Heating System Modification Schemes for Heat-Power Decoupling of Cogeneration Unit and Economic Analysis

Focusing on solving the interference of the heating supply and power generation under relatively high heating load conditions, heating-power decoupling of the cogeneration units can lower the power output of the generation units to a great extent while meeting the external heating load requirement. With its distinctive advantage of low investment, the solution of the existing heating steam system modification is strongly recommended for increasing the flexibility of the cogeneration unit. Model-based software is utilized for the performance simulation of the 300MW subcritical cogeneration unit manufactured by STC under various heating steam modification schemes. Three possible heating steam modification schemes are considered in the modeling building-up process, and the critical operation parameters and limits are explained for the modification schemes. The high pressure supplement steam is taken from the IP turbine inlet hot reheat steam and HP turbine exhaust cold reheat steam and No.4 steam extraction respectively for Scheme No.1, No.2 and No.3. The results of the minimum power loading capability under maximum heating load condition are calculated. It is shown that with the increase of the proportion of the high pressure steam, the minimum load that could be reached is decreased while maintaining the maximum heating load. From the point view of the peak load adjustment improvement, scheme No.1 has apparent and significant effect and scheme No.2 has average and moderate effect while scheme No.3 has the worst effect. The performance data of the unit is also provided for the various modification schemes. It's shown that the unit performance under 200t/h IP inlet heating steam condition in scheme No.1 is very close to the 75% heating load condition of the original IP-LP crossover piping heating steam scheme.