report on urea production and process analysis.docx

8/14/2019 Report on Urea Production and Process Analysis.docx

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SUMMER VOCATIONAL TRAINING, 2013

PROJECT REPORT ON

UREA PRODUCTION ANDPROCESS ANALYSIS

SITE: NATIONAL FERTILIZERS LTD. VIJAIPUR.(FROM 06.06.2013 TO 05.07.2013)

Training Incharge:

Mr. M.K. Biswas (Chief manager & HOD- Lab)

Training co-ordinators: SUBMITTED BY

Mr. B.N Sharma (Sr. manager-Lab) SAMEER SAXENA

Mr. D.P. Shrivastava (SR. Manager-Lab) 3rd

YEAR,


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Mr. N.S Hada (Manager-Lab) IMD INDUSTRIAL CHEMISTRY

IIT (BHU), VARANASI.

knowledgementI am thankful to Mr. D.R. Chowdhury (Chief Manager (HRD))

for granting me permission to pursue vocational training in Central

laboratory from 06.06.2013 to 05.07.2013.

My sincere acknowledgement goes to Mr. M.K. Biswas (Chief

Manager, Head of Department-Lab) for allowing me to perform

experiments and use the facilities of Central Laboratory during my

training tenure.

I am also thankful to Mr. B.N. Sharma (Sr. manager-Lab), Mr.

O.P. Sharma (Manager-lab), Mr. N.S. Hada (Manager-Lab) and

Mr. K.P. Saxena (Sr. Chemist-Lab) who helped a lot in clearing my

concepts in the subject and solving my pertinent doubts, without

which my training would have never achieved its real meaning.

I am also thankful to Mr. R.P. Gupta (A.M. (HRD)) for the kind

opportunity he gave me to pursue my summer training in the NFL,

Vijaipur plant.

Last but not the least I would also like to thank those individual in the

Central laboratory that made my vocational training memorable and

pleasant.

Sincerely

Sameer Saxena

11411EN002

3rdyear, IMD, Industrial Chemistry


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Indian Institute of Technology (B.H.U), Varanasi.

INDEX

Sr. no. Contents Page No.1. About NFL 4

2. WATER CHEMISTRY

OVERVIEW

PTPDemineralization PlantCPP

5

12-16

17-33

34-42

3. AMMONIA PRODUCTION

PROCESS

43-52

4. UREA TECHNOLOGY AND

DEVELOPMENT

53-60

5. VARIOUS EQUIPMENTS

AVAILABLE FOR QUALITY

CONTROL and LAB TESTING

AT CENTRAL LAB, NFL

VIJAIPUR

61-75

5. VARIOUS WATER QUALITY

CONTROL TESTS CARRIEDOUT AT CENTRAL LAB,

NATIONAL FERTILIZERS LTD.

VIJAIPUR

76-96

6. EFFLUENT TREATMENT

FACILITIES

97-101


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7. CONCLUSION 102

National Fertilizers Limited (NFL)

NFL is a schedule A and Mini Ratna Company which was

incorporated on 23rd

August,1947 for implementation of two

fertilizers plants based on gasification technology of Feed stock/ Low

Sulphur Heavy Stock at Panipat (Haryana) and Bhatinda(Punjab)

having an installed capacity of 5.11 lakh tonnes of urea.

In April 1978, the Nangal Group of Plants of fertilizer corporation of

India (FCI) was transferred to NFL consequent upon reorganization of

NFL-FCI. The Government of India, in 1984, entrusted the company

to execute the countrys first inland gas based fertilizers project of

7.26 lakh tonnes Urea capacity in District Guna in Madhya Pradesh.

This project was completed well within time & approved coast and

received the First prize for Excellence in Project Management

`from the Ministry of Programme Implementation, Government of

India. The Department of Fertilizers subsequently reassessed the

annual installed capacity of Vijaipur plants from 7.26 lakh tonnes of

urea to 8.64 lakh tonnes with effect from 1st April, 2000.

In order to sustain and enhance the companys growth, NFL

successfully completed the revamping of urea plant at Nangal andcommercial production commenced from 01.02.2001. The annual

installed capacity of Nangal plant thus increased from 3.30 lakh

tonnes to 4.78 lakhs tonnes of Urea. Thus, the total annual installed

capacity of urea at NFL has reached to 32.31lakh tonnes.

NFL Vijaipur unit is very advance and well computerised and called

as jewel of crowns of NFL. Vijaipur produces:

Kisan Urea


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Bio-Fertilizers

WATER CHEMISTRY OVERVIEW

Wateris achemical substance with thechemical formulaH2O.A water

molecule contains oneoxygen and twohydrogenatoms connected bycovalent

bonds. Water is aliquid atambient conditions,but it often co-exists onEarth

with itssolid state,ice,andgaseous state (water vapour orsteam). Water also

exists in aliquid crystal state nearhydrophilic surfaces. Under nomenclature

used to namechemical compounds,Dihydrogen monoxide is the scientific name

for water, though it is almost never used.

Water covers 70.9% of theEarth's surface and is vital for all known forms of

life.On Earth, 96.5% of the planet's water is found in oceans, 1.7% in

groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a

small fraction in other large water bodies, and 0.001% in theair asvapour,

clouds (formed of solid and liquid water particles suspended in air), and

precipitation.Only 2.5% of the Earth's water is freshwater, and 98.8% of that

water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers,lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater

(0.003%) is contained within biological bodies and manufactured products.

Water on Earth moves continually through thehydrological cycle of

evaporation andtranspiration (evapotranspiration),condensation,precipitation,

andrunoff,usually reaching thesea.Evaporation and transpiration contribute to

the precipitation over land.

Uses of Water in an industry:-

i.) Water is used as a coolant.ii.) Water is used as a solvent.iii.) Raw Water is used to prepare Demineralised (DM) water for the

preparation of steam in boilers, for make-up and analysis in

Laboratories.

iv.) To create Hydraulic pressure in plant processes.v.) As a chemical reactant.vi.) To obtain hydrogen (which is present as 2 parts in 1 part water).
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Q. HOW WATER BECOMES IMPURE?

Water is one of the basic requirements in production of steam. In naturewater is available in abundance. Its physical and chemical characteristicsvary depending upon the source and strata on which it flows. It picks up

mineral salts from the soil, which go in to solution.

Water, therefore contains mineral salts in dissolved condition, in varyingproportions, composition and degree. It gets polluted further with

multifarious organic and in organic impurities due to disposal of

industrial and domestic wastes.

Decayed vegetation and micro-organism also contribute to contamination.Water also contains coarse substance in suspended form, constituting of

silt and clay matters, generally termed as turbidity.

Silicate matters are present in dissolved as well as in colloidal forms,proportion of which varies depending mainly on the following conditions:

TemperatureSeasonal ConditionsChemical characteristics of the particulateVelocity of the flow.


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TYPE OF IMPURITIES

Dissolved mineral matters present in water are composed of metallic

Component (cations) and acidic component (anions) in equal quantity ofPositively charged cations & negatively charged anion.

Ionic &Dissolved Non-ionic And

Undissolved

Gaseous

Cationic Anionic Turbidity, Silt Carbon Dioxide

Calcium Bicarbonate Mud ,Dirt And

Other SuspendedMatters.

Hydrogen

Sulphide

Magnesium Carbonate Colour Methane

Sodium Hydroxide Organic Matter Oxygen

Potassium Sulphate Colloidal Silica Chlorine

Ammonium Chloride

Iron Phosphate

Manganese Bisilicate

(HSiO3),

Silicate

(SiO3),

Silicic Acid(H2SiO3)

Micro-organism

Plankton, Bacteria

Organic

Matter

Oil And Corrosion

Products


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SOLUBLE AND SUSPENDED IMPURITIES FOUND IN WATER AND

THEIR FFFECTS:-

Constituent Chemical

formula

Difficulties caused Means of

treatment

1. Turbidity None.Expressed

In analysis

as

units

Imparts unsightly

appearance to

water; deposits in

water lines,

Process equipment,etc.

Coagulation,

settling,

and filtration

2. Hardness calciumand

magnesiu

m

salts,

expressed

as

CaCO3

Chief source of scale

in heat

exchange equipment,

boilers, pipe

lines, etc.; Forms

curds with soap,

Interferes with

dyeing, etc.

Softening;

demineralizatio

n;

internal boiler

water

treatment;

surface

active agents

3. Carbondioxide

CO2 Corrosion in water

lines, particularly

steam and condensate

lines

Aeration, de-

aeration,

neutralization

with

alkalis

4. Sulphate SO42- Adds to solidscontent of water, butin itself is not usually

significant,

combines with

calcium to form

calcium sulphate

scale

Demineralizatio

n, reverseosmosis, electro

dialysis,

evaporation

5. Fluoride F- Causeof mottled enamel in

teeth;also used for control

Adsorption with

magnesium

hydroxide,calcium


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of dental decay:

not usually

significant

industrially

phosphate, or

bone black;

alum

coagulation

6. Sodium Na+

Adds to solidscontent of water:

when combined with

OH-, causes

corrosion in boilers

under certain

conditions

Demineralization, reverse

osmosis, electro-

dialysis,

evaporation

7. Iron Fe2+(ferrous)

Fe

3+

(ferric)

Discolours water on

precipitation;

source of deposits inwater lines,

boilers etc.;

Interferes with

dyeing,

tanning,

papermaking, etc.

Aeration;

coagulation and

filtration; limesoftening;

cation

exchange;

contact

filtration;

surface active

agents for iron

retention

8. Manganese Mn2+ Same as iron Same as iron9. Oxygen O2 Corrosion of water

lines, heat

exchange equipment,

boilers,

return lines, etc.

Deaeration;

sodium

sulphite;

corrosion

inhibitors

10.Hydrogensulphide

H2S Cause of "rotten

egg" odour.

Corrosion

Aeration;

chlorination;

highly basic

anion

exchange

11.Ammonia NH3 Corrosion of copperand zinc alloys by

formation of complex

soluble ion

Cation

exchange with

Hydrogen

zeolite;

chlorination;

12.Dissolvedsolids

None Refers to total

amount of dissolved

Lime softening

and cation


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matter, determined

by evaporation;

high concentrations

are objectionable

because of processinterference and

as a cause of foaming

in boilers

exchange by

hydrogen

zeolite;

demineralizatio

n,reverse osmosis,

electro dialysis,

evaporation

13.Suspendedsolids

None Refers to the measure

of undissolved

matter, determined

gravimetrically;

deposits in heatexchange equipment,

boilers, water lines,

etc.

Subsidence;

filtration,

usually

preceded by

coagulation andsettling

14.Total solids None Refers to the sum ofdissolved and

suspended solids,

determined

gravimetrically

See "dissolved

solids" and

"suspended

solids"

15.Free mineralAcid

H2SO4,

HCl

etc.,

expressed

as

CaCO3

Corrosion Neutralization

with

alkalis

16.Nitrate NO3- Adds to solidscontent, but is not

usually significant

industrially, highconcentrations cause

methemoglobinemia

in infants; useful

for control of boiler

metal embrittlement

Demineralizatio

n,

reverse osmosis,

electro dialysis,evaporation

18.Chloride Cl- Adds to solidscontent and increases

corrosive characterof water

Demineralizatio

n,

reverse osmosis,electro dialysis,


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evaporation.

19.Alkalinity Bicarbonate

(HCO3

-),carbonate

(CO3

2-),

and

hydroxide

(OH-),

expressed

as CaCO3

Foam and carryover

of solids with

steam; embrittlement

of boilersteel; bicarbonate

and carbonate

produce co2 in steam,

a source of

corrosion in

condensate lines

Lime and lime-

soda

softening; acid

treatment;hydrogen zeolite

softening;

demineralizatio

n

dealkalization

by anion

exchange

20.Aluminium Al3+ Usually present as aresult of floc

carryover from

clarifier; can cause

deposits in cooling

systems and

contribute to complex

boiler

scales.

Improved

clarifier and

filter operation

21.Silica SiO2 Scale in boilers andcooling water

systems; insoluble

turbine blade

deposits due to silica

vaporization

Hot and warm

process

removal by

magnesium

salts;

adsorption by

highly basic

anion

Exchange

resins.


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PRE-TREATMENT PLANT

Introduction

Water flowing through canal from Gopi Krishna Sagar enters thecanal water pump sump. Prior to this, it passes MS vertical bar screen, where in

floating substances are arrested, which are removed whenever required by

lifting these screen by means of chain pulley block provided. A provision of MS

gate has also been made in order to stop the flow of water into canal water sump

pumps during any maintenance or repairing work. Also it stops the flow of

water from the canal sump to the canal when the water is drawn from the raw

water storage tanks.

At one end of canal water sump, pump house accommodates four

pumps with motors and control valves. Provision for fifth pump has also been

provided. During normal operation three pumps will be working at a time,

transmitting a flow of 1500 m3/hr to raw water storage for circulation and 3000

m3/hr to the pre-treatment.

An interconnecting line along with electrically operated electrically

operated butterfly valve and manually operated butterfly valve has been

provided between raw water storage tank and canal water sump. When the levelin canal water sump goes below the low water level, the electrically operated

butterfly valve opens and water starts flowing from raw water storage tank starts

flowing from the raw water storage tank into the canal water sump to maintain

the required level there.

Water flowing to the plant is conveyed through 800/1000 diameter

MS pipeline. Flow of water coming from the canal water pump is controlled by

means of 800 mm electrically operated butterfly valve provided in the upstream

of the chlorine contact vessel.

PURPOSE OF AERATION

Aeration is necessary to promote the exchange of gases between the water and

the atmosphere. In this plant it is provided for the following purpose:

1. To add oxygen to water for imparting freshness


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2. Expulsion of chlorine and other volatile substance3. To precipitate impurities like iron and manganese in certain forms

To ensure proper aeration, cascade type aerator is provided. In this

type water is discharged through a riser pipe and distributed on to a series

of steps through which the water falls in thin film to the base of the

collection basin. From here water passes through partial Flume to the

flash mixers.

CHEMICAL DOSING

In this treatment plant following treatments is given:

1. Pre-chlorination by chlorine solution dosing in chlorine contact vessel2. Coagulation by alum and PAC solution dosing for the main stream and

the demineralization stream water at the downstream side of the aerator

3.pH correction by lime solution dosing at the downstream side of theaerator

4. Post-chlorination by chlorine solution dosing for sanitary water only inthe sanitary water reservoir.

5. Chlorination by bleaching powder dosing as alternative chlorine dosing.PURPOSE OF ALUM DOSING

This is used for coagulation. It is a process for combining or

flocculating the colloidal or larger particles of suspended matters so that they

are more readily settled out of the water and filtered out effectively with aminimum of resistance when trapped as sand bed.

There is one specific pH zone of water in which good flocculation

occurs in the shortest time with a good dose of coagulant. In case of water

containing low mineral contents or in the presence of interfering organic matters

while dosing alum constant attention is needed.


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PURPOSE OF LIME DOSINGIn the case of coagulation with alum, the control over the alkalinity

is very important. Not only should the water contain sufficient alkalinity tocompletely react with the aluminium sulphate but there should be a sufficient

residual to ensure that the treated water is not corrosive. Reduction of alkalinity

should be taken into consideration and sufficient alkalinity should be added to

water if necessary. For this purpose, hydrated lime, Ca(OH)2 is use here.

PURPOSE OF CHLORINATION

Chlorination is an important disinfectant for drinking water and

waste water. Pre-chlorination in the application of chlorine to water prior to any

unit treatment process is for control of biological growths in raw water line,

promotion of improved coagulation, prevention of mud ball and slime formation

in filters, reduction of taste, odour and colour and minimize the post-

chlorination dosages.

Post-chlorination in the application of chlorine to filtered water

before it enters the distribution system for disinfection by maintaining the

required amount of free chlorine.

FLASH MIXERS

Process and purpose

Flash mixing is an operation by which the coagulant is rapidly and uniformly

dispersed throughout the mass of water. This helps in the formation of micro

flocs and results in proper utilization of chemical coagulant preventing

localization of concentration and premature formation of hydroxides which lead

to less effective utilization of the coagulant. In this plant the chemical coagulant

that is alum is dosed in the both streams flash mixing tanks. Lime solution is

also added in the both stream flash mixer for correcting the pH value of water.

For draining the Flash mixer tanks, a provision of 100 mm diameter sluice valvewith extension spindles is made.


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CLARIFLOCCULATORS

Working

The coagulated water from Flash Mixer is introduced through the

hollow center pair of the clariflocculator tank. It enters the flocculatorcompartment below the liquid surface through opening in the center pier. Here

the specially designed paddles produces a gentle controllable motion to provide

the most effective contacting between the newly formed flocs and the incoming

liquid without damaging the flocs system . By this section the flocs are given

intimate impact with the finely divided particles, which are thereby scrubbed

out of suspension.The completely flocculated liquid flows through the opening in the

bottom of the flocculator tank into the clarifier compartment where the flocs are

given sufficient time to settle down. In this case we have considered this time as

2.5 hours. The settled solids are being conveyed to the central sludge collection

sump by means of scrapper blades attached to the paddles arms for dischargeinto the clarifier drain sump.

General description and working

Candy Filter Floor essentially consists of rows of earthenware pipes having

holes at regular intervals to accommodate Candy Filter nozzles and embedded

in concrete. Once the filter floor is laid, the nozzles are screwed into the

respective nozzles holes.

Over this filter floor the filter media of about 850 mm depth of

graded sand will be filled.

During normal filtration process, the inlet and the outlet valves are

in open position and rest of the valves are in closed position. The settled water

having turbidity not more than 20 ppm first enters into wash water and then

overflows over the filter media and the water after filtration passes through the

outlet. During the filtration process the suspended matter and other impurities in

the water are retained on the top of the sand bed.

The amounts of the chemicals used, their dose, and point of application aretabulated below:


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Name of

Chemical

Dose

(ppm)

Point of

application

Flow

rate of

water

(m3/hr

)

Chemicals

required

(kg-s/hr)

Chemical

solution

flow rate

(LPH)

Solution

strength/

solution

ratio

Purpose

Chlorine

:for pre-

chlorination

5

Chlorine

Contact

Vessel

3000 15 15000 0.1% Disinfect

ion

Alum 50

Downstrea

m

Side of

aerator

3000 150 1500 10% Coagulat

ion

Lime

30

Downstrea

m side of

aerator3000 90 1800 5%

pH

correctio

n

Chlorine

:for post-

chlorination

2

Sanitary

water

reservoir300 0.6 600 0.1% Disinfect

ion

Bleaching

Powder

(alternative to

chlorine

dosing for

post-

chlorination)

2

Sanitary

waterreservoir

300 3.6 109 3.3% Disinfect

ion


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DEMINERALISATION PLANT

1. Treatment Scheme

The steps followed in the demineralization of water are as follows:

1. The filtered water is passed through heat exchanger with a view to coolthe condensate coming from the turbine and process so that condensate

with reduced temperature can be treated in condensate plant.

2. Removal of excess chlorine in filtered water by passing through activatedcarbon filter.

3. Removal of positive ions by passing through a pair of weakly acidic(WAC) and strongly acidic (SAC) exchangers.

4. Removal of CO2present in decationised water in atmospheric forced drafttype degassers.

5. Removal of negative ions by passing through a pair of weakly basic(WBA) and strongly basic (SBA) anion exchangers.

6. Passing SBA treated water through mixed bed exchanger (MB) to polishoff remaining ions to get ultra-pure water.

Regeneration of the ion exchangers is carried out when the treated water

quality is not satisfactory or when the unit has delivered its specified output

between the regenerations, whichever is earlier. The SAC and WAC are

regenerated with sulphuric acid using thoroughfare regeneration technique.

Caustic solution is used for the regeneration of WBA and SBA units using

thoroughfare technique. Caustic for SBA and WBA is injected at

approximately 45 C using heat exchanger with a view to obtain low silica

residual from SBA units. Counter-current technique is employed forregeneration of SAC with a view to minimize sodium ion slippage from SAC

outlet.

For MB, resins are first separated, and then anion resin is

regenerated with alkali and cation with acid. Injection of acid from bottom and

alkali from top is carried out simultaneously. The resultant effluent is drained

through the middle collector. As MB units act as a polisher, the same to be

taken up for regeneration once the specified quantity of water has been treated.


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Neutralization pit comprising of three compartments and lined with acid proof

material is provided for collection of effluent coming out during regeneration of

exchanger units. Acidic effluent coming out during cation regeneration is

collected in the first section of the pit. Alkali effluent coming out during anion

regeneration is collected in the third section of the pit. The acidic and alkaline

effluents are discharged separately to the main effluent plant or they are

discharged to the center pit for neutralization. As the resultant effluent will be

acidic, lime or caustic is added to neutral the effluent to the required pH

between 6 and 8. Mixing in center pit is carried out by air agitation and the

effluent is re-circulated till the desired pH is obtained. Thereafter the effluent is

discharged to the storm water drain.

2.DESCRIPTION:-

The de-mineralized water treatment plants consist of three chains in

parallel each comprising: -

1. ACF, WAC/SAC, WBA/SBA and MB exchangers,1. 3 Nos. of filtered water pumps, 2 Nos. atmospheric degassers,2. 1 Nos. degassed water tank,3. 5 Nos. degassed water pumps (3 Nos. for service and 2 Nos. for

regeneration) and,

4. 2 Nos. DM water storage tanks.From DMWT SBA treated water is pumped with the help of DM water pump

through MB and stored in polished water storage tank.

pH correction of polished water storage tank is done with ammonia solution

dosing pump before the polished water is discharged to the end use by means of

polished water pumps.


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ACTIVATED CARBON FILTER

It is a mild steel vessel painted internally with epoxy based paint. It

is externally fitted with MS pipe-work, diaphragm and butterfly valves, pressure

gauge at the inlet and sampling valves both at the inlet and outlet, DPI is

provided to check the pressure drop across the carbon bed. An alarm will be

sounded in case the pressure drop across the bed increases beyond the set limit.

A calibrated orifice board in the drain sump is also provided for controlling the

backwash flow rate.

Mild steel, epoxy painted both internally and externally, bell mouth type single

arm distributor is provided for inlet. This distributor becomes outlet duringbackwash operation.

Bottom collecting system is of header lateral type. Header is of mild

steel painted externally and internally with epoxy. To this header are screwed

PVC laterals. There are small holes drilled throughout the length of the laterals.

With a view to obtain a horizontal surface, the bottom-dished end is

filled with concrete. With a view to ensure that the carbon does not leak through

the bottom collecting system, different layers of under bed materials arecharged. Each layer consists of different size of pebbles with bigger size at the

bottom most and fine silex on top. Above fine silex, activated carbon is charged.

Rate of flow indicator is provided at the inlet to check the hourly flow rate.

Regeneration is done in two stages:

1. BackwashThis operation is carried out to loosen the bed and remove suspended

impurities.

2. RinseThis operation is carried out to ascertain that the performance of the unit

with respect to quality is in order.


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WEAK ACID CATION UNITS (WAC)

This is a mild steel vessel lined internally with rubber. It is

externally fitted with rubber lined pipe-work, diaphragm and butterfly valves,

pressure gauge at the inlet and sampling valves both at the inlet and outlet, DPI

is provided to check the pressure drop across the bed. A calibrated orifice board

in the drain sump is also provided for controlling various regeneration flows.

Inlet water distribution is of three arms. The water is distributed

from the top and each arm is provided with PVC perforated pipes for uniform

distribution. Backwash outlet is provided separately internally which essentially

consists of rubber lined rubber covered bell mouth.

Acid distributor is also of three arms made out of mild steel and

lined internally as well as externally with rubber.

Bottom collecting system is of header lateral type. It consists of

mild steel rubber lined and rubber- covered header into which mark V strainers

are fitted.

The vessel is charged with weakly acid cation resin. The

regeneration of the unit is done in thoroughfare with SAC. Flow indicator

totalizer is provided at the outlet and a rate off low indicator is provided at the

inlet.

STRONG ACID CATIONS UNIT (SAC)

This is a mild steel vessel lined internally with rubber. It is


pressure gauge at the inlet and sampling valves both at the inlet and outlet, DPI

is provided to check the pressure drop across the bed. A calibrated orifice board


Regeneration of SAC and WAC is carried out simultaneously. Theregeneration is carried out in five stages.


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1. Backwash / Sub-surface washBackwash operation is carried out to loosen the bed and to remove the

suspended impurities from the resin. The operation is carried outindependently. For SAC sub-surface wash is carried out. Backwash

operation for SAC is optional and should be carried out once in 15

regenerations or when pressure drop across the unit increases beyond

acceptable limits whichever occurs earlier. When backwash is given to

SAC, double quantity of acid is to be injected to ensure that bottom layer

of the resin is highly regenerated.

2. SettleBackwash resins are allowed to settle under gravity to get uniform resin

surface.

3. Acid Pre-injectionThis operation is carried out to set the power flow rate to the required

flow before injecting acid.

4. Acid injectionAcid of required strength and quantity is injected into SAC and WAC by

injection pump. The acid is injected in SAC and the effluent from the

middle collector is passed through WAC unit. The effluent is collected in

the drain sump. During injection to prevent the fluidization of SAC bed, a

down-flow of water is maintained.

5. Acid transferTo ensure optimum utilization of acid this operation is carried out. The

excess acid in the SAC unit after acid injection is transferred to WACwith the help of power water. Down-flow of water is maintained during

this stage also. Inlet water distributor is of three arms. The water is

distributed from the top and each arm is provided with PVC perforated

pipe for uniform distribution. Backwash outlet is provided separately

internally which essentially consists of rubber lined rubber covered bellmouth. Bottom dished portion of the vessel is fitted with concrete which


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acts as dead weight and thus prevents the divisional plate from getting

buckled due to the weight of water and resin.

The vessel is charged with strong acid cation resin when the

desired output from the pair of units (WAC and SAC) is obtained or

when the quality of outlet water from the SAC with respect to sodiumions is deteriorated then the unit should be regenerated in thoroughfare

with WAC using H2SO4as regenerant.

A resin trap with DPI is provided to trap ion exchange resins

in the unlikely event of failure of the bottom collecting system.

A conductivity comparator is provided at the outlet of the unit

comprising of two conductivity cells and a comparator.

6. RinseThis operation is carried out to remove excess acid and liberated cations

from both WAC/SAC units. This operation is carried out simultaneously but

independently.

7. BackwashAs WAC resin gets compact due to contraction after regeneration, this

operation is carried out for 2 minutes to loosen the bed.


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WEAK BASE ANION (WBA)This is a mild steel vessel lined internally with rubber. It is


pressure gauge at the inlet and sampling valves both at the inlet and outlet. DPIis provided to check the pressure drop across the bed. A calibrated orifice board


Inlet water distributor is of three arms. The water is distributed from

the top and each arm is provided with PVC perforated pipe for uniform

distribution.

Backwash outlet is provided separately internally which essentially

consists of rubber lined rubber covered bell mouth with SS mesh fixed on it toprevent resin carryover.

Alkali distributor is also of three arms and made of mild steel and

lined internally as well as externally with rubber. Bottom collecting system is of

header lateral type. It consists of mild steel rubber lined and rubber covered

header into which PVC laterals with mark V strainers are fitted.

The vessel is charged with weak base anion resin. The unit is

regenerated in thoroughfare with SBA.

A resin trap with DPI is provided to trap ion exchange resins in the

unlikely event of failure of the bottom collecting system. Rate of flow indicator

is provided at the inlet and outlet.

STRONG BASE ANION UNIT (SBA)

It is a mild steel vessel lined internally with rubber. It is externally

fitted with rubber lined pipework, diaphragm and butterfly valves,

pressure gauge at the inlet and sampling valves both at the inlet and

outlet. DPI is provided to check the pressure drop across the bed. A

calibrated orifice board in the drain sump is also provided for controlling

various regeneration flows.


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distribution.

Backwash outlet is provided separately internally which essentiallyconsists of rubber lined rubber covered bell mouth with SS mesh fixed on it to

prevent resin carryover. Alkali distributor is also of three arms and made of

mild steel and lined internally as well as externally with rubber.

Bottom collecting system is of header lateral type. It consists of

mild steel rubber lined and rubber covered header into which PVC laterals with

mark V strainers are fitted.

The vessel is charged with strongly basic anion resin. The unit isregenerated in thoroughfare with WBA using NaOH as regenerant, when the

quality of treated water from SBA outlet with respect to silica is deteriorated.


unlikely event of failure of the bottom collecting system. A conductivity

indicator is provided at the outlet of the unit to give alarm in case the

conductivity increases beyond the acceptable limit.

Flow indicator is provided at the outlet.

Regeneration of SBA and WBA is carried out simultaneously. The

regeneration is carried out in six stages:

1. BackwashBackwash operation is carried out to loosen the bed and to remove

the suspended impurities from the resin.

2. Settle

Backwash resins are allowed to settle under gravity to get uniform

resin surface.


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3. Acid Pre-injection

This operation is carried out to set the power flow rate to the

required flow before injecting acid.

4. Acid injectionSpecified quantity of caustic is injected by means of primary and

secondary rejecters to regenerate the exhausted resins.

5. Acid transfer

To ensure optimum utilization of alkali this operation is carried out.

The excess alkali in the SBA unit after caustic injection is transferred to

WBA with the help of power water.

6. Rinse

This operation is carried out to remove excess caustic and liberated

anions from both WBA/SBA units. This operation is carried outsimultaneously but independently.


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MIXED BED (MB)

It is a mild steel vessel lined internally with rubber. It is externally

fitted with rubber lined pipework, diaphragm and butterfly valves,

pressure gauge at the inlet and sampling valves both at the inlet and

outlet. DPI is provided to check the pressure drop across the bed. A

calibrated orifice board in the drain sump is also provided for controlling

various regeneration flows.



distribution.

Backwash outlet is provided separately internally which

essentially consists of rubber lined rubber covered bell mouth with SS mesh

fixed on it to prevent resin carryover.

The middle collector and bottom collecting system are of header

lateral type. The header is of mild steel rubber lined and rubber covered to

which PVC laterals are fitted. Mark V strainers are used for the bottom

collecting system and mark 801 is used for the middle collecting system.

Bottom dished portion of the vessel is fitted with concrete to prevent

the divisional plate from getting buckled due to the weight of water and resin.

The vessel is charged with a mixture of both strongly acidic cation

resin and strongly basic resin. When the desired output from the unit is obtained

or when the quality of outlet water with respect to either silica or conductivity

is deteriorated then the unit should be regenerated, cation resin with H2SO4and

anion resin with NaOH.


unlikely event of failure of the bottom collecting system.

In addition to rate of flow indicator provided at the unit inlet,

following instruments are provided at the MB outlet:

(1)Conductivity indicator to give alarm in case the treated waterconductivity increase beyond the acceptable limit.

(2)pH indicator to give alarm for both low and high pH


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(3)Flow indicator/totalizer to determine the quantity of water treatedbetween successive regenerations.

(4)Silica analyser with multiposition switch is provided at common outletto give alarm.

(5)At common rinse outlet line conductivity indicator is provided to givealarm once acceptable limit is obtained.

Regeneration of MB is carried out in 13 stages:

1. Backwash

This operation is carried out to separate the resin beds prior to injectingthe chemicals. Due to difference in densities, the resins during backwash

get separated into two distinct layers with cations being at the bottom and

anions at the top.

2. Sub-surface wash

This operation is basically carried out to clean the middle collector strainers

to ensure proper distribution/collection during injection of chemicals.

3. Settle

Resins after backwash and sub-surface wash are allowed to settle under

gravity to obtain uniform bed surface.

4. Acid and Alkali pre-injection

This operation is carried out to set the power water flow rates before

starting the injection of both acid and alkali.

5. Acid and Alkali injection


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Injection of acid and alkali is carried out simultaneously. Acid from the

bottom and alkali from top and the resultant effluent is drained through the

middle collector. The purpose of regeneration is to regenerate the exhausted

resins.

6. Acid and alkali rinse

This operation is carried out simultaneously to remove excess regenerants

from respective resin beds.

7. Drain down

With a view to reduce excess load on air blower, excess water in MB vessel

is drained through the middle collector. The purpose of the injection is

to regenerate the exhausted resins.

8. Air mix

This operation is carried out to mix the two resins. This operation is veryimportant as improper mixing will lead to inferior treated water quality.

Air mixing is carried out with the help of blowers.

9. Force settle

In order to prevent the resins from getting separated after mixing,

this operation is carried out.

10. Refill-1

This operation is carried out to fill the MB units with water.

11. Refill-2

This operation is carried out to release air and to pressurize MB unit.


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12. Rinse to drain

This operation is carried out to remove the traces of acid/alkali from the

mixed bed.

13. Final rinse recycle

This operation is carried out to reduce the wastage of DM water whose

quality though not of acceptable quality is good enough to be recycled back into

DM water storage tank. Once water of acceptable quality is obtained during

recycle operation the unit is taken in service to fill the polished water storage

tank.


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RESINS USED IN DEMINERALISATION PROCESS

In the demineralization of water wide variety of resins are used.

However, resins most commonly used are indicated below:

1. Strong acid cation exchange resinThis is a sulphonated cross-linked styrene/ di-vinyl benzene polymer. These are

available in the form of beads of size ranging between 0.3 mm and 1.2mm and

total exchange capacity of 2 to 2.2 milli-equivalents per ml. These are normally

quite stable at all pH range and against normal chemicals encountered in water.

These resins can be regenerated by the use of strong acid like hydrochloric acid,sulphuric acid, and nitric acid. The operating capacity normally lies between 30-

70 grams per litre depending on regeneration level and water characteristics.

Regeneration efficiency varies between 0.3 to 0.45 under normal co-current

regeneration. Reactions involved in the treatment of water and regenerations are

as follows:

Exhaustion reaction:

RH + M(Cl, SO4, NO3, CO3, HCO3, SiO2)

RM + (HCl, H2SO4, HNO3, H2CO3, H2SiO3)

Regeneration reaction:

RM + (HCl, H2SO4, HNO3) RH + M(Cl, SO4, NO3)

RResin phase

MCation


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2. Weak acid cation resin

These are copolymers of acrylic acids and di-vinyl benzene having

active carboxylic group. The resins are obtained in the form of beads of sizes

0.3 mm to 1.2 mm having total exchange capacity of 3-4 milli equivalents perml. These resins can react only with the alkalinity of water with the

production of carbonic acids. The regeneration can be done by any acid using

slightly more than the stoichiometric quantity. The operating capacity depends

on the period of exhaustion and water characteristics and lies between 30-

100 grams per litre. The reactions involved with these resins are as follows:


2RCOOH + MCO3 RCOOM + H2CO3


RCOOM + (HCl, H2SO4, HNO3) RCOOH + M(Cl,SO4, NO3)

3. Strong base anion resin (Type-1)

These are quaternary ammonium compounds of resin obtained from

cross- linked styrene di-vinyl benzene by amination. These are obtained in the

form of beads between 0.3 to 1.2 mm of size and total exchange capacity of 1.2

milli equivalent per ml. These resins can react with free acids (including weakacid like silicic and carbonic acid) with the production of water. This can

also react with neutral salts absorbing the anions and producing the

corresponding hydroxide. Regeneration of this resin can be carried out by use of

sodium hydroxide.

The operating capacity depends on the regeneration level

and the characteristics of water and normally ranges from 20 to 30 grams per

litre. Reactions involved with these resins are as follows:


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ROH + (HCl, H2SO4, HNO3, H2CO3, H2SiO3)

R(Cl, SO4, NO3, HCO3, HSiO3) + H2O


R(Cl, SO4, NO3, HCO3, HSiO3) + NaOH

ROH + Na(Cl, SO4, NO3, SiO3, CO3)

4. Strong base anion resin (Type-2)

These are obtained in the same manner as a type-1 resin only in

the quaternary ammonium group an alkanol group is present. These have got a

capacity of 1.2 milli equivalent per ml and operating capacity are higher than

that of type-1 resins ranging between 30 to 45 grams per litre. However, the

efficiency of removal of weak acid is less than that of type-1 resins, but theregeneration efficiency is higher.

5. Weak base anion exchange resins

These are prepared in the same manner as strong base resins from styrene

di-vinyl benzene co-polymer, only amination is carried on by primary orsecondary amine so that a tertiary ammonium compound is obtained. These are

also obtained in the form of bead of 0.3 to 1.2 mm having exchange capacity up

to 1.6 milli equivalent per ml. Because of low basicity they can absorb only free

strong acids but they cannot remove weak acid or react with neutral salts. The

regeneration efficiency is very high and only stoichiometric quantity of alkali is

required for its regeneration. These resins can be regenerated by caustic soda,

sodium carbonate or even by ammonia. The reactions involved are:



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RN + H(Cl, SO4, NO3) RN(HCl, H2SO4,HNO3)


RN(HCl,H2SO4,HNO3) + NaOH RN + Na(Cl,SO4,NO3) + H2O

Resins described above are used in the gel form normally but isoporous

and macroporous forms of these resins are also available and can be used

where they are required. A judicious selection of the resin is the

primary requirement in the design of a demineralization system.


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CAPTIVE POWER PLANT

The CPP unit in NFL deals of with two tasks:

(i) Power Generation(ii) Steam generationHere, I have given outline of the Steam generation process of the

CPP.

BOILER OPERATION:

Operation modes-Heat recovery unit (HRU) in conjunction with gas turbine generator

(GTG) is composed of the following operation modes.

1. Steady operation modes(a)Stop mode

HRU is in stop mode and all dampers are so positioned as to allow

GTG to operate in open cycle condition.

(b)Cogeneration modeGTG exhaust gas is introduced to HRU and HRU generates HP steam with

supplementary fuel.

(c)FDF operation modeFD fan is adopted, in place of GTG to supply combustion air and HRU

generates HP steam only by fuel firing.

2. Operation mode change between above mentioned modes involveautomatic sequence control as follows:

(a) Start-up modes

: From (a) to (b), hot/cold start-up modes by GTG exhaust gas

: From (a) to (c), start-up mode by FDF

(b) Change over modes

: From (b) to (c), change over mode automatically initiated by

GTG trip


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DESCRIPTION OF HEAT RECOVERY UNIT

The boiler of the heat recovery unit is of KAWASAKI type naturalcirculation, two drums, water-tube, self-standing and front firing boiler which

consists of steam drum, water drum, furnace, super heater, convection tube

bank, economizer, inter-connecting flue gas duct, stack and the associatedequipment.

BOILER PARTS

1. STEAM DRUM

Steam drum has sufficient capacity for separating maximum generatingsteam and has sufficient capacity to minimize water level fluctuation resulting

from start and stop or quick load change.

The construction of the steam drum is of boiler steel plate fusion welded

longitudinal and circumferential seams are automatically welded by an electric

arc welding process. One round manhole with a hinged cover is provided at

each ortho-ellipsoidal end plate of the drum.

The steam drum is fitted with steams separating internals and chevron dryer,

which are designed to assure high purity in every load.

The wet steam entering the drum from the riser tubes is collected in a

small compartment formed by the internal baffles and dry steam is separated

through the separator connected at the top section of this compartment, so as not

to mix the generating steam into drum water. This is essential for the design of

minimizing the water level fluctuation in steam drum. Steam drum id fitted with

other internals of feed water distribution pipe, chemical feed pipe andcontinuous blow down pipe. All pipe connections on the drum are welded.

2. WATER DRUMThe construction of the steam drum is of boiler steel plate

fusion welded. The longitudinal and circumferential seams are

automatically welded by an electric arc welding process. One round


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manhole with a hinged cover is provided at each ortho-ellipsoidal end

plate of the drum.

The water drum serves as mud drum and is fitted withbottom

blow nozzles. For heating up of boiler, steam injection nozzle is equipped inthis drum.

3. FURNACEFurnace has sufficient size for burning fuel gas as basic design

and fuel oil in future plan.

For the furnace wall, Tight Wall- totally welded gas tight

membrane tube wall is employed. Where the tubes penetrate the wall, all

gaps are completely sealed with seal plate and sleeves of tube elements.

4. SUPERHEATERA convection super heater is installed in the high temperature gas

area in the fore front of the convection tube bank.

Since super heater tubes are installed in the convection

area, radiation heat from the furnace can be intercepted. And therefore,

thermal load on the superheating tubes is limited in the reasonable range and

overheating or damage by burning of the tubes is totally prevented at the boiler

start or its partial operation. Super heater tubes are of bare tubes and are

arranged in triangular pitch, vertical run and serpentine pattern.

Steam temperature at the outlet of the superheater is controlled

through de-superheating by means of boiler feed water in the steam flow.

5. CONVECTION TUBE BANK

Convection tube bank has compact heating surface divided into threesections by two baffle plates which are employed for turning over gas


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flow. Convection tubes are of bare tubes and are arranged in line and

vertical run. Each tube is completely joined to steam drum and water drum

by expanding.

6. ECONOMIZERThe economizer is located behind the convection tube bank.

The arrangement of the tube is in triangular pitch. Its tubes are spiral-finned

tubes which are welded by high frequency resistance welding process. Spiral fin

tubes have sufficient fin spacing considering not only gas firing but, fuel oil

firing condition in future.

The economizer is divided in upper tube bank and lower tube

bank. The boiler feed water is supplied to the bottom header of upper tube bank

of economizer, flows upward and is corrected in the top side header. And the

corrected water is supplied for further heating up to the bottom header of lower

tube bank of economizer, flows upward and is corrected in the top side header.

Above flow pattern is employed to serve steady water flow so as to eliminate

the problems of steam vapour lock and air lock in tubes.

OPERATION AND MAINTENANCE

The boiler possesses a number of advantages in maintenance as follows:

1. Because of tight wall construction, the wall of the furnace never suffersfrom damages and thus no repair work is required.

2. Because the burner cone is covered with many water tubes, repairing ofrefractories of the burner cone is hardly required. As an adequate air

pressure head is provided, air distribution to the respective burners can be

made uniformly, thus eliminating the possibility of damaging the burner.

3. Drain valves and blow valves of the boiler are gathered at one position onthe side of the boiler for facilitating the operation of the boiler.

4. Adequate working spaces and manholes are provided for easymaintenance.


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WATER QUALITY CONTROL

Among accidents occurred during the boiler operation, the trouble

resulted from the quality control of the water is one of the most serious

accidents. Interests in the quality control of the boiler water have soared up.

Parameters of water quality control:-

1. pH

As well known, pH is an index showing acidity and alkalinity. For purified

water or neutral solution, pH is 7, for acidic solution pH is less than 7 and for

alkaline solution pH is more than 7. Since, iron as main construction materialis soluble not only into acidic water but also into neutral water, pH of boiler

must be raised a little in orders to minimize corrosion. But there is a limit to this

as higher pH may cause alkaline corrosion as stronger alkalinity gives injurious

effects on iron and especially on copper alloy, so there is an upper limit to pH of

feed water.

2. Hardness

Hardness in this criterion is a quantity in ppm of calcium carbonate equivalentto that of calcium and magnesium dissolved in water. Sticking of scales on the

inside of the drum and heating tubes or deposits of sludge are mainly caused by

this hardness component. These scale and sludge will result in a loss of

boiler efficiency through worsened heat transfer.

3. Fats

Fats inside of boiler, adhere to the heating surface, are heated, carbonized

and invite a tube burst resulting from overheat due to the inability of fatty layer

to conduct heat properly.

4. Dissolved oxygen

Dissolved oxygen is one of the most injurious corrosive factors in boiler and its

corrosion is very complicated, generally the progress of corrosion is considered

due to the formation of oxygen concentration cell or destruction of

ionic equilibrium in the solution.


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5. Iron and Copper

Most of the iron and copper contained in boiler water will become solids in

suspension as hydroxides and oxides, and deposit on every surface becauseof their large specific weights. Precipitated and accumulated sludge obstruct the

water circulation and also heat transfer, when depositing on the heating

surfaces, causing an overheat and furthermore give the origin for the corrosion

by concentration cell and the alkaline corrosion owing to formation of

alkaline concentration layer based on local heating.

6. Silica

The purpose of limiting the amounts of silica in the boiler water is first to

prevent it from combining with calcium and magnesium when these are

coexisting, precipitating and producing hard scale, and secondly to prevent the

selective carry-over which would cause the silica in the boiler water to dissolve

itself into the generated steam.

CaO + SiO2heat

CaSiO3

MgO + SiO2heat

MgSiO3


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7. Alkalinity

Alkalinity in boiler water is expressed in ppm of equivalent calcium

carbonate (CaCO3) to acidic quantity, which is necessary for neutralizing thealkaline quantity in boiler water. In boiler water, appropriate amounts of NaOHmust be included in order to make silica soluble, to give the generated sludge a

floating nature and to produce a protecting film against corrosion over the iron

surface. If these amounts however are in excess, they may cause caustic fragility

of the steel material.

8. Total solids

Total solids mean total residual substances from evaporation and are the sum ofdissolved solids and suspended solids. In case, that amounts of total solids are

larger in boiler water, carry-over is liable to occur, thus contaminating

the generated steam owing to transfer of boiler water into the steam.

9. Chlorine ion

Chlorine ion in boiler water destroys the protection film formed over themetal surfaces and delays its restoration. As the precipitation of these

processes promotes corrosion, higher concentration makes its injuries larger.

10. Phosphoric ion

If sodium phosphate is added to boiler water calcium phosphate of soft, floating

nature would be generated and further generation of hard scale would be

prevented. Nevertheless, excessive addition is not only un-economical but also

accelerative in the foaming of boiler water which invite carry-over and easy

to generate magnesium phosphate inside of tube.


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AMMONIA PRODUCTION PROCESSAN OUTLINE

Ammonia is acompound ofnitrogen andhydrogen with theformulaNH3. It is a

colourlessgas with a characteristicpungentodour.Ammonia contributes

significantly to thenutritional needs of terrestrial organisms by serving as a

precursor tofood andfertilizers.Ammonia, either directly or indirectly, is also a

building-block for the synthesis of manypharmaceuticals.Although in wide

use, ammonia is bothcaustic andhazardous.In 2006, worldwide production

was estimated at 146.5 million tonnes.[6]It is used in commercial cleaning

products.

Ammonia, as used commercially, is often called anhydrous ammonia.This term

emphasizes the absence of water in the material. Because NH3boils at 33.34

C (28.012 F) at a pressure of 1 atmosphere, the liquid must be stored under

high pressure or at low temperature. "Household ammonia" or "ammonium

hydroxide"is a solution of NH3in water.

The ammonia molecule has atrigonal pyramidal shape with a bond angle of

107.8, as predicted by thevalence shell electron pair repulsion theory (VSEPR

theory). The central nitrogen atom has five outer electrons with an additionalelectron from each hydrogen atom. This gives a total of eight electrons, or four

electron pairs that are arranged tetrahedrally. Three of these electron pairs are

used as bond pairs, which leaves one lone pair of electrons. The lone pair of

electrons repel more strongly than bond pairs, therefore the bond angle is not

109.5, as expected for a regular tetrahedral arrangement, but is measured at

107.8.

Ammonia is found in trace quantities in the atmosphere, being produced fromtheputrefaction (decay process) of nitrogenous animal and vegetable matter.

Ammonia and ammonium salts are also found in small quantities in rainwater,

whereasammonium chloride (sal-ammoniac), andammonium sulphate are

found in volcanic districts; crystals ofammonium bicarbonate have been found

in Patagonian guano. Thekidneys secrete NH3to neutralize excess acid.[8]

Ammonium salts also are found distributed through all fertile soil and in

seawater.
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Ammonia is produced from a mixture of hydrogen (H2) & Nitrogen (N2) where

the ratio of H2 to N2 should be 3:1 besides these two compounds the mixture

will contain chart gases to be a limited degree, such as organ (Ar) & methane

(CH4).

For the ammonia plant at Vijaipur the source of H2in water & hydrocarbon inthe form of Natural Gas. The source of N2 is an in all ammonia plants the

atmospheric air.

The process steps which are necessary for producing ammonia from the above

mentioned raw materials are as follows :-

a) Hydrocarbon feed in completely desulphurized in the desulphurizationsection. If naphtha is used it is pre-reformed to methane, hydrogen &

carbon-dioxide in an adiabatic pre-reformer.

b) The desulphurized hydrocarbon is reformedwith steam and air to rawsynthesis gas. This gas contains mainly hydrogen & nitrogen and also

carbon monoxide (CO) & carbon dioxide (CO2). The reforming takes

place at about 30-35 kg/cm2.

c) In the gas purification section, CO in first converted to CO2 and H2with steam in order to increase the H2yield. CO2in then removed in theCO2removal section and residual CO & CO2in afterwards reacted with

H2in methanatorto form CH4.

d) In the ammonia synthesis section, the purified synthesis gas aftercompression to pressure about 220kg/cm2, in converted into NH3

(Ammonia) by Habers Process.

e) Process condensate is treated in the process condensate stripper.f) For further purification, it is sent to CPU (condensate polishing unit)

make de-mineralised water for steam generation.


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Reaction in CO2 removal:

K2CO3+ CO2+ H2O 2 KHCO3

(VII.) Methanation :-

After the CO2 removal the gas still contains small quantities of CO and CO 2,

which are poisonous to the ammonia catalyst. The CO & CO2 are therefore

converted into methane in methanator.

Reactions :-

CO + 3H2 CH4+ H2O + HeatCO2+ 4H2 CH4+ H2O + Heat

(CO + CO2 content is normally reduced to


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Steps:-

A)Methaned gas mixture is compressed in syn. Gas compressor to apressure of 210220 kg/cm2g.

B)The reaction temperature in the catalyst bed in 360 525 C which isclose to optimum level.

C)The catalyst is a promoted iron catalyst containing small amount of non-reducible oxides.

D)Ammonia synthesis 100Pa compression.E) Waste heat recovery by generation of high pressure steam and preheat of

boiler fixed water (BFW).

F) Gas-Gas heat exchanger for preheat of the converter feed gas.G)Water cooler in which a significant part of the product ammonia in

condensate.

H)Ammonia chillers, at different pressure levels, for further condensation ofthe product ammonia.

I) Gas heat exchangers for recovery of the refrigeration energy.J) Product ammonia separator & start up heater (electric). The ammonia

formed in refrigerated at 33 C and stores in the atmospheric tanks. The

waste heat generated in various stages of exothermic reactions in utilized

to produce steam at 105ata pressure. This steam coupled with thatfrom an auxiliary boiler provides power for all the devices in ammonia

plant and satisfies the process steam requirement, reliability & energy

efficiency. In ammonia plant Line-II the process air compressor used in

Natural Gas turbine drive & exhaust of gas turbine and additional firing

in heat recovery units (HRU) are used to produce HP steam at 117

MT/hr. The ammonia concentration at converter inlet is dependent on the

cooling level in refrigeration chillers and the operating pressure. 5.6%

NH3at converter inlet correspond to 12 degree Celsius at a pressure of

209 kg/cm2

g in the ammonia separately.


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UREA TECHNOLOGY DEVELOPMENT AND LATEST STATUS

Ureaor carbamideis anorganic compound with thechemical formula

CO(NH2)2. The molecule has two -NH2groups joined by acarbonyl (C=O)functional group.

Urea serves an important role in themetabolism of nitrogen-containing

compounds by animals and is the main nitrogen-containing substance in theurine ofmammals.

It is solid, colourless, and odourless (although theammonia that it gives off in

the presence of water, including water vapour in the air, has a strong odour). It

is highly soluble in water and non-toxic. Dissolved in water, it is neitheracidic

noralkaline.

The body uses it in many processes, the most notable one being nitrogen

excretion. Urea is widely used infertilizers as a convenient source of nitrogen.

Urea is also an importantraw material for thechemical industry.The synthesis

of this organic compound byFriedrich Whler in 1828 from an inorganicprecursor was an important milestone in the development of organic chemistry,

as it showed for the first time that a molecule found in living organisms could

be synthesized in the lab without biological starting materials (thus

contradicting a theory widely prevalent at one time, calledvitalism).

Urea was first prepared synthetically in 1828 from Ammonia & Cyaunric Acid(HCNO):

NH3+ HCNO NH2CONH2

The present method of synthesizing Urea from Ammonia & CO2 has been

known since 1868 but the commercial production by this method started only in

1922 in Germany. Since then, this has been the most popular method of

producing Urea.

More than 90% of world production of urea is destined for use as a nitrogen-

release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous

fertilizers in common use. Therefore, it has the lowest transportation costs per

unit of nitrogennutrient.The standard crop-nutrient rating of urea is 46-0-0.{ICIS,http://www.icis.com/v2/chemicals/9076559/urea/uses.html}
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Many soil bacteria possess the enzymeurease,which catalyzes the conversion

of the urea molecule to twoammonia molecules and onecarbon dioxide

molecule, thus urea fertilizers are very rapidly transformed to the ammonium

form in soils. Among soil bacteria known to carry urease, some ammonia-

oxidizing bacteria (AOB) such as species ofNitrosomonas are also able toassimilate the carbon dioxide released by the reaction to make biomass via theCalvin Cycle,and harvest energy by oxidizing ammonia (the other product of

urease) to nitrite, a process termednitrification.[8]Nitrite-oxidizing bacteria,

especiallyNitrobacter,oxidize nitrite to nitrate, which is extremely mobile in

soils and is a major cause of water pollution from agriculture. Ammonia and

nitrate are readily absorbed by plants, and are the dominant sources of nitrogenfor plant growth. Urea is also used in many multi-component solid fertilizer

formulations. Urea is highly soluble in water and is, therefore, also very suitable

for use in fertilizer solutions (in combination withammonium nitrate:UAN),

e.g., in 'foliar feed' fertilizers. For fertilizer use, granules are preferred over

prills because of their narrower particle size distribution, which is an advantagefor mechanical application.

MANUFACTURING PRINCIPLES:

The urea is produced by direct synthesis of liquid Ammonia & Carbon di-oxide

gas by following reactions.

2 NH3+ CO2 NH2COO NH4 + 37.64 Kcal/Mole -- (i)

Ammonium Carbamate

NH2COO NH4 NH2CONH2+ H2O - 6.32 Kcal/Mole -- (ii)

Urea

The formation of Ammonium Carbamate through reaction (i) is instantaneousand completes very fast. It is highly exothermic in nature. Reaction no. (ii) for

Urea formation is, however, rather slow and little bit endothermic. An idealprocess at 1 ata and 25C will, therefore, yield a net heat of 31.32 Kcal/Mole.

In actual practice the Urea Production process is energy consuming due to the

following reasons.

a) Heat is lost in evaporation of liq. NH3 & water formed in reaction.b) Keeping the Urea formed in molten stage.

c) Synthesis is done on high pr. &temperature for better conversion.

d) Heat is added to decompose unconverted Carbamate

e) Power is required to feed back the separated CO2 and NH3 to the reactorpressure.
http://zim//A/A/Urease.htmlhttp://zim//A/A/Ammonia.htmlhttp://zim//A/A/Carbon%20dioxide.htmlhttp://zim//A/A/Nitrosomonas.htmlhttp://zim//A/A/Calvin%20Cycle.htmlhttp://zim//A/A/Nitrification.htmlhttp://zim//A/Urea.html#cite_note-7http://zim//A/Urea.html#cite_note-7http://zim//A/Urea.html#cite_note-7http://zim//A/A/Nitrobacter.htmlhttp://zim//A/A/Ammonium%20nitrate.htmlhttp://zim//A/A/UAN.htmlhttp://zim//A/A/UAN.htmlhttp://zim//A/A/Ammonium%20nitrate.htmlhttp://zim//A/A/Nitrobacter.htmlhttp://zim//A/Urea.html#cite_note-7http://zim//A/A/Nitrification.htmlhttp://zim//A/A/Calvin%20Cycle.htmlhttp://zim//A/A/Nitrosomonas.htmlhttp://zim//A/A/Carbon%20dioxide.htmlhttp://zim//A/A/Ammonia.htmlhttp://zim//A/A/Urease.html


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The formation of urea is represented by (ii) reaction which proceeds towards

equilibrium state and is governed by the operating pressure and temperature of

synthesis mixture, mole ratio of NH3/CO2 and H2O/CO2 and residence time.

FACTORS EFFECTING UREA PROCESS:

Effect of Temperature: Reaction (i) is exothermic and therefore, low

temperature favors forward reaction. Reaction (ii) is endothermic and favored athigh temperature. To get sufficient conversion, an optimum temperature is

selected. It is observed that maximum equilibrium conversion occurs at 190 -

200C.

Effect of Pressure: There is reduction in volume in the overall reaction and so

high pressure favors the forward reaction. Reactor pressure is selected

according to temperature so that it remains higher than the dissociation pressure

of Carbamate to avoid reversal of (i) reaction.

Effect of Concentration of reactants: Increase in NH3 or CO2 concentration

should theoretically increase the percentage conversion in the Reactor.

However, in actual practice it has been observed that excess CO2does not help

much but excess NH3greatly enhances the CO2conversion.

Presence of water shifts the (ii) reaction in reverse direction. Hence lesser

H2O/CO2 ratio favors urea formation. However, water has to be maintained in

system to help recycling unconverted CO2& NH3back to reactor & maintainingthe temperature in reactor.

Higher Residence Time: The reaction to form urea approaches to chemical

equilibrium & the reaction rate decreases with time. It can only be increased

with the increase in residence time. Higher residence time can also compensateother unfavorable conditions.

The outlet product from the urea reactor consists of Urea, unconverted

Carbamate, excess NH3 and water. This mixture is processed further to

recover and recycle back the unconverted reactants. The various processes

available so far differ principally in the manner in which these unconverted

reactants are recovered and recycled back to the Reactor or otherwise, processedfurther in other plants for producing different type of fertilizers. The second

reaction (ii) of urea formation indicates that volume increases in forwarddirection and therefore, favored at low pressure. Also this reaction is


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endothermic and thus reaction rate increases with increase in temperature to

increase urea conversion. It is, therefore, obvious that recovery of unconverted

Carbamate shall be achieved by decomposition by reducing pressure and adding

heat.

Fig1. BASIC PROCESS FLOW DIAGRAM OF NFL UREA PLANT


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STRIPPING PROCESS:

The stripping concept is based on the application of the Law of Mass Action to

the Carbamate formation / decomposition equilibrium. If the concentration ofone of the component in reactor effluent solution is artificially lowered, the

ammonium Carbamate will decompose until the correct equilibrium is

restored. This is done by passing the reactor effluent through a steam heated

stripper working at same pressure level as of reactor, which is injected with one

of the gaseous feeds. This has the effect of raising the partial pressure of the

component used as the stripping gas, which reduces the partial pressure of theother gas and help in decomposing of Carbamate.

As per Henry's law, the partial pressure of a component in vapour mixture is

proportional to the concentration of that component in the solution at system

pressure.

Pa ~ Ca

If the partial pressure of any of the component i.e. NH3& CO2 in stripper is

raised artificially by adding any of the component, the partial pressure of the

other component reduces and correspondingly, the concentration of that

component in solution reduces by decomposition of Carbamate. This causes

decomposition of Carbamate solution. The heat for decomposition is supplied

from outside. This heat is at a higher level but requirement is less because

decomposition is assisted by stripping effect. The heat of condensation of theevolved gases is sufficient enough to recover it by producing low pressure

steam instead of wasting to cooling water.

As the stripper & Carbamate condenser operates at reactor pressure, no pump isrequired to recycle the condensed Carbamate solution back to the reactor. It

results in establishment of an internal recycle of both ammonia and CO2in urea

reactor system to the maximum extent. The left over Carbamate is passed on to

the downstream section for recovery which is very less in quantity and thus

requires low energy for decomposition. The operating pressure of the synthesisloop has also been brought down which means direct saving in power for feed

and pumping back the recovered Carbamate.


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(2) STAMI CARBON'S CO2STRIPPING PROCESS:

This process is based on the stripping process using carbon di oxide gas as the

stripping media. This process was developed in 1960. The process has greatlybeen improved since its inception. In original process synthesis took place at140 ata pressure and 180-185C. A mole ratio of NH3& CO2is maintained at

around 2.9. About 58% of CO2 is converted to urea in the reactor per pass.

More than 80% of the unconverted NH3& CO2is recovered in the stripper itself

where CO2is fed as stripping media. Medium pressure decomposition stage is

also eliminated as the process does not contain excess ammonia. Heat ofCarbamate condensation is recovered in the form of Low Pressure Steam.

Urea solution from the stripper is directly letdown to 3-6 Kg./Cm2 and

recovered Carbamate vapours are recycled back to H.P. Stripper after

condensation. Urea solution from LP section is concentrated in two stage

vacuum system & then prilled.

(3) ACES PROCESS(Advanced Process for Cost & Energy Saving):-

This process of Toyo Engineering combines a total recycle process with

stripping process using CO2 feed as stripping agent. Reactor operates at 176

Kg./Cm2pressure and ata temperature of 190C with mole ratio of NH3/CO2 of4.00. About 68% of the CO2 is converted to urea in reactor per pass. More

than 65% of unconverted Carbamate is stripped off in the stripper. Stripped off

gases are recycled back to the reactor after condensation in high pressure

condensers no. 1 & 2 . LP steam is generated in one of the condenser whereasthe second condenser is utilized for decomposition in the MP section. In

addition, the MP section condensation heat is further utilized in evaporation

section. This has brought down the energy consumption in ACES plant to a low

level.

(4) IDR PROCESS: (Isobaric Double Recycle):-

This process of Montedison is an economical process of production of urea by

using two strippers working in series with NH3 and CO2as stripping agent in

each stripper. The reactor is divided in two parts by partition plate along-with

mixing trays. Synthesis takes place at 200 ata pressure and at temperature of

185 - 190C. A ratio of NH3/CO2 equal to 4.25 is maintained in the reactorwhich helps in converting 70% of the CO2in urea per pass. NH3feed in divided

into two parts i.e. one part going to NH3stripper & other one to the reactor tomaintain the temperature profile in reactor. CO2feed is directly sent to second


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stripper. The unconverted stripped off gases from 1st stripper are sent to upper

portion of reactor & from 2nd stripper to Carbamate condenser. The condensed

Carbamate is recycled to the reactor along-with Carbamate solution from the

downstream recovery sections. Steam of 7 ata rating is generated in the

Carbamate condenser which is utilized in the recovery section.


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Historically, spectrophotometers use amonochromator containing adiffraction

grating to produce the analytical spectrum. The grating can either be movable or

fixed. If a single detector, such as aphotomultiplier tube orphotodiode is used,

the grating can be scanned stepwise so that the detector can measure the light

intensity at each wavelength (which will correspond to each "step"). Arrays of

detectors, such ascharge coupled devices (CCD) orphoto diode arrays (PDA)

can also be used. In such systems, the grating is fixed and the intensity of each

wavelength of light is measured by a different detector in the array.

UV-visible spectrophotometry

The most common spectrophotometers are used in theUV andvisible regions of

the spectrum, and some of these instruments also operate into the near-infraredregion as well.

Visible region 400700 nm spectrophotometry is used extensively in

colorimetry science. Ink manufacturers, printing companies, textiles vendors,

and many more, need the data provided through colorimetry. Scientists use thisinstrument to measure the amount of compounds in a sample. If the compound

is more concentrated more light will be absorbed by the sample; within small

ranges, theBeer-Lambert law holds and the absorbance between samples varywith concentrati

report on urea production and process analysis.docx

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