Punjab State Board of Technical Education & Industrial Training

A Four Weeks Industrial Training Report

On

National Fertilizers Limited Bathinda

Submitted To:

Submitted By:

Mr. G.S. Dhaliwal

Gaurav lubana(H.O.D.ME) 009795312842 ( 5thmech. Engg. A) PREFACE The Training report on the working of National Fertilizers Limited, Bathinda has been prepared in accordance with the requirement of schene of diploma in mechanical engineering at Regional Polytechnic College, Behman Diwana.

In this course, industrial training is an integral part of the curriculum and can be undertaken in any reputed industry. I have done this training at National fertilizers limited, bathinda which is situated on Bathinda - Goniana road and is very well connected with rail and road. it is very well known for its excellent performance over the past years.

It is pleasure to face the industrial life that helped me to convert my theoretical concepts into practical knowledge, during training i came across from many problems that surely explains me, what actually industrial life is. This training has totally changed, my way of looking at the new things and despite of the technical knowledge, it also taught me how to be a professional.

Gaurav lubana ACKNOWLEDGEMENT The industrial training in an industry / project site is an essential part of curriculum for competition of diploma. I am grateful to authorities at the National Fertilizers Limited, Bathinda for permitting me to undergo for the four weeks industrial training in their esteemed organization.

During training, I have learnt a lot for which I pay my heartiest gratitude to (HRD Manager) Mr.D.K. Bora & other staff members of National Fertilizers Limited, Bathinda who helped me in all respects in fulfilling my cherished desire of getting a successful industrial training.

I am thankful to Mr.H.K.Lambha (S.R.manager) and all supervisors & other official for providing me complete process details of their respective plants.

I am also very thankful to Mr.Gurpyar Singh Dhalliwal (HOD of mechanical Engg.),Gurpreet Singh Sandhu and all other staff members in mechanical department of Regional Polytechnic College who helped me to deside that which industrial place is good for training.

Gaurav lubanaTable of ContentsTOPIC PAGE NO.

INTRODUCTION 3 4 COMPANY PROFILE 5 UREA PLANT 6-10

STEAM GENERATION PLANT 11 - 13 CAPTIVE POWER PLANT 14 - 20 PROJECT STUDY 20 22INTRODUCTION

NFL is known in the industry for its work culture; value added human resources, safety, environment, concern for ecology and its commitment to social upliftment. All NFL plants have been certified for ISO-9002 for conforming to international quality standards and International Environmental Standard i.e. ISO-14001. With the certification of Corporate Office/Marketing operations under ISO-9001:2000, NFL has become the first Fertilizer Company in the country to have its total business covered under ISO-9001 Certification. On 23rd August 1974, NFL was formed and registered to set up two modern large capacity Nitrogenous Fertilizers plants.

NFL, Bathinda (Punjab)

NFL, Panipat (Haryana)

NFL was incorporated on 23rd August 1974 in order to implement this project contract were entered into with M/s " TOYO ENGINEERING CORPORATION " a well known Japanese Engg. Company and Engg. India Ltd (EIL), a public sector and Engg. Organization .This contract becomes effective on September 26, 1974 with a guaranteed Feed in on the Bathinda Fertilizers project to implement within 36 months from the zero date.

Due to the power requirements and some other factors, later on it was planned to set up its own power house known as Captive Power Plant (CPP) with 2 turbo generators of 15 MW each.

National Fertilizers Limited (N.F.L.) is the largest manufacturer of nitrogenous fertilizers in the Northern India. It is presently operating four large fertilizers plants, two of which are located at Nangal and Bathinda in the Punjab State, one at Panipat in Haryana and one at Guna in M.P. While plants at Nangal, Bathinda and Panipat are fuel-oil based, the one at Guna is gas-oil based. The overall installed capacity of NFL plants is 10.42 lakh MT per annum.

The old plant at Nangal was commissioned in 1961 followed by expansion which was commissioned in 1978. Bathinda and Panipat plants were commissioned in 1979. Guna Plant which is the latest plant of NFL was commissioned in Dec, 1978 and is now in full production.

NFL was incorporated on 23rd August, 1974 with two manufacturing Units at Bathinda and Panipat. Subsequently, on the reorganization of Fertilizer group of Companies in 1978,

The Nangal Unit of Fertilizer Corporation of India came under the NFL fold. The Company expanded its installed capacity in 1984 by installing and commissioning of its Vijaipur gas based Plant in Madhya Pradesh. NFL Corporate office: Noida

The Vijaipur Plant was a land mark achievement in project management in India. The plant was completed well within time and approved project cost. In recognition of this achievement, the project was awarded the First Prize in Excellence in Project Management by Govt. of India. Subsequently the Vijaipur plant doubled its capacity to 14.52 lakh MTs by commissioning Vijaipur Expansion Unit i.e. Vijaipur-II in 1997. The plant annual capacities have now been re-rated w.e.f. 1.4.2000 from 7.26 lakh MT of Urea to 8.64 lakh MT for Vijaipur-I & Vijaipur-II Plants each.

Three of the Units are strategically located in the high consumption areas of Punjab and Haryana. The Company has an installed capacity of 35.49 lakh MTs of Nitrogenous Fertilizers and has recordedan annual sales turnover ofRs.3, 474 crores during 2004-05.

Strategically Located - Urea Plants

Leading Producer of Nitrogenous Fertilizers in the Country.

PRODUCTION

Capital Cost, Feed Stock & Plants Capacity

PlantsCapital Cost(Rs.Crore) Feed StockExisting Capacity MT/Year(Lakh MT/Yr.)Ammonia Urea CAN Bio-Fert.Nangal-I91.26

Naptha0.66-3.181-Nangal-II299.19

F.Oil/LSHS2.974.785**--Panipat338.41F.Oil/LSHS2.975.115--Bathinda349.41F.Oil/LSHS2.975.115--Vijaipur-I516.00Natural Gas5.016*8.646*--Vijaipur-II1071.00Natural Gas5.016*8.646*--Indore1.42Strains---100Total2666.5519.60232.3073.181100

UREA PLANTTYPES OF PROCESS

CONVENTIONAL

MOLE RATIO NH3:CO2 4:1

H20:CO2 0.54:1

%CONVERSION 70%REACTION CONDITION:

PRESSURE:

CO2 250 kg/cm2 Carbamate 250 kg/cm2 Ammonia 250 kg/cm2TEMPERATURE:

2000 C

UREA PROCESS CLASSIFIED IN FOUR SECTION

1. Synthesis section.2. Decomposition section.3. Crystallization & Prilling section.4. Recovery section.PRESSURE MEASUREMENT

(PNEUMATIC SYSTEM)

For the measurement of pressure the single control loops method. The no. of component used for this are:

Pressure gauge

Pressure transmitter

Pneumatic controller

Actuator

Positioner

Control valvesOPERATION

PRESSURE GAUGE measures the actual pressure in the pipeline.

PRESSURE TRANSMITTER takes actual pressure in its primary and secondary part converts this pressure into 0.2 ~1.0 kg/cm2 signal. A 1.4 kg/cm2 supply is providedto pneumatic controller.

Controller follows pressure transmitter signal and with set point value. Controller gives output according to desired set point value and produces a output signal of 0.2 ~ 1.0 kg/cm2. Positioner accepts this signal and produces output signal i.e. given to the actuator.

Positioner acts according to controller signal.

Actuator diaphragm moves up & down according to positioner signal and control valves moves accordingly. In this way pressure in a pipeline is controlled.

ACTUATOR

A fluid powered or electrically powered device that supplies and motion to a valve closure member.

DIAPHRAGM

A flexible pressure responsive element that transmits force to the diaphragm plate and actuator stem.

FORCE PLATE

The support plate which gives support to the diaphragm and exerts force uniformly.

CONTROL VALVE

A valve with actuator that automatically, fully or partially opens or closers that valve to a position dictated by signals transmitted from controlling instruments can be called as CONTROL VALVE.The control valve is most important and widely used final element in auto control loop. A control valve functions as a variable resistance in a pipeline. So by controlling the flow, the valve indirectly controls the process variables that may be level, temperature, pressure etc.VIBRATION MEASUREMENTIf the observed surface is rotating and rapidly changing the gap distance the RF envelope is not constant amplitude but varies in direct proportion to the peak to peak movement of the observed surface. This peak to peak movement of the observed surface causes the RF envelope to be amplitude modulated.

VIBRATION AND AXIAL DISPLACEMENT

Transducer system is non contacting shaft vibration and relation position measurement system. The system include a probe with an integral cable, extension cable and proximate. The transducer system measurement the gap between the probe fit and an absorbed metal surface and convert this distance to a proportional negative voltage.

The system measures both static and dynamic system probe tips are also each calibrated to a specific probe type cable electrical length and temperature range. The scale factor is 200MV/mil(1mil=1/1000inch).

GAP MEASUREMENT24 volts normally drive the proximator from an external source such as a power supply or monitoring device. The proximator converts the DC drive voltage into an RF signal that is applied to the probe through 95 ohm coaxial extension probe radiates the RF signal into surrounding area as a magnetic field. If there is no conductive material within a specified distance to intercept magnetic field. There is no power loss in RF signal the output signal of proximator output terminals is max. 16volts. When a conductive material approaches the probe tip, eddy current generated on the surfaces on the material resulting power loss in RF signal. As a power loss is developed in RF signal, the output at proximator output terminal is reduced proportionately. As the conserved conductive surface come closer to the probe tab, the eddy currents on the surface of material observed more power. When the gap reached specified minimum distance from the conductive material surface. The material absorbs the total RF energy radiated by the probe. This is reflected as the maximum power loss the RF signal resulting a minimum DC output signal at the proximator output terminal. The proximator measure the magnetic of the RF envelopes and provide a DC output signal proportional to the packs of envelopes. Thrust measurement and eccentricity measurement are the merely gap measurement at the slow rate of change in the gap. LEVEL MEASUREMENT

WHAT IS LEVEL?

The level may be expressed in term of pressure exerted over a datum level or in term of the length of the liquid column.

WHY IT IS MEASURED?

To ensure that right amount of liquid/solid are added to the vessel at right time and for safe operation.WHY ITS MEASUREMENT IS IMPORTANT?

Level measurement is one of the important parameter in any process industry like our fertilizer plant. The level has a significant effect on process quality, controllability, process stability and optimization. Hence precise, accurate and reliable level measurement is necessary. A wide variety of level measurement techniques are available to meet the diverse level requirement of the process industry evolved over the years.

STEAM GENERATION PLANT Steam Generation plant is mainly installed for production of steam and then distributed to various parts of the plant.

Here this section of plant installed in National Fertilizers Limited, Bathinda unit produces and supplies steam at 100 Kg / cm2 pressure and nearly 480C temperature to Ammonia Plant.

In todays world steam has gained importance in Industries. It may be used for power processes and heating purposes as well.

BENEFITS OF STEAM

It is colorless, odourless and tasteless.

Very economical

Non-polluting

Can be used as heat exchanger.

It can be easily distributed to various sections of plant.

Steam is generated in Boilers (Water tube boilers mounted on common base fitted with mountings and fittings) and then distributed to other parts of plants. For governing the quantity of fuel to be burned and for maintaining the required pressure their are many automatic fuel feeders, equipments and auxiliaries like pressure gauge etc.

In the Boilers used at National Fertilizers Limited (Bathinda unit); coal, oil natural gas are used as a fuel for production of steam.

NFL , Bathinda is using steam for two purposes ; first and the main reason is for running prime mover and other reason is to exchange heat in the processes taking place their.

There are three boilers capable of producing steam at the rate of 150 Tonnes/hr installed in CPP which were supplied and erected b BHEL. Generally two boilers are enough to meet the requirements but third boiler is simultaneously running because if steam load consumption increases then the third boiler plays its part in order to avoid any faulty condition.

FUELS USED:

Coal :

To obtain steam of desired Temperature and pressure, coal is burned to give major source of heat.

Initially coal is stored at Coal Handling plant brought from coal sites. It is this section of plant where coal is crushed by crushers in order to make small pieces of coal, then after crushing it the coal pieces rare passed through heavy electromagnet where iron is separated from coal if present. Coal is then sent to Bunkers from where it goes to Grinding mill. Grinding mill is grinding coal into powder form.

Conveyor Belts are being used in the whole plant for transportation of Coal. The powder form of coal is sent to the Boilers through pump as pump sucks the coal from grinding mills and throws it into the boiler for combustion.

Fuel Oil :

As the Boilers are designed to work on both Coal as well as Fuel Oil so fuel oil can also be pumped to Boiler for combustion.

Generally coal alone is not burnt Initially but Fuel Oil (LSHS) is mixed coal and then sent to the furnace for combustion in order to get desired temperature .

WHY AND WHERE STEAM IS REQUIRED

As National Fertilizers Ltd, Bathinda unit has its own Steam Generation Plant where steam is produced which is used for driving Turbo Compressors, Heating Purposes, for various reactions taking place in the plant itself.

Steam is mainly consumed in the Ammonia Plant as nearly 6 to 7 tonne of steam is required to produce 1 tonne of Ammonia. High Pressure Turbines are being used where high pressure and temperature is to be maintained so SGP section plays a important role for maintaining the said condition.

There are three boilers (VU-40 type supplied by M/S BHEL) of 150 tonne/hr capacity .These boilers are Water Tube Boilers i.e. water is inside the tubes and hot air surrounds it when coal is burnt, this makes the water in the tubes boil and steam formation takes place. In the beginning coal is burnt with fuel oil in order to get desired temperature. WATER AND STEAM SYSTEM As the steam being used should be free from impurities like minerals, silica, oxygen, Iron etc. in order to insure Safe and Efficient working of Steam turbines and Boilers. For this purpose Raw Water is physically and chemically treated and finally supplied to Steam Generation Plant from Ammonia plant. This water is called Boiler Feed water which is further heated to 240 C by the flue Gases and taken to Steam Drum. Steam Drum Acts as storage tank and also separates water from the steam at 315 C and 106 kg/cm2 pressure water then enters the Ring Header formed at on the bottom of outside the furnace and rises by gravity through water wall tubes on the all the four sides, taken heat from furnace and enters steam drum as a mixture of steam and water.FLUE GAS SYSTEM

The products of combustion in the furnace consist of carbon-di-oxide, nitrogen, ash, oxygen and sulphur-di-oxide. After leaving the furnace the heat

Of these gases called FLUE GASES, is utilized at various levels.

First the steam from steam drum is heated in two super heaters to get the required temperatures of 4950C and then feed water in BANK TUBES is also heated and the gases leave bank tubes at around 4970C next the heat is utilized to heat feed water in the ECONOMIZER and gases are cooled down to 3200C. These gases are further cooled down to 1500C in ROTARY AIR HEATER where the air is required for combustion and conveying the coal is heated up. Temperature is not reduced further because at lower temperature oxides of sulphur present in flue gases are converted to ACID which damages the down stream equipments. These gases then pass through ELECTRO STATIC PRECIPITATOR (ESP) where ash is removed.

CAPTIVE POWER PLANT

INTRODUCTION: National Fertilizers Limited has set a Captive Power Plant (CPP) at their complex at BATHINDA, to ensure availability of stable, uninterrupted power and stream to the Ammonia and Urea plant. This will minimize the tripping of the Fertilizer Plant due to transit voltage dips and power cuts.

Since inception, Bathinda unit was drawing electric power from Punjab State Electricity Board (P.S.E.B). Electricity is the main driving force after steam in the plant, being used for moving auxiliary equipments. The unit requires 27MW of power/hr when running at full load. There are two 15 MW turbo-generators to generate power. Under normal running conditions of the plant and healthiness of the P.S.E.B. grid, we generally run in synchronism with the grid merely drawing the power corresponding to the minimum charges to be paid to state electricity board. In case of any disturbance in the grid, our system gets isolated from the grid automatically. With both generators running, we are able to feed power to the whole plant, thus production is not affected. In case only one turbo generator is in line and grid cuts off, urea plant is cut off automatically to balance the load with one generator. As soon as the grid becomes stable, the generators are again synchronized with it. The power generation of each generator can be varied with 2 MW to 15 MW maximum, provision exists to run the generator on 10 % extra load continuously for one hour only.

Operation of C.P.P. is based upon microprocessor based computerized instrumentation which allows automatic operation, start up, shut down of the whole or part of the plant.

Latest instrumentation has been used in this plant. It allows controlling process variables like flow, pressure, temperature, power factor, voltage, frequency, etc. There is operator interface unit (IOU) Like a TV screen on which various parameters can be displayed and controlled. It allows fully automatic start-up, shut-down of boiler, turbine and other auxiliaries.

NEED FOR C.P.P:

It was thought to install a captive power plant in which electric power for our requirement shall be generated in a COAL FIRED BOILER. The benefits envisaged were:

1. Any disturbance in the PSEB grid used to trip the whole plant. Lot of money was lost due to this as each re-startup costs around 40 to 50 lakhs rupees. Moreover, frequent trippings had an ill effect on machines and equipments extending the re-startup period.

2. Three boilers of 150Te/hr steam capacity were initially installed in SGP to keep 25 boilers running and one stand by as designed steam requirement was less than 300Te/hr. but in actual operation steam requirement was more and all three boilers had to be run and there was no breathing time for their maintenance. As new boiler was to be installed for CPP, its capacity was so designed that it could export around 60Te of steam for process requirement so that only 2 boilers of SGP would be run keeping the 3rd as stand by.

With these points in mind CPP was installed. The functioning of CPP can be sub-divided into parts:

BOILER AND ITS AUXILIARIES: For generation of high pressure superheated steam.

TURBO-GENERATOR AND ITS AUXILIARIES: To generate power, using steam from the boiler.

Operation of CPP is based upon microprocessor based computerized instrumentation which allows automatic operation, start up, shut down of the whole or the part of the plant.

BOILER

The basic principle of this boiler is the same as discussed earlier for SGP boiler that is formation of steam by heating boiler feed water inside furnace fired by coal and heavy oil, utilization of heat of the gases and venting these gases at a safe height. Main differences between the two boilers are:

SGP boiler is tangentially fired where as CPP boiler is front fired with 6 coal burners and 6 oil gun fixed inside the coal housing.

SGP boiler can be loaded up to 30% load with oil firing only whereas CPP boiler can be fully loaded with oil alone.

Height of combustible zone in CPP boiler is more and it has residence time of 1.5 sec where SGP boiler has 1.0 sec.

Mills used for pulverizations of coal in SGP are negative pressure bowl mills whereas in CPP ball tube mill are used which are positive pressure mills.

Due to more residence time and better pulverization the efficiency of CPP boiler is about 4% higher.

Boiler feed water required for steam generation can be fully generated in CPP itself.

A part of the steam generated is exported for process use in ammonia plant and rest is utilized for power generation in turbo generators as described below:

DESCRIPTION

MITSUI RILEY TYPE BOILER

Maximum evaporation 2, 30,000kg/hr

Design process for boiler 124 kg/cm2G

Steam temp at outlet 4950C

Heating surface 1250M2

POWER GENERATION:

In C.P.P. two generators of 15MW capacity generate a voltage of 11KV which is fed to the two transformers in the yard. The rating of the transformers is 31.5/25 KVA, these two values depend upon the cooling which we provide, as here 25KVA capacity is when cooling is oil natural air natural and 31.5KVA capacity is when cooling is oil natural air forced. Both these transformers step up the voltage level to 132KV. From the transformers the three phases pass through the lightning arrestors (LA). After this they pass on to the isolator. After this the two lines pass on to the TRANSMISSION pole called DOUBLE CIRCUIT TRANSMISSION. Then these lines go to the M.R.S. i.e. main receiving station.

TURBINE:

The turbine used is supplied by M/S SGP of AUSTRIA. It is condensing cum extraction turbine designed as single casing reaction turbine with single control stage and high pressure (HP), mild pressure (MP) and low pressure (LP) reaction parts.

The turbine is fed with high pressure steam at 100kg from boiler and flows through various control valves for normal and emergency operation. It gets high velocity through the nozzle group and then passes over the impellers fixed on to the rotor and fixed diffusers thus rotating the turbine. The enthalpy of steam is utilized in steps. Steam is also extracted from various stages. HP1 at 10.4kg/cm2, HP2 at 8.1kg/cm2, feed water bleed at 4.3kg/cm2 and LP bleed at 0.9kg/cm2.

The exhaust steam from the turbine is condensed in a condenser maintained under vacuum to extract maximum steam enthalpy. The output of the turbine depends on flow of steam and heat difference that is on condition of steam at the main steam valve and the pressure at the turbine outlet or condenser pressure. The turbine is connected to the generator through speed reducing gears.

The exhaust steam is condensed in a condenser using cooling water. The resulting condensate can be fed back to LP heater but is normally sent to the polishing water plant.

As shall be clear from the attached block diagram various bleeds from the turbine are utilized for heating purpose. HP1 and HP2 are used for heating boiler feed water in HP1 and HP2 heaters. Feed water bleeds is used for heating the feed water tank and LP bleed is used for heating the polish water make up to the feed water tank.

A lubrication system is also there to lubricate the various bearings of the turbine, gears and generator. Normally the oil pump driven by the turbine shaft supplies oil but auxiliary motor driven pumps are used for start up and during shutdown. A turning gear has been provided for slow cooling of turbine rotor.

Latest instrumentation has been used in this plant. Baileys net work-90 microprocessor based instrumentation system is being used. The NETWORK 90 SYSTEM is a distributed process control system. Using a series of integrated control nodes. The network 90 system allows controlling process variables like flow, pressure and temperature according to a control configuration. There is operator interface unit (OIU) like a TV screen on which various parameters can be displayed and controlled. It allows fully automatic start-up/shut-down of boiler, turbine and other auxiliaries.

DESCRIPTION:-

Make

Simmering Graz Panker, Austria

Type Multifunction (28 stages)

Capacity 65 T/H at 15 MW

RPM 6789 at 50 Hz

Critical speed 3200-3600 RPM

GENERATORS

CPP is having two number turbo generators of capacity 15MW each. The generators are type SAT three phase, 50Hz, 11kV, 984amps, at 0.8 power factor rating supplied by M/S JEUMONT SCHNEIDER OF FRANCE. These are totally enclosed self ventilated type with two lateral airs to water coolers for cooling. The alternators are able to bear 10% overload for one hr with an increase in temp. of 100C while maintaining the voltage as near as possible to the rated one. The excitation is compound and brush less with exciter rotor and Rectifier Bridge mounted on the extended main shaft on non driving end. The excitation is controlled automatically with automatic voltage regulator and a PLC controller. All protection relays installed for protection of generator are solid state having high accuracy, quick response and low power consumption. Under normal running conditions of the plant and healthiness of the PSEB grid, we generally run in synchronism with the grid merely drawing the power corresponding to minimum charges to be paid to state electricity board. In case of any disturbance in the grid measured by higher low frequency, high rate of change of frequency, low voltage etc. our system gets isolated from the grid automatically. With both generators running, we are able to feed power to the whole plant, thus production is not affected.

UNINTERRUPTED POWER SUPPLY: - The uninterruptible power supply system is connected between a critical load, such as digital drives & automation, distributed digital process control system, telecom equipment, programmable logic controller, mission critical applications, computer and its three phase mains power supply under all rated load and input supply conditions.

The system offers the user with the following advantages: -

Increased power supply: -

The UPS has its own internal voltage and frequency regulator circuits which ensure that its output is maintained within close tolerances independent of voltage and frequency variations on the mains power lines.

REDUNDANT Vs NON REDUNDANT CONFIGURATIONS:-

In a non-redundant configuration the system is sized such that both UPS modules are required to feed the potential load and if one of the two modules develops a fault or for some reason shut down, the other module also automatically shuts down.

In such an event the load is transferred to an unprocessed bypass supply.

In a redundant module configuration the system is sized such that the potential load can be provided by just one of the two modules. Under normal circumstances both modules are operational and share the load current equally; but if one module develops a fault, or

is shut down, the second module is able to take over the full load demand and continue to provide it with processed, backed-up power.

7400 Module Design:-

The UPS basically operates as an AC- DC-AC converter. The first conversion stage (from AC to DC) uses a 3 phase fully controlled silicon controlled rectifier (SCR) bridge rectifier to convert the incoming mains supply into a regulated 432V DC bus bar.

The DC bus bar produced by the rectifier provides both battery charging power and power to the inverter section-which is of a transistorized / IGBT based pulse width modulation (PWM) design and provides the second conversion phase i.e. reconverting the DC bus bar voltage back into an AC voltage waveform.

AMMONIA PLANT

Ammonia is the major constituent in the production of urea and separately in the ammonia plant. This plant has production capacity of 900 M.T. of liquid ammonia per day. We can easily divide the whole process into following different section and discuss.

Then separately according of function of these section:

1. AIR SEPARATION UNIT (A.S.U.)

2. SHELL GASSIFICATION AND CARBON RECOVERY

3. DE-SULPHURION (RECOVERY-1)

4. SHIFT CONVERTOR (CO SHIFT CONVERSION)

5. CARBIN DIOXIDE REMOVAL

6. NITROGEN WASH UNIT (N.W.U.)

7. AMMONIA SYNTHESIS SECTION

1. AIR SEPARATION UNIT (A.S.U.)

Air has following composition:

Nitrogen 78.03%

Oxygen 20.93%

Argon 0.93%

Carbon 0.93%

It is provided for getting oxygen and nitrogen required for production of NH3 from air is the first section from atmosphere and is pre-cooled. Then further cooled in air chiller. Then moisture and dust etc. are removed by passing through alumunia molecular seves.

Final products i.e. N2 and O2 are obtained when air is rectified in the rectifying column.

Product O2 is the first compressed and then led to reactors in shell gasification process. For partial oxidation of food stock for producing raw gas is separated toH2, H2S and CO2, CO2 is send to the urea plant, H2S is sent to sulphur recovery plant. On the other hand N2 and H2 are given to N.W.U. in the ratio of 1:3 to get pure synthesis gas to manufacture NH3.

2. SHELL GASIFICATION AND CARBON RECOVERY

Lines of O2 feedback and stream led to the gasifier column where in the presence of high temperature of the order 13500 C produce raw gas containing CO, H2S, HCN, heat is generated in this unit. This heat is not washed but utilized to produce steam in the waste boiler.

Some unburnt carbon is also present along with other gases in raw gas, as it can check the line. It is removed by stages water wash and there is final scrubbing stage. HCN is also removed in this stage.

3. DE-SULPHURISATION

Sulphur compound are removed in this section because otherwise these poison the catalyst present in the next section. Methanol has a property of absorbing different gases at different temp. Absorption process is carried out at low temp. and high pressure, H2O and COS are removed in the raw gas to only 0.1 PPM in this unit by absorbing with MeOH. MeOH is regenerated by N2 by stripping and H2S is sent to sulphur recovery plant.

4. SHIFT CONVERTOR

In this unit get CO2 and H2 from CO and steam at high temp. by passing the gas catalyst as per the following reaction:

CO(g) +H2O(steam) ......... H2 + CO2In this industrial method of producing H2 as per le chatlier principle for high concentration of product excess is to be introduced and temp. should kept low and reaction rate is high. So compromise is made and temp. is around 350-500 oC. Fe is used as catalyst in reaction.

5. CO2 REMOVAL

In this unit we get a mixture of gas(H2, CO2) from shift conversion and CO2 is removed from H2 by absorbing CO2 with methanol of low temp. This mixture of MeOH and CO2 is stripped by N2 where CO2 is regenerated and send to UREA PLANT, in this unit we get 98% of H2 and send to N.W.U.

6. NITROGEN WASH UNIT (N.W.U.)

Even a little of CO still remains in raw gas after the shift convertor process. This is removed in N.W.U. where liquid N2 is sprayed on raw gas of 98% H2 from the top of the tank. Before leaving this section, purified H2 gas is mixed with N2 in the ratio 3:1 and forms an admixture without reaction, it is called synthesis gas.

7. AMMONIA SYNTHESIS SECTION

The synthesis gas from N.W.U. is compressed from 37 kg/cm2 to 230 kg/cm2 in the centrifugal type synthesis compressor. Then the gas enters the synthesis hot exchanger with hot effluent gas from synthesis economizer. At the outlet of the compressor the gas contains 16% ammonia.

N2 + 3H2 2NH3

1