火电机组余热梯级供热技术的综合分析

Comprehensive analysis of cascade heating technology based on wasteheat of thermal power units

针对传统供热技术平均(火用)效率低的问题,提出了乏汽余热梯级供热技术。该技术有效地利用了机组乏汽余热,并减少了汽轮机的冷源损失,避免了中排抽汽参数过高造成的能量损失,提高了机组供热经济性。以某电厂为例,本文基于热力学定律与单耗分析理论,建立了乏汽余热梯级供热系统的单耗分析模型,应用该模型对其进行了(火用)分析和附加燃料单耗分析,为节能降耗提供了理论依据。分析结果表明,发电煤耗率由改造前的249.69g/(kW·h)降低到149.9g/(kW·h),降低了99.79g/(kW·h),机组供热负荷较由改造前的788.4MW增加到1673.9MW,增加了885.5MW;改造后传热温差在非严寒期只有7℃、严寒期为26.94℃,比改造前大幅降低;在非严寒期和严寒期,加热器蒸汽入口平均比(火用)比改造前分别降低了524.73kJ/kg、418.2kJ/kg,供热系统的平均(火用)效率比改造前分别提高了51.35%、32.58%,供热系统的平均附加燃料单耗分别为3.11g/(kW·h)、7.98g/(kW·h)。可见通过"乏汽余热梯级供热技术"改造后,节能效果显著,该技术具有广阔的推广应用前景。

To solve the problem of low average exergy efficiency of traditional heating technology, acascade heating technology based on waste heat of exhausted steam was proposed. The technologyeffectively uses waste heat of exhausted steam and reduce the cold source loss of steam turbine, avoid theenergy loss caused by the high extraction parameters of steam from intermediate pressure cylinder outlet,and the heating economy of the unit was improved.Taking a power plant as an example,the fuel specificconsumption analysis model of cascade heating system based on waste heat of exhausted steam wasestablished based on the law of thermodynamics and fuel specific consumption analysis theory,the exergyanalysis and additional fuel specific consumption analysis were carried out by using the model, whichprovides a theoretical basis for energy saving and consumption reduction. The results indicate that: thecoal consumption for power generation decreased from 249.69g/(kW·h) before the transformation to 149.9g/(kW·h), a decrease of 99.79g/(kW·h), the heating load of unit increased from 788.4MW before thetransformation to 1673.9MW, an increase of 885.5MW;the heat transfer temperature difference after thetransformation was only 7℃ at the non-frigid period and 26.94℃ at the severe cold period, which was much lower than that before the transformation;the average exergy of steam inlet of heater decreased by524.73kJ/kg and 418.2kJ/kg respectively compare with before the transformation, the average exergyefficiency of heating system increased by 51.35% and 32.58% respectively compare with before thetransformation,the average additional fuel specific consumption of heating system was 3.11g/(kW·h) and7.98g/(kW·h) at the non-frigid and severe cold period. This shows that after the transformation of“acascade heating technology based on waste heat of exhausted steam”, the economic benefit is remarkable,so it has a broad application prospect in the field of the cascade heating technology based on waste heat ofexhausted steam.