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INTRODUCTION:-
N.F.C.L (Nagarjuna Fertilizers and Chemicals Limited) manufactures the product Urea (NH2-CO-NH2). The plant is based on the latest technology from M/s Snamprogetti, Italy for the Urea process and Haltertopsop for ammonia process, with an installed capacity of 1500 Mt/day for each stream, later it has been increased to 1800Mt/day for each stream through the process of revamping (study of plants to enhance the production)..
The Industry has two Ammonia plants, two Urea plants, Bagging Plant and Utilities & Power Plants.
The Raw materials used for manufacturing the Ammonia and Urea are:-
1) Natural Gas - From Krishna Godavari basin through GAIL.
2) Natural air - Atmosphere.
3) Water - From SAMALKOT through a canal.
1.1 PROCESS:-
In NFCL by reforming and synthesizing natural air and Natural gas, Ammonia is manufactured.
By mixing the carbon dioxide, which is the byproduct of ammonia process with Ammonia in required proportion, urea will be manufactured in urea plant. Ammonia & Urea manufacturing is a continuous process. Such a continuous process requires continuous power without interruption. Hence captive generators are installed at N.F.C.L. and the electrical energy required in N.F.C.L. is for driving various equipments like pumps, compressors, fans, Illumination etc. The power required for Utilization purpose in NFCL is around 25 M.W. Detailed process for the Ammonia, Urea, 0ff sites, Power plant & Bagging plants is given in the Annexure-01.
However, N.F.C.L has 6 M.V.A contract demand with APTRANSCO to meet any exigencies. However, NFCL does not rely on APTRANSCO power but this power is being used as a stand by power supply incase any one generator trips. At present this power is feeding non critical loads like bagging plant, Main stores and work shop.
CHAPTER-2
GENERATION
GENERATION
2.1 ELECTRICAL SYSTEM IN NFCL:-
NFCL has its own power generation plants. There are three gas turbine generators.
Gas turbine generator ‘A’ having capacity of 8.6 MVA.
Gas turbine generator ‘B’ having capacity of 8.6 MVA &
Gas turbine generator ‘C’ having capacity of 33 MVA
The total captive power plants capacity altogether is 50 MVA. Normally two generators ‘A’ & ‘B’ are in running condition to meet the entire load of (Approx. 25 MW) the both the plants. Diesel generators’ power is used as an emergency power in case of any Gas turbine generator trips. NFCL has two nos. of 1375 KVA generators of DG sets used as a Auto Mains Failure ( AMFs –i.e. Emergency power) in case of normal GT power failure.
2.2 WORKING OF GAS TURBINE:-
At starting the HP shaft is driven by the Diesel Engine (which has a D.C motor for initial starting with the help of battery). The Diesel Engine shaft rotates at the speed 2100r.p.m. The compressor placed on the HP shaft takes the atmospheric air and compresses the air to required pressure and then the compressed air is given to the combustion chambers. There are six interconnected combustion chambers. The Natural gas is also given to the combustion chambers. There is a spark plug in combustion chambers, which gives ignition in combustion chamber. After combustion the fuel gases are given to the Turbine through Nozzle.
The fuel gases rotate the HP turbine blade thus the HP shaft picks up the speed and rotates constantly at 7200r.p.m. Later the Diesel Engine will be stopped automatically by disengaging from the HP shaft. The fuel gases passes to the LP turbine blades through the Inlet Guide vanes and rotates the LP shaft at 6500r.p.m. The LP shaft is coupled to Gear Box and this is coupled to the alternator shaft this makes the alternator shaft to rotate at 1500r.p.m. The LP shaft always rotates at 6500r.p.m by controlling the Inlet Guide Vanes.
2.3 Production of GT:-
Gas turbine A:
It produces 7.5MW / 60MTPH
Gas turbine B:
It produces 7.5MW / 60MTPH
Gas turbine C:
It produces 18.5MW / 100MTPH
And gas turbines produce the current (power) at the rate of 11KV.
2.4 CONSTRUCTION:-
The shaft of Alternator is coupled to gearbox of gas turbine. On the shaft exciter armature winding, rotating diode bridge and Alternator main field are placed. Over the rotors respective stators are placed with the help of Bearings and End covers.
2.5 WORKING OF GT-A/GT-B Generator:-
The excitation system used for these Generators is brush less excitation system.
As the shaft rotates at 1500rpm, by giving excitation to the pilot exciter stator A.C. voltage is generated in its rotating armature. Generated voltage in the exciter armature is given to the main field of the Alternator through rotating Rectifier –Diode unit. As a result alternator generates power at 11 kV. The generated voltage is connected to SS-1 11 kV switchgear through a generator breaker. Alternator’s 11 kV supply is given to the powering P.T (Potential Transformer). The output of the P.T is connected to A.V.R. This serves as a power source for the AVR and also as a feedback in controlling the output of the alternator voltage always at 11 kV. Another input to the A.V.R is 125 V D.C for working of A.V.R and is given by the station batteries.
The hot exhaust gases from the gas turbine are given to the H.R.S.G (Heat Recovery Steam Generation) – nothing but boiler. Another input to the H.R.S.G is Dematerialized water. The output of the H.R.S.G i.e., steam is utilized in main process.