投运低压省煤器后汽轮机背压变化分析

机组投运低压省煤器后，锅炉的烟气余热进入回热系统，排挤回热系统的抽汽返回低压缸，排汽量增加，从而引起汽轮机背压的变化。该文根据等效焓降理论，建立了背压变化的计算模型。通过某220MW机组的试验分析，验证了该模型在220MW工况下，汽轮机背压上升0.29 kPa，背压变化修正后"等效焓降法"节能量减少0.19%，与"热力试验法"节能量更加接近。说明"等效焓降法"在分析投运低压省煤器节能效果中，还需要考虑背压变化对节能量的影响。

Analysis on the Change of Steam Turbine Back Pressure Under Operation of Low Pressure Economizer

After low pressure economizer was put into the unit, waste heat of boiler flue gas enters the regenerative system. The extraction steam returns to low pressure cylinder, and the steam volume increases, which causes the change of the back pressure of the steam turbine. According to the equivalent enthalpy drop theory, the calculation model of back pressure change was established. The model is verified through the test and analysis of one 220MW unit. Under 220MW working condition, the steam turbine back pressure is increased by 0.29 kPa. After the correction of the back pressure, the energy saving of "equivalent enthalpy drop method" decreases by 0.19%, which is closer to the energy saving of the "thermal test method". It shows that in the energy saving effect analysis of operating low-cost economizer with the "equivalent enthalpy drop method", the impact of back pressure changes on energy savings need to be considered.