Combined heat and power plants integrated with steam turbine renovations: Optimal dispatch for maximizing the consumption of renewable energy

Steam turbine renovations, including the high back-pressure (HBP) renovation and the low pressure turbine zero power output (LZPO) renovation, can enlarge the loads supply range of one single combined heat and power (CHP) unit. Focusing on renewable energy consumption and coal saving, the problem regarding the optimal dispatch of a case CHP plant with renovated CHP units is addressed in this study. The energy and exergy analysis models are developed to evaluate the performance of various types of CHP units. The models of the minimum power load and the coal consumption for the whole plant are established based on the unit combinations in case 1 to case 4. The adaptive mutation particle swarm optimization (AMPSO) algorithm is adopted to seek the optimal value and the corresponding loads distributions. Results show that the maximum energy efficiency of the HBP renovated unit and LZPO renovated unit are 87.1% and 88.2%. Moreover, the maximum exergy efficiency of the HBP renovated unit and LZPO renovated unit are 41.3% and 32.1%. In brief, the HBP renovated unit has higher exergy efficiency and lower energy efficiency than LPZO renovated unit. In terms of optimization methods, AMPSO has better performance than PSO in terms of convergence speed and getting rid of local optimum solutions. After reasonably redistributing the loads of the case plant integrating the HBP and LZPO renovations, approximately 0.191 billion kWh more renewable energy would be consumed, and about 0.069 million tons of coal and 0.181 million tons of CO2 emissions could be saved during the heating season. Optimization results show that the LZPO renovations are more effective in consuming renewable energy, and the HBP renovations can be considered as the preferable coal-saving option. This study provides a method for optimizing the operation of renovated CHP plants. In addition, for the un-renovated CHP plant such as case 1, the renovation patterns in case 2 to case 4 provide some reference once the steam turbine renovations to be considered.