Patent ES-343105-A1 (ES)
Title: Automatic fire control for coal fired furnace
IPC: F23N1/00
Filed: 1967-07-15
Abstract: In an electrical control system for a vapour generator having coal burners supplied from pulverizing mills and burners supplied with other fuel for igniting the coal burners, the rate of operation of the burners and mills is automatically controlled to maintain generator output constant despite changes in load, and a seriesparallel arrangement of switches responsive to load and other operating conditions select appropriate burners and mills for operation. In Fig.1, a steam boiler 12 has a furnace 22 lined with tubes 24 in which steam is generated and passed through a line 26 to a turbine 14 driving an A.C. generator 16. Steam valve 28 is automatically regulated in known manner in response to changing load demand. Burner assemblies 32 are disposed at each of the four corners of the boiler furnace for tangential firing. Each assembly consists of valve-controlled pulverized coal burners 34, oil burners 36, and auxiliary air nozzles 38 alternately spaced at different levels. The oil burners, which are ignited by pilot torches (not shown), are turned on in succession, at those levels at which not more than one burner is inoperative, for initial warm-up of the boiler and operation at low loads. Under these conditions, variation of boiler output pressure with load is detected at 30 and automatically corrected by a regulator 20 which varies the supply of water to the boiler and the datum of an automatic flow control system (not shown) associated with the oil burners. When, after A.C. generator 16 is synchronized and connected to its power network, the oil flow to the burners exceeds a value corresponding to a predetermined load, one of the coal pulverizing mills 42B-K is started up automatically to supply its associated coal burners which are ignited by adjacent oil burners. This is effected by a unit 106 which operates valves and motors associated with the mill in a properly timed sequence during starting. If unit 106 detects by means of inter-connected switches that proper conditions for the mill first chosen do not obtain, e.g. because an adjacent oil burner is not operating for ignition or because conditions such as valve settings or mill temperature are not correct, then the other mills are explored in sequence until a mill in a satisfactory condition for operation is found. With the coal burner operating, fuel to the oil burners is reduced to a minimum and cut off from those burners not required for ignition. Regulator 20 then maintains boiler pressure despite variations in load by varying the datum of an automatic speed control system for a motor-driven conveyer supplying coal to the mill and, simultaneously, adjusting the setting of a valve controlling the supply of hot air to the mill for drying and conveying the coal which is extracted from the mill by an exhaust fan and supplied to the coal burners through a conduit 44. Air temperature in the mill is detected and maintained constant by automatic control of the relative setting of valves in ducts supplying hot and cold air which are mixed to form the supply to the mill. When the pulverizing mill is operating at 80% capacity, as determined by the rate of operation of its coal conveyer, a second mill is started up automatically so that additional burners operate to meet the load. Further mills start up as required to maintain the average mill loading within 80% of the maximum.