Applied Thermal and Hydraulic Engineering(2140907) Gas turbine cycle (open and closed gas turbine cycle)

1. 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

2. 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.

3. Classification of Gas Turbine Cycle
 Gas turbine cycle are broadly classified in to two
types, namely
1. Open cycle gas turbine
2. Closed cycle gas turbine

4. Open Cycle Gas Turbine

5. 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.

6. 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.

7. 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.

8. Closed Cycle Gas Turbine

9. 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.

10.  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

11. 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.

12. Disadvantages of Closed Cycle Gas Turbine:
 External furnace for combustion process
 More complicated and costly
 System 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.