Introduction to Combine Cycle Power Plant

ByLeelananda Pilanawithana

Power plants• Categorized by functional type– Base load– Peak load and emergency Base load• Run continuously, stop only for maintenance. Generate

power most in any given year.• Have lowest operating cost.

– Its type» High efficient combined cycle plants fueled by natural

gas or liquid fuel» Nuclear Power Plants» Conventional steam power plants fueled primarily by

coal or fernours oil» Hydropower plants

Peak load and emergency• Run during peak load demand period or an emergency.• Operating cost is high, but cheap to built.• Fast start and loading.

– Type» Open Cycle (Simple cycle) gas turbine plant.» Diesel engine plants.» Hydropower plant

Power plants

Definition

• Combine – When several different things add together

• Cycle– Process is repeated or moving around a circle. – In Thermodynamic point of view,

Rankine, Diesel, Otto , Carnot, Brayton,are some of the thermodynamic cycles.

Definition

– Those cycles are always associated with one of the two type of combustion processes.Internal Combustion Gas Turbines, Diesel engines, Gasoline enginesExternal Combustion

Steam Engines (Boiler and steam turbine)

Cycle Definition• Combine Cycle– Employ more than one thermodynamic cycles.

• Brayton cycle, • Rankine cycle.

– Improve the simple Brayton cycle efficiency by capturing wasted energy in Brayton cycle and use it in Ranking Cycle.• Brayton cycle, – Engine used extensively is a Gas Turbine» utilize only a portion of the energy

from the fuel that is being used Open cycle or

» Reminder if not recovered is wasted. Simple cycle Open cycleConfiguration

Combine cycleConfiguration

Cycle Definition

• Rankine cycle– Engine used is Heat Recovery Boiler (HRSG) plus Steam

Turbine.

Basic equipment arrangement Temperature Entropy Diagram

Advantages of Combine Cycle Power Plant• Low installation cost / MW• High efficiency among all practical power cycles.• Low auxiliary power consumption/MW (2 – 3%)• Less manpower/MW ratio.• High reliability and availability. • Clean operating Condition.• Less Gestation period.• Fast starting characteristics.• Less water requirement.

• Less pollution problems.• Flexibility in locating power plant.• Fuel flexibility.• Less space requirement.• Gas turbine can be operated as peak load plant and

Steam turbine as base load plant by supplementary firing in HRSG unit

Advantages of Combine Cycle Power Plant

• Need good quality fuel specifically low sulfur, vanadium and lead content .

• Fuel treatment process is costly.• GT performance severely deteriorate with

ambient temperature.• High Nox pollutant.• GT life is less due to corrosion problems.• Uneconomical partial load operation.

Disadvantages of Combine Cycle Power Plant