By Marty Ellman, Project Director at Nexus Engineering Group

As we near 2021, energy efficiency and emissions reduction remain top priorities for our clients across sectors. Government and industry leaders are taking bold action to meet global goals of achieving carbon neutrality by 2050. Centralized electric distribution systems are transforming to support the transportation industry’s shift to large scale electric vehicle use. Distributed generation is evolving as well, with microgrids forecasted to contribute significantly to energy efficiency, reliability, and resiliency.

Blue diesel and gas engine powering a CHP Power System

A diesel and gas engine generator from a CHP unit

Combined heat and power (CHP) systems are playing an important role in this evolution, providing large scale efficiency gains by repurposing waste heat from power generation to meet a facility’s heating and cooling needs. As industrial and institutional facility managers consider CHP additions to support their facility’s electrical and thermal loads, they must decide which CHP technology will best meet betvictor apptheir operational, economic, and social goals.

With a variety of equipment solutions available, understanding the benefits and tradeoffs of each is an important step to right-fitting a CHP solution that will maximize the value of this decade-plus asset.

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Combined heat and power is a cleaner, higher-efficiency approach to generating electricity and useful thermal energy from a single fuel source. Power production is located at or near the end-user’s site. While the power plant generates all or a portion of the site’s electricity, the heat released from the production of electricity is repurposed to help heat or cool the facility. This makes CHP applications a smart, high-efficiency way to cost-effectively meet a facility’s thermal requirements.

One of the most common CHP applications consists of a single topping cycle CHP cogeneration system utilizing a combustion turbine or reciprocating engine with a heat recovery unit.

Flow Chart illustrating a CHP Power System

Source: U.S. Environmental Protection Agency

Available Equipment for Cogeneration Systems

Consider the following when evaluating CHP solutions for your facility.

  • Reciprocating engines using fuel oil, natural gas, or bio-gas have long been the work horses for providing back-up, stand-by, peak shave, and prime power, typically in the range from <1MW-20MW. Gas engines are reliable, easy to maintain, and flexible, making them very desirable for generating electric power. Their ability to provide low-scale heat recovery for hot water or low-pressure steam applications is a plus.
betvictorA diesel generator at a power generation plant
betvictorA diesel generator at a power generation plant
  • Gas Turbines using fuel oil, natural gas, or bio-gas for fuel combustion have been the preferred CHP topping cycle solution for providing small to large-scale prime power from 1MW-100MW. Their ability to provide high-scale heat recovery for high or low-pressure steam applications as well as hot water is another advantage.
A gas turbine engine
A gas turbine engine
  • Boiler/Heat Recovery Steam Generators (HRSGs) with or without supplemental firing can be configured as simple heat recovery equipment. They can be outfitted with economizers, auxiliary burners, and selective catalytic reduction equipment (SCRs) to function in a super-heated steam capacity. Boiler operators often are required full-time to run the equipment, so facility managers should consider the staffing implications when choosing this technology.
An HRSG undergoing maintenence
HRSG heat exchanger tubes
  • Steam turbines ranging from <1MW-100MW can be used standalone in a bottoming cycle application, or with a topping cycle application to provide a full combined-cycle system. Water quality is essential to steam turbine operation, therefore these systems regularly involve extensive water treatment systems and associated costs.
An industrial steam turbine
An industrial steam turbine
  • Microturbines ranging from 25-500KW use natural gas, hydrogen or propane. They offer all the advantages of large-scale combustion turbines, and they can be used individually or in groupings to meet the needs of smaller facilities.
betvictor appA microturbine (Photo credit: Sheboygan WWTP)
betvictor appA microturbine (Photo credit: Sheboygan WWTP)
  • Fuel cells boast efficiencies of 60% and very low emissions, making them desirable in CHP systems. However, they also have the highest total installed cost profile, which has limited their adoption to date. Continued advancements in fuel cell technology are expected to improve efficiency and further reduce costs.
A P.E.M. Fuel Cell diagram
A Proton exchange membrane fuel cell
  • Electric chillers or steam-driven absorption chillers that produce chilled water for building cooling can boost the overall economics of a CHP system. When paired with power and thermal loads, the system is known as a trigeneration system, or a combined cooling, heat and power system (CCHP).
A water chiller system supplying an industrial air conditioner
A water chiller system supplying an industrial air conditioner

An Example of a CHP Power System

A gas turbine-powered cogeneration power plant

A gas turbine-powered cogeneration power plant

A typical large-scale combined cycle facility using combustion turbines, heat recovery steam generators, and steam turbines. When sized in the 100MW range, this system uses full outdoor design considerations rather than smaller systems housed within facility building additions.

Combined heat and power technology: size, cost & performance

The EPA, in its CHP Partnership Catalog of CHP Technologies, provides the following comparison for help determining which solution may best fit your facility requirements.

EPA CHP Partnership Catalog of CHP Technologies

For help evaluating and right-fitting combined heat and power technology
for your facility, contact the Nexus energy team.

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Marty Ellman, Nexus Engineering Group

About the Author

Marty Ellman joined Nexus in 2020 and has more than 35 years of power and energy consulting engineering experience. He is a registered professional engineer, certified energy manager (CEM), and distributed generation certified professional (DGCP), specializing in power systems, control systems, utility substation design, transmission, power generation, power distribution, cogeneration, SCADA data acquisition systems, and facility PLC/DCS systems.

To learn more about Nexus’s capabilities, download our brochure or visit our Energy page.