Clearing the Air: CHP Systems Reduce Harmful Emissions



By Margaret Cook, Ph.D., Research Associate, HARC 

As we move toward a low-carbon future, many solutions will be needed. Combined heat and power (CHP) can provide site-specific, resilient heat and power and a pathway to reducing conventional air pollutants and greenhouse gas emissions. 

Current Potential for Emission Reduction 

CHP technologies provide a variety of benefits that lead to reduced air emissions.  CHP is fuel flexible and can accommodate multiple fuel types. While natural gas makes up the bulk of capacity installed, over half of installations use another fuel, many of which are renewable or low carbon. For example,  many smaller capacity systems use biogas, biomass, waste heat, process waste, and hydrogen. Installing CHP today doesn’t mean you are locked into a carbon-based fuel forever. It’s possible to switch to renewable natural gas (RNG), hydrogen, and other fuels, particularly with dual fuel modules like the 2-G module used by Yuengling in Pennsylvania. 

In addition to being fuel-flexible, CHP is a highly efficient way to generate power and thermal energy. This high efficiency means less fuel is burned to meet the same electricity and heat needs and results in reduced carbon emissions in the near- or mid-term compared to the current dirtier grid, particularly in areas powered by natural gas steam turbines and coal. Because of this reduction, CHP saves significant carbon emissions today. Given that carbon dioxide stays in the atmosphere for hundreds of years, this near-term reduction is a considerable benefit. In addition to greenhouse gas reductions, using CHP also reduces associated conventional air pollutants like Carbon Monoxide, Nitrogen Oxides, Particulate Matter, Sulfur Dioxide, and Volatile Organic Compounds. 

Facilities are already seeing these greenhouse gas reductions as they transition from grid power to CHP. For example, Texas A&M University built a 45-megawatt (MW) facility using one natural gas-fired combustion turbine, one heat recovery steam generator, and two steam turbines. The facility then achieved  an estimated 20% reduction in carbon dioxide emissions  with this setup. 

The University of Arkansas campus in Fayetteville, Arkansas, has been operating since 2016 with a 5.2 MW power generating capacity. The plant diverts approximately 35,000 metric tons of CO2 equivalent from the atmosphere. This project contributed to the University of Arkansas Climate Action Plan (version 2.0, approved in 2014) and allowed the university to approach its 2021 mid-term emission goal five years ahead of schedule. The central station electric power this CHP unit replaced was 75% coal-fired. 

Rice University in Houston, Texas, has two natural gas-fueled turbines with CHP providing a combined 7.4 MW of power to 50 buildings providing steam generation and chilled water. Rice reports that they  reduced NOX emissions by two-thirds and that the CHP system has positively impacted their carbon footprint, supporting the Zero Carbon Campus goal. It is also a key component of their Integrated Climate & Energy Master Plan.  These examples show natural gas CHP can be a tool to produce significant reductions in carbon dioxide and other conventional air pollutants today. However, the question remains: what is the long-term role of CHP in the path to decarbonization?

Future Decarbonization Potential

CHP plays a key role moving forward, particularly in providing energy services to markets and processes that don’t easily lend themselves to electrification. CHP technologies currently use renewable fuels, low carbon waste fuels, and hydrogen mixtures where available. They will be ready to use higher levels of renewable natural gas (RNG) and hydrogen in the future. Using hydrogen can lead to higher greenhouse gas reductions because fuel cell CHP applications use natural gas or biogas reformed into hydrogen, then react to generate electricity. The trend toward these alternative fuels means CHP could ultimately be carbon-free using renewable natural gas or hydrogen and carbon capture, all while maintaining the efficiency, emissions, and resilience advantages for which CHP is known. 

 RNG or hydrogen-fueled CHP with carbon capture could help decarbonize critical facilities that need on-site power for long-duration resilience and operational reliability. Additionally, CHP can reduce a facility’s need for carbon-based fuels and create a system for on-site generation for greater stability and security, and thermally-based industrial processes that are difficult to electrify. CHP can also enable greater integration of renewables microgrid applications, while helping enhance resilience as businesses adapt to changing conditions. Moreover, CHP can easily pair with greenhouses and other carbon dioxide consumers with significant power demands. 

 Finally, employing waste heat to power (WHP) can be a crucial method for decarbonization by utilizing a facility’s existing waste heat rather than requiring new fuels and increasing associated emissions. Let’s look at one more case study in Veyo, Utah, where exhaust gas from existing combustion turbines fuels the heat and power. This site was the recipient of Utah’s 1st tax-exempt green bond for a carbon-free power plant. There is no new creation of air emissions, and there is no water use except the potable water trucked into the site. WHP already plays a key role in industrial applications and will continue to do so by providing energy savings, reduced emissions, and opportunities for resiliency. 

Determine Your Potential 

You can calculate your facility emissions savings using the Environmental Protection Agency’s CHP Energy and Emissions Calculator . The DOE CHP TAPs can also perform those calculations for you as part of a no-cost advanced technical assessment of your potential new CHP facility. Please reach out to us to learn more about how we can help you reach your goals with CHP. 

Hat tip – Bruce Hedman/Entropy Research, LLC