Patent GB-264831-A (GB)
Title: Improvements in and connected with the control of the superheat of steam
IPC: F22G5/14
Filed: 1927-01-17
Abstract: 264,831. La Mont Corporation, (Assignees of La Mont, W. D.). Jan. 23, 1926, [Convention date]. Controlling superheat.-The degree of superheat in steam generators of the kind in which the superheater tubes are disposed closely adjacent and substantially parallel to the generator elements, and subjected to the whole of the furnace gases, is controlled manually or automatically. Fig. 1 shows a water-tube boiler in which the superheater tubes 7 are arranged between the generator tubes 4, while the superheater tubes 10 are disposed in the boiler space between the generator tubes and the feed-water heater 12, the steam passing through a main 16 and branc 17, 18 to the superheater tubes. The steam flow through the branch pipes is automatically controlled by a thermostat 281, which ranged in the superheated steam main, and which, through an electric switch cont steam valves 19, 20. Byepass valves 117 are provided around the valves 19, 20 the steam main 16 and the superheaters relieve the pressure in the main 16 du throttling effect of the valves 19, 20. At low load, the valve 19 is set about three-quarters open and the valve 20 is closed, while as the load and the superheater temperature increase the thermostat effects the opening of the valve 20 so that a greater proportion of the steam flows through the cooler superheater tubes 10. As the pressure in the steam main 16 rises above that in the superheater tubes 7 the diaphragm 126, Fig. 7, of the valve 119 and the rod 127 are displaced to the right, 'the projection 129 on the rod striking a projection 170 on the switch arm 132 so as to break the circuit to the armature of the valve 20 and make that to the valve 19 which is thus opened to a greater extent. Continued increase in the load results in the pressure in the steam main rising still higher than that in the superheater tubes so that the byepass valve 117 is opened to relieve the pressure in the main. One relief valve is controlled by the valve 120, which is similar to the valve 119, but which is operated when the pressure difference between the steam main 16 and superheater tubes 10 is greater than that between the main and the superheater tubes 7. Fig 3 shows a modification in which the superheater tubes 85, 86 are disposed between groups of generating tubes and are connected at their upper ends through valve-branch pipes 90, 91 to the steam main 69 and at their lower ends to a superheated steam main 68. The steam flow through the valved-pipes is controlled automatically by the thermostat 281 in the superheated steam main, while the flow of the furnace gases over the superheater tubes 85 is regulated through a step-by-step electric motor 89 which controls the position of a hinged damper 88. In another arrangement, the superheater tubes are located in three groups of generator tubes and communicate through hand-controlled valvedbranch pipes with the steam main. Fig. 4 shows a La Mont film-tube boiler having a steam and water vessel 99 and a superheated steam vessel 100, the water being forced by a pump 94 through the pipes 98, 43 44 to the generating tubes 22, 35 which communicate with the vessel 99 from which the steam flows through the pipes 38, 40, 41 to the superheater tubes 25, 31 which communicate with the vessel 100. Tubes 28 serving both to generate and superheat steam are disposed between the superheater tubes 25, 31. The superheat temperature is controlled automatically by thermostats 34, 104 which regulate the valves 95, 96 controlling the admission of water to the tubes 22, 28. Fig. 8 shows a modification of the boiler shown in Fig. 3, in which the superheater tubes 61, 64, 67 are arranged in series, and in which the steam flow through the superheater tubes is countercurrent to that of the furnace gases. In this arrangement, valves, controlled either manually or automatically by a thermostat located in the superheated steam main 68, are provided for by-passing some or all of the superheater tubes so as to control the superheat temperature. Fig. 9 shows a Wickes water-tube boiler comprising upper and lower drums 192, 193 which are connected by watertubes. The water-tubes are divided by baffles into four groups between which the superheating tubes 208 - 210 are disposed. The superheating tubes are connected in series and the steam flow through them is opposite to that of the furance gases. The gas passages are progressively decreased in sectional area towards the flue to allow for the contraction in volume of the furnace gases consequent on the fall in temperature. Fig. 10 shows a locomotive boiler, in which the superheating tubes 221 are disposed in the fire-tubes and communicate with the saturated and superheated steam headers 222, 226 respectively. The degree of superheat is controlled by injecting either hot or cold water into the fire-box. Fig. 15 shows a water-tube boiler having superheater tubes 263, 266 arranged between the generating tubes and at the back of the furnace respectively. The tubes 263 communicate with the steam drum 254 and the superheated steam main 270, while the tubes 266 communicate with the water header 256 of the boiler and a header 265 which is connected by a pipe 272 with the superheated steam main. Water is supplied to the tubes 266 in which it is converted into steam which is then superheated, the supply of water being regulated by a valve 268 that is controlled by the thermostat 276 in the superheated steam main. Steam can be passed directly into the superheated steam main through a pipe 277 having a valve 278 which is controlled by the thermostat. When the superheat temperature rises, the thermostat opens the valve 268 so that possibly more water flows into the tubes 266 than can be evaporated and consequently water collects in the header 265. The water level in this header is maintained constant by a control device 279 which controls the opening of the valve 280 and the operation of 'the pump 273 by which the water is returned to the boiler when its level in the header exceeds a predetermined level. Fig. 16 shows a boiler comprising headers 283, 284, 285 in communication with a lower header 282 which is connected to a pump 291 by which water fed into the pipe 292 through a pipe 297 having a water level control device 299 is circulated. The feed water flows through the valved pipes 293, 294 to the headers 283, 285. Saturated and superheated steam respectively are generated in the tubes 283 and 285 and after mixing in the lower header pass upwardly through the superheater tubes 287 to the main 300. The valves 295, 296 may be controlled either manually or automatically by a thermostat in the main 300. Specification 171,735, [Class 123 (ii), Steam generators], is referred to.