All process plants need electrical power and thermal energy and almost always there is a concurrent demand for both of these energy streams. The ability to use one form of primary fuel (typically, natural gas) to simultaneously provide two forms of energy (thermal and power) is known as combined heat and power (CHP) or cogeneration. One of the most common forms of CHP is use of a natural-gas-fired gas turbine generator (GTG) operating in conjunction with a heat recovery steam generator (HRSG). The GTG provides electrical power and the HRSG provides steam at the required pressure.
Plants also have natural- or fuel-gas-fired boilers that generate steam at required pressure. The energy efficiency of boilers depends on several factors but primarily on the heat recovery equipment, excess-air controls and the boiler load. Most of these boilers have an operating energy efficiency of ~80–85%.
Now let’s take a look at the cogeneration system.