlet temperature = 700C = tG2

Heated air temperature = 850 = t2

Exhaust air temperature = 400C = t1

Latent heat of water vapour = 600 K cal/Kg (from grain parameters table 6.3)

Thickness of grain bed to be dried = 45 cm

Bulk density of pulses at 12% w.b.m.c. = 770 kg/m3 (from grain parameters

table 6.2)

Dimensions of plenum chamber = 8 x 7 = 56 ft2

Drying time = 1 hr

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Assumption – specific heat of grain = 0.3934 Kcal/Kg0C (from grain

parameters table 6.5)

Height of the dryer

H = height of bin + height of plenum chamber + 3

H = 2.5 + 0.75 + 3 = 6.25 ft

Volume of plenum chamber

V = 8 x 7 x 0.75 = 42 ft3

Volume of drying chamber

39

3

1024.3

247.3770

2500

mm

mV

×=

==

Air requirement :-

- Bone dry paddy = 2500 ( 1 – 0.12 )

= 2200 Kg

- Initial moisture content = 17% w.b = bdm

m. 100

100×

−

= bd. 482.2010017100

17 =×−

Final moisture content = 12% W.b.= bdm

m. 100

100×

−

= bd. 64.1310012100

12 =×−

Weight of moisture evaporated

= Weight of bone dry paddy x ( x1 – x2)

= 2200 ( 0.20482 – 0.1364 )

= 150.604 Kg

From psychrometric chart ( Appendix 1) :-

Absolute humidity of ambient air = 0.019 Kg/Kg

- Humid heat of ambient air

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S = 0.24 + 0.45 H

S = 0.24 + 0.45 x 0.019

S = 0.24855 Kcal/Kg0C

Let G be the rate of air supply in Kg/min

Heat supplied by the air in 60 min

= G. S. ( t2 – t1 ) θ

= G (0.24855) (85-40) x 60

= 6.71.085 G

Heat Utilised :-

i) As sensible heat of grain

= B. D. grain x Sp. Heat of grain x temperature rise

= Wd x Cp9 x ( tG2 – tG1 )

= 2200 x 0.3934 x ( 70 – 30 )

= 34,619.2 Kcal

ii) As sensible heat of water

= total weight of water x sp.heat of water x temperature rise

= Wd (X1) x CPW ( tG2 – tG1 )

= 2200 x 0.20482 x 1.0 x ( 7.0 – 30 )

= 18024.16 K cal

iii) As latent heat of water vapour

= Water evaporated x latent heat of water

= 150.604 x 600 = 90,362.4 Kcal

- Total heat utilized = sum of above heats

= 34,619.2 + 18,024.16 + 90,362.4

= 143005.76 K cal

Suppose heat loss = 10%

Net heat required = 143005.76/0.9 = 1,58,896 Kcal.

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C.O.E.&T.,Akola


Hence,

671.085G = 1,58896

G = 236.774 Kg/min

- From psychrometric chart humid volume of the ambient air = 0.88 m3/Kg

So air required = 236.774 x 0.884

= 209.308 m3/min

= 209.308 x 35.34

= 7396.94

= 7397 cfm

Static pressure drop

- Surface area of plenum chamber = 8 x 7 = 56ft2

- Since maximum 50% area is perforated area through which air passes = 28 ft2

Air requirement per ft 2ft/cfm 18.26428

7397=

from shedd’s curve ( Appendix 2)

60 cfm = 0.7 inch of water per 1 ft grain depth

∴for 264.18 cfm/ft2 = 3.0821 per 1ft grain depth

Depth of grain = 1.5 ft

So pressure drop = waterofinch 62315.41812

0821.3 =×

Packing of grain in bin may cause 50% higher resistance air flow than the values shown

∴Total pressure drop = 6.934725 in of water

Add the static pressure drop from the duct and floor, usually about ¼ in water if the air

velocity is kept at 1,000 fpm or less

∴Total pressure drop = 6.935 + 0.25 = 7.184725 in

= 7.185 x 2.54 = 18.25 cm

- Density of air = 1.13 Kg/m3

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Pressure drop in terms of air column = 1.13

1000

100

25.18 ×

= 161.5 m

H.P. required

hp 10hp 949.84500

774.2365.1614500

min)/kg( rate flow air)m( column air of Height

≈≈=

×=

×=

Heating System :-

Fuel consumption :-

Diesel

hr/Kg1712.161865.4/4126311

158896

C ,

'qF

nexb

a

≈=××

=

ηηη=

Same as above

Petrol = 15.13 ≈ 16 Kg/hr Bagase dry = 35.76 ≈ 36 Kg/hr

Kerosene = 15.32 ≈ 16 Kg/hr Cotton batting = 40.19 ≈ 41 Kg/hr

L.P.G. = 14.33 ≈ 15 Kg/hr Wheat straw = 38.13 ≈ 39 Kg/hr

Wood = 31.77 ≈ 32 Kg/hr

Selection/Design of a Centrifugal blower :-

1) Specific speed (Ns)

rpmPs

QNNs

75.0= Where Q = cfm ; Ps = inch

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C.O.E.&T.,Akola


rpm 2822185.28220

185.7

7397144075.0

≈=

=

= 28221 rpm

2) Figure 6.1 indicates that two types of air units are quite efficient at Ns = 28,221 rpm a

forward curved. Centrifugal blower and a backward curved (wide) centrifugal blower. While

the forward curved centrifugal blower seems to have a substantially higher static efficiency

Table shows that both the pressure and flow coefficient of forward curved centrifugal blower

are high. Therefore, a forward curved unit is selected.

3) from Table 6.1 ψ = 1.5

4) Since 22

8

dN

Ps1035.2 ×=ψ

5.1)1440(

185.71035.2d

2

82 ××=

d = 23.29 ≈ 24” = 609.6 ≈ 610 mm

5) from table 6.1 φ = 0.62

2Nd

Q175W

φ=

2)29.23(144062.0

7397175

×××=W

W = 2.67” = 67.89 ≈ 68 mm

Blower housing

Width of housing = M

M = 1.25 W + 0.1 d

M = 1.25 x 68 + 0.1 x 610

M = 146 mmDiffuser angle

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C.O.E.&T.,Akola


C1012.9w

1610

14612w

0≈=α

−=α

Table 8.1 :- Air, fan, heat, fuel, Blower and H.P. requirements for Drying pulses with

heated air from different percentage of m. c. & different grain depths

Pulses Capacity 2.5 tonnes/hr

Grain mois-ture cont-ent % w.b

Practical grain depth, ft

Static pressure drop water inch/mm of water

Recomm-ended minimum air flow rate, cfm or m3/min

Heat required Kcal/hr

Fuel consumption, Kg/hr

Blower requirement

H.P.Required

Ini Final17 12 1.5 7.19/183 7397/210 158896 Diesel-17

Kerosene-16LPG-15

Ns=28221rpmd=610mmW=68mm

10

15 12 1 4.079/104 5328/151 114497 Diesel-11Kerosene-10LPG-9

Ns=36620rpmd=446mmW=82mm

3-5

Suggested Drawing

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Technical Specification Model 1 Model 2

Heat output Kcal/hr 1,60,000 1,15,000Drying capacity kg/hr 2,500 2,500Moisture removing capacity (from initial moisture content of 17)

%/hr 5 3

Fuel consumption 1) Diesel Kg/hr 17 172) Kerosene Kg/hr 16 103) L.P.G. Kg/hr 15 9Power Supply 415 V 50 Hz 3 phase 4 wireElectric loading Blower motor HP 10 3.5Fuel pump motor HP 0.5 0.5

Cost Estimation

Particulars Cost Rs. Reference Burner ( Diesel fired) 40,000 Quotation (attached )Heat Exchanger 10,000 Local madeBlower (centrifugal) 5,000 Local madeBlower motor 15,000 Standard Dryer structure fabrication

considering 25% labour cost

30,000 Local made

Unforeseen cost 5000Prod. cost 1,05,000Profit 20% 21,000Selling price 1,26000

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CATALOGUE

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DESIGN OF SUGGESTED MODEL FOR DRYER FOR FARMERS

Case I : SORGHUM

Design a rectangular bin batch dryer having holding. Capacity of 2.5 tonnes of

paddy with 10% moisture content w.b.

Solution: - Assume the following data.


Relative humidity of ambient air = 70%

Initial moisture content of paddy = 15% w.b.

Final moisture content of paddy = 10 % w.b.


Grain outlet temperature = 700C = tG2

Heated air temperature = 850C = t2


Latent heat of water vapour = 600 Kcal/kg (from grain parameter tables 6.3)


Buck density of paddy grain at 10% moisture = 752.9 kgm3 (from grain

parameter tables 6.2)


Drying time = 1 hrs.

Assumptions: -

Specific heat of grain = 0.3934 Kcal/kg0C (from grain parameter tables 6.5)

Height of the dryer: -

H = height of bin and height of plenum chamber

H = 1.5 + 0.75 +3

H = 2.25 ft + 3 = 5.25 ft

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Volume of plenum chamber: -

V = 8 x 7 x 0.75 = 42 ft3

Volume of drying chamber: -

39

3

3

1032.3

3320494

32049409.39.752

2500

mmx

cm

mV

==

==

Air requirement: -

Bone dry paddy = 2500 ( 1 – 0.10 ) = 2250 kg

Initial moisture content = 15%, w.b. = 100 100

xm

m

−

= bd. 65.1715100

15 =−

Final moisture content = 10%w.b. = 11.111db

Weight of moisture evaporated: -

= wt. of bone dry paddy x (x1-x2)

= 2250 (17.65 % - 11.11%)

= 2250 (0.1765 – 0.1111)

= 147.06 Kg

From psychrometric chart: - ( Appendix 1)


Humid heat of ambient air

S = 0.24 + 0.45 H

S = 0.24 + 0.45 x 0.019

S = 0.24855 Kcal/Kg0C

Let, G be the rate of air supply in Kg/min

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C.O.E.&T.,Akola


= G.S. ( t2 - t1 ) Co

= G (0.24855) (85-40) x 60

= 671.085 G

Heat Utilised: -


= S.D. grain x Sp. Heat of grain x temperature rise

= Wd x CP9 x (tG2 -tG1)

= 2250 x 0.3934 (70-30)

= 35406 Kcal

ii) A = sensible heat of water

= total Wt of water x sp.heat of water x temperature rise

= Wd (X1) x CPw (tG2 – tG1)

= 2250 x 0.1765 x 1.0 x (70-30)

= 15885 K cal



= 147.06 x 600

= 88236 K cal

Total heat utilized = sum of above heats

= 35406 + 15885 + 88236

= 1,39,527 K cal


Net heat required = 9.0

139527 = 1,55,030 Kcal

If heat loss = 20%


139527 = 1,74,08.75 K cal.

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C.O.E.&T.,Akola


Hence, 671.085G = 155030

G = 231.013955 kg/min

From psychrometric chart humid volume of the ambient air

= 0.88 m3/Kg

So air required = 231.013955 x 0.884

= 204.22 m3/min

= 205 m3/min = 205 x 35.34 = 7244.7 cfm.

Static pressure drop:-

Surface area of plenum chamber

= 8 x 7 = 56 ft2

Since maximum 50% area is perforated, area through which air passes = 28 ft2

Air requirement per ft2 = 28

7.7244 = 258.74 cfm/ft2

From shedd’s curve ( Appendix 2 ) static pressure drop

For 260 cfm/ft2 = 3 inch of water per 1 ft grain depth.

Depth of grain = 1.5 ft.

So pressure drop = 5.41812

3 =x inch of water

- Packing of the grain in bin may cause 50% higher resistance to airflow than the values

shown

∴ Total pressure drop = 6.75 inch of water

- Add the static pressure drop from the duct and floor, usually about ¼ in water if the air

velocity is kept at 1,000 fpm or less.

∴ Total pressure drop = 6.75 + 0.25 = 7 inch of water = 17.78 cm

Density of air = 1.13 Kg/m3


1000

100

78.17 ×

= 157.345 m

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C.O.E.&T.,Akola


H. P. required: -

= 4500

min)/Kg( rate flow air)m( column air of Height ×

4500

013955.231345.157 ×=

= 8.077

≈ 9 hp = 10 hp

Heating System: -

Fuel Consumption: - nexb

a

C.

'qF

ηηη=

f = 1865.4/41263 1 1

030,55,1

xx

f = 15.729 ≈ 16 Kg/hr

Using Net heating value

F = 1865.4/40785 1 1

155030

xx

F = 15.91 ≈ 16 Kg/hr

Calculated same as above ----

Petrol = 15 Kg/hr Bagass (dry) = 35Kg/hr

Kerosene = 15 Kg/hr Cotton batting = 40Kg/hr

L.P.G. = 14Kg/hr Wheat = 38 Kg/hr

Wood = 32 Kg/hr

Selection/Design of a Centrifugal blower: -

1) Specific Speed (Ns)

rpmPs

QNNs

75.0=

Where N – speed of motor rpm = 1440

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C.O.E.&T.,Akola


θ - Air flow rate m3/min or cfm

Ps = static press m wake gauge or inch.

Ns = 75..07

72451440

Ns = 28481.19

2) Fig 6.1 indicates that two types of air units are quite efficient at Ns = 28451.19 a forward

curved centrifugal blower. While the forward curved centrifugal blower seems to have a

substantially higher static efficiency Table 6.1 shows that both the pressure and flow

coefficient of forward curved centrifugal blower are high. Therefore, a forward curved unit is

selected.


4) Since 22

8

dN

Ps1035.2 ×=ψ

ψ

×=2

32

N

Ps1035.2d

5.1)1440(

71035.22

32 ××=d

d = 22.99 ≈ 23”

d = 584.2 ≈ 585 mm

5) From Table 6.5 φ = 0.62

W = 2Nd

Q175

φ

W = 2)99.22(144062.0

7245175

×××

W = 2.687”

W = 68.246 ≈ 67 mm

71

C.O.E.&T.,Akola


- A review of manufacturer’s literature is done to see that whether blower wheel of

calculated dimensions is available. If it is not available, then slightly smaller or larger

wheel is selected and the performance requirement is revised.

Blower housing: -

- Width of housing = M

M = 1.25 W + 0.1 d Where M = housing width

M = 1.25 x 67 + 0.1 x 585 W = impeller width

M = 142.25 ≈ 143 mm d = impeller diameter

Diffuser angle

−=α 1

585

14312w

010067.9w ≈=α

TABLE : Air, Fan, Heat, Fuel, blower and H.P. Requirement for drying sorghum grains

with heated air from different percentage of M.C. and different grains depths.

Sorghum Capacity







Blower requirement

H.P.Required

Ini Final17 10 2 8.256/2 20 9323/264 200402 Diesel -21

L.P.G. -20Wood - 40

Ns-2762d-640 mmW-69 mm

13

15 10 1.5 7/178 7245/205 155030 Diesel -21 Wood - 40cotton Batting -40

Ns -28482 rpmd-585 mmW-67 mm

10

17 10 1 7/178 5201/148 111771 Diesel -12 Petrol -11Cotton Batting -29

Ns -24132 rpmd-585 mmW-49 mm

5-7.5

Case II : Udid or Mug or soyabean

72

C.O.E.&T.,Akola


Design a rectangular bin batch dryer having holding capacity of 2.5 tonnes of

Udid or Mug or soyabean with 13% w.b.

Solution: - Assume the following data.


Relative humidity of ambient air = 70%

Initial moisture content of paddy = 20% w.b.

Final moisture content of paddy = 13% w.b.


Grain outlet temperature = 700C = tG2

Heated air temperature = 850C = t2


Latent heat of water vapour = 600 K Cal/Kg (From grain parameters table 6.3)


Bulk density of paddy grain at 13% w.b.m.c.= 752.9 Kg/m3 ( From grain

parameters table 6.2)


- Drying time = 1 hr

Assumption – Specific heat of grain = 0.4469 Kcal/Kg0C (From grain parameters table 6.4)

- Height of the dryer


H = 1.5 + 0.75 + 3 = 5.25 ft

- Volume of plenum chamber

V = 8 x 7 x 0.75 = 42 ft3

- Volume of drying chamber

39

3

1032.3

320449409.39.752

2500

mm

mV

×=

==

73

C.O.E.&T.,Akola


Air requirement :-

- Bone dry paddy = 2500 ( 1 – 0.13 )

= 2175 Kg

- Initial moisture content = 20% w.b. = d.b 100x 100 m

m

−

= .. 2510020100

20bd=×

−

- Final moisture content = 13% w.b. = bdm

m. 100

100×

−

= bdx . 943.1410013100

13 =−

- Weight of moisture evaporated

= Weight of bone dry paddy x ( x1 – x2 )

= 2175 ( 0.25 – 0.14943 )

= 218.74 Kg

From psychrometric chart :-

Absolute humidity of ambient air = 0.019 Kg/Kg.

- Humid heat of ambient air

S = 0.24 + 0.45 H

S = 0.24 + 0.45 x 0.019

S = 0.24855 Kcal/Kg0C

Let G be the rate of air supply in Kg/min

Heat supplied by the air in 60 min

= G. S. ( t2 – t1 ) θ

= G ( 0.24855) (85-40) x 60

= 671.085 G

Heat utilised :-


74

C.O.E.&T.,Akola


= B D. grain x Sp. Heat of grain x temperature rise

= W d x Cp9 x ( t G2 – tG1 )

= 2175 x 0.4469 x ( 70 – 30 )

= 38,880.3 K cal

ii) As sensible heat of water

= total weight of water x Sp. Heat of water x temperature rise

= Wd (X1) x Cpw (tG2-tG1)

= 2175 x 0.25 x 1.0 x (70 –30)

= 21,750 K cal



= 218.74 x 600 = 13,1244 Kcal

- Total heat utilized = sum of above heats

= 38,880.3 + 21750 + 131244

= 1918743 ≈ 1,91,875 K cal


Net heat required = Kcal 194,13,29.0

191875 =

Hence 671.0854 = 213194

G = 317.69 Kg/min

- from psychrometric chart humid volume of the ambient air

= 0.88 m3/Kg

So air required = 317.69 x 0.884

= 280.834 m3/min

≈ 281 m3/min

= 281 x 35.34 = 9925 cfm

- Static pressure drop

75

C.O.E.&T.,Akola


- Surface area of pleneum chamber

= 8 x 7 = 56 ft2

- Since maximum 50% area is perforatged area through which air passes = 28 ft2

Which air passes = 28 ft2

Air requirement per ft2 = 2ft/cfm 46.35428

9925 =

- from shedd’s curve ( Appendix)

for 100 cfm/ft2 = 1 inch of water per 1 ft grain depth.

∴ for 354.46 cfm/ft2 = 3.55 inch per 1 ft grain depth

- Depth of grain = 2.5 ft

So pressure drop = water of inch 325.51812

55.3 =×

- Packing of the grain in bin may cause 50% higher resistance to airflow than the values

shown.

∴Total pressure drop = 7.9875 inch of water

- Add the static pressure drop from the duct and floor, usually about ¼ in water if the air

velocity is kept at 1,000 tpm or less.

∴Total pressure drop = 7.98 + 0.25

= 8.2375 inch of water

- Density of air = 1.13 Kg/m3 = 8.2375 x 2.59 = 20.92325 cm


1000

100

92325.20 ×

= 185.162 m

- H. P. required

hp 07.134500

69.317162.1854500

min)/Kg( rate flow air x )m( column air of Height

=

×=

=

76

C.O.E.&T.,Akola


Heating System :-

Fuel consumption :-

Diesel

1865.4/4126311

213194

C .

'qf

nexb

a

××=

ηηη=

./ 2263.21 hrKgf ≈=

Same as above

Petrol = 20.30 ≈ 21 Kg/hr Bagase dry = 47.98 ≈ 48 Kg/hr

Kerosene = 20.56 ≈ 21 Kg/hr Cotton Batting = 53.92 ≈ 54 Kg/hr

L. P. G. = 19.23≈ 20Kg/hr Wheat = 51.16 = 51.16 ≈ 52 Kg/hr

Wood = 42.63 ≈ 43 Kg/hr

Selection/Design of a Centrifugal blower :-

1) Specific Speed (Ns)

rpm Ps

QNNs

75.0= Where Q - cfm ; Ps - inch

75.02375.8

99251440=Ns

Ns = 29,504.019 rpm

2) Figure 6.1 indicates that two types of air units are quite efficient at Ns = 29,504.019 rpm a

forward curved. Centrifugal blower and a backward curved (wide) centrifugal blower. While

the forward curved centrifugal blower seems to have a substantially higher static efficiency

Table shows that both the pressure and flow coefficient of forward curved centrifugal blower

are high. Therefore, a forward curved unit is selected.


4) Since ψ = 22

8

dN

Ps1035.2 ×

77

C.O.E.&T.,Akola


mmd

d

d

63466.633

"2594.24

5.1)1440(

2375.81035.22

82

≈=≈=

××=

5) from table φ = 0.62

mm 80"1276.3W

)94.24(144062.0

9925175W

Nd

Q175W

2

2

≈=××

×=

φ=

Blower housing

Width of housing = 14

M = 1.25 W + 0.1 d

M = 1.25 x 80 + 0.1 x 634

M = 163.4 ≈ 164 mm

Diffuser angle.

−=α 1

684

16412w

0989.8w ≈=α

Table : Air, fan, heat, Fuel, Blower and H.P. requirements for Drying Udid, Mug and

Soyabean grains with heated air from different percentage of m.c and different grain

depths.Grain mois-ture cont-ent % w.b






Blower requirement

H.P.Required

Ini Final20 13 1.5 5.325/136 9925/281 2,1319

4Diesel-22Wood-43Wheat straws-52

Ns-29505rpmd-634mmW-80mm

15

78

C.O.E.&T.,Akola


17 13 1 4.29/109 6605/187 142590 Diesel-15Kerosene-14Wood-29


5

15 13 0.667 2.392/61 4595/130 98749 Wood-20Bagase-23 Wheat straws -24


2

Case III : Paddy

Design a dryer having holding capacity of 2 tonnes of paddy with 15%

m.c.(w.b.)

Solution :-

Assume the following data .

Ambient air temperature = 300 = t

Relative humidity of ambient air = 70% = H

Initial m.c. of paddy = 30% (w.b.) = m1

Final m.c. of paddy = 15% (w.b.) = m2

Grain inlet temperature = tG1 = 300C

Grain outlet temperature = tG2 = 700C

Heated air temperature = t2 = 850C

Exhaust air temperature = t1 = 400C

Latent heat of water vapour = 600 Kcal/kg (from grain parameter table - 6.3)

Angle of repase = 450

Thickness of grain bed to be dried = 45cm

Bulk density of paddy grain at 15% m.c. = 575 Kg/m3 (from grain parameter table - 6.2)

Drying time = 3 hrs

Assumption specific heat of grain = 0.4 Kcal/Kg0C. (from grain parameter table 6.5)

79

C.O.E.&T.,Akola


- Height of the dryer


H = 1.5 + 0.75 + 3 = 5.25 ft

- Volume of plenum chamberV = 8 x 7 x 0.75 = 42 ft3

- Volume of drying chamber

39

3

1032.3

320449409.39.752

2500

mm

mV

×=

==

Air requirement :-

Weight Bone dry paddy = Wd = 2000 - 100

15x2000

Wd = 1700 Kg

Initial moisture content = 30% W.b.

M (d.b.) = 100xm100

m

−

= 100x30100

30

−

= 42.857 % d.b. (X1)

Final moisture content = 15% w.b.

= 17.647 % (d.b.) (X2)

Weight of moisture evaporated

= Weight of bone dry paddy x ( x1 - x2 )

= 1700 ( 0.42857 - 0.17647 )

= 428.57 Kg

80

C.O.E.&T.,Akola


From psychrometric chart (Appendix)


Humid heat of ambient air

S = 0.24 + 0.45 H

S = 0.24 + 0.45 x 0.019

S = 0.24855 Kcal/Kg0C

Let G be the rate of air supply in Kg/min.

Heat supplied by the air in 180 minutes

= G. S. (t2 - t1) θ

= G ( 0.24855 ) (85 - 40) x 3 x 60

= 2013.255 G

Heat utilised


= B.D. grain weight x specific heat of grain x temperature rise

= 1700 x 0.4 x ( 70 - 30 )

= 27200 Kcal

ii) As sensible heat of Water

= total weight of water x specific heat of water x temperature rise

= Wd x (x1) x CDW (+G2 - +G1)

= 1700 x 0.42857 x 1.0 x ( 70 - 30 )

= 29142.46 ≈ 29143 K cal

iii) As latent heat of water Vapour

81

C.O.E.&T.,Akola



= 428.57 x 600

= 2,57,142 K cal

∴Total heat utilised = Sutn of above heats

= 27200 + 29143 + 257142

= 3,13,485 KCal



313485

= 3,48317 Kcal

∴from heat balance

2013.2554 = 348317

G = 173 Kg/min

from psychrometric chart (Appendix - 1) humid volume of the ambient air = 0.88m3/Kg

So air required = 173 x 0.884

= 152.94 m3/min

≈ 153 m3/min

Air required = 5404 CFM

Static pressure drop

Surface area of planum chamber

= 7 x 8 = 56 ft2

∴50% of the area is perforated, area through which air passes = 28 ft2

82

C.O.E.&T.,Akola


Air requirement per m2 = 28

5404

= 193 cfm/ft2

from shedd's curve (Appendix 2 )

Static pressure drop for 30 cfm/ft2 = 0.6 inch of water per 1 ft. grain depth.

∴for 193 cfm/ft2 = 3.86 inch per

1 ft grain depth.

But grain depth is 1.5 ft.

= 18x12

86.3

= 5.79 inch

Packing of grain in bin may cause 50 % higher resistance to air flow than the values

shown

∴Total pressure drop = 8.685 inch of water

Add the static pressure drop from the duct and floor, usually about 1/4 inch of water if the air

velocity is kept at 1000 fpm

∴Total pressure drop = 8.685 + 0.25

= 8.935 inch

= 22.6949 cm

Density of air = 1.13 Kg/m3


1000x

100

6949.22

= 200.84 m

83

C.O.E.&T.,Akola


H.P. required

= 4500

rate flow air x )m( column air of Height

= 4500

0116983.17384.200 ×

= 7.72 hp ≈ 7.5 hp

Heating System :-

fuel consumption

Diesel F = nexb

a

C

'q

ηηη

F = 1865.4/4126311

348317

××

= 35.33 ≈ 36 Kg

= 12 Kg/hr.

Same above

Petrol = 11 Kg/hr Bagase dry = 25 kg/hr.

Kerosene = 11 Kg/hr Cotton batting = 27 Kg/hr

Wood = 21 Kg/hr Wheat strain = 30 Kg/hr

Design of a Centrifugal blower

1) Specific speed (Ns)

Ns =75.0Ps

QN rpm

84

C.O.E.&T.,Akola


= 75.0935.8

54041440

= 20483.268 ≈ 20484 rpm

2) Fig 6.1 indicates that two types of air units are quite efficient at Ns = 28451.19 a

forward curved centrifugal blower. While the forward curved centrifugal blower seems to

have a substantially higher static efficiency Table 6.1 shows that both the pressure and flow

coefficient of forward curved centrifugal blower are high. Therefore, a forward curved unit is

selected.

3) from table 6.1 ψ = 1.5

4) Since

mm 6602698.25d

5.1)1440(

935.81035.2d

dN

Ps1035.2

11

2

B2

22

B

=≈=

××=

×=ψ

5) from table (6.1) φ = 0.62

mm 40"57.1W

)98.25(144062.0

5404175W

Nd

Q175W

2

2

==××

×=

φ=

Blower housing

M = 1.25 W + 0.1 d

M = 1.25 x 40 + 0.1 x 660

M = 116 mm

Diffuse angle

85

C.O.E.&T.,Akola


αW = 12

−1

660

116

0108.9W ≈=α

TABLE : Air, Fan, Heat, Fuel, blower and H.P. Requirement for drying Paddy with

heated air from different percentage of M.C. and different grains depths.

Paddy Capacity - 0.67 tonnes/hr







Blower requirement

H.P.Required

Ini Final30 15 1.5 8.935/227 5404/153 116106 Diesel -12

Wood - 21Cotton Batting - 27

Ns-20484 rpmd-660 mmW-40 mm

7.5

25 15 1 4.15/106 3616/103 77716 Diesel -9Wood - 16Bagas - 18

Ns -29781 rpmd-450 mmW-58 mm

2-3

20 15 0.667 1.71/44 2042/59 44149 Diesel -6 Wood-9Cotton Batting -12

Ns -43516 rpmd-289 mmW-73 mm

0.5-1

Note :

1) From above table we can say that farmers may use wood, cotton batting, wheat straw

as a fuel for drying grains in drying system as it is easily available at free of cost for

them.

86

C.O.E.&T.,Akola


2) Also industrial user of dryers can use diesel, kerosene, LPG as a fuel for drying system

which is economical and efficient for them.

Suggested Drawing

87

DRYER IN COMPLETE ASSEMBLED CONDITION

C.O.E.&T.,Akola


Technical Specification Model Paddy (3)

Heat output Kcal/hr 44,149Drying capacity kg/hr 667Moisture removing capacity

(from initial moisture

content of 20)

%/hr 5

Fuel consumption 1) Kerosene Kg/hr 52) Wood Kg/hr 93) Cotton batting Kg./hr 12Power Supply 240 V 50 Hz single phaseElectric loading Blower motor HP 0.5 - 1

Cost Estimation

Particulars Cost Rs.

Burner ( Diesel fired) 10,000

Blower (centrifugal) 3,000

88

C.O.E.&T.,Akola


Blower motor 1,000

Dryer structure fabrication considering 25% labour cost 5,000

Unforeseen cost 2000

Prod. cost 21,000

Profit 20% 4,000

Selling price 25,000

CHAPTER IX

COMPARISON OF VARIOUS DAL MILL DRYERWe visited to various dryer users, from their information we compare our

suggested models with their running models as follows.

Industry

Factors

R.R. Udyog

Niranjan Dal mill

Bhala Dal mill

Geeta Udyog

Gajanan Udyog

Our suggested model

Manufacturer Thermax

ltd

local made local made local made Super thermal

engg. works Nagpur.

-

Capacity

(tonnes/hr)2.5 4 3 3 2.5 2.5

Sample initial

m.c.(%)9.1 9.5 13.9 9.4 10.3 12

Sample final

m.c.(%)8.5 8.6 8.6 8.8 8.1 10

Reduction in

moisture (%)0.6 0.9 5.3 0.6 2.2 2

Power

consumption

(Watt)

7460 7460 7460 7460 7460 2238

Heat

requirement

(Kcal)

1,20,000 1,20,000 1,20,000 1,20,000 1,20,000 50,000

89

C.O.E.&T.,Akola


Fuel used Diesel Kerosene Kerosene Diesel Coal/woodDiesel,kerosene,

LPG, wood.Fuel

consumption

(kg/hr)

10-12 12-15 12-15 13-15 125 5-6

Cost in Lacks 3.5 2.5 2 2 2 1.25

* Note : By comparing various dryers with our suggested models for reducing 2% m.c.

As we seen a comparison of various dryers in Dal mills in the above table 9.1.

It is very clear that the available dryers are not efficient. We have tested different samples of

pulses before drying and after drying at Dr. P.D.K.V. Akola.

We found that moisture removed after drying on an average 1.8% and fuel

consumption is of cost 264-336 (Rs./hr) which is very costly as compared our suggested

model to Dal Millers. It is very efficient as we can remove 1.8% moisture with fuel

consumption is of cost 192 Rs/hr which is always economical.

This is not enough data as we are also saving large power consumption. As

available dryer consumes 9698 watts power and we are using 2238 watts of power. Which

means that we are saving 80% of powers and it is helpful in reducing operating cost of dryer

user.

Different Visited Dryers

THERMAX INDIA LTD. AVAILABLE AT R.R. UDYOG, MIDC AKOLA

90

C.O.E.&T.,Akola


THERMAX INDIA LTD. AVAILABLE AT R.R. UDYOG, MIDC AKOLA

KOREAN DRYER AVAILABLE AT PDKV, AKOLA

5

91

C.O.E.&T.,Akola


WOOD FIRED DRYER, AVAILABLE AT GAJANAN UDYOG, MIDC AKOLA .CHAPTER X

DIFFERENT DRYER MODELS

SUNCUE GRAIN DRYER

92

C.O.E.&T.,Akola


Specification Chart

Item Model NPC 130Minimum CapacityCapacity (Maize) 13100 KGS

Dimensions Overall Ht.(mm) 7792

Overall Length (mm) 3609Overall width (mm) 1941

Power Consumption 3 phase, 220V/380V/440,50Hz/60Hz6.5 Kw

Fuel BurnerType Gun Type, High pressure spray burning

Ignition High pressure automatic ignition Combustion Max. Combustion 17.5 liter/hour

Fuel Kerosene or Premium dieselGas Burner

Type GIgnition High Pressure automatic ignition

Combustion 150000 Kcal/HrGas Natural Gas

FunctionLoading 55 min (Approx)

Unloading 50 min (Approx)Drying Rate 1.0 ~ 1.5 %/ hour

Safety Devices Thermo Over relay, air pressure switch full

load buzzer, timer, control fuse, burner

alarm, abnormal combustion sensor.

93

C.O.E.&T.,Akola


( Model A ) ( Model B )

TECHNICAL SPECIFICATION

Model Cap. Tons/Batch

Drying Tray (LxBxH) cm

Heat Exchanger

(LxDia) max

Burner Output Keal/hr Max. single stage

burner

Fuel consumption

LPH with single stage

burner

Blower Cap. CMH

Electric motor

HP 440 V 3 Ph.

A.C.

Fuel

Model A

2305x183x12

22440x760 1,00,000 10-12

12,000 at 50 mm

WGSP

7.5

Light oil,

diesel oil

Model B

551x51x18 each tray

244x76x122

96,300 8-12

5,000 cfm at 5cms

WGSP

5 HSD

CHAPTER - XI

OPTIMUM ACHIEVEMENTS

Ultimate Achievements of this project work

Highlighted specific problems of farmers and grain processors.

94

C.O.E.&T.,Akola


At a glance information of effects of temperature on various parameters of grain such

as chemical composition proteins, fats, carbohydrates and quality of grain.

Provided information about various types of drying methods which can be used in

various circumstances.

Guidelines for selection of grain dryers, depending on various characteristics and

parameter of grain.

Provided a simple approach towards designing of grain dryers.

Simple approach towards checking of dryer performance.

Suggested high performance, low cost model for Dal Mill farmers as a option to

costlier imported companies dryers. Our proposed model cost is around is Rs.1.25

lacks while other dryers available in market is 3 to 5 lacks and above.

Thirteen solved problems to find out heat and air requirements for particular type of

grain.

Tables are provided gives information of calorific values of various fuels so that any

body can easily fix up the amount of fuel required for particular application.

At glance information of air requirement static pressure drop, fuel consumption,

blower, HP required in the table is provided to design the drier for various crops in

various grain depths.

Project work gives information about various models available in market.

95

C.O.E.&T.,Akola


CHAPTER - XII

CONCLUSION

There is heavy loss of grain on field which can be avoided by providing simple

and low cost (Rs.25000 dryer design to the farmers. This cost Rs.25,000/- in within reach of

small farmers.

The loss of 10,800 million rupees per year during harvesting of grains can be

saved. It is observed that number of dal millers are using local made dryers of low

performance which are not suitable for their purpose. But they are helpless at the cost of

reputed company driers. Hence the model and design which we have suggested is high

performance, best suited, comparatively low cost and within reach of average dal miler.

The design will definitely improve. Cost of fuel and electricity saved by dal

miller per season ( if 500 tonnes output ) is approximately Rs 10 lacks considering 200 dal

mill in Akola total saving of approximately Rs 20 crores.

If high performance dryers with proper design is suggest one can save crores of

rupees lost due to excessive power and fuel consumption and definitely our project work

gives scientific approach towards designing of high performance dryers matching to the

requirements of particular user.

96

C.O.E.&T.,Akola


BIBLIOGRAPHY

Elements of Agricultural Engineering.

- Dr. Jagdishwar Sahay

Design and Storage of Agricultural Crops

- C.W. Hall

Post Harvest Tech. of Cereal Pulses and Oilseeds

- A. Chakraverty

Unit Operations of Agricultural Processing

- K.M. Sahay

- K.K. Singh

Unit Operations

- McAbey and Smith

Seed Processing and Handling.

- Handerson and Perry

Agricultural Engineers Handbook

- C.B. Richey

- Paul Jacobson

- Carl W. Hall

www.osawagro.com

97

C.O.E.&T.,Akola


APPENDIX 1

C.O.E.&T.,Akola


APPENDIX 2

C.O.E.&T.,Akola


ACKNOWLEDGEMENT

It is challenging task to complete the project work. it is difficult to complete the

project work without any guide line of respective field persons But we have completed the

project,"DESIGN & STUDY OF GRAIN DRYER" under the guidance of our

respective guide Prof. S. K. Patil. He is not only master person in hydraulic &

pneumatic but also key person in technical field, as he designs & fabricates number of

agricultural equipments successfully.

We are thankful to our H.O.D. Prof. C. V. Deshmukh for his valuable

guidance and encouragement. We are also thankful to all staff members of production

department and our friends who help us directly or indirectly in our work.

We are kindly thankful to Prof. R.T. Kausal (M.Tech.) Asst. Prof. Seed

Tech. Dept. Dr. P.D.K.V., Akola. Also B.Sc. B.Tech. Agriculture Engg. Students giving their

valuable knowledge about drying technology.

We are also thankful to the firm owners in MIDC Akola; Mr. R.R. Rathi of

R.R.Udyog and Mr. Bhala of Gajanan Udyog.

Last but not the least Mr. Sachin Shirbhate for co-operating with us for the

completion of Project.

PROJECTEES

C.O.E.&T.,Akola


INDEXSr. No. Particulars Page No.

1 Introduction 012 Theory of Grain Drying 093 Methods of Grain Drying 204 Grain Dryers 235 Selection of Grain Dryers 286 Design Procedure of Grain Dryers 317 Dryer Performance and Testing 508 Suggested Models 559 Comparison of Various Dal Mill dryers 9010 Different Dryer Models 9311 Optimum Achievements 9612 Conclusion 97

Bibliography 98Appendix

design study of grain dryer

Documents