SUBJECT – APPLIED THERMAL AND HYDRAULIC ENGINEERING (2140907)BRANCH – ELECTRICAL TOPIC – GAS TURBINE CYCLE (OPEN AND

CLOSED GAS TURBINE CYCLE)NAME – HIMAL DESAI (140120109008)GUIDED BY: PROF. ADITYA SINGH

Gandhinagar Institute Of Technology

Introduction

A gas turbine, also called a combustion turbine, is a type of internal combustion engine.

It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in between.

The basic operation of the gas turbine is similar to that of the steam power plant except that air is used instead of water. 

Joule and brayton independently proposed the cycle that is ideal prototype.

Classification of Gas Turbine Cycle

Gas turbine cycle are broadly classified in to two types, namely

1. Open cycle gas turbine2. Closed cycle gas turbine

Open Cycle Gas Turbine

Working:

Open gas turbine cycle are composed of three main components: compressor, combustor and power turbine.

Air at ambient conditions is drawn into the compressor, where its temperature and pressure are raised.

The high pressure air proceeds into the combustion chamber, where the fuel is burned at constant pressure.

The high-temperature gases then enter the turbine where they expand to atmospheric pressure while producing power output.

Some of the output power is used to drive the compressor and the remaining is available as shaft work.

The exhaust gases leaving the turbine are thrown out (not re-circulated), causing the cycle to be classified as an open cycle.

Advantages of Open Cycle Gas Turbine:

Simplicity:  A simple open cycle gas turbine has only three components, compressor ,combustion chamber turbine. The combustion chamber is inexpensive, light weight and small with a high rate of heat release. It can be designed to burn almost all hydrocarbon fuels ranging from gasoline to heavy diesel oil.

Low weight and size: Open cycle gas turbine has lower specific weight and requires less space per unit power output.

Low capital cost: Since open cycle gas turbine has only minimum components and has low weight and size per unit power output ,the capital cost is less compared to other plants.

Disadvantages of Open Cycle Gas Turbine:

Sensitivity: The simple open cycle gas turbine is sensitive to changes in the component efficiencies. A reduction in the efficiencies of compressor and turbine will rapidly lower the efficiency of the cycle.

The open cycle gas turbine is sensitive to changes in the atmospheric temperature. An increase in atmospheric temperature lowers the thermal efficiency.

Closed Cycle Gas Turbine

Working:

In closed cycle gas turbine , the working fluid does not come in contact with atmospheric air. The working fluid is air or some other suitable gas.

The compression and expansion processes remain the same, but the combustion process is replaced by a constant-pressure heat addition process from an external source.

The exhaust process is replaced by a constant-pressure heat rejection process to the ambient air.

The cold gas is drawn into the compressor, where its temperature and pressure are raised.

The high pressure air proceeds into the combustion chamber, where the fuel is burned at constant pressure.

The high-temperature gases then enter the turbine where they expand to atmospheric pressure while producing power output.

Some of the output power is used to drive the compressor and the remaining is available as shaft work.

The exhaust gases leaving the turbine are cooled in heat exchanger called sink where it reject heat. The gas is restored to its initial state.

Therefore, in this cycle the same working fluid is recirculate causing the cycle to be classified as closed cycle

Advantages of Closed Cycle Gas Turbine:

There is no Corrosion and Accumulation of Deposits of Carbon or Tar on the Blade and Nozzles of the Turbine. No internal cleaning required.

Any Fuel of High Calorific Value may be used, as the products of combustion do not mix with the working fluid.

By making an Inert Gas like Helium as the working medium, use can be made for materials in the Turbine Design, like Molybdenum Alloys. This has High Stress Properties at elevated Temperature above 1000 degree centigrade. By such means the Turbine Plant efficiency at over 50% can be achieved.

The waste Heat of the Combustion Gases from the Heat and Re-heaters can be further used for Heating Water. This can be used for Hot Water supply for Industrial or Domestic purpose.

Disadvantages of Closed Cycle Gas Turbine:

External furnace for combustion processMore complicated and costlySystem must be strong enough to resist high

pressures.Coolant is used for pre-cooling whereas no coolant is

required in open cycle gas turbine. Atmosphere act as sink.

Thank

you