Unit 2 GT Based Power Plant

GAS TURBINE BASED POWER PLANTS (Open Cycle & Combined Cycle)

Refer to text books for addl. points / ideas

For internal circulation only

TURBINES: Machines to extract fluid power from flowing fluids

Steam Turbine Water Turbines Gas Turbines Wind Turbines

Aircraft Engines Power Generation

High Pressure, High Temperature gas Generated inside the engine Expands through a specially designed TURBINE

GAS TURBINE BASED POWER PLANTS

Gas Turbines Invented in 1930 by Frank Whittle

Patented in 1934

First used for aircraft propulsion in 1942 on Me262 by Germans during second world war

Currently most of the aircrafts and ships use GT for propulsion.

Used for power generation

Manufacturers: General Electric, Pratt &Whitney, Rolls Royce, Honeywell, Siemens Westinghouse, Alstom, BHEL.


Gas Turbine

Hot gases move through a multistage gas turbine.

Like in steam turbine, the gas turbine also has

stationary and moving blades.

The stationary blades

guide the moving gases to the rotor blades

adjust its velocity.

The shaft of the turbine is coupled to a generator.


Types of Gas Turbine Power Plants

The gas turbine power plants can be classified mainly into two categories. These are : i). Simple or open cycle gas turbine power plant and ii). Closed cycle gas turbine power plant.

Open Cycle (simple cycle) Gas Turbine Power Plant: In this

type of plant, the atmospheric air is charged into the combustor through a compressor and the exhaust of the turbine is also discharged to the atmosphere.

Combined Cycle Gas Turbine Power Plant: The combined cycle aims at utilizing the heat of exhaust gases from the gas turbine thus, improve the overall plant efficiency. The popular designs are:

1. Heating feed water with exhaust gases. 2. Employing the gasses as combustion air in the steam boiler.


Simple Cycle

Operate When Demand is High Peak Demand

Operate for Short / Variable Times

Designed for Quick Start-Up

Not designed to be Efficient but Reliable.

Not Cost Effective

Combined Cycle

Operate for Peak and Economic Dispatch

Designed for Quick Start-Up

Designed to Efficient, Cost-Effective Operation

Types of Gas Turbine Plants


Main Components of GT based Plant (Open Cycle)

Inlet system Air Compressor Regenerator Combustion Chamber Gas Turbine Alternator Starting Motor


Comp- ressor

air

Combustion Chamber

fuel

Gas Turbine

gases to the stack

Gen

compressed air

hot gases

Gas Turbine Based Power Plant s (Open cycle)

2-2-16

Gas turbine based power plants

Air compressor:

Sucks in air and compresses it, thereby increasing its pressure.

The air compressor and turbine are mounted at either end on a common shaft, with the

combustion chamber between them.

Gas turbines are not self starting. A starting

motor is used.

Inlet system: Collects and directs air into the gas

turbine. Often, an air cleaner and silencer are part of the

inlet system. It is designated for a min. pressure drop

while maximizing clean airflow into the gas turbine.

Combustion chamber:

In the combustion chamber, the compressed air combines with fuel and the resulting mixture is burnt. The output power of the gas turbine is directly proportional to the

combustor firing temperature.

The greater the pressure of air, the better the fuel air mixture burns.

Modern gas turbines usually use liquid fuel, but they may also use gaseous fuel, natural

gas or gas produced artificially by

gasification of a solid fuel.



Gas Turbine:

Hot gases move through a multistage gas turbine.

Like in steam turbine, the gas turbine also has stationary and moving blades.

The stationary blades

guide the moving gases to the rotor blades

adjust its velocity.

The shaft of the turbine is coupled to a generator.

Working principle : Air is compressed(squeezed) to high pressure by a

compressor.

Then fuel and compressed air are mixed in a combustion chamber and ignited.

Hot gases are given off, which spin the turbine wheels.

Gas Turbine Based Power Plants

R. Shanthini 15

Aug 2010

Gas Turbine driving a Jet Engine

Brayton Cycle Gas Turbine Cycle (open cycle) GAS TURBINE BASED POWER PLANTS

Efficiency is 20 to 30% whereas that of steam power

plant is 38 To 40%

Advantages Storage of fuel requires less area and handling is easy. The cost of maintenance is less. It is simple in construction. There is no need for boiler, condenser & other accessories as in the case of steam power plants. Gas turbine plants can be used in water scarcity areas. Less pollution and less water is required.


Disadvantages 66% of the power developed is used to drive the compressor. Therefore the gas turbine unit has a low thermal efficiency. The running speed of gas turbine is in the range of (10,000 to 30,000 rpm) and the operating temperature is as high as 1100 12600C. For this reason special metals and alloys have to be used for the various parts of the turbine. High frequency noise from the compressor is objectionable.


What is a Combined Cycle Power Plant?

A combined cycle system uses the same heat energy

to generate power by using two different

thermodynamic cycles.

The advantage : high overall efficiency of the plant electrical energy out compared with heat energy in is greatly improved over either the simple gas turbine

cycle or simple steam turbine cycle.

This plant uses two distinctly different thermodynamic

cycles to perform useful work (generate electricity).

The Brayton (Gas Turbine) Cycle The Rankine (Steam Plant) Cycle.


Combined Cycle: The plant contains a gas and a steam turbine. The hot exhaust gases of the gas turbine

feed a steam generator which supplies a steam turbine. The gas turbine is similar to a large aircraft engine.

Both turbines drive a generator and produce electrical power.

The plant efficiency is high.

CompressorCombustion

Turbine

Cooling Tower

CondenserFeedwater Pump

Hot

Exhaust

Gases

Warm

Exhaust

Gases

Air

Gas/Oil Fuel

Steam

TurbineHeat Recovery

Steam Generator

Steam Line Generator

Gas Turbine (Brayton) Cycle

Steam (Rankine) Cycle

Generator


Heat recovery steam generator

Steam turbine plant

Exhaust gas

Life steam

Condensate

Electrical energy

4

9 8

10

Cooling tower

Cooling air

Electrical energy

6 5 1 2 3

Air Fuel

Gas turbine plant

Gas turbine plant:

11

12

7

9

Fresh water

1 Air intake

2 Compressor

3 Gas turbine

4 Heat recovery steam generator

5 Generator

6 Transformer

Steam turbine plant:

7 Steam turbine

8 Condenser

9 Feeding pump

10 Generator

11 Transformer

12 Circulating pump

Schematic of a Combined Cycle Power Plant


Adv. & Dis-adv. (combined cycle)

Advantages

High efficiency

Less cost per unit (KW) ?

Disadvantages

Complexity

Fuel requirement


Applications of gas turbine:

drive pumps, compressors and high speed cars.

aircraft and ships.

Power generation (used for peak load and as stand-by unit).


End of Unit 2, Part 2

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Unit 2 GT Based Power Plant