Urea Kamal

8/10/2019 Urea Kamal

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MANUFACTURE OF UREA

( Capacity : 1500 MTD )

PROJECT REPORT

Submitted to Panjab University,Chandigarh

In Partial Fulfillment of the requirements

For the Degree ofBACHELOR OF CHEMICAL ENGINEERING

2011

Submitted By:

KAMAL BHARTI

Univ Roll no:CH7228Univ. Institute of Chemical Engineering & Tech.

Panjab University,Chandigarh


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ACKNOWLEDGEMENT

I would like to thank my Department authorities for giving me this

opportunity to work on this project which helped me in increasing my

knowledge as well as in giving me an opportunity to put my theoretical

knowledge to practical use.

I would also like to offer my sincere thanks to my project supervisor

Dr. Shantanu Basu for providing inspiration and encouragement throughout

my work. I have enjoyed free and informal discussion with him and his

valuable suggestions have gone a long way in the completion of my work.

Thanks to all the teachers and staff of University Institute Of

Chemical Engineering And Technology for their time to time guidance.

Kamal Bharti


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CERTIFICATE

This is to certify that Mr Kamal Bharti, Roll No.-CH-7228, a finalyear student of the University Institute of chemical Engineeringand Technology, Panjab University, Chandigarh has completed hisproject entitled MANUFACTURE OF UREA BY MITSUITOATSU PROCESS under my supervision.This report of theproject may be accepted for the evaluation as a part of therequirement of B.E. CHEMICAL degree.

DR. SHANTANUBASU

UICET,PU

TEACHER SIGNATURE


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TABLE OF CONTENTS

1. INTRODUCTION 5

2. MANUFACTURING OF UREA 6

3. IMPORTANCE OF UREA..6

4. PROPERTIES OF UREA 7

5. VARIOUS UREA SYNTHESIS PROCESS8

6. PROCESS SELECTION.9

7. PROCESS FLOW DIAGRAM10

8.

PROCESS DESCRIPTION11

9. MATERIAL BALANCE..15

10.ENERGY BALANCE..30

11.DESIGN38

(a)REACTOR DESIGN..42(b)HIGH PRESSURE DECOMPOSER DESIGN..54

12.

COST ESTIMATION61

13.GENERAL SITE CONSIDERATIONS..69

14.UTILITIES ...74

15.INSTRUMENT & CONTROL.77

16.INSTRUCTIONS FOR OPERATION.........82

17.STARTUP OF PLANT .83

18.SAFETY84

19.

ENVIRONMENTALCONSIDERATIONS..91

20.REFERENCES.92


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Introduction

Urea is synthetic origined nitrogenous material, NH2CO NH2. Its nitrogen content is 46.6

%( when pure). At room temperature urea is colorless, odorless and tasteless.

When it is dissolved in water it hydrolyzes very slowly to ammonia and carbon dioxide.

Urea today occupies the key position amongst the various solid nitrogenous fertilizers by

virtue of its highest content which allow a consumption saving in transportation and

distribution cost.

The process of urea synthesis is of immense importance as it was the first organic

compound to be synthesized from inorganic compound in laboratory. Wholer obtained

urea from ammonium cyanide in 1828. Today various manufacturing process use the

reaction between liquid ammonia and carbon dioxide gas to give ammonia carbonate

which on the sub sequent dehydration yield urea and water.

The technology and engineering if urea production has therefore undergone rapid

development in the last two decades so with the result that stream plants of 1500 MTPD

capacity and even higher have been designed and engineered.

The chemical fertilizer manufacturing in India started during the early 40s with only two

small plants, today it is the fourth producer of fertilizer and occupies the third position in

the fertilizer consumption in world.


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Manufacture of Urea

Urea is commercially produced by the direct dehydration of ammonium carbonate

(NH2COONH4) at elevated temperature and pressure. NH2COONH4is obtained by direct

reaction of NH4and CO2. The two reactions are usually carried out simultaneously in a

high pressure reactor.

H = -38000 cal/gmol

H = +7500 cal/gmol

Importance of Urea

1. Fertilizer grade urea is mainly used as fertilizer in the form of prills. 90% of urea

produced in India is used as fertilizer.

2. Technical grade urea is used in the manufacture of thermosetting resins.

3. Used in pharmaceutical industry. It promotes healing of wounds.

4. Feed grade urea is used for the purpose of animal feed as a protein supplement.

5. Used in manufacture of explosives


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Properties of Urea

S.No. Property Assigned value

1.

Formula weight 60.06

2. Melting point 132.7C

3. Boiling point Decomposes at atmospheric

pressure(< boiling)

4. Index of refraction 1.484 - 1.602

5. Crystalline form Tetragonal

6. Specific gravity 1.335

7. Bulk density 0.74 g/cm

Specific Heat of Urea:

Temperature (C) Specific Heat (cal/g C)

0 0.344

50 0.397

100 0.451

150 0.504


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Various urea synthesis processes

The basic reactions that are involved for the production of urea are same for all the

processes. The difference between the different processes is the way in which the

unconverted reactants are treated:

1. Once through process

In this process, the unconverted reactants after the decomposition are released

and are used for making other nitrogenous fertilizers like ammonium sulphate

and ammonium nitrate. One of the drawback of this type of urea process is

that, relatively large amount of ammonium salts accompany the production of

urea.2.

Partial recycle process

In this process, a part of unconverted reactant is recycled and the remaining

off gases NH3, CO2and H2O are used for making other nitrogenous fertilizers.

Since the demand for urea is more as compared to other nitrogenous fertilizers

because of its high nitrogen content, this process is obsolete these days.

3. Total recycle process

This is the most widely used process. It is sub divided into three types:

a)

Hot gas recycle Here the hot decomposed NH3 and CO2gases are

compressed and recycled. Since the corrosion problems are more in

this case it is also obsolete.

b) Gas separationIn this process, the off gases after the decomposition

of the carbonate are scrubbed with selective solvent. Then, the

separated NH3and CO2are mixed with made up reactants entering the

reactor. The advantage of this process is no water is recycled and the

conversion efficiency is high.

c) Solution recycle In this method, the decomposed gases NH3, CO2

and H2O are condensed to form aqueous ammonium carbamate which

is recycled to the reactor. This method is most widely used.


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Various advanced technologies

1. Mitsui Toatsu process

2. Stamicarbon process

3.

chemical process

4. Snam Progetti process

5. Inventa process

6. Montedison total recycle process

Process Selection

I am selecting MITSUI TOATSU total recycle process for urea manufacture.

In this greatly improved process, the various advanced techniques from research and

development are incorporated into the commercially proven total recycle improved

process.

This process is widely used because of certain advantages:

1.

Temperature in the reactor is controlled by the recycle stream which is recycled

back to the autoclave. Part of the heat evolved (reaction being exothermic) is used

for heating the recycle stream to bring its temperature to reactor temperature and

the rest is dissipated to the atmosphere.

2. The consumption of raw materials i.e. NH3and CO2per mega tonne (MT) of urea

is less compared to other process.

3. Biuret content in the final product is around 0.6% and the moisture content is

0.4%.

4. Simple operations.

5. Easier maintenance.

6. Efficiency is good.


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PROCESS FLOW DIAGRAM


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PROCESS DESCRIPTION

The raw material required for urea manufacture is NH3and CO2. NH3reacts with CO2to

form ammonium carbamate, which decomposes urea. The reactions which take place are:

(1)

. (2)

The reaction 1 can be easily carried to completion but reaction 2 usually has conversion

of only 50-70 %. Since both the reactions are reversible, therefore, the equilibrium

depends on temperature, pressure and concentration of various components.

Since removal of water favors the formation of urea in reaction 2, therefore, the molarratio of NH3to CO2is 4 and the molar ratio of H2O to CO2is 0.8.


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Synthesis section:

The suction temperature of CO2 is maintained at 35-37C and it is compressed to 230

kg/cm2in a four stage compressor and is injected to the reactor. NH 3is pressurized to a

pressure of 230 kg/cm2and is injected to the reactor through NH3preheated with which

maintains its temperature at 75-80C. The stream of ammonium carbonate solution

having temperature of about 95C from high pressure absorber is recycled to the reactor.

The maintained temperature in the reactor is 200C. The percent conversion is 60%.

Decomposition Section:

1. High pressure decomposer:

The effluents from the reactor which are at 120C flows to high pressure

decomposer which operates at 155C and 16 kg/cm2 pressure. The reactor

effluents flow down in high pressure decomposer which is conventional 1-1

exchanger which is heated by steam at a pressure of 13 kg/cm2. As a result,

ammonium carbamate is decomposed and NH3and CO

2are released. The vapors

from the high pressure decomposer are fed to the high pressure absorber and the

liquid from high pressure decomposer is fed to low pressure decomposer.

2. Low pressure decomposer:

The liquid from high process decomposer which operates at a temperature of

155C flows down in low pressure decomposer which operates at a temperature

of 130C and a pressure of 1.5 kg/cm2. As in case of high pressure decomposer,

steam is also used here but a pressure of 6 kg/cm 2. Most of the remaining

ammonium carbamate gets decomposed here along with the liberation of NH3.

The vapors from low pressure decomposer is fed to high pressure absorber

whereas the liquid (urea solution) to the separator.


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crystallizer where the urea solution containing 35-40% urea crystals are taken out

from the bottom. It is further fed to centrifuge (i.e. crystals and mother liquor).

Biuret in feed urea solution remains in mother liquor because of the difference of

solubility and so a part of mother liquor is returned to reactor (via recovery

section) for preventing accumulation of biuret in mother liquor. Biuret in reactor

is decomposed to urea again.

Drying and Prilling:

Urea crystals obtained from centrifuge is sent to drier where the crystals are dried upto

0.3% moisture by passing hot air of about 120C. It is then conveyed pneumatically to

prilling tower. At the top of prilling tower, urea is separated from air with the help of

cyclone separator. Urea is then fed to remelter. The molten urea coming out of the melter

is fed to prilling bucket. The mother urea coming out of the prilling tower and encounters

a cold air flow which causes its solidification and subsequent cooling. The urea prills thus

obtained are fed to the rotary screen where oversize products are removed. After this the

urea prills are sent to product storage silos with the help of belt conveyors.

Selection of feed stock:

The basic raw materials needed for the production of urea is NH3 and CO2 which are

obtained from NH3 plant which is situated adjacent to urea plant. The feed stock for

manufacture of NH3and CO2can be naphtha, natural gas, heavy fuel oil, etc.


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MATERIAL BALANCE


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OVERALL MATERIAL BALANCE:

BASIS: 1500 MT of urea per day

1 day operation

The final composition of prilled urea is:

Urea = 99.1%

Water = 0.3%

Biuret = 0.6%

So the final product per day is:

Urea = 1486.50 MT

Water = 4.50MT

Biuret = 9.00MT

Biuret is formed according to the reaction:

Urea Biuret

(Mol. Wt: 60) (Mol. Wt.: 103)

Now Biuret in final product = 9.00MT

9.00MT of Biuret will be formed from = 60 x 2 x9.00/ 103

=10.48MT of Urea


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Therefore, total urea in the final product = 1486.50 + 10.48

=1497.00MT

Raw material used for manufacture of urea is NH3 and CO2. The reaction is:

Ammonia Carbon dioxide Ammonium Carbamate

(Mol.Wt. =70) (Mol. Wt. =44) (Mol.Wt. =78)

(Ammonium Carbamate) (Urea)

(Mol. Wt. = 78) (Mol.Wt. = 60)

Reaction 2 is spontaneous so it gets converted or completed very fast. While reaction 3 isslow and its conversion depends on the synthesis conditions which are 195C and 230

kg/cm2.

We take CO2to be the LIMITING COMPONENT

Molar feed ratio of NH3to CO2 = 4.0

Assuming conversion of ammonium carbamate to urea by reaction (3) be 60%.

Now, for 1497.00MT of urea, ammonium carbamate required will be

78 x 1497.00/ 60 x 100/60 = 3243.50MT


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For 3243.50MT ammonium carbamate CO2required is = 44 x 3243.50 / 78

= 1829.65MT

Since, molar ratio of NH3to CO2in feed is = 4.0

Therefore, NH3required is = 4 x1829.65 x 17 /44

= 2827.64MT

The composition weight percentage of input to autoclave is

CO2= 32.02 %

Urea = 8.01 %

NH3= 49.49 %

H2O = 10.48 %

Since, CO2in the input =1829.65MT

Therefore, total input is =1829.65/0.3202 =5714.08MT

So, in the input

CO2= 1829.65 MT

NH3= 5714.08 x .4949 = 2827.90 MT

Urea = 5714.08 x .0801 = 457.70 MT

H2O = 5714.08 x .1048 = 598.83 MT

Ammonium Carbamate leaving the reactor =3243.50 x 0.4

=1297.40 MT


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By reaction (3) H2O produced in reactor = 18 x 1497.00/60

= 449.10 MT

Total water coming out of the reactor = 598.83 + 449.10 MT

= 1047.93 MT

As CO2is the limiting component in the reactor, therefore NH3required for 1829.65 MT

of CO2 = 2 x 17 x1829.65/ 44

= 1415.82 MT

NH3coming out of the reactor = (2827.901413.82) MT

= 1414.08 MT

Urea coming out of the reactor = (Urea in input) + (Urea formed in the reactor)

= 457.70 + 1497.00

= 1954.70 MT

Therefore, composition of outlet from the reactor is:

Urea = 1954.70 MT

NH3 = 1414.08 MT

H2O = 1047.93 MT

Ammonium Carbamate = 1297.40 MT


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High Pressure Decomposer:

Assumption :90% of ammonium carbamate reverts back to give NH3and CO2and also

90% NH3and 15% of water goes out in the vapor stream to high pressure absorber.

Amount of ammonium carbamate decomposed = 1297.40 x .90

= 1167.66 MT

Amount of ammonium carbamate going to low pressure = 1297.40 x .10

Decomposer = 129.74 MT

1167.66 MT of ammonium carbamate decomposed will give NH3 = 2 x 17 x 1167.6/ 78

= 508.98 MT

Total weight of NH3in high pressure decomposer = 508.98 + 1414.08

= 1923.06 MT

NH3going out in vapor stream =1923.06 x 0.9

= 1730.75 MT

NH2in low pressure decomposer = 1923.06 x .10

= 192.30 MT

Also, ammonium carbamate decomposed will give CO2 = 44 x 1167.66 / 78

= 658.68 MT

All the CO2goes back to the vapor stream

CO2in the vapor stream = 658.68 MT


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Amount of water leaving in the vapor stream = 0.15 x 1047.93

= 157.19 MT

Amount of water in low pressure decomposer = 1047.93 x .85

= 890.74 MT

Low Pressure Decomposer

Assumption :Assuming that 85% of ammonium carbamate reverts back to NH3 and

CO2and 90% of NH3 and 15% H2O goes out in the vapor stream i.e. to high pressure

absorber.

Amount of ammonium carbamate decomposed = 129.74 x 0.85

=110.28 MT

Amount of ammonium carbamate going to separator = 129.74 x .15

= 19.46 MT


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Ammonium carbamate decomposed will give NH3 = 2 x 17 x 110.28/ 78

= 48.07 MT

Total amount of NH3in low pressure decomposer = 48.07 + 192.31

= 240.38 MT

Amount of NH3going in vapor stream = 240.38 x 0.90

= 216.34 MT

Amount of NH3going in gas separator = 240.38 x .10

= 24.04 MT

Also ammonium carbamate decomposed will give CO2 = 44 x 110.28 / 78

=62.21 MT of CO2

Amount of Water in vapor stream = 890.74 x .15

= 133.61 MT

Amount of Water going to gas separator = 890.74 x .85

= 757.13 MT


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GAS SEPERATOR

Assuming all the ammonium carbamate decomposed to give NH3and CO2. All the NH3

and CO2produced goes o the gas condenser and 15% of water goes to gas condenser.

Ammonium carbamate decomposed to give NH3 = 2 x 17 19.46 / 78

= 8.48 MT

Total ammonia in gas separator = 8.48 + 24.04

= 32.52 MT

Ammonium carbamate decomposed to give CO2 = 44 x 19.46 / 76

= 10.98 MT


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Crystallizer

In the crystallizer 80% of water is evaporator or vaporized

Amount of H2O vaporized = 0.8 x 643.56

= 514.85 MT

Amount of H2O left in urea solution = 0.2 x 643.56

= 128.71 MT


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Drier

Assuming that 80% of water is removed. Also 0.6% of urea gets converted to biuret by

reaction (1)Water removed from the solution = 0.80 x 25.74

= 20.58 MT

Water left in the solution = 0.20 x 25.4

= 5.15 MT

Biuret formed = 0.006 x 1497.00

= 9.00 MT

Total feed to reactor is:

Urea = 457.70 MT

CO2 = 1829.65 MT

NH3 = 2827.90 MT

H2O = 598.83 MT

Recycle to reactor is:

Urea = 457.70 MT

CO2 = 731.87 MT

NH3 = 593.88 MT

H2O = 587.34 MT


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Gas Condenser

Assuming we add 80 MT of water to gas condenser.


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High pressure absorber

Assuming 30% of total NH3in high pressure absorber gets recycled to the reactor.


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ENERGY BALANCE


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Basis:One day operation

In the reactor, the fresh NH3enters at 80C and 230 kg/cm2while CO2enters at 35 C

and 230 kg/cm2. The recycle stream returning from high pressure absorber enters the

reactor at 95C and 230 kg/cm2.

The effect of pressure is very significant in case of gases but is not appreciable in solids

and liquids and can be assumed to be negligible.

Mean specific heat of liquid NH3between 25 to 200C:

= ( Cpof liquid NH3at 25C + Cpof liquid NH3at 200C ) / 2

= (1.147 + 1.341) / 2

= 1.244 cal/gmC

= 1.244 x 17

= 21.148 cal/gm mol C

Mean specific heat of gaseous NH3is = Cpmean between 25 to 200C

T

= Cp dT / (T-To)

To

473

= (6.70 + 0.00630) T dT/ (473-298)298

= 11.56 cal/gmolC

Mean specific heat of H2O is = Cpmean between 25 and 200C

= (1.0 + 1.2) / 2

= 1.1 cal/gmC

= 1.1 x 18

= 19.80 cal/gmolC


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Mean specific heat of urea = Cpmean between 25 and 200C

= (0.370 + 0.555) / 2

= 0.4625 cal/gmC

= 0.4625 x 60

= 27.75 cal/gmolC

Mean specific heat of ammonium carbamate = Cpmean between 25 and 200C

= ( 0.410 + 0.62) / 2

= 0.515 cal/gmC

= 0.515 x 78

= 40.17 cal/gmolC

Mean specific heat of CO2 = Cpmean between 25 and 200C

= T

= (+T-/T2) dT / (T-To)

To

= {10.34(473-298) + (0.00274/2) (4732-2982) + 195500 (1/4731/298)}/ (473-298)

= 10.009 cal/gmolC

Cpmean of H2O vapor between 25 and 200C

T

= Cp dT / (T-To)To

= [8.22(473-298) + (0.00015/2) (47322982)] / (473298)

= 0.456 cal/g mol C


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Reactor

From material balance

In stream (1),

NH3 = 2827.90593.88

= 2234.02 MT

Also,

T1 = 80C

Therefore,

H1 = 2234.02 x 103x 1.244 x (80-25)

= 152.85 x 106Kcal

In stream (2),

CO2 = 1829.65731.87

= 1097.78 MT

Also,

T2 = 35C

Therefore,

H2 = 1097.78 x 103x 10.009 x (35-25) / 44

= 2.52 x 106Kcal


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In stream (3),

Urea = 457.70 MT

NH3 = 593.88 MT

CO2 = 731.87 MT

H2O = 587.34 MT

Also,

T3 = 95C

Therefore,

H3 = [(457.70 x 0.4625) + (593.88 x 11.56/17) + (731.87 x 10.01/44)

+ (587.34 x 1.1)] x 103x (95-25)

=99.97 x 106Kcal

In stream (4),

Urea = 1954.70 MT

NH3

= 1414.08 MT

H2O = 1047.93 MT

Amm.carbamate = 1297.40 MT

Also,

T4 = 120C

Therefore,

H4 = [(1954.70 x 0.4625) + (1414.08 x 11.56 / 17) + (1297.4 x 0.515)

+ (1047.93 x 1.1)] x 103x (120-25)

=251.70 x 106Kcal


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In the reactor two reactions progress,

Hr1= -38000 cal/gmol

Hr2= +7500 cal/gmol

Amount of Urea formed in reactor = 1954.70457.70= 1497.00 MT

= 24.95 ton mol

So Hr2 = 24.95 x 103x 7500

= 187.125 x 106 Kcal

Total amount of ammonium carbamate before it decomposes to urea:

= 24.95 + 1297.4/78

= 41.583 ton mol

Total heat of reaction (1) at 25C = 41.583 x (-38000) x 103

Hr1 = -1580.154 x 106Kcal

Total heat of reaction (2) at 25C

Htotal = Hr1+Hr2+ (H4- H1 - H2- H3)

= [-1580.154 + 187.125 + 251.70152.852.5299.97] x 106

= -1396.67 x 106Kcal/day

Since it came negative i.e. heat is released.


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High pressure decomposer

Now,

For stream (1)

H1 = 251.70 x 106Kcal ( from reactor energy balance)

T1 = 120C

For stream (2)NH3 = 1730.75 MT

CO2 = 658.68 MT

H2O = 157.19 MT

Also, T2 = 55C

H2 = [(658.68 x 10.01/44) + (157.19 x 0.456) + (1730.75 x 11.56/17)] x 103x (55-25)

= 39.92 x 106Kcal

For stream (3)


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NH3 = 192.31 MT

Urea = 1954.70 MT

H2O = 890.74 MT

Amm. Carbamate = 129.74 MT

T3 = 130C

H3 = [(1954.70 x 0.4625) + (890.74 x 1.1) + (192.31 x 11.56/17) + (129.74 x 0.515)] x 103x

(13025)

= 218.55 x 106Kcal

Now,

The reaction in progress in high pressure decomposer is

H = 38000 cal/gmol

Ammonium carbamate decomposed at 25 C = 1297.40129.74

= 1167.66 MT

= 14.97 ton mol

So,

Hr = 14.97 x 38000 x 103

= 568.86 x 106Kcal

Htotal = Hr+ H2+ H3- H1

= [568.86 + 39.92 + 218.55251.70] x 106

= 575.63 x 106Kcal/day

Therefore, total heat requirement in high pressure decomposer = 575.63 x 106Kcal/day


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REACTOR PROCESS

DESIGN


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The rate expression for urea formation is found from different mechanism involved. The

mechanism is as follows:

The formation of urea takes place according to reaction (5).

Hence its rate expression is:

Therefore,


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Similarly,

Also,

So,

Putting the value of CHO CNfrom (7) in (8), we get

Assuming k6to be very small and hence neglecting it, we have

From (6) and (9), we get


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Also,

NH2 COO NH4is an intermediate.

So,

Substituting in (10), we get

Substituting in the main rate expression, we have

Putting

Since the rate expression corresponds to stoichiometric equation the reaction iselementary.


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DESIGN OF REACTOR


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Where,

A represents CO2

B represents NH3

C represents Urea

D represents H2O

So,

CA= CAO(1-XA) / (1+AXA)

CB= CBO(1-XB) / (1+ BXB)

But,

CBOXB = 2 CAOXA

AndAXA BXB

= (2-3) / 3

= - 1/3

So, putting these conditions in general rate equation


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Where,

Feed to the reactor is on one day basis.

So,

= 1.1540 m3/min

Similarly,


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= 3.3859 m3/min

= 0.2464 m3/min

= 0.4301 m3/min

Therefore,

Total volumetric flow rate = 1.1540 + 3.3859 + 0.2464 + 0.4301

= 5.2164 m3/min

Now,

()

= 28.877 kmol/min

Therefore,

= 5.5358 Kmol/m3

Similarly,

()

= 115.519 kmol/min

Therefore,

= 22.1453 Kmol/m3


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Also,

= 4

The value of rate constant k for this reaction is k = 2.71 x 10-4(m3/Kmol)2min-1

Substituting these

values in equation

(1)

Now,

CSTR with recycle

For CSTR with recycle we have,


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Also,

Therefore,

Putting the value of rate equation in this equation, we get

Here CAO = 5.5358

So, Volumetric flow rate of Outlet

= 0.6984 m3/min

= 1.6931 m3/min


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= 1.0523 m3/min

= 0.7527 m3/min

Therefore,

Total volumetric flow rate in outlet = 0.6984 + 1.6931 + 1.0523 + 0.7527

=4.1965m3/min

Again,

Volumetric flow rate of recycle

= 0.4616 m3/min

= 0.7111 m3/min

= 0.2464 m3/min

= 0.4266 m3/min

Therefore,

Total volumetric flow rate in recycle = 0.4616 + 0.7111 + 0.2464 + 0.4266

= 1.8457 m3/mi


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The reactor used for manufacture of urea has recycle stream as well. The recycle ratio R

may be defined as:

Volumetric flow rate of product leaving the system after recycle = 4.19651.8457

= 2.3508 m3/min

Therefore,

= 0.7851

Also,

And

XAf= 0.6

Therefore,

( )

= 0.2639

Now putting these values in the equation we get


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where

Now, lets plot the graph between f(XA) and XA

XA 0 0.1 0.2 0.3 0.4 0.5 0.6

f(XA) 0.0625 0.0695 0.0784 0.090 0.106 0.1286 0.1633


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Therefore,

t = 214.82 x (Area of the rectangle shown)

= 214.82 x (0.6-0.2639)x0.16

= 11.55 min

But,

So,

V = t x V0

= 11.55 x 5.2164

= 60.25 m

3

Dimensions : any convenient L/D ratio can be chosen.

Let L/D = 4

Volume of reactor,

60.25 = D2x 4D / 4

D = 2.68 m

Length, L = 4D

=10.71m

Design and Selection of Head:

The heads may be ellipsoidal, dished conical, hemispherical, flat. Standard ellipsoidal

heads are somewhat stronger than dished heads of the same gage. Hemispherical heads

are also stronger than formed heads but they are costlier. So taking cost into


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consideration I have selected the ellipsoidal head for the autoclave. The thickness of

standard ellipsoidal head is given by thickness of standard ellipsoidal head is given by

where,

P = design pressure

D = average diameter of shell

S = allowable unit stress

e = efficiency of joint (say 80%)

therefore,

= 0.1743 m

Therefore,

Thickness of ellipsoidal head = 174.3 + 6 mm = 180.3 mm

For ellipsoidal head the inside depth is equal of inside dia of the shell. Therefore,

( )

So, the inside depth of ellipsoidal head is 39.9 cm.


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SPECIF ICATION SHEET

Equipment : Urea Autoclave

Plant : Urea Plant

Type : Plug Flow

Position : Vertical

No. of uni ts : 1

Service : synthesis of Urea from NH3and CO2

Operation : Continuous

DESIGN DATA

Operati on temperature : 200C

Operating Pressur e : 230 kg/cm2

Design Temperatur e : 200C

Capacity : 43.703 m3

Volumetri c F low rate : 4.1965 m3/min

I nternal Diameter : 2.68 m

Shell thickness : 0.1803 m

Height : 10.71 m

Types of top & bottom heads : Ellipsoidal

Materi al of construction : Carbon Steel 1020

Li ning Material : Titanium


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HIGH PRESSURE DECOMPOSER DESIGN

High pressure decomposer is employed for decomposing ammonium carbonate to liberate

NH3and CO2. In high pressure decomposer ammonium carbonate is heated by stream at

13 kgf/cm2 pressure. The effluents from the reactor which are at 120C flows to high

pressure decomposer which operates at 155C and 16 kgf/cm2 pressure, high pressure

decomposer is a reboiler which is conventional 1-1 heat exchanger, vertical thermosiphon

type.

Total heat duty = 575.63 x 106kcal/day (from energy balance)

= 23.984 x106kcal/hr

Amount of stream required can be calculated as:

Pressure of stream entering = 13 kgf.cm2

Temperature of stream entering = 187C

Latent heat of stream at this pressure = 470.743 kcal/kg

But,

Q = m x Latent Heat

Therefore,

23.984 x 106 = m x 470.743

m = 50.95 x 103kg/hr

= 849.15 kg/min

Therefore, steam requirement is 849.15 kg/min.

Selection of shell side and tube side fluids:The effluents from reactor can be passed on tube side whereas stream can be passed on

shell side. The advantage of passing stream on shell side is that the steam that condensing

can easily be removed by using a stream rap connected o shell. Secondly, the non

condensable gases in stream can be vented easily by providing a vent value in shell.


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Tube side => Effluents from reactor

Shell side => Stream

Stream Effluents from reactor

Temp in 187C 120C

Temp out 187C 155C

T1 = 187155

= 32C

T2 = 187120

= 67C

Evaluation of properties:

Average temp of effluents from reactor = (120+155)/2

= 137.5 C

1.Specific Heat:

Cpof NH3at 137.5C = 0.546 Kcal/kgC

Cpof H2O at 137.5C = 1.10 Kcal/kgC

Cpof Urea at 137.5C = 0.492 Kcal/kgC

Cpof Amm. Carbamate at 137.5C = 0.576 Kcal/kgC

Average value of specific heat of effluents = 0.594 Kcal/kgC

2. Viscosity:

Viscosity of urea = 3.25 cp

Viscosity of NH3 = 0.014 cp

Viscosity of H2O = 0.207 cp

Since, the viscosity of urea is more, the average viscosity can be taken as that of

urea.

Therefore,


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average viscosity of effluents = 3.25 cp

3. Density:

Density of water = 928.12 kg/cm3

Density of Urea = 1226 kg/cm3

Density of NH3 = 580 kg/cm3

Heat duty of reboiler = 23.984 x 106 Kcal/ hr

Assume overall heat transfer coefficient = 600 W/m2 oC

According

Q = U x A x LMTD

A = 984.6 m2

Assuming

Tube outer diameter = 20 mm

Inside diameter = 16 mm

Length = 4.83 mm

So surface area = 3.14 x D x L

= 0.303 m2

No. of tubes = (984.6 / 0.303)

= 3250 tubes

Assuming no. of passes = 4

So no. of tube/ passes = 3250 / 4

= 812

Cross section area of tubes = 3.14 x (16x10-2)2/4

= 2.1x10-4

So total flow area = 812 x 2.1x10-4

= 0.170 m2

Mass velocity of effluent

= (1414.08 + 1954.70 + 1047.93 +1297.40) x 103 / (24x3600)


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= 66.135 Kg/sec

Average density of effluent

= 911.37 Kg/m3

Mass velocity of effluent

= 66.135 / 0.170

= 389.03 Kg/m2/sec

So velocity = 389.03 / 911.37

= 0.4268 < 1 m/sec

So consider 8 tube passes

No. of tube/pass = 3250/8

= 406 tubes

So flow area = 406 x 2.1x10-4

= 0.0853 m2

Mass velocity = (66.135 / 0.0853)

= 775.32 kg/m2sec

Velocity = 775.32 / 911.37

= 0.851 m/sec

Finding Reynolds no.

avg = 3.25x10-3poise

= 3818.22

L/D = 302

So using graph Re v/s jHfor different L/D


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jH = 6.0x 10-3

To calculate Pr

Kcarb.= 0.138 w/moc Xcarb. = 0.22

Kwater= 0.68 w/moc Xwater = 0.18

Kurea = 0.28 w/moc Xurea = 0.26

Kammonia= 0.032 w/moc Xammonia = 0.24

So Kmix = KiXi

= 0.23 w/moc

Similarly

Cpmix = CpiXi

=2.4x103KJ/KgoC

Pr no. = Cp/K

= 34.64

So tube side coefficient

h D / k = jH*Re*Pr0.33

By putting all values, we get

h = 1269/10 w/m2 oc

Assuming shell side coefficient = 1600 w/m2 oc

Therefore ,

Overall heat transfer coefficient

(1/Uo) = (1/ho) + (do/dixhi) + (doln(do/di)/2kcu)

= 604.38 >600

so satisfactory.

So this is 1-8 type shell and tube heat exchanger having U = 605 w/m2 oc

To find tube side Pressure Drop:

Pt= NP{8 Jf(L/di)(/w)-m+2.5}ut

2/2

Where ut=tube side fluid velocity

NP=no of tube side passes


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Putting values,

Pt=8*{8*6.81*10-3(4.83/16*10-3)+2.5}911.37*0.851*0.851/2

Pt=50018.977Pa =50.018kPa or kN/m2

Shell Diameter:-

Bundle Diameter, Db=20(3250/0.0365)1/2.675

=1.1469m

Shell diameter from graph12.1=80+1.1469=81.1469m

Assume baffle cut=25%

Baffle spacing=Ds/5=1.469/5=0.299m

Tube Pitch=1.25do=1.25*20*10-3

=25mm

Shell Side area=As=(Pt-do/Pt)*Ds*Bs

=0.894m2

Mass velocity Gs=849.15/0.0894=9498.322kg/m2

Velocity=9498.322/s=21.93m/s

De=1.27/d

o(P

t2-0.785d

o2)

De=19.7485mm

Re=DeGs/ =179024

J f=3.2*10-2(from Graph)

Again For pressure drop,

Ps=8J f(Ds/De)(L/Bs) sus2/2(/w)

-0.14

=31234Pa=312.34kPa

Which is too high, it can be reduced by increasing baffle pitch .Doubling the pitch values,

reduces Pressure Drop by

Ps =312/4=78kPa.


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SPECIF ICATION SHEET

Equipment : High Pressure Decomposer

Plant : Urea Plant

Type : Fixed, Head

Position : Vertical

No. of uni ts : 1

DESIGN DATA

UNIT DATA SHELL SIDE TUBE SIDE

Fluid Steam Effluents from reactor

Temp. Inlet C 187 120

Temp. Outlet C 187 155

Operating pressure kg/cm2 13 16

No. of passes 1 1

Fouling factor

Pressure drop kPa 78 50.018

Density kg/m3 1226

Viscosity Cp 3.25

Specific heat kcal/kg C 0.594

Latent heat kcal/kg 470.743

CONTRUCTION:

Type of unit = Decomposer

Tube pitch = 1 triangular

Shell material = Carbon Steel

Diameter = 35 inch

Tube Material = Stainless Steel

No. of tubes = 3250

Outside Diameter = 1


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COST ESTIMATION


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Marshall & Swift index

For the capacity of 60000 ton/yr

Fixed capital investment in the year 1990 = 8 mn $

But we have a capacity of 1500 tonn/day

=360*1500 tonn/year

Marshall & Swift index in the year 1990 = 904

Marshall &Swift installment equipment index in the year 2008 = 1384

So Fixed capital investment in urea production plant of capacity 360000 tonn/yr

= C (Fe) Rx

Where ,

R = capacity of plant divided by the capacity of reference

X = power factor for plant capacity ratio

= 0.7

Fe = ratio of index

C = 8 mn$ *(1384/904)*(547500/60000)0.7

= 57.573 mn$

Estimation of capital investment cost(I) Direct Costs:

1. Installation costs = 10% of fixed capital

= $ 57.573 x 106x 0.10

= $ 5.757 x 106

2. Piping and instrumentation = 10 % of F.C.I.

= $ 57.573 x 10

6

x 0.10= $ 5.757 x 106

3. Electrical cost = 5 % of F.C.I.

= $ 57.573 x 106x 0.05

= $ 2.878 x 106


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4. Building cost = 10 % of F.C.I.

= $ 57.573 x 106x 0.10

= $ 5.757 x 106

5. Service facility = 5 % of F.C.I.

= $ 57.573 x 106x 0.05

= $ 2.878 x 106

6. Land cost = 5 % of F.C.I.

= $ 57.573 x 106x 0.05

= $ 2.878 x 106

Total direct cost = 1 + 2 + 3 + 4 + 5 + 6

= $ 25.906 x 106

(II) Indirect Costs:

1.

Design and Engg. Cost = 25 % of Direct cost

= $ 25.906 x 106x 0.25

= $ 6.476 x 106

2. Contractors feeCost = 10% of Direct cost.

= $ 25.906 x 106x 0.10

= $ 2.59 x 106

3. Contingency allowance = 10% of Direct cost.

= $ 25.906 x 106

x 0.10= $ 2.59 x 106

Total Indirect cost = 1 + 2 + 3

= $ 11.656 x 106


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Working Capital

Working Capital is the additional investment needed, over and above the fixed capital, to

start the plant and operate it to the point when income is earned.

It includes the cost of

1. Start up

2. Initial catalyst charges

3. Raw material and intermediates in the process.

4. Finished product inventories

5. Funds to cover outstanding accounts from customers.

Most of the working capital is recovered at the end of the project. The total investment

needed for a project is the sum total of the fixed and working capital.

Working Capital = 15 % of Total Capital Investment

= 0.15 x TCI

Now,

Total Capital Investment = total F.C.I. + W.C.I.

= F.C.I. + 0.15T.C.I.

Total Capital Investment = F.C.I. / 0.85

= 57.573 / 0.85

= $ 67.733 x 106

= Rs 338.66 x 107

Estimation of Total Product Cost

It includes direct cost, fixed charges and plant overhead cost.

Manufacturing cost = Direct cost + Fixed charges + plant overhead cost

(1.) Direct product cost


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(a) Raw material cost

Cost of ammonia = 280$/unit

Cost of carbon dioxide = 100$/ unit

Cost of ammonia used = 2827.90*280*360

= 285.05 mn$

Cost of carbon dioxide = 1829.65*100*360$

= 65.86mn$

So ,

Raw material cost = 285.05+65.86

= 350.91mn$

(b) Fixed charges:

Life span for plant = 50 years

(1.) Depreciation = Fixed capital investment/ life span

= 57.573/ 50

= 1.15mn$/yr

(2.) local taxes

Taking 1% of FCI = 0.5757 mn$

Insurance = 0.2878 mn$

So ,

Total fixed cost = 2.0135mn $

(c) Plant overhead cost:

= 5%of FCI

= 0.05*57.573 mn$

= 2.8786 mn$

So manufacturing cost


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= 355.80 mn$

General expenses = 15% of FCI

= 0.15*57.573

= 8.636 mn$

So ,

Total production cost = 364.436mn$

Cost of urea = 800 $/ton

Urea produced from reactor = 1954.70MT/day

= 360*1954.70MT/yr

Total income = 1954.70*360*800

= 562.95mn$

So ,

Profit = 562.95- 364.436

= 198.51 mn$

Taxes = 30% of gross earning

= 0.30*198.51

= 59.55mn$

So ,

Net profit = 138.95 mn$

And

Annual rate of return = 41.03%


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COST OF MAJOR EQUIPMENT

(1.) Cost of reactor (Plug flow with recycle)

Diameter = 2.68m

Height = 10.71m

From the graph

Equipment purchase cost = 80,000 $

For carbon steel,

Material factor (MF) = 1

Pressure factor (PF) = 2.2 (for pressure >60 bar)

So,

Purchase equipment cost for the year 2004

= 80000 $ *(MF * PF)

= 80000$ *(1*2.2)

= 176000$

So, purchase equipment cost for the year 2008

= 176000* 1384/ 1277.33

= 190697.28 $

(2.) Cost of heat exchanger

Type of heat exchanger: shell & tube type

No. of tube passes = 8

No. of shell passes = 1

From log-log graph,Cost = 98000 $

And,

For carbon steel,

Material factor = 1

Pressure factor = 1.3(for pressure up to 65 bar)


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So,

Purchased equipment cost of heat exchanger in 2004

= 98000$ * 1*1.3

= 127400 $

So in 2008,

= 127400*1384/ 1277.33

138039.19 $


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GENERAL SITE CONSIDERATIONS

PLANT LOCATION AND SITE SELECTION

The location of the plant can have a crucial effect on the profitability of a project, and the

scope for future expansion. Many factors must be considered when selecting a suitable

site. The principal factors to consider are:

1. Location, with respect to the marketing area.

2. Raw material supply.

3. Transport facilities.

4. Availability of labor.

5. Availability of utilities: water, fuel, power.

6. Availability of suitable land.

7. Environmental impact and effluent disposal.

8. Local community considerations.

9. Climate.

10. Political and strategic considerations.

Marketing areaFor materials that are produced in bulk quantities; such as cement, mineral acids, and

fertilizers, where the cost of the product per tone is relatively low and the cost of

transport a significant fraction of the sales price, the plant should be located close to the

primary market. This consideration will be less important for low volume production,

high-priced products; such as Pharmaceuticals. In an international market, there may be

an advantage to be gained by locating the plant within an area with preferential tariff

agreements; such as the European Community (EC).

Raw materialsThe availability and price of suitable raw materials will often determine the site location.

Plants producing bulk chemicals are best located close to the source of the major raw

material; where this is also close to the marketing area.


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Transport

The transport of materials and products to and from the plant will be an overriding

consideration in site selection. If practicable, a site should be selected that is close to at

least two major forms of transport: road, rail, waterway (canal or river), or a sea port.

Road transport is being increasingly used, and is suitable for local distribution from a

central warehouse. Rail transport will be cheaper for the long-distance transport of bulk

chemicals. Air transport is convenient and efficient for the movement of personnel and

essential equipment and supplies, and the proximity of the site to a major airport should

be considered.

Availability of labor

Labor will be needed for construction of the plant and its operation. Skilled construction

workers will usually be brought in from outside the site area, but there should be an

adequate pool of unskilled labor available locally; and labor suitable for training to

operate the plant. Skilled tradesmen will be needed for plant maintenance. Local trade

union customs and restrictive practices will have to be considered when assessing the

availability and suitability of the local labor for recruitment and training.

Utilities (services)Chemical processes invariably require large quantities of water for cooling and general

process use, and the plant must be located near a source of water of suitable quality.

Process water may be drawn from a river, from wells, or purchased from a local

authority. At some sites, the cooling water required can be taken from a river or lake, or

from the sea; at other locations cooling towers will be needed. Electrical power will be

needed at all sites. A competitively priced fuel must be available on site for steam and

power generation.

Environmental impact, and effluent disposalAll industrial processes produce waste products, and full consideration must be given to

the difficulties and cost of their disposal. The disposal of toxic and harmful effluents will

be covered by local regulations, and the appropriate authorities must be consulted during


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the initial site survey to determine the standards that must be met. An environmental

impact assessment should be made for each new project, or major modification or

addition to an existing process.

Local community considerationsThe proposed plant must fit in with and be acceptable to the local community. Full

consideration must be given to the safe location of the plant so that it does not impose a

significant additional risk to the community. On a new site, the local community must be

able to provide adequate facilities for the plant personnel: schools, banks, housing, and

recreational and cultural facilities.

Land (site considerations)Sufficient suitable land must be available for the proposed plant and for future expansion.

The land should ideally be flat, well drained and have suitable load-bearing

characteristics. A full site evaluation should be made to determine the need for piling or

other special foundations.

ClimateAdverse climatic conditions at a site will increase costs. Abnormally low temperatures

will require the provision of additional insulation and special heating for equipment and

pipe runs. Stronger structures will be needed at locations subject to high winds

(cyclone/hurricane areas) or earthquakes.

Political and strategic considerations

Capital grants, tax concessions, and other inducements are often given by governments to

direct new investment to preferred locations; such as areas of high unemployment. The

availability of such grants can be the overriding consideration in site selection.


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SITE LAYOUT

The process units and ancillary buildings should be laid out to give the most economical

flow of materials and personnel around the site. Hazardous processes must be located at a

safe distance from other buildings. Consideration must also be given to the future

expansion of the site. The ancillary buildings and services required on a site, in addition

to the main processing units (buildings), will include:

1. Storages for raw materials and products: tank farms and warehouses.

2. Maintenance workshops.

3. Stores, for maintenance and operating supplies.

4. Laboratories for process control.

5. Fire stations and other emergency services.6. Utilities: steam boilers, compressed air, power generation, refrigeration, transformer

stations.

7. Effluent disposal plant.

8. Offices for general administration.

9. Canteens and other amenity buildings, such as medical centres.

10. Car parks.

When roughing out the preliminary site layout, the process units will normally be sited

first and arranged to give a smooth flow of materials through the various processing

steps, from raw material to final product storage. Process units are normally spaced at

least 30 mapart; greater spacing may be needed for hazardous processes. The location of

the principal ancillary buildings should then be decided. They should be arranged so as to

minimize the time spent by personnel in travelling between buildings. Administration

offices and laboratories, in which a relatively large number of people will be working,

should be located well away from potentially hazardous processes. Control rooms will

normally be located adjacent to the processing units, but with potentially hazardous

processes may have to be sited at a safer distance. The sitting of the main process units

will determine the layout of the plant roads, pipe alleys and drains. Access roads will be

needed to each building for construction, and for operation and maintenance.


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Utility buildings should be sited to give the most economical run of pipes to and from the

process units. Cooling towers should be sited so that under the prevailing wind the plume

of condensate spray drifts away from the plant area and adjacent properties. The main

storage areas should be placed between the loading and unloading facilities and the

process units they serve. Storage tanks containing hazardous materials should be sited at

least 70 m (200 ft) from the site boundary.

A TYPICAL PALNT LAYOUT


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UTILITIES

The word "Utilities" is now generally used for the ancillary services needed in the

operation of any production process. These services will normally be supplied from acentral site facility; and will include:

1. Electricity.

2. Steam, for process heating.

3. Cooling water.

4. Water for general use.

5. Demineralised water.

6. Compressed air.

7. Inert-gas supplies.

8. Refrigeration.

9. Effluent disposal facilities

ELECTRICITYPower is required for chemical process, motor, lightening, pumps, compressor, & other

general & mechanical purposes. It may be purchased from local supply authority or

generated at plant by steam turbine, generator.

STEAMThe steam for process heating is usually generated in water tube boilers; using the most

economical fuel available. The process temperatures required can usually be obtained

with low-pressure steam, typically 2.5 bar (25 psig), and steam is distributed at a

relatively low mains pressure, typically around 8 bar (100 psig).


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COMBINED HEAT AND POWER (CO-GENERATION)The energy costs on a large site can be reduced if the electrical power required is

generated on site and the exhaust steam from the turbines used for process heating. The

overall thermal efficiency of such systems can be in the range 70 to 80 per cent;

compared with the 30 to 40 per cent obtained from a conventional power station, where

the heat in the exhaust steam is wasted in the condenser. Whether a combined heat and

power system scheme is worth considering for a particular site will depend on the size of

the site, the cost of fuel, the balance between the power and heating demands; and

particularly on the availability of, and cost of, standby supplies and the price paid for any

surplus power electricity generated.

COOLING WATERNatural and forced-draft cooling towers are generally used to provide the cooling water

required on a site; unless water can be drawn from a convenient river or lake in sufficient

quantity. Sea water, or brackish water, can be used at coastal sites, but if used directly

will necessitate the use of more expensive materials of construction for heat exchangers.

WATER FOR GENERAL USE

The water required for general purposes on a site will usually be taken from the local

mains supply, unless a cheaper source of suitable quality water is available from a river,

lake or well.

DEMINERALISED WATER

Demineralised water, from which all the minerals have been removed by ion-exchange, is

used where pure water is needed for process use, and as boiler feed-water. Mixed and

multiple-bed ion-exchange units are used; one resin converting the cations to hydrogen

and the other removing the acid radicals. Water with less than 1 part per million of

dissolved solids can be produced.


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REFRIGERATION

Refrigeration will be needed for processes that require temperatures below those that can

be economically obtained with cooling water. For temperatures down to around 10C

chilled water can be used. For lower temperatures, down to30C, salt brines (NaCl andCaCl2) are used to distribute the "refrigeration" round the site from a central refrigeration

machine. Vapor compression machines are normally used.

COMPRESSED AIR

Compressed air will be needed for general use, and for the pneumatic controllers that are

usually used for chemical process plant control. Air is normally distributed at a mainspressure of 6 bar (100 psig). Rotary and reciprocating single-stage or two-stage

compressors are used. Instrument air must be dry and clean (free from oil).

INERT GASES

Where large quantities of inert gas are required for the inert blanketing of tanks and for

purging this will usually be supplied from a central facility. Nitrogen is normally used,

and is manufactured on site in an air liquefaction plant, or purchased as liquid in tankers.

EFFLUENT DISPOSAL

Facilities will be required at all sites for the disposal of waste materials without creating a

public nuisance.


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INSTRUMENT AND PROCESS CONTROL

Instrumentation is the most important factor in ensuring safety and smooth working of

the plant. A separate control room is provided in modern plants where on panels

indicators and recorders are present.

Instruments are used in the industry to measure process variables such as temperature,

pressure, density, level specific heat, conductivity, humidity, flow rate, chemical

composition etc.

The primary objectives of the designer when specifying instrumentation and control

schemes are:

1. Safe plant operation:(a) To keep the process variables within known safe operating limits.

(b) To detect dangerous situations as they develop and to provide alarms and

automatic shut-down systems.

(c) To provide interlocks and alarms to prevent dangerous operating

procedures.

2. Production rate:To achieve the design product output.

3. Product quality:To maintain the product composition within the specified quality standards.

4. Cost:To operate at the lowest production cost, commensurate with the other objectives.

These are not separate objectives and must be considered together.


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TEMPERATURE CONTROL / MEASUREMENTS

Various instruments are used for e.g.

1. Thermocouple

2. Resistance Thermometers

3. Thermistors

4. Mercury in Glass Thermometers.

Controllers are used to maintain temperature within specified limits. Every temperature

control problems is essential one. The temperature lay involved in the measurement of

this variable is an important factor. Thermal element is usually placed in a well to protect

it and allow servicing of element without interrupting the process. The location of the

temperature element often has as much to do with the efficiency element often as other

parts of the control loops. Temperature bulb should always be located at point where the

coefficient of heat transfer will be as large as possible e.g. if vapors and liquid are at

same temperature, then bulb should be kept in liquid because of high heat transfer

coefficients.

PRESSURE CONTROL / MEASUREMENTS

It is quite necessary for most system handling vapours of gas. It can be measured by

using pressure gauges.

Self operated pressure regulation is often used in pressure control. It is installed directly

in the line the control sensing apparatus is paced about 10 diameters from the unit. This

location eliminates erroneous pressure caused by turbulence. Sudden change in velocity,

shock and vibrations difficulties often occur when self operated regulation are used with

liquids.


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LEVEL CONTROL / MEASUREMENT

The measurement of level can be defined as the determination of location of interface

with respect to a fixed plane. The main objective of a level control system is to maintain

the level of the liquid in a tank at the Act point value. The different is pressure transmitter

senses the pressure difference / a function of liquid level in the tank) and gives out an

electrical signal, which after signal conditioning is given to the P.I.D. controller. The

controller compares the measured variables with the set point and depending upon the

error, gives an output to the control valve. The control value, in turn controls the flow.

Due to the control of flow, the level is controlled to its set point.

FLOW CONTROL / MEASUREMENTS

It is defined as volume per unit time at specific temperature and pressure conditions. It is

generally measured by positive displacement of rate meters.

The process flow-sheet shows the arrangement of the major pieces of equipment and their

interconnection. It is a description of the nature of the process. The Piping and Instrument

diagram (P and I diagram) shows the engineering details of the equipment, instruments,

piping, valves and fittings; and their arrangement. It is often called the Engineering Flow-

sheet or Engineering Line Diagram.

The P and I diagram shows the arrangement of the process equipment, piping, pumps,

instruments, valves and other fittings. It should include:

1. All process equipment identified by an equipment number. The equipment should be

drawn roughly in proportion, and the location of nozzles shown.

2. All pipes, identified by a line number. The pipe size and material of construction

should be shown. The material may be included as part of the line identification number.

3. All valves control and block valves, with an identification number. The type and size

should be shown. The type may be shown by the symbol used for the valve or included in

the code used for the valve number.

4. Ancillary fittings that are part of the piping system, such as inline sight-glasses,

strainers and steam traps; with an identification number.


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5. Pumps, identified by a suitable code number.

6. All control loops and instruments, with an identification number.

REACTOR CONTROL

The schemes used for reactor control depend on the process and the type of reactor. If a

reliable online analyzers is available, and the reactor dynamics is suitable, the product

composition can be monitored and the reactor conditions and feed flows controlled

automatically to maintain the desired product compositions and yield. More often, the

operator is the final link in the control loop, adjusting the controller set points. Reactor

temperature will normally be controlled by regulating the flow of heating and cooling

medium. Pressure is usually held constant.


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INSTRUCTIONS FOR OPERATION

Before starting, always make sure that the followings:

No visible damage is evident in the system.

All electrical switches are turned off.

All water valves are closed.

All valves are tightly closed.

Start up procedure.

Check the level in the tank.

Switch on the main supply.

Turn on the main pump.

Open valve for pump.

Start mechanical pump.

Open the steam valve.

Check the flow, temperature& pressure during the operation.

System shut down.

Reduce the flow of the feed & steam.

Reduce all flow rates & wait for pasture to drop.

Turn off the pump.

When the flow slow down close the valve tightly to avoid cavitations.

Disconnect the packing line.


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N START UP OF PLANT

The testing phase of the start up requires about 10 days. First of all the utility systemconsisting of high and low pressure steam, process and instrument air, cooling water and

electric power have to be tested. Pumps are greased and checked for absence of kindage.

After all utilities and moving systems are ready, water is introduced in the system instead

of feed and tightness of the plant is established on water testing. Instruments are checked

for response and accuracy. The feed is then introduced in place of water and is allowed

gradually to displace the water in the system.

After the process has been fairly well stabilized on hand control, it is then placed on

instrument control, and then the entire operation is brought under automatic process

control. Each step is so adjusted that it gives most efficient performance.

The first consideration must be given to the quality of products. The conversion of

carbamate to urea in the reactor is greatly affected by temperature and pressure in the

reactor. Hence skilled persons are required to maintain these constants at the required

conditions.


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SAFETY

General rules for the protection of personnel from moving machinery, hot equipment are

to be observed, pipes and large equipments containing steam at high temperature and

pressure and installed in the plant. Protection of the personnel from burns where blowing

out of these materials can occur should be provided.

Since the plant is an open air installation, hence the risks of poisoning and unnecessary

housing should be avoided. Storage of combustible material at the site should be avoided.

In the case of unconsciousness due to poisoning, artificial respiration should be applied.

Hand operated fire extinguishers, fire carpets and emergency showers should be placed

where ever possible. The extinguishers should be used against small fires and the firecarpets and the showers should be used when clothing has caught fire. The showers

should also be used against burns from chemicals. Eye washers should be installed

wherever necessary. Smoking should be forbidden in the plant.

In case of fire it is normal to use water to keep the surrounding cool, until the leak

resulting in the fire is shut off. All sparks should be avoided and welding should be

exercised keeping in view that no combustible material is in close vicinity.

For the protection of the personnel the following equipments should be available:

1.

Safety helmets and shoes which should be worn by persons when they are

working.

2. Goggles for protection against liquid and gases.

3. Gloves for protection against heat.

4. Respiration masks with filters for dust for protection against poisonous gases like

NH3, etc.

5. Ear stuffers or other devices for protection against noise.

Ammonia vapours have pungent smell and they are alkaline. Even a small concentration

of NH3 vapour or liquid may cause fatal damages. Persons employed in handling of

gaseous and liquid NH3should wear gloves and respiratory masks with special filters.


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manufacturing processes are, to a greater or lesser extent, inherently unsafe, and

dangerous situations can develop if the process conditions deviate from the design values.

The safe operation of such processes depends on the design and provision of engineered

safety devices, and on good operating practices, to prevent a dangerous situation

developing, and to minimize the consequences of any incident that arises from the failure

of these safeguards.

The term "engineered safety" covers the provision in the design of control systems,

alarms, trips, pressure-relief devices, automatic shut-down systems, duplication of key

equipment services; and fire-fighting equipment, sprinkler systems and blast walls, to

contain any fire or explosion.

THE HAZARDS

Toxicity

Most of the materials used in the manufacture of chemicals are poisonous, to some

extent. The potential hazard will depend on the inherent toxicity of the material and the

frequency and duration of any exposure. It is usual to distinguish between the short-term

effects (acute) and the long-term effects (chronic). A highly toxic material that causes

immediate injury, such as phosgene or chlorine, would be classified as a safety hazard.

Whereas a material whose effect was only apparent after long Exposure at low

concentrations, for instance, carcinogenic materials, such as vinyl chloride, would be

classified as industrial health and hygiene hazards. The permissible limits and the

precautions to be taken to ensure the limits are met will be very different for these two

classes of toxic materials. Industrial hygiene is as much a matter of good operating

practice and control as of good design.

Control of substanceshazardous to health

The employer is required to carry out an assessment the flanged joints (liable to leak),

Ventilation: use open structures, or provide adequate to evaluate the risk to health, and

establish what precautions are needed to protect employees. A written record of the

assessment would be kept, and details made available to employees. The designer will be


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concerned more with the preventative aspects of the use of hazardous substances. Points

to consider are:

1. Substitution: of the processing route with one using less hazardous material or,

substitution of toxic process materials with non-toxic, or less toxic materials.

2. Containment: sound design of equipment and piping, to avoid leaks. For example,

specifying welded joints in preference to gasket

ventilation systems.

4. Disposal: provision of effective vent stacks to disperse material vented from pressure

relief devices; or use vent scrubbers.

5. Emergency equipment: escape routes, rescue equipment, respirators, safety showers,

eye baths,

In addition, good plant operating practice would include:

1. Written instruction in the use of the hazardous substances and the risks involved,

2. Adequate training of personnel.

3. Provision of protective clothing.

4. Good housekeeping and personal hygiene.

5. Monitoring of the environment to check exposure levels. Consider the installation

of permanent instruments fitted with alarms.

6. Regular medical check-ups on employees, to check for the chronic effects of toxic

materials.

Flammability

The term "flammable" is now more commonly used in the technical literature than

"inflammable" to describe materials that will burn, and will be used in this book. The

hazard caused by a flammable material depends on a number of factors:

1. The flash-point of the material.

2. The auto ignition temperature of the material.

3. The flammability limits of the material.

4. The energy released in combustion.

Explosions


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An explosion is the sudden, catastrophic, release of energy, causing a pressure wave

(blast wave). An explosion can occur without fire, such as the failure through over-

pressure of a steam boiler or an air receiver. When discussing the explosion of a

flammable mixture it is necessary to distinguish between detonation and deflagration. If a

mixture detonates the reaction zone propagates at supersonic velocity (approximately 300

m/s) and the principal heating mechanism in the mixture is shock compression. In a

deflagration the combustion process is the same as in the normal burning of a gas

mixture; the combustion zone propagates at subsonic velocity, and the pressure build-up

is slow. Whether detonation or deflagration occurs in a gas-air mixture depends on a

number of factors; including the concentration of the mixture and the source of ignition.

Unless confined or ignited by a high-intensity source (a detonator) most materials will

not detonate. However, the pressure wave (blast wave) caused by a deflagration can still

cause considerable damage. Certain materials, for example, acetylene, can decompose

explosively in the absence of oxygen; such materials are particularly hazardous.

Sources of ignition

Though precautions are normally taken to eliminate sources of ignition on chemical

plants, it is best to work on the principle that a leak of flammable material will ultimately

find an ignition source.

Electrical equipment

The sparking of electrical equipment, such as motors, is a major potential source of

ignition, and flame proof equipment is normally specified. Electrically operated

instruments, controllers and computer systems are also potential sources of ignition of

flammable mixtures.

Static electricity

The movement of any non-conducting material, powder, liquid or gas, can generate static

electricity, producing sparks. Precautions must be taken to ensure that all piping is

properly earthed (grounded) and that electrical continuity is maintained around flanges.


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Escaping steam, or other vapors and gases, can generate a static charge. Gases escaping

from a ruptured vessel can self-ignite from a static spark.

Process flames

Open flames from process furnaces and incinerators are obvious sources of ignition and

must be sited well away from plant containing flammable materials.

Miscellaneous sources

It is the usual practice on plants handling flammable materials to control the entry on to

the site of obvious sources of ignition; such as matches, cigarette lighters and battery-

operated equipment. The use of portable electrical equipment, welding, spark-producing

tools and the movement of petrol-driven vehicles would also be subject to strict control

Exhaust gases from diesel engines are also a potential source of ignition.

Pressure

Over-pressure, a pressure exceeding the system design pressure, is one of the most

serious hazards in chemical plant operation. Failure of a vessel, or the associated piping,

can precipitate a sequence of events that culminate in a disaster. Pressure vessels are

invariably fitted with some form of pressure-relief device, set at the design pressure, so

that (in theory) potential over-pressure is relieved in a controlled manner.

Temperature deviations

Excessively high temperature, over and above that for which the equipment was

designed, can cause structural failure and initiate a disaster. High temperatures can arise

from loss of control of reactors and heaters; and, externally, from open fires. In the design

of processes where high temperatures are a hazard, protection against high temperatures

is provided by:

1. Provision of high-temperature alarms and interlocks to shut down reactor feeds, or

heating systems, if the temperature exceeds critical limits.

2. Provision of emergency cooling systems for reactors, where heat continues to be

generated after shut-down; for instance, in some polymerization systems,


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3. Structural design of equipment to withstand the worst possible temperature excursion.

4. The selection of intrinsically safe heating systems for hazardous materials.

Steam, and other vapour heating systems, is intrinsically safe; as the temperature cannot

exceed the saturation temperature at the supply pressure. Other heating systems rely on

control of the heating rate to limit the maximum process temperature. Electrical heating

systems can be particularly hazardous.

Fire protection

To protect against structural failure, water-deluge systems are usually installed to keep

vessels and structural steelwork cool in a fire. The lower section of structural steel

columns are also often lagged with concrete or other suitable materials.

Noise

Excessive noise is a hazard to health and safety. Long exposure to high noise levels can

cause permanent damage to hearing. At lower levels, noise is a distraction and causes

fatigue.

The basic safety and fire protective measures that should be included in all chemical

process designs are listed below:-

1. Adequate, and secure, water supplies for fire fighting.

2. Correct structural design of vessels, piping, steel work.

3. Pressure-relief devices.

4. Corrosion-resistant materials, and/or adequate corrosion allowances.

5. Segregation of reactive materials.

6. Earthing of electrical equipment.

7. Safe location of auxiliary electrical equipment, transformers, switch gear.

8. Provision of back-up utility supplies and services.

9. Compliance with national codes and standards.

10. Fail-safe instrumentation.

11. Provision for access of emergency vehicles and the evacuation of personnel.

12. Adequate drainage for spills and fire-fighting water.


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ENVIRONMENTAL CONSIDERATIONS

All individuals and companies have a duty of care to their neighbors, and to the

environment in general. In the United Kingdom this is embodied in the Common Law. In

addition to this moral duty, stringent controls over the environment are being introduced

in the United Kingdom, the European Community, the United States, and in other

industrialized countries and developing countries. Vigilance is required in both the design

and operation of process plant to ensure that legal standards are met and that no harm is

done to the environment.

Consideration must be given to:

1. All emissions to land, air, water.

2. Waste management.

3. Smells.

4. Noise.

5. The visual impact.

6. Any other nuisances.


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REFERENCES

1. Sinnot, R.K, Coulson and Richardsons Chemical Engineering, vol-6, Fourth

edition, 2005

2. Perry, Robert H, Green, Don W., Chemical Engineers Handbook, 1999

3. McCabe, Warren L, Smith, Julian C, Harriott Peter Unit Operations of

Chemical Engineering, Sixth edition, 2001

4.

Eckman, Donald P., Industrial Instrumentation, 1991

5. Hesse, Herman C., Rushton, J.Henry, Process Equipment Design

6. Peters, Max S.,Timmerhaus,Klaus D. Process Design and Economics for

Chemical Engineers, Fourth edition , 1958

7. Levenspiel, O., Chemical Reaction Engineering., 2ndEd., John Wiley.

8. Hesse, H.C. and Rushton, J.H., Process Equipment Design, Niki D Van

Nostrand Company Inc.

9. Chapmon, Alan, J, Heat Transfer, 4thEd., Mc Millan.

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