optimization of amdp-abrod furnace for rice and grain drying

Optimization of AMDP-ABPROD Rice Hull Furnace

Optimization of AMDP-ABPROD Rice Hull Furnace for Grain Drying

G. B. Barrias1, E. V. Casas

2, A. R. Elepaño

3, E. K. Peralta

3, and K. F. Yaptenco

4

ABSTRACT

Dying is an important step in preparing the grains for milling or storage as at

harvest time; grain moisture is too high for subsequent operations that require

reducing to 14%wb for safe processing and storage. In view of this, mechanical dryers

play a vital role in the absence of good weather during the rainy days of the year.

Developing furnaces that rely on agricultural wastes like rice hull for drying will ease

the burden of high prices of petroleum products used by mechanical dryers.

Airflow rate increased the burning efficiency but had no effect on furnace

capacity, efficiency, and overall thermal efficiency. Fuel feed rate increased the

burning efficiency, furnace efficiency and overall thermal efficiency with time interval

of ash removal not affecting the response parameters. Optimization resulted in fuel

feeding rate of 10kg/hr, air flow rate of 0.01m3/s and ash discharge time of 45

minutes as optimum.

Keywords: evaluation, optimization, rice hull furnace, grain drying, furnace

efficiency, furnace capacity, overall thermal efficiency

1 Undergraduate Student. Agricultural and Bioprocess Division, Institute of Agricultural Engineering, College of

Engineering and Agro-Industrial Technology, UP Los Baños, College, Laguna. [email protected] 2 Affiliate Assistant Professor. Agricultural and BioProcess Division, Institute of Agricultural Engineering,

College of Engineering and Agro-Industrial Technology, UP Los Baños, College, Laguna.

[email protected] 3 Associate Professor. Agricultural and BioProcess Division, Institute of Agricultural Engineering, College of

Engineering and Agro-Industrial Technology, UP Los Baños, College, Laguna 4 Assistant Professor. Agricultural and BioProcess Division, Institute of Agricultural Engineering, College of

Engineering and Agro-Industrial Technology, UP Los Baños, College, Laguna. [email protected]

mailto:.%[email protected]

mailto:.%[email protected]


Introduction

Fuel and other forms of energy consumption increase due to industrialization. Coal and

petroleum have the greatest demand for transportation and industrial fuels. With these

demands, prices will increase continuously as these fuels are depleting. The Philippines

greatly relies on imported fuels to supply for the daily demands of the transport and

manufacturing industries. Aside from the consistently increasing prices, the use of fossil fuels

also contributes to environmental problems due to emissions of noxious products detrimental

to health and contributes to global warming.

Biomass like agricultural crops contains chemical energy and organic materials and

converted into resource of heat and power. Agricultural waste materials are cheap and not

hazardous to the environment like rice hulls, the largest by-product of rice paddy after milling

operation. Rice hull is about 25% of paddy production by weight used as fuel for dryer

furnaces, as landfills, and as fuel for stoves. In the Philippines, more than 1.6 million metric

tons of rice hulls are generated each year from more than 14,000 rice mills around the

country (Elepaño and Satairapan, 2000).

The study evaluated and optimized the AMDP-ABPROD rice hull-fed furnace for

grain drying. Specifically, this study determined the technical performance of rice hull-fed

furnace in terms of capacity, efficiency, drying air temperature; determined the effect of fuel

feed rate on the capacities (heat exchanger and furnace) and efficiencies (heat exchanger,

furnace and over all heat transfer) of the furnace; determined the effect of volumetric air flow

rate on the capacities (heat exchanger and furnace) and efficiencies (heat exchanger, furnace

and over all heat transfer) of the furnace; determine the effects of ash removal time interval

on heat generation; and determined and present possible most favorable conditions in

combusting rice hull within an indirect-fired furnace.


Methodology

The Agricultural and Bio-Process Division, College of Engineering and Agro-Industrial

Technology (ABPROD, CEAT) developed with funding from the Agricultural Mechanization

Development Program (AMDP). Figure 1 shows the schematic diagram of the AMDP-

ABPROD furnace.

The feeding system, combustion chamber, mechanical ash removal system, heat

exchangers, flue gas exit, and electric motors for feeding system, ash removal, and blower;

and power transmission assembly comprised the furnace.

Performance Testing

Rice hulls acquired from the Rice Milling Plant in Pila, Laguna of mixed varieties

thus assumed of uniform size, shape, and moisture content. Nguyen (1995) cited the heating

value (14.278 MJ/kg) of rice hulls based on the average of heating values (Beagle, 1978).

a. Left Side View b. Front View

Flue Gas Chimney

Combustion Chamber

Feed Roller

Heat

Exchangers

Screw Conveyor

for Ash Removal Ash Discharge

Outlet

Blower Outlet


Figure 1. AMDP-ABPROD furnace schematic diagram

1. Moisture Content Determination

Four samples of rice hulls (@10g) were selected randomly from the sacks of rice hulls

and placed in tin foil cans for moisture content determination. The pre-weighed samples

were dried in the Carbolite™ Oven at 100oC for 48 hrs. After drying, Adventurer

TM

Electronic Balance measured the final weight of each sample and the moisture contents (wet

and dry basis) were computed using the formulae:

(1)

where, %MCwb = moisture content percentage, wet basis

%MCdb = moisture content percentage, dry basis

Wi = initial weight, g; and

Wf = final weight, g

2. Ash Content Determination

Four samples of rice hull (@1gram) were randomly selected from the different sacks

of rice hulls, placed in crucibles and analyzed for ash content. Thermolyne 1300 electric

furnace burned samples for five (5) hrs at 900oC. Adventurer

TM Analytical balance weighed

the ash samples after burning. Equation 2 expresses ash content dry basis as:

(2)

where, %Ash = ash content, dry basis

Wrh = initial weight of rice hull sample, g; and

Wa =weight of ash, g


3. Feed Rate Determination

The fuel feed rate at each motor setting (1 to 9) was determined by getting the mass of

rice hulls fed per unit time. One (1) kilogram of test fuel was fed into the furnace and

recording the time elapsed in consuming the pre-weighed hulls without burning.

4. Airflow Rate Determination

Alnor® velometer (Figure 2) measured the airflow rate at 50mm return air duct using

6070 diffuser probe at ten (10) trials per opening.

a) b)

Figure 2. a) Alnor® velometer; and b) 6070 Diffuser Probe

5. Preliminary Firing

Coconut shells, husks, dried woods, and kerosene started the combustion process.

Matchsticks initialized firing and tests started when drying air was at least 35oC, while the

fire inside combustion chamber was continuous.

6. Temperature Measurement

A thermocouple thermometer, at the end of the duct measured the temperature of the

heated air. Measurements proceeded at 5 minutes interval from the start of firing until the

temperature drops again to 35oC. A sling psychrometer measured the wet and dry bulb

temperatures of the surrounding air. Figure 3 shows the temperature measuring points.


7. Ash Analysis

Ash residues from the burnt hulls from the bottom of the ash discharge outlet were

collected for analysis. Twenty (20) grams of ash samples from each run were weighed in

AdventurerTM

electronic balance and collected in plastic bag, further burned in Thermolyne®

Electric Furnace (Figure 4) at 900oC for five hours, then set aside to cool down for final

weights determination.

8. Flue Gas Analysis

Only qualitative observation ensued on flue gas in the absence of an accurate

instrument. Observation took note of the presence of dark smoke during rice hull

combustion.

Evaluation of Response Parameters

1. Burning Efficiency

Percent Weight Volatized Method calculated burning efficiency that measured the

remaining combustible materials in the ash samples. Equation 3 expresses burning efficiency

as:

b

(3)

r

(4)

where, Effb = burning efficiency, %

Ar = ash residue (dry basis) in the sample collected from the

furnace, %


15 14 6

18 7 5 8

16 17 9

a) Left Side View b) Right Side View

12 11

12 11

2

4 3 13 10

1

c. Front View d. Top View

Figure 3. Temperature Measuring Points on the furnace

Figure 4. Thermolyne® 1300 Electric Furnace

A = ash (dry basis) in rice hull sample after complete burning,

%

As = weight of ash residue sample, g and


Ab = weight of ash residue after further burning in an electric

furnace, g

2. Heat Exchanger Capacity and Furnace Capacity

The furnace capacity combined heat transferred through the heat exchanger and loss

at chimney and through walls of the furnace. The formulas below computed furnace capacity

as:

– (5)

(6)

(7)

where Q1 = heat transfer at the heat exchanger, kJ/hr

= heat exchanger capacity, kJ/hr

Q2 = furnace capacity, kJ/hr

m1 = mass flow rate of heated air at the heat exchanger, kg/hr

V = volume flow rate of air, m3/hr

D = density of heated air, kg/m3

Cp1 = specific heat of heated air at the heat exchanger, kJ/kg-K

T1 = heated air temperature at the heat exchanger, oC; and

Ta = ambient air temperature, oC

The surrounding air assumed blowing for all the test runs used convective coefficient

h = 100 W/m2K (Van Wylen, 1998) for the computation of heat loss at the flue gas exit.

Bausas (2009) computed the overall coefficient as 8.64 W/m2K for the calculation of heat


loss through the furnace walls. Five (5.0) mm concrete inner layer and 2.5mm thick iron

sheet outer layer formed the furnace walls. Equations 8 and 9 estimated heat losses as:

(8)

where, Qloss1 = heat loss through walls, kJ/hr

U = overall heat transfer coefficient, kJ/s-m2K

A1 = surface area of walls perpendicular to heat flow, m2

ti = temperature inside the furnace, oC; and

ta = ambient temperature, oC

(9)

where, Qloss2 = heat loss at flue gas exit, kJ/hr

h = convective coefficient, kJ/s-m2K

A1 = surface area flue gas exit perpendicular to heat flow, m2

to = temperature inside the furnace, oC; and

ta = ambient temperature, oC

3. Heat Exchanger Efficiency and Furnace Efficiency

The burning efficiency that calculates the heat available is incorporated in the

computation of the heat exchanger efficiency. Conversely, furnace capacity and total heat

available compute furnace efficiency as:

(10)


(11)

– (12)

(13)

(14)

where, Eff1 = heat exchanger efficiency, %

Qa = heat available, kJ/hr

Qs = heat supplied, kJ/hr

mrh = rice hull consumed, kg/hr

Hv = gross heating value, kJ/kg

mair = mass flow rate of heated air, kg/hr

Vair = volume flow rate of heated air, m3/hr

Dair = density of heated air, kg/m3

Cpair = specific heat of heated air, kJ/kg-K

Tair = average temperature of heated air, oC and

Tamb = average temperature of ambient air, oC

Experimental Design and Statistical Analysis

A three level three-parameter fractional factorial, Box-Behnken design of experiment

matrix with 15 runs represented the experiments. Table 1 shows the independent while


dependent parameters consisted of drying air temperatures, burning efficiency, and heat

exchanger and furnace capacities and efficiencies.

SAS v.8 software using Response Surface Regression estimated Analysis of Variance

(ANOVA) that determined the effects of the independent parameters on the response

parameters at 90 and 95% levels of confidence. Statistica Version 7 general linear model

response surface regression algorithms analyzed the optimum furnace operating conditions

with predicted responses.

Table 1. Independent parameter combination for each test run

Combustion

Test Runs

Independent

Parameters Fuel Feed

Rate, kg/hr

Air Flow

Rate, m3/s

Ash Discharge

Time, min Level

1 -1 1 0 10 0.009 60

2 0 0 0 15 0.006 60

3 0 0 0 15 0.006 60

4 -1 0 -1 10 0.006 45

5 0 -1 1 15 0.003 75

6 1 0 -1 20 0.006 45

7 0 -1 -1 15 0.003 45

8 0 1 -1 15 0.009 45

9 1 0 1 20 0.006 75

10 0 1 1 15 0.009 75

11 -1 0 1 10 0.006 75

12 1 -1 0 20 0.003 60

13 -1 -1 0 10 0.003 60

14 1 1 0 20 0.009 60

15 0 0 0 15 0.006 60

Results and Discussion

Preliminary tests checked the uniformity of the fuel feeding, primary air supply, and airflow rate of

the main blower driving the heated air for drying.


1. Rice Hull Moisture Content

Carbolite™ Air oven determined the moisture contents of the rice hulls (25g for

72hrs), randomly obtained from the sacks of test fuel resulted in average moisture content of

10.67%wb.

2. Ash Content

Rice hulls used in the test and evaluation had an average ash content of 20.1% as per

ash analysis, within 18 – 24.5% cited by Nguyen (1995).

3. Feeding of Rice Hull

A roller feeder fed the rice hulls from the hopper to combustion chamber powered by a

1.0kW variable speed motor with manual agitation when clogging occurs. Table 2 summarizes

the design feeding rates based on 30 kg per hour rice hull maximum for small dryer

applications.

Table 2. Feeding Rate Considered for the Experimental Runs

Motor Number

Setting

Average Feeding Rate,

kg/hr

1 10

2 15

3 20

4. Air Flow Rate Determination

Airflow rates were determined by Alnor® velometer (Table 3). At 100% blower opening

(fully opened) the corresponding airflow rate was 0.013 m3/s; at 50% and 25% blower openings

resulted in 0.006 and 0.003 m3/s, respectively, measured at the center of the return air pipe.

These airflow rates were lower compared to the airflow rates used by Bausas (2008) at 0.09,

0.075, and 0.06m3/s resulting from the reduced pipe cross sectional area with the installation of

air control valve. Figure 6 shows the source of the return air that serve as the primary air

supplied during combustion of rice hulls.


Table 3. Computed Air Flow Rates of Primary Air

Opening at the

return air pipe

Average Air Flow

Rate, m3/s

Full 0.013

½ 0.006

¼ 0.003

Figure 6. Pipe for the return air or primary air supply

Performance Testing and Evaluation

Fifteen (15) runs represented the experiments that evaluated the effects of the feeding rate, air flow rate

and time of ash removal on the burning efficiency of hulls, drying air temperature at the blower, heat

exchanger capacity and efficiency, furnace capacity and efficiency, and overall thermal efficiency of the

furnace.

Sometimes coconut husks and dried woods with kerosene assisted the initial firing of rice hulls

that generated smoke for about five (5) minutes inside the combustion chamber and passed through the

hopper and chimney. When drying air temperature reached 35oC and fire stabilized, infra red

thermometer measured furnace and ambient air temperatures. Throughout the combustion run, an orange

flame may arise signifying the presence of carbon (Figure 7).


Figure 7. Color of the fire during test runs

Rice hull burned immediately as it dropped from the hopper through the feed roll groove with

flame peaked after 45 minutes to one hour of combustion. Table 4 summarizes of the experimental

results showing the independent variables and the response variables.

1. Ash Removal

A screw conveyor (75.0mm dia.) removed ashes from the combustion chamber

dropping through the grates and discharge outlet. A 375W electric motor controlled the speed of

the conveyor by belt and pulley transmission. Tests determined the effects of ash removal time

interval on heat generation inside the combustion chamber.

Some rice hulls fell directly on the conveyor passing through the grates without

complete burning. The supply of primary air for combustion aided the removal of ash and

prevented caking of ash. Figure 8 shows the ash discharge assembly.

a) b)

Figure 8. a) Ash discharge assembly and b) Power transmission


2. Furnace Temperature

Furnace temperatures ranged from 200 to 318oC as measured by infrared thermometer.

Run 6 had the highest average furnace temperature while run 11 had the lowest (Table 4). No

slagging and caking of ash residues occurred during combustion due to the presence of primary

air supply and mechanical ash conveyor.

3. Ash Analysis and Burning Efficiency

The Percent Volatilized Method of rice hull analysis estimated the burning efficiency

of the furnace. The lowest computed burning efficiency was 70.8% while 92.3% was the highest

taken from ash samples. Unburned rice hulls from the sides of the combustion bed were not

considered during ash analysis.

Run 1 showed the lowest burning efficiency at the lowest feeding rate of 10 kg/hr

while the supplied air volumetric flow rate was the highest (0.009m3/s) due to some heat going

with the combustion air exiting through the flue gas exit pipe. Runs 5 and 7 showed the highest

burning efficiency with 92.3 and 91.38%, respectively. As the supply of combustion air increases

more heat will be lost to the flue gas exit that result in lower furnace efficiency.

4. Heat Losses

Table 5 summarizes the heat losses on the flue gas chimney and combustion chamber

walls. The average heat loss at the flue gas is 1701kJ/hr, the highest exhibited by Run 6 at

2126kJ/hr lower compared to the study of Bausas (2008) with an average heat loss of 27,250kJ/hr.

This can be attributed to the lower flow rate of the primary air at the combustion chamber.

Similarly, the average heat loss at the furnace walls is 23,371kJ/hr lower than those of Bausas

(2008), attributed also to the lower combustion airflow rates.


Table 4. Experimental Data of the Computed Capacities and Efficiencies (Heat Exchanger and Furnace)

Run Tair, oC

Tamb, oC

Tinside, oC

ρair,

kg/m3

Cpair,

kJ/kg-K

Hv,

kJ/kg

Ql

kJ/hr

Qf,

kJ/hr

Qa

kJ/hr

Qs,

kJ/hr

Effb,

%

Efff,

%

Overall

Thermal

Eff, %

1 39.0 24.3 208.4 1.169 1.0064 14278 18305.8 19134.8 98582.2 829.0 70.81 19.4 13.74

2 39.9 25.8 250.8 1.169 1.0064 14278 22373.0 22748.4 163189 375.4 77.56 13.9 10.81

3 39.4 26.8 272.3 1.169 1.0065 14278 24407.5 24743.1 168161 335.7 79.74 14.7 11.73

4 41.5 29.5 276.5 1.169 1.0066 14278 24558.2 24877.6 112113 319.5 79.75 22.2 17.70

5 44.2 32.0 307.3 1.169 1.0067 14278 27373.2 27511.8 196681 138.6 92.30 14.0 12.91

6 38.4 24.5 318.3 1.169 1.0064 14278 29216.0 29586.3 232414 370.3 82.45 12.7 10.50

7 35.6 24.5 292.5 1.169 1.0064 14278 26647.4 26773.1 194589 125.8 91.38 13.8 12.57

8 37.0 25.8 273.8 1.169 1.0064 14278 24654.8 25283.5 183477 628.7 86.49 13.8 11.92

9 38.4 25.5 275.3 1.169 1.0064 14278 24833.8 25179.5 237020 345.6 83.97 10.6 8.92

10 38.1 24.4 211.5 1.169 1.0064 14278 18607.0 19381.1 180621 774.1 85.23 10.7 9.15

11 36.6 24.3 200.9 1.169 1.0064 14278 17558.2 17887.2 111280 329.0 79.20 16.1 12.73

12 37.0 26.1 240.5 1.169 1.0064 14278 21322.0 21445.5 226155 123.4 80.39 9.5 7.62

13 35.9 26.5 278.4 1.169 1.0065 14278 25050.3 25156.6 164457.7 106.4 84.08 21.2 17.82

14 36.4 25.9 265.6 1.169 1.0064 14278 23836.6 24429.2 119364.7 592.6 89.45 9.6 8.62

15 42.5 34.0 253.5 1.169 1.0068 14278 21826.4 22053.5 147115.2 227.1 81.53 12.8 10.44 Tair Average temperature of drying air Ql Total heat loss

Tamb Average ambient temperature Qf Furnace Capacity ρair Density of drying air Effb Burning efficiency Cpair Specific heat of drying air Efff Furnace efficiency Hv Gross heating value of rice hull Tinside Average inside temperature of furnace


Table 5. Heat loss at chimney and furnace walls

Run

Heat Loss

at Chimney,

kJ/hr

Heat Loss at

Furnace

Walls, kJ/hr

1 1332.6 18305.8

2 1628.7 22373.0

3 1776.9 24407.5

4 1787.8 24558.2

5 1992.7 27373.2

6 2126.8 29216.0

7 1939.8 26647.4

8 1794.8 24654.8

9 1807.8 24833.8

10 1354.5 18607.0

11 1278.2 17558.2

12 1552.2 21322.0

13 1823.6 25050.3

14 1735.2 23836.6

15 1588.9 21826.4

Average 1701.4 23371.3

5. Heated Air Temperature

Continuous feeding of fuel resulted in increased drying air temperature. Since only a specific

amount of test fuel fed into the hopper, the highest temperature occurred before feeding of fuel

stopped. Figure 9 and Table 6 show the average drying air temperatures for each test run.

The test runs indicated the highest average heated air temperature of 44oC in Run 5 at feeding

rate, airflow rate, and ash removal of 15.0kg/hr, 0.003 m3/s, and 75 minutes, respectively. Bausas

(2008) found large temperature changes in most test runs due to the large supply of primary

combustion air and small capacity of the drying air blower. With these heated air temperatures, the

furnace is suitable for thin layer drying where the grain bed is 20.0cm in thickness or less. Nag and

Ilyas (2005) stated that the rate of drying increases with the rise of air temperature up to 60oC without

significant changes on grain quality.


Average Drying Air Temperature, oC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Test Run

0

5

10

15

20

25

30

35

40

45

50

Ave

rag

e D

ryin

g A

ir T

em

p,

oC

Figure 9. Average drying air temperature per test run

6. Furnace Capacity and Efficiency

The furnace capacity ranges from 17887.0kJ/hr to 29586.0kJ/hr as exhibited by test Runs

11 and 6, respectively. On the other hand, the highest furnace efficiency resulted from Run 4 while

the lowest was from Run 12 with 22.0% and 10%, respectively. Run 4 used a feeding rate of

10.0kg/hr while Run 12 used a feeding rate of 20.0kg/hr. Setups with lower feeding rates and shorter

time of ash removal resulted in higher furnace efficiencies. At lower feeding rates and shorter ash

removal time, temperature rise was low but more heat was transferred since more combustion air was

supplied at the fuel bed.

Figure 12 shows the furnace capacity at different run while Figure 13 shows the furnace

efficiencies. Run 4 showed the highest furnace efficiency of 22.0% while Run 12 indicated the

lowest at 9.0%


Furnace Capacity, kJ/hr

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Test Run

0

5000

10000

15000

20000

25000

30000

35000

Fu

rna

ce

Ca

pa

cit

y,

kJ

/hr

Figure 12. Furnace capacities

Furnace Efficiency, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Test Run

0

2

4

6

8

10

12

14

16

18

20

22

24

Fu

rna

ce

Eff

icie

nc

y,

%

Figure 13. Furnace efficiencies

Highest furnace efficiency was recorded at 22.0% exhibited by Run 4 with 10kg/hr feeding rate,

0.006 airflow rate and 45minute interval of ash removal. Run 12 showed the lowest furnace efficiency of

9.5% conducted at 20kg/hr feeding rate, 0.003m3/s air flow rate, and 60minute ash removal interval.

7. Overall Thermal Efficiency

The overall thermal efficiency of the system is accounted from all aspects of the

combustion and the heat distribution in all combustion runs. Burning, heat exchanger and furnace

efficiencies comprised the overall thermal efficiency.

Figure 14 shows the range of the overall thermal efficiency for the 15 test runs ranging

from 8.6% to 17.7% with Run 4 having the highest and Run 12, the lowest. This indicates that

approximately 80% of the heat generated by the furnace was lost to the surroundings through the


Overall Thermal Efficiency, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Test Run

0

2

4

6

8

10

12

14

16

18

20

Overa

ll T

herm

al E

ffic

iency, %

walls and chimney. However, this result is higher than the overall efficiency obtained by Bausas

(2008) of 10% indicating that time of ash removal affected the overall efficiencies of the furnace.

Figure 14. Overall thermal efficiencies

Effects of Independent Parameters on the Responses

ANOVA using response surface regression (PROC RSREG) of SAS program v8 analyzed the

significant effects of independent parameters on the response variables. Table 6 shows the summary

of the effects of independent parameter on the dependent variables.

Airflow rate significantly increased the heat exchanger capacity, efficiency, and burning

efficiency at 95% confidence. Fuel feed rate significantly increased burning, heat exchanger, furnace,

and overall thermal efficiencies at 95% confidence. The time of ash removal significantly increased

burning efficiency 95% confidence. No independent parameters affected significantly heated air

temperature and furnace capacity at 95% confidence level.

Table 7 presents the ANOVA for the response parameters showing the linear, quadratic and

interaction. Burning efficiency, heat exchanger capacity and efficiency, furnace and overall thermal

efficiency, and total model established linear model at 95% level of confidence. On contrary, burning


efficiency adequately fit quadratic model equation. In addition, cross product terms only affected the

burning and heat exchanger efficiencies of the generated regression models.

All response variables showed no significant lack of fit test that determined the sufficiency of the

regression models to represent the experimental data. Hence, the second degree polynomial equations

generated sufficiently represents the response variables.

The coefficient of determination (r2) conveys the proportion of the total variation in the values of

the response parameters that can be accounted for (Dioquino, 2007). ANOVA (Table 7) shows that heat

exchanger capacity had the highest r2 of 0.9747 while heated air temperature had the lowest r

2 of 0.4779.

The model equation defines 97% and 48% of the total variation in the heat exchanger capacity and heated

air temperature, respectively.

The coefficient of variation (CV) indicates the degree of precision on the data gathered. It

expresses the standard deviation as percentage of the mean (Dioquino, 2007). Higher CV means higher

variation or higher inconsistency of data gathered. Heat exchanger efficiency exhibited the highest CV of

26.7%, still acceptable considering the lower efficiencies obtained among indirect furnaces. Burning

efficiency had the lowest CV of 2.1% indicating that the presence of return air pipe supplying the primary

air for combustion improved the performance of the furnace and adequacy of the model.

Optimal Furnace Operating Conditions

General Linear Model (GLM) and response surface regression methodology of Statistica v.7 analyzed and

determined the optimum combustion conditions. The optimization included all independent parameters

affecting the response parameters that could be interpreted using the generated profiles for the predicted

values and desirability within the limits of the independent variables tested during the experiments.

The optimization suggests a fuel feed rate of 10.0kg/hr, airflow rate of 0.01m3/s, and ash

discharge time of 45minutes. These independent parameter combinations resulted in predicted furnace


capacity of 24,278.0kJ/hr, furnace efficiency of 22%, and overall thermal efficiency of 16.70% with 73%

desirability.

Figure 15 shows the graphical relationships of the optimum conditions and predicted response.

Verification of Optimum Conditions

Three (3) additional runs verified the established optimum furnace operating conditions as Table 8

reflects. Percent error difference between predicted and actual responses range from 0.59 to 12.56 with

furnace efficiency as the most accurate evaluated. Burning efficiency with 13% error was the least

accurate when compared to predicted response at optimum conditions.

Figure 15. Predicted Values and Desirability at optimum conditions

Profiles for Predicted Values and DesirabilityFuel feed rate, kg/hr

20.000

33.890

40.522

47.154

55.000

Primary airrate, m3/s Ash removal interval, min Desirability

0..5

1.

35.0

00

40.0

00

45.0

00

Dry

ing a

ir t

em

p,

oC

-5E4

24278.

29895.

4E5

0. .5

1.

19000.

24500.

3000E

2

Furn

ace

capacity,

kJ

/hr

-60.00

34.834

91.206

147.58

200.00

0..5

1.

12.0

00

52.0

00

92.0

00

Burn

ing

eff

icie

ncy,

%

4.0000

18.536

22.063

25.58930.000

0.

.5

1.

9.0

000

16.0

00

23.0

00

Furn

ace e

ff,

%

4.0000

14.204

16.703

19.20224.000

0.

.5

1.

8.0

000

13.0

00

18.0

00

Overa

ll th

erm

al

eff

, %

10. 20.

.73398

.003 .0105 .013 45. 75.

Desirability


Table 6. ANOVA for dependent parameters as affected by the independent variables

Independent

Variables

Sum of Squares

Heated Air

Temp

HE

Capacity

Furnace

Capacity Effb HE Eff Furnace Eff Overall Eff

Feed Rate 21.861368 ns

25024 ns

38482744 ns

228.053528** 0.211680 ** 180.835528** 97.090119**

Air flow Rate 22.157546 ns

734661** 40526238 ns

241.781197** 0.417597** 5.942673 ns

13.066825ns

Ash Discharge Time 15.650013 ns

9908.97 ns

54190346 ns

84.041546 ** 0.005113

ns 20.728561

ns 15.602448

ns

* Significant at 90% confidence level

** Significant at 95% confidence level ns

Not significant

Table 7. ANOVA of dependent variables showing linear, quadratic and cross product components

Source

Sum of Squares

DF Heated Air

Temp

HE

Capacity

Furnace

Capacity Effb HE Eff Furnace Eff Overall Eff

Total Model 9 42.118913ns

740810** 111780127 ns

425.16854** 0.537376** 202.697999** 116.59983**

Linear 3 6.238857ns

711543** 77301965 ns

77.094550** 0.426228** 184.816784** 103.59628**

Quadratic 3 19.921298ns

1582.741 ns

12387627 ns

214.00955** 0.014289 ns

12.284826ns

4.122627 ns

Cross Product 3 15.958759ns

27684 ns

22090534 ns

134.06444** 0.096858 ** 5.596388

ns 8.880918

ns

Total Error 5 46.013739ns

19231 ns

38616925 ns

15.474035 ns

0.020321 ns

13.269167 ns

8.395634 ns

Lack of Fit 3 40.646958ns

7443.699 ns

34718337 ns

7.568235 ns

0.015279 ns

11.427335 ns

7.508741 ns

Pure Error 2 5.366781 11788 3898588 7.905800 0.005043 1.841832 0.886893

r2

0.4779 0.9747 0.7432 0.9649 0.9636 0.9386 0.9328

CV

7.8496 16.5496 11.7034 2.1207 26.7489 11.3635 10.9700

* Significant at 90% confidence level

** Significant at 95% confidence level ns

Not significant


Table 8. Predicted and actual values of dependent parameters at optimum conditions

Drying Air Temperature,

oC

Furnace Capacity, kJ/hr

Burning Eff, %

Furnace Eff, %

Overall Eff, %

Predicted 40.52 24 278.25 91.21 22.06 16.70

Actual 41.46 24 877.64 79.75 22.19 17.70

% Error 2.27 2.41 12.56 0.59 5.65

SUMMARY AND CONCLUSIONS

The study assessed the performance and optimized operation of ABPROD-AMDP furnace. The

furnace had heat exchangers directly installed above the combustion chamber; featured screw

conveyor controlled by a 375 W electric motor for ash removal. Tests evaluated the effects of fuel

feed rate, air flow rate, and ash removal time interval resulted in drying air temperatures ranging from

35.6oC to 44.2

oC. The heat capacities ranged from 17887.0kJ/hr to 29586.0kJ/hr with furnace

efficiencies ranging from 9.5% to 22.2% and highest overall thermal efficiency of 18.0%.

Airflow rate significantly increased heat exchanger capacity, furnace and burning efficiencies.

Fuel feed rate significantly increased the burning efficiency, heat exchanger efficiency, furnace

efficiency and overall thermal efficiency. However, the time interval of ash removal significantly

increased only the burning.

Optimization procedures resulted in fuel feed rate of 10.0kg/hr, airflow rate of 0.006m3/s and

ash discharge time of 45 minutes. At these conditions, the predicted values for the heated air

temperature, burning efficiency, furnace capacity and efficiency and overall thermal efficiency were

40.52oC, 91.21%, 24,278.25 kJ/hr, 22.06%, and 16.70%, respectively with a desirability of 73%.


REFERENCES

Bausas, M. DLS. 2009. Performance Evaluation and Optimization of AMDP-ABPROD Rice Hull

Furnace. Undergraduate Thesis, University of the Philippines Los Baños.

Braunbeck, C. M. 1998. Development of a Rice Husk Furnace for Pre-Heating of the Drying Air of a

Low Temperature Drying System. PhD Dissertation, Germany.

Chandrasekar, V. 2005. Design and Development of Rice Husk Furnace for Paddy Drying. PhD

Dissertation, Tamil Nadu Agricultural University, Coimbatore.

Dioquino, O. A. Jr. 2007. Design Modification, Testing and Evaluation of Biomass Furnace with

Waste Heat Recovery System Using Corncob as Fuel. Undergraduate Thesis, University of

the Philippines Los Baños.

Elepaño, A. R. and K. T. Satairapan. 2000. Development of a Rice Hull Cyclonic Furnace for Drying

Applications. <http://www.retsasia.ait.ac.th/ Publications/ WREC%202000-UPLB.pdf>

Hawkey, R. 1977. Rice Husk Utilization. Proceedings of the Rice By-Products Utilization

International Conference. Spain.

Hien, H. H. 1993. Rice Husk Combustion for Crop Drying. PhD Dissertation, University of the

Philippines Diliman.

Juliano, B. O. 1985. Rice: Chemistry and Technology. 2nd

Edition. USA: American Ass. of Cereal

Chemist, Inc.

Kaupp, A. 1987. Gasification of Rice Hull: Theory and Praxis. Friedrich Vieweg and Sohn, Germany.

Lozada, E. P. 2005. Biomass Combustion of Rice Hull. University of the Philippines Los Baños.

Maheshwari, R. C. and T. P. Ojha. 1977. Fuel Characteristics of Rice Husk. Proceedings of the Rice

By-Products Utilization International Conference. Spain.


Nayak, B. C. and S. N. Jena. 2005. “Rice Statistics”. Rice in Indian Perspective. Chapter 2. Today &

Tomorrow’s Printers & Publ.: Darjaganj, New Delhi, India.

Nguyen, T. N. 1995. Design and Development of a Direct-Fired Rice Husk Furnace For Flat Bed

Paddy Dryer. Graduate Thesis, University of the Philippines Los Baños.

Olivier, P. A. 2005. The rice hull house. <http://www.axwoodfarm.com/ PAHS/RiceHulls.html>.

Ramos, C. L. 2003. “Anatomy and Properties of Rice Grain”. Rice Postproduction Technology.

Philippine Rice Postproduction Consortium: Quezon City, Philippines.

Romanillos, M. O. 2006. Design Modification, Testing and Evaluation of Rice Hull-Fed Furnace with

Waste Heat Recovery System. Undergraduate Thesis, University of the Philippines Los Baños.

The DOE Information Technology and Management Services. 2005. Renewable Energy. <

http://www.doe.gov.ph/ER/BioOSW.htm>.

Tiangco, V. M. 1990. Optimization of Specific Fuel Conversion Rates for a Rice Hull Gasifier

Coupled to an Internal Combustion Engine. PhD Dissertation, UMI.

Van Wylen, G. J. 1998. Fundamentals of Thermodynamics. 5th Edition. John Wiley & Sons, Inc.

Singapore.

optimization of amdp-abrod furnace for rice and grain drying

Documents