变工况下超超临界机组抽汽过热度利用方案的比较分析

Comparison and Analysis of the Superheating Degree Utilization Versions for a Ultra-supercritical Unit Under the Off-design Operating Conditions

针对大型超超临界机组热力系统回热抽汽过热度偏高的问题,研究了变工况条件下超超临界机组回热系统抽汽过热度的变化特点,并且对外置式蒸汽冷却器和回热式小汽轮机两种过热度利用方案的热力性能及节能效果进行了比较和分析。结果表明:外置式蒸汽冷却器方案和回热式小汽轮机方案在各种工况均能有效地降低超超临界发电机组的抽汽过热度,降低机组煤耗;回热小汽机方案可以同时降低多级抽汽过热度,因而其节能效果要好于一级外置式蒸汽冷却器的过热度利用方案,在设计工况下回热小汽机方案可节能1.34g/(k W·h),约为外置式蒸汽冷却器方案的2倍;当负荷降低时,外置式蒸汽冷却器方案的节能效果略有增强,而回热式小汽轮节能效果则明显降低,两方案节能效果相接近。

In the light of the problem that the superheating degree of the recuperative steam extracted in the thermal systems of large-sized ultra-supercritical units is excessively high,studied were the specific features of the change in the superheating degree of the steam extracted in the thermal system of a ultra-supercritical unit and compared and analyzed were the thermal performance and energy-saving effectiveness of two kinds of superheating degree utilization version,i. e. externally installed type steam cooler and recuperative type small-sized steam turbine. It has been found that both externally installed type steam cooler and recuperative type small-sized steam turbine versions can effectively lower the superheating degree of the steam extracted from the ultra-supercritical unit under various operating conditions and reduce the coal consumption of the unit. The recuperative type small-sized steam turbine version can lower the superheating degree of the steam extracted from several stages at a same time,thus its energy-saving effectiveness is better than that of the superheating degree utilization version by using a one-stage externally-installed type steam cooler. Under the design operating condition,the recuperative type small-sized steam turbine version can save coal by 1. 34 g / k Wh,two times higher than that of the externally-installed type steam cooler version. When the load goes down,the energy-saving result of the externally-installed type steam cooler version slightly becomes good,however,that of the recuperative type small-sized steam turbine version conspicuously becomes poor,thus the results achieved by adopting both energy saving versions get close to each other.