Cogeneration Improvement Based on Steam Cascade Analysis

In site utility systems, very high pressure (VHP) steam is generated from fuel combustion in boilers and gas turbines heat recovery steam generators. VHP steam is distributed to lower pressure steam mains to satisfy process heating demand. The steam cascade in the utility system is determined by utility VHP steam from boilers, process heating and cooling demands, and process indirect heat recovery through the utility medium. Utility power is generated by fuel combustion in gas turbines and steam expansion or condensation in steam turbines. Steam mains selection, process heating and cooling demands, and process indirect heat recovery affect utility VHP steam target, the steam cascade and cogeneration. This work presents an extended graphical approach based on steam cascade analysis to explore how steam mains selection influences cogeneration improvement. The interaction among process heating and cooling demands, processes indirect heat recovery, and utility targets of VHP steam demand and cooling medium are quantified graphically. This graphical method would be helpful to scope the potential cogeneration improvement by variation of steam mains. The insights gained can be used to simplify the optimization of the utility system.