Combined Heat and Power Microturbines

This fact sheet provides a review of combined heat and power (CHP) technologies for use at water resource recovery facilities (WRRFs). CHP, also called “co-generation,” is defined as the concurrent production of electricity and thermal energy from a power-generating device. Individually, microturbines are on the smaller end of the spectrum of CHP units and, at 92 MW of total installed capacity, they only comprise 0.1% of the total CHP capacity in the United States (U.S. Department of Energy, 2015). Their small size and modular design allow for widespread applicability, and, in terms of number of CHP sites using microturbines as their chosen technology, microturbines comprise approximately 8% of the U.S. CHP market (U.S. Department of Energy, 2016).

Microturbines make use of a Brayton cycle, where air is first drawn into the engine and compressed to high pressure by a radial compressor and is then mixed with fuel in the combustion chamber and continuously ignited. The compressed air is used to drive a turbine that provides torque to both the compressor drawing the air in and an electrical generator. Modern microturbines also make use of a recuperator stage, where hot exhaust air passes by the compressed air entering the combustion chamber, preheating the air before combustion and increasing thermal efficiency.

Microturbines of 30 to 300 kW are an economical option, with the ability to parallel multiple modular units (U.S. Department of Energy, 2016). In December 2019, only 36 sites with a total capacity of 7.4 MW within the U.S. water resource recovery industry were demonstrating this technology and its economic benefits (U.S. Department of Energy, 2019). U.S. installations at WRRFs range in size from 30 kW to 1.6 MW (U.S. Department of Energy, 2019).