Power

Balance of Plant

Many corporate and public entities are building their own small power plants to save costs. These plants aren’t simple scaled-down versions of the utility size. In some ways, they’re more complex.

Leaders at the University of California-Irvine, Irvine, Calif., wanted their own power plant to save money and to produce greener power. Of course, they didn’t need a utility-scale plant of 800 MW or so. What they wanted was something an order of magnitude and then some smaller – 20 MW or a bit less.

Specifically, UC-Irvine leaders wanted a cogeneration plant that produced steam as well as electricity – steam it could use to run its campus-wide heating and cooling systems. The campus already had boilers and chillers; the power plant had to connect to them and control some aspects of their functioning.

Building such a small power plant is an interesting project. The natural-gas-fueled 20-MW plant has all the same pieces as an 800MW plant – fitted into a much smaller space. A part that might be several feet in diameter in the big plant is one-quarter the size in this one.

The flow of the plant is this: A gas-fired turbine, basically a large jet engine, drives a generator that produces electricity. Then the cogeneration part begins. Waste heat exhausted from the turbine goes into a heat-recovery steam generator (HRSG) containing boilers that heat water to make steam.

The steam is routed to an existing facility that contains boilers and chillers. Upon entering, the steam can be divided, depending on the need, to heat water to circulate through the two-mile loop of heating pipes, and/or to drive a centrifugal chiller to chill water that circulates through the parallel loop of cooling pipes.

The HRSG also is connected to a steam turbine generator, which can produce up to 5 MW of electricity as part of the plant’s total, add to the heating capacity or drive a steam driven chiller to chill water to cool the campus.