INDEX

CHAPTER 1.        INTRODUCTION

CHAPTER 2.        PLANT UTILITIES

CHAPTER 3.        POWER GENERATION PLANT

          A)      GAS TURBINE

          B)      GTG

          C)      EDG

          D)      DG SET

CHAPTER 4.        OFF-SITE,AMMONIA AND UREA(ELECTRICAL)

          A)    BASIC EQUIPMENT ASSOCIATED WITH ELECTRICAL IN                      THE PLANT

          B)      UPS

          C       BATTERY CHARGER

          D)      CAPACITOR BANK

          E)      TRANSFORMER

          F)      MOTOR INSTALLED IN AMMONIA PLANT

          G)      MOTOR INSTALLED IN UREA PLANT

          H)      MOTOR INSTALLED IN DM PLANT

          I)      MOTOR INSTALLED IN INSTRUMENT AIN COMPRESSOR

          j)      MOTOR INSTALLED IN COOLING TOWER

CHAPTER 5.        OFF-SITE

           A)      BORE WELL

           B)      COOLING TOWER

           C)      DM PLANT

           D)      ETP

           E)      GAS METERING

           F)      AMMONIA STORAGE

           7)      FLARE SYSTEM

CHAPTER 6.         AMMONIA PLANT

CHAPTER 7.        UREA PLANT

A)     GAS TURBINE:

To meet the power consumption of the total plant two number of gas turbine are installed of 22.4 MW each. Under normal condition only one GAS Turbine will be running at 14.5MW load.

DESCRIPTION

GAS Turbine mainly consists of combustion chamber, compressor, turbine, generator and auxiliary. The air is sucked from the atmosphere and compressed in the compressor. It is then sent to the combustion chamber {10nos} where the fuel is burnt. The high temperature gases at high pressure then expand at the turbine nozzles and make the turbine to rotate by utilizing the heat of combustion. A part of energy supplied is consumed by the compressor to compress the air to 7Kg/cm2.balance energy is used to generate electricity.

INTRODUCTION TO GAS TURBINE

Gas turbines have been used for electricity generation for many years. In the past, their use has been generally limited to generating electricity in periods of peak electricity demand. Gas turbines are ideal for this application as they can be started and stopped quickly enabling them to be brought into service as required to meet energy demand peaks. However, their previously small unit sizes and their low thermal efficiency restricted the opportunities for their wider use for electricity generation. There are two basic types of gas turbines- aeroderivative and industrial. As their name suggests, aeroderivative units are aircraft jet engines modified to drive electrical generators. These units have a maximum output of 40 MW. Aeroderivative units can produce full power within three minutes after start up. They are not suitable for base load operation.
Industrial gas turbines range in sizes up to more than 260 MW. Depending on size, start up can take from 10 to 40 minutes to produce full output. Over the last ten years there have been major improvements to the sizes and efficiencies of these gas turbines such that they are now considered an attractive option for base-load electricity generation. Industrial gas turbines have a lower capital cost per kilowatt installed than aeroderivative units and, because of their more robust construction, are suitable for base load operation.

HOW DOES A GAS TURBINE WORK

Gas turbines use the hot gas produced by burning a fuel to drive a turbine. They are also called combustion turbines or combustion gas turbines. The main components of a gas turbine are an air compressor, several combustors (also called burners) and a turbine.
The air compressor compresses the inlet air (raises its pressure). Fuel is mixed with the high pressure air in burners and burnt in special chambers called combustors. The hot pressurized gas coming out of the combustors is at very high temperature (up to 1350° C). This gas then passes through a turbine, giving the turbine energy to spin and do work, such as turn a generator to produce electricity. As the turbine is connected to its compressor, the compressor uses some (about 60%) of the turbine's energy. Because some of its heat and pressure energy has been transferred to the turbine, the gas is cooler and at a lower pressure when it leaves the turbine. It is then either discharged up a chimney (often called a stack) or is directed to a special type of boiler, called a Heat Recovery Steam Generator (HRSG), where most of the remaining heat energy in the gas is used to produce steam.

The attached cross section of a typical large gas turbine and photo of a similar large gas turbine with its top half casing removed, show these major components.

AIR COMPRESSOR

The air compressors used in gas turbines are made up of several rows of blades (similar to the blades on a household fan). Each row of blades compresses and pushes the air onto the next row of blades. As the air becomes more and more compressed, the sizes of the blades become smaller from row to row. The row of largest blades can be seen at the left end of the compressor in the photo above; with the smallest blades to the right (the direction of air flow is from left to right). Note: A row of blades fixed to the outer casing of the compressor is also located after each row of moving blades. Filters are used to remove impurities from the inlet air. However, as they can never completely eliminate all impurities, "washing" of the compressor blades must be carried out whenever blade fouling becomes too severe. This washing can be carried out on line (with the gas turbine operating) or when the compressor is stopped. Demineralised water and detergent are commonly used for washing. Erosion of the blades can be caused by hard particles in the air entering the compressor. Inspections for fouling and erosion are usually carried out at defined intervals of operating time. This type of air compressor can change its capacity (mass of air sucked through the air compressor) only by changing its speed of rotation. However, when the gas turbine is used to generate electricity, the speed of rotation of the generator, gas turbine and air compressor must remain constant (3000 rpm in Australia). The mass of air being compressed therefore remains constant regardless of the amount of air required for combustion of the fuel at partial loads. The energy used to compress this excess air accounts for most of the reduction in efficiency of a gas turbine at partial loads.

FUEL
Gas turbines can operate on a variety of gaseous or liquid fuels, including
Liquid or gaseous fossil fuel such as crude oil, heavy fuel oil, natural gas, methane, distillate and "jet fuel" (a type of kerosene used in aircraft jet engines);
Gas produced by gasification processes using, for example, coal, municipal waste and biomass; and Gas produced as a by-product of an industrial process such as oil refining.
When natural gas is used, power output and thermal efficiency of the gas turbines are higher than when using most liquid fuels.
The fuel must be free of chemical impurities and solids as these either stick to the blades of the turbine or damage the components in the turbine that operate at high temperature. The fuels used in gas turbines power generation plants are often relatively more expensive and in smaller quantities than those required by power generation plants using other fuels (such as coal).

INLET AIR

The air coming into the compressor of a gas turbine must be cleaned of impurities (such as dust and smoke) which could erode or stick to the blades of the compressor or turbine, reducing the power and efficiency of the gas turbine. Dry filters or water baths are usually used to carry out this cleaning. The power and efficiency ratings of a gas turbine are usually based on the inlet air being at ISO conditions of 15° C and 65% relative humidity. If the inlet air is hotter and drier than ISO conditions, the power of the gas turbine decreases. This effect can be reduced by cooling the air (by equipment similar to air conditioners) or, more usually, by passing the air through an evaporative cooler (the air evaporates droplets of water, thus cooling the air). The inlet air is usually passed through silencers before it enters the compressor.

Burners and Combustors
The compressed air and fuel is mixed and metered in special equipment called burners. The burners are attached to chambers called combustors. The fuel & air mixture is ignited close to the exit tip of the burners, and then allowed to fully burn in the combustors. The temperature of the gas in the combustors and entering the turbine can reach up to 1350° C. Special heat resistant materials (such as ceramics) are used to line the inside walls of the combustors. The area between the combustors and the turbine are also lined.
Water or steam can be injected into the combustors to reduce the concentration of NOx (oxides of nitrogen) in the exhaust gas (by reducing the temperature of the flame). Special burners (usually called "dry low NOx burners") are used to reduce the concentration of NOx in the exhaust gas to less than 25 ppm at full load, without the use of water or steam injection. These dry low NOx burners usually cannot operate effectively below about 60% load. At this point, another type of burner takes over and allows the fuel to be burnt stably down to low loads. These "low load" burners produce significantly higher concentrations of NOx (over 100 ppm). Some burners incorporate both types of burner into the one arrangement (called "hybrid" burners). Note: the values of NOx concentrations and loads depend on the design of the equipment and on the fuel used.
When a gas turbine starts, the combustor quickly heats up. When the gas turbine shuts down, the combustor cools. This rapid heating and cooling produces stresses in the combustor and can cause cracking, particularly in the heat resistant lining material. The combustors must be inspected for cracks after a certain number of starts. The turbine (also called the "power" turbine) consists of several rows of blades (the "moving" blades) that are fastened to the rotating shaft of the turbine. A row of "fixed" blades is located after each row of the "moving" blades. These fixed blades are attached to the casing of the turbine and do not rotate.
As the hot gas from the combustors passes through the moving and fixed blades of the turbine, energy is transferred from the hot gas to the turbine, causing it to rotate. This energy transfer reduces the pressure of the gas and causes the gas to become cooler as it passes through the turbine. The blades of the turbine become larger from row to row to accommodate the expansion of the gas as its pressure reduces. The smallest row of blades can be seen at the left end of the turbine in the photo of the gas turbine with its top half casing removed, with the largest blades to the right (the direction of gas flow is from left to right). The moving blades in the turbine are subjected to extreme temperature (from the hot gas exiting the combustors) and stress (from the combination of their rotation and the pressure of the hot gas). The efficiency of the gas turbine improves if the hot gas temperature rises. New materials and techniques used to manufacture the turbine blades have resulted in a significant increase in operating temperatures. Currently, turbine blades are made from exotic alloys that retain their strength at the high temperatures experienced in the turbine. Ceramic blades offer the possibility of still higher operating temperatures. However, materials to withstand the higher temperatures are usually more expensive than those that can withstand lower temperatures. The materials for the turbine blades (and other components of the turbine) are therefore selected to give a balance between hot gas temperature (and efficiency) and material selection (and cost). Research into better (and cheaper) materials for these high temperatures, high stress duties are ongoing.
Turbine blades can be manufactured with passages inside the blades that allow air to pass through the blades to keep them cool. The compressor section of the gas turbine provides this cooling air. This allows the blades to operate in combustion temperatures that would otherwise be too hot for the material of the blades.
At these high operating temperatures, hard particles and chemical impurities in the air and fuel (even at extremely low levels) can damage the blades of the turbine, thus reducing their effectiveness. The ability of the gas turbine to do work and the efficiency of the gas turbine are consequently reduced. Some of this reduction can be regained by maintenance of the gas turbine. The type and cleanliness of the air and fuel used therefore has a major impact on the amount of maintenance performed on the gas turbine. Various coatings for turbine blades have been developed as another way to minimise this high temperature damage to the blades.
The hot components of the turbine, particularly the blades, are also subject to "creep" failure. Metals at high temperature & high stress gradually change their metallurgical properties and plastically deform ("creeps"). This deformation could result in the moving parts touching the fixed parts with possible catastrophic results. The turbine components most subject to conditions causing creep are regularly inspected and tested.

Exhaust Gases
The temperature of the exhaust gas from the gas turbine is typically in the range of 500°C to 640°C, depending on the design of the gas turbine and the fuel used. The heat energy in this gas can be extracted in a Heat Recovery Steam Generator (HRSG) to produce steam that can be used to produce electricity (Combined Cycle generating plant) or used for process heating. If the exhaust gas is not passed to a HRSG, it is ducted through a silencer and then discharged up a stack. The exhaust gas is usually visually clear and free of particles. Refer to "emissions" for information on the chemical compositions of the exhaust gas.

Emissions
The main chemical emissions from a gas turbine are dependent on the type of fuel used. However, some generalizations can be made.NOx (oxides of nitrogen) can be controlled either by injecting water or steam into the combustors or by using special dry low NOx burners. Further details of these are given in the "burners and combustors" section above.
SOx (oxides of sulphur) are usually not a problem as most fuels used in gas turbines have low sulphur contents. The concentration of CO2 (carbon dioxide) in the exhaust gas is dependent on the carbon content of the fuel used. The amount of CO2 produced per unit of electrical energy is also highly dependent on the thermal efficiency of the gas turbine.

Power Output
Gas turbine output power values are usually given for ISO conditions of 15° C, 60% relative humidity and an atmospheric pressure equivalent to average sea level conditions. Variations in these conditions during the operation of the gas turbine will result in changes to the power output of the gas turbine as indicated below.

B)          GTG (GAS TURBINE GENERATOR)

In the plant the power is generated by 2 no. GTG (one running and one stand by) made by BHARAT HEAVY ELECTRICAL LIMITED, HYDERABAD.

GENERATOR

The two pole generator uses direct air cooling for the rotor winding and indirect air cooling for the stator winding. The losses in the remaining generator component; such as iron losses,friction and winding losses and stray losses are also dissipated through air.

The generator consists of the following components:

1. STATOR

Stator frame

Stator core

Stator winding

Generator filter

Stator end cover

2. ROTOR

Rotor shaft

Rotor winding

Rotor retaining rings

3. BEARINGS

4. SKID

The following additional auxiliaries are required for generator operation:

OIL SUPPLY SYSTEM

EXCITATION SYSTEM

SPECIFICATION OF GAS TURBINE GENERATOR

A)  GAS TURBINE

MAKE                         :          BHEL

FUEL                          :          NATURAL GAS/NAPHTHA

BASE LOAD              :            20810/20260 KW

COMPRESSOR          :      17 STAGES

TURBINE                   :      2 STAGES

RPM                            :      1100

AIR IN TEMP             :      40 DEG C

EXHAUST TEMP       :     520 DEG C

B) GTG MOTOR DETAILS

A) 88 VG (LOAD GEAR COMPT VENT FAN), 415 VOLT

      THREE PHASE INDUCTION MOTOR, 415V

      KW        :       3.7

      RPM                      :       1430

      FLC                        :      7.6A

      FRAME                        :      LE112

      BEARING               :      6306ZZ/6206ZZ FOR DE/NDE

      INS CLASS             :      B

      PROTECTION        :      FLAME PROOF (EX)

      MAKE                     :      KIRLOSKAR

B)  88 FT/BT (COOLING AIR FAN MOTOR)

       THREE PHASE INDUCTION MOTOR, 415V

       KW                        :      7.5

       RPM                        :       1450

       FLC                        :       15A

       INS CLASS              :       H

       BEARING SHOULD BE 6309ZZ/6309ZZ FOR DE/NDE

       PROTECTION        :       FLAME PROOF (EX)

       FCP                         :       GROUP I

       MOUNTING               :       B3

       FRAME                         :      E160L

       MAKE                         :      CROMPTON GREAVES

       IP                                 :      55

       AMB                         :      50DEG C

C) SCANNER FAN

      THREE PHASE INDUCTION MOTOR, 415V

       KW        : 15

       RPM        : 2900

       FLC        : 27A

       INS CLASS        : F

       BEARING SHOULD BE 6309ZZ/6309ZZ FOR DE/NDE

       PROTECTION        : FLAME PROOF (EX)

       MOUNTING        : B3

       FRAME        : E160L

       MAKE        : CROMPTON GREAVES

1. AVR SENSING P.T  & C.T  DETAILS

AVR SENSING P.T:-RATIO 11KV/3 / 110/ 3

                                     BURDEN- 40VA/ PHASE

                                     ACC. CLASS – 0.5

AVR SENSING C.T:- RATIO 2000/1 AMP

                                      BURDEN – 40VA

                                      ACC. CLASS – 0.5

                                      CT2 MOUNTED IN L2 PHASE, CT1 MOUNTED IN L1 PHASE

2. GENARATOR DATA

• RATED APPARENT OUTPUT      :-28MVA
• RATED ACTIVE OUTPUT            :- 22.4MW
• RATED VOLTAGE                  :-11KV
• RATED CURRENT                          :-1469.6A
• RATED POWER FACTOR              :-0.8LAG
• RATED FREQUENCY                     : -50Hz
• RATED SPEED                                :-3000RPM
• FIELD RESISTANCE AT 20ºC       :-0.2085 OHMS

    3)   MAIN EXCITER DATA

• RATED OUTPUT                                :-121KW
• RATED VOLTAGE                               :-196V
• RATED CURRENT                               :-650A
• CEILING VOLTAGE FOR 10SEC         :- 294V
• CEILING CURRENT FOR 10SEC         :-896A
• RATED SPEED                                :-3000RPM
• FIELD RESISTANCE AT 20ºC         :-3.3OHMS

4) PERMANENT MAGNET GENERATOR DATA

• RATED OUTPUT                         :-8KVA
• RATED VOLTAGE                        :-220V
• RATED CURRENT                        :-26A
• RATED FREQUENCY                           :-150Hz
• RATED SPEED                                    :-3000RPM

D) AOP (Flame proof induction motor)

• KW                                                      37

• RPM                                                    2950

• VOLT                                                  415
• AMP                                                     62
• DUTY                                                   S1
• INS.CLASS                                          ST  F
• PH                                                         3
• FRAME                                                BLE 225M
• ROTOR CONNECTION                     DELTA
• IP                                                          55
• GROUP                                                2A,2B  ENCLOSURE

E)   DS MOTOR (DC MOTOR)

• HP                                                             10
• RPM                                                          1750
• VOLT                                                        125 V DC
• INS.CLASS                                               F
• FLD VOLT                                               125
• FLD AMP                                                 1.0
• AH                                                             473
• WOUND                                                    SHUNT

• MAX .AMB. TEMP                                  65 DEGC

F)  AHOP

• KW                                                                      9.3

• RPM                                                                    1450

• FLC                                                                     18.5 A
• VOLT                                                                  415 AC
• FRAME                                                               E160LC

G)  EOP

• KW                                                                                  7.5
• RPM                                                                                1750
• Volt                                                                                  120V DC

 H)  HR (RACHET MOTOR)     

• HP                                                                                   0.75
• RPM                                                                                1725
• Volt                                                                                125V DC

EXCITOR

The excitor consist of RECTIFIER WHEEL,3 PHASE PILOT EXITOR,3 PHASE MAIN EXITOR,METERING AND SUPERVISORY EQUIPMENT.

BASIC ARRANGRMENT OF EXCITATION SYSTEM

1. PMG (PERMANENT MAGNET GENERATOR)

2. AVR (AUTOMATIC VOLTAGE REGULATOR)

3. MAIN EXITOR

4. ROTATING DIODE

The 3 phase PILOT EXITOR has a revolving field with permanent magnet poles. The 3 phase a.c is fed to the field of main excitor via a stationary regulator and rectifier unit. The 3 phase a.c induced in the rotor of main excitor is rectified by the rotating rectifier bridge and fed to the field winding of generator rotor through the dc load in the rotor shaft.

The 3 phase PILOT EXCITOR is a 6 pole revolving armature unit. Each pole consists of separate permanent magnet which is housed in non magnetic metallic enclosure.

The 3 phase main excitor is a 6 pole revolving armature unit arranged in the frame is the poles with the field and damper winding. The field winding is arranged on the laminated magnetic poles. The rotor consists of stacked lamination which is compressed by through bolts over compression rings. The 3 phase winding is inserted in the slot of the laminated armature.

AVR (AUTOMATIC VOLTAGE REGULATOR)

The AVR is a solid state, THYRISTOR CONTROLLED EQUIPMENT with very fast response. It has two channels” auto channel” for voltage regulation and “manual channel” for field current regulation. Each channel has its own firing circuit and thyristor converter for reliability. All the circuitry work on the power supply 220 volt, 150 HZ, 3 phase provided by PMG.

Specification

AVR

• MODEL NO.                                              :-1-48-2570-01,1-48-2572-01
• DPG. NO.                                            :- 3-655-00-05094
• REGULATOR TYPE                                :- THYRISTOR CONTROLLED
• ACCURACY                                         :- ±0.5% Un
• TEMP. RANGE OF OPERATION                            :- 0-50ºC
• NORMAL INPUT VOLTAGE TO AVR            : - 220V, 1Ph, 150Hz.
• STATION DC SUPPLY                              :- 220V, +10%, -15% DC FROM BATTERY
• FOR ILLUMINATION & HEATING                 240V , 1Ph, 50 Hz
• TEST SUPPLY TO AVR                                : - 415V, 3Ph, 50Hz.
• MAIN EXCITER FIELD REQUIREMENT

AT RATED GEN. VOLTAGE ON NO LOAD         :-4.4A, 17V

• MAIN EXCITER FIELD REQUIREMENT

AT RATED LOAD & PF OF GEN.                               :-12.0A, 48.3V

• MAIN EXCITER FIELD REQUIREMENT

DURING CEILING CONDITION                          :-32A, 120V FOR 10 SEC

EDG SET

  This is unique feature in our plant that we don’t have any other source of power supply other than GTG. The total demand of plant is met by GTG. During any failure in Gas turbine the minimum requirement for the safe shutdown of the plant and GTG restart up is met by EDG. It is 22.4 MW diesel generating power set at 415 KV. Provision has been made that in case of power failure the diesel engine will take start automatically and will supply power within 15-20 Second to some of the important equipment kept at emergency power supply.

SPECIFICATION

Crompton greaves brushless exciter

RECT DC KW                                                            17.5

RPM                                                                            1000

POLES                                                                        16

FREQUENCY                                                            133.3 HZ

RECT DC VOLT                                                        60 AMP            291

FIELD VOLT                                                             80 AMP             8.0  

INS.CLASS                                                                 F

FRAME                                                                      XL 53/16

M/C NO.                                                                     DG 9301                                  

OFF-SITE,AMMONIA AND UREA (ELECTRICAL)

A) BASIC EQUIPMENT ASSOCIATED WITH ELECTRICAL IN PLANT:

UPS (UNINTERRUPTIBLE POWER SUPPLY)

Make TATA LIBERT

7400 SERIES 1+1 CONFIGURATION

The one-plus-one UPS system is connected between critical loads like computer, MK-IV DAS, interconnecting panel etc. and its three phase mains power supply.

System offers the user the following:

1. Increased power quality
2. Increase noise rejection
3. Power blackout protection

The one plus one system comprises two standard 7400 series UPS modules which are modified to allow their outputs to be connected in parallel. These can then be used in a Redundant or non-redundant configuration. The advantage of redundant over non redundant system in terms of over all system reliability.

7400 Module design- 7400 UPS single module block diagram shown in figure 1.UPS basically operates as an AC-DC-AC converter. First conversion stage from AC to DC uses a fully controlled SCR bridge rectifier convert incoming main supply to a regulated 432 V dc bus bar. The DC bus bar produced by the rectifier provides both the battery charging power and power to Inverter section which is a transistorized pulse width modulation design and provides the second conversion phase i.e. reconverting DC bus bar voltage into an ac voltage wave form. Static switch contains an electronically controlled switching circuit which enables the critical load to be connected either to the inverter output or to a bypass power via the static bypass line.

During normal operation both rectifier and inverter section are active and provide regulated load power also charging the battery. In the event of mains power failure Rectifier becomes inoperative and inverter is powered from battery. Critical load power is maintained under this condition until the battery is fully discharged. The end of battery discharge is assumed when battery voltage falls to 320v dc.

The period for which load can be maintained followed a mains power failure is known as system’s Autonomy time. This depends upon the battery A/Hr capacity and applied load. To provide a clean load transfer between the inverter output and static bypass line, they must be fully synchronized during normal operating condition. This is achieved by the inverter control electronics which make the inverter frequency track that of the static bypass supply.

Second maintenance bypass supply is also incorporated for the purpose is to enable a critical load to be powered from the mains (bypass) while the UPS is shut down for maintenance or troubleshooting.

The load is unprotected against mains power supply failure when it is connected to static bypass or maintenance bypass supply.  

DC Source (Battery bank and battery charger)

Dc source is essential in a substation for the following purpose:

1. Protective relaying
2. Circuit breaker operation
3. Telephone exchange
4. Emergency lighting systems etc.

Various dc systems in our plant are at 220V, 110V, 125V, 48V, 24Vetc.

Low voltage dc system comprises of battery bank, battery charger, bus bar and dc distribution panel, protection system etc.

Procedure for commissioning a new battery bank:

1. Battery bank installed in a special room. Battery room should have adequate ventilation and lighting. Floor and walls should have acid resistance tiles. Battery cells are placed on racks. Rubber or porcelain insulation is provided between each cell and rack. The terminals are covered by grease or Vaseline.

2.  Electrolyte preparation: while preparing electrolyte, acid should be poured in water and never water into acid. Specific gravity of electrolyte should be maintained 1.22 to 1.23.

              Specific gravity                                         State of charge

                    1.22 to 1.23                                                100% charged

                  1.2 to 1.21                                                75% charged

1.175 to 1.185                                        50% charged                                 1.15 to 1.16                                                25% charged        

             Below 1.15                                                discharged

Charging: while charging positive terminal of charger connected to positive terminal and negative of charger connected to negative terminal of battery. During charging, water from electrolyte evaporates. It should be made up by adding small quantity of distilled water. Charging of battery is indicated by evolution of gas bubbles. Voltage rating of initial charging should be 1.15xNxV where N is the no. of cell and V=2.75V.

      Capacity of battery system is specified in ampere-hours. It is AH which can be obtained from charged battery before reaching to minimum voltage. It is a product of discharge current and time of discharge.

Max. Discharge current = cont. load + short time load

                                             Rated voltage

The battery gets discharged at its own even when not in use due to impurity in electrolyte cause sulphation. Hence to avoid this battery should keep constantly charged at trickle charging.

Open circuit voltage                                state of charge

2.07 and above                                        fully charge

2.05                                                        ¾ charge

2.03                                                        ½ charge

2.00                                                        ¼ charge        

 Below 1.75                                                fully discharge

Charging of battery done by battery charger. Battery charger is generally static rectifiers and tapped transformer dc supply. Source of battery should have a 2.5V min. per cell.

 BATTERY

BATTERY ARE USED TO CONVERT CHEMICAL ENERGY INTO ELECTRICAL ENERGY THROUH ELECTROCHEMICAL PROCESS

1. PRIMARY BATTERY: WHICH CANNOT BE RECHARGED.
2. SECONDARY BATTERY: WHICH CAN BE RECHARGED.

TYPES OF SECONDARY BATTERIES:

1. LEAD ACID BATTERY.
2. Ni – Cd BATTERY, etc.

THERE ARE TWO TYPES OF SECONDARY BATTERY AVAILABLE IN THE MARKET :

1. MAINTENANCE FREE
2. BATTERIES WHICH REQUIRE PERIODIC MAINTENANCE

   DIFFERANT TYPE OF LEAD ACIDBATTERIES:

1. STATIONARY, TUBLER PLATE S
2. STATIONARY, PLANTE PLATES
3. SEALED LEAD-ACID BATTERY.

    WE ARE USING:

HERE WE ARE USING ‘EXIDE’ LEAD ACID BATTERIES   WHICH HAS RUGGED TUBLAR POSITIVE PLATES AND PASTED NEGATIVE PLATES.

THE POSITVE ACTIVE MATERIAL IS ENCASED IN A ONE –PIECE, MULTI-TUBE WOVEN GAUNTLET OF HIGH TENSILE ACID-RESISTANCE POLYSTER.THE POLYSTER ‘GAUNTLET’ WHICH IS RESIN IMPREGNATED, COMBINES HIGH TENSILE STRENGTH WITH RESILIENCE AND ENABLES THE ELECTROLYTE TO PENETRATE FREELY.      

THE PASTED NEGATIVE PLATES ARE DESIGNED TO MATCH THE                  POWER AND LONG LIFE OF THE TUBLAR POSITVE PLATES. THE NEGATIVE PLATE IS RETAINED FIRMELY IN PLACE BY THE STURDY GRIDS DESIGNED TO LOCK IT IN.THE CHEMICAL REACTION TAKE PLACE DURING CHARGING & DISCHARGING AT ANODE (Pb02) & CATHODE (Pb) ARE GIVEN BELOW:

CHARGING:  

ANODE:        PbSO4 + SO2 + 2H2O                                PbO2 + 2H2SO4

CATHODE:            PbSO4 + H2                                 Pb + H2SO4

        * ANODE BECOME DARK CHOCLATE BROWN ( PbO2 ) & CATHODE BECOME   GRAY ( Pb )

* SP. GRAVITY INCREASE AS WATER CONSUMES.

* RISE IN VOLTAGE.

DISCHARGING:

ANODE:       PBO2 +H2 + H2SO4                   PBSO4 + 2H2O

CATHODE:  Pb +H2SO4                  PbSO4 + H2            

 * BOTH ANODE & CATHODE GET WHITE DUE TO FORMATION OF PbSO4.

 *SP. GRAVITY DECREASES AS WATER FORMS.

 *CELL VOLTAGE DECREASES.

FLOT / TRICKLE CHARGING: BATTERIES ARE TO BE MAINTAINED WITHIN THE FLOT VOLTAGE RANGE 2.25 TO 2.30 VOLTS PER CELL.

THE TRICKLE CHARGING OF THE CELL IS SO ADJUSTED, ANYWHERE BETWEEN THE MAXIMUM AND MINIMUM ALLOWED LEVELS GIVEN IN PRESCRIBED TABLE (e.g. 600 TO 2400 mAMP FOR TL600H TYPE BATTERY), SUCH THAT INDIVIDUAL CELLS REMAIN FULLY CHARGED.

MAINTENANCE:  THE CONVENTIONAL LEAD-ACID BATTERIES SHOULD BE MAINTAINED IN FOLLWING MANNER,

1. LEVEL OF ELECTROLYTE SHOULD BE MAINTAINED BETWEEN PRESCRIBED LIMIT BY ADDING DM / DI WATER. BUT DON’T ADD ACID.
2. MEASUREMANT OF CELL VOLTAGE AND SPECIFIC GRAVITY. SP. GRAVITY SHOULD BE BETWEEN 1.180 TO 1.200. IF IT IS BELOW 1.800 THEN THERE IS SOME PROBLEM IN BATTERY. CELL VOLTAGE SHOULD NOT BE LESS THEN 1.8 VOLTS
3. DAMAGE  & FAULTY CELL SHOULD BE REPLACED
4. TERMINAL SHOULD BE CLEAN & COVERED WITH GELLY.

CHARGING & DISCHARGING SHOULD BE DONE TO AVOIDE SULPHANATION

Capacitor bank:

Boiler Feed Water pump (11 KV 1300 KW Motor)

Specification         :                IS325                                CONN                  :         STAR

Frame                   :                1LA7805 2HE902                AMB. TEMP       :        46C

DUTY                           :                CONT.                        STATOR AMP    :         78.2

KW                               :                1300                                ROTOR TYPE    :         CAGE

RPM                     :                2985                                PROT                    :         1PW55

STATOR VOLT :                11KV                                DE / NDE              :         125X115

TEMP. RISE       :                74C                                  SR.NO.                :        42018A421-21-04

INSUL CLASS    :                 F                                DEVISION            :         BHOPAL

PHASE                 :                3                                YEAR                    :         1994

HZ                        :                50

3.3 KV , 565 KW motor

This motor is used in application of CO2 booster compressor Specification of the motor is as follows-

Make: BHEL                                        Spec Ref: IS-325

Frame: 1MA 7630                                Rotor Type: SQ CAGE

Duty:  Cont                                        DE   Sleeve 100x120

KW   :  565                                        NDE Sleeve 85x100

RPM: 2975                                        Insulation Class: F

VOLT: 3300V, 3Phase, 50Hz                        Degree of Protection: IPW-55

Amb: 46 deg c                                        Stator Amp: 118

Heater Rating: 240V, 630W                        Weight: 4600kg

Sr. No.42017A411-31-01                        Mfr. Year: 1993

Oil Flow: 2.5LPM,                                Oil pressure: 0.2bar

Lube Oil: IOC Servo system 40 or equivalent  

 OFFSITE AND UTILITIES

       INTRODUCTION:  M/S KRIBHCO SHYAM FERTILISERS LTD, Shahjahanpur is one of the Natural gas based plant approved by Govt. of India. It is based on Natural gas as raw material for the fuel and feed in Ammonia plant supplie by M/S GAIL, through HBJ pipeline network.

  The off-site plant is meant to supply all the utilities requtred for the production of Ammonia and Urea in this

Ammonia-Urea complex.The company known utilities required by any of the industry are Power, Water, Air and

Steam supply of all these utilities are controlled by Off-site plant. This plant consists of following sub plant:

Power generation

Steam generation

Raw water

Dm water

Fire water and fire pump house

Cooling water

Instrument air

Effluent treatment plant

EDG set

Ammonia storage

Naphtha storage

Nitrogen storage

                                 Motor selection in hazardous area

The normal motors are considered as potential explosion hazard under abnormal condition due to their high probability of energy release for the following reasons:

1.  High surface temperature due to heat generation by inevitable losses.

2.  Generation of spark between the live terminal and earth.

3.   Partial discharges occurring in embedded insulation in the slots.

4.   Sparks in air gap of high speed machine due to vibration of cage rotor bar in the slot.

There are seven different types of explosion protection of machine and enclosures are identified:

1. Ex’i’     :        intrinsic safety

2. Ex’d’    :       flameproof enclosure

3. Ex’e’    :       increased safety features

4. Ex’p’    :       pressurized enclosure

5. Ex’o’    :       oil immersion

6. Ex’q’    :       powder filled

7. Ex’n’    :       non-sparking

 Ex--------------

 Place

1st   Ex- explosion proof

2nd   Ex-type of protection :( ‘n’, ‘e’, ‘d’, ‘p’)

3rd    gas group    :( 1, 2A,2B,2C)

4th    ignition temperature class    (T1…………..T6)

                                  Selection of enclosure type

It is governed by four factor of gases

1.  frequency of presence of a dangerous concentration of gases or mixture of explosive gases.

2.  arcs or sparks in apparatus which under normal condition do not produce any arc or spark.

Time ‘te’:  it is the time taken for the A.C winding to reach the limiting temperature(as per temperature class) from the temperature under rated service at maximum ambient temperature, when the starting current is flowing in the primary parts.

Time ‘te’ shall not be less than 5 seconds.

Features:

1. Stator winding temp.limit under normal operation shall be 10 deg C less than normal

2. Motor to be squirrel cage only.

3. Degree of protection should be at least IP 23 for the motor and IP55 for the terminal box.

Features of non-sparking Ex’n’ motors

1. non-sparking (vibration proof terminals)

2. Adequate creepage distance and clearances.

3. Adequate tightness of rotor bars in the slots and brazed end rings to prevent sparking while starting.

4. Adequate clearance between motor and stator.

5. IP 55 enclosure by virtue of the location.

6. Terminal box to withstand through fault without damage.

Features of pressurized Ex’p’ motors:

A protective gas(inert gas or air) is continuously maintained at a minimum over pressure above that of   Above that of external atmosphere.

INSULATION ASPECT OF H.T MOTORS AND MAINTENANCE OF WINDINGS:

Mica is the main constituent as dielectric material. The binders i.e. epoxy or polyester resin plays an important role in deciding electrical, mechanical, environmental properties of the insulation system.

Mica being an inorganic material degradation due to thermal and electrical stresses is minimal.

  1.Zone                    Probability of explosion                                     Type of protection

                                     hazard

                                                                                     Ex’e’                  Ex’d’                   Ex’p’                        

  0                        Always                                        ……………        not permitted        ……………..

  1                        frequent                                       not permitted       …………….         Permitted

  2                         occasional seldom                                                      Permitted

   Type of motor: Squirrel cage motors are permitted with all type of protection.

   Type of duty: continuous (S1)

    Ignition temperature group:

    Flame proof enclosure: the essential apparatus with flame proof enclosure is…..

1. That hazardous atmosphere is not excluded from entry in to the enclosure.

2. That an explosion/ignition may occur with the apparatus but the construction of the enclosure is such as to

a) Withstand the internal explosion/pressure build up without any damage.

b) Prevent the spread of flame from internal ignition of gases to the surrounding explosive atmosphere.

SOME IMPORTANT COMPONENT OF FLAMEPROOF MOTORS:

STATOR FRAME: The stator frame is of welded construction. It is made from extra thick plates to withstand explosion pressure .The end shield at DE and NDE are disk shaped.

The degree of explosion hazard at a particular place has been classified in to three principal zones:

• ZONE 0(Div 0): Area where an explosive gas atmosphere is continuously present. no electrical motor are allowed to be used.
• ZONE 1(Div1): Area where an explosive gas atmosphere is likely to occur during normal operation  electrical motor with explosion containment (Ex’d’) or with explosion prevention (Ex’p’) are allowed to be used.
• ZONE 2(Div 2): Area where an explosive gas atmosphere is not likely to occur during normal operation, if it is only for short period. Motors with increased safety features (Ex’e’,Ex’n’) are allowed to be used.

The type of explosion hazard is further classified by ignition temperature of explosive gas mixture

This is designated as temperature class as shown below….

TEMPERATURE CLASS                                             MAX. SURFACE TEMPERATURE

T1                                                                                                450

T2                                                                                                300

T3                                                                                                200

T4                                                                                                135

T5                                                                                                100

T6                                                                                                85

The explosive mixture is further classified depending upon the minimum energy required to raise the temperature threshold of ignition temperature as gas group:

 GAS(PRINCIPAL)                             GROUP NO.           MIN.IGNITION ENERGY

 Methane                                                      1                                              280

Propane                                                        2A                                           260

Ethylene                                                       2B                                           85

Hydrogen                                                     2C                                           19                                        

MOTORS IN AMMONIA PLANT (HT AND LT MOTOR)

LIFT MOTOR IN PRILLING TOWER

Specification

.MACHINE NO.                                                     : AEV39793T

KW                                                                         : 10.3/2.58

VOLT                                                        :415+-10%

AMB TEMP                                                           : 50 DEG CELSIUS

RPM                                                                       : 975/246

POLES                                                                   : 6/24

HP                                                                          : 14/3.5

IP                                                                           : 55

FRAME                                                                 : E 280M

IS                                                                           : 325,2148

TRANSFORMER SPECIFICATION

1.      2 MVA TRANSFORMER (CROMPTION GREAVES)

KVA                                                 2000

VOLT (No load)                               HV      11000

                                                          LV   433

AMP                                       HV   105

                                                          LV   2666.7

PHASE                                             HV   3

                                                          LV   3

TYPE OF COOLING                      ONAN

FRQUENCY                                    50 HZ

CONNECTION SYMBOL              DYN 11

CORE AND WINDING                  2570 KG

WT. OF OIL                                    1310 KG

TOTAL WT.                                    6010 KG

OIL                                                   1415 LITRE

MAX TEMP RISE IN OIL              50 DEG C

2.    2.5 MVA TRANSFORMER

     KVA                                                              2500

     VOLT (NO LOAD)                          HV       11000

                                                               LV        3450

     AMP                                                 HV         131.2

                                                               LV         418.4

      PHASE                                            HV         3

                                                               LV          3

      FREQUENCY                                 50 HZ

      TYPE OF COOLING                      ONAN

      CONNECTION SYMBOL              DYN 11

    CORE AND WINDING                    3750 KG

     WT. OF OIL                                     2500 KG

    TOTAL WT.                                      8980 KG

    OIL                                                     2850 LITRE

     MAX TEMP RISE IN OIL               50 DEG C

    3.     6 MVA TRANSFORMER

    KVA                                                              6000

    VOLT(NO LOAD)                                       HV  11000

                                                                          LV   3450

 AMP                                                                 HV    314.9

                                                                           LV     1004.1

 PHASE                                                             HV    3

                                                                           LV     3

TYPE OF COOLING                                        ONAN

 FREQUENCY                                                  50 HZ

CONNECTION SYMBOL                                DYN 11

         TRANSFORMER MAINTENANCE AND PROTECTION

1.   INTRODUCTION:

 In electrical distribution system transformer is used for efficient distribution of electrical energy from generation

 To end consumer and comes in between .therefore to ensure continues uninterrupted power to equipment at user end maintenance of transformer should be proper as well as suitable protection to provide to protect transformer from abnormality.

TRANSFORMER may have been of different type according to use or construction features, like power

Transformer, distribution transformer, step-up or step-down etc and they may be of shell type, core type etc.

There are no of components contains complete unit and these should be maintained properly for long life of transformer

as well as with no breakdown.

TRANSFORMER MAINTENANCE:

• TRANSFORMER WINDING:

Recording of IR value with respect to earth,between primary and secondary and resistence every year and

comparing with commissioning value these should be equal or more.

• TRANSFORMER OIL:

Used for cooling and insulation,therefore breakdown value(BDV) of oil should be tested every year it may be around 45KV.

Dissolve gas analysis and other test should should be carried out once in a two yearwhich indicate different type of fault developing in side of transformer and condition of oil.

• RADIATOR:

Its function is to dissipate heat carried by oil from winding to atmosphere hence all walve should be open and fins are cleaned

as well as no leakage of oil from there.

• BREATHER:

It is used for breathing when transformer oil contract and expand according to temperature variation hence path should be clear and silica gel to be checked daily for change in color(always blue) and oil in cup up to marked level.

• CONSERVATOR TANK:

No leakage of oil and should be air tight.

• EXPLOSIVE VENT:

Used for release of sudden pressure while any fault occurs in side of transformer as diaphragm rupturing therefore diaphragm rupturing therefore diaphragm should be proper and it is not broken otherwise undesired path of breathing may take place.

• OIL AND WINDING TEMPERATURE INDICATOR:

Should be in working condition because protection of transformer depends on these indicators. Tight all CT connection

and fill oil pot with oil. Reading of OTI &WTI should be recorded once a day and WIT should be more than OTI.

• BUSHINGS:

All primary and secondary side and CT bushing should be checked for any oil leakage and tightness.

• OIL LEVEL GAUGE:

MOGL and glass level should be checked for any stuck up and reading to be noted once on a day.

• BUCHHOLZE RELAY:

This is a gas operated relay for protection of transformer during the fault and should be tested once in a year.

All connection should be tight.

• MARSHALING BOX:

All connection should be tight and alarm contact should be simulated for proper checking of circuit.

• METHOD OF CHECKING TRANSFORMER OIL:

      A sample of insulating oil is taken from the bottom of transformer tank in a standard   oil test cell. Oil in a good condition has pale yellowish color. It is tested by means of a

portable oil testing set which consist of auto transformer,voltmeter,tripping device etc. Oil in a good condition should withstand 45KV RMS for one minute in a standard oil testing cup with 4mm gap between electrode.

PI= ln R 10 min/ln R1 min

PI gives a quantitative information about the insulation with respect to moisture dist etc.Recommended PI value

For clean dry machine winding for class A insulator is 1.5 or more,for B insulation 2.0 or more. As a rule,a machine could

Be safely returned to service if PI is 1.5 or more.

PROTECTION OF TRANSFORMER:

1.By local accessories mounted on the transformer.

2.By external relaying mountrd on the control panel.

1. Protection by local accessories mounted on the transformer.

a) Oil temperature indicator (OIT)                          Alarm-70                               Trip-75

b) Winding temperature indicator (WTI)                 Alarm-80                               Trip-85

c)Explosion vent                          

d)MOG(Magnetic oil gauge)

e) Bucholz relay (gas actuated relay)

f) Sudden pressure relay (for more than 25MVA T/F)

g)lighting arrester(for more than 25MVA T/F)

h) DGA (Dissolve Gas Analyzer)

Basically seven type of gases which are found as dissolved gases in oil. The limit are given

As:

S.NO.       PARAMETERS                   PROBABLE CAUSE                          LIMITS (ppm)

1.              Methane (CH4)                        local overheating                                          120

2.              Ethane                                      overheating                                                   65

3.              Ethylene                                   thermal degradation of oil                          60

4.              Acetylene                                 arcing and sparking                                      35

5.              Carbon mono oxide                  thermal aging of paper                               350

6.              CO2                                        cellulose decomposition                               N/A

7.              Hydrogen                                  thermal/electrical fault                                  100

Protection of transformer by external relaying mounted on the control panel:

1. over current protection protection relay:

     1)  JTRSA300 Relay on HT side (in case of TML Transformer)

                  2)  CDG31 Relay on LT side (in case of TML Transformer)

2. Instantaneous earth fault Relay for restricted earth fault-CAG type

3. STAND BY earth fault relay-CDG type

4. under voltage relay-VAGM type

5. Fuse failure relay-VAPM type

6. Differential protection relay-DTH (for large size of transformer>5MVA)

WORK PERFORMED IN PLANT DURING VOCATIONAL TRAINING

• CIRCUIT BRAKER has been changed in GAC (GEN.AUXILIARY COMPARTMENT)

     Earlier  there was SF6 gas circuit braker but now it has been changed and is replaced by

     VCB( VACCUME CIRCUIT BRAKER). SF6 has been replaced due to unavailability of its

      parts. SF6 and VCB are having the following specification.

SPECIFICATION

GCB (GAS CIRCUIT BRAKER)

TYPE                                          6-SFG-406

STD                                                 1S2516

RATED VOLTAGE                       12KV

RATED NORMAL CURRENT      2000A

RATED SHORT CKT

    BREAKING CURRENT             40 KA

RATED LIGHTING IMPULSE

     WITHSTAND VOLTAGE         75 KVp

 RATED GAS PRESSURE              5  KG/CM2g (20 DEG C)

RATED COIL VOLTAGE                 220 V DC

TRIPPING                                           220 V DC

MOTOR VOLTAGE                           220 V AC/DC

AUX CKT                                           230 V,50 HZ

SR NO.                                                13-07 CS

YEAR                                                 1993

RATED MAKING CURRENT          100 KAp

RATED SHORT TIME

   CURRENT                                         40 KA FOR 3 sec

GAS WT.                                           1.5 KG

TOTAL WT                                       280 KG

VCB

TYPE                                                   VK-10P40

FREQUENCY                                      50 HZ

RATED VOLTAGE                            12 KV

RATED CURRENT                             2000 AMP

PF                                                          28 KV

RATED BREAKING CURRENT       40 KA

RATED MAKING CURRENT            100 KAp

WT OF BREAKER                              110 KG

RATED SHORT TIME CURRENT     40 KA FOR 3 sec

SR.NO.                                                  B-14129

•  AVR voltage was collapsing on 6th July 20007, during auto to manual changeover. It should be stable in both auto and manual mode as per normal.

Voltage was neither increasing nor decreasing from push button (manual raise/ lower) from GTG control panel.

After checking the manual thyristor bank, 1 no. thyristor in manual showing high resistance 200 ohm (gate to cathode).

On removing the  thyristor it was found loosely fitted on heat sink.

      After removing the suspected thyristor replaced with new spare thyristor by applying

       heat compound on both thyristor face and heat sink for better heat dissipation .

 looseness of thyristor may cause the irritatic behaviour due to which it is not conducting properly

Material Replaced:

1. RE-300 of 220 volts DC                 - 01 No.
2. Thyristor                                            - 01 No.

AMMONIA PLANT

 The raw material to produce Urea are Ammonia and Carbon-di-oxide, which are produced in Ammonia plant.

 Ammonia are produced by the following reation:

   N2   +3H2   =2NH3 +Heat

 Feed stock to manufacture Ammonia

 Raw material, as evident from the reaction, to produce ammonia is Nitrogen and Hydrogen.

Source of Nitrogen is atmospheric air which has 79% Nitrogen. Hydrogen is produced from Natural gas.

KSFL uses Natural gas Feed stock and Natural gas/Naphtha were used as fuel in furnace.

Natural gas is supplied by GAIL via HVJ pipeline from Bombay High.

Process description

AMMONIA PLANT          

Technology                             Haldor Topsoe, Denmark

Basic Engineering                      PDIL

Design Capacity                                1520 MTPD

Following are the main process steps for manufacture of ammonia:

DESULPHURISATION

Natural Gas mainly containing methane (98%) and higher hydrocarbon has 10-50ppm of sulphur. In desulphurization process sulphur content is reduced to 0.05ppm.

Hydrogenation consists of the following reaction:

H2    +S     =    H2S              (Catalyst Ni and Mo )

After hydrogenation the process gas is passed through the absorption vessels where the H2S is absorbed on ZNO as follows:

ZnO     +  H2S     =  ZnS +  H2O           (catalyst ZnO

PRIMARY REFORMER

It consists of a gas fired tubular primary reformer with flue gas heat recovery section. Natural gas is reformed with steam to produce a mixture of hydrogen, carbon monoxide, carbon dioxide and methane (11.12%).

The steam reforming of hydrocarbons can be described by the following reaction:

CH4   + 2H2O    =    CO2 + 4H2 – Heat (catalyst Ni)

 CO2   +   H2     =    CO   + H2O – Heat

SECONDARY REFORMER-

Function of secondary Reformer is to reform the Primary Reformer exit residual methane and to add Nitrogen to the process gas.

This is achieved by mixing a stoichiometric quantity of process air to the primary reformer exit gases in Secondary Reformer.

Secondary Reformer outlet gas mixture contains hydrogen, nitrogen, carbon monoxide and methane (0.3%).

WASTE HEAT RECOVERY-

High temperature process gas exit secondary Reformer is cooled down in Waste Heat Boiler and in turn high pressure steam is produced. Steam produced is utilized as process steam and as driving force for major rotatory equipments.

SHIFT CONVERSION-

Carbon monoxide is converted to carbon dioxide in two stage shift conversion bringing down the carbon monoxide content from 12.95% to 0.3% in the process gas.

    CO     +     H2O    =    CO2  + H2  +  Heat (catalyst iron oxide)

CARBON DIOXIDE REMOVAL-

Giammarco Vetrocoke (GV) solution is used to absorb carbon dioxide from the process gas thus reducing carbon dioxide content from 17.72% to 0.05% in gas mixture in CO2 absorber.

GV solution contains

a) Potassium Carbonate

b) Glycine

C) Di Ethanol Amine

d) Vanadium penta oxide

GV solution rich in carbon dioxide is regenerated in HP and LP regenerators by giving heat and Carbon dioxide is sent to Urea Plant.

METHANATION-

Oxides being harmful for synthesis converter catalyst, Carbon monoxide and Carbon dioxide are converted in to methane in this step.

   CO     +   3H2   =   CH4   + H2O  + Heat(catalyst Ni)

   CO2    +   4H2   =   CH4   +2H2O  + Heat

The exit process gas (Synthesis gas) contains mainly a mixture of hydrogen and nitrogen in the ratio of 3:1.

SYNTHESIS GAS COMPRESSION-

Synthesis of nitrogen and hydrogen takes place at high pressure, hence the mixture is compressed to 220 Kg/cm2g in synthesis gas compressor.

AMMONIA SYNTHESIS-

Conversion of this gas mixture in to Ammonia takes place in TOPSOE-S200 radical flow converter.

The Ammonia synthesis takes place in Ammonia Converter according to the following reaction:

   3H2   +   N2   =   2NH3   +  Heat(catalyst Elemental iron)

    REFRIGERATION SYSTEM-

      Gas mixture containing ammonia is cooled down to separate liquid ammonia from the gases by providing ammonia refrigeration. Separated liquid ammonia is sent to Urea Plant is not in operation, product Ammonia can be sent to Ammonia Storage.    

UREA KSFL have two units of urea plant 1) Unit – 11 2) Unit – 21 UREA PLANT CAPACITY- 1100*2= 2200MTPD Urea plant technology- SNAM progatti Italy Raw material- 1) NH3                         2) CO2 Physical condition- 1) NH3- liquid phase                                 2) CO2 – Gas phase    Chemistry of urea plant- The total urea manufacturing process can be broadly divided in to following three steps:

1) Urea synthesis

2) Decomposition and Recovery

3) Concentration and Prilling

1) UREA SYNTHESIS AND EFFECT OF VARIABLES

Urea is produced by synthesizing liquid ammonia and gaseous carbon dioxide under high pressure and temperature. The reaction to produced urea completed in two steps

A) Ammonia and carbon dioxide reacts to form ammonium carbamate, and

B) A portion of which is dehydrated to form urea and water.

Different reactions involved in urea synthesis are-

            2NH3 + CO2 = NH4COONH2 + 38.1 KCAL ………… (1)

                 Amm. Carbamate

            NH4COONH2 = NH2CONH2 -7.1 KCAL …………….. (2)

                 Urea

The first reaction is highly exothermic, instantaneous and goes to completion, the second reaction is endothermic occurs slowly determine the reaction rate. The overall reaction is exothermic hence reaction heat has to be removed continuously for equilibrium reaction to proceed.

Other reactions involved are:

 NH3 + H2O   = NH4OH + 8.4KCAL ……… (3)

2NH3 +CO2+ H2O = (NH4)2CO3 …………… (4)

                  Amm.Carbonate

NH2CONH2 +NH2CONH2 = NH2CONHCONH2 + NH3 …………… (4)

                      Biuret

NH2COONH4          = NH3 + CO2

Urea synthesis takes place in the liquid phase so the temperature must be maintained higher than melting points of urea, ammonium carbamate and biuret. Urea synthesis reaction is a vapor liquid heterogeneous reaction system. All along the reactor both the vapor phase (containing free CO2, ammonia, some water and inert) and liquid phase (containing ammonia, ammonium carbonate, ammonium bicarbonate, urea and water) are present. The reactants are progressively transferred from vapor phase to liquid phase where CO2 reacts with ammonia producing ammonium carbamate and then urea and water with continuous exchange of CO2 and ammonia between phases.

The conversions of ammonium carbamate to urea depend on the following variables:

1) Reaction temperature

2) Pressure

3) Molar ratio of NH3/CO2

4) Molar ratio of H2O/CO2

5) Retention time

6) Geometry of reactor vessel and its internal

The urea plant consists of two identical streams of 1100 TPD each based on SNAM-PROGETTI Ammonia stripping technology. The production of ammonia and CO2 consists of following reaction.

                2NH3 + CO2 = NH2CONH2 + H2O 

The above reaction takes place at a Temperature of 180 degree C and under pressure of 157 kg/ cm2 with a reactant ratio (NH3: CO2) 3.6: 1 and high pressure recovery.

Purification of the reacted product takes place in the low pressure section. In this section excess NH3 un reacted CO2 are being separated and recovered.

The purified urea solution is concentrated to 99.7% urea melt under two vacuum stages.

Prilling of urea melt is done in prilling          tower to get desired prills.

Removal of NH3 and CO2 from process condensate is being carried out in Hydrolyser-stripper system.

CO2 compression 

Gaseous Carbon Dioxide along with small quantity of O2 in the form of air is compressed in Co2 compressor and fed to Urea Reactor.

UREA SYNTHESIS 

Liquid Ammonia is pumped by Ammonia Reactor feed pump and Fed to the Urea Reactor via Corbamate ejector along with Corbamate solution. The CO2 react with Liquid Ammonia & forms Urea in Urea Reactor.

STRRIPERING 

Solution containing urea, CO2, Ammonia and water is sent to a falling film titanium tube stripper. In this Stripper solution is heated by saturated steam. The urea Carbamate Solution is stripped of the Ammonia Gas. The Ammonia & CO2 gas are removed from this solution to vapor phase. The Urea Carbamate solution leaving the stripper is having 46% urea.

M.P & L.P Decomposition

Urea Carbamate solution containing 46% urea is concentrated in falling film steam heated MP decomposer and steam heated LP decomposer to get 63% urea and 72% urea solution respectively.

VACCUME CONCENTRETION

Urea solution containing 72% urea is further concentrated in two stage steam heated vacuum concentrator at 0.3 ata and 0.03 ata in order to get 95% and 99.7% urea melt respectively .

PRILLING 

Urea melt obtained from the second stage evaporator (99% urea) is pumped to the spinning prill bucket, located at the top of the prilling tower by urea melt pump.

Prilled urea collected at bottom of prilling tower by double arm rotatory scrapper is sent to conveyor located at the bottom of the prilling tower. A system of conveyor is used to carry urea in the bagging plant.

AMMONIA STRIPING & HYDROLYSIS 

The condensate collected from the vacuum separator containing urea, ammonia, CO2 and water is first stripped in ammonia distillation tower and then hydrolyzed in deep urea hydrolyser to recover ammonia and CO2. The condensate exit of distillation tower is cooled & sent to D.M.Plant for further purification for making it boiler feed water. Thus there are no liquid effluents from urea plant under normal operation.

RECOVERY OF AMMONIA AND CORBONDIOXIDE 

The recovered ammonia and CO2 thus condensed is used to absorbed carbamate vapor from LP decomposer which in turn is used to absorb MP decomposer vapors in MP condenser and MP absorber. The MP carbamate solution is pumped to HP carbamate condenser where in vapor from stripper are condensed and fed back to reactor at carbamate solution.

The excess ammonia is recovered in MP absorber and the condensed ammonia is sent back to reactor along with the make up ammonia. Low pressure steam is produced in HP carbamate condenser and used in the urea plant. Excess LP steam is fed to the LP header of the complex.