热电厂供热蒸汽管道㶲效率分析

为了评价长距离输送蒸汽管道的能效水平，提出了采用㶲效率作为管道能效计算的一个重要衡量指标，并建立了管道内蒸汽一维流动模型，对某长度为2 km的蒸汽管道的热效率及㶲效率进行了计算。计算结果表明，在蒸汽流量不变时，随着管道直径的增加，管内蒸汽流速不断降低，管道的压力损失及其热效率也随之降低，但是管道㶲效率先增加后降低，有一最大值。在以管道㶲效率为优先目标设计蒸汽管道时，相比较现有的设计规范，管道内蒸汽压力损失因为流速降低而减少，因此在保证用户用汽压力的情况下汽轮机抽汽压力可以有较大幅度的降低，在抽汽流量为250 t/h时，汽轮机因为抽汽压力降低可额外输出约3 330 kW的电功率。因此，管道内蒸汽流速根据投资成本的大小在0~25 m/s范围内选取更为合理。

Exergy Efficiency Analysis of Heating Steam Pipeline for Cogeneration Power Plant

In order to evaluate the energy efficiency of long-distance steam pipe, the exergy efficiency is proposed as an important evaluating indicator to determine the energy efficiency of the steam pipe. A one-dimensional model for flow through steam pipe is established. And then the thermal efficiency and exergy efficiency of the 2 km-long steam pipe are calculated. The calculation results show that under constant steam flow rate, with the increase of the pipe diameter, the steam flow rate in the pipe as well as the pressure loss and thermal efficiency of the pipe will continuously decrease. However, the exergy efficiency of the pipe will increase at first and then decrease, with a maximum value in between. If exergy efficiency of steam pipelines is prioritized as the design target, compared with the existing design specifications, the steam pressure loss in the pipeline will be reduced as a result of the flow rate decrease. As long as enough steam pressure for the user is ensured, the extraction pressure of the steam turbine is allowed to be reduced substantially. At the extraction flow of 250 t/h, the turbine can output an additional 3330 kW of electrical power due to reduced extraction pressure. Therefore, it is more reasonable to select the steam flow rate in the pipeline within the range of 0~25m/s according to the investment cost.