Abstract:
A feed injector for use in a gasification apparatus comprising plural concentric tubes converging at an outlet tip, at least one interior tube of the plural concentric tubes having a plurality of static, helically-twisted mixing elements fixed to an exterior surface thereof.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to fuel gasification apparatus typically associated with gas turbine power generation plants, and specifically, feed injectors used to introduce fuel components into a boiler or other combustion device.  
         [0002]     Frequently, steam is added to the oxygen stream and steam and/or soot containing black water is added to the fuel stream. This invention is a device designed to enhance the mixing of steam with oxygen and/or to enhance the mixing of fuel and black water streams within the feed injector itself.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0003]     In accordance with an exemplary embodiment of this invention, a mixing device is incorporated into an otherwise conventional feed injector to enhance better mixing of the feed streams. In the exemplary embodiment, a plurality of static, helically-twisted mixing elements are added to the external surface of the radially innermost tube of the injector to assure that the fuel and black water streams flowing in the middle annulus between the center and intermediate tubes of the injector are homogeneously mixed (emulsified) and uniformly delivered to all points in the vicinity of the injector tip. In the exemplary embodiment, six or more sets of mixer elements are added to the exterior surface of the center tube. These mixing elements are located as far down the center tube or barrel as possible, for example, within about 12 inches from the injector tip. This location minimizes the chance of re-agglomeration of the black water in the fuel. In the exemplary configuration, pairs or sets of mixing elements are arranged in left and right hand directions, with each mixing element extending approximately 180° about the periphery of the center tube.  
         [0004]     Accordingly, in one aspect, the exemplary embodiment comprises a feed injector for use in a gasification process comprising plural concentric tubes converging at an outlet tip, at least one interior tube of the plural concentric tubes having a plurality of static, helically-twisted mixing elements fixed to an exterior surface thereof.  
         [0005]     In another aspect, the exemplary embodiment comprises a feed injector for use in a gasification apparatus in which streams of different fuel components are mixed, the feed injector comprising a plurality of concentrically arranged tubes defining at least two annular passages and one center passage converging at an outlet tip of the injector; and a plurality of static, helically-twisted mixing elements fixed on an internal one of the plurality of concentrically arranged tubes, the mixing elements arranged in alternating left and right hand pairs of such elements.  
         [0006]     In still another aspect, the exemplary embodiment comprises a method of supplying fuel components to a combustion device through a feed injector comprising (a) providing a feed injector comprising plural concentric tubes including an outer tube, an intermediate tube and a center tube forming two annular passages and a single center passage converging at an outlet tip; (b) fixing a plurality of static, helically-twisted mixing elements to at least a peripheral surface of the center tube, within a radially inner one of the two annular passages; and (c) supplying fuel components through the two annular passages and the center passage for discharge through the outlet tip.  
         [0007]     The invention will now be described in detail in connection with the drawings identified below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a side elevation of a conventional gasifier feed injector;  
         [0009]      FIG. 2  is a left end elevation of the injector shown in  FIG. 1 ;  
         [0010]      FIG. 3  is a partial cross section through the tip of the injector shown in  FIG. 1 ;  
         [0011]      FIG. 4  is a simplified side elevation of a gasifier feed injector incorporating static mixing elements in accordance with an exemplary embodiment of the invention;  
         [0012]      FIG. 5  is a partial side elevation of the center tube taken from the injector in  FIG. 4 ; and  
         [0013]      FIG. 6  is a perspective view of the center tube as shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIGS. 1-3  illustrate a conventional gasifier feed injector  10  that includes generally a first radially outer tube or barrel  12 , a second intermediate tube or barrel  14  and a center tube or barrel  16 . The outer barrel  12  extends from the forward tip  18  of the injector rearwardly to an approximate midpoint of the injector where it terminates at a first coupling  20 . The first outer barrel is provided with an inlet  22  adjacent the coupling  20 . The intermediate barrel  14  extends from the tip  18  rearwardly beyond the coupling  20  to a second coupling  24  at which the barrel  14  terminates. Adjacent the coupling  24 , the barrel  14  is provided with an inlet  26 . The radially centered tube or barrel  16  extends from the forward tip  18  rearwardly beyond the first and second couplings  20 ,  24  to a third coupling  28  at which point the center tube or barrel  16  terminates. Adjacent the coupling  28 , the center tube or barrel  16  is provided with an inlet  30 . Thus, the configuration as described creates three longitudinally arranged, concentric passages or annuli  32 ,  34  and a center passage  36  that converge at the forward tip  18 . In a typical gasification process, inlet  22  serves as the primary inlet for supplying oxygen/steam to the radially outer annulus  32 ; inlet  26  serves as the primary inlet for supplying fuel/steam or water (blackwater) to the intermediate or middle annulus  34 ; and inlet  30  serves as a secondary inlet for supplying oxygen/steam to the radially inner or center passage  36 . The specific feed components are exemplary only.  
         [0015]     A cooling coil  38  surrounds the tip of the injector and water is supplied to the coil via inlet  40  and exits the coil via outlet  42 . To this point, the description applies to known gasifier injectors.  
         [0016]     In accordance with an exemplary embodiment of this invention, as shown in  FIGS. 4-6 , static mixing elements  44  are added to the exterior of the center tube or barrel  16 . In the exemplary embodiment, mixer elements  44  are secured to the periphery of the center tube or barrel  16 . The mixing elements are formed by helically-twisted, rigid plates, each twisted 180° in either a right or left hand direction. As shown in  FIGS. 4 and 5 , there are 3 sets (or pairs of) left hand elements  46  and 3 sets (or pairs) of right hand elements  48 . The twelve elements or plates are located as close as possible to the forward tip  18  of the injector, for example, about 12 inches from the tip. This location minimizes the chance of re-agglomeration of the blackwater in the fuel.  
         [0017]     The stator mixing elements may be welded to the exterior surface of tube  16 . For all but the last pair of elements adjacent tip  18 , each element could have three 1 inch weld segments (two on the ends, one in the middle). The final pair of elements  44  closest the tip  18  should have full welds. This arrangement ensures that if one element  44  detaches from the tube  16 , the elements  44  adjacent tip  18  will “catch” it before it exits the tip. In addition, a typical axial length of each element is 5.89 inches, and the axial length of the entire static mixer section applied to the center tube may be on the order of 35-38 inches for an injector that is about 84 inches long. The dimensions are exemplary only, however, and nay vary depending on the injector size, mixing requirements, etc.  
         [0018]     It will be appreciated that the number of mixer element sets  46 ,  48  on the tube  16  and the pitch of the elements, and may be varied depending on the degree of mixing required. It will also be appreciated that mixer elements may also be applied to the exterior of the intermediate tube  14  if desired, to thereby enhance mixing within passage  32  as an alternative to, or in addition to, the mixing elements added to the center tube  16 .  
         [0019]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.