Abstract:

Air-cooling power units have high back pressures in summer due to high environment temperatures, reducing the power output, thermal efficiency and operation safety. In this study, a wet-dry hybrid cooling system is analyzed with part of exhaust steam cooling by circulating water to decrease the unit back pressure in summer. A mathematic model is established for the effect of wet-dry hybrid cooling system on the thermal economy. Variations of back pressure and net power output with the live steam flow rate, exhaust steam distribution and environmental temperatures are analyzed for a 330 MW direct air cooling power unit. The results show that the power output increases from 326.266 MW to 330 MW and the back pressure drops from 46.8 kPa to 31.9 kPa as the live steam flow rate increases to1120 t·h^-1 and the distribution steam flow rate with wet cooling increases to 175 t·h^-1. The heat consumption rate decreases 110.9 kJ·(kW·h)^-1 and generation standard coal consumption rate decreases 4 g·(kW·h)^-1.

Key words: air-cooling, back pressure, wet-dry hybrid cooling system, heat transfer, model, thermodynamics, thermal economy

摘要：

受环境温度影响, 空冷机组夏季工况的运行背压高, 严重限制了机组的带负荷能力, 并影响机组的热经济性和安全性。分析了一种干-湿混合冷却系统, 将汽轮机排汽分流出一部分通过循环水冷却, 以降低机组夏季工况背压。建立了干-湿混合冷却系统对机组热经济性影响的数学模型, 并以某330 MW直接空冷机组为例揭示了机组背压和净功率随主蒸汽流量、湿冷分流量以及环境温度的变化规律。结果表明:主蒸汽流量为1120 t·h^-1、湿冷分流量为175 t·h^-1时, 机组出力从326.266 MW达到330 MW满负荷运行, 提高了3.734 MW, 背压由46.8 kPa下降到31.9 kPa, 机组的热耗率降低了110.9 kJ·(kW·h)^-1, 发电标准煤耗率降低了4 g·(kW·h)^-1。

关键词: 空冷, 背压, 干-湿混合冷却系统, 传热, 模型, 热力学, 热经济性