Using steam to produce electricity

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The photo on the left shows a back pressure steam turbine and the photo on the right shows the electrical generator that it is coupled with. Most hospitals utilize large amounts of steam even when the ambient weather is warm in order to serve their medical instrument sterilizers, cafeteria services, laundry services, and air conditioning reheat systems. Cogeneration, also called Combined Heat and Power (CHP), is a technique that can be used to produce electricity from steam or in some cases, create heat from sources of electricity generation.

This particular steam generator is being integrated with Gundersen Health System’s new biomass boiler, which utilizes a renewable fuel. Most steam on a hospital campus is produced at a high pressure and then distributed to its point of use and reduced in pressure for its specific application through steam reduction valves. This practice diminishes the piping cost because high pressure steam uses smaller diameter pipes. However, when the pressure is reduced through a steam reduction valve the potential mechanical energy is wasted. Back pressure steam turbines can also reduce the steam pressure to the proper level for its intended use, however the mechanical energy of the steam is not wasted but rather turns a turbine which can then produce electricity through a generator. The higher the drop in pressure, the more electricity you can make. In this case, the steam turbine will take 400 psi steam and reduce it to 100 psi which will produce approximately 2500 mWh of electricity annually and substantially reduce the amount of electricity purchased from the grid. Since the steam and heat are needed anyway, this is a very good way to reduce fossil fuel energy use and its negative effects on health and the environment. It is also a considerable cost savings. If you have steam production on your campus, this may be a good way to capture a wasted resource and use it to your advantage.

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