GB1091891A - Improvements in or relating to control systems for vapour generating installations - Google Patents

Abstract

1,091,891. Automatic control of boilers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. and JOHN BROWN LAND BOILERS Ltd. Jan. 26, 1965 [Jan.27, 1964], No.3409/64. Heading G3R. In an automatic control system for a boilersuperheater installation, pressure error signals, and temperature error signals corresponding to the highest of a number of temperatures at points which are scanned periodically, are applied to a selector which chooses the smaller to control the boiler fuel supply. As shown, signals from a pressure gauge 31 associated with a steam boiler 1 are compared at 33 with a desired value set at 33M. Thermocouples (not shown) located at various points on superheater tubes 9, 11 are periodically scanned by a unit 41 and the highest signal, stored capacitatively, compared at 43 with a maximum permitted value set at 43M. Error signals from comparators 33, 43 which may include integral and differential terms are applied to a unit 45 which selects the lesser to control the fuel supply by altering (a) the datum of follow-up servosystems 55A-55D adjusting the coal feed to pulverizers 15A-15D supplying rows of burners 5A-5D in the boiler furnace and/or (b) the datum of a pneumatically actuated flow control system 65 adjusting the oil supply to pilot burners (not shown) in the boiler furnace. The error signals selected by unit 45 are also applied to a unit 71 which controls the number of burners and/or pilot burners in operation according to the magnitude of error and the time it has persisted. Initially, at starting, the firing is by oil alone and temperature soon becomes the controlling factor until steam flow through the superheater tubes builds up and pressure becomes the controlling factor.