Abstract :
The Holtwood Steam Plant is located in Lancaster County, Pa., on the Susquehanna River, about 24 miles above tidewater, adjacent to and closely coordinated with the 111,000-kw. hydroelectric plant of the Pennsylvania Water & Power Company, and through the latter company´s customers, it is a part of a hydro-steam system including Baltimore, Md., and Lancaster, York, and Coatesville, Pa., with a total installed generator capacity of about 370,000 kw. and with high-tension connections to two other large systems. It is a pulverized fuel burning station, containing at present two 10,000-kw. generators and three 1400-h. p. boilers. The plant is laid out for an ultimate capacity of at least 120,000 kw. The station went into operation in July 1925. The paper gives the reasons for building a steam plant at Holtwood, some of them being general advantages in such a location for a plant, which is supplementary to a run-of-river hydroelectric plant, and others being the particular advantage, in this instance. In general, during the low-flow period, the steam plant carries the base load or belt generation, and during high flow, when the hydroelectric plant is operated at maximum capacity whenever the load permits, the steam plant carries the peaks. This station was especially planned to suit such conditions of operation and was designed for mechanical sturdiness, reliability of service, quick starting, ability to float in at no load and for maximum coordination with the hydroelectric plant rather than for maximum economy or minimum first cost. A number of special features incorporated to carry out this aim is described in the paper, among them being arrangements to facilitate quick starting and floating in, and a special governor so constructed that the speed regulation may be changed by remote control while the unit is running. A comparative analysis of starting times of hydroelectric and steam units at Holtwood is given, showing that in spite of special design, the st- am unit requires a much longer time than the hydroelectric unit. The pulverized fuel process was adopted in order to secure better sustained efficiency over a wide range of boiler rating, to reduce banking losses and because it was desired to burn bituminous coal of various grades in the same furnaces with river bottom anthractite coal which is dredged from the upper end of the pond formed by the Holtwood dam. This has been successfully accomplished, approximately one-third of all the coal burned, so far, having been river anthracite. During short periods, anthractire alone has been burned, but most of the time the two kinds of coal are mixed before being dried and pulverized. Maintenance costs at the pulverizing plant when burning 100 per cent anthractire are very high. Data are presented showing the first cost of the plant, fuel rates, costs of preparing river anthractite, outage time of the generating units and other operating results. A brief summary is given also of minor difficulties. On account of the unusual operating requirements as to loading, fuel supply, etc., the design and operation of this plant involved a number of interesting problems in design and operation, for the solution of which only a limited amount of experience was available. It is believed that nearly all of the major problems have been solved satisfactorily, but there is still need for further experimentation to secure the best possible results from the equipment installed.
