Patent GB-762172-A (GB)
Title: Improved methods of and apparatus for controlling the temperature of superheated vapour
IPC: F22G5/10
Filed: 1952-11-19
Abstract: 762,172. Steam-generator furnaces. BAILEY METERS & CONTROLS, Ltd. Nov. 19, 1952 [Nov. 19, 1951], No. 29210/52. Class 51 (1). [Also in Groups XIII and XXIX] In a vapour generating, superheating, and re-heating unit having the superheater and re-heater surfaces disposed in damperco ntrolled, parallel gas passes, control means operating over a range of loads on the unit is provided for adjusting the superheat temperature and reheat temperature in the same sense towards their control point values while, at the same time, maintaining the two temperatures at their respective values by adjustment of the dampers in the gas passes, and either the superheater dampers or the re-heat dampers remain fully open over the selected load range. In an embodiment, the walls of the furnace 1, Fig. 1, are made up of vertical water tubes comprising a vapour generating section. The heating gases pass from the furnace through a tube screen 3, secondary superheater 4, primary super-heaters and a reheater 7 in parallel, an economizer 9, and an air heater 10. An economizer section 8 is situated in a passage by-passing the superheaters and reheater 7 and economizer 9. The main and bypass gas passages are controlled by dampers 13, 11, respectively, 13 representing three sets of dampers, each of which separately controls the passage in which it is situated. A forced draught fan 19 supplies secondary air through the air heater 10 to the burner boxes 17. Some of the outgoing gas downstream of dampers 11, 13 is withdrawn by a fan 21 and passed back to the lower part of the furnace, and dampers 22 control this flow. The method of regulation constituting the invention may be carried out by an attendant observing the conditions under which the plant is operating and actuating switches controlling electric motors which adjust the various dampers, &c. In the automatic operation of the unit, the measure of the final steam temperature operates a pilot valve 32, Fig. 4, which applies .an output pressure to the A chamber of a relay 38. Similarly, the final re-heat temperature operates the pilot valve 30 which applies an output pressure to the A chamber of a relay 36. Relays 36, 38 are similar to the " standardizing " relay described in Specification 461,389, [Group XXIX], and they each give an output signal which is proportional to the input and to its time-integral thereof. The output pressures from the relays 36, 38 are applied, respectively, to relays 40, 41. The load on the unit is ascertained by measuring either the steam flow from, or the air flow through, the unit and this measurement is applied to a pilot valve 34; and the output pressure from this valve is applied through restrictions to the C chambers of both relays 40, 41. The output pressures from relays 40, 41 are proportional to and depend upon the surn of the input pressures and they are applied to the B and A chambers respectively of a relay 46, and the normal pressure inlet and exhaust ports of this relay are connected to its B and A chambers respectively. The output of relay 46 is applied through a manual-automatic selector valve 53 to operate the by-pass dampers 11 and also through relays 48, 50 and a manual-automatic selector valve 52 to operate the dampers 22 in the recirculating gas passage. The input to relay 48 is applied to the A and C chambers thereof so that the output pressure is double the input pressure, and relay 50 gives a low or high output pressure according as the input pressure is high or low, respectively. The output pressure from relay 40 is also applied through a relay 54 similar to the reversing relay 50, and through a manual-automatic selector valve 55, to operate the dampers 13 in the reheater path. The dampers 12, 14 controlling the primary super-heater passes are similarly controlled from the output pressure from relay 41. Thus, the re-heat dampers are under the control of the load with a check back on final re-heat temperature, the superheater dampers are under control of the load with a check-back on final superheat temperature; and the recirculation and bypass dampers are selectively controlled by the load and final steam and re-heat temperatures, with the control due to relay 46 being in accordance with steam final temperature or re-heat final temperature, whichever has the lower unregulated value. Reference has been directed by the Comptroller to Specification 706,965, [Group XIII].