Content area
Full Text
Consulting engineers should understand the criteria for determining the feasibility of using combined heat and power in their design projects.
Learning objectives
* Know whether combined heat and power is appropriate for a project.
* Learn about steam and electrical load and capacity of CHP systems.
* Understand how to select appropriate generation systems for a facility to achieve maximum performance.
------------
Combined heat and power (CHP) systems generate both electricity and usable heat. These cogeneration systems are often used on college or industrial campuses and in hospitals. They offer high-efficiency operation, ease of system maintenance, and sustainable design. Conventional power generation using a turbine generator is generally only 40% to 45% efficient. The turbine mechanically powers the shaft of the generator, but heat from the combustion of natural gas is exhausted to the atmosphere. Cogeneration uses that otherwise wasted thermal energy to boost the thermal efficiency to more than 80%. This can be done by using a heat recovery steam generator (HRSG).
In addition to improving overall system efficiency, CHP reduces emissions of air pollutants and provides other environmental benefits. The U.S. Environmental Protection Agency [http://www.epa.gov/] offers additional information on the environmental benefits of CHP [http://www.epa.gov/chp/documents/faq.pdf].
Designing an actual CHP plant
A project being designed by Stanley Consultants involves adding a natural-gas-powered turbine generator and an HRSG in a new facility adjacent to the existing boiler house of an industrial campus. Electricity will be generated on-site and will supplement campus utility power. Heat from the turbine exhaust will be used to create steam to supplement the boiler plant production.
The new facility will include a nominal 6.5-MW gas turbine generator with an HRSG. The system will include a bypass damper and bypass stack to allow the gas turbine to operate without the HRSG in operation. Electricity from the turbine generator will supply power to a substation and provide auxiliary power for the new CHP facility.
The turbine generator will burn natural gas to produce electricity (6,200 to 6,800 kW) to supplement the electrical supply for the campus. Exhaust gas from the turbine will be used for creating process and heating steam to supplement the steam capacity of the boiler plant.
The HRSG will replace an old gas-fired boiler and will have a steam capacity...