Moss Landing Power Plant
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The Moss Landing Power Plant is a electricity generation plant located in Moss Landing, California, at the midpoint of Monterey Bay. The plant's large smoke stacks are landmarks that can be seen throughout the Monterey Bay Area.
The building of the Moss Landing Power Plant started in 1949 with the first five units that are now retired. Producing 560MW, these units started commercial generation in 1950. Today, the eight associated 225-foot tall stacks have been removed and the boilers are being decommissioned progressively after 45 years of electricity generation, between 1950 and 1995. In 1964, the construction of two additional units begins and two new stacks of 500-foot are being raised in the Monterey Bay. These two units producing 750MW each, with 180-foot tall boilers use a newer technology using supercritical gas at 3600 psi. In the last few years, two new units have been build where there used to be 19 fuel oil storage tanks: these are combined cycle units, 50% more efficient than the other units because they use two turbines : a first gas turbine, and a steam one. They produce 530MW each, 170MW per gas turbine, with two of those per unit, and 190MW per steam turbine. Of a much smaller scale than the supercritical units, their use is also more flexible with a starting time of only an hour against 24 hours for the older units.
Today the Moss Landing Power Plant has a maximum capacity of 2560MW, but units 6 and 7, the supercritical ones, are only turned on during the peak period, between June and September. Owned by Duke Energy since 1998, the plant was the property of Pacific Gas & Electric until then but as a consequence of deregulation, the latter sold the 236 acre asset with a few improvements like clean burners to reduce emissions of nitrogen oxides. Today, after 7 years of upgrades in capacity, efficiency, emission reductions and a half billion dollars new generation complex, Duke Energy is selling the plant again citing the high prices of natural gas and uncertainties in the post-deregulation electricity market.
Today, the plant produces energy with two different processes : supercritical boilers for units 6 and 7, and combined cycle for the new units 1 and 2. For the old units, gas is injected in one end of the boiler to be burned, water coming is injected in the other end of the boiler to receive the heat produced. The gas is simply coming from a gas pipeline and combustion products go up the stack and in the atmosphere (to be simple), water has a much more complicated path. It is pumped out of the Monterey Bay or the nearby Elkhorn Slough estuary. Then it is purified and used to cool down the water coming from the turbines and rejected in the ocean. On the other hand, the primary water flow is pre-heated before entering the boiler. Exiting the boiler, the hot steam is directed into a first turbine working at high pressures and afterward in a low pressure turbine, the two turbines generating the electricity for the grid. To comply with more and more restrictive regulation in terms of pollution, The two units have been upgraded in 1998 with two new features : a selective catalytic reduction unit and digital control systems.
The new units 1 and 2 are combined cycle turbines: a steam turbine generates electricity in each unit, but there is also two gas turbines of 170MW which totals 6 rotating axles for the two units. The gas turbine has one non negligible advantage from an environmental point of view: they don’t need any water to transport energy because it’s the pressure of combustion products which drive the turbine. First air is sent through the air intake to the compressor (driven by the axle), then it is burned with gas in the combustion chamber, then it goes through the actual turbine (driving the axle). This is the standard Brayton cycle from a thermodynamic standpoint. Because the units use a combined cycle, Some of the heat in the exhaust gas is recovered through a heat exchanger and transferred to water that flows into a steam turbine after that, just like for units 6 and 7. This power plant has, at first, one obvious impact on its environment: it can be seen from as far as Santa Cruz with its 500-foot tall stacks. As useful as it can be to California citizens, it is certainly not how people picture the ideal way of landscaping the coast in Monterey Bay. Then there is the problem of the exhausts: in October 2005, on a year to date basis, the Moss Landing Power Plant complex released almost 900,000 tons of CO2, 60 tons of NOx and 4 tons of SO2 in the atmosphere (without operating units 6 and 7). These amounts can be seen as relatively small given the amount of power produced, and especially small when compared to other facilities burning coal, but they still come with some problems. The last but not least important environmental impact is on the water of the Elkhorn Slough and the Monterey Bay : under certain conditions, the water is allowed to be released at a temperature 40oF higher than it is taken, therefore perturbing if not killing the surrounding aquatic plants and animals. Each day, it is roughly 1.2 billion gallons of water that is cycled in the power plant! From an economical point of view, first on a local basis, the plant has certainly favored local activity during the construction of the new combined cycle units, but on a long term basis, the number of people actually working in the plant has seriously decreased in the last ten years (from more than a hundred to forty). On a more global basis, because the old units 6 and 7 are far from being used at full capacity, one can wonder about the price it costs to have it ready to function without ever actually turning it on.
