HRSG Pinch Point & Approach Temperature Calculator
Calculate evaporator pinch point (ΔTpinch), economizer approach temperature (ΔTapproach), heat transfer surface trade-offs, and steaming prevention in HRSG boilers.
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Frequently Asked Questions
What is the pinch point temperature in an HRSG?
The pinch point temperature difference (ΔTpinch) is the minimum temperature gap between the hot exhaust gas exiting the evaporator and the boiling water saturation temperature (Tsat) inside the steam drum: ΔTpinch = Tgas,evap_out - Tsat. Typical design values range from 15°F to 25°F.
What is the approach temperature and why is it critical?
The approach temperature is the difference between saturation temperature in the drum and water temperature leaving the economizer: ΔTapproach = Tsat - Twater,out. A positive approach of at least 10°F to 20°F is mandatory to prevent water from boiling inside the economizer tubes during sudden turbine load swings (steaming economizer).
What is the economic trade-off of lowering the pinch point?
Lowering the pinch point extracts more heat from the gas, boosting steam production and plant electrical efficiency. However, as ΔTpinch approaches zero, the required heat transfer surface area approaches infinity, leading to steep capital costs for tube bundles.