An updated report is given on the University of Connecticut’s gas turbine combined heat and power plant, now in operation for 13 years after its start in 2006. It has supplied the Storrs Campus with all of its electricity, heating and cooling needs, using three gas turbines that are the heart of the CHP plant. In addition to saving more than $180 million over its projected 40 year life, the CHP plant provides educational benefits for the University.
#38 MAY 2019
Here at the Storrs campus of the University of Connecticut (UConn), we have been provided for all our electricity, heating and cooling needs by natural gas fueled gas turbines since 2006. As an update to what I have written about them in the past, [1,2] let me use my column here to give a brief account of 13 years of our very successful gas turbine power plant operation.
Combined Heat and Power
Gas turbines (aka, combustion turbines) have been the fundamental element of most of the growing number of combined heat and power plants in use today.
CHP (also called cogeneration) is an energy efficient technology that generates electricity from fuel combustion and captures waste heat to also provide useful thermal energy for space heating, cooling and industrial processes. Gas turbines used for both aviation propulsion and electric power, were first successfully operated in 1939. By the late 1900’s efficiency improvements brought gas turbine exhaust temperatures up to levels (about 900 F and above) such that the exhaust gases could be used in heat recovery steam generators (HRSGs) to provide useful thermal energy.
In 1993 I proposed building a gas turbine CHP power plant for the Storrs 15,000 student campus to our University of Connecticut president. Ten years later, in 2003, construction started on a 25 MW CHP plant. The U.S. Environmental Protection Agency portrayal in Fig. 1 clearly shows the advantage UConn had in going to gas turbine CHP.
Up to 2003, UConn’s Storrs campus had its dormitories, kitchens, classrooms, laboratories, and other facilities heated by steam generated in central plant natural gas-fired boilers. During warmer months, campus buildings were cooled by individual electric-powered air conditioning units or by central plant chilled water, cooled by central plant refrigerant units. All campus electric power was purchased from the local regulated electric utility company and dispatched to the rural Storrs campus via a dedicated power line. In 2002, this amounted to annual energy costs of $15 million, substantially consuming 20% of the campus physical plant budget.
The UConn CHP Plant
In 2006 the 25 MW CHP plant was completed, and went on line to supply all of the campus electricity, heating and cooling needs. The plant is described in detail in the schematic given in Fig. 2. (More details are given in  - .).
The plant’s initial cost was $81 million, a figure which included modifications to existing utility facilities. An estimate of its true cost is about $50 million, or $2000/ kW. It is expected to save the University $180 million in energy costs over its forty year design life. (More recently, it has been reported the expected savings are twice that by capitalizing on changing energy markets and more favorable refinancing .) Its overall efficiency (see Fig. 1) is about 80%. Other measures show that under a demand rate of 25 MW of electricity and 200,000 pounds/hr of steam, UConn’s CHP plant uses only 52% of the fuel consumed by conventional non-CHP means (see Fig. 1 and ).
The heart of the UConn CHP plant consists of three 7 MW gas turbines, driving water-cooled electrical generators, to produce 20-25 MW of electrical power distributed throughout the campus. The gas turbines are Taurus units, made by Caterpillar’s Solar Turbines, in San Diego, CA. They are fueled with natural gas, with fuel oil as a backup (despite their maker’s name and sunny location). Since online operation started in 2006, a Solar gas turbine is removed for refurbishment after about 40,000 hours of operation and replaced with a rebuilt Taurus unit.
Gas turbine exhaust heat (at about 900°F) is used to generate up to 200,000 pounds per hour of steam in heat recovery steam generators (HRSGs). The HRSGs provide high pressure steam (600 psi) to power a 4.6 MW steam turbine generator set for more electrical power, and low pressure steam (125 psi) for campus heating.
As shown in Fig. 2, the waste heat from the steam turbine contained in low pressure turbine exhaust steam is combined with the HRSG low pressure steam output, for campus heating. Thus, careful waste heat engineering and management allows three energy usages (gas turbines, steam turbine and campus heating) for only one unit of gas turbine fuel.
During the warmer months, when heating is only needed for some campus kitchens and laboratories, the low pressure steam (from both the steam turbine and the HRSGs) is used to power low pressure steam turbines which drive four refrigeration compressors to supply up to 8400 refrigeration tons of chilled water. The chilled water is distributed to campus buildings for air conditioning. A small part of the chilled water output can also be used to cool hot day inlet air to the gas turbines, thereby maintaining high gas turbine thermal efficiency (nominally 34% at 59°F inlet) and predictable electrical power output. Thus careful waste heat management also provides campus cooling and the maintenance of high electrical power needs during hot summer months.
My own assessment is that since the CHP plant went online, the university administration pays more attention to campus energy issues. More heedfulness is now given to energy conservation and improving energy related infrastructure.
For instance, in the past, the UConn campus was known for “smoking” manhole covers during winter, since its old steam-heating condensate return piping system, dating back to the 1930’s, leaked. Recent work on the system has greatly improved the return of condensates to the plant—formally a low 30%—and now currently 65% and increasing.
The Second Law of Thermodynamics requires that a power plant must reject heat, no matter how efficient. Roof mounted cooling towers provide UConn’s means of heat rejection, but they used substantial amounts of the University’s fresh water supply, as much as 250,000-450,000 gallons/day. In 2013 a $30 million Reclaimed Water Facility went online to pump treated water from the University’s sewage treatment plant to the CHP plant for both cooling towers and for boiler makeup water, eliminating the need to use drinking water.
With the 13 year success of the UConn CHP plant and the continued growth of the University—now at about 30,000 students, faculty and staff—we are designing a second CHP plant. Called the Tri-Generation Supplemental Utility Plant it will also be gas turbine powered and construction is scheduled to start later this year.
Let me finish by briefly listing some unique benefits provided by the UConn CHP plant for the purpose of the University—education.
Thus far, two engineering graduate students (one PhD, one Masters) have carried out research on the plant’s many interacting control systems. Through student employment, 20 engineering students have supplemented their education by working with the Plant Manager on various CHP plant projects.
The plant has a class room that is used for instruction not only for engineering students but also for those from other university disciplines. The classroom is outside the security areas of the power plant, so that students can come and go as in a regular class room.
We also use it to prepare for regular tours of the power plant, where trained tour guides can organize tours and issue safety equipment. This is a unique experience for many students since most power plants usually don’t encourage tours for safety, insurance and security reasons. The tours are very popular with our students, and outside groups.
In conclusion, our UConn more than a decade long experience has shown that a gas turbine CHP plant is a natural economic, environmental and educational resource for a university or college.