TECHNOLOGICAL ENERGY CAPACITY OF COMBINED CYCLES OF STEAM GAS STATIONS

Abstract

Offers a means of increasing the efficiency of the cycle by reducing par asitic loads such as the excess air compressor load and of capturing energy that might otherwise be wasted. However, this is not always the most effective way of increasing overall efficiency of energy conver sion. For large gas turbine based plants in particular, the best way of improving efficiency is to add a steam turbine bottoming cycle, creat ing a combined cycle power plan. A combined cycle plant is simply what its name suggests. Instead of relying on a single thermodynamic cycle to convert energy into electricity the plant uses more than one. These piggy-back one another with the first cycle using the highest temperature thermodynamic working fluid, followed by a second using the intermediate temperature fluid . In fact combined cycle plants with more than two cycles are not used commercially although they are theoretically possible. Much more significant for the modern power generation industry is the addition of a bottoming cycle to a gas turbine power plant. In this case the bottoming cycle is usually a steam turbine cycle, with heat from the gas turbine exhaust exploited to raise steam. This is the most common combined cycle power plant. It would be possible to add a third cycle to exploit the low grade heat remaining after steam generation. This could be achieved with a closed cycle turbine such as an organic Rankine cycle. Such turbines can exploit low grade heat to produce electricity and are used in some geothermal plants where the temperature of the geothermal reservoir is relatively low. However, it is unlikely to be economically viable to add this third cycle to a modern combined cycle plant. To determine the technological energy intensity of such stations, the whole cycle of energy production was considered. The main characteristics of combined cycles are given and the technological energy intensity of energy supply is calculated. The main advantages and disadvantages of these installations are given, and also the comparison of steam turbine and steam and gas stations is made with definition of possible potential at replacement.