Question

For a vapor power system, either increasing the boiler pressure or increasing the turbine inlet vapor temperature will improve the thermal efficiency of the system. Which method is mostly applied in real applications and why

Answer 1

1)For increasing the thermal efficiency of the vapour power systems the method of increasing the boiler pressure is used in real application. The reason is if we increase the turbine inlet temperature then we have to use high grade materials. The materials used in real application have less capacity to withstand high temperature. Hence due to material restrictions we increase boiler pressure. When boiler pressure is increased the quality of steam at turbine exit is low hence to increase quality of steam, reheating is used ( which is possible) and two stage turbine is used.

2) In vapour power cycle the working fluid is in vapour state in one process and changed to liquid phase in another process (consider rankine cycle). The same working fluid is recovered and reused. So the vapour power cycles are closed cycles. The working fluid condense to liquid and evaporates to vapour.

But in gas power cycles the working fluid remains as gas and cannot be recovered and reused as like vapour hence gas power cycles are open cycles. and in every gas power cycles the product after combustion is smoke which cannot be reused.