1.1 9HA (GE Gas Turbine) Combined Cycle Power Plant

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9HA (GE Gas Turbine) Combined Cycle Power Plant

Gas turbine and combined cycle

The first practical gas turbine was developed at the end do Second World War II in Europe in 1939 for aircraft. Shortly after the war, first industrial gas turbine was developed for production and other industrial application such as driving of locomotive were introducing Gas turbine use another type of cycle called the Brayton Cycle named after its inventor . The first, commercial, industrial gas turbines were relatively inefficient, typically having low thermal efficiency of 16% to 17%. Gas Turbines reached their peak of popularity in early 1970s.
The first major component of combined cycle power plant is gas turbine. In installation where the gas turbine exhausts directly to the atmosphere. It is said to in operating open cycle mode when gas turbine exhausts into the heat recovery steam generator HRSG and the resultant steam is used to operate the steam turbine generator the plant is referred to as combine cycle power plant.

Components of Combined Cycle Power Plant (9HA-GE Gas Turbine and Steam Turbine)

Gas Turbine

Gas turbine power plant has relatively low cost and can be quickly put into commission it requires less space this plant Is heavy capacity and is mainly use for peak load services. Gas turbine power plant is very promising for the region where liquid or gas fuel Is available in large quantities common arrangement of gas turbine driving an electric generator the gas turbine consist of a compressor, combustion chamber, gas turbine and rotor. Air is driven into the compressor from atmosphere, which raises the pressure pf air. The temperature of air also increases with compression its depend upon the design of compressor.

Gas Turbine is an internal combustion engine, like all other combustion engines, gas turbine’s compressor compress air, take in fuel for combustion, and use the resultant volume of hot gases to develop shaft horsepower. Referring the three primary sections of a gas turbine engine are:

1.Compressor
Air is drawn into the air inlet by the compressor. With-in  the compressor air in compressed and at corresponding temperature rise in incurred. The hot compressed air is discharged to the combustion section of the engine,

2 .Combustor
Fuel is admitted into the combustion section by the fuel nozzles. The fuel/air mixture is ignited and combustion occurs.

3. Turbine
The hot and rapidly expended gases are directed through the turbine rotor assembly. Their thermal and kinetic energy are converted into mechanical energy. The gases are expelled out to be the turbine exhaust.

Heat Recovery Steam Generator (HRSG)

The HRSG basically is a heat exchanger composed of High pressure (HP) drum, Low Pressure (LP) drum, High pressure (HP) Super Heater, HP evaporator , HP economizer, and LP evaporator section. These sections are positioned gas inlet to gas outlet to maximizing the heat recovery from the gas turbine exhaust gases The heat recover in the HRSG is used to supply steam to steam turbine at the proper temperature and pressure. For the HRSG feed water requirements a complete feed water system is provide composed of a feed water storage tank, LP feed water pumps, HP feed water pumps and feed water piping system.

Steam Turbine

Steam is an important medium o producing mechanical energy. Steam has the advantage that it can be raised from water, which available in abundance. It does not react with the material of the equipment of power plant and stable at the temperature required in plant. Steam is used to drive steam engine, steam turbines etc. Steam power station is most suitable where all types of fuel are available. Thermal electrical power generation is one of the major methods. For the thermal power plant the range of pressure may vary from (40 bar to 57bar) and the range of temperature is (500 C to 530 C).

The steam Turbine based components include:

·         An Energy resource in the form of flue gases to convert water into steam: Exhaust gases (Gas turbine ) or Flue gases from burning fuel (Oil/gas) directly in a furnace.

·         Steam generator or boiler containing water, Heat generated in the furnace is utilizes to convert water into steam.

·         Main power unit such as a turbine to use the energy of steam and perform work

·         Piping system to convey steam and water

·         Condenser and hot well

·         Cooling water cooling tower and Closed water circulating water pumps.

·         Condensate extraction pumps

·         Air extraction pumps

·         HP & LP Boiler feed water pumps

·         Make up water pumps

Major Electrical Equipment In Power Plant

A power station equipped with electrical equipment for power generation and supply of electrical power. The major electrical equipment in power plant are the following.

1       Generator

2       Transformers

3       Exciters

4       Circuit Breakers

5       Reactors

6       Switch Board

7       Control Board Equipment’s

8       Other Auxiliaries

Generator

It is an importan part of a power palnt all modern types of alternating current generators essentially consist of a fixed stator and revolving rotor

Stator consist of following three parts

•         Stator Frame
•         Stator core
•         Stator winding

The stator frame is of circular in shape and is made of welded steel plates. The core is made of stamping soft high permeability, low hysteresis and eddy current losses. The stator is generally built in cylindrical form and diameter of rotor is limited . Large numbers of deep slots are machined in the rotor to accommodate the field windings which will carry field currents. Generators coupled directly to the steam turbine are turbo generators and those coupled directly to water turbine are called water wheel-generator.

Generator Constants

The following details of generator should be known to determine their performance in the power system under different loading conditions.

1.      KVA Rating

2.      Number of Phases

3.      Frequency

4.      Number of Poles

5.      Voltage

6.      Temperature rise limits

7.      Power Factor cos ɸ

8.      Star connection of stator

Generator Cooling Methods

The two methods commonly used for generator cooling are as follows:

1      Air Cooling

2      Hydrogen Cooling

Hydrogen Cooling is far more effective than that of Air cooling because of the cooling capacity of hydrogen. As cooling is generator is directly related to its effectiveness to convert mechanical power into electrical energy, hydrogen cooling is now being used in heavy duty generators to increase the production capacities of generator as compared to that generators with air cooling.

Power Block Main Components

Main Components of a power plant include:

1       Gas Turbine-main prime mover

2       HRSG –Exhaust gas boilers

3       Steam Turbine – Secondary power prime mover

4       Generators – Coupled with prime movers either on same shaft or different shafts

5       Power Transformers- To step up the Voltage produce in generator to distribute electrical power

6       Auxiliary Transformers – To step down voltages from main generator to supply power to auxiliary components (which require much lower voltages to that produce in main generators)

7       Breakers (on load device) – Heavy duty circuit breakers to On and OFF high voltage lines

8       Isolators (off load device) – To electrical isolate the equipment to ensure safety

9      Switchyard – the Station of power transformers, isolators, Bus bars, protection relays, electrical feeders and breakers etc.

1     Hydrogen Plant – To generate and store hydrogen gas to fill in the generators when require

1    

           Water Treatment – To treat water to get water with specific quality to ensure no corrosion, scaling, mud accumulation and to any other treatment to be done to safe piping and related equipment.

       DEMI Plant – De mineralized the water to use for steam production

1     Fuel Gas Supply system – To supply gas at specific pressure, temperature and quality

1     Fuel Gas Conditioning system – To treat the gas before inserting into turbine combustion chambers

1     Liquid fuel storage tanks and supply pumps – To ensure quantity of liquid to be used in emergency and fuel change over

      Liquid fuel Injection pumps – To inject the liquid in atomize form required certain high pressure pumps

Power Plant Auxiliaries

1 Gas Turbine(GT GE 9HA) Auxiliaries

·         GT Start-up system LCI(Line Commutated Inverter)

·         GT Turning gear motor

·         GT Lube Oil Pumps and system

·         GT Fuel Gas supply system

·         GT Liquid Fuel system

·         GT compartments exhaust and inlet blowers for cooling

·         GT Generator Excitation System

2  HRSG Auxiliaries

·         High Pressure Boiler Feed water pumps

·         Low Pressure boiler Feed water Pumps

3  Steam Turbine Auxiliaries

·         ST Lube Oil pumps and system

·         Condensate Extraction Pumps

·         ST Generator seal oil system

·         ST Generator Excitation System

GE 9HA Gas Turbine Components

Gas Turbine plant contains parts and sections:

·         Gas Turbine

·         Gas Turbine Auxiliary systems

·         Gas Turbine Auxiliary system modules

·         Acoustic Enclosures

·         Generator

·         Generator Auxiliary systems

·         Electrical Starting means

·         Electrical energy evacuation

·         Power Distribution systems

It contain information related to AC and DC supply. It may include the parts below as applicable:

1.      Battery, battery rack and related accessories

2.      Battery charger

3.      Motor control center

4.      LV switch Board Container

5.      MV Switch Board Container

6.      Container, Miscellaneous Functions

·         Control Equipment

These equipment include the parts below:

1.       Packaged Electrical/ Electronic Control Compartment (PEECC)

2.       Gas Turbine speedtronic Control System (Mark-VI E)

3.       Human Machine Interface or DCS

4.       Generator control System

5.       Generator Protection Panel

6.       Generator Excitation Panel

7.       Auxiliary Panel

·         Monitoring Equipment

This volume Includes monitoring equipment such as:

1.      Vibration monitoring

2.      Hazardous gas monitor

3.      Smoke Analyzer

4.      Station Vibration Data Manager

5.      Partial Discharge Analysis Monitor

·         Balance Of Plant (BOP Equipment)

·         Combined Cycle(CC) Equipment

Further Insight into Gas Turbine GE 9HA

·         Gas Turbine Instrumentation (control/measuring devices)

·         Lubrication System

·         Cooling and Sealing Air System

·         Trip Oil system

·         Closed Cooling Water System (CCW)

·         Starting means system (Turning gear & LCI/SFC/Starting Motor)

·         Gas fuel System

·         Water Injection System

·         Fire detection & protection system

·         Hydraulic supply system

·         Heating and Ventilation System

·         Cleaning System

·         Compressor Washing system (off-line and 0on-line Washing)

·         Inlet Guide vanes system (IGV)

·         Inlet and exhaust system

·         Variable Stator vanes (VSV)

·         Hazardous Gas detection system

·         Fuel Purge system

·         Performance System

·         Liquid Fuel Inhibitor System

·         Accessory and Load gear system

·         Miscellaneous piping connections

Combine Cycle Power Plant(Reciprocating Engine and Steam Turbine)( Flexicycle)

Combine Cycle Power Plant-Engine + Steam Turbine

This combination combine Reciprocating Engine's(Otto cycle/Diesel cycle) and Steam Turbine's ( Rankine Cycle).
The reciprocating engine's exhaust gases are made to pass through exhaust gas boiler which extract their energy to make steam which in turn use in steam turbine to convert it into electrical energy by electric generator.

    

These power plants have combine cycle efficiency of 45-48%.

This vapor cycle is also called Flexicycle. Wartsila is the most efficient engine manufacturer internationally with model 31 SG Engine to be world's most efficient Engine.  For Flexicycle Overview
https://www.youtube.com/watch?v=NPI1P6ex9_Y   

These power plant are of small capacity with power generation capacity ranging from a few MW to 400MW and these power plant are supportive plant for emergency power source or for any maintenance work taken as stand by for bigger power plant such CCPP(gas turbine+steam turbine) and Steam turbine of Capacity from 1200MW to 4800MW and also for Hydel Power Plant of capacity from 150MW to 22000MW. 

Engines' efficiency depend upon the category like Slow, Medium and High speed engine with slow speed engine to be more efficient (45-50%)as the thermal process efficiently followed in them as compared to that in medium/high speed.

And Diesel Engines are less efficient than petrol engine but their power producing range are much higher than that of petrol engine as their compression ratio (15 to 23) is higher as compared to that of  petrol engine (8 to 12).

Diesel engines are often run on furnace oil which is cheap but having less calorific value and render engines to higher maintenance outages. And these engine produce more environmental problem as this fuel is most dirty fuel from refineries.

With the readily available less fuel cost of Gas fuel( LNG, CNG), with lower maintenance routines gas engines run on Otto cycle are becoming more famous in today's energy mix.

Gas engines CC power plant are of less power producing capacity (5MW to 100MW ) as compared to Diesel Engine CC power plants.

Gas engines power plants are cleaner and required less auxiliary equipment because of cleaner fuel as compared to that diesel engines. So installation cost and auxiliary load are lesser for gas engine CC power plants.

Single Cycle Steam Turbine Cycle Efficiency

Single Cycle Steam Turbine 

When it comes to thermal engines and vapor power cycles, pressure and temperature or Enthalpy  or simply the energy level  which of the fluid ( working fluid ) entering into the engine is the one of most important factor on which engines are designed and efficiency with which energy is extracted. 

Steam turbine cycle is called Rankine Cycle which is the combination of thermal processes which made a thermal cycle completed and effective practically. Rankine Cycle Ideally contain four processes two of them add energy into a fluid and other two extract energy from other fluid.

The Processes are as follows:

• Isentropic expansion of steam in turbine( energy extraction for Electricity from Turbine ).
• Constant Pressure heat removal in condenser.
• Isentropic compression in a pump( famously known as Feedwater Pump)
• Constant Pressure heat addition in boiler.

This Cycle wasn't efficient enough to produce electricity, efforts after designing of blades, were done to increase its efficiency which include:

• Reheating 
• Regeneration 
• Super Critical cycle

Reheating 

The Idea is to use the energy of the steam (at around 50 bar, 550 C)  first at higher enthalpy , at first portion (High pressure turbine) and then this steam expands and give energy to turbine and this steam reaches at lower pressure( around 30 bar, 380 C ) and then here only option to increase the temperature which is done by reheating the steam in Super-heater of boiler and increase its temperature. Then this steam at IP portion(intermediate pressure turbine) same pressure but higher temperature ( with higher enthalpy as compared to at the end of HP turbine) enter into IP turbine.

Usually in higher capacity power plants, steam turbine with double reheating is being used, more than two reheat is theoretically won't be effective.

Double reheating is done by reheat the steam at the end of IP turbine in the super-heater and then the same process is done with now at lower pressure and temperature. Steam then enter into the last portion of turbine which called LP turbine( Low Pressure Turbine).

Regeneration

There is regeneration cycle which is called Stirling cycle, follows in Stirling Engine, whose ideal efficiency is same as Carnot Cycle and Ericsson Cycle, which are ideal cycle.
In power plant, regeneration cycle or regeneration is used to achieve the positive side of regeneration cycle along with reheating, co generation and super-critical cycle to increase overall efficiency.

This regeneration cycle is used by extracting high pressure and temperature steam from turbine intermediate stages to different other equipment(Auxiliaries of steam turbine cycle steam heater,ejector, deareator etc.). Air used for combustion of fuel is preheated and feed water is heated using steam etc.

Steam Turbine Thermal  Efficiency is maximum to the date is 42 % .