电站汽轮机低压缸排汽焓近似计算模型研究

Research on Approximate Calculation Model of LP Steam Turbine Exhaust Enthalpy in Power Plant

凝汽式汽轮机低压缸排汽段通常处于湿蒸汽区,排汽焓值难以直接测量。提出一种汽轮机排汽焓的计算方法,以级内损失理论为基础,将各类损失划分为与容积流量相关的排汽损失、与湿度相关的湿汽损失和与理想焓降相关的其他损失。排汽损失由排汽容积流量决定;湿汽级焓降占总焓降的比例系数通过低压缸热力过程线中的相似三角形关系求出;根据速比与理想焓降的关系,将其他损失的系数简化成只与理想焓降有关的二次多项式。通过理论计算和量纲分析证明排汽流量的误差对计算结果影响较小。应用提出的方法,根据设计数据计算了不同厂家生产的不同容量级别汽轮机机组的低压缸排汽焓,并与设计值进行了对比。结果表明,该方法在设计数据条件下计算精度较高,证明了该方法的可行性,为现场的实际应用奠定了基础。

The exhaust enthalpy of the turbine is difficult to measure because the last stages of LP turbine are in wet steam region. A new approximate thermodynamic method based on the stage loss theory is proposed. In this model, the various types of stage losses are classified as the exhaust loss related to volume flow, the wet steam loss related to humidity and other losses related to ideal enthalpy drop. The exhaust loss is determined by exhaust volumetric flow and the coefficient of wet steam loss is obtained by similar triangle of thermodynamic process line. Whereas, the coefficients of other losses are expressed as a form related with ideal enthalpy drop only. The error of exhaust flow is proved to be a little influence on the calculated exhaust enthalpy. The exhaust enthalpies of different turbines are calculated and compared with the designed values, demonstrating the feasibility of the method. The result indicates that the proposed calculation method has enough precision and it can be used for the calibration and online testing of exhaust enthalpy.