SLIDING PRESSURE ANALYSIS USING THE 2ND LAW

Over the last 20 years many technical papers have been written by manu facturers on the concept of reducing or sliding the turbine inlet pres sure at lower loads to reduce frictional losses. This paper takes a un ique look at why sliding pressure is needed using both the first and s econd laws of thermodynamics. The derived equations are applied to the flow of steam across a single valve and then applied to a simplified turbine control valve system. The optimal control point at which to in itiate sliding pressure is analyzed. It is also shown that the optimal operating point is not when the second-law efficiency is maximum, but when the first-law efficiency is maximized.