Gas Turbine Report.docx

HALMORE POWER GENERATION COMPANY LIMITED

Gas Turbine A mechanical power engine installed in a plant to drive a generator to supply an electrical network.

Definition The gas turbine is a machine, which converts the chemical energy of the fuel into heat energy (produced in its combustion chamber), part of this heat into mechanical (rotational) energy which is used to generate power at the Generator end.

Description Gas turbines generate a large volume of very hot air. The exhaust is also high in oxygen content as compared to other combustion exhausts, as only a small amount of oxygen is required by the gas turbine combustor relative to the total volume available. Gas Turbines are only able to use a portion of the energy generated from fuel combustion (up to 40%). The remaining heat (e.g. hot exhaust gases) from combustion is wasted in a simple cycle.

Benefits of Combined Cycle Combining two or more "cycles" such as the Brayton Cycle (gas turbines) and Rankine Cycle (Steam turbine) results in improved overall efficiency. The heat energy from the hot exhaust gases is further utilized in the HRSG (Heat Recovery Steam Generator) for steam generation, thereby improving overall thermal efficiency of the plant. In a combined cycle power plant (CCPP), a Gas Turbine generator generates electricity and the heat from the hot exhaust gases is used to make steam in (HRSG) to generate additional electricity via a Steam Turbine to enhances the efficiency of electricity generation.

Working Principle of Gas Turbine A cycle describes what happens to air as it passes into, through, and out of the gas turbine. The cycle usually describes the relationship between the space occupied by the air in the system (called volume, V) and the pressure (P) it is under.

Brayton Cycle

The Brayton Cycle shown in graphical form as a pressure-volume diagram, is a representation of the properties of a fixed amount of air as it passes through a gas turbine in operation. A schematic diagram for a simple-cycle, single shaft gas turbine is shown in figure above. Air enters the axial flow compressor at point 1 at ambient conditions. Since these conditions vary from day to day and from location to location, it is convenient to consider some standard conditions used by the gas turbine industry are 15C, 1.013 bar and 60% relative humidity, which are established by the International Standards Organization (ISO) and frequently referred to as ISO conditions. Air entering the compressor at point 1 is compressed to some higher pressure. No heat is added; however compression raises the air temperature so that the air at the discharge of compressor is at a higher temperature and pressure.

Upon leaving the compressor, air enters the combustion system at point 2, where fuel is injected and combustion occurs. The combustion process occurs at essentially constant pressure. Although high local temperatures are reached within the combustion zone (approaching stoichiometric conditions), the combustion system is designed to provide mixing, burning, dilution and cooling. Thus, by the time the combustion mixture leaves the combustion system and enters the turbine at point 3, it is at a mixed average temperature. The hot compressed air at point 3 is then allowed to expand (from point 3 to 4) reducing the pressure and temperature and increasing its volume. In the engine, this represents flow through the turbine to point 3' and then flow through the power turbine to point 4 to turn a shaft. In the turbine section of the gas turbine, the energy of hot gases is converted into work. This conversion actually takes place in two steps. In the nozzle section of turbine, the hot gases are expanded and a portion of thermal energy is converted into kinetic energy. In the subsequent bucket of the turbine, a portion of the kinetic energy is transferred to the rotating buckets and converted to work. Some of the work developed by the turbine is used to drive the compressor, and the remainder is available for useful work at the output flange of the gas turbine. Typically, more than 50% of the work developed by the turbine sections is used to power the axial flow compressor.

Gas Turbine Components The gas turbine consists essentially of:

• A multi- stage axial compressor. • A combustion chamber • A multi-stage axial turbine The compressor and the turbine have a common rotor, which is supported by two bearings, located outside the pressurized region. In the gas turbine, the turbine section is arranged such that the power of both the compressor and the generator is transmitted to one side of the gas turbine. This means that the rotor between the turbine and the compressor section transfers more than double the generator power in the form of rotational energy. The compression energy is recycled in the turbine.

The gas turbine power engine includes an axial airflow compressor, a multi chamber combustion system and a three stages turbine.

• The axial airflow compressor is 18 (0-17) stages compressor with: a. Adjustable inlet guide vanes (IGV) to control the airflow during starting and loading sequences. b. Bleed valves to bypass part of the air flow for starting and shut down to escape from surging.

• The combustion system comprises: a. Fuel nozzles fitted on the combustion chamber’s cover. b. Six combustion chambers where the fuel burns permanently from firing speed to full load c. Six cross fire tubes connecting the combustion chamber d. Six transition pieces downstream the combustion chamber connected to the first turbine stage nozzle. e. Two spark plugs for the fuel ignition. f. A set of flame detectors.

The three stages turbine include: first, second and third stage nozzle and first, second and third wheel. The turbine and the axial flow compressor belong to the same shaft connected to the generator at the front end.

Compressor • The eighteen-stage, axial flow compressor is designed with an ISO base pressure ratio of 15.8:1, and airflow of 212 kg/second. • All turbine engines have a compressor to increase the pressure of the incoming air before it enters the combustor. • Compressor performance has a large influence on total engine performance. • This Compressor is called an axial compressor because the flow through the compressor travels parallel to the axis of rotation. • The axial-flow compressor section consists of the compressor rotor and the compressor casing. Within the compressor casing are the variable inlet guide vanes, the various stages of rotor and stator blades, and the exit guide vanes. • In the compressor, air is confined to the space between the rotor and stator where it is compressed in stages by a series of alternate rotating (rotor) and stationary (stator) airfoil shaped blades. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters the following rotor stage at the proper angle. The compressed air exits through the compressor discharge casing to the combustion chambers. Air is extracted from the compressor for turbine cooling and for pulsation control during startup. • The function of the axial flow compressor is to furnish a large volume of high pressure air to the combustion chambers for the production of the hot gases necessary to operate the turbine. Only a portion of this air is used for combustion, the remainder is used as dilution air to lower the temperature of the products of combustion and also serves as a source of cooling air for the turbine nozzles, turbine wheels, transition pieces and other portions of the hot–gas path • Compressors in gas turbine engines use convergent and divergent ducts to generate the high pressures necessary to (a) provide a “wall of pressure,” preventing expanding hot gas from exiting through the engine inlet as well as through the exhaust; and (b) provide the proper ratio of air-to-fuel for efficient combustion and cooling of the combustion chamber.

• Pressure decreases through convergent ducts and increases through divergent ducts, expansion through a divergent section then increases pressure and air volume, dispersing the paint in an atomized mist

Combustor The dry low NOx control system regulates the distribution of fuel delivered to a multi-nozzle, total premix combustor arrangement. The fuel flow distribution to each combustion chamber fuel nozzle assembly is calculated to maintain unit load and fuel split for optimal turbine emissions. • The combustion system is of the reverse-flow type with the 6 combustion chambers arranged around the periphery of the compressor discharge casing. Combustion chambers are numbered counterclockwise when viewed looking downstream and starting from the top of the machine. This system also includes the fuel nozzles, a spark plug ignition system, flame detectors, and crossfire tubes. Hot gases, generated from burning fuel in the combustion chambers, flow through the impingement cooled transition pieces to the turbine. • High pressure air from the compressor discharge is directed around the transition pieces. Some of the air enters the holes in the impingement sleeve to cool the transition pieces and flows into the flow sleeve. The rest enters the annulus between the flow sleeve and the combustion liner through holes in the downstream end of the flow sleeve. This air enters the combustion zone through metering holes for proper fuel combustion and through slots to cool the combustion liner. • Fuel is supplied to each combustion chamber through six nozzles designed to disperse and mix the fuel with the proper amount of combustion air. Fuel is injected into the forward end of the liner where it mixes with the compressor discharge air and combustion takes place, thereby creating hot gases with temperatures in excess of 3000°F (1650°C) in the flame zone.

Description • As well as being used for combustion, the relatively cool compressor discharge air acts as a blanket to protect the liners from the heat of combustion and also mixes with the combustion gases downstream of the combustion reaction zone, cooling and diluting the gases which now pass through transition pieces to the turbine first– stage nozzle. The amount of air necessary to

cool the liner wall and dilute the hot gas to the temperature desired at the first–stage nozzle is about four times that required for complete combustion. • The cylindrical combustion liners connect to arc– shaped segments of the first stage nozzle through transition pieces. As well as being used for combustion, the relatively cool compressor discharge air is used to cool and protect the liners and transition pieces from the heat of combustion. • The overall function of the combustion system is to supply the heat energy to the gas turbine cycle. This is accomplished by burning fuel in the air downstream of the compressor and diluting the combustion products with excess air to achieve the desired gas temperature at the discharge of the first–stage turbine nozzle.

Different Parts of Combustion Chamber •

Crossfire Tubes

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Spark Plugs

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Ultraviolet Flame Detectors

Turbine All gas turbine engines have a turbine located downstream of the combustor to extract energy from the hot flow and turn the compressor. Work is done on the turbine by the hot exhaust flow from the combustor. Since the turbine extracts energy from the flow, the pressure decreases across the turbine. • The three-stage turbine section is the area in which energy in the form of high temperature pressurized gas, produced by the compressor and combustion sections, is converted to mechanical energy. • The stationary nozzles have a high pressure drop across them that converts the high pressure gases from the combustion system into high velocity jets that impinge against the turbine blades (buckets) that are attached to the turbine rotor.

• The kinetic energy of the hot gases is converted into useful rotational, mechanical energy by the turbine buckets. This produces the power necessary to meet the load requirements and to drive the axial–flow compressor. • Turbine blades exist in a much more hostile environment than compressor blades. Sitting just downstream of the combustor, the blades experience flow temperatures of more than a thousand degrees Fahrenheit. Turbine blades must be made of special materials that can withstand the heat, or they must be actively cooled. In active cooling, the nozzles and blades are hollow and cooled by air which is bled off the compressor. The cooling air flows through the blade and out through the small holes on the surface to keep the surface cool, of the three stage turbine section, the first and second stage turbine nozzles and buckets are air cooled. • The turbine rotor is cooled to maintain reasonable operating temperatures and, therefore, assure a longer turbine service life. Cooling is accomplished by means of a positive flow of cool air extracted from the compressor and discharged radially outward through a space between the turbine wheel and the stator, into the main gas stream. This area is called the “Wheelspace”.

Auxiliary Systems of GT •

Electrical Starting System

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Lubrication System

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Trip Oil System

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Hydraulic Supply System

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Gas Fuel System

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Liquid Fuel System

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Fuel Purge System

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Inlet Air Heating System

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Water Injection System

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Atomizing Air System

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Flow Inlet And Exhaust System

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Air Processing Unit

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Inlet Guide Vanes System

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Compressor Washing System

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Fire Protection System

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Gas Detection System

Cooling & Sealing Air System

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Cooling Water System

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Heating And Ventilation System

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Load Gear System

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Performance Monitoring System

STEAM TURBINE A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft.

Abstract A Combined Cycle Power Plant (CCPP) can be roughly divided into 3 parts; Gas Turbine, Boiler & Steam Turbine (ST includes turbine, condenser, condensate pumps, de-superheating pumps, feed water system, bypass system and the electric generator. Steam from boiler is supplied in which K.E of steam is used to drive the turbine to obtain Mechanical Energy.

Principle of Operation • An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly isentropic, however, with typical isentropic efficiencies ranging from 20–90% based on the application of the turbine. • The Rankine cycle is a model that is used to predict the performance of steam turbine systems. The Rankine cycle is an idealized thermodynamics cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. • The steam energy is converted mechanical work by expansion through the turbine. The expansion takes place through a series of fixed blades (nozzles) and moving blades each row of fixed blades and moving blades is called a stage. The moving blades rotate on the central turbine rotor and the fixed blades are concentrically arranged within the circular turbine casing which is substantially designed to withstand the steam pressure.

General Description • Steam turbines are machines that are used to generate mechanical (rotational motion) power from the pressure energy of steam. Steam turbines are the most popular power generating devices used in the power plant industry primarily because of the high availability of water, moderate boiling point, cheap nature and mild reacting properties. The most widely used and powerful turbines of today are those that run on steam. From nuclear reactors to thermal power plants, the role of the steam turbine is both pivotal and result determining. A steam turbine basically has a mechanical side, and an electrical side to it. The mechanical components include the moving parts (mechanical), such as the rotor, the moving blades, the fixed blades, and stop valves, while the electrical side consists of the generator and other electrical components to actually convert the energy into a usable, easily transferable form. • Steam flows through the turbine is in the axial direction. After leaving the body of the emergency stop valve, the live steam enters the valve chest which the control valves which form

an integral casting with the upper half of the outer casing. The valve chest is designed as a transverse tube with openings at both ends for assembly. • The turbine casing is divided into an admission and an exhaust section. Backpressure as well as condensing turbines have admission sections of identical design. Depending on the initial steam conditions, the admission sections of comparable size are designed with casting of different wall thickness. The admission section will be completed by an exhaust section of adequate size. Turbine of type ranges SC have the exhaust section assembled to the admission section by bolts. • The turbine casing is horizontally split. The upper and lower casing halves are flanged and assembled by bolts.

Steam Turbine Auxiliaries •

Control Oil System

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Lube Oil System

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Vacuum System

Trip Oil System

Conclusion It has been a great learning experience at the Halmore Power Generation Company Limited. I got a lot to learn about the Gas Turbine and Steam Turbine and how they work in a combined cycle. I also learnt about the auxiliaries of both the turbines . To conclude with, I would like to thank Halmore Power Generation Company Limited for providing me with a great chance of getting the experience regarding the power plant and how it works. I would like to work with the company in the near future and serve the organization in the best possible way.