Boiler and a supported heat transfer bank arranged thereto

Abstract: The invention relates to a boiler comprising a reactor chamber (10) with a first tube bank (42, 46) arranged therein, the tube bank consisting of a plurality of heat transfer tubes attached rigidly to each other and supported to two opposing walls (20, 22) of the reaction chamber. A second tube bank (40, 44, 48) has been arranged into the reaction chamber above or below the first tube bank and perpendicularly to it. A means or a retaining lug has been arranged onto the second tube bank to stiffen the first tube bank sideways and/or to support it.

Description: The present invention relates to a boiler, consisting of a reaction chamber with at least one first heat transfer panel or a tube bank, formed by several horizontal heat transfer tubes attached one on top of the other, and in which the ends of the heat transfer panel or the tube bank are supported to two opposing walls. The boiler can be provided with e.g. a circulating fluidized bed, in which case solid material and fluidizing gas are introduced into the lower portion of the reaction chamber so that the solid material is fluidized and at least partly transported with the fluidizing gas into the upper portion of the reaction chamber, the particle suspension formed by gas and solid material thus filling the so-called free board area of the reaction chamber. The particle suspension is further directed via an opening arranged on the upper portion of the reaction chamber to a particle separator, arranged in contact with the reaction chamber, in order to separate the solid material from the gas. The particles separated are recycled from the particle separator to the lower portion of the reaction chamber, wherefrom they flow again with the fluidizing gas into the upper portion of the reaction chamber, thus forming a circulating fluidized bed into the boiler. Boilers with fluidized beds are especially suitable for burning numerous solid materials, for example coal, peat and waste materials. The heat is recovered with heat surfaces arranged in the boiler and in the convection part after the boiler. The walls of the boiler can be formed of so-called water walls, and separate tube banks or heat transfer panels can be arranged into the boiler to lower the temperature in the combustion chamber. Separate heat transfer surfaces, supported from the upper portion of the boiler, can be e.g. evaporator or superheater surfaces. The evaporator or superheater surfaces are formed by, for example, welding tubes parallel to each other so that they form a rigid tube bank or panel. The tube banks can be supported vertically from the roof of the reaction chamber or arranged to span the combustion chamber from one wall to the opposing wall, the walls thus supporting the tube banks. In this case the tube banks go through the walls and are connected to collector boxes outside the boiler. The tubes are usually rigidly supported to one wall and flexibly, with e.g. bellows construction to the other wall. The bellows construction absorbs the thermal expansion of the tube bank and simultaneously seals the tubes' passage through the combustion chamber wall. As the size of the boilers has increased, it has been necessary to utilize ever longer tube bank constructions. The width of the boilers is often more than 7 to 8 meters, even 15 to 25 meters, and the depth over 5 meters. It has been proved difficult to use separate heat transfer banks because the tube banks will have to be supported also in the middle of the combustion chamber, a support at the end of the banks only being inadequate. Large banks are prone to resonance, deformation or bending. The flow of gas, or in a fluidized bed boiler also the flow of solid material, causes pressure fluctuations in the combustion chamber of the boiler and thus resonance and deformation in the tube banks. The liquid or other fluid, such as air, flowing in the tubes can also cause fluctuations in pressure, leading to resonance and deformation of the tube banks. The longer the tube banks are, the more liable they are to vibrate or bend downward. The rigidity of the tube panel is not always enough to keep the tube banks straight, but they have to be supported and/or stiffened. Resonance and bending can cause deterioration of the tubes' mechanical strength, wear of the tubes, fatigue of the tube material and increased corrosion. High temperature and particles flowing in a fluidized bed boiler usually worsen the situation. Tube banks for circulating fluidized bed boilers are often made of so called omega tube banks, in which tubes having a mainly rectangular outer diameter have been attached together into plain banks. In fluidized bed boilers the wearing effect of the circulating solid material has been minimized in these vertical, plain banks. Nevertheless, the resonance or bending of the vertical bank will cause a change in the flow of the solid material suspension surrounding the bank, thus increasing turbulence of the stream of solid material adjacent to the bank, causing local wear of the bank. U.S. patents 4,706,614, 4,753,197, 4,307,777 and 4,331,106 disclose attempts to vertically support the tube banks either with support means extending from the bottom portion of the combustion chamber or with support means suspended from the roof of the combustion chamber. U.S. patent 4,955,942 further discloses a tube bank, in which the tubes have been supported by each other with plates between the tubes. When utilizing support means extending from the lower or upper portion of the combustion chamber, the support means have also to be cooled or they will not last in the hot conditions. Local overheating can be fatal to the strength of the support means. Therefore the support means require a cooling circulation of their own and thus increase the cost of the boiler. Uncooled extensions fastened to the support means are liable to burn out quickly. In addition to the fact that the thick particle suspension in e.g. the lower portion of a fluidized bed boiler is a very abrading and thus an undesirable surrounding for support means, all extra structures in the combustion chamber of a fluidized bed boiler should be avoided, as they have a negative effect on the flow of the gas and particle suspensions. Furthermore, structures as such cause complexity in the structure of the combustion chamber. The object of the present invention is to provide a boiler with a better supported and more rigid heat transfer bank than in previously known heat transfer bank arrangements. A special object of the present invention is to provide a heat transfer bank, the sideways movement of which has been minimized. Thus, the object of the present invention is also to provide a boiler, the heat transfer banks of which are more durable and less prone to wear than in prior art. The object of the present invention is also to provide a simple and functional arrangement for supporting and/or stiffening the heat transfer banks in a boiler, especially in a fluidized bed boiler. In order to accomplish the above objects, a boiler with a heat transfer bank arranged in the reaction chamber is, according to the invention, characterized in that in the reaction chamber, in addition to a first heat transfer panel or tube bank, there is, perpendicularly to and above and/or below the first bank or panel, at least one second heat transfer panel or tube bank, made of a plurality of horizontal heat transfer tubes, attached rigidly on top of each other and the ends of which are supported to the other two opposing walls of the reaction chamber, or a single heat transfer tube, the ends of which are supported to the two other opposing walls, and that a means or retaining lug has been arranged to the second heat transfer panel, tube bank or heat transfer tube to stiffen the first heat transfer panel sideways and/or support it. According to the invention, the negative effects caused by the bending or resonance of the tube banks can be minimized by arranging heat transfer banks or even single heat transfer tubes perpendicularly to each, other, thereby supporting or stiffening them in a simple manner. Supported and stiffened tube banks remain vertical and essentially unbended and free of vibrations, and both gas and particle streams can flow upwards past the tube banks essentially undisturbed in the direction of the banks, in which case the wearing effect of the streams on the banks is minimized. In large elongated boilers with a heat transfer tube bank arranged longitudinally through the boiler, two or more perpendicular heat transfer banks in a horizontal plane, with a distance between them, can be arranged below and/or above and perpendicularly to the long tube bank to support and stiffen it. Whether arranged above or below the heat transfer bank, the second perpendicular bank or panel will stiffen and/or support the bank. According to a preferred embodiment of the invention, the first and second tube banks or panels, arranged perpendicularly to each other, are supported to each other with e.g. retaining lugs, arranged at the crossing points and preventing sideways movements. Thus, e.g., two retaining lugs are welded on the uppermost tube of the transverse second tube bank, at the crossing point of the tube banks, the lugs being arranged at a distance approximately equalling the diameter of the tube from another. A longitudinal tube bank is installed above the transverse tube bank so that the lowermost tube of the longitudinal tube bank passes through the opening defined by the retaining lugs, the lugs thus preventing any sideways movement of the lowermost tube and simultaneously thereby stiffening the whole upper tube bank. Accordingly, retaining lugs can be arranged on the lowermost tube of the second tube bank at the crossing point, and thus any movement of the uppermost tube of the long tube bank, arranged below the second tube bank, can be prevented. Also other heat transfer panels, not made of tubes, can be supported to each other this way. According to a second embodiment of the invention, two tube banks are fastened to each other with the aid of the individual tubes of the tube banks. At the crossing point, the outermost tube of the tube banks is bent outward from the other tubes so that an opening or a "loop" is defined, the size of which is adequate to allow the correspondingly outward bent tube of the transverse tube bank to pass through the opening. With these tube fastenings, the tube banks can thus be fastened together during the installation. Several heat transfer banks can of course be arranged on top of each other. Perpendicular tube banks can be fitted in the gaps between the heat transfer banks as needed, either in every gap or for example only in every second gap. A single transverse heat transfer bank can in a boiler support two long heat transfer banks, one arranged above and the other below the transverse bank. In heat transfer banks, or tubes according to the invention the heat transfer fluid is preferably water or steam, but other fluids - such as gas - can also be utilized, depending on the process and temperature. The arrangements according to the invention are simple and they are easily realizable into existing boilers. They do not need separate external support structures. No openings will have to be made into the walls of the boiler for the support structures' lead-through. The support elements according to the invention do not need separate cooling, as the heat transfer banks or panels are already cooled as such. Retaining lugs can be made of such materials and shaped so that they do not overheat or that their heating is not critical. In the following the invention is disclosed in more detail with reference to the accompanying drawings, of which Fig. 1 illustrates a circulating fluidized bed reactor, with heat transfer banks arranged thereto and supported according to the invention; Fig. 2 is a cross-sectional view along the line A-A of the boiler of Fig. 1; Fig. 3 is a cross-sectional view along the line B-B of the boiler of Fig. 2; Fig. 4 is an enlargement of heat transfer banks of Fig 1 and their support; Fig. 5 illustrates the support of heat transfer banks according to a second embodiment of the invention and Fig. 6 illustrates the support of heat transfer banks according to a third embodiment of the invention. Figs. 1, 2, and 3 illustrate a circulating fluidized bed reactor according to a preferred embodiment of the invention, comprising a reactor chamber 10, i.e., a combustion chamber or a combustor, a particle separator 12 and a conduit 14 for recycling the particles separated. The combustion chamber has a rectangular cross-section and is formed of water walls 16, 18, 20 and 22, of which the long walls 16 and 18 are illustrated in Fig. 1 and the short walls 20 and 22 in Fig 2. The water walls are preferably formed of vertical water tubes joined together. The walls of the lower portion of the reactor chamber are protected with a protective lining 24. The bottom of the reactor chamber comprises a nozzle plate 26, the plate being provided with nozzles or openings 28 for introducing fluidizing gas from airbox 30 to maintain a fluidized bed in the reactor chamber. Solid material is introduced via inlet 32. Fluidizing gas or air is introduced with a velocity capable of causing some of the fluidized bed material to constantly flow upwards together with the gas into the upper portion of the chamber, and from there via an opening 34 arranged in the upper portion of the chamber to the particle separator 12. The gases are withdrawn from the particle separator via conduit 36. Heat transfer banks or tube banks 40, 42, 44, 46, 48, 50, 52 and 54 are arranged in the upper portion of the reactor chamber 10. Some of the banks, 42 and 46, span the reactor chamber longitudinally from wall 20 to wall 22, forming thus the long heat transfer banks of the boiler. Other banks 40, 44, 48, 50, 52 and 54, span the reactor chamber from one long wall 16 to the other long wall 18, forming thus short, transverse heat transfer banks supporting the long heat transfer banks. Both heat transfer banks are supported to the wall structure and pass through the walls to distribution boxes 56, 58, 60, 62, 64 and 66 disposed outside the walls. One end 68, 70, 72 of each tube bank is supported to the walls 18 and 22 in a fixed manner, whereas the other end 74, 76, 78 is attached to the walls 16 and 20 by bellows construction 80, 82, 84, which allows thermal expansion of tube banks. Fig. 4 is an enlargement of the crossing point of the tube banks 40 and 42 of Fig. 1. The tube banks are formed of water tubes 86 and 88, that have been welded together into vertical banks. Two retaining lugs 92 and 94 have been fastened at the crossing point on the uppermost water tube 90 of the tube bank 40. In the embodiment illustrated in the picture the retaining lugs are shaped like bollards. Two bars or rods 98 and 100 have been welded onto the lowermost water tube 96 of the tube bank 42, supporting the tube 96 between retaining lugs 92 and 94. Thus any sideways movement of the upper water tube bank 42 is prevented and the bank is kept vertical and unbended. The heat transfer banks can, as has been stated before and is shown in Fig 5, be made of omega tubes 186 and 188, in which case the outer surfaces of the water tube banks 140 and 142 are almost completely plain. In this case the cross-section of the retaining lugs 192 and 194 can be e.g. triangular, as is illustrated in the figure. Other kinds of lamellar walls can also be supported correspondingly. Fig. 6 illustrates another embodiment of the invention, in which the outermost water tubes 290 and 296 of two water tube banks 240 and 242 have been bent to form bends 291 and 297 so that openings 293 and 295 are defined between the outermost tubes and other tubes 286 and 288 of the tube banks, so that one outermost tube 290 can be arranged to go through the opening 295 formed by the other outermost tube 296. The tube panel 242 is thus supported at its lower portion to tube panel 240 and cannot move. This arrangement according to the invention is relatively easily realizable during the installation of the tube banks.

Claims: A boiler, comprising a reaction chamber or combustion chamber (10) with at least one first heat transfer panel or tube bank (42, 46, 142, 242) arranged therein, the bank or panel being made of a plurality of horizontal heat transfer tubes (86, 96, 186, 286, 296) attached rigidly atop each other, and in which boiler the ends of the heat transfer panel or tube bank have been supported on two opposing walls (20, 22) of the reaction chamber, characterized in that in addition to the first heat transfer panel or tube bank there is, above and/or below it and perpendicularly to it, in the reaction chamber at least one second heat transfer panel or tube bank (40, 44, 48, 50, 52, 54, 140, 240), made of a plurality of horizontal heat transfer tubes (88, 90, 188, 288) attached rigidly on top of each other and the ends of which are supported to the other two, opposing walls (16, 18) of the reaction chamber, or a single heat transfer tube, the ends of which are supported to the two other opposing walls, and that a means (291, 297) or a retaining lug (92, 94, 192, 194) has been arranged to the second heat transfer panel, tube bank or heat transfer tube to stiffen the first heat transfer panel sideways and/or support it. A boiler as recited in claim 1, characterized in that the first tube bank (42, 46) has been arranged to span the boiler longitudinally from one end wall (20) to the other end wall (22) and that the second tube bank (40, 44, 48, 50, 54) or heat transfer tube has been arranged to span the boiler transversely. A boiler as recited in claim 2, characterized in that below the first longitudinal tube bank (42) has been arranged, in a horizontal plane, more than one transverse tube bank (40, 50) or heat transfer tube. A boiler as recited in claim 1, characterized in that the lower tube bank (40, 50) has been arranged to support the upper tube bank (42). A boiler as recited in claim 1, characterized in that at least two superimposed first tube banks (42, 46) have been arranged into the boiler, and in every space between them has been arranged a perpendicular second tube bank (42, 46) or a heat transfer tube with a means for preventing any sideways movement of the first tube banks. A boiler as recited in claim 1, characterized in that more than two superimposed first tube banks (42, 46) have been arranged into the boiler, and in every second space between them has been arranged a perpendicular tube bank (44) or heat transfer tube with a means for preventing any sideways movement of the first tube banks situated above and below. A boiler as recited in claim 1, characterized in that onto the lowermost and/or uppermost tube of the perpendicular second heat transfer bank or onto the perpendicular heat transfer tube (90) connected with the first tube bank, at the crossing point of the tube banks, has been arranged retaining lugs (92, 94) that prevent any sideways movement of the first tube bank. A boiler as recited in claim 1, characterized in that the tubes (290, 296) contacting each other of two perpendicular tube banks have at the crossing point been bent to form a bend (291, 297) so that a first opening (295) is defined between the lowermost tube (296) and the second lowermost tube of the first tube bank and, correspondingly, a second opening (293) is defined between the uppermost tube (290) and the second uppermost tube of the second tube bank and that the lowermost tube (296) of the first tube bank is led through the second opening (293) and the uppermost tube (290) of the second tube bank is led through the first opening (295), thus binding the tube banks together.

Inventors: HULKKONEN TUOMO, HULKKONEN, TUOMO
Applicants: AHLSTROEM OY, A. AHLSTROM CORPORATION
Application year: 1991
Main classification: F22B37
IPC codes: F22B17, F22B31, F22B1, F23C10, F22B37, F23M5