POWER PLANT WITH A BED VESSEL FOR FUEL COMBUSTION IN A FLUIDIZED BED

Abstract: Power plant with a bed vessel for fuel combustion in a flu­ idized bed. The bed vessel (3) is rectangular and has plane walls. Because of the pressure differences prevailing be­ tween the space in the bed vessel (3) and the surrounding space, the walls (41a,41b) are subjected to great forces. In a PFBC power plant with the bed vessel enclosed within a pressure vessel with compressed air, said forces are in­ wardly-directed. The forces are transmitted to a force-ab­ sorbing framework (21) by means of bars or links (43). To prevent different degrees of expansion from causing intolerable stresses in the walls of the bed vessel (3), the framework (21) and the bars or links (43) which connect the bed vessel and the framework, and the connections between the walls (41a,41b) and the framework (21) at the corners (47) are constructed such that the corners can be displaced in relation to the framework (21). These corner connections include auxiliary beams (61) which are substantially par­ allel to the walls (41a,41b), and are at one of their ends articulately connected to the framework (21). The auxiliary beams (61) and the walls (41a,41b) are connected by bars, links or brackets (65,67,69), preferably also in an articu­ late manner.

Description: The invention relates to a power plant with a bed vessel for fuel combustion in a fluidized bed according to the pre-characterising part of Claim 1. In the bed vessel of power plants of this kind fuel is burnt in a fluidized bed of particulate material, the bed material usually being a sulphur absorbent. The combustion can take place at a pressure near the atmospheric pressure or at a considerably elevated pressure. In the latter case, the pressure may amount to 2 MPa or more. Combustion gases generated in the bed vessel are then utilized in one or more turbines for driving a compressor for supplying the bed vessel with combustion air and a generator which delivers current to an electricity supply system. A power plant with combustion at elevated pressure is usually internationally designated a PFBC power plant, the letters "PFBC" being the initial letters in the expression P ressurized F luidized B ed C ombustion. In such a plant, the bed vessel and usually also a cleaning plant for combustion gas are enclosed within a pressure vessel. In power plants of the above-mentioned kind, the bed vessel has normally a rectangular horizontal cross section with large substantially plain side walls and end walls. These walls are subjected to great forces because of the pressure difference between the inner and outer side of the bed vessel. In a PFBC power plant with the bed vessel en closed within a pressure vessel and surrounded by compressed combustion air, a pressure difference arises in operation between the space in the pressure vessel surrounding the bed vessel and the space inside the bed vessel, because of pressure drops in the supply nozzles for air for fluidization of the bed material in the lower part of the bed vessel and in the fluidized bed. This pressure difference may amount to the order of magnitude of 0.1 MPa (1.0 bar). The side walls may have the size of 10 × 20 m, and therefore the forces acting on the bed vessel walls are very great, which, in addition to a high temperature, involves design problems which are difficult to master. The walls of the bed vessel are usually cooled and consist of panels of spaced apart vertical tubes and intermediate flanges connecting these tubes. The walls can be cooled by feed water circulating in the tubes. These walls are not capable of taking up the forces produced by the pressure difference between the two sides of the walls. The bed vessel is therefore surrounded by a force-absorbing framework which is suitably provided with stiff corners. The bed vessel is joined to this framework by means of force transmitting bars or links. In the case of a cold plant, the framework and the bed vessel have the same temperature. In operation the wall of the bed vessel assumes the temperature of the circulating coolant and the framework assumes the temperature of the surrounding air. Because of the temperature differences thus arising between the wall of the bed vessel and the force-absorbing framework, the bed vessel may expand or shrink in relation to the framework. The connection between the framework and the bed vessel must be made in such a way that the difference in expansion between the bed vessel and the framework does not give rise to dangerous stresses in the bed vessel walls, in the frame work, or in the connection means between the bed vessel and the framework. DE-A-2 055 803 shows one way of constructing the connection between a conventional boiler and a force-absorbing framework. The DE-B-1 146 499 refers to a boiler for generating steam which boiler accommodates panels of vertically oriented tubes. These tubes are arranged side by side and may be connected to each other by welding. In order to stabilize such tube panels of considerable vertical extension the panels are surrounded by flat iron ribbons which are welded to the tubes of the panel. These ribbons are supported by stiff and strong horizontal beams. To accommodate the different heat expansions of the tube panels on the one hand and said beams on the other hand the latter are connected to said flat iron ribbons at their ends by articulatetly arranged links. There are no forces to be taken up by the outer wall of the boiler, and said stabilizing and supporting beams have no direct connection to the outer wall of the boiler. The DE-B-1 273 737 discloses a similar steam generator as described in the DE-B-1 146 499. Again, the walls of the steam generator consist of a water-cooled tube panels which are supported by rigid horizontal outer beams. These beams are connected by links, articulatetly connected to the tube walls and the beams so that the tube walls and the beams can expand independently from each other according to their different temperatures. The forces which are transmitted by the tube walls to the beams on rising pressure in the boiler are absorbed by special pulling rods that pair-wise connect the two beams extending along opposing boiler tube walls. These rods can slide along the tube walls so that they can expand independently from the tube walls. Thus, each pair of opposing tube panels remains unaffected of the forces that are transmitted from the other pair of two opposing tube panels to their respective supporting beams. None of these prior art devices deals with fluidized bed vessels that are subjected to an overpressure from outside. The invention aims at developing a power plant with a bed vessel for fuel combustion in a fluidized bed that is designed in a simple manner to effectively prevent the occurrence of intolerably high temperature-related stresses in the bed vessel walls. To achieve this aim the invention suggests a power plant according to the introductory part of Claim 1, which is characterized biy the features of the characterizing part of Claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention, at least two bars or links at the corners of the bed vessel are connected to an auxiliary bar, which is substantially parallel to the beams of the framework and is articulately attached to the frame at its end located furthest away from the corner of the frame. When the auxiliary bar and the bed vessel are connected to each other by bars, these must be elastically deformable. The auxiliary bar is suitably connected to the bed vessel wall by means of links which are articulately joined to both the auxiliary bar and the bed vessel wall as well as by a bracket on the bed vessel at the corner of the bed vessel to which the auxiliary bar is articulately joined. The invention will now be described in greater detail with reference to the accompanying drawings showing _ by way of example _ in Figure 1 schematically a PFBC power plant with a bed vessel which is surrounded by a force-absorbing framework, Figure 2 schematically a corner portion of the framework and of the bed vessel when there is no mentionable temperature difference between the framework and the bed vessel walls, Figure 3 the same comer portion when the bed vessel wall has attained a higher temperature than that of the framework, Figure 4 the same comer portion when the framework has attained a higher temperature than that of the bed vessel wall. In the drawing, 1 designates a pressure vessel, 3 a bed vessel and 5 a gas cleaning plant of cyclone type enclosed within a pressure vessel 1. Only one cyclone is shown, but in reality the cleaning plant 5 comprises a plurality of parallel groups of series-connected cyclones. Combustion gases generated in the bed vessel 3 are passed through the conduit 7 to the cleaning plant 5 and from there through the conduit 9 to a turbine 11. The turbine 11 drives a compressor 13 which, via a conduit 15, supplies the space 17 in the pressure vessel 1 with compressed combustion air with a pressure which may amount to 2 MPa or more. The turbine 11 also drives a generator 19, which feeds out energy to an electricity supply system. The generator 19 may also be utilized as a starter motor. The turbine-compressor part 11, 13 may be built up in many different ways in accordance with known technique. The plant also includes a fuel feed system and an ash discharge system (not shown), as well as other conventional auxiliary equipment. The bed vessel 3 is surrounded by a framework 21 built up of vertical and horizontal beams 23 and 25, respectively. The bed vessel 3 and the framework 21 are both suspended from a beam system comprising longitudinal and transverse beams 27 and 29, respectively, the longitudinal beams extending perpendicular to the plane of the paper in Figure 1. The beams 27 are attached to the wall of the pressure vessel 1 or supported by columns (not shown). The framework 21 and the bed vessel 3 are suspended from the beams 27 and 29 in separate pendulums so as to enable movement there-between. The bed vessel 3 has a bottom 31 with air nozzles. Through these nozzles the bed vessel space 33 is supplied with air for fluidization of the particulate bed material and for combustion of fuel supplied to the bed. The bottom 31 is made with openings allowing consumed bed material to fall down into the space 35 and be discharged through the discharge conduit 37. The space 35 accommodates a tubular coil 39 having openings through which cooling air may be supplied to the space 35 to cool bed material that is to be discharged. The bed vessel 3 comprises a gas-tight sheet metal wall 41 with longitudinal walls 41a and transverse walls 41b. Owing to the resistance in the nozzles of the bottom 31 and in the fluidized bed, a pressure difference arises between the space 17 around the bed vessel 3 and the space 33 in the bed vessel. The pressure difference may amount to 0.1 MPa. The walls 41a and 41b, which may have a length of 20 m and 10 m, respectively, and a height of 10 m or more, will thus be subjected to very great forces. For absorbing these normally inwardly-directed forces, the walls 41a and 41b of the bed vessel 3 are articulately joined to the horizontal beams 25 of the framework 21 by means of links 43 preventing the walls 41a and 41b from bending inwards and buckling under compressive forces in the plane of the walls 41a, 41b. The walls 41a, 41b of the bed vessel 3 consist of vertical panels built of spaced apart tubes 55 which are interconnected by flanges 57. On their outer sides the walls 41a and 41b are provided with a heat insulating layer 59. The walls 41a and 41b are cooled, for example, by water fed to steam generating tubes (not shown) arranged in the bed vessel 3. As shown in Figures 2-4, in the corner portions the walls 41a and 41b of the bed vessel 3 are indirectly connected to the beams 25 of the framework 21 by means of auxiliary bars 61, links 63, 65, 67 and a bracket 69. The link 63 is articulately journalled in the bracket 71 on the framework beam 25 and articulately connected to the auxiliary bar 61. The links 65 and 67 are articulately connected to brackets 73, and 75 on the wall 41a and 41b. The auxiliary bar 61 is articulately connected to the corner bracket 69 which is. fixedly connected to the bed vessel walls 41a and 41b, respectively. Figure 2 shows the bed vessel 3 and the framework 21 in the case of a cold plant. When putting the plant into operation, both the bed vessel 3 and the framework 21 are heated. The bed vessel walls 41a, 41b assume approximately the same temperature as the cooling water in the tubes 55, and the framework 21 assumes the temperature of the compressed air in the space 17 in the pressure vessel 1. If the bed vessel walls 41a, 41b attain a higher temperature than the framework 21, the bed vessel 3 will expand stronger than the framework 21 and its corner 47 will be displaced along the diagonal 49 of the bed vessel 3 to a new position, shown in Figure 3. The deformation arising in the relatively slender walls 41a, 41b involves no problems from the point of view of stresses produced by this deformation. If the framework 21 should assume a higher temperature than that of the bed vessel walls 41a, 41b, the corner 47 is respectively displaced inwards as is clear from Figure 4.

Claims: 1. Power plant with a bed vessel for fuel combustion in a fluidized bed of particulate material, the bed vessel (3) being of rectangular shape in its horizontal cross-section and surrounded by a framework (21) of beams (23, 25), and with a number of bars or links (43) orientated substantially perpendicularly to the walls (41a, 41b) of the bed vessel and the framework (21) and being connected to said walls, these bars or links (43) being adapted to transmit forces, acting on the bed vessel walls (41a, 41b), to the framework (21), characterized in that at the corners (47) of the bed vessel (3) there are auxiliary bars (61) which are substantially parallel to the beams (25) of the framework (21) and articulately connected to the framework (21) at their ends facing away from the corners, and that the walls (41a, 41b) of the bed vessel (3) are connected to each of said auxiliary bars (61) by at least two bars, links or brackets (65, 67, 69). 2. Power plant according to Claim 1, characterized in that bars (65, 67, 69) between the bed vessel walls (41a, 41b) and the auxiliary bars (61) are articulately connected to the auxiliary bars (61) and/or to the bed vessel walls. 3. Power plant according to any of Claims 1 or 2, characterized in that said force-transmitting bars or links (43) are articulately connected to the walls (41a, 41b) and the auxiliary bars (61). 4. Power plant according to any of the preceding claims, characterized in that the auxiliary bars (61) are articulately connected to a common bracket (69) or to separate brackets which is/are fixedly connected to the walls (41a, 41b) of the bed vessel (3) at the corner (47) of the bed vessel (3). 5. Power plant according to any of the preceding Claims, characterized in that the bed vessel (3) and the framework (21) are housed in a common pressure vessel (1).

Inventors: JONSSON, ARNE
Applicants: ASEA STAL AKTIEBOLAG
Application year: 1987
Main classification: F22B37
IPC codes: F22B37, F22B31, F23C10