Two-stage wet waste gasifier and burner

Abstract

In a two-stage wet waste burner, a first-stage combustion chamber has a symmetrical grate arrangement. The grate comprises spaced individual upright air supply tubes with flat horizontal upper surfaces swept by ash-removal plates. The height and width of the air supply tubes are selected to provide an upper surface profile approximating the natural angle of repose of the waste. Twin waste feed distribution augers span the chamber and rotate in mating troughs. The axis of rotation of each auger is sloped so that the discharge end of the auger is higher than the feed inlet end, and the trough sidewalls are inclined downwardly from the inlet end to the discharge end; these attributes promote even discharge of waste across the span of the chamber. Vertical walls of the air supply tubes are provided with air ports for supplying combustion air; the vertical orientation of the apertures and a degree of shielding of the upper surfaces of the air supply tubes inhibit clogging of the air ports. Drivers for the ash-removal plates comprise pendular arms each pivoting about an upper pivot point lying substantially in the vertical plane of symmetry, each arm being pivotally connected directly or indirectly to the ash removers. A burner of the foregoing type may be combined with a dryer for drying a portion of the waste and with a mixer that mixes dried waste with raw wet waste and feeds the mixed waste to the burner. The mixed waste can be efficiently burned yet can be efficiently conveyed. Such combination is particularly suitable for combustion of sewage sludge.

1 . In a two-stage waste burner, a first-stage combustion chamber having disposed therein a grate arrangement having a waste support means geometry approximating the natural angle of repose of the waste.  
   
   
       2 . Apparatus as defined in  claim 1 , wherein the grate arrangement is substantially symmetrical about a vertical plane.  
   
   
       3 . Apparatus as defined in  claim 1 , wherein the grate arrangement comprises spaced support elements having varying height and width, the profile of the upper surfaces thereof approximating the natural angle of repose of the waste.  
   
   
       4 . Apparatus as defined in  claim 3 , wherein the support elements comprise air supply tubes.  
   
   
       5 . In a two-stage waste burner, a first-stage combustion chamber having disposed therein a feed arrangement generally spanning the chamber and whose feed mechanism, slope and feed constraint walls are selected to distribute waste in the feed arrangement approximately uniformly across the span of the chamber.  
   
   
       6 . Apparatus as defined in  claim 5 , wherein the feed arrangement comprises at least one auger whose axis of rotation is sloped so that the distal discharge end of the auger is higher than the proximal feed inlet end thereof.  
   
   
       7 . Apparatus as defined in  claim 6 , wherein the auger is mounted for rotation within a trough whose sidewalls are inclined downwardly from the proximal feed inlet end to the distal discharge end thereof.  
   
   
       8 . Apparatus as defined in  claim 5 , wherein the feed arrangement comprises two closely spaced parallel augers each of whose axis of rotation is sloped so that the distal discharge end of the auger is higher than the proximal feed inlet end thereof.  
   
   
       9 . Apparatus as defined in  claim 8 , wherein each said auger is mounted for rotation within a trough whose outer sidewalls are inclined downwardly from the proximal feed inlet end to the distal discharge end thereof.  
   
   
       10 . In a two-stage waste burner, a first-stage combustion chamber having disposed therein a grate array comprising spaced waste support elements each having a generally horizontal upper surface; and for each said support element, an associated pair of sliding ash removers for sweeping from the upper surface ash off the upper surface; and drive means for driving the ash removers horizontally from side to side of the upper surface in synchronism.  
   
   
       11 . Apparatus as defined in  claim 10 , wherein the support elements are generally symmetrically disposed about a substantially vertical plane.  
   
   
       12 . Apparatus as defined in  claim 10 , wherein the waste support elements are air supply tubes for the supply of air into the chamber for combustion of the waste.  
   
   
       13 . Apparatus as defined in  claim 12 , wherein the support elements are generally symmetrically disposed about a substantially vertical plane.  
   
   
       14 . Apparatus as defined in  claim 12 , wherein the air supply tubes have substantially vertical side walls in which apertures are provided for the supply of air from within the tubes into the combustion chamber.  
   
   
       15 . Apparatus as defined in  claim 14 , wherein the upper surfaces provide at least partial shielding of the air apertures so as to inhibit clogging of the apertures.  
   
   
       16 . Apparatus as defined in  claim 15 , wherein the support elements are generally symmetrically disposed about a substantially vertical plane.  
   
   
       17 . Apparatus as defined in  claim 16 , wherein the drive means comprises pendular arms each pivoting about an upper pivot point lying substantially in the vertical plane and pivotally connected directly or indirectly to the ash removers.  
   
   
       18 . Apparatus as defined in  claim 16 , wherein the support elements are of a width and height selected so that the upper surfaces thereof correspond in gross profile generally to the natural angle of repose of the waste.  
   
   
       19 . Apparatus as defined in  claim 18 , wherein the drive means comprises pendular arms each pivoting about an upper pivot point lying substantially in the vertical plane and pivotally connected directly or indirectly to the ash removers.  
   
   
       20 . A method of burning wet waste having a relatively high moisture content, comprising pre-drying a selected portion of the waste to a relatively dry solid consistency such that water binding of the waste is substantially reduced, processing the dry solid waste into lumps or particulate matter, mixing the processed dry solid waste with wet waste in proportions selected to support two-stage combustion of the mixed product and to support ease of conveyance of the mixed product, and burning the combustible portion of the mixed product in a two-stage combustion process.  
   
   
       21 . The method as defined in  claim 20 , wherein the waste includes biomass.  
   
   
       22 . The method as defined in  claim 20 , additionally comprising applying effluent gases from the two-stage combustion process to the generation of electricity.  
   
   
       23 . The method as defined in  claim 20 , additionally comprising subjecting effluent gases resulting from said method to a selective catalytic reaction of a type selected to eliminate or reduce the quantity of noxious gases in the effluent finally released to the atmosphere.  
   
   
       24 . Apparatus for burning continually flowing wet waste having a relatively high moisture content, comprising 
 a) a divider for dividing the waste proportionally into a direct-feed component and a component to be dried, the proportion being selected so that subsequent to pre-drying, the dried component and direct feed component will together have a moisture content sufficiently low that relatively efficient combustion of the components mixed together is promoted;    b) a e-dryer for receiving from the divider and drying the waste component to be dried to a relatively dry solid consistency such that water binding of the waste is substantially reduced;    c) a mixer for receiving and mixing dried waste with wet waste in proportions selected to support two-stage combustion of the mixed product and to support ease of conveyance of the mixed product; and    d) a burner for burning the combustible portion of the mixed product.    
   
   
       25 . Apparatus as defined in  claim 24 , wherein the burner is a two-chamber two-stage burner for burning the combustible portion of the mixed product in a two-stage combustion process.  
   
   
       26 . Apparatus as defined in  claim 24 , additionally comprising gas-driven generation means for receiving combustion gases from the burner and applying them to the generation of electric power.  
   
   
       27 . Apparatus as defined in  claim 26 , wherein the gas-driven generation means comprises 
 a) a steam generator for receiving combustion gases and generating steam;    b) a superheater for receiving combustion gases and superheating the steam produced by the steam generator;    c) a steam turbine for receiving the superheated steam from the superheater and being driven thereby;    d) an electric power generator coupled to and in operation driven by the steam turbine and generating electric power thereby; and    e) an economizer in operation heated by combustion gases and receiving effluent from the steam turbine as condensed water for heating and passing to the steam generator;    wherein, in operation, combustion gases from the burner pass in sequence through the steam generator, superheater and economizer for heating water or steam therein.    
   
   
       28 . Apparatus as defined in  claim 26 , additionally comprising a selective catalytic reactor for receiving effluent gases from the gas-driven generation means and subjecting them to a catalytic reaction of a type selected to eliminate or reduce the quantity of NOx gases in the effluent finally released to the atmosphere.  
   
   
       29 . Apparatus for burning wet waste having a relatively high moisture content, comprising 
 a) a dryer for drying a portion of the waste to a relatively dry solid consistency such that water binding of the dried waste is substantially reduced;    b) a mixer for receiving and mixing dried waste with wet waste in proportions selected to support two-stage combustion of the mixed product and to support ease of conveyance of the mixed product; and    c) a burner for burning the combustible portion of the mixed product.    
   
   
       30 . Apparatus as defined in  claim 29 , wherein the burner is a two-stage wet-waste burner.  
   
   
       31 . Apparatus as defined in  claim 30 , wherein the first stage of the burner comprises a first-stage combustion chamber having disposed therein a grate arrangement having a waste support means geometry approximating the natural angle of repose of the waste.  
   
   
       32 . Apparatus as defined in  claim 30 , wherein the first stage of the burner comprises a first-stage combustion chamber having disposed therein a feed arrangement generally spanning the chamber and whose feed mechanism, slope and feed constraint walls are selected to distribute waste in the feed arrangement approximately uniformly across the span of the chamber.  
   
   
       33 . Apparatus as defined in  claim 30 , wherein the first stage of the burner comprises a first-stage combustion chamber having disposed therein a grate array comprising spaced waste support elements each having a generally horizontal upper surface; and for each said support element, an associated pair of sliding ash removers for sweeping from the upper surface ash off the upper surface; and drive means for driving the ash removers horizontally from side to side of the upper surface in synchronism.  
   
   
       34 . In or for use in a first-stage gasification chamber of a two-stage waste burner, a grate comprising an array of vertically and horizontally spaced and longitudinally aligned waste support means, vertically and horizontally spaced and longitudinally aligned ash support and removal means, and vertically and horizontally spaced and longitudinally aligned air supply means, the air supply means being separate from the ash support and removal means, the air supply means having ports for introducing air into the gasification chamber, the ports being spaced from the ash support and removal means and, in operation, the ports introducing the air into the gasification chamber in streams at a substantial angle to vertically upwards, thereby limiting interference between the air supply means and the ash support and removal means.  
   
   
       35 . A grate as defined in  claim 34 , wherein the ash support and removal means comprise vertically and horizontally spaced, stacked, longitudinally aligned and horizontally movable ash removal plates having varying widths increasing from top to bottom of the grate and each in extended position overlying a unique associated stationary grate support plate.  
   
   
       36 . A grate as defined in  claim 35 , wherein the dimensions of the exposed portion of the upper surface of each said grate support plate when the associated ash removal plate is retracted are substantially equal to the dimensions of the associated ash removal plate.  
   
   
       37 . A grate as defined in  claim 35 , wherein the ash support and removal means comprise reciprocating means for imparting to the ash removal plates synchronized reciprocating horizontal motion transverse to the longitudinal extension of the ash removal plates, thereby to direct ash downwardly from higher to lower ash removal plates.  
   
   
       38 . A grate as defined in  claim 37 , substantially symmetrical about a vertical plane parallel to the longitudinal alignment of the ash removal plates.  
   
   
       39 . A grate as defined in  claim 38 , wherein the waste support means have a profile approximating the natural angle of repose of the waste.  
   
   
       40 . A grate as defined in  claim 38 , wherein the waste support means includes the ash support and removal means.  
   
   
       41 . A grate as defined in  claim 40 , wherein the distance of travel of each said ash removal plate imparted by the reciprocating means varies with the width of such ash removal plate.  
   
   
       42 . A grate as defined in  claim 41 , wherein the reciprocating means comprises a pendular drive having in the vicinity of its upper end a pivotally mounted driving arm, and for each said ash removal plate, means for pivotally coupling such support plate directly or indirectly to the pendular drive at an associated pendular drive coupling means, the pivot axis of each said coupling being horizontal and extending generally parallel to the longitudinal extension of the ash removal plates, the pendular drive coupling means being generally vertically spaced from one another along the driving arm at intervals generally corresponding to the vertical spacing between the ash removal plates.  
   
   
       43 . A grate as defined in  claim 42 , wherein the driving arm includes at least one generally longitudinally extending sliding pivotal coupling, each said sliding pivotal coupling extending in length sufficiently to accommodate the vertical component of the arcuate swinging motion of the arm, thereby facilitating the impartation by the arm to the ash removal plates of a substantially horizontal motion.  
   
   
       44 . A grate as defined in  claim 42 , comprising, for each said ash removal plate, an associated unique connecting arm pivotally coupled to the driving arm at an associated one of said pendular drive coupling means, said connecting arm also being coupled to an associated unique one of said ash removal plates.  
   
   
       45 . A grate as defined in  claim 41 , wherein, in operation, the ports provide substantially horizontal air streams.  
   
   
       46 . A grate as defined in  claim 41 , wherein the ports are located in substantially vertical walls.  
   
   
       47 . A grate as defined in  claim 46 , wherein the air supply means comprises an array of vertically and horizontally spaced air supply conduits generally longitudinally aligned with the longitudinal extension of the ash removal plates, each of said conduits underlying an associated unique one of said ash removal plates, the ports being located in outwardly facing walls of said conduits.  
   
   
       48 . A grate as defined in  claim 47 , wherein the ash removal plates at least partially shield the ports so as to limit interference by ash with the air supply.  
   
   
       49 . A grate as defined in  claim 48 , wherein the ash support removal means are of a width and height selected so that the outer edges of the uppermost surfaces thereof have a gross profile conforming generally to the natural angle of repose of waste materials expected to be partially combusted in the gasification chamber.  
   
   
       50 . A gasification chamber including therein a grate as defined in  claim 34 .  
   
   
       51 . A gasification chamber including therein a grate as defined in  claim 37 .  
   
   
       52 . A gasification chamber including therein a grate as defined in  claim 42 .  
   
   
       53 . A gasification chamber including therein a grate as defined in  claim 46 .  
   
   
       54 . A gasification chamber including therein a grate as defined in  claim 49 .  
   
   
       55 . In or for use in a first-stage gasification chamber of a two-stage waste burner, a grate comprising ash support and removal means in turn comprising an array of vertically and horizontally spaced and longitudinally aligned horizontally movable ash removal plates substantially symmetrically arrayed about a vertical plane parallel to the longitudinal alignment of the ash removal plates, the ash support and removal means comprising reciprocating means for imparting to the ash removal plates synchronized reciprocating horizontal motion transverse to the longitudinal extension of the ash removal plates, thereby to direct ash downwardly from higher to lower ash removal plates, and wherein the distance of travel of each said ash removal plate imparted by the reciprocating means varies with the width of such ash removal plate.  
   
   
       56 . A grate as defined in  claim 55 , wherein the movable ash removal plates having varying widths increasing from top to bottom of the grate.  
   
   
       57 . A grate as defined in  claim 56 , wherein the reciprocating means comprises a pendular drive having in the vicinity of its upper end a pivotally mounted driving arm, and for each said ash removal plate, means for pivotally coupling such support plate directly or indirectly to the pendular drive at an associated pendular drive coupling means, the pivot axis of each said coupling being horizontal and extending generally parallel to the longitudinal extension of the ash removal plates, the pendular drive coupling means being generally vertically spaced from one another along the driving arm at intervals generally corresponding to the vertical spacing between the ash removal plates.  
   
   
       58 . A grate as defined in  claim 57 , wherein the driving arm includes at least one generally longitudinally extending sliding pivotal coupling, each said sliding pivotal coupling extending in length sufficiently to accommodate the vertical component of the arcuate swinging motion of the arm, thereby facilitating the impartation by the arm to the ash removal plates of a substantially horizontal motion.  
   
   
       59 . A grate as defined in  claim 57 , comprising, for each said ash removal plate, an associated unique connecting arm pivotally coupled to the driving arm at an associated one of said pendular drive coupling means, said connecting arm also being coupled to an associated unique one of said ash removal plates.