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1200 TPD Ammonia production By Vikrant Rana(DCET)
Introduction
Ammonia is an important ni trogenous material used as fert i l izer.
Most of ammonia is made synthetically.It is also obtained as by-product in
some cases.
Ammonia gas is used directly as fertilizer in heat treatment, paper pulping, nitric
acid and nitrate manufacturing, nitric acid esters and nitrocompound manufacture,
explosive of various types and as a refrigerant.
The most important field is of fertilizer. Importance of ammonia in this field is due
to the fact that it is by far the most simple form of actual nitrogen which can be
administrated and the most economical source of other nitrogen chemicals. Hence
ammonia is the backbone of Nitrogen fertilizer processes. Its production is the first
consideration in the initiation of a fertilizer industry. Great strides have been made in the
last few year in the economy and efficiency of ammonia processes.The synthesis of ammonia from Nitrogen and hydrogen was f irst
chemical react ion to be carr ied out under high pressure on commercial
scale. This synthesis reaction has probably been studied more extensively
and is better understood than any other high presure reactions.
The name of Haber, Corl Bosch, Claude, Casale, Fauser, Mont Cenis
s tand out f rom those of ear ly engineers and scient is ts , worked for the
development of first commercial synthesis.
In India, t i l l 1948, the only factory which was producing synthetic
ammonia was small concern, Mysore Chemicals and Fert i l izers Company
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Ltd. at Belegula, Mysore. The Fer t i l izer Factory at Sindr i , Indias f i rs t
major state-owned enterprise, went into production on October 30, 1961. a
gradual expansion followed and soon fert i l izer plants were commissioned
at Nangal (1961), Trombay (1968), Namrup (1969), Durgapur (1974) and
Barauni (1976).
In 7 t h decade of 20 t h century,a revolution in ammonia manufacturing
came about as the reciprocat ing compressors common at that t ime were
replaced by centrifugal units. At that time, the ammonia
process was regarded as highly ef f icient , a mature process , but careful
examination of the process step by step and the severe economic pressure
led to major improvements and cost drop approaching to 50 percent. Some
of the impor tant developments are bet ter catalys ts , bet ter conver ters ,
r eplacement of r ec iprocating compressors to cent ri fugal unit s, lone
pressure techniques, energy conservation, digital computer control process
and the most recent development on which researches have been made and
c om me rc ia l b ac kg ro un ds a re b ei ng s tu die d i s t o c om mi ss io ne d a
Compressor Ammonia Plant . High pressure ammonia synthesis becomes
economically attractive with this technique of compressorless manufacture
process of ammonia. As without application of compressor, high pressure
synthesi s gases are obta ined which have many advantages over low
pressure techniques e.g. at high pressure ammonia condenses at normal
cooling water temperature, reduced amount of recirculat ion thus replacing
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recirculat ing compressure by a stat ic ejector . Trend in again in favour of
high pressure techniques for ammonia manufacture.
Process And Process Selection
Ammonnia manufacturing consists of six phases :-
1. Manufacture of Reactant gases.
2. Purification
3. Compression
4. Catalytic reaction
5. Recovery of ammonia formed
6. Recirculation
RAW MATERIAL-
Raw material requirement consists of a sources of hydrogen, the nitrogen is
obtained from air, the feed stock supplies the hydrogen. The production of ammonia
depend upon cost and operability of available raw material for hydrogen. Different raw
materials for hydrogen can be
Wood
Coal Refinery gas
Electrolysis of water Naphtha
Coke oven gas Fuel oil
Natural gas Crude oil
Liquid petroleum gas
MANUFACTURING PROCEDURES-
The principal manufacturing process that are used for synthetic ammonia
production are steam water gas process, the steam hydrocarbon process, the coke oven
gas process & electrolysis of water.
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Much research work is s t i l l diverted to f ind cheaper manufacturing
methods .Many new plants use ethanol amine to remove carbon dioxide
from gas streams instead of high pressure water.
Nitrogen required for synthesis gas is obtained usual from an air liquefaction
plant. In water gas and natural gas process, nitrogen is obtained in same manufacturing
process as hydrogen. Air is added in secondary reforms of natural gas process and reacts
with carbon monoxide to furnish carbon dioxide and nitrogen.
Cost is greatly influenced by the pressure, temperature, catalysts and
raw material used. Raw material selection depends upon the availabil i ty
and cos t of r aw mater ia l . I f the p lant i s near some ref inery then raw
material can be naphtha, natural gas or LPG, but in case i t is near a coal
mine, one should depend on coal as raw material for hydrogen. There may
be some other cases where electricity is readily available to meet the
r eq ui re me nt s f or e le ct ro lys is th en h yd ro ge n c an b e o bt ai ne d b y
electrolysis of water
Comparsion of processes
Many variation of the original Haber process for the synthesis of ammonia are now used
in commercial practice, some varying to such an extent that they are identified by a name,
often that of group of men developing them. Important among these are modified Haber
Bosch, Claude, Casale, Fauser, and Mont Cenis processes. All of them are fundamentally
the same in that nitrogen is fixed with hydrogen as ammonia in the presence of a
catalyst , but have variation in arrangement and construction of equipment , composition
of catalyst, temperature and pressure used. Table C gives a condensed comparison of
different processes 40% conversion of the gas upon passes through a single converter and
85% conversion after passes through a series of converter . gas is vented after one pass
through the converter.
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Table C : Synthesis Ammonia Systems
Designation Pressure Temp.
0C
Catalyst Recir-
culation
Conver.
%
Haber-Bosch 200-350 550 Doubly
Promoted
iron
Yes 8
Modified
Haber-Bosch
200-300 500-550 -Do- Yes 20-22
Claude 900-1000 500-650 Promoted
iron
No 40-85
Casale 600 500 Promoted
iron
Yes 15-18
Fauser 200 500 Promoted
iron
Yes 12-23
Modified Haber- Bosch Process
The ammonia concentration in the circulation gas leaving the catalyst is 10-11
mole %. In the condenser the ammonia concentration is reduced by condensation to
equilibrium at the exit temperature of the condenser. The condensed ammonia is
separated from the circulating gas, and the gas is boosted in pressure by a circulating
compressor to overcome the pressure drop in the synthesis loop.
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The Claude Process
This process depar t f rom the Haber process more than any of the
o ther ammonia s yn thes es p rocess , t he r es idua l gas i s was ted t o t he
a tmosphere or u ti li zed for i ts heat content. The l arge amount of heat
evolved in operating at space velocit ies of 100,000 with as much as 40%
of the hydrogen n it rogen mixture conver ted to ammonia in one pass ,
called for a special converter design. In his original process, Claude used
-+ from the liquefaction of air.
Among advantages claimed for the Claude process are the following:
1. Greater compactness, simplicity, and case of
construction of the converter , s ince under the high pressure used
the gases have smaller volume.
2 . E li mi na ti on o f t he expensi ve hea t exchanger s r equi red i n
processes operated at lower pressure.
3. Removal of ammonia wi th water cool ing alone, rather than by
ammonia refrigerators or scrubbing processes.
Ci ted agains t these advantages are the shor ter l i fe of conver ters , high
apparatus upkeep in the high-pressure operation, and the efficiency loss in
wasting approximately 20% of the makeup gas , which is unconverted.
Modifications of the Claude process include recycling of the gas through
the synthesis converters.
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The Casale Process
Pressure of 500-900 atm are used in this process which is otherwise distinguished by
the method used for controlling catalyst temperature in the specially designed
converter. A method involving recirculating gas around a synthesis loop,
similar to the Haber process, is used. As in the Claude process, the higher
pressures allow liquefaction of the ammonia at temperatures that can be
attained by water cooling. The basis for heat control of the catalyst is to leave 2
or 3% ammonia in the gas to the converter, thereby showing down the rate of
formation of ammonia and eliminating excessive heating of the catalyst.
The Fauser Process
This pressure incorporates some features not previously mentioned. Electrolytichydrogen from Fauser cells and nitrogen from liquid air unit or from a purification unitutilizing tail gases from absorption towers in the ammonia oxidation plant are used. Themixture of hydrogen and nitrogen is compressed to 200-300 atm and, after passingthrough an oil separator goes to an oxygen burner.
In the oxygen burner any oxygen contained in the gas mixture combines with hydrogen
in the presence of a copper catalyst the water formed is condensed out in a cooler and
removed in a water separator.
The Mont Cenis Process
This process was originally developed to use hydrogen separated from coke oven
gas by a liquefaction process, and nitrogen was obtained by the liquefaction of the air.
The essential characteristics of the Mont Cenis process are its operating pressure of 100
atm or less.
Mixed hydrogen and nitrogen, after being compressed to 100 atm and heated to about
3000C in interchangers, passes through a carbon monoxide purifier. In the purifier, while
in contact with a nickel catalyst, carbon monoxide and oxygen contained in small
quantities in the gas react with hydrogen to form methane and water.
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Material Balance
Ammonia Production = 1200 TPD=2941.18 kmol/hr
N2 + 3H2 2 NH3
Let % conversion=20%
Which means, 1 kmol N2 forms 2x0.2=0.4kmol NH3
Assuming losses=8%
Amoonia production=2941.18/0.92=3196.93kmol/hr
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Hence, N2 required=3196.93/0.4=7992.34kmol/hr
Air required=7992.34x100/79=10,117kmol/hr=10117x22.4=226621 Nm3/hr
Siimilarly, H2 required=3x7992.34=23977kmol/hr
Reaction taking place in the gasifier isCnHm + n/2O2 nCO + 2H2OCnHm + nH2O nCO + (m/2+n)H2O
At high temperature,
CnHm + ( n + m/4)O2 nCO2 + m/2H2O
Composition is given in weight percent.
C = 84.98%
H = 12.07%
S = 1%
N = 0.4%
O = 1.5%
Composition of gases coming out of the gasifier is given as-
CO = 42%
H2 = 51.23%
H2S = 0.23%
CO2 = 5.7%
N2 = 0.18%
Ar = 0.02%
CH4 = 0.5%
Material balance across H2S absorber
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Basis: 100 kmoles or Raw gas
CO = 42 kmoleH2 = 51.23 kmole
H2S = 0.23 kmole
CO2 = 5.7 kmole
N2 = 0.18 kmole
Ar = 0.09 kmole
Now, maximum concentration of H2S in H2S free raw gas in limited to 0.3 ppm.
Amount of H2S to be removed = 0.229997 kmole
In H2S free gas
H2 = 51.23 kmole % of H2 = 51.23/99.77x100 = 51.34
CO = 42 kmole % of CO = 42/99.31 X 100 = 42.09
H2S = 0.3 ppm % of H2S = 0.3 ppm
CO2 = 5.77 kmole % of CO2 = 5.77/99.31x 100 = 5.78
CH4 = 0.5 kmole % of CH4 = 0.5/ 99.31x 100 = 0.501N2 = 0.18 kmole % of N2 = 0.18/99.31x 100 = 0.18
Ar = 0.09 kmole % of Ar = 0.09/99.31x 100 = 0.09
Total no. of moles = 51.23 + 42.09 + 0.00003 + 5.77 + 0.5+0.18 + 0.09 = 99.77 kmol
Material balance across CO shift converter
Basis 100 kmole of H2S free gases
Now since 97% of CO is converted in converter
Therefore kmoles of CO2 in product = 5.78 + 42.09 x 0.97
= 5.78 + 40.8 = 46.6 kmoles
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similarly, kmoles of H2 in the
Product = 51.34 + 40.8 = 92.14
Kmole of CO = 42.09 40.4 = 1.26
Kmole of H2S = 0.3ppm
Kmole of CH4 = 0.501 kmole
Kmole of Ar = 0.09 kmole
Kmole of N2 = 0.18 kmole
Total no of moles in the product stream = ( 46.4 + 92.14 + 1,26 + 0.501 + 0.09 + 0.18 )
= 140.77 kmole
H2 in the product = 92.14/ 140.77 x 100 = 65.45%
CO2 in the product = 46.6/140.77 x 100 = 33.1%
H2S = 0.3 ppm
CH4 = 0.501/140.77 x 100 = 0.36%
Ar = 0.09/140.77 x 100 = 0.063%
N2 = 0.18/140.77 x 100 = 0.13%
Material balance across CO2 Absorber
Basis 100 mole of converted gas
Taking efficiency of the absorber to be 92%
CO2 to be removed = 0.92 x 33.1
= 30.45 kmole
CO2 in the product stream = 2.65 kmole
Total no of moles in the product stream
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= ( 2.65 + 65.45 + 0.89 + 0.13 + 0.06 + 0.36 )
= 69.54 kmole
CO2 = 2.65/69.54 X 100 = 3.8
H2 = 65.45/69.45 X 100 = 94.2
CO = 0.89/69.45 X 100 = 1.3
CH4 = 0.36/69.45 X 100 = 0.518
N2 = 0.13/69.45 X 100 = 0.19
Ar = 0.064/69.45 x 100 = 0.09
H2S = 0.3 ppm
Material balance across Adsorber
The main function of absorber is to adsorb H2S, CO & CO2. They are reduced to an
amount which is negligible.
Moles remained = 100 3.8 1.3 = 94.9 kmole
% of gas after adsorption
H2 = 94.2/95 X 100 = 99%
CH4 = 0.54
Ar = 0.095
N2 = 0.19/95 = 0.2
N2 is added in such a way that
H2 : N2 becomes 3 : 1
Suppose x mole of N2 is added
99 = ( 0.18 + x ) x 3
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x = 32.80
Total no of moles = 99 + 32.80 + 0.54 + 0.095
= 132.43 kmole
% of N2 in the product = 32.80/132.43 x 100
= 24.76 %
% of H2 in the product = 99/132.43 x 100
= 74.76%
% of Ar = 0.072%
% of CH4 = 0.54/132.43 X 100 = 0.4%
Material balance across NH3 Separator
Now in NH3 Separator 3 streams are there out of which 2 are going out and one is making
in the stream that moves in F13 & stream that gives main product is F14 & F 15.
F16 is recycle stream moving to compressor.
Suppose the moles of F 13 stream are as follows
N2 = a
H2 = 3a
NH3 = b
Ar = c
CH4 = d
Now solubility of H2 , N2 , Ar, NH4 in liquid NH3 is given as
Solubility of H2 = 0.0998 cm3 of H2 at NTP/gm of liq NH3
Solubility of N2 = 0.1195 cm3 of N2 at NTP/gm of liq NH3
Solubility of Ar = 0.154 cm3 of Ar at NTP/gm of liq NH3
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Solubility of CH4 = 0.304 cm3 of CH4 at NTP/gm of liq NH3
For F 14 stream
H2 = 0.0998/22414 x 17 x 3a x 22 x 298/273
= 5.45 x 10-3 a
N2 = 0.1195/22414 x 17 x a x 22 x 298/273
= 2.18 x 10-3 a
Ar = 0.154/22414 x 17 x c x 22 x 298/273
= 2.8 x 10-3 c
CH4 = 0.304/22414 x17 x d x 22 x 298/273
= 5.54 x 10-3 d
Now we want 1200 TPD production
Therefore NH3 production in F 14
= 1200 x 1000/(17x24)
= 2941.18 kmole/hr
Now for F15 stream
Equilibrium of NH3 in gas phase with liq. NH3 in separator = 5.9%
Assuming that total inert conc. In stream from the separator = 5%
H2 + N2 = 100 5.9 5 = 89.1%
H2 = x 89.1 = 66.83%
N2 = x 89.1 = 22.28 %
NH3 = 5.9%
Ar + CH4 = 5%
Since CH4 is 2.5 times the Ar.
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Ar = 1.43%
CH4 = 3.57%
Now applying material balance on NH3
separator
F 13 = F 14 + F 15
H2 balance : 3a = 0.6683 F15 + 5.45 x 10-3 a (1)
N2 balance : a = 0.2228 F 15 + 2.18 x 10-3 a (2)
NH3 balance : b = 2450.98 + 0.059 F 15 (3)
CH4 balance : d = 5.54 x 10-3d + 0.0357 F 15 (4)
Ar balance : c = 2.8 x 10-3c + 0.0143 F 15 (5)
From (5)
0.9945d = 0.0357 F15 (6)
d = 0.0359 F15
From eqn. (1)
2.99478 a = 0.6683 F15
a = 0.223 x F15 (7)
From eqn. (4)
0.9972 c = 0.0143 F 15
c = 0.01434 F 15 (8)
Now total moles in product stream F14
= 2941 + ( 2.18 + 5.45 ) x 10-3 x 0.223 x F15 + 2.8 x 10-3 x
0.0143 F 15 + 5.54 x 10-3 x 0.0359 F15
= 2941 + 1.9404 x 10-3 F15
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of NH3 separator = 98.5%
Therfore
2941 = 0.985
2941 + 1.9404 x 10-3 F15
2941= 2414.22 + 1.9113 x 10-3 F 15
F 15 = 2302kmol/hr
0.0019113
From (7)
a = 5133.7 kmol/hr
From (8)
c = 330.12 kmol/hr
From (6)
d = 826.45 kmol/hr
& from (3)
b = 4299.24 kmol/hr
Now for F-13 stream
H2 = 3 x 5133.7 = 15401.1 kmol/hr
N2 = 5133.7 kmol/hr
NH3 = 4299.24 kmol/hr
Ar = 330.12kmol/hr
CH4 = 826.45 kmol/hr
Total no of moles = 25990.61kmol/hr
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H = 15401.1 = 59.26%
25990.61
N2 = 19.75%
NH3 = 16.52%
Ar = 1.28%
CH4 = 3.18%
For F14 stream
NH3 = 2941 kmol/hr
H2 = 5.45 x 10-3 a
= 5.45 x 10-3 x 5133.7
= 27.98kmol/hr
N2 = 2.18 x 10-3 x a
= 2.18 x 10-3 x 5133.7
= 11.19 kmol/hr
CH4 = 5.54 x 10-3 x d
= 5.54 x 10-3 x 826.45
= 4.58 kmol/hr
Ar = 2.8 x 10-3c
= 2.8 x 10-3 x 330.12
= 0.924 kmol/hr
Total no of moles in product
= 2985.67 kmol/hr
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NH3 = 2941 = 98.5%
2985.67
H2 = 27.98 = 0.94%
2905.67
N2 = 11.19 = 0.38%
2985.67
CH4 = 4.58 = 0.15%
2985.67
Ar = 0.924 = 0.03%
2985.67
Material balance across NH3 converter
Suppose in F12 stream
N2 = x kmole
H2 = y kmole
NH3 = z kmole
Assuming 20% conversion
For N2 balance
X [1 0.2] = 5133.7
X = N2 = 6417.125 kmol/hr
H2 = 3 x 6417.125 = 19251.4 kmol/hr
NH3 formed = 2 x 0.2 x 6147.125
= 2566.85kmol/hr
NH3 in F12 = 4299.24 - 2144.48
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= 1732.4 kmol/hr
CH4 in F12 = 826.45 kmol/hr
Ar in F12 = 330.12kmol/hr
Total no of moles in F12 = 28557.5 kmol/hr
N2 = 6417.125 X 1000 = 22.47%
28557.5
H2 = 19251.4 X 1000 = 67.42%
28557.5
NH3 = 1732.4 X 1000 = 6.04%
28557.5
CH4 = 826.45 X 1000 = 2.89%
28557.5
Ar = 330.12 X 1000 = 1.17%
28577.5
Applying material balance across compressor
F11 + F 16 = F 12
F11 + F 16 = 28557.5
Applying H2 balance
0.7476 F11 + 0.6683 F 16 = 0.6742 x 28557.5
0.7476 [285557.5 F16] + 0.6683 F 16 = 0.6742 X 23855.25
Therefore F16 = 26432.79 kmol/hr
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Recycle = 26432.79 kmol/hr
F11 = 28557.5-26432.79
= 2124.79 kmol/hr
Suppose the kmole of feed gases coming from absorber is A
A x 0.99 = 2124.71 x 0.7476
A = 1588.43 kmol/hr
Amt of N2 Added = 2124.71 x 0.2476
= 526.1kmol/hr
Across the absorber applying overall material balance.
H balance,
F10 x 0.942 kmol/hr
F10 = 1422.8025 kmol/hr
Applying material balance across CO2 removal
F8 x 0.6545 = F10 x 0.942
F8 = 1422.8025 x 0.942 = 2047.79 kmol/hr
0.6545
Applying material balance across shift converter
F7 x 0.534 = 2286.17 x 0.6545
F7 = 2914.49 kmol/hr
Applying material balance across H2S removal
F5 x 0.5123 = 2914.49 x 0.5134
F5 = 2920.75 kmol/hr
H2S removed = 2920.75 x 0.0023 2914.49 x 0.3 x 10-4
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= 6.63 kmol/hr
For H2S gas
W = 0.094, TC = 373.K PC =89.63 bar
P =49 bar T = -220C = 2510 K
Tr = 257 = 0.67
373.5
Pr = 49 = 0.55
39.63
B0 = 0.083 - O.42 2 = - 0.59
( 0.67)1.6
kg/m2B = 0,139 - 0.172 = -0.78
( 0.67)4.2
Z = 1 - 0.59 x 0.55 = 0.52
0.67
PV = Z n RT
49 x V = 0.082 x 0.55 x 251 x 5.94
V = 1.297 m3
Solubility of H2S in Methanol
= 60 m3 of H2S at - 22
0C & 49 atm
m3 of methanol
Weight of methanol required
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= 1.534 = 2.56 x 10-2 x 1215
60 = 31.1 kg
kmol of methanol required = 31.1 = 0.97 kmol/hr
32
3% by weight of carbon is converted into coke, therefore only 97% of carbon is present
in raw gas.
Coke formed = 20556.22 x 0.8489 x 0.03
= 523.5 kmol/hr
Applying mass balance across carbon recovery unit;
F3*=F5*- mass of coke formed (* denotes mass per unit time)
F3*=2920.75x14.6-523.5x12=36361 kg/hr
Applying mass balance across gasifier
F1*=F3*-F2*=36361-462.42x32=21564 kg/hr
Hence, Fuel Oil requirement=21,564 kg/hr
Energy Balance
Data for Specific heats
For Gases Cp/R= A+ BT +CT2 +DT2
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A 103 B 106 C 10-5 D
CH4 1.702 9.081 -2.164
CH 3 OH 2.211 12.216 -3.450
NH3 (g) 3.578 3.020 -0.186
CO 4.376 1.257 - 0.031
CO 2 5.457 1.045 - 1.157
H 2 4.249 0.422 0.083
H2S 3.931 1.490 - 0.231
N2 3.280 0.593 0.040
O2 3.639 0.506 - 0.227
SO2 5.699 0.801 - 1.015
H2S (vap) 3.470 1.450 0.121
For liquids Cp/R =A +BT +CT
2
A 103 B 106 C
NH3 (l) 22.626 - 100.75 192.77
Methanol 41.653 - 210.32 427.20
Water 8.712 1.25 - 0.18
For Solids Cp/R = A +BT + CT2
A 103 B 10-5 C
Carbon (s) 1.771 0.771 - 8.67
S 4.114 - 1.728 - .78
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Since, the assumed conversion=97% , from graph Inlet Temperature=3500C
Reaction is, CO +H2O CO2 +H2
( H)298 = (HCO2 + HH2 ) (HCO +HH2O)
= (-393509)- (- 110525 285830)
= 2846 kj/kmole
Mole, of CO converted =583.6 kmole/hr
( H)298 = 2846x 583.6
= 16.6 x 105 kj/hr
( H)R = -2.27 x 107 kj/hr
For adiabatic condition, HR + HF8 + H298 = 0 Hp =2.17 x 107 kj/hr
460 (T- 298) + 1.17/2 x 10 3 (T2 2982 )
+0.3 x 105 (1/T 1/298) = 1954.07
Solving this equation by heat & trail we get
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T = 622.50 K
i.e.t = 349.50C
In cooler converted gas is cooled from 349.5 to 42.50C, i.e. from
Heat lost by converted gas = 1335.5 x 8.314 {4.6 (622.5-315.5)+ 1.17x 10-3/2 (622.52 315.52 6332 ) 0.3x105 (315.5 622.5)}
=22.9 x 107 kj/hrIf m be amount of water required for cooling
M 4.18 x 25 =22.9 x 10
6
Therefore M =2.19 x 107 kg/hr
Taking refernce temp. =298k for balance around the
Converter . Feed to converter is at 3500C
( H)F12 = 12585.8x 8.314 [4.12(298-923) + 0.8319/2 x
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10-3(298 2 623 2) + 0.0565 x 10 5 (1/623 1/298)]
= - 15.36 x107 kj/hr
NH3 formed =1167.66 kmole/hr
( Hrxn) = -46110 KH/kmole
( Hrxn)298 =700.6 x 46110 =- 3.23 x 107 kj/hr
If product is heated to a tamp . of T1 then
( H)F13 = 8.134 x 7145.79 [3.845 (T- 298) + 1.1299 x 10-3
(T2 2982) + 0.040 x 105 (1/T 1/298)]
For adiabatic condition,
(H)F12 + ( H)F13 + ( Hrxn)298 = 0
( H)F13 =12.45 x107 =3.845(T 298) + 1.1299 x 10-3 /2
+ (T2 2982 ) + 0.040 x 105 (1/T-1/298)
= 12.45 x 107 /7145.79 x 8.314
= 2095.60
Solving this equation by hit and trial wet dot, T= 773 k
Temperature of outlet gas = 500.50C
Product gases are cooled from 500.50C to 4100C while heating
The feed gases from 2580C to 350 0C
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Specification Sheet for Heat Exchanger design
Number required : 5
Function : To cool the gases coming out of shift
Converter
Type : 1- 4 shell and tube with floating head.
Shell side:
Number of shell passes : 1
Shell side fluid : Hot Gases
Shell internal diameter : 1067 mm
Baffle spacing : 534 mm
Entering temp. of gases : 132 0C
Leaving temp. of gases : 400C
Tube side:
Number of passes : 4
Number of tubes : 738
Tube length : 4.88 m
Tube side fluid : Cooling Water
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Tube pitch : 31.75 mm
Outside diameter of tube : 25.4 mm
Inside diameter of tube : 22.1 mm
Entering temperature of Water : 200 C
Leaving temperature of Water : 350 C
Reactor Design
CATALYST
A triply promoted ( K2O-CaO-Al2O3) iron oxide catalyst will be used. The iron oxide
(Fe2O3-FeO) is in the form of nonstoichiometric magnetite. It is made by fusing the
magnetite with the promoters. The catalyst is reduced in situ, and the removal of oxygenyields a highly porous structure of iron with promoters present as interphases between
iron crystals and as porous clusters along the pore walls. The pores range from 500A to
1000A and intraparticle diffusion is diffusion to occur by the bulk mechanism.
Alumina prevents sintering and corresponding loss of surface area and also bonds
the K2O, preventing its loss during use. The K2O and CaO neutralize the acid character of
Al2O3. Both K2O and CaO decrease the electron work function of iron and increase its
ability to chemisorb nitrogen by charge transfer to the nitrogen.
PROPERTIES
Particle size: Granules, in size range 6-10 mm
Bulk density: 1200kg/m3
Particle density: 305 lb/cu ft (4.9 g/cm3)
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Activity loss in service, 30-35% in 3yr depending on severity of operating conditions and
presence of poisons. Catalyst is slowly deactivated at operating temperatures above
9850F.
CATALYSTS POISIONS
In addition these poisons, hydrocarbons such as lubricating oils and olefins can crack
and plug pores. Sulphur, phosphorous and arsenic compounds should not exceed 15ppm.
Though temporary poisons, they cause crystals growth and attendant area decline.
Chlorine compounds form volatile alkali chlorides with promoters.
CHEMISTRY AND KINETICS
The overall stoichiometric equation is
1/2N2 + 3/2H2 NH3Extensive studies of ammonia synthesis on iron catalysts
suggest that the reaction occur through the following steps
N2 (g) 2N (ads)
H2 (g) 2H (ads)
N (ads) + H (ads) NH (ads)
NH (ads) + H (ads) NH2 (ads)
NH2 (ads) + H (ads) NH3 (ads)
Nh3 (ads) NH3 (g)
A rate equation based on nitrogen adsorption as the slow step is the most
commonly used although other forms have been development that also correlates the data
Since the effectiveness factor of ammonia catalyst is less that unity in a commercial
size pellets, it is desirafinely ground catalyst and employ and effectiveness factor
correction for other sizes. Ammonia synthesis is another example of an old reaction with
sufficient data existence to make this procedure feasible. The following equation in term
of activity has been recommended.Design of shift converter
F12=28557.5kmol/hr F13=25990.61 kmol/hrPlug Flow Reactor
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Step -1 Reaction occurring in PFR
N2 + 3H2k 2NH3
Or A + 3B k C
Reactor Kinetics
The only reaction that needs to be considered is the formation of ammonia from H2 and
N2,
N2 + 3H2 2NH3
A common rate equation for ammonia synthesis is the Temkin-Pyzhev equation given
where R is the rate of nitrogen consumption per unit volume of catalyst, f is a catalystactivity factor, and Pi is the partial pressure of component i in the gas. Values for K1 andK2:
K1 = ko1exp(-E1/RT)K2=ko2exp(-E2/RT)
Ko1 = 1.78954 x 104 kgmol/m3-hr-atm1.5E1 = 20,800 kcal/kgmol
Ko2 = 2.5714 x 1016 kgmol-atm0.5/m3-hrE2 = 47,400 kcal/kgmol
One limitation of this rate equation is that the rate will be infinite if the amount ofammonia in the gas is zero, and this may occur in a reactor being fed with fresh make-upgas. To avoid this numerical problem, the rate equation may be multiplied by a factorK3PNH3/(1+K3PNH3) ; this will avoid the approach to infinity at low PNH3 while having littleeffect at high ammonia pressures. This modification re-casts the rate equation into the
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Langmuir-Hinshelwood-Haougen-Watson (LHHW) form, which is one of the options forthe RPLUG reactor block in Aspen:
Assume that f = 1.0 and K3 = 2 atm-1.
Assume that the bulk density of the catalyst is 1200 kg/m3 and that the catalyst costs$12/kg.
Now, reactor temperature is 450 degree Celsius
Therefore, k1= 0.00873 kmol/m3-hr-atm1.5
K2=106.3 kmol-atm0.5/m3-hr
Also, pi=pio(1-Xi)/(1+EiXi) ; where i=A,B,C
EA=(2-4)/2=-0.5 & XB=3XA,XC=2XA
Using pAO=0.2247*200=44.94atm,pBO=0.6742*200=134.84atm,pCO=0.06*200=12atm
Finally, we get
pA=44.94(1-XA)/(1-0.5XA)
pB=134.84(1-3XA)/(1-1.5XA)
pC=12(1-2XA)/(1-XA)
1228.6(1-XA)(1-3XA)1.5 9.78(1-2XA)2(1-1.5XA)1.5(1-0.5XA)(1-1.5XA)
1.5 (1-XA)2(1-3XA)
1.5
(-rA) =24(1-2XA)
1 +(1-XA)
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Now plug flow reactor design equation
dxA = V
(-rA) FAO
Where FAO -- feed rate of A
From
V = dxA ( limits from 0 to 0.2)
FAO (-rA)
XA 0 0.04 0.08 0.12 0.16 0.20-rA 48.7 25 24.5 23.9 23.5 23.23
1/-rA 0.02 0.04 0.04 0.04 0.04 0.04
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1/(-rA) vs XA
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 0.05 0.1 0.15 0.2 0.25
XA
1/(-r
ASeries1
Area under curve = 30x0.005x0.05=7.6 x 10-3
V = FAO x (R+1)x 7.6 x 10-3
V = 28557.5 x 10.4 x 7.6 x 10-3
V = 16.362m3
Take factor of safety = 10%
New volume = 1.1 x 16.362
= 18 m3
Assume L/D = 4
Volume = /4 x D2 x L
18 = /4 x D2 x (4D)
D3 = 5.729
D = 1.212 m
Hence length (L) = 4 x 1.212
= 4.848 m
Now catalyst is divided in 2 beds in ratios 1:2.5
(as upper bed : lower bed)
Volume of catalyst in 1st bed = 18/3.5
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= 5.14 m3
Volume of catalyst in 2nd bed = (18 5.14)
= 12.86 m3
Bulk density of catalyst = 1200 kg/ m3
Weight of catalyst in 2nd bed = 12.86 x 1200
= 15.432 tonne
Weight of catalyst in 1st bed = 5.14 x 1200
= 6.168 tonne
Now giving allowance for space for gas movement upward and downward and insulation
be 0.5 m
Hence diameter of reactor becomes = 1.212 + 0.5
= 1.712 m
Pressure at which reactor works = 200 kg/m2
Let factor of safety = 20%
Design pressure = 1.2 x 200
= 240 kg/m2
We use carbon steel with internal lining of titanium
Allowable stress = 66,000 psi {hesse & ruston}
= 4494 kgf/cm2
Now Allowable stress = PD(1/k2 1) (from Hesse)
Where PD = design pressure
4494 = 240(1/k2 1)
k = 1.0337
Do = kDi
Do = 1.0337 x 1.212
= 1.252 m
Thickness of shell = (1.252 1.212)/2=20mm
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Specification sheet for Ammonia Convertor
Operating pressure : 200 kg/m2
Design pressure : 240 kg/m2
Temperature : 300 520oC
Allowable stress : 4494 kgf/cm2
Material of construction : Cr Mo steel
Diameter inside of converter : 1.212 m
Bulk density of catalyst : 1200 kg/m3
Total volume of catalyst : 18 m3
Diameter of catalyst bed : 1.252 m
Thickness of the shell : 20mm
Volume of 1st catalyst bed : 5.14 m3
Volume of 2nd catalyst bed : 12.86m3
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Weight of 1st catalyst bed : 6.168 tonne
Weight of 1st catalyst bed : 15.432 tonne
MECHANICAL DESIGN OF SHELL & TUBEHEAT EXCHANGER
Carbon steel(corrosion allowance=3mm)Allowable stress=11,000/14.7=749atm
[ref.PED by hesse & ruston,pg.60,table3.1]SHELL SIDE
No. of pass=1Fluids in shell are hydrogen ,nitrogen ,ammonia & inerts like argon& methaneDesign pressure=51 kgf/sq. cm=51atmShell diameter=1067mm
THICKNESS OF SHELL= [pD/2fJ-p]+c
Where;
P=design pressureD=shell ID
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F=allowable stressJ=joint efficiciencyC=corrosion allowance
Shell thickness= [51x1067/(2x749x.85-51)]+3=48mm
SHELL HEAD : assuming dished heads(because Pressure
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TUBE THICKNESS= pD/(2fJ-p)J=1(seamless tube)
Working pressure=1atm
Design pressure=1.1 times 1atm=1.1atmTube ID=22.1mmTube thickness=0.02mm( required)Tube thickness=(OD-ID)/2=1.65mm(actual)Hence, tube design is safe.
MECHANICAL DESIGN OF REACTOR
Material used is Carbon SteelThickness of reactor=pD/2fJ-p + C
Treactor=(1.1 x 200)x 1.212/(2x 4494 x 0.85-200)+ 3 mm= 39 mm
therefore, OD of Reactor=ID+2 x t=1.212+2x .039=1.29m
let head be the dished headsknucke radius=0.06x OD of reactor = 0.06x 1.29
= 77.4 mm
Crown radius, L= ID of reactor-6inches= 1.212-6x .0254= 1.06 m
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Head thickness= 0.833pL/fJ= 0.833x 1.1x 200x 1.06/0.85x 4494= 51 mm
h= depth of head=L-(L2-D2/4)1/2 =190 mm
e ffective length = 4.848+2x 0.190= 5.228 m
Surface area = 6.28Lh= 6.28x 1.06x 0.190
= 1.265 m2
Cost Analysis
Cost estimation is a specialized subject and profession in its own right. Chemical plants
are built to make a profit. An estimate of the investment required and the cost of
production needed before the profitability of project can be assessed.
Cost in plant can be classified as-
1. Fixed capital2. Working capital
(1) Fixed capital:-
Fixed capital is the cost of the plant ready to start up. It includes
1. Design
2. Equipment and interaction
3. Piping instrumentation and control system
4. Building and structure
5. Auxiliary facilities such as utilities
(2) Working capital
Working capital is additional investment needed over and above fixed capital to start up
the plant. It includes
1. Start up
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2. Catalyst cost
3. Raw material
4. Finished product inventories
These costs are required to be corrected to the specific
capacity and index price of the given year.
Correction of index price
Cost in yr. A = Cost in yr. B x Cost index of yr. A
Cost index of yr. BCorrection of capacity
C2 = C1 (S2/S1)n
C2 = Capital cost at capacity S2
C1 = Capital cost at capacity S1
n = power factor
(From Peter Timmer Haus, page 186)
Ammonia plant capacity = 100,000 ton/yr.
Fixed capital investment = 24 x 106 $ (Based on 1979)
Power factor for ammonia = 0.55
Our plant capacity = 1200TPD
Equation (2) C2 = C1 (s2 )n
s1
Taking that our plant runs for 335 days /yr. deducting the
time for normal shut down period.
Capacity = 1200 x 335 tons/yr. = 402000 tons/yr.
C2 = 24 x 106 x (402000) 0.55
100000
= 51.59 x 106$
Cost index = 1200
From chemical engineering journal
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CI =585.9(based on 1979)
Cost in yr. 2008 = cost in yr. 1979 x C.I. 2008
C.I.1979Thus,
Cost in yr. 2008 = (51.59 x 106) x 1200
585.9
=105.663 x 106 $
From Peter Timer Haus -
Working capital = 15% [fixed + working capital]
W.C. = F.C. x 15
85
W.C. = 105.663 x 15 x 106
85
= 18.646 x 106 $
Therefore total capital investment
= 105.663 x 106 + 18.646 x 106
= 124.31 x 106 $
Taking currency exchange rate as 1 $ = 44 Rs.
Total capital investment = 546.964 crore
Total capital investment = 124.31 x 106 x44
=5469.64 x 106
=Rs.546.64 crore
DIRECT COST
Component Given range Assumed range(%FCI) Cost (Rs.crores)Purchased equip. 15-40 25 116.25
Installation 06-14 09 41.85
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Instrumentation 02-18 07 32.55
Piping 03-20 08 37.20
Electrical 02-10 05 23.25
B
uilding 03-18 05 23.25
Yarest 02-05 02 9.3
Service facilities 08-20 15 69.75
Land 01-02 01 4.65
Total direct cost = Rs. 358.05 crore
Indirect costEngineer and supervision 04-25 10 46.5
Construction expenses 04-16 12 55.8
Contractor fee 02-06 02 9.3
Contingency 05-15 08 37.20
Total Indirect cost = Rs. 148.8 crore
Direct + Indirect cost = Rs 506.85 crore
COST OF REACTOR
Volume of cylinder=3.14*l*(OD2-ID2)/4
OD=1.290m
ID= 1.212m
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Length,l=4.848m
Therefore, vol of cyl. Material = 0.743m3
Density of Carbon Steel=7820 kg/m3 , Price of carbon steel= Rs 45/kg
Therefore, Cost of Reactor material = 0.743 x 7820 x 45=2.62 lakh
CATALYST
Volume of catalyst = 18 m3
Price of catalyst = $12/kg
Density of catalyst = 1200 kg/m3
Therefore, Cost of catalyst = 18 x 1200 x 12 x 44 = 1.141 Crores
Now, taking fabrication cost = 70% of total cost of equipment= 2.26 x 0.7/0.3 = 5.273 lakh
Hence, total cost of reactor (including catalyst) = 1.141+.05273+.0262= 1.22 Crores
COST OF HEAT EXCHANGER
Volume of shell material = 3.14 x length x (OD2-ID2)/4
OD = 1.115mID = 1.067m
Length=16 ft=16 x 12 x .0254m
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Volume of shell material = 0.4012 m3
Volume of one tube = 3.14 x length x (OD2-ID2)/4
OD=.0254mID = .0221m
Length= 16 ftVolume of single tube = 6 x 10-4 m3
Total vol. of tubes= 6 x 10-4 x 730= 0.4383 m3
Density of material(carbon steel) = 7820 kg/m3
Cost of material = Rs 45/kg
Therefore, Cost of heat exchanger material = (0.4012+0.4383) x 7820 x 45
= 2.954 lakh
total cost of heat exchanger(including fabrication)= 2.954 x 1/0.3= 9.847 lakh
Safety And Hazards
FIRE AND EXPLOSION HAZARDS
Due to high vapour pressure of ammonia, container for ammonia should not be exposed
to the Sun and other sources of heat and should be properly insulated.
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Ammonia vapours are flammable in certain percentages in air, but since these high
concentrations are seldom encountered, the relative fire and explosion hazard is small.
Experience has shown that ammonia is hard to ignite, so it is generally treated as a non
inflammable compressed gas. However, certain safe practices should be followed.
Electrical apparatus and fixtures should be vapour proof and plugged in at
locations free from ammonia gas.
Equipment, tanks and lines that contain ammonia should not be welded without
first being thoroughly washed or steamed. Aqueous fire extinguishers are
satisfactory for ammonia fires.
Since ammonia is readily soluble in water, hose streams can be used effectively to
remove ammonia from the air in contaminated areas.
CLOTHING AND PROTECTIVE EQUIPMENT
Persons subject to exposure should be provided with gas masks of ammonia the type
approved by the Bureau of Mines, rubber hats, suits, gloves and boots. Garment worth
beneath rubber clothing should be cotton. Eye gogg1es or full face masks should be
provided. Easily accessible safety showers and bubble fountains for washing the eye
is .recommended.
FIRE PREVENTION STEPS IN AMMONIA
1. Fire fighting extinguishers
2. Water and foam tenders
3. Breathing apparatus, gas mask, ear plugs, aluminized suits for rescue purpose,
pressure bags for lifting heavy equipments
4. High expansion foam generator5. On site emergency plant
Apart from the above, fire alarms, smoke detectors and fire hydrants are also provided in
plant.
CORROSION
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Since ammonia is corrosive to alloys of copper and zinc, these materials must not be used
in ammonia service- iron or steel should usually be the only metal used for ammonia
storage tank, piping and fittings.
Cleaning and Repairs of Equipments
Wherever possible, ammonia tanks and other equipment should be cleaned and repaired
from the outside. When it is necessary to enter an ammonia vessel all lines leading to the
vessel should be disconnected and provided with blind flanges. Danger signs should be
placed at appropriate points to wary other work men and all electric apparatus should be
turned off. One person keeps close watch outside the tanks and has dosed at hand the
proper emergency equipment, respirator, and fire outing wishes. The tank should 'be
filled with water and drained before being entered and should purge with air and tested
for explosive atmospheres.
FIRST AID
A person who has been overcome of burned by ammonia should be placed under the case
of physician at once. The patient should be removed from contact with ammonia as soon
as possible and kept warm and quiet.
Physiological response to various concentration of ammonia
ppm
Least detectable odor - 53
Least amount causing immediateirritations to eyes- 698
Least amount causing immediateirritations to the throat- 408
Least amount causing coughing- 1720Max. Conc. allowable for
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Prolonged exposure- 100
HAZARDS OF AMMONIA
1. Toxic hazards
In general ammonia gas under high concentration causes irritation to eyes.
2. Explosive Hazards
Ammonia is explosive with air in the range of 16 to 25% by volume. Its auto ignition
temperature is 651C since such temperature are not encountered in practice; the
chance of fire and explosive hazards due to ammonia is relatively remote.
The presence of oil in mixture of ammonia with other combustible materials will increase
the /fire hazard. The explosive range of ammonia is;
1. Temperature and pressure higher than atm conditions.
2. Presence of chlorine higher than ammonia causes chlorine to react with ammonia
and form a violently explosive compound.
SAFETY IN AMMONIA PLANTS
Wear ear plugs
wear approved respirator & protective clothing
Wear safety helmet, goggles, hand glows, safety shoes.
Keep away from heat, flames, spark & oxidizing material
Keep area ventilated & report the leakage
Keep people away from hazardous area.
Pollution Control
1) Ash Slurry treatment Scheme
The ash slurry from steam generation plant is pumped by the existing sat of pumps to the
proposed ash ponds. The ash is settled in the ponds by gravity settling. The clear
overflow from the ponds is discharged into sump from where the clear water is pumped
to steam generation plant for de-ashing purpose or can be drained to the river sump
directly.
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2) Oily Effluent Treatment Scheme
Two nos. of oil separators are provided to receive oil effluent. Each separator has about
75 m3 capacity and both put together can receive 150m3 of effluent per day. Oil
separators are to be operated alternately. They are building with stilling, inlet chamber,
and deoiler pipe, baffle for retaining the floating oil and overflow weir. Oil separates andfloats to the surface by gravity separation.
3) Reuse of Process condensate as boiler feed water make up
In ammonia plant, the main source of liquid effluents is process condensate. It is well
known that steam is used in excess of stoichioimetric requirements for reforming and
shift conversion in ammonia plant. This excess steam is subsequently removed as process
condensate which contains impurities like carbon dioxide, ammonia, methanol etc. This
condensate cannot be directly used anywhere due to the presence of impurities.
4) Non-Chromate based cooling water treatment
Cooling water treatment is of vital importance for all the chemical process industry.
When the original plant was commissioned in 1974, chromate based cooling water
treatment was adopted. About 15-20 ppm chromate was maintained in the circulating
cooling water. The chromate is toxic and harmful to the environment. This hexavalent
chromate was converted into trivalent chromate and separated out as sludge.
To overcome chromate sludge storage problem and to adopt environmental friendly
system, non-chromate based cooling water treatment was adopted in Apirl,1998.
Non-chromate treatment programme are mainly based on o-phosphate and zinc with
different combinations. o- phosphate concentration of 6 ppm minimum and
Zincconcentration of 1 ppm maximum is maintained as corrosion inhibitor. Polymer
based bio-dispersant and boicides are also added.
Three different biocides are shock dosed alternatively in addition to chlorination for
micro biological growth control as per requirement. Dispersants are added to keep the
salts of circulating water in dispersion condition. All the chemicals used for non chromate
treatment are biodegradable chemicals.
5) Condensate Stripper Overhead vapour condensation
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Overhead vapours about 6000 kg/hr from condensate stripper were vented to atmosphere.
the overhead vapours contain ammonia, methanol, amines and CO2. Ammonia present in
the overhead vapours is about 5000 ppm. The limit specified by Gujarat Pollution Control
Board (GPCB) for ammonia is 100 ppm. To avoid the venting of ammonia to
atmosphere,
the overhead vapours from the top of the condensate stripper are diverted to the vent
condenser (172-C). All the vapours are condensed and non-condensables mainly CO2 is
vented to atmosphere. The condensate from the vent condenser can either be sent to
Ammonia recovery and stripping system in ammonia plant or to hydrolyser stripper
system in urea plant by condensate transfer pump. The system is shown as annexure - VI.
The system has reduced the 720 kg/d ammonia to atmosphere and pollution norms has
been also met.
6) Biological Treatment of Effluent
After giving treatment, the effluent is further bio-degraded in the effluent ponds having a
holding capacity of 1, 00,000 m3 before final discharge to the river Damodar.
Factory effluent mixed with sanitary waste methanol water and is treated with the help of
bacteria. The bacterial actions consist of hydrolysis, nitrification and denitrification.
HYDROLYSIS
In the process of metabolism through heterotrophic bacteria.complex carbohydrates,
proteins and insoluble fats present in sanitary waste are hydrolyzed into soluble sugar,
amino acids and fatty acids.
Hydrolysis of urea takes place and converts organic nitrogen to ammonium carbonate.
(NH2)2C03 +2H2O (NH4)2 C03
Biochemical oxygen demand (BOD) is reduced by hydrolysis under aerobic condition in
presence of baceotrophic bacteria.
NITRIFICATION
Ammonical nitrogen is converted to nitrites and then to nitrate form in a presence of
autotrophic bacteria under aerobic condition.
N H4++ 3/2 O2 NO2
- + H2+ + H20
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N02- + 1/2 O2 - N03
-
NH4+ +2O2 - NO3H + H2O
DENTRIFICATION:
Heterotrophic bacteria in anaerobic condition reduce nitrite (N02) and Nitrate (N03) to
gaseous N2. An organic carbon, as methanol, acetic acid, acetone, ethanol or sugar is
reduced to act as a hydrogen donor to supply carbon for biological synthesis. The
required BOD is supplied by waste methanol (6000 ppm) which serves as an energy
source for survival and growth of bacteria.
First methanol reduces:
3O2 + 2 CH3OH - 2 CO2 + H2O
Then bacterial reduction of N02 & N03 takes place.
6 NO3- + 5 CH3OH - 3 N2 + 5CO2 + 7 H2O + 6OH
-
2 NO2- + CH3OH N2 + CO + H 2O+ 2 OH
-
Aeration is helpful for the removal of gaseous product and increase dissolved oxygen in
the effluent. In the step of hydrolysis urea (500 ppm) degrades to 50 ppm level.
Instrumentation
The even operation of a process is dependant upon the control of process variables. These
are defined as the conditions in the process material and equipments which are
subjected to change. There may be several materials and several pertinent operating
factors which may change in the simplest of process; the maintenance of control over an
entire process is an important aspect of process design. In Ammonia manufacture
temperature and pressure are two process variables on which operation of whole plant
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depends upon. Instrumentation of each equipment is done separately.
1. REACTOR
Feed to the converter is at 750C which is made to pass through the internal heat
exchangers so that it may gain heat from outgoing gases to attain reaction initiation temp.
This temperature of gas at the inlet of catalyst bed is taken into account by TIC (temp.
indicator controller) put in line with the start up heater.
In case temperature goes below the reaction initiation temperature.
Then automatically start up heater works and temperature of product gas is increased
which in turn heats the incoming gases to the required reaction initiation temperature.
But if the temperature goes high then a portion of by pass feed controls the temperature.
Temperature control is necessary because in first case, reaction would not start till therequired temperature is attained. And in the later case, temperature goes too high then
catalyst may get spoiled. Pressure inside the reactor is 300 atm. and any change in
pressure will effect the conversion therefore pressure control is also necessary so we will
have to employ pressure gauges and pressure controller valves.
Temperature indicator devices are put on both inlet and outlet streams and if temperature
of outgoing gases goes below 162C the water flow in the heat exchanger (waste heat
boiler) is reduced with the help of a hand controller valve.
2. AMMONIA COOLED CONDENSER
A level indicator controller is installed in the ammonia refrigeration loop so as tomaintain a constant level which is necessary to get required refrigeration to bring downthe temperature of gas to -S C where required condensation of ammonia is acting.
3. AMMONIA SEPARATOR
Here also a level indicator controller is required to maintain a particular level of liquid
ammonia in it so no gas but only liquid product is obtained.
4. AMMONIA STORAGE
Ammonia is stored at a pressure of 40 psig and temperature 25.8 0 F. However, efficient
may be the insulation. Some of heat enters the tank from ambient and vapors of ammonia
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are formed. Pressure inside the tank increases so there must be some arrangement to
reduce this pressure. A safety valve may be provided at the top of 'Horton Sphere'.
Whenever pressure inside the vessel rises some of the vapors are vented. These vented
gases either released at. 6 ft. high stack or can be compressed and condensed in a close
loop to reduce atmospheric pollution. In a closed loop system vent are stored in a small
vessel from where those gases are compressed, condensed and then fed to the storage
tank.
TEMPERATURE MEASUREMENT
Temperature measurement is done by using thermocouples. Since ammonia corrodes
metals like Cu and Zn. The thermocouple selected is chromel (Ni 90%, Cr 10%)
Alumd (Ni 94%, Mn 3%, Al 2%). It can be used in temperature ranging from 600 to 2100
of vertically in the converter. Slight variations of temperature inside the converter are
transmitted through the transmitter to the error is passed on to a diaphragm motor valve
which controls the flow of gases to the converter.
INSTRUMENT AND FITTINGS
Gasket material most suitable for anhydrous ammonia service is hard finished. Such as
flange facings where the gasket material is retained in a groove. And on gasket material is
retained in a groove. And on gasket bodies, lead may be used. Aluminum has been
applied satisfactorily as a gasket material for flat faced and grooved flanged joints but. is
not. Generally recommended Rubber rings cannot. be used. All ammonia piping should
be extra heavy (sch. 80). Steel piping may be used where joints are welded. Galvanized
pipe should never be used. Welded pipes should be used wherever possible. Welded pipe
flanges may be used on all pipe joints of 1.25" or larger. Under no circumstances brazed
joint be used, as they will deteriorate rapidly.
Industrial Applications of Ammmonia
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Explosive Industry
The explosive industry is one of the largest consumers of ammonia.
It is used principally in the form of Nitric acid for the manufacture of compounds such as
TNT, Nitroglycerine, nitrocellulose, nitro starch, Pentaerythrital t1tranitrate, tetraethyl
and ammonium nitrate.
Textile Industry
In textile industries, ammonia is used in the production ff synthetic fibres such as
cupraammonium rayon and nylon. In the production of rayon, the ammonia is used in the
preparation of ammonical copper hydroxide solution (Schweiter's reagent) for dissolving
the cotton linters.
In the rayon process ammonia is used in the production of hexamethylene diamine, which
is considered with-adipic acid to form the monomer, which in turn is polymerized and
speen into polyamide fibres.
Fertilizer Industry
The fertilizer industry is a heavy consumer of ammonia and its compounds. The main
nitrogenous fertilizers are
- Anhydrous ammonia
- Ammonia liquor
- Ammonium Nitrate
- Urea
- Ammonium Sulphate
- Calcium Cynamide
- Sodium Ammonium Nitrate.
Ammoniation of phosphatic fertilizer produces fertilizer mixture with improved physical
properties.
Pharmaceutical Industry
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Ammonia is an important ingredient in the manufacture of sulfa drugs such as
sulfanilamide sulphath1azole and sulfapyridine. It. is also used in the manufacture of
vitamins and antimalarials.
Petroleum Industry
In the refining of crude oils, ammonia is used as neutralizing agent to prevent corrosion
in acid condensers, heat exchangers etc. of the distillation equipment.
Ammonia is also used to neutralize final traces of acid in acid-treated lubricating oil
stocks and pressure distillates,
Rubber Industry
Ammonia is used to raw latex to prevent coagulation during transportation from the
rubber plantation to Ammonia is also used in the nuconization the factory process for the
manufacture of fabrics, boots, shoes etc.
Refrigeration
Ammonia is most commonly used refrigerant, especially for large industrial installations.
It can be used in both compression and absorption system for
1) Production of ice
2) Refrigeration cold-storage plants
3) Quick freezing units
4) Food-lockers
5) Air conditioning large industrial plants
Certain characteristics of ammonia such as high latent heat of vaporization low vapour
density. Chemical stability and low corrosion to compressor parts, make operating costs
per ton lower for ammonia than for any other refrigerants used in industrial systems.
Inorganic Chemicals Industry
A large number of ammonium salts having numerous industrial applications are produced
by direct neutralization of their respective acid with ammonia.
Important industrial compounds produced are ammonium nitrate, ammonium sulphate
mono and diammonium phosphate and ammonium acetate.
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Acid Manufacture
In the lead chamber process for sulfuric acid manufacture, Ammonia is oxidized to give
Nitrogen oxide to provide required oxygen required for conversion of SO2 to sulphuric
acid.
Pulp and Paper Industry A recent development is the substitution of ammonia for
calcium in the bisulphate process for pulping wood. The ammonia base is said to improve
the yield and Quality of pulp.
Leather Industry
Ammonia is used as slime and mold preventive in tanning liquors.and as a. curing agent
in making leather.
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Bibliography
1. Perry, R.H., "Perry's Chemical Engineers Handbook", 6th
Ed., McGraw Hill Company, 1984.
2. McCabe Warren L., Smith Julian C., Harriot Peter, "UnitOperations of Chemical Engineering", 4th Ed., McGraw Hill,
Inc., 1981.
3. Levenspiel Octave, "Chemical Reaction Engineering 2nd
Ed., Wiley Eastern Ltd., 1991.
4. Peters M.S., Timmerhaus K.D., "Plant Design and
Economics for Chemical Engineers", 4th Ed., McGraw Hill,
1991.
5. Treybal R.E., "Mass Transfer Operations", 3rd Ed., McGraw
Hill Company, 1981.
6. Hesse, Herman C. and Rushton, J. Henry "Process
Equipment Design" Affiliated East-West Press Pvt. Ltd.,
New Delhi.
7. Richardson & coulson Vol 6
8. Operating Manual, "Ammonia Plant" of National Fertilizers ltd. Bathinda
9. Elementary Principles of Chemical Processes by Felder