A steam-generating installation including a forced-flow once-through boiler

摘要

943,020. Forced-flow steam boilers. SIEMENS-SCHUCKERTWERKE A.G. March 11, 1960 [March 12, 1959], No. 8737/60. Heading F4A. In a once through boiler of a unit power plant comprising an economiser 2, evaporation stages 3, 4 and a superheater 5, temporary deficiency and excess of water in the stages 3, 4 on sudden increase and decrease of load is offset by increasing or decreasing the rate of water injection between the stages. A feed pump 1 supplies water to the economiser 2 through a valve 8 which is set by a controller 6 in response to load as measured at an orifice 7 so that under steady load conditions about 85% of the total feed enters the economiser. Of the remaining 15% of feed water, about 5% is injected before the superheater to control the final steam temperature whilst 10% is injected at a point 9 where the steam content of the working medium is from 50 to 80%. The injection rate at 9 is controlled by a valve 11 which is adjusted by a controller 10 according to load as measured at the orifice 7. At steady loads the controller keeps the rate of injection at a constant percentage of the steam output. If the load suddenly increases the controller 10 effects a rapid increase in the injection rate to offset the deficiency of water in the zone 4, a timing ele ment causing the increased injection rate gradu ally to be cancelled out until the boiler control system has become adjusted to the new load. A sudden decrease in load effects a rapid decrease in the water injection rate to offset the excess of water in the zone 4. Follow-up control signals for the controllers 6, 10 are obtained from flow measuring orifices 20, 21 in the main feed and injection lines respectively.