US2947288A - Radiant tubular heat exchanger - Google Patents

Description

Aug. 2, 1960 E. NICKEL RADIANT TUBULAR HEAT EXCHANGER Filed Aug. 20, 1957 2,947,288 7 Patented Aug. 2 1960 United States PatentOffice 2,947,288 RADIANT TUBULAR HEAT EXCHANGER Eberhard Nickel, 'Stuttgart -Wa'ngen; Germany, assignor to Kohlenscheidungs-Gesellschaft,m.b.H., a corporationofGermany t. I

Filed Aug. 20, 19 57, 'Ser.No.67 9, 21ll 1 Claim. (01 122-418 5 The invention relates to a radiant tubular heat ex changer and is particularly applicable to a heat exchanger 7 of the remaining heat energy.

In steam generators of the above type having both superheaters and reheater in one furnace, difliculties are encountered when these steam generators are initially put on the line or when for operational reasons they are periodically shut down and againstarted up. These difficulties arise out of the fact that when starting up a boiler of this type no steam is flowing through the reheater tubes while these tubes are exposed to the high temperature of the combustion gases and are therefore in danger of being damaged by overheating and burning.

Attempts'have been made heretofore to meet the above diificulties by arranging the reheater heating surface in gas passages behind the superheater so that the combustion gases produced in the furnace are initially cooled by flowing over the steam generating and superheater heating surfaces before they come in contact with the reheater tubes. The temperature of these gases is thereby reduced to a value which is not much higher than'the' required reheat steam temperature. 7

However, in a steam generator in which the reheat vheating surface is disposed in the manner'above described, a large amount of surface must be provided in the reheater because of the small temperature differen'ce between the heating gases and the final reheat steam temperature. Because this large surface generally consists of high tempera-ture alloy steel tubing, the initial cost of a steam generator of thistypeis .very high.

Furthermore, in cases where it is,required.that a reheat steam temperature be obtained which is higher than the superheat' steamtemperature, the above described arrangement is not feasible, since it then becomes necesfill one.

The herein disclosed invention provides a novel apparatus which permits the starting up of a reheat steam generator without exposing the reheater to excessive gas temperatures and without incurring the above described operational disadvantages inherent in organizations heretofore employed for the solving of the problem.

It is accordingly the general object of my invention to arrange the reheaterheating surface within the furnace chamber in such a manner, in relation to the superheater heating surface and the water wall heating surface, that the danger of overheating and burning of the reheater tubes is greatly reduced, if not eliminated, when starting up the boiler without the beneficial cooling effect of steam flowing through the reheater tubes.

With this and other objects in view which will become apparent from the following description, reference is made to the accompanying drawing forming a part of this specification and illustrating my invention without intention of limiting the invention to any particular form or use. 1 Inthe drawing, Fig. 1 is a sectional side elevation of the steam generator incoi'porating my inventive improve- 'ments; v Fig. 2 is an elevational cross section taken along lines -.-2-2 of Fig. 1. I 'l Referring now to Fig 1 the illustrated steam generator comprises a furnace chamber F bounded by side walls 10, 12, -14 and 16 all of which are lined with steam generating water wall tubes 18. These tubes originate in lower water-wall headers 19 and terminate in a steam and water drum 20. This drum serves the purpose of collecting the generating steam and water mixture and also of receiving feed water from an economizer 21 by way of tubes 22 which line the rear wall 23 and roof 24. The Water entering drum 2! flows downwardly through tubes 26 into an intermediate header 28 and through other connecting tubes 30 into lower water wall headers 19. Fuel and airyfor combustion is discharged into the furnace chamber F by way of burners B. These burners in the illustrative embodiment hereof are located inor near the corners of the furnace chamber F and are discharging fuel and air in directions tangential to an imaginary firing circle centrally located within the'fur nace chamber and produce a rotating column or stream of gases rising within 'the furnace chamber towardsa furnace gas oiftake or gasfoutlet 32. A horizontal gas passage 34 adjoins the furnace gas outlet 32 and leads into a vertical downward pass 36 having a horizontal gas duct 38 at its lower end through which the gases pa ss to an induced draft fan 40 discharging the gases into the atmosphere by way of stack 42. Economizer '21 is located in this vertical pass 36 and an air heater 43 may additionally be employed to reduce the temperature of the gases. r i i The steam and water mixture delivered to drum 22' by tubes 18 passes through avsteam and Waterseparator (not shown) located within drum 20 for the separation of the steam from the water. The separated. steam leaves the drum by way of connecting tubes 44 to enter low temperature superheater section 46 located in horizontal gas pass 34, from whence the steam flows to' a high temperature superheater section 48 located in'th e upper portion of furnace chamber F. superheater 48 comprises a serise of tubular panels spacedly arranged within the central portion of the furnace chamber'F as shown in Fig. '2. t V The superheated steam is heated to the desiredmaximum temperature in superheater panels 48 from whence it flows through pipe 47 to the high pressure stag e'of a turbine A. After having given. up someof its energy through loss in pressure andttemperaturefthe steam leaves that stage by way of pipe '49 to'entei and fiowtlirough low temperature reheater section 50 from whence the partially reheated steam continues through tube 5*). to enter the high temperature section 54 of the reheater wherein the temperature of the steam is raised to the final reheat temperature. The steam thereupon flows through pipe 56 and passes through the low pressure stage of the turbine T where the major portion of the remaining the atmosphere until the steam pressure is sufiiciently high to operate the turbine.

The present invention provides a most economical and novel solution to the above problem by arranging the superheater heating surfacewithin a central zone of the rising gas stream in the furnace,'and locating the reheater heating surface within a peripheral zone of the rising gas stream adjacent the water cooled furnace walls. In this manner the gases in the center of .the gas stream, which are of a higher temperaturethan-the gases'passing along a peripheral zone because the latter give up heat to the water walls, serve the. purpose of superheating the steam in the superheater, and do not comeinacontact with reheater heating surface whichat' thetime of initial operation is devoid of cooling steam flow; In accordance with this inventionthe reheater heating surface such as 54 of the illustrative embodiment is exposed to the peripheral gases which have been cooled by the water wall steam generating tubes 18 covering the lower portion of the furnace chamber walls 14 and 16. Consequently the danger of overheating these reheat tubes 54 is considerably minimized and the unit can be put on the line with greater safety and speed.

Furthermore, the invention provides novel facilities whereby the temperature of the gases rising along the side walls and passing over the reheater can further be reduced. This is accomplished in the illustrative embodiment of the invention by admitting relatively cool gases or air through a row of nozzles 60 provided in the'two opposing. side walls 14 and 16 which are parallelly disposed with respect to the reheater panels 54. These nozzles 60 are located directly below the lower portion of reheater'panels 54 as shown in Fig. 2. In accordance with the invention the reheater panels 54 which are arranged adjacent the water walls 14 and 16 are substantially shorter than the centrally located superheater panels 48 and the cooled gases are directed into a pocket 53 formed by the outermost superheater panel and the side wall below the reheater tubes. A gas recirculating duct 62 is provided which delivers cooled gases from the outlet side of induced draft fan 40 to nozzles 60. A damper 64 in duct 62 permits control of the flow of these recirculated cooled gases. These gases are discharged through nozzles 60 in a direction towards the lower ends of the tubes of reheater panels 54 as shown in Fig. 2. This permits additional cooling of the rising peripheral gas mass to which the reheater heating surfaces are exposed and further minimizes or even eliminates the danger of overheating of the reheater tubes at the time of the start-up operation of the unit.

Although the invention, as hereinabove described is used in'connection with a radiant steam generating-reheat unit, the invention can with equally beneficial results be applied to a radiant heat exchanger in connection with a power plant wherein an other working medium than steam and water is used, such as air or other vapors, fluids, or gases.

While I have illustrated and described a preferred embodiment of my novel organization it is to be understood that such is merely illustrative and not restrictive and roof lined with heat-absorbing steam generating water walltubes and having acombustion gas outlet at the upper end of said furnace chamber; burner means for discharging fuel and air -for burning into said chamber through the walls thereof at points remote from said gas outlet to produce a stream oflhot combustion gases flowing from said burner means through said chamber in heat exchange relation with said wall tubes for the generation of steamv and out through said gas outlet; superheating tubes 'for superheating said steam; said superheating tubes forming elongated upright panels extending downwardly into said furnace chamber from said roof a predetermined distance, said superheater panels being spacedly arranged within a central zone of said chamber and forming a horizontally extending tube bank consisting solely of superheater tubes and maintaining a predetermined space between the sides of said bank'and each of said two opposing side walls; reheater tubes for reheating said superheated steam, said reheater tubes forming elongated upright panels extending downwardly into said furnace chamber from said roof a substantially shorter distance than said predetermined distance, said reheater panels being spacedly arranged for occupying said space provided between each side of said superheater tube bank and said opposing side walls, said reheater panels forming a tube bank consisting solely of reheater tubes and forming a vacant pocket immediately therebelow which extends from each side of said superheater tube bank to each opposing side wall; means for conducting recirculated cooled combustion gases from a point downstream of said superheater tube bank in the gas flow sense to the furnace chamber at a location directly below said reheater tube bank; and means for introducing said recirculated gases into said vacant pocket provided between said superheater tube bank and each opposing side wall, and immediately below said reheater tube bank, whereby said reheater tubes are exposed to a gas stream portion the temperature of which having been reduced by the cooling action of said water wall tubes, said extended superheater tubes and said recirculated gases to a greater extent than the temperature of the gas stream portion to which said centrally located superheater tubes are exposed.

References Cited in the file of this patent UNITED STATES PATENTS 1,952,542 Ehlinger Mar. 27, 1934 2,685,279 Caracristi Aug. 3, 1954 FOREIGN PATENTS 726,244 Great Britain Mar. 16, 1955

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