Abstract:
This invention relates generally to high temperature burners such as a solid fuel burner of the type commonly referred to as a gasifier or gasifier combustor. The invention includes a refractory wall structure having an array of tubular members. Refractory material is arranged about the tubular members so that the tubular members protrude from a wall defined by the refractory material by a distance smaller than the diameter of the tubular members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is continuation of International Application No. PCT/AU01/01655 filed 21 Dec. 2001. This application claims the benefit of Australian Application No. PR 2292, filed 22 Dec. 2000. The disclosure(s) of the above applications are incorporated herein by reference. 

   This invention relates generally to high temperature burners and has particular, though not exclusive, application to a solid fuel burner of the type commonly referred to as a gasifier or gasifier combustor. 
   BACKGROUND ART 
   A gasifier generally includes a primary combustion chamber into which solid fuel is loaded on to a grate structure on which it is first dried and gasified via controlled primary combustion. The resultant gas is then transferred into a secondary combustion chamber, which may conveniently be a cycloburner, for further combustion to produce a high temperature relatively clean flue gas able to be used for a variety of purposes, eg. power generation or heating. There is a small residue of inorganic matter. 
   A gasifier of the general type to which the present invention relates is disclosed, for example in U.S. Pat. No. 4,716,842, and the technology generally is of particular interest in waste recycling, especially with an emphasis on so called “green power” generation. Specific solid fuels which may conveniently be gasified in this way include biological waste, agricultural byproducts, wood waste and biomass. 
   As with any burner or furnace construction operating at high temperatures, the housing is typically provided with an appropriate renewable lining of refractory material, typically ceramic castings capable of withstanding very high combustion temperatures over extended periods. It has been appreciated in accordance with a first aspect of the present invention that it is possible to improve refractory wall structures for burners and furnaces, whether of the presently discussed type or more generally, in an advantageous manner, by providing what may be viewed as an inverted skeletal configuration. 
   In a separate aspect, the invention is concerned with enhancing control of the passage by which combustion gases are directed from the primary combustion chamber to the secondary chamber. 
   SUMMARY OF THE INVENTION 
   The invention accordingly provides, in a first aspect, a refractory wall structure including an array of tubular members and intervening refractory material arranged so that the tubular members protrude from a nominal internal wall surface defined by the refractory material by a distance smaller than the diameter of the tubular members. 
   Advantageously, the array of tubular members comprises an array of pipes connected for conveying, in use of a burner or furnace containing said wall structure, fluid (liquid or gas) for cooling the refractory wall structure. 
   In a conventional refractory wall arrangement, the cooling water pipes are wholly embedded within the refractory material, which is itself typically in tile, brick or otherwise segmented form, or a monolithic casting. It is believed that, as this conventional refractory lining wears away, it is more susceptible than the presently proposed material to cracking and the loss of substantial segments. The proposed refractory material is supported on the skeletal array of protruding cooling water pipes. 
   Preferably, in the first aspect of the invention, there is further provided a solid fuel burner including:
         first wall structure including a roof defining a first combustion chamber;   generally curved wall structure defining a second combustion chamber which operates as a cycloburner; and   slot port means arranged adjacent said roof through which the flow of hot combustible gases from said first chamber passes enroute to said second chamber where gas combustion takes place;   wherein at least said roof or said curved wall structure, and optionally both are provided by refractory wall structure according to the invention, with said protruding tubular members exposed to the respective combustion chamber(s).       

   In an advantageous application, the burner is a gasifier and the first combustion chamber is a gasification chamber. 
   In a second aspect of the invention, there is provided a gasifier including:
         first wall structure defining a gasification chamber;   generally curved wall structure defining a combustion chamber which operates as a cycloburner and where gas combustion takes place;   slot port means arranged for admitting a flow of hot combustible gases from said gasification chamber to said combustion chamber; and   moveable control damper means mounted for controlling said flow of hot gases through the port means whereby to manage the respective combustion profiles in said chambers.       

   In a preferred embodiment the invention extends to a solid fuel gasifier incorporating both aspects of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a diagrammatic vertical longitudinal section of a solid state gasifier incorporating an embodiment of both aspects of the invention; 
       FIG. 2  is a diagrammatic enlargement, with some additional detail, of part of  FIG. 1 , in the region of the secondary combustion chamber or cycloburner; 
       FIG. 3  is a fragmentary isometric view of the suspended water-cooled refractory lining structure of  FIG. 1 ; 
       FIG. 4  is an elevational view at A in  FIG. 2 ; 
       FIG. 5  is a detailed cross-sectional view of the refractory wall structures; and 
       FIG. 6  is a view similar to  FIG. 2  of a modified embodiment; and 
       FIG. 7  is a front elevational diagram of a multi-segment damper arrangement. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The solid fuel gasifier  10  of  FIG. 1  (which includes a figure of a man  11  to provide a dimensional context), includes an outer housing  12  about a primary combustion or gasification chamber  14  extending from a fuel delivery auger  9  towards a separately walled cycloburner  16  that defines a secondary combustion chamber  17 . A grate structure  20  includes a preheating grate  22  adjacent the delivery end of auger  9 , and, downstream in the overall direction of flow of the solid fuel, a gasifier grate  24 . The two grates  22 ,  24  each include stepped pairs of fixed  30  and reciprocating  32  grate segments and are linked by a near vertical grate  40  with multiple angled and controllable openings  42  for admission of combustion air from below the grate structure into the fuel load above. It will be seen that the solid fuel inlet  21  into chamber  14  from auger  9  is generally behind the grate structure  20  relative to the general direction of projection of the grate structure and the overall direction of flow of the solid fuel. 
   In general, solid fuel delivered via auger  9  accumulates as a deep load or burden  70  on the grate structure while being dried and preheated on grate  22  and gasified above grate  24 . Combustible gas (syngas) is drawn through a transverse slot port  19  into chamber  17 , from one end  15  of which is recovered combusted flue gas or syngas useable for subsequent heating or power generating purposes. Inorganic solid residue or ash that falls over the downstream end of grate  24  is directed by a baffle device  50  into an ash grate  52  arranged on the heated floor  13  of the housing. The ash is gradually agitated and moved along the floor  13  while remaining carbon is oxidised, for transverse removal and recovery by conveyor  54 . 
   An overhead water-cooled refractory lining  56  is suspended from the roof  11  of housing  10  and merges into the wall structure of cycloburner  16 . Lining  56  also defines one edge of slot port  19  through which combustion gases pass from the primary chamber  14  to the secondary chamber  17 . Roof  11  supports an emergency exhaust stack  58 . 
   Refractory lining  56  essentially comprises an array of longitudinally extending parallel tubular members or pipes  100 , protruding by somewhat less than half their diameter from a nominal wall surface  103  ( FIG. 5 ) defined by a uniform body or layer  102  of refractory material. The overlying supporting substrate is a steel plate  104  to which pipes  100  are attached by spaced U-shaped strips serving as saddles  106 . Other types of attachment can be employed. In a preference arrangement, a ceramic fibre blanket  108  lines plate  104 . Typically, the blanket is 20 mm thick, the refractory material 100 mm thick and the pipes  100  protrude by about 5 mm. 
   The pipes  100  are essentially arranged in sets linking respective transverse tubular manifolds  110 ,  112  and  113 . Manifold  110  is at the rear of suspended gasification chamber lining  56  just above the inner end of delivery auger  9 , while manifolds  112 ,  113  are respectively located directly above and below cycloburner  16 . A first set of pipes  100   a  extends longitudinally of suspended gasification chamber lining  56  to just inside the top of secondary combustion chamber  17 , before looping up to manifold  112 . Interlaced between these pipes, pipes  100   b  (as particularly well seen in  FIG. 3 ) loop from the other side of manifold  112  then around the back wall of secondary chamber  17  before diverting away to manifold  113 . A denser parallel array of pipes  100   c , at closer centres than the other arrays, links the front wall  16   a  of cycloburner  16 , ie. the wall separating primary and secondary combustion chambers  14 ,  17 , to a transverse tube  120  which is linked to manifold  112  by a set of pipes  122 . Tube  120  itself cools the edge of slot port  19  and moreover provides a pivot bearing or guide for linear damper or beak  140  (FIG.  2 ). 
   In a modified construction which may better suit some applications, the pipes  100  are omitted from the roof lining  56  and provided only in the walls of secondary chamber  17 . 
   Damper  140  is of generally outwardly tapered cross-section, with a smoothly semi-circular curved free tip edge or rim  142 . It is made from two cast elements  144  of high temperature cast alloy fixed together by bolts  145  with a secondary internal transverse cavity  141 . 
   It will be seen from  FIG. 2  in particular that by pivoting damper  140  between, say, the positions illustrated in full lines and broken lines, the slot port  19  may be controlled. In particular, damper  40  may be used to close or restrict the passage of syngas from the gasifier chamber  14  and into the cycloburner chamber  17 . This beak or damper  40  acts as a damper and constant velocity device. It closes the inlet area as the gasifier chamber  14  is throttled down and therefore maintains a relatively constant velocity of gas through the inlet. This is believed to reduce or particulate and NOx emissions. 
   Thus, by controlling the inlet gases into the cycloburner  14  using the adjustable beak or damper it is possible to reduce particulates and NOx. The controllable beak in effect acts as an inter-stage damper which provides better control of the output of the cycloburner. It allows greatly increased turn-down capability when heat output is required to decrease, this decrease being achieved by restricting gas flow into the cycloburner and gas flow within the gasifier chamber  17 . 
   Cycloburner  16  is fitted with a further air inlet port  150  at a position substantially diametrically opposite slot port  19 . This port is associated with an adjacent transverse chamber  152  in which the air may be heated by the proximate combustion processes, but supply and access of the air is controlled with an air inlet damper  154 . 
   In a modified embodiment illustrated in  FIG. 6 , in which like parts are indicated by like primed reference numerals, damper  40 ′ is pivotably suspended from roof lining  56 ′ for movement between an open condition (broken lines  40   a ) in a transverse recess  200 , in which the damper does not lie in the floor path, and a closed condition in which the outer edge  201  of the damper contacts the front wall  16   a ′ of cycloburner  16 ′ and closes slot port  19 ′. This front wall  16   a ′ tapers past the damper to an aerodynamic edge  202  shaped and positioned to minimise turbulence where the entering and revolving flows merge. 
   It may be preferable for the damper  40  or  40 ′ to be closed at the minimal cross-section of the passage forming slot port  19 ,  19 ′. 
   Damper  40  or  40 ′ may be provided in sections  204  that can be selectively open or closed.  FIG. 7  depicts this arrangement, showing some damper sections  204   a  closed and some  204   b  open. This allows an advantageous flexibility in the total area of the passage, and therefore the total volume of flow, from the primary chamber into the secondary chamber. 
   It is preferred that damper sections  204  are either fully open or fully closed. 
   In another alternative arrangement (not illustrated), damper  40  is provided as a one or two part plate that slides laterally of the passage, from one or both sides, to vary the width of the port.