Abstract:
A multiple rake sootblower reciprocates over an area to clean an entire surface using a minimum of space for the sootblower stroke. An internal valving manifold and a plurality of bushings inside of a plenum isolate the rakes from each other and operate one rake at a time. This maintains the required sootblowing media pressure at the nozzles of each of the rakes. The internal valving manifold may either be reciprocated or rotated to select the desired rake.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to sootblowers used for cleaning surfaces that are subject to ash fouling. Specifically, the invention involves multiple rake sootblowers with internal valving manifolds. 
     In the design of sootblowers for any particular application, there are three basic goals. The first goal is to provide complete coverage of the entire area that is subject to ash fouling. Second, sufficient sootblowing media pressure should be available at each nozzle. The third goal is to minimize the space requirements for the stroke of the sootblowers to provide the complete coverage. 
     In the case of a long but narrow area such as heat exchanger plates, there are two common rake-type sootblower designs which are often used. One involves the use of a plurality of single rake sootblowers, usually side by side, to cover a long, narrow area. Each one of the rakes only needs a short stroke to cover its assigned area. This requires an actuator for each rake and the rakes are operated one at a time so that each rake has sufficient sootblowing pressure. The other design is the half-track design. This usually uses two rakes extending into a long area from opposite ends with each rake covering one half of the long, narrow area although there are other variations. This design requires one actuator for each of the two rakes. There are usually more nozzles in each of the two rakes than with the single rake design which results in reduced sootblowing pressure at each nozzle. Therefore, it can be seen that each of these designs has its limitations and disadvantages. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a sootblower with a minimum of space required for the sootblower stroke, with complete coverage, with sufficient sootblowing media pressure at each nozzle and with simple controls. The invention involves a multiple rake sootblower with an internal valving manifold to isolate each of the multiple rakes and select which of the multiple rakes is actuated. As many rakes are provided on a single sootblower as are needed to cover the area and minimize the stroke. The valving maintains the media pressure at each one of the many nozzles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a sootblower arrangement of the prior art including a control system using a half-track sootblower design to cover an area. 
     FIG. 2 illustrates another sootblower arrangement of the prior art using a plurality of single rake sootblowers to cover a similar area. 
     FIG. 3 illustrates the general arrangement of a sootblower of the present invention. 
     FIG. 4 is a plan view of the outer manifold of the invention. 
     FIG. 5 is a side elevation view of the outer manifold of FIG.  4 . 
     FIG. 6 is an end view of the outer manifold. 
     FIG. 7 is a side elevation view partially in cross section of an inner manifold of the indexing type inside of an outer manifold. 
     FIG. 8 is a side elevation view partially in cross section of an inner manifold of the rotary type inside of an outer manifold. 
     FIGS. 9A to  9 D illustrate the operating cycle of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For comparison purposes, FIGS. 1 and 2 illustrate prior art rake-type sootblower arrangements. FIG. 1 is a so-called half-track sootblower arrangement with the area to be covered defined by the long, narrow rectangle  12 . This area can, for example, be all or a portion of a heat exchanger plate that is subject to ash fouling from flue gas. In this half-track arrangement, one rake-type sootblower  14  extends into the long, narrow area from one end while the other sootblower  16  extends into the area from the other end. In this arrangement, each one of the sootblowers covers one half of the area. Each sootblower is illustrated as having two rakes  18  and the sootblower  14  is shown fully inserted while the sootblower  16  is shown fully withdrawn. It can be seen that the stroke of each sootblower to obtain complete coverage of the area  12  is equal to about the distance between the rakes  18 . For an area 40 feet long and with the two rakes per sootblower, the stroke of each sootblower is about 12 feet. Of course, for longer areas, more rakes could be used on each sootblower or the stroke could be increased. 
     The sootblowers are driven in and out by the drive means generally indicated at  20  which can be any conventional sootblower drive means. The drive means  20  are connected into and actuated by the control unit  22 . This control unit  22  also operates the valves  24  in the lines  26  between the source  28  of the sootblowing medium and the sootblowers  14  and  16 . The sootblowing medium is normally high pressure air or steam. Since each sootblower has a plurality of rakes and a considerable number of total nozzles, and even though the sootblowers are operated one at a time, the sootblowing pressure to each nozzle is reduced (over that of a single rake sootblower) or a higher pressure media source must be used. 
     The second prior art arrangement is shown in FIG.  2  and employs a plurality of single rake sootblowers  30 ,  32 ,  34  and  36  side by side and entering from the side of the long dimension of the area  12 . Only a short stroke is required to cover the narrow dimension of the coverage area. For example, to cover a 40 foot by 10 foot area, four sootblowers side by side as shown each with a stroke of 12 feed are used. In this arrangement, four drives  20  and four valves  24  are required and these would be connected into a control unit similar to that shown in FIG.  1 . Once again, these sootblowers would be operated one at a time to assure sufficient media pressure. 
     The general sootblower arrangement of the invention is illustrated in FIG.  3 . This involves a single sootblower  38  having multiple rakes to cover the same area  12 . In this example of the invention, there are four rakes  40 ,  42 ,  44  and  46  on the sootblower although the number of rakes can be varied. The sootblower comprises an outer manifold  48 , which comprises a plenum  50  and the previously mentioned rakes  40 ,  42 ,  44  and  46 , and an inner manifold  52  as will be described in detail later. The outer manifold  48  is driven by the drive unit  54  in the same manner as the prior art sootblowers previously described. The drive unit  54  may be any desired type of linear drive but the preferred type employs a traveling carriage assembly to which the plenum  50  is mounted. The traveling carriage is reciprocated by a chain which is connected through a gearbox to an electric motor. Such a drive is commercially available from ABB Power Products Mfg., Boiler Cleaning Equipment Div., of Chattanooga, Tenn. The inner manifold  52  is driven in relation to the outer manifold  48  by the drive unit  56 . It will be seen later that this drive unit  56  may either reciprocate or rotate the inner manifold  52 . When the inner manifold  52  is reciprocated, the drive unit  56  may be mounted to the end of the plenum  50  and be of the same chain drive type just described. The operation of the outer and inner manifolds is controlled by the control unit  58  as is the flow of sootblowing medium from the source  60  through the valve  62  to the inner manifold  52 . 
     FIGS. 4,  5  and  6  show the structure of the outer manifold  48  which comprises the plenum  50  and the rakes  40 ,  42 ,  44  and  46 . The plenum  50  is a tube closed at the end  64  with the interior of the tube connected through the holes  65  to the nipples or small tubes  66  and to the interior of the tubes comprising the rakes  40 ,  42 ,  44  and  46 . Each of the rakes is provided with a series of nozzles  68  which direct the sootblowing media onto the surface to be cleaned. Although these nozzles have been illustrated only on one side of the rakes, nozzles can be located anywhere around the rakes as desired. 
     FIG. 7 shows a sootblower assembly according to one embodiment of the invention which is referred to as the indexing version. Inside of the plenum  50  are bushings  70  on each side of each of the holes  65  and the nipples  66 . Extending through the center of the plenum  50  and through the bushings  70  is the inner manifold  52 . This inner manifold  52  is a tube which has holes or openings  72 ,  74 ,  76  and  78  communicating with the interior of the tube. This inner manifold  52  is connected to the sootblowing media as shown in FIG.  3 . The openings  72 ,  74 ,  76  and  78  are spaced along the inner manifold as shown in FIG. 7 such that only one of the openings at a time lines up with a hole  65  and a nipple  66 . As seen in FIG. 7, the opening  72  lines up with a hole  65  and a nipple  66  while the other openings  74 ,  76  and  78  are not lined up with nipples. In this position, the sootblowing media inside of the inner manifold  52  exits only through the opening  72  and into the corresponding nipple and rake which would be the rake  40  in FIG.  3 . The entire sootblower would then be reciprocated for the rake  40  to cover its assigned area. The inner manifold  52  is then indexed to the next position within the outer manifold  50  which involves moving the inner manifold axially with the drive unit  56  such that the opening  74  lines up with the hole  65  and the nipple  66  associated with the rake  42 . In that position, the other three openings will not be lined up with nipples. The procedure of reciprocating the sootblower would then be repeated. The same procedure for indexing the inner manifold and reciprocating the sootblower would then be followed with respect to the openings  76  and  78 . 
     The embodiment of the invention shown in FIG. 8 is the rotary version with the inner manifold  52  being rotated to line up the openings in the inner manifold with the nipples  66 . In this version, the bushings  80  inside of the outer manifold  50  are solid bushings surrounding each of the holes  65  and the nipples  66  each with a hole  82  which is lined up with one of the holes  65  and nipples  66 . The inner manifold has openings or holes  84 ,  86 ,  88 , and  90  with each opening being located inside of one of the bushings  80  and being located at staggered positions around the inner manifold as seen in FIG.  8 . With four rakes, these holes are offset from each other by 90°. As shown, the opening  84  is lined up with a hole  82 , a hole  65  and a nipple  66  while the other holes  86 ,  88  and  90  are not so aligned. Therefore, the rake  40  of FIG. 3 would be the only rake being supplied with the sootblowing media. The same general procedure as previously described with respect to the indexing version would be followed with the exception that the inner manifold  52  would be rotated to line up holes instead of moved axially as with the indexing version. In this case, the drive unit  56  would be a drive which rotates the inner manifold the required increments. Once again, such a drive can be mounted on the end of the plenum  50  and be of any desired type. For example, an electric motor can be connected with a drive gear which engages a gear attached to the inner manifold  52 . 
     FIGS. 9A to  9 D show the operating cycle of the invention. In FIG. 9A, the rake  40  is actuated and the sootblower is moved in the path and direction shown by the arrow  92  to cover a first area. Then, in this new position, the rake  42  is actuated and the sootblower moved in the path and direction of the arrow  94  as shown in FIG. 9B to cover a second area. The procedure is continued with the rake  44  and path  96  as in FIG.  9 C and with the rake  46  and path  98  as in FIG. 9D to complete the coverage of the areas. 
     With the invention, there is no theoretical limit to the number of rakes on a single sootblower. This allows the addition of rakes to cover a longer area or to reduce the required stroke to cover a given area. Further, each rake is isolated thereby providing full sootblower media pressure to each rake as contrasted to the half-track design of the prior art previously described. Additionally, a single sootblower with multiple rakes has the same coverage as two half-track sootblowers or four or more single-rake sootblowers. Only one drive unit is required for the outer manifold and one for the inner manifold and only one valve is required regardless of the number of rakes. 
     Although the invention has been illustrated in the drawings as having the rakes  40 ,  42 ,  44  and  46  perpendicular to the plenum  50 , the rakes can also be parallel to the plenum. Such an arrangement is particularly applicable for a rotary regenerative heat exchanger where the sootblower extends generally radially across an end of the rotor and blows into the moving rotor.