Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J15/00—Arrangements of devices for treating smoke or fumes
  • F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
  • F23J15/022—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow
  • F23J15/027—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow using cyclone separators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23B—METHODS OR APPARATUS FOR COMBUSTION USING ONLY SOLID FUEL
  • F23B1/00—Combustion apparatus using only lump fuel
  • F23B1/16—Combustion apparatus using only lump fuel the combustion apparatus being modified according to the form of grate or other fuel support
  • F23B1/18—Combustion apparatus using only lump fuel the combustion apparatus being modified according to the form of grate or other fuel support using inclined grate
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23B—METHODS OR APPARATUS FOR COMBUSTION USING ONLY SOLID FUEL
  • F23B5/00—Combustion apparatus with arrangements for burning uncombusted material from primary combustion
  • F23B5/02—Combustion apparatus with arrangements for burning uncombusted material from primary combustion in main combustion chamber
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L1/00—Passages or apertures for delivering primary air for combustion 
  • F23L1/02—Passages or apertures for delivering primary air for combustion  by discharging the air below the fire

Definitions

• the present invention relates to a method in burning solid fuels of different types in a furnace, wherein the fuel is supplied to the upper end of an inclined grate and is burnt on the grate wh le primary air, possibly mixed with flue gas, is blown from below through the grate and the fuel bed thereon to provide a zone of sus ⁇ pended fine fuel particles above the fuel bed.
• the fuels tjiat are possible in this case are uncut firewood, wood chips, bark, shavings, tilled peat, lump peat, cut straw, coal dust, lump coal, brown coal (briquettes), house waste (pellets, briquettes] to mention the most common solid fuels only, Practically all the fuels l sted above excepting uncut firewood, lump coal and briquettes, contain some propotion of fine fractions of a particle size between 0 and 3 mm. Thus, up to 60 % e.g.. of coal dust may com ⁇ prise such fine fractions. Tilled peat and' straw contain some proportion of fine fractions in the form of dust.
• the primary air is allowed to flow at a low speed through the fuel bed, the fine fractions of the fuel bed obstructing locally the air flow through the bed.
• This condition provides a slow drying and gasification progress in these local regions where the air passage is prevented or retarded, and a high temperature in the combustion zone due to insuf- ficient cool ng.
• the fine fractions are separated or are burnt more or less suspended in the combustion air and the flue gases in the furnace while the rest of the fuel is burnt in common manner on the grate.
• the fine fractions may be separated from the rest of the fuel before the fuel is supplied to the furnace, and may be blown into the furnace to be burnt by means of a separate burner. This system is expensive and complicated.
• the method a.ccording to the invention is of this last-mentioned type, and the object of the invention is primarily to make possible that humid fuels, dry fuels, fuels with high ash content, and fuels containing different size fractions, are burnt in an economic way and with the possibility of extensive automation of the combustion progress, at lower combustion temperature than that normally applied and with generation of a minor amount of NO than that obtained in conventional firing methods, no preheating of the air being required for h.umid fuels.
• the flue gas curtain at the upper end portion of the grate then prevents backfiring where the supply of the fuel takes place, the fine fractions in the sus ⁇ pension above the fuel bed at the same time being burnt by blowing-up of the fine fractions in the fuel bed by means of the air and/or flue gas supplied. Since the returned material is blown into the fuel bed at the lower portion of the grate where the main combustion region of the fuel bed is located, the combustion temperature will be reduced there particularly if flue gas is blown into the bed, and accordingly the combustion of existing tar products will be accelerated. Moreover, the fuel bed is stirred and fine particles are turbulently blown up, said particles being burnt in suspension with the primary air and secondary air present in the region of the main combustion zone.
• the final combustion is utilized for drying and gas fyi ng the fuel .
• the final combustion gas which is meagre as to oxygen but has a high drying and gasifying effect lowers the combustion temperature and reduces the the presence of local combustion progress in the fuel bed, i,e, the risk of slagging in the first grate section is reduced and lower values of NO can be expected.
• FIG, 1 is a diagrammatic vertical sectional view ⁇ of a furnace for workin ⁇ the method according to the invention
• FIG, 2 is an end view of a convection unit with cyclone separator, connected to the furnace,
• FIG. 3 s a sectional view along line A - A in FIG, 1 of the first grate section in the furnace
• FIG. 4 is an enlarged cross-sectional view along line B - B in FIG. 1 of the second grate section in the furnace
• FIG. 5 is a plan view of the second grate section.
• the furnace is designated generally with 10 and comprises a conventional water type system not shown in detail here.
• a water- -cooled grate consisting of an upper portion 11 which is arranged as an inclined grate and slopes downwards from a shaft 12 for the supply of solid fuel and connects at the lower end thereof to a lower grate portion (bottom grate) 13 at the upper end thereof, also the lower grate portion being arranged as an inclined grate with the lower end thereof connecting to an ash discharge 14.
• the grate is arranged as a two-section grate, the portion 11 forming a first grate section which is a typical drying and gasifying section and is formed as a self-feeding completely cooled stationary grate.
• the grate portion 11 is formed as a trough (grate chute). Therefore, primary air can be supplied in a simple manner to the gasification zone above a fuel bed located on the grate.
• slag breakers 15 are arranged, because some fuels such as coal tend to cake to larger pieces together w th softened ash constituents, if any, in the main combustion zone which is located at the transition between the two section portions.
• the slag breakers 15 consist of circular sector plates which are arranged on end between the water tubes in the grate po tion 11 and are mounted to a shaft 16 which can be rotated back and forth by means not shown here in detail , e.g. a hydraul c cylinder, for oscillating the slag breakers 15 between the upwardly projecting position shown and a lowered position,
• the grate portion 13 is provided with a stoker for feeding the fuel bed progressively down towards the ash discharge 14.
• this stoker comprises a number of mutually parallel rods 17 extending in the longitudinal direction of the grate,, which in groups of three rods are connected to a hydraulic cylinder 18 outside the furnace for recip ⁇ rocation of the rods.
• transverse carriers 19 are arranged which have an edge chamfer on the upper side 20 thereof, which faces the upper end of the grate portion 13 such that the carriers when moving towards the upper end of the grate portion 13 are displaced under the fuel bed on the grate portion so as to dis- place the fuel bed downwards towards the ash discharge 14 when moving later towards the lower end of the grate portion.
• the frequency of the stroke of the cylinders 18 preferably should be adjustable.
• a conduit 21 is connected for the supply of primary air under the grate portion 13.
• the primary air after having passed through the grate portion 13 is supplied together with flue gases to the lower side of the grate portion 11 to pass through this portion to the combustion compartment above ' the double grate.
• a mixture of flue gas and air is obtained, which means a high gas temperature in the region between the grate portions 11 and 13. This results in a many times increased volume of the gas flow through the fuel bed 36 and thus an improved blowing through the fuel bed.
• the flue gas outlet 22 of the furnace 10 is conno ed -through a cyclone separator 23 to a convection unit 24 the outlet of which can be connected through an economizer to a stack, which is not shown in more detail here.
• the cyclone separator 23 comprises a flame tube
• a turbu- lator 27 Inside the flame tub.e there is provided between the ends of the tube a turbu- lator 27 while a cone 28 is arranged at the left hand end, said cone being formed with a number of slots 29 spaced around the curved surface thereof.
• the cone has a mouth portion 30 communicating with the convection unit while an annular space 31 between this mouth portion and the flame tube 26 communicates with a tangential outlet 32.
• a further conduit 35 opening into the furnace through the grate portion 11 at the upper region thereof. is also connected to the furnace 10, In .s.aid region, the conduit 35 can be connected to a distribution box or a nozzle ramp extending transversely of the grate portion 11 downwards of the location where the fuel is supplied from the fuel shaft 12.
• the conduit 35 is connected to a fan not shown here for the supply of air and/or flue gas under high pressure through the conduit 35. __.
• the solid fuel supplied to the furnace 10 through the fuel shaft 12 forms a fuel bed 36 on the grate portion 11 and a fuel bed 37 on the grate portion 13 as has been indicated by dash lines in FIC. .1.
• Air or flue gas is - supplied under pressure through the conduit 35 for_ providing a curtain screeni ng-off the fuel shaft from the furnace and also blowing-up fine fractions, if any, in the fuel from the fuel bed 36.
• substantially drying and gasification takes place while the main combustion shown is located at 38 at the transition between the two grate portions.
• the primary air is supplied through the conduit 21 under the grate portion 13 and passes through the fuel bed 37 on this grate portion where the final combustion takes place.
• the heated primary air mixed with flue gas from the fuel bed 37 continues to the grate portion 11 , passes through this portion and the fuel bed 36 located thereon to dry and gasify the fuel of said bed, and continues to the
• the temperature of the mixture of flue gas and air can be controlled by controlling the feeding speed of the fuel bed on the grate portion 13. A higher feeding speed provides a higher temperature of the final combustion and thus a higher temperature of the mixture as can be necessary when burning humid fuel.
• the flue gas escaping from the combustion compartment through the flue gas out ⁇ let 22 contains of course a great portion of solid particles (dust) ⁇ and the major part of these fine fractions is separated in the cyclone separator 23 to he transported by the fan 33 through the conduit 34 back to the furnace where flue gas and entrained dust areblown into the main combustion zone 38.
• the method of the invention can be applied to furnaces of other types than that described here.
• the fundamental construc- tion of the furnace described is particularly well suited for the application of the method of the invention.
• the furnace has a conventional tube system and also in other respects it is constructed in the manner which is conventional as to furnaces of the type described here haying a reversing compartment between the combustion compartment and the flue gas out ⁇ let - ⁇ ith necessary doors., etc. although such details have not been menti oned -here .
• the dust separator can of course be of another type e.g. of the filter type, but the cyclone separator is preferred, because it is reliable in operation and requires negligible attendance, said separator at the same time being v e ry efficient. ..

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Solid-Fuel Combustion (AREA)

Applications Claiming Priority (2)

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• 1982
  • 1982-10-13 WO PCT/SE1982/000331 patent/WO1983001498A1/en active IP Right Grant
  • 1982-10-13 EP EP19820903085 patent/EP0091458A1/en not_active Withdrawn
• 1983
  • 1983-06-13 SE SE8303334A patent/SE437875B/sv not_active IP Right Cessation
  • 1983-06-14 FI FI832156A patent/FI74794C/fi not_active IP Right Cessation

Non-Patent Citations (1)

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