Industrial natural gas CHP – Gas turbines with heat recovery steam generators
Combined Heat and Power units (CHPs) are the most efficient way to convert fuels into useful energy (IEA-ETSAP, 2010). The most common conventional industrial CHPs are the natural gas-fired gas turbine with heat recovery steam generators (GT-HRSG), and the combined-cycle gas turbine (CCGT), which is a combination of a gas turbine and a steam turbine. The high temperature heat from the gas turbine exhaust can be used to produce high pressure steam of temperatures up to 593 °C (US EPA CHP Partnership, 2017). The hot exhaust from the gas turbine can be directed through a steam turbine to generate additional electricity, or can be used to provide steam for industrial processes.
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In the industry, CHPs are primarily deployed to provide the steam necessary for industrial processes (Energy Matters, 2015). This factsheet provides techno-economic data (costs and energy inputs and outputs) on gas turbines with heat recovery steam generators, although technical dimensions applied to the industry sector cover both GT and CCGT. Techno-economic data for CCGT can be consulted in Niessink (2019).
The two main types of turbines used in gas turbine CHPs are aeroderivatives and heavy duty turbines. Aeroderivatives are derived from the airplane industry and provide up to 50MWe. They heat up relatively fast (15-45 minutes) and operate with 2-3 axes. Heavy Duties are especially designed for heavy industry, with capacities up to 150MWe, high reliability and long lifetimes. This type takes up to 1,5 hour to heat up and is less flexible in steam volume as it has only one turbine. It needs 60% of its full-load to function as a minimum (Energy Matters, 2015). According to CBS (2020) data, gas turbine CHP are deployed in all type of industries. CCGTs are mainly used in the chemical industry. Gas turbines are most common in chemical industry and refineries (CBS, 2020).
The advantages of GT-CHPs over other types of CHP are high reliability, low emissions and the ability to produce high grade heat. Disadvantages include the required high pressure of input gas, and poor efficiency at low loading (US EPA CHP Partnership, 2017).
A typical industrial CHP application for gas turbines is a chemical plant with a 25MW simple cycle gas turbine supplying base-load power to the plant with an unfired heat recovery system generator (HRSG) on the exhaust. This gas turbine CHP system will produce approximately 29MW thermal (MWth) of steam for process use within the plant.