01-12-2012, 11:54 AM
A Vocational Training Report On National Thermal Power Corporation In Dibiyapur (Auraiya)
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Overview of NTPC
NTPC was set up in the central sector in the 1975 in response to widening demand & supply gap with the main objective of planning, promoting & organizing an integrated development to thermal power in India. NTPC is poised to become a 40,000 MW giant corporation by the end of XI plan i.e. 2012 AD. Lighting up one fourth of the nation, NTPC has an installed capacity of 19,291 MW from its commitment to provide quality power. Today NTPC contributes more than 3 / 5th of the total power generation in India.
NTPC Limited is the largest thermal power generating company of India. NTPC ranked 317th in the ‘2009, Forbes Global 2000’ ranking of the world’s biggest companies. NTPC has embarked on plans to become a 75,000 MW company by 2017. Installed capacity of NTPC is 27,904 MW through its 15 coal based (22,895 MW), 7gas based (3,955 MW) and 4 Joint Venture Projects (1,054 MW).
NTPC International Cell
Keeping its proactive tradition, NTPC launched a separate International Cell to meet the varied needs of IPPs (Independent Power Producers) and other International clients who are looking for a world class service in power sector. The Cell is especially tuned to meet the requirements of International clients in terms of quick response, flexible service options and to deliver value for money.
NTPC International Cell
Keeping its proactive tradition, NTPC launched a separate International Cell to meet the varied needs of IPPs (Independent Power Producers) and other International clients who are looking for a world class service in power sector. The Cell is especially tuned to meet the requirements of International clients in terms of quick response, flexible service options and to deliver value for money.
Introduction to Gas Power Plants
With this intention in mind the Government asked NTPC to take up the construction of Kawas, Auraiya, Anta, Dadri and Gandhar Gas Power Project along the HBJ Gas pipe line. The plant receives gas through the HBJ pipeline. The plant works on the combined cycle which has a very high efficiency of 48.33% as opposed to the 32% offered by the open cycle. The main fuel is natural gas and the alternate being HSD. The power plant consists of gas turbine generating units waste heat recovery boilers, steam turbo generator, ancillary electrical and mechanical equipments. In the Power Sector, gas turbine drive generators are used.
Gas turbines range in size from less than 100 KW up to about 140.000 KW. The gas turbine has found increasing application due to the following potential advantages over competive equipment.
• Small size and weight per horsepower
• Rapid loading capability
• Self-contained packaged unit
• Moderate first cost
• No cooling water required
• Easy maintenance
• High reliability
• Waste heat available for combined cycle application
• Low Gestation Period
• Low Pollution Hazards
The function of a gas turbine in a combined cycle power plant is to drive a generator which produces electricity and to provide Input heat for the steam cycle. Power for driving the compressor is also derived from gas turbine.
Combined cycle
Combined cycle power plant integrates two power conversion cycles namely. Brayton Cycle (Gas Turbines) and Rankine Cycle (Conventional steam power plant) with the principal objective of increasing overall plant efficiency.
Brayton Cycle
Gas Turbine plant-operate on Brayton Cycle in which air is compressed this compressed air is heated in the combustor by burning fuel combustion produced is allowed to expand In the Turbine and the turbine is coupled with the generator. Without losses the theoretical cycle process is represented by 1’2’3’4’
Gas Turbine Starting System
The function of the starting system is to crank the gas turbine up to the required speed until: it becomes self sustaining.
One method of starting large gas turbine is by using a motor driven hydraulic starting system. Alternatively, the GTG can be started by using a frequency converter to rotate the generator which drives the turbine for starting. A typical hydraulic starting system for each gas turbine consists of the following:
• Starting motor, electric AC induction motor
• Hydraulic torque converter
• Auxiliary Gear
• Couplings
The electric starting motor drives the hydraulic torque generator through a coupling. The hydraulic torque converter consists of an impeller, which forces the fluid against hydraulic starting motor. The hydraulic torque converter is coupled to the accessory gear, which is connected to the gas turbine shaft. The torque converter receives hydraulic fluid from hydraulic and lube oil reservoir during operation. When gas turbine reaches self-sustaining speed the starting device is disconnected and shut down.
Static Frequency Converter (SFC)
A gas turbine generator is not self starting machine i.e. it can not accelerate to rated speed from standstill/from turning gear speed; by its own energy (combustion and force of hot gases). Separate power is required for startup. For this a static frequency converter is installed. Generator is run as motor which accelerate. At 480 RPM ignition takes place and at 600 RPM combustion in combustion chamber starts. The whole mass accelerated up to 2100RPM with SFC and turbine power. At this speed SFC switched off. At this speed turbine accelerate with its own power achieved through flew gases and reaches to rated speed of 3000 RPM.
Black Start System
To start a gas turbine in the event of AC-power failure an emergency black start system is provided. It also helps in safe coasting down of the gas turbine and its auxiliaries following a ‘trip’ in the event of grid collapse. The black start system consists of a separate diesel engine or a gas turbine driven synchronous generator connected to station switch gear bus. It can be operated manually from local or remote and also it automatically comes into operation following a black out condition.
Fuels used in Gas turbines
Gas turbines are capable of burning a range of fuels including naphtha, distillates, crude oils and natural gas. Selection of fuel depends on several factors including fuel availability, fuel cost and cleanliness of fuel. Liquid fuels, particularly heavy oils, usually contain contaminants, which cause corrosion and fouling in the gas turbine.
Naphtha Pressuring System
By the forwarding pumps, Naphtha is pumped up to the GTs and kept under recirculation. For firing the naphtha is the GT, separate pressuring system with high pressure pump, allied filters and measurements and recirculation system is used. This pressuring is required because in the naphtha burner this fuel is mechanically atomized.
Fuel Gas System
The purpose of the fuel gas system is to take gas from the custody transfer point, process it to the quality and pressure conditions required by the gas turbine and to distribute it and monitor its use. Fuel gas system consists of the off base system and the on base system.
Basic conditions for plant operation
Basic conditions for plant operation are as follows:-
• Start up or shut down of G/T, WHRB and S/T of each module is performed separately from the other module (except for S/T gland steam back-up and heating steam back up systems).
• Start up/shut down mode is selected freely form among those mentioned.