GB898157A - Method of and apparatus for regulating the output temperatures of superheaters in a steam generating plant - Google Patents

Abstract

898,157. Fluid-pressure servomotor-control systems. SULZER FRERES S.A. March 10, 1959 [March 12, 1958], No. 8236/59. Class 135. [Also in Group XIII] In a method of regulating the output temperatures of a live steam superheater and at least two intermediate superheaters of a steam generating plant comprising influencing the firing intensity in dependence upon load, and using a regulating device to effect combined regulation of the superheaters in dependence on the output temperature, the device influences adjustment members on the one hand to vary the heat exchange between live steam, intermediate steam and feed water, and on the other hand to vary at least two of the following factors, i.e. the amount of fuel, the amount of combustion air, the centre of heat transfer and the quantity of feed water. Steam generating plant.-Feed water is pumped from a hot tank 1, Fig. 1, to an economiser 4, the outlet from which branches into a cooling line 5, passing through a second intermediate superheater 6, and a by-pass line 7, both lines leading to a distributing valve 8 leading to an evaporator 9 having a water separator 11.. The steam passes through a primary live steam superheater 12 to a distributer valve 13 connected to both a heating line 14, leading to a first intermediate superheater 15, and a by-pass line 16, which two lines are connected to a secondary live steam superheater 17 supplying a high pressure turbine stage 19, the expanded steam from which flows to the superheater 15 and thence via a line 24 to a medium pressure turbine stage 27, the line 24 being provided with a temperature sensing device 25 and a flow meter 26. The low pressure steam from the stage 27 flows through the superheater 6 and a line 33 to the low pressure turbine stage 36, the line 33 incorporating a temperature sensing device 34 and a flow meter 35. The turbine drives an electric generator 39 embodying a centrifugal governor 41, and the condensate from a condenser 38 is delivered by pumps 42 via pre-heaters to the tank 1. In a modification (Fig. 2, not shown), the superheater 15 is arranged in two interconnected parts, one part being connected to the line 22 and the other part to the line 24 whilst the superheater 16 is disposed between these two parts in the flue gas passage. If both superheaters 6, 15 are arranged for heating and cooling then burner swivelling and flue gas recirculation may be dispensed with; if only one of these superheaters is so arranged then its outlet temperature is regulated by the inlet temperature or flow rate of the cooling or heating medium, whilst the outlet temperature of the other superheater is regulated by burner swivelling, flue gas recirculation or by-pass, water injection, and disconnecting and regulating groups of burners. The burner may be swivelled away from the intermediate superheaters which adjustment may also be transmitted to the fuel or feed water regulator. In another modification (Fig. 3, not shown), the heating and cooling is effected by the exchange of steam between the intermediate superheaters. In a further modification, an evaporator 103, Fig. 4, which is disposed in the combustion chamber 102, is followed by a first live steam superheater 104. A flue gas passage 105 divides into a main and by-pass passages 106, 107, both rejoining in an end chamber 108 ; in passage 106 are two intermediate superheaters 112 and in passage 107 is a part 113 of a second live steam superheater, the other part 114 of which is in passage 105. An economiser 115 in chamber 108 has its outlet connected to both a cooling line 116 in the end of superheater 112, and through a by-pass 117 to a valve 118 into which leads an outlet line 119 from line 116. A hinged valve 121 for the passage 107 and similar valves 122 are conjointly but oppositely operated by a servomotor 123. The valve 118 regulates the cooling effect of line 116. If the intermediate superheaters are arranged for heating or cooling they may be connected with the heating or cooling lines in parallel or series relationship ; they may also be connected after or between the pre-heaters or economisers or bridge these members. Heating lines may be connected to the live steam line before a final superheater in the high pressure part or in the case of series connection a superheater may be located therebetween. Servomotor control system.-Any change in the generator speed causes the governor to move a lever 200, Fig. 1A, connected to a valve 203 transmitting a signal to a fuel regulator control valve 153 connected to a piston 152 controlling a valve 152<SP>1</SP>; a line 158 also connects the signal directly to the valve 152<SP>1</SP>. The signal acting on valve 153 produces an integral effect on the output of valve 152<SP>1</SP> since the fluid supply to the piston 152 controlled by the valve 153 is throttled. The valve 152<SP>1</SP> is connected to two further valves in parallel, one controlling the combustion air inlet valves or blower motor speed via a piston 48, and the other regulating the fuel supply valve by a piston 47. If the fuel quantity is increased the temperature at the outlet of the evaporator 9, Fig. 1, rises and causes increased opening of a feed water valve 51 through a connection member 50 controlled by a temperature sensing means 49; the increased output temperature of the superheater 17 is signalled by a sensing device 54 and a piston 150, Fig. 1A, to a valve 151 controlling a piston 56 for swivelling a burner 57. If the output temperature of superheaters 6, 15, Fig. 1, is still too high the valve 13 is operated to increase the flow in by-pass line 16 by a piston 63, Fig. 1A, controlled from the temperature sensing device 25 through a valve 161, piston 163, an adjustably spring- loaded three-dimensional cam 164, valve 167, comparator piston 169 and valve 185 ; the valve 8 is also operated to decrease the flow in the by-pass line 7 by a piston 65 through a similar control chain from the temperature sensing device 34. The intensity of firing alone may be adjusted by pistons 47, 48 in which case swivelling of the burner 57 is dispensed with. Alternatively, the burner is swivelled when signals are received from both temperature sensing devices 25, 34 whilst individual signals from either of the latter operates one of the valves 13 or 8, respectively. The superheaters of the medium and low pressure stages may be heated with live steam only, and a mixture of live and medium pressure superheater steam, respectively, whilst cooling is effected by a mixture of feed water and superheater steam from the low pressure stage and feed water only, respectively. The intermediate superheaters 6, 15 consist partly of lengths of piping fitted one inside the other. Regulation is also performed by injecting water into superheaters 17, 12, Fig. 1, under the control of regulators 71, 72 and temperaturesensing devices 54, 73, respectively. Any change in the steam flow rate in line 24 causes operation of valve 13 through a flow detecting orifice 170, Fig. 1A, diaphragm 171, cam 173, valve 176, piston 178 and the three dimensional cam 164. Any change in the rate of flow in line 33 is passed to a valve 167<SP>1</SP> by apparatus identical with that associated with valve 167, the valve 167<SP>1</SP> controlling movement of the piston 150, and being connected to piston 169; the signal from valve 167 is also communicated to piston 150. The control valves of pistons 47, 48 are biased by springs 253, 250, the loadings of which are adjusted by cams responsive to the rate of fuel flow and temperature of combustion air, respectively. Throttle valves are provided in the lines to pistons 63, 65, 56 and 152. The regulators are constructed to give a proportional, integral, or differential control or a control having combinations thereof. If heating of one and cooling of the other intermediate superheater is required, the appropriate regulating device provides that one effect, e.g. heating, is utilized before the other effect becomes operative or both effects may be used simultaneously. If more than two adjusting members are provided for the heating and cooling lines, both effects may be used at once or heating of one intermediate superheater is augmented at the same time as the other is reduced until the adjusting member is in the end position when the cooling only is controlled.