热电联产机组热能深度梯级利用的研究

Research on thermal energy step utilization in cogeneration units

在分析热电联产汽轮发电机组运行与热网加热特点的基础上,提出了热电联产机组低位能分级混合加热供热技术,即通过改变传统的热电联产热网加热方式,由汽轮机低压缸排汽的低位能替代中压缸排汽的高位能加热热网循环水,实现热能转换的梯级利用。以某典型200 MW级湿冷机组抽凝式供热为例,分析了低位能供暖系统的热力学特性和节能效果。结果表明,低位能改造后,机组在供热初末期、维持全厂发电负荷不变的情况下,燃煤量减少5.45 t/h,供热负荷增加208.7 GJ/h。供热热源蒸汽代价焓减少150.68 kJ/kg,效率提高23.73%,折合单机供电煤耗下降84.26 g/kW·h。严寒期维持全厂单位h燃煤量不变,电负荷增加12.62 MW,热负荷增加306.1 GJ/h,供热热源蒸汽代价焓减少98.5 kJ/kg,效率提高14.3%,发电煤耗相对下降79.0 g/kW·h。运行表明该低位能改造技术,系统稳定可靠、经济效益显著,节能减排效果明显,具有广阔的推广应用前景。

Based on analysis of operation characteristics in cogeneration units and heat-supply mode,a cascade mixing heating system which can deeply utilize low-grade energy is presented. This technology changes the traditional heat-supply mode by means of replacing the heating steam source,namely,the heating steam from the intermediate pressure cylinder exhaust steam is replaced by the low pressure cylinder exhaust steam. This realizes the step utilization of thermal energy. As an example,the thermodynamic properties and energy-saving effects of a classic 200 MW extraction condensing heating unit is analyzed. The results show that,after the transformation,for the case of constant generation,load the coal consumption reduced 5. 45 t /h. Heating quantity increased 208. 7GJ /h,and the enthalpy exergy cost reduced 150. 68 kJ /kg. Exergy efficiency raised 23. 73 % and net coal consumption rate of single unit reduced 84. 26 g /kW·h at the beginning and end of the period. In the hard winter,under the condition of constant hourly coal consumption,the power load increased 12. 62 MW,and the heating quantity increased 206. 1GJ /h. Enthalpy exergy cost reduced 98. 5kJ /kg. Exergy efficiency raised 14. 3 % and net coal consumption rate of single unit reduced 79. 0g /kW·h. It shows that the low-grade energy heating system is stable and reliable. Economic benefit is remarkable. Energy conservation and emissions reduction effect is obvious. The technology has very broad application prospects.