Cogeneration system simulation and control to meet simultaneous power, heating, and cooling demands

Gas turbines are projected to meet increasing power demand throughout the world. Cogeneration plants hold the promise of increased efficiency at acceptable cost. In a general case, a cogen plant could be able to meet power heating and cooling demands. Yet those demands are normally uncoupled. Control and storage strategies need to be explored to ensure that each independent demand will be met continuously. A dynamic model of a mid-capacity system is developed, including gas and steam turbines, two heat recovery steam generators (HRSG) and an absorption-cooling machine. Controllers are designed using linear quadratic regulators (LQR) to control two turbines and a HRSG with some novelty. It is found that the power required could be generated exclusively with exhaust gases, without a duct burner in the high-pressure HRSG. The strategy calls for fuel and steam flow rate modulation for each turbine. The stability of the controlled system and its performance are studied and simulations for different demand cases are performed.