The Cogeneration Facility's main purpose is to generate and distribute steam to the various buildings on the University campus and to the University of North Carolina Hospitals. Steam is critical to the operation of the University and the UNC Hospitals. Steam is used primarily for heating and cooling but also for heating domestic hot water, sterilization, humidification, cooking, and cleaning.
The Cogeneration Facility also generates electricity as a byproduct of the steam generation. The plant contains two 250,000 pounds of steam per hour circulating fluidized bed (CFB) boilers which burn primarily coal, one 150,000 pounds per hour oil/gas package boiler, and one 28 megawatt steam turbine generator. The operating budget of the Facility is about $17,000,000, and it has sold over $4,000,000 of electricity to Duke Power Company during the 1996 fiscal year.
Three key technologies are in use at the Cogeneration Facility which are worthy of note - district energy, cogeneration, and circulating fluidized combustion. The University is utilizing the district energy concept in consideration of energy, efficiency, and the environment. The University operates a central plant to produce steam at the Cogeneration Facility, central plants to produce chilled water from four large plants, and two electric substations where electricity is purchased and distributed. Each of these three utilities - steam, chilled water, and electric - are interdependent whereas steam is used to generate electricity and chilled water; and electricity is used to generate steam and chilled water. These utilities are operated in coordination to optimize energy efficiency and cost while meeting the demands for steam, chilled water, and electricity imposed by the University and UNC Hospitals.
The University recognizes that the alternative to district energy, self-contained heating and air conditioning systems within each of the buildings, would be costly and inefficient compared to the operation of the central plants. The Cogeneration Facility utilizes coal, the most economic fuel available, which would not be practical in self-contained building systems. The Cogeneration Facility also meets stringent environmental standards which would not apply to smaller building systems.
The UNC Chapel Hill cogeneratlon concept involves the simultaneous production of electricity with the production of steam for use on the University campus. Steam is passed through a turbine which drives a 28 megawatt generator and is extracted and used again for heating, cooling, and other purposes. The combination results in an overall thermal efficiency for the Cogeneration Facility of twice that of any plant built solely for the purpose of power generation.
Steam is used in the buildings of the University and LING Hospitals instead of wasted to a condenser. This energy efficiency minimizes environmental impact.
The Cogeneration Facility generates steam in two large circulating fluidized bed (CFB) boilers. The CFB process is relatively new to the U.S. although it has been in use in other countries for some time. It is primarily used in this country to reduce the emission of acid rain producing components, primarily sulfur dioxide and nitrous oxides. Sulfur dioxide is reduced by the addition of a calcium containing product such as limestone to the combustion chamber. The limestone calcines producing calcium oxide which combines with the sulfur dioxide to produce calcium sulfate. The calcium sulfate precipitates from the combustion process with the remaining ash.
Nitrous oxide production is minimized by controlling the combustion temperature at a level which is low relative to a conventional fossil fuel combustion process. The UNC boilers operate with a combustion temperature which averages about 1600 degrees Fahrenheit as compared to conventional technology which operates with combustion temperatures greater than 2200 degrees.
The UNC Cogeneration Facility is located on Cameron Avenue in a residential area approximately a half mile from the main campus. Concerns about appearance and noise have resulted in a plant which is designed for esthetics. Features include blue tinted glass exteriors on the boiler and turbine buildings, active coal storage in silos, totally enclosed coal and ash handling, extensive landscaping, and the reuse of the old stately power plant building for maintenance shops, warehousing, and administration.
Extensive efforts have abated noise generated by the Facility to remarkable levels. Exhaust vents have silencers, fans have inlet silencers and noise dampening enclosures, and operating procedures have been implemented with considerations to noise abatement.
Raymond E. DuBose
ray@fac.unc.edu
Cogeneration Facility Manager
The University of North Carolina at Chapel Hill
Tel 919-962-1167
Fax 919-962-4376