Reducing energy costs, cutting carbon emissions.
Combined heat and power (CHP) uses byproduct heat from electric generation as the energy source for other applications such as steam for space heating, domestic hot water and/or absorption cooling. CHP, sometimes also called co-generation, represents an opportunity to dramatically increase total system efficiency. These applications often use natural gas as the primary energy source. When systems replace coal-fired electric power plants or coal-fired heating plants, they also reduce total emissions and virtually eliminate sulfur oxide and particulate emissions.
Makes sense for universities
Many universities supply energy to dozens or even hundreds of buildings from central power and heating plants. This is an exceptional opportunity for CHP. The central heating plant usually supplies medium- and high-pressure steam for space heating, laundry and sometimes food service and laboratory operations. In some cases, the university is also affiliated with healthcare facilities, which have additional requirements for steam and hot water. The university often also supplies chilled water for chillers and other purposes.
In most cases, the demand for electric power, heat and chilled water is year-round, 24 hours a day. Thus, the heat captured from power generation can be fully utilized. A supplementary steam system may sometimes used for peak winter heating periods.
DOE report indicates potential
According to a March, 2016 report by the U.S. DOE titled “Combined Heat and Power (CHP)Technical Potential in the United States,” there currently are 272 applications of CHP by colleges and universities in the U.S. These facilities have a total capacity of 2,674 MWe. Thus, the average university system is about 10 MWe. Most of these systems are natural gas-fired steam turbines, gas turbines and engines. The report notes that for many educational institutions, the demand for electric power and for steam is often coincident, thus making these systems especially attractive.
The report indicates that the national potential for these systems is 13,932 MWe. Thus, to date we have achieved 20% of the potential in this area. In many cases, adoption of CHP is being considered in conjunction with decommissioning or mothballing coal-fired generation and heat plant units.
University of Arkansas
A recent example of an institution that has taken this route is the University of Arkansas at Fayetteville. Scott Turley, Executive Director of Campus Utility Services, explains that a decision was made in 2013 to install a 5.2 MWe gas turbine generating unit to supply campus electric energy. This unit was sized to the school’s base steam demand, and uses a heat recovery steam generator (HRSG).
Turley explains, “The CHP system can satisfy the full campus requirement for steam for five months of the year. Under winter-load conditions, the HRSG system can furnish approximately 35% of the campus steam requirement.” This installation was an important element in the university’s Climate Action Plan, which is based on reducing source air emissions. Because the central station electric power it replaces is 75% coal-fired, the contribution was significant.
Solar turbines taurus unit
The gas turbine and HRSG are located in the existing 1956 heating plant building. The building currently also houses ten Miura high pressure steam boilers. The CHP system went into operation in February of 2016. The turbine used is manufactured by Solar Turbines. According to Chris Lyons from Solar Turbines, the unit is a Taurus 60-7301 with an ISO-rated output of 5.2 MWe.
Lyons indicates that these turbines have very long major maintenance intervals. “Approximately every 30,000 hours the engine is overhauled to bring it back to new conditions. In addition, Solar Turbines does semi-annual inspections to assure the units do not have any issues.”
According to Lyons, this unit used alone has an efficiency of 30%, but when used with an appropriately sized HRSG, the system efficiency jumps to 77.8%, and when used with supplemental firing of the exhaust heat, can increase to 88.8%. The HRSG is manufactured by Cleaver-Brooks, and can produce up to 29,500 pph of 250 psig saturated steam.
Fuel efficiency soars
Because of this high system efficiency, it is estimated that the project will divert 35,000 metric tons of carbon dioxide equivalent emissions from the atmosphere. The University cites this as a major step to its goal of complete carbon neutrality, while also saving money for the school. According to Turley, based on the first six months of operation, the CHP system is projected to reduce utility bills for the University by $420,000.
A recent speaker at a Technology & Market Assessment Forum, sponsored by the Energy Solutions Center, was Dalia El Tawy from Siemens Energy. She presented information on a variety of CHP applications, several of which were university campus projects. One was the University of New Hampshire, where a recent installation includes a 7.8 MWe Siemens gas turbine, which can operate on natural gas or landfill biogas collected at a nearby site.
Cuts emissions from power plants and landfills
Through use of a HRSG, the facility also supplies up to 12 MW of heat for campus heating and cooling. Again, this facility contributes to carbon emission goals not only by reducing campus and utility emissions, but also by reducing landfill gas atmospheric emissions. According to Tawy, the facility has achieved 99.02% average availability.
Engine generation CHP
Smaller campuses can also benefit from CHP. Another example cited by Tawy is Wesleyan University in Middletown, Connecticut, where a 676 kWe Guascor engine-generator at an athletic facility also feeds into the campus microgrid, and the byproduct heat is used for heating and domestic hot water applications. It is estimated that this project provides savings of $1,000 per day.
Another large-scale example is the recent completion by the University of Minnesota of a CHP facility on the Mississippi River in St. Paul. The facility serves the sprawling university campus and uses a 25 MWe GE gas turbine with a waste heat boiler, plus supplementary duct heaters to also supply steam for campus heat and domestic hot water.
According to University Director of Energy Jerome Malmquist, the guiding principles of the University’s utility operations are reliability, sustainability and cost management. He adds, “The campus has a goal to reduce carbon emissions 50% by the year 2020, and to zero by 2050. Modeling predicts that this project will reduce the carbon footprint by 60,000 tons or 10% to 13%. The same models show annual operations savings of $2 million. With regard to reliability, this system has the capacity to power all critical loads on this research and medical campus.”
Major portion of campus steam needs
University Vice President for Facilities Management Mike Berthelsen notes that the plant will supply approximately 85% of the campus steam needs, and will annually generate 166 million kilowatt-hours of energy. A specific need for the high-pressure steam is for sterilization and other research purposes at large campus medical and laboratory facilities.
The University recently completed an electric energy interconnection agreement with electric power supplier Xcel Energy. The natural gas supplier to the University, CenterPoint Energy, recently gave its “Most Innovative Project of the Year” award to the University for the project.
CenterPoint energy worked with university
Paul Albinson, key account manager for CenterPoint, worked closely with the university on this project. He notes, “To ensure financial sustainability and reliability, the University worked with CenterPoint Energy to put into service a new service line to the CHP plant to provide natural gas, and also negotiated long term delivery contracts for this to be a successful project for all. We expect to provide large rebate for the conservations efforts within the facility, mainly the energy recovery from the heat recovery steam generator.”
Hitting both energy and environmental targets
With states and governing bodies looking for ways to cut operating costs at educational institutions, CHP is a major opportunity. With these projects, the sponsoring institutions may be motivated not only by energy and dollar savings, but also by the potential of CHP projects to contribute to lowering atmospheric carbon emissions and other air pollutants. It is an investment that can pay dollar and environmental dividends for decades.
MORE INFO:
DOE CHP Database
https://doe.icfwebservices.com/chpdb/state/WI
General Electric Power Generation
https://powergen.gepower.com
Guascor Engines
https://www.dresser-rand.com/products-solutions/guascor-gas-diesel-engines
Solar Turbines
https://mysolar.cat.com/en_US/about-us.html
This article originally appeared in the Gas Technology Spring 2017 issue .
