Designs with Low Pinch and Approach Points
Pinch and approach points determine HRSG temperature profiles. If we have to work with only a single-pressure HRSG and there is no additional heat recovery equipment such as a deaerator coil or condensate heater, we can use low pinch and approach points to maximize steam generation. However, the surface area requirements increase due to the low log-mean temperatures in the evaporator and economizer, which adds to the cost of the HRSG slightly and increases the gas pressure drop. The major components of the HRSG such as controls and instrumentation, drum size, casing, and insulation do not change in a big way, and the additional cost of heating surfaces may not be that significant if we look at the overall picture. However, an economic evaluation may be done as shown in Q8.40.