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WEEK 04: GENERATION: AUXILLIARIES Auxiliary Systems: Flue & Waste Sections: Circulating-Water | Flue & Waste | Diesel Plant Governing Speed regulation for a diesel is defined the same as for any other prime mover. Modern diesel engines are equipped with either a nonisochronous or isochronous governors. An isochronous governor, usually of relay type, is one that has, or can be adjusted to have, a zero speed droop or zero speed regulation. These are used for diesels that will be paralleled or that are prime movers for an electric distribution system. In that event, one of two diesels may be operated with an extremely small regulation (1% or less) and the other at a higher regulation (say, 3%). The unit with the small regulation will take the load swings while the one with the higher regulation will be base loaded. A nonisochronous governor maybe either a mechanical governor in which the power to regulate the fuel flow is obtained from flyweights, or it may be a relay type employing a hydraulic or electric, including electronic, system. All diesel engines should be supplied with emergency overspeed governors to stop the unit when it reaches an excessive speed, say, 10% overspeed. Air Intake System Diesels take from 2 to 6 cfm of air per rated horsepower. The location of the intake is selected to provide as short and straight an inlet pipe to the engine as possible, yet it should not be a location where it will receive ground dust, snow or hot air from an exhaust or cooling system. The intake system should include a combination intake muffler and air filter if within a building, or an air filter, pipe, flexible tubing and possibly a muffler is outside air is used. Exhaust System Masonry exhaust system is not used because they cannot withstand thermal expansion. A separate exhaust system should be used for each engine. Most systems include an exhaust silencer, frequently of the spark-arresting type. In some instances, mufflers are not necessary for turbo-supercharged engines. Starting Systems Small diesels may be started by electric starters driven by batteries such as used for an automobile engine. Electric motors, air motors (usually used on medium-sized), gasoline engines, and even blank gun shells have been used on smaller units. Compressed air, at 250 up to 350 psig, injected into one or more cylinders of the engine is the most common method of starting low- and medium-speed diesels. Cooling-Water Systems similar to above, see Circulating-Water System.. Lubricating-Oil Systems Medium- and large-sized engines will consume 0.005 to 0.009 gal of lube oil per kWh, Lube-oil storage capacity should be sufficient to store reclaimed oil and to store the plant consumption of new oil between deliveries. An oil system should always include a strainer to remove the larger impurities and to accomodate the full oil flow of the enginer. Also, a filter or purifier for further purifying the lube oil is provided, to remove smaller particles. These filters are made of unbleached cotton waste, cellulose, clay, fuller's earth. |
