FLUIDIZED BED WITH IMPROVED NOZZLE CONSTRUCTION ANTECEPEN ES PE INVENTION The invention relates to a fl uidized bed apparatus and has particular application in a fl uidized bed combustion apparatus in steam generation apparatuses. While the present invention has primary application to a combustion process in a steam generation system, it will be understood that the present invention can also be employed in a wide variety of fluidized bed apparatus. Those skilled in the art will further recognize that fl uxed beds have been employed for decades in non-combustion reactions, where complete mixing and intimate contact of reagents in a fluidized bed results in high product throughput, with improved time economy and energy. The flue gas bed combustion apparatus can burn coal efficiently at sufficiently low temperatures to avoid many of the combustion problems in other modes. The term "fluidized bed" refers to the condition in which solid materials are given a free flowing fluid type behavior. As a gas is passed upwards through a bed of solid particles, the gas flow produces forces that tend to separate the particles from each other. At low gas flows, the particles remain in contact with other solids and tend to resist movement. This condition is referred to as a fixed bed. As the gas flow increases, a point is reached at which the forces in the particles are barely sufficient to cause separation. The bed is then considered fluidized. The gas cushion between the solids allows the particles to move freely giving the bed a characteristic liquid type. The combustion of the fluidized bed makes possible the burning of fuels that have a high concentration of ash, sulfur and nitrogen that can ordinarily be considered inadequate. By using this process it is possible, at least in some cases, to avoid the need for gas scrubbers while still meeting the emission requirements. In combustion of the fluidized bed, the fuel is burned in a bed of hot incombustible particles suspended by an upward flow of fluidizing gas. Typically, the fuel is a solid such as coal, although liquid and gaseous fuels can be easily employed. The fluidizing gas in general is combustion gas and the gaseous combustion products. When no sulfur capture is required, the fuel ash can be supplemented by inert materials such as sand or alumina to maintain the bed. In applications where sulfur capture is required, limestone is used as the sorbent and forms a portion of the bed. Two main types of fluidized bed combustion systems are (1) bed of bubbling fluid (BFB = bubbling fluid bed) wherein the air in excess of that required to fluidize the bed passes through the bed in the form of bubbles. The bubbling fluid bed is further characterized by a modest rate of mixing in bed solids and relatively low solids entrapment and in the flue gas and (2) circulating fluid bed (CFB) which is characterized by higher speeds and finer bed particle sizes. In these systems, the fluid bed surface becomes diffuse as the entrapment of solids increases, since there is no longer a defined bed surface. Circulating fluid bed systems have a high proportion of material circulating from the combustor to the particle recycling system and back to the combustor. The present invention has particular application to circulating fluid bed boilers, although those skilled in the art may recognize other applications. Characteristics and apparatus of this general type are also described in the publication "Combustion Fossil Power" (Energy of Fossils for Combustion) edited by Joseph G. Singer, P.E. and published by Combustión Engineering, Inc; a subsidiary of Brown Boveri Area, 1000 Prospect Hill Road, Windsor, Connecticut 06095 1991. In a steam generator the fluidised bed with conventional circulation, cracked fuel and sorbent is mechanically or pneumatically limited to the inner portion of a combustor. Primary air is supplied to the bottom of the combustor through an air distributor, with secondary air that is fed through air gates at one or more elevations in the lower part of the combustor. The combustion is carried out through the combustor, which is filled with bed material. Combustion gases and trapped solids leave the combustor and enter one or more cyclones, where the solids are separated and fall into a seal container. From the seal container, the solids are recycled to the combustor. Optionally, some solids can be diverted through a stopper valve to an external fl uxed bed heat exchanger (FBHE = fluidized-bed heat exchanger) and back to the combustor. In the FBHE, bundles of tubes absorb heat from the fluidized solids. The distribution of air within the fluidized bed is achieved within the prior art apparatus by a plurality of mutually parallel stainless steel pipes that extend vertically from the base plate to the fluidized bed. The upper end of each of these pipes is extremely finished. Each pipe has a plurality of holes that extend radially to direct air through the bed to achieve fluidization. Each of the holes in these pipes is typically between .1778 to 2286 cm (.070 to .090") in diameter.These pipes are usually molded and then drilled holes in their walls.Due to the stainless steel material, the attempts to molding the pipes with removable pins to form the holes has not been successful.Thus, the manufacturing expense of these pipes is substantial.These constructions of the technique are also vulnerable to transpolation of the holes due to airborne contaminants supplied. to the fluidized bed This requires maintenance to clean the holes In some cases, these can result in non-operational time for the steam generation apparatus Even if the steam generation apparatus is operational for other maintenance there is always competition to perform various maintenance procedures inside the oven and therefore it is highly convenient to minimize the requirement to clean the air distribution system and the fluidized bed apparatus. In CH-A-659 876, such an apparatus of the prior art is described and illustrated. As seen in CH-A-659 876, a fluidized bed system is provided which includes a housing (1), a floor (2) comprising a plurality of generally parallel tubes (4) joined by fins (3) intermediate to adjacent tubes (4) and a plurality of nozzle mounts extending generally vertical in mutually parallel relation. Furthermore, according to the document CH-A-659 876 each of the nozzle assemblies includes a cylindrical body (20) having a central line arranged in a generally perpendicular relation to the floor (2) and each of the cylinder bodies (20) includes a plurality of heads (21) extending generally radial therefrom at a remote axial end of the floor (2). An object of the present invention is to ensure complete mixing and intimate contact of the reagents in a fluidized bed apparatus. It is an object of the present invention to provide an apparatus for air distribution in a fluidized bed assembly that will require less maintenance. Another object of the invention is to provide an apparatus that can be manufactured more easily and at less cost than the known apparatus. Still another object of the present invention is to provide an apparatus that will more effectively distribute air in the fluidized bed apparatus and thus not require as many individual structures as in the prior art apparatus. COMPETITION OF THE INVENTION It has now been found that these and other objects of the invention can be achieved in a fluidized bed system that includes a housing, a floor comprising a plurality of generally parallel tubes joined by intermediate fins to adjacent tubes. A plurality of nozzle mounts extend generally vertically in mutually parallel relation to the floor, each nozzle assembly includes a generally cylindrical body having a central line disposed in a generally perpendicular relationship to the floor, each of the bodies includes a plurality of heads that generally extend radially there in a remote radial extremity of the floor. In some embodiments of the invention, each of the heads is evenly spaced around circumferential extension of each of the bodies and each of the heads is generally cylindrical and has a central line. Each of the center lines of the heads may be arranged at an angle with respect to the horizontal plane and the angle may be approximately 20 °. In some forms of the invention some of the nozzle mounts each have four heads and some of the nozzle mounts have two heads. In other 15 modes, all nozzle mounts have two heads. In other embodiments, all nozzle assemblies have four heads. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the accompanying drawing in which: Figure 1 is a partially schematic elevational view of a vapor indicator of the typical circulation fluidized bed, where the present invention may be employed.
Figure 2 is a plan view taken on line 2-2 of Figure 1, illustrating a fragment of the plate supporting the fluidized bed. Figure 3 is a plan view of one embodiment of the fluidized bed nozzle according to the present invention. Figure 4 is a cross section of the nozzle illustrated in Figure 3 taken on a vertical plane as indicated by line 4-4 of Figure 2. Figure 5 is a view similar to Figure 3 of another embodiment of the apparatus according to the invention. Figure 6 is a fragmentary view of the apparatus of Figure 5 and is generally similar to the view of Figure 4 except that the lower portion has been removed for simplicity. DESCRIPTION OF THE PREFERRED MODALITIES Now with reference to Figure 1, a steam generator of the conventional circulating fluidized bed is illustrated 10. Crushed fuel and solvents are fed mechanically or pneumatically to the inner portion of a combustor 12. Primary air is supplied to the combustor bottom
12 through an air distributor 14, with secondary air which is fed through air gates 16 at one or more elevations in the lower part of the combustor. The combustion is carried out through the combustor 12, which is filled with bed material. Combustion gases and trapped solids leave the combustor and enter one or more cyclones 16, where the solids are separated and fall to a seal container 20. From the seal container 20, the solids are recycled to the combustor 12. Optionally, some solids can be diverted through a stop valve (not shown) to an external fluidized bed heat exchanger (FBHE) 22 and back to the combustor 12. In the FBHE 22, bundles of tubes absorb heat from the fluidized solids. Combustion gas is directed from the cyclones to a convection passage 24. Now with reference to Figures 2, 3 and 4 a first embodiment of a nozzle 30 according to a preferred form of the invention is illustrated. It will be understood that the support 14 for the fluidized bed comprises a plurality of tubes 32 which are joined by respective fins 34. The tubes 32, 32 convey the water that is heated in the steam generating apparatus illustrated in Figure 1. As it will be seen from Figure 2, a large amount of the nozzle 30 extends vertically from the floor or support 14 for the fluidized bed. Each nozzle 30 includes a generally elongated cylindrical body 36 which is elbowed to a slightly larger diameter essentially in half from its axial extension. The suitably elbowed portion in primary form is not convenient, primarily due to the limited space available intermediate to the adjacent tubes 32. In this way, the spacing of the tubes 32, 32 limits the maximum diameter of the body 36 at its lower end. A slightly larger diameter is preferable in the upper extension of the body 36 to provide better flow to the four heads 38, 38, 38, 5 38. The four heads 38 each are generally cylindrical and the respective center lines of the heads 38 in this preferred embodiment are arranged in first and second planes that are mutually perpendicular. In a preferred form of the invention, the individual heads have a
_) Lower diameter of about 2794 cm (1.1"). Body 36 has an inner diameter in its lower portion of 6.35 cm (2.5") and an inner diameter in its extension of upper shaft of 7.67 cm (3"). Preferably, the center lines of the heads 38 each slopes at an included angle of 20 ° with respect to a horizontal plane.In a typical installation, the nozzle 30 has a total height of 45.72 cm (18") and the spacing between center lines of tubes 32, 32 is 17.78 cm (7"). Those skilled in the art will recognize that substantially different dimensions or dimensions will be employed in other fluidized bed constructions specific to other specific applications. in a form that allows the molding of the entire nozzle in a single sand molding process.The sand molding process simultaneously 5 will form the body 36, the four heads 38 and the dome 40.
Advantageously, the nozzle 36 is not so vulnerable to plugging by the air that it is directed to the fluidized bed because openings in the respective heads 38 are much larger than the holes in the constructions of the prior art. In addition, there are far fewer nozzle assemblies required than the prior art design pipes. This requirement for fewer nozzle assemblies 30 than the prior art pipes follows due to (a) the size of the openings in the heads 38 and (b) the angular orientation in the heads 38. Because the nozzle mounts 30 can be manufactured by a simple molding operation, the cost of a nozzle 30 is approximately 50% the cost of previously used pipes. An additional saving is possible due to the greater flow capacity of each nozzle 30 compared to a prior art tubing. More specifically, with the new design and according to the present invention there are 50% fewer nozzle assemblies 30 than the pipes required in the prior art assemblies. The combined effect results in approximately a 75% cost reduction when compared to the prior art systems. Now with reference to Figures 5 and 6, another embodiment of the nozzle assembly according to the present invention is illustrated. The assembly of nozzles 50 is similar to the assembly of nozzles 30 except that it only has two heads 38.
The heads 38 each are generally cylindrical and each inclined with respect to a horizontal plane as in the assembly of nozzles 30. Also as in assembly of nozzles 30, the center lines of the heads 38 are disposed in a common plane. The body 36 of the nozzle assembly 50 is substantially identical to the body 36 of the nozzle 30. The dome 52 may differ somewhat in shape from the dome 40 of the nozzle 30 but the differences are not substantial. The nozzle assembly 50 has a primary application for use adjacent to the walls of the combustor 12. The nozzle assembly 50 also has application for some modification applications in production, although it will be understood that the nozzle 30. In those applications where it is convenient using the nozzle assembly 50, more nozzle assemblies will be required than those required if the nozzle assembly 30 will be incorporated into the system. However, there will still be nozzle assemblies 30 that without the prior art pipes would be designed as part of the system. The invention has been described with reference to its preferred embodiment illustrated. People with skill in the specialty of these devices may be exposed to the present teachings to conceive other variations. For example, the invention has been described in terms of both a four-head and two-heads modality, those skilled in the art will recognize that other variations such as a three-head embodiment are within the scope of this invention. These variations are considered covered by the invention, the invention is limited only by the following claims.