Report on Urea Production and Process Analysis.docx
-
Upload
sameer-saxena -
Category
Documents
-
view
266 -
download
2
Transcript of Report on Urea Production and Process Analysis.docx
-
8/14/2019 Report on Urea Production and Process Analysis.docx
1/102
1
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,
-
8/14/2019 Report on Urea Production and Process Analysis.docx
2/102
2
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
3/102
3
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
4/102
4
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
5/102
5
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).
http://zim//A/A/Chemical%20substance.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/Molecule.htmlhttp://zim//A/A/Oxygen.htmlhttp://zim//A/A/Hydrogen.htmlhttp://zim//A/A/Atoms.htmlhttp://zim//A/A/Covalent.htmlhttp://zim//A/A/Liquid.htmlhttp://zim//A/A/Standard%20conditions%20for%20temperature%20and%20pressure.htmlhttp://zim//A/A/Earth.htmlhttp://zim//A/A/Solid.htmlhttp://zim//A/A/Ice.htmlhttp://zim//A/A/Gaseous.htmlhttp://zim//A/A/Water%20vapor.htmlhttp://zim//A/A/Steam.htmlhttp://zim//A/A/Liquid%20crystal.htmlhttp://zim//A/A/Hydrophile.htmlhttp://zim//A/A/Chemical%20compounds.htmlhttp://zim//A/A/Chemical%20compounds.htmlhttp://zim//A/A/Earth.htmlhttp://zim//A/A/Life.html#Range_of_tolerancehttp://zim//A/A/Atmosphere.htmlhttp://zim//A/A/Vapor.htmlhttp://zim//A/A/Cloud.htmlhttp://zim//A/A/Precipitation%20%28meteorology%29.htmlhttp://zim//A/A/Hydrological%20cycle.htmlhttp://zim//A/A/Evaporation.htmlhttp://zim//A/A/Transpiration.htmlhttp://zim//A/A/Evapotranspiration.htmlhttp://zim//A/A/Condensation.htmlhttp://zim//A/A/Precipitation%20%28meteorology%29.htmlhttp://zim//A/A/Runoff%20%28water%29.htmlhttp://zim//A/A/Sea.htmlhttp://zim//A/A/Sea.htmlhttp://zim//A/A/Runoff%20%28water%29.htmlhttp://zim//A/A/Precipitation%20%28meteorology%29.htmlhttp://zim//A/A/Condensation.htmlhttp://zim//A/A/Evapotranspiration.htmlhttp://zim//A/A/Transpiration.htmlhttp://zim//A/A/Evaporation.htmlhttp://zim//A/A/Hydrological%20cycle.htmlhttp://zim//A/A/Precipitation%20%28meteorology%29.htmlhttp://zim//A/A/Cloud.htmlhttp://zim//A/A/Vapor.htmlhttp://zim//A/A/Atmosphere.htmlhttp://zim//A/A/Life.html#Range_of_tolerancehttp://zim//A/A/Earth.htmlhttp://zim//A/A/Chemical%20compounds.htmlhttp://zim//A/A/Hydrophile.htmlhttp://zim//A/A/Liquid%20crystal.htmlhttp://zim//A/A/Steam.htmlhttp://zim//A/A/Water%20vapor.htmlhttp://zim//A/A/Gaseous.htmlhttp://zim//A/A/Ice.htmlhttp://zim//A/A/Solid.htmlhttp://zim//A/A/Earth.htmlhttp://zim//A/A/Standard%20conditions%20for%20temperature%20and%20pressure.htmlhttp://zim//A/A/Liquid.htmlhttp://zim//A/A/Covalent.htmlhttp://zim//A/A/Atoms.htmlhttp://zim//A/A/Hydrogen.htmlhttp://zim//A/A/Oxygen.htmlhttp://zim//A/A/Molecule.htmlhttp://zim//A/A/H2O.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Chemical%20substance.html -
8/14/2019 Report on Urea Production and Process Analysis.docx
6/102
6
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
7/102
7
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
8/102
8
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
9/102
9
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
10/102
10
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,
-
8/14/2019 Report on Urea Production and Process Analysis.docx
11/102
11
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
12/102
12
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
13/102
13
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
14/102
14
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
15/102
15
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:
-
8/14/2019 Report on Urea Production and Process Analysis.docx
16/102
16
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
17/102
17
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
18/102
18
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
19/102
19
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
20/102
20
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
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.
Regeneration of SAC and WAC is carried out simultaneously. Theregeneration is carried out in five stages.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
21/102
21
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
22/102
22
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
23/102
23
WEAK BASE ANION (WBA)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. DPIis 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 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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
24/102
24
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 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.
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
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
25/102
25
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
26/102
26
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.
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 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.
A resin trap with DPI is provided to trap ion exchange resins in the
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
27/102
27
(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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
28/102
28
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
29/102
29
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
30/102
30
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
31/102
31
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:
Exhaustion reaction:
2RCOOH + MCO3 RCOOM + H2CO3
Regeneration reaction:
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:
-
8/14/2019 Report on Urea Production and Process Analysis.docx
32/102
32
Exhaustion reaction:
ROH + (HCl, H2SO4, HNO3, H2CO3, H2SiO3)
R(Cl, SO4, NO3, HCO3, HSiO3) + H2O
Regeneration reaction:
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:
Exhaustion reaction:
-
8/14/2019 Report on Urea Production and Process Analysis.docx
33/102
33
RN + H(Cl, SO4, NO3) RN(HCl, H2SO4,HNO3)
Regeneration reaction:
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
34/102
34
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
35/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
36/102
36
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
37/102
37
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
38/102
38
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
39/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
40/102
40
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
41/102
41
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
42/102
42
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
43/102
43
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.
http://zim//A/A/Chemical%20compound.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Hydrogen.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Gas.htmlhttp://zim//A/A/Pungent.htmlhttp://zim//A/A/Odour.htmlhttp://zim//A/A/Nutrition.htmlhttp://zim//A/A/Food.htmlhttp://zim//A/A/Fertilizer.htmlhttp://zim//A/A/Pharmaceuticals.htmlhttp://zim//A/A/Caustic%20%28substance%29.htmlhttp://zim//A/A/Hazard.htmlhttp://zim//A/Ammonia.html#cite_note-Ullmann-5http://zim//A/Ammonia.html#cite_note-Ullmann-5http://zim//A/Ammonia.html#cite_note-Ullmann-5http://zim//A/A/Ammonium%20hydroxide.htmlhttp://zim//A/A/Ammonium%20hydroxide.htmlhttp://zim//A/A/Trigonal%20pyramid%20%28chemistry%29.htmlhttp://zim//A/A/Valence%20shell%20electron%20pair%20repulsion%20theory.htmlhttp://zim//A/A/Putrefaction.htmlhttp://zim//A/A/Ammonium%20chloride.htmlhttp://zim//A/A/Ammonium%20sulfate.htmlhttp://zim//A/A/Ammonium%20bicarbonate.htmlhttp://zim//A/A/Kidney.htmlhttp://zim//A/Ammonia.html#cite_note-7http://zim//A/Ammonia.html#cite_note-7http://zim//A/Ammonia.html#cite_note-7http://zim//A/Ammonia.html#cite_note-7http://zim//A/A/Kidney.htmlhttp://zim//A/A/Ammonium%20bicarbonate.htmlhttp://zim//A/A/Ammonium%20sulfate.htmlhttp://zim//A/A/Ammonium%20chloride.htmlhttp://zim//A/A/Putrefaction.htmlhttp://zim//A/A/Valence%20shell%20electron%20pair%20repulsion%20theory.htmlhttp://zim//A/A/Trigonal%20pyramid%20%28chemistry%29.htmlhttp://zim//A/A/Ammonium%20hydroxide.htmlhttp://zim//A/A/Ammonium%20hydroxide.htmlhttp://zim//A/Ammonia.html#cite_note-Ullmann-5http://zim//A/A/Hazard.htmlhttp://zim//A/A/Caustic%20%28substance%29.htmlhttp://zim//A/A/Pharmaceuticals.htmlhttp://zim//A/A/Fertilizer.htmlhttp://zim//A/A/Food.htmlhttp://zim//A/A/Nutrition.htmlhttp://zim//A/A/Odour.htmlhttp://zim//A/A/Pungent.htmlhttp://zim//A/A/Gas.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Hydrogen.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Chemical%20compound.html -
8/14/2019 Report on Urea Production and Process Analysis.docx
44/102
44
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
45/102
45
-
8/14/2019 Report on Urea Production and Process Analysis.docx
46/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
47/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
48/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
49/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
50/102
50
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
51/102
51
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
52/102
52
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}
http://zim//A/A/Organic%20compound.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Carbon.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Carbonyl.htmlhttp://zim//A/A/Functional%20group.htmlhttp://zim//A/A/Metabolism.htmlhttp://zim//A/A/Urine.htmlhttp://zim//A/A/Mammal.htmlhttp://zim//A/A/Ammonia.htmlhttp://zim//A/A/Acidic.htmlhttp://zim//A/A/Base%20%28chemistry%29.htmlhttp://zim//A/A/Fertilizer.htmlhttp://zim//A/A/Raw%20material.htmlhttp://zim//A/A/Chemical%20industry.htmlhttp://zim//A/A/Friedrich%20W%C3%B6hler.htmlhttp://zim//A/A/Vitalism.htmlhttp://zim//A/A/Vitalism.htmlhttp://zim//A/A/Vitalism.htmlhttp://zim//A/A/Nutrient.htmlhttp://www.icis.com/v2/chemicals/9076559/urea/uses.html%7Dhttp://www.icis.com/v2/chemicals/9076559/urea/uses.html%7Dhttp://zim//A/A/Nutrient.htmlhttp://zim//A/A/Vitalism.htmlhttp://zim//A/A/Friedrich%20W%C3%B6hler.htmlhttp://zim//A/A/Chemical%20industry.htmlhttp://zim//A/A/Raw%20material.htmlhttp://zim//A/A/Fertilizer.htmlhttp://zim//A/A/Base%20%28chemistry%29.htmlhttp://zim//A/A/Acidic.htmlhttp://zim//A/A/Ammonia.htmlhttp://zim//A/A/Mammal.htmlhttp://zim//A/A/Urine.htmlhttp://zim//A/A/Metabolism.htmlhttp://zim//A/A/Functional%20group.htmlhttp://zim//A/A/Carbonyl.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Nitrogen.htmlhttp://zim//A/A/Carbon.htmlhttp://zim//A/A/Carbon.htmlhttp://zim//A/A/Chemical%20formula.htmlhttp://zim//A/A/Organic%20compound.html -
8/14/2019 Report on Urea Production and Process Analysis.docx
53/102
53
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 -
8/14/2019 Report on Urea Production and Process Analysis.docx
54/102
54
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
55/102
55
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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
56/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
57/102
57
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
58/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
59/102
59
(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
-
8/14/2019 Report on Urea Production and Process Analysis.docx
60/102
60
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.
-
8/14/2019 Report on Urea Production and Process Analysis.docx
61/102
-
8/14/2019 Report on Urea Production and Process Analysis.docx
62/102
62
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