District Heat and Power Boiler

a boiler unit in a district heat and power plant that simultaneously furnishes steam to heat and power turbines and generates steam or hot water for production processes and heating. Unlike the boilers in condensation electric power plants, district heat and power boilers normally use contaminated return condensate as feedwater. The most suitable unit for such operating conditions is the drum-type boiler with staged evaporation, which produces uncontaminated steam but requires relatively little boiler blowdown.

District heat and power boilers installed at district heat and power plants used predominantly for heating usually have seasonal variations in operating conditions, which hampers their consistent optimum performance; therefore, boilers at most district heat and power plants have cross-connections for steam and water. District heat and power plants in the USSR usually use drum-type boilers that produce 420 tons of steam per hour at a pressure of 14 meganewtons per sq m (MN/m²) and 560°C. Since 1970 single units with flow-through boilers that generate 545 tons of steam per hour at 25 MN/m² and 545°C have been used at powerful district heat and power plants used mainly for heating, at which almost all the condensate is returned in pure form.

Another type of district heat and power boiler is the peak-load hot-water boiler unit, which is used as an auxiliary water heater when the heating load exceeds the maximum the turbine outflow can accommodate. In such units, the water is initially heated to 110°–120°C by steam in preheaters and then to 150°–170°C in steam generators. In the USSR, boilers of this type are usually installed in district heat and power plants together with the main units; in case of a delay in start-up of the district heat and power plant, the hot-water boilers can be used instead of apartment-building boilers to serve the district temporarily. The use of comparatively inexpensive peak-load hot-water boiler units to shave short-duration peaks from the heating load greatly increases the operating life of the primary heat and power equipment and improves its economy of operation.