**2. Background of a combined heat and power (CHP) system**

For a majority of process plants, the bulk of the energy required is supplied through the utility system. On most facilities, the required heating is provided by combined heat and power (CHP) systems. A CHP system is a combination of two or more systems that are used in the generation and distribution of steam and power through gas turbine generators (GTGs), heat recovery steam generators (HRSGs), boilers, and steam turbines. The use of CHP plants means that the efficiency of the processing facility in terms of its energy consumption is reliant on efficiency of both the process side and the operation of the utility system. Steam is used for various purposes such as heating, drying, and providing a heat source for air conditioning or motive energy for a power generation via steam turbines.

As illustrated in **Figure 1** (Gas-Turbine-Based CHP Plant), a typical CHP starts with the Bryton Thermodynamic cycle where the combustion of a fuel and air mixture in a gas turbine combustion chamber occurs, the combustion product is then channeled through a series of blades attached to a rotating shaft and a generator, which then generates power and hot flue gas through the gas turbine exhaust system. The exhaust gas, which has a high energy content, becomes the heating

*Industrial Design Energy Efficiency and GHG Emission Reduction via Steam and Power… DOI: http://dx.doi.org/10.5772/intechopen.102544*

**Figure 1.** *Gas-turbine-based CHP plant.*

**Figure 2.** *Boiler-based CHP plant.*

medium in the next heat recovery Rankine Cycle of the CHP, the flue gas is channeled through an HRSG to heat up boiler feed water and produce steam. The generated steam is then used to drive a steam turbine generator (known as a combined cycle) or sent to a process plant to be used as a heating medium in a heat exchanger or to mechanically drive rotating equipment such as pumps and compressors (known as cogeneration).

**Figure 2** (Boiler-Based CHP Plant) illustrates an alternative type of CHP system. In a boiler-based CHP system, one or more boilers are used to generate steam, and steam turbine generators (STGs) are then used to generate power. In certain configurations, steam is extracted from the steam turbine generator (STG) to be used for process heating via heat exchangers. Most of Saudi Aramco's facilities or plants have a combination of both gas turbine and boiler-based CHP systems. For example, see [2].
