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Background
PAKARAB FERTILIZERS PVT LTD MULTAN
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MANUFACTURING PROCESS
FERTILIZER PRODUCTS CAPACITY PRODUCTION
Calcium Ammonium Nitrate (CAN) 1500 (MTPD)
Nitro-phosphate (NP) 1015 //
Urea 280 //
The intermediate products are Ammonia and Nitric Acid. The company plant therefore has five units excludingPower Generation, Utility and Bagging & Shipping facilities. Production capacities of intermediate plants are
summarized below:
INTERMEDIATE PRODUCTS CAPACITY PRODUCTION
Ammonia 960 (MTPD)
Nitric Acid 1380 //
Nitric Acid (New plant) 1200 //
Nitric Acid Plant (Old) 180 //
Ammonia Nitrate Crystals. On demand.
Product specification
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NP:
N : 22 + 1 %
P2O5 : 20 + 1 %
Moisture : < 0.7 %
CAN:
N : 26 + 0.5 %
CN : < 1.1 %
Moisture : < 0.8 %
Urea:
N : 46 min. %
Biuret : < 1.2 %
Moisture : < 0.5 %
NH3 : < 300 Ppm
Pakarab Fertilizers Limited is an agriculture based company. The core business is manufacturing
of chemical fertilizers. Pakarab is the Pakistan's one of the largest producers of compound
fertilizer situated at Khanewal Road, Multan. The three main products of the company are:
CAN (Calcium Ammonium Nitrate)
NP (Nitro Phosphate)
Urea
Nitro PhosphateIt is unique combination of phosphoric and nitrogen, having balance proportion of nitrogen
(N) and phosphorus (P). It provides synergetic effect in terms of efficiency. It is only
compound N & P contains nitrate type of nitrogen. It is unique in shape and no body can
adulterate it with any other material. It is equally good for application at the time of sowing or
after sowing. It is the best source of early stage nutrient supplement in case of vegetables and
transplanted crops. Its chemically reaction is acidic having pH 3.5. This gives an edge over
other basal fertilizers. Pakistans most of soils are alkaline in reaction and its acidic reaction
makes it more favorable to plant to recover nutrient from soils. It is equally good for manual
or mechanical application. It has good storage capacity.
Calcium Ammonium NitrateIt is only nitrogenous fertilizer having synergetic combination of nitrate and ammonical type
of nitrogen. This makes it superior over urea. Its nitrate portion starts working right after
irrigation and ammonical source works later on. Its N is not lost thru volitization or
leaching as other fertilizers. It works in conditions when soil has very low moisture when noother nitrogenous fertilizer can be applied. It can be used when there is good dew on soil
surface in winter. It is neutral in pH hence farmers can use it with liberty at any stage of crop.
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It is safe and has no phototoxic effect on plant. It is free flowing and can be applied
mechanically or manually. It is technically proven to be the best source of nitrogen
supplement to the crop in case of saline and water logged (salt effected soils and water logged
soils). It works 20 % longer period than other source, means it is more in term of lasting
effects. It is free from adulteration. It contains 2% SOP, an ideal source of potassium and
sulfur supplement. This is also the best fertilizer for fertigation (application after dissolving it
in irrigation water).
In house products Nitric Acid
Ammonia
WATERTREATMENTINTRODUCTION
Water treatment is a very important process in any industry where water is used. Water treatment
is basically used to remove certain impurities or salts from water in order to avoid corrosion or
scaling in pipes or other parts of equipments. These are basic two types of impurities.
Physical Impurities
Chemical Impurities
PHYSICAL IMPURITIESPhysical impurities consist of taste, odor, color, turbidity etc. Taste & odor may be due to
presence of organic matter, industrial wastes etc. Color & turbidity (cloudiness) in water is mainly
caused by the suspended particles like clay, sand etc.
REMOVALOF PHYSICAL IMPURITIESPhysical impurities can be removed by applying sieves in order to separate sand & clay
particles. Physical impurities are removed by
Screening
Sedimentation or Settling
Coagulation
Filtration
CHEMICAL IMPURITIES
Chemical impurities are due to.
Dissolved Salts
These are Carbonates, Bicarbonates, Chlorides & Sulphates of Ca, Na, Mg, K etc.
Dissolved Gases
These are N2, CO2, O2, SO2, & H2S etc.
HARDNESSOF WATERWater which on treatment with soap which produced lather is called hardness.
TYPESOF HARDNESSTEMPORARY HARDNESS
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Temporary hardness is caused by soluble bicarbonates of Ca & Mg such as Ca(HCO 3)2 &
Mg(HCO3)2. Temporary hardness of water is removed by boiling of water.
Ca(HCO3)2 CaCO3 + CO2 + H2O
Carbonates of Ca & Mg thus formed are insoluble & are deposited as scale at bottom of
container, & thus can be removed. No chemicals are used for removal of temporary hardness.
PERMANENT HARDNESS (NON-CARBONATE HARDNESS)This is due to presence of chlorides & sulphate of Ca, Mg, & other heavy metals. This is
not removed by boiling. Chemicals like Ca(OH)2, Na2CO3 are used to remove hardness. Different
process like hot & cold process are used. Hot methods are preferred because it also results in
removal of dissolved gases & capacity of plant in increased. Process of removing hardness of
water is called softening of water.
REMOVALOF CHEMICALIMPURITIESORREMOVALOF WATERHARDNESSThe presence of chemical impurities (dissolved impurities) result in hardness of water.
Removal of softening of water.
THEREAREFOURMETHODSFORWATERSOFTENING. Lime Soda Method
Zeolite Method
Demineralization Method or Ion Exchange Method
Reverse Osmosis
In the power house at Pakarab fertilizers factory we use demineralization method for the
water treatment.
DEMINERALIZATION METHOD.
All natural water contains dissolved salts, which dissociate in water & form charged
particles called ions.
Positively charged particles called cat ions (such as Ca++, Mg++) etc .
Negatively charged particles are called Anions (such as Cl-, SO4--) etc.
DEMIN WATERPLANT
GENERAL DESCRIPTIONThe boiler feed water treatment consist of:
- 3 Cat ion exchangers
- 1 Degasifying tower
- 3 Anion exchanger
- 3 Mixed beds exchangers
- Regenerating equipment for HNO3, NH4OH and NaOH regeneration
Specifications:Plant capacity (200 m3 design) but now a days plant is operated at a capacity of 160-170 m3.
3 Cation Filter
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- Diameter 2600 mm- Height on straight 3060 mm
- Operating pressure 2.54 kgf/cm2
- Design pressure 5.5 kgf/cm2
- Design temp max. 80 0C
- Capacity 1100 m3
- Volume of the cation resin 10,000 ltr Duolite C-20 A- Volume of an inert resin 1550 ltr
1 Degasifier tower
- Diameter 2000 mm- Straight side 4000 mm
- Material welded mild steel, internally rubber lined
- Wall thickness 6 mm
- Packing material 2" saddles, 7 m3 - 1.5" Rashing rings
- Air blowers 2 of Capacity 4350 Nm3/ hr, 5 HP motor, 2900 RPM
2 Degasifying water booster pump- Medium for transportation Cation water pH 2-3
- Specific gravity 1.0
- Capacity 232 m3/hr
- Pressure at inlet 0.1 kgf/cm2
- Pressure at outlet 3.8 kgf/cm2
- Operational temperature ambient
- Suction size 125 mm
- Discharge size 100 mm
- Motor 37 kw, 2900 RPM
3 Anion Filter- Diameter 2300 mm
- Height on straight 3060 mm
- Operating pressure 4 kgf/cm2
- Design pressure 5 kgf/cm2
- Design temp max. 80 0C
- Capacity 990 m3
- Volume of the anion resin 3400 ltr Duolite A-368 PRD
3600 ltr Duolite A-368 DD
- Volume of an inert resin 1200 ltr
3 Mixed Bed Exchanger
- Diameter 1500 mm- Height on straight 2040 mm
- Operating pressure 4 kgf/cm2
- Design pressure 5 kgf/cm2
- Design temp max. 80 0C
- Capacity 12000 m3
- Volume of the cation resin 800 ltr Duolite C-20 MB
- Volume of the cation resin 800 ltr Duolite A-101 D
PROCESS DESCRIPTION
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1. CATION FILTERS (C.I AND C.II)
Raw water run via a flow indicators and water meters to the cation filters and is distributes
at the top of the filters by a distributor over a whole filter surface.
After passing the resin bed the water is collected in the bottom and runs to Co 2
degassifier The cation exchangers are equipped with pressure differential meters.
2. CO2 DEGASSIFIER. (T.I)
The cation water is fed into the top of the Co2 tower and by a distributor over the tower
surface. The water flows through the Rashing rings filling and is collected in the concrete sump in
the bottom of the tower. It is also possible to bypass the tower and to lead the cation water to the
degassed water sump. For the removal of the free Co2 out of the water, air is blown in the up flow
direction through the tower, by a fan. The air leaves the tower together with the free Co 2 at the top
of the tower. In the inlet of the tower the butter fly valve controlled by a level controller is
installed. The sump is equipped with level indicator and a level switch to stop the booster pump in
case of the low pump level.
3. BOOSTER PUMP (P.I AND P.II)The pump are fed with Co2 free cation water from the degassed water pump.
The pump deliver the water to the anion exchanger and are equipped with a pressure gauge in the
discharge line.
4. ANION FILTERS (A.I AND A.II)
The water from the booster pump flows to the anion exchanger via a flow indicators and is
distributed at the top of the filter over the whole surface. After passing the resin bed, the water is
collected in the bottom and flow to the mixed bed exchanger. The filters have pressure differential
meter. To control the effluent quality a conductivity meter is installed. A conductivity alarm is
provided in case of the too high effluent conductivity.
5. MIXED BED FILTERS (MB.I AND MB.II)
The water from the anion exchanger flows to the mixed bed exchangers where it is divided
by a distributor over the total surface. After passing the resin bed, the water is collected at the
bottom and runs via a security resins trap to the treated water tank. This resins trap is provided
with a pressure differential meters, which given an alarm at high differential pressure across the
trap. In the outlet line the water meter is installed by means of the which the treated amount of the
water can be checked. To control the effluent quality of the mixed bed filters, a conductivity
meter with the recorder is installed. A conductivity alarm is provided in case of the too highconductivity of the water.
BACK WASHING OR REGENERATION
1. Cation filters are regenerated with 7 7.5% conc.
2. Anion filters are regenerated with Ammonium hydroxide and casting soda.
IMPORTANT NOTES
1. Back wash of the cation unit can be carried out before or after acid injection.
2. If a back wash is carried out, a double quantity of acid has to be used for regeneration.
FEW DEFINITIONS IN CONNECTION WITH THE ION EXCHANGE
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1. Ion exchange material are synthetic copolymers of the styrene and divinyl benzene.
Reacted with the functional groups which provide the specific ion exchange
characteristics.
2. Free mineral acidity is the total amount or strong acid in effluent from hydrogen
exchanger
3. Total exchangeable ions; are these able to be removed from water by ion exchange. In
hydrogen cation units, it is usually the sum of the concentrations of Ca
++
, Mg
++
and Na
++
.In hydroxide anion units. It is usually the sum of HCo3, Cl, So4, NO3 and HSio3.
4. End point or break through occurs when an un exchanged ions in the effluent exceed a
present limit.
5. Exchange capacity is expressed as KG or ions removed per Cubic feet of resins before
break through.
6. Leakage devotes the steady appearance of unwanted ions in exchanger effluent.
7. Regerant level is no. of Kgs of Regerant chemical applied per cubic meter of resin
8. Regenration efficiency in Kgs of pure Regerant chemicals required per Kgs. of ion
removed .
9. The meaning of pH in water chemistry: the pH scale indicates the acidity or alkalinity of a
solution .
Definition of the pH is the logarithm of the reciprocal of the hydrogen ion concentration
Scale range is usually 0 14 MID point is 7.0 and solution with this pH is said to be neutral. High
value devotes alkalinity and lower value acidity.
CONDUCIVITY
The conductivity of aqueous solution is a function of the kind and quality of the % age of ions
present in the solution. For dematerialized water the conductivity is the straight line function of
the concentration of the any ion present. The conductivity of an aqueous solution is equivalent to
the sum of the conductance of individual ion present in that solution. The conductivity of the
solution is definitely affected by temp. which it is measured free carbon dioxide and ammoniawhen in solution appreciably affect the conductivity
GENERAL RESINS PROBLEMS
Physical degradation of the ion exchange resins may take place through any of the following
mechanism.
1. osmotic shocks.
2. Thermal shocks.
3. Copper fouling.
4. Organic fouling.
5. Oil fouling.6. Micro biological fouling.
7. Mechanical strains.
8. Iron fouling.
9. Insoluble hardness fouling.
10. Calcium sulphates fouling.
11. Aluminum fouling.
12. Silica fouling.
ANALYSIS OF RAW WATER
Total hardness 150 170 ppm as CaCo3Ca++ 40 45
Mg++ 11 15
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Na+ 100 110
K+
Ca++ 40 45
Bicarbonates 268 317 ppm
Sulphates 90 115 ppm
Chlorides 12 20 ppmSilica 10 23 ppm
Total solids 440 480 ppm
Suspended solids 1 1.2 ppm
Free Co2 3 5 ppm
Conductivity 720 740 s / cm
pH 7.5 8.0
KMnO4 consumption 1 1.6 mg/l
COOLING TOWER
The cooling towers are used to provide an economical heat sink. Cooling towers are chosen
because they minimize heat rejection cost while water is being conserved. Water cooling is
generally takes place by evaporation and heat losses. Approximately 1000 BTU are lost from
water for every pound of water evaporated. The amount of the heat lost by the tower through the
sensible heat loss depends on the temperature rise of the ambient air before it leaves the cooling
tower This indicates that both the dry bulb and wet bulb temperature are of great importance. The
wet bulb temperature is the maximum temperature to which the water can be cooled by cooling
tower evaporation. It is not practical to design the cooling tower to bring the sump temperature
equal to the wet bulb temperature since the heat rejection is done primarily by the evaporation of a
portion of the cooling water, cooling towers are designed to bring into contact the maximum
air/water contact.
Types
1. Natural draft cooling towers
2. Mechanical draft cooling towers
Mechanical draft cooling tower
A mechanical draft cooling towers are further divided into two categories:
a). Forced circulation type.
b). Induced circulation type.
Induced draft cooling towers are further classified as below:
FORCED DRAFT COOLING TOWERThe forced draft system pushes the air into the tower where it is directed out form the
tower. The water trickles from the top and air passage is from the bottom thus causing a counter
flow.
COUNTER FLOW
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The counter flow provides the means of the more efficient heat transfer because coolest
water came in contact with the coolest air initially.
CROSS FLOWIn cross flow design air flow is normal to water movement more fill is required to transfer the
given amount of heat. The cross flow has the advantage of an easier path for the HP also the cross
flow has the lower air pressure drop.
HEAT TRANSFERUsually heat transfer occurs within the tower fill area, typically this consist of the wood, asbestos,
cement, plastic fills glasses polyester reinforced polyester grids for supporting the fill poured or
pre cast support beam and columns. Asbestos, Cement or PVC drift eliminators are used to
separate the droplets of the water and prevent them to escape. The selection of the packing
depends upon the installed design
There are two type of arrangement
1. Film Type
2. Splash Bars type
Film type packing are often used in the counter flow type cooling towers
Splash Bars are usually used in the counter flow type of cooling towers
CATEGORIZATION BY AIR-TO-WATER FLOW
Cross flow
Cross flow is a design in which the air flow is directed perpendicular to the water flow (see
diagram below). Air flow enters one or more vertical faces of the cooling tower to meet the fillmaterial. Water flows (perpendicular to the air) through the fill by gravity. The air continues
through the fill and thus past the water flow into an open plenum area. A distribution orhot water
basin consisting of a deep pan with holes ornozzles in the bottom is utilized in a cross flow tower.
Gravity distributes the water through the nozzles uniformly across the fill material.
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Counter flow
In a counter flow design the air flow is directly opposite of the water flow (see diagram below).
Air flow first enters an open area beneath the fill media and is then drawn up vertically. The water
is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air
flow.
Common to both designs:
The interaction of the air and water flow allow a partial equalization and evaporation of
water.
The air, now saturated with water vapor, is discharged from the cooling tower.
A collection orcold water basin is used to contain the water after its interaction with the
air flow.
Both cross flow and counter flow designs can be used in natural draft and mechanical draft
cooling towers.
COOLING TOWER AS A FLUE GAS STACK
At some modern power stations, equipped with flue gas purification like the Power Station
Staudinger Grosskrotzenburg and the Power Station Rostock, the cooling tower is also used as a
flue gas stack(industrial chimney). At plants without flue gas purification, this causes problems
with corrosion.
Wet cooling tower material balance
Quantitatively, the material balance around a wet, evaporative cooling tower system is governedby the operational variables of makeup flow rate,evaporation and windage losses, draw-off rate,
and the concentration cycles:[4]
Sohaib Shamshad Ali
http://en.wikipedia.org/wiki/Flue_gas_desulfurizationhttp://en.wikipedia.org/wiki/Power_Station_Staudinger_Grosskrotzenburghttp://en.wikipedia.org/wiki/Power_Station_Staudinger_Grosskrotzenburghttp://en.wikipedia.org/wiki/Power_Station_Rostockhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flow_ratehttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Image:Counterflow_diagram.PNGhttp://en.wikipedia.org/wiki/Flue_gas_desulfurizationhttp://en.wikipedia.org/wiki/Power_Station_Staudinger_Grosskrotzenburghttp://en.wikipedia.org/wiki/Power_Station_Staudinger_Grosskrotzenburghttp://en.wikipedia.org/wiki/Power_Station_Rostockhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flow_ratehttp://en.wikipedia.org/wiki/Evaporation -
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M = Make-up water in m/hr
C = Circulating water in m/hr
D = Draw-off water in m/hr
E = Evaporated water in m/hr
W = Windage loss of water in m/hr
X = Concentration inppmw (of any completely soluble salts usually chlorides)
XM = Concentration ofchlorides in make-up water (M), in ppmw
XC = Concentration of chlorides in circulating water (C), in ppmw
Cycles = Cycles of concentration = XC / XM (dimensionless)
ppmw = parts per million by weight
In the above sketch, water pumped from the tower basin is the cooling water routed through the
process coolers and condensers in an industrial facility. The cool water absorbs heat from the hot
process streams which need to be cooled or condensed, and the absorbed heat warms the
circulating water (C). The warm water returns to the top of the cooling tower and trickles
downward over the fill material inside the tower. As it trickles down, it contacts ambient air rising
up through the tower either by natural draft or by forced draft using large fans in the tower. That
contact causes a small amount of the water to be lost as windage (W) and some of the water (E) to
evaporate. The heat required to evaporate the water is derived from the water itself, which cools
the water back to the original basin water temperature and the water is then ready to recirculate.
The evaporated water leaves its dissolved salts behind in the bulk of the water which has not been
evaporated, thus raising the salt concentration in the circulating cooling water. To prevent the salt
concentration of the water from becoming too high, a portion of the water is drawn off (D) for
disposal. Fresh water makeup (M) is supplied to the tower basin to compensate for the loss of
evaporated water, the windage loss water and the draw-off water.
A water balance around the entire system is:
M = E + D + W
Sohaib Shamshad Ali
http://en.wikipedia.org/wiki/Parts_per_notationhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Condenser_(steam_turbine)http://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Salthttp://en.wikipedia.org/wiki/Image:CoolingTower.pnghttp://en.wikipedia.org/wiki/Parts_per_notationhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Condenser_(steam_turbine)http://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Salt -
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Since the evaporated water (E) has no salts, a chloride balance around the system is:
M (XM) = D (XC) + W (XC) = XC (D + W)
and, therefore:
XC / XM = Cycles of concentration = M (D + W) = M (M E) = 1 + [E (D + W)]
From a simplified heat balance around the cooling tower:
E = C T cp HV
where:
HV = latent heat of vaporization of water = ca. 2260 kJ / kg
T = water temperature difference from tower top to tower bottom, in C
cp = specific heat of water = ca. 4.184 kJ / (kg C)
Windage (or drift) losses (W) from large-scale industrial cooling towers, in the absence of
manufacturer's data, may be assumed to be:
W = 0.3 to 1.0 percent of C for a natural draft cooling tower without windage drift eliminators
W = 0.1 to 0.3 percent of C for an induced draft cooling tower without windage drift eliminators
W = about 0.005 percent of C (or less) if the cooling tower has windage drift eliminators
Cycles of concentration represents the accumulation of dissolved minerals in the recirculating
cooling water. Draw-off (or blowdown) is used principally to control the buildup of these
minerals.
The chemistry of the makeup water including the amount of dissolved minerals can vary widely.
Makeup waters low in dissolved minerals such as those from surface water supplies (lakes, rivers
etc.) tend to be aggressive to metals (corrosive). Makeup waters from ground water supplies
(wells) are usually higher in minerals and tend to be scaling (deposit minerals). Increasing the
amount of minerals present in the water by cycling can make water less aggressive to piping
however excessive levels of minerals can cause scaling problems.
As the cycles of concentration increase the water may not be able to hold the minerals in solution.
When the solubility of these minerals have been exceeded they canprecipitate out as mineral
solids and cause fouling and heat exchange problems in the cooling tower or the heat exchangers.
The temperatures of the recirculating water, piping and heat exchange surfaces determine if and
where minerals will precipitate from the recirculating water. Often a professional water treatment
consultant will evaluate the makeup water and the operating conditions of the cooling tower and
recommend an appropriate range for the cycles of concentration. The use of water treatment
chemicals, pretreatment such as water softening,pH adjustment, and other techniques can affect
the acceptable range of cycles of concentration.
Concentration cycles in the majority of cooling towers usually range from 3 to 7. In the United
States the majority of water supplies are well waters and have significant levels of dissolvedsolids. On the other hand one of the largest water supplies, New York City, has a surface supply
quite low in minerals and cooling towers in that city are often allowed to concentrate to 7 or more
cycles of concentration.
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Besides treating the circulating cooling water in large industrial cooling tower systems to
minimize scaling and fouling, the water should be filtered and also be dosed withbiocides and
algaecides to prevent growths that could interfere with the continuous flow of the water. [4] For
closed loop evaporative towers, corrosion inhibitors may be used, but caution should be taken to
meet local environmental regulations as some inhibitors use chromates.
Ambient conditions dictate the efficiency of any given tower due to the amount of water vapor theair is able to absorb and hold, as can be determined on a psychrometric chart.
Cooling towers and Legionnaires' disease
Another very important reason for using biocides in cooling towers is to prevent the growth of
Legionella, including species that cause legionellosis orLegionnaires' disease, most notablyL.
pneumophilia[5]. The variousLegionella species are the cause ofLegionnaires' disease in humans
and transmission is via exposure to aerosolsthe inhalation of mist droplets containing the
bacteria. Common sources ofLegionella include cooling towers used in open recirculating
evaporative cooling water systems, domestic hot water systems, fountains, and similar
disseminators that tap into a public water supply. Natural sources include freshwater ponds andcreeks.
French researchers found thatLegionella spread through the air up to 6 kilometres from a large
contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. That outbreak
killed 21 of the 86 people that had a laboratory-confirmed infection.[6]
Drift (or wind age) is the term for water droplets of the process flow allowed to escape in the
cooling tower discharge. Drift eliminators are used hold drift rates typically to 0.001%-0.005% of
the circulating flow rate. A typical drift eliminator provides multiple directional changes of
airflow while preventing the escape of water droplets. A well-designed and well-fitted drift
eliminator can greatly reduce water loss and potential for Legionella or other chemical exposure.
Sohaib Shamshad Ali
http://en.wikipedia.org/wiki/Scalinghttp://en.wikipedia.org/wiki/Foulinghttp://en.wikipedia.org/wiki/Filter_(water)http://en.wikipedia.org/wiki/Biocidehttp://en.wikipedia.org/wiki/Algaecidehttp://en.wikipedia.org/wiki/Corrosion_inhibitorshttp://en.wikipedia.org/wiki/Chromatehttp://en.wikipedia.org/wiki/Legionellahttp://en.wikipedia.org/wiki/Legionellosishttp://en.wikipedia.org/wiki/Particulatehttp://en.wikipedia.org/wiki/Scalinghttp://en.wikipedia.org/wiki/Foulinghttp://en.wikipedia.org/wiki/Filter_(water)http://en.wikipedia.org/wiki/Biocidehttp://en.wikipedia.org/wiki/Algaecidehttp://en.wikipedia.org/wiki/Corrosion_inhibitorshttp://en.wikipedia.org/wiki/Chromatehttp://en.wikipedia.org/wiki/Legionellahttp://en.wikipedia.org/wiki/Legionellosishttp://en.wikipedia.org/wiki/Particulate -
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Nitric Acid Plant
Introduction:The nitric acid plant is designed in two parallel lines: the capacity of each line is 600
metric ton per day.
The process selected for the plant is the medium pressure process. This provides significant
advantages compared with other process as high ammonia conversion efficiency low platinum
losses. Thus allowing 4 6 months operating intervals between catalyst changes, high reliability,
low operating and maintenance costs.
Ammonia and air are the raw materials. NH3 is taken from the storage tank of ammonia and air
from the atmosphere.
1. Ammonia SeparatorIn the ammonia separator, the ammonia is separate by heating from the liquid. Almost 38
% ammonia is evaporated in this loop.. The liquid ammonia is evaporated in evaporator 50% of
liquid ammonia is evaporated in the main evaporator at a temperature of 15 20 C 0 and pressure
is 6 kg/cm2. Ammonia gas stream from both the ammonia separator and evaporator are combined
and heated upto 60 C0 by steam heating in the ammonia heater to avoid carrying over of a liquid
ammonia droplet or mist.
2. Ammonia filtersAfter heating the ammonia, the gas is filtered in the ammonia filters, which is equipped
with filters candles from special ceramics to retain all impurities which might contaminate
through catalyst gausses.
3. Air CompressorsThe process air is taken from air compressor. First the air is filtered through air filters. The
air compressors is driven by steam turbine at one shaft end and by tail gases expander turbine at
the other end of the shaft. The hot air leaving the compressor is cooled down before using in
process in the tail gas heater.
4. Tail gas heaterIn the tail gas heater, the air is separated in to two systems, primarily air which is cooled to
244 0C and used for ammonia oxidation and the secondary air which is further cooled to 100 0C in
the same exchanger. This secondary air is used to bleach the nitric acid product in the bleaching
tower. The tail gas heated from 19 0C 153 0C
5. Ammonia air mixerPrimarily air enters the ammonia air mixer (here it is also heated and filtered) in to which
the heated and the filtered ammonia is introduced and then mixed with air. The mixture contain
10% by volume of ammonia and it leaves the mixer at a temperature of 203 0C.
6. Ammonia burner
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The mixture enters the burner and passes through the catalyst bed consisting of 14 layers
of Platinum and Rhodium silk fine gausses. This alloy consist of 90% Pt. 10% Rh. The burner bed
is equipped with circular bottles and perforated plates to provide uniform distribution of the
mixed gases. Over the total exposed catalyst area of optimum conversion efficiency. The reaction
of ammonia oxidation, initiated by the catalyst, rises the gas temperature up to 890 0C. The hot
burner gases is now passed through the waste heat boiler, by which the most of the heat reaction is
used to generate steam of 41.5 kg/cm
2
. Now the gas is cooled to 490
0
C. This steam is used todriver air compressor and the balanced is exported to utility plant. The reaction involved in this
process is given below.
4NH3 + 5O2 4NTQ + 6H2O
2NO + O2 2NO2
3NO2 + H2O 2HNO3 + NO (g)
The ammonia burner provided gas leaves the W.H.B (waste heat boiler) at a temperature of 2400C and passes through the tail gas heater where it exchanges heat. There are two tail cooler
condensers in parallel with the split flow gases inlet on one end. In the condenser the product gas
is cooled from 205 0C to 50 0C where almost all of the gas is separate from water by condensation,forming a weak HNO3 with approximate 38% HNO3 is pumped into the absorption towers on a
trays with nearly the same acid strength
7. Absorption towerThe process gases leave the condenser and enter in to the absorption column. There are
two A.T in series equipped with 73 sieve trays on which the nitrous oxides are absorbed in the
process water, introduced on the last tray in counter flow to the gas stream.
In the absorption tower first 40 trays are cooled with cooled water while other are cooled
with ammonia in order to maintain gas temperature of approximate 20 0C to achieve the emission
of NOX less then 500 ppm
8. BleachingThe acid product of first absorber is fed to the bleaching tower by using the pump where it
is fed over the rashig rings packing to free from the dissolved colored compounds
The final product, water clear HNO3 with 60% strength and a temperature of 460C enters
the storage tank from where it may be pumped by product acid pump.
OVERALL REACTION
NH3 + 2O2 + H2O HNO3(g) + H2O
Sohaib Shamshad Ali