Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
  • F23G7/02—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of bagasse, megasse or the like
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
  • F23G7/10—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of field or garden waste or biomasses
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2201/00—Pretreatment
  • F23G2201/70—Blending
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2204/00—Supplementary heating arrangements
  • F23G2204/10—Supplementary heating arrangements using auxiliary fuel
  • F23G2204/101—Supplementary heating arrangements using auxiliary fuel solid fuel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/12—Heat utilisation in combustion or incineration of waste

Definitions

• the invention relates to a method according to the preamble of claim 1 for co-firing wood, waste wood or other type of biofuel along with conventional coal in a boiler designed for burning coal, brown coal, peat or other particulate fossil fuel as the main fuel.
• US Pat. No. 5,609,1 13 describes one technique of burning wood fuel in energy pro- duction.
• the boiler combustion chamber is fired with pulverized coal and wood-derived material, the latter being comminuted to a precisely determined particle size.
• Separate feed nozzles or burners are used for the pulverized coal and the wood particles, complemented with oil burners.
• This burning technique is hampered by a typical problem related to wood combustion.
• the particle size of the wood fuel must be very small and the amount of large particulates in the infeed fuel relatively small in order to maintain a stable flame in the burner without using a pilot fuel such as gas or oil.
• the go ⁇ l of the invention is achieved according to the invention by virtue of mixing biofuel in particle form into the flow of the main fuel after the coal mill, but before the fossil fuel is fed into a flame.
• the invention offers significant benefits.
• the biofuel can be made cost-efficiently, e.g., from waste wood or other RDF (refuse-derived fuel) material, whereby also such waste can be utilized that otherwise is difficult to put in use.
• the method according to the invention is even applicable to fuel mixtures containing plastic or other combustible material that is present in some amount in RDF fuels, for example.
• biofuel refers to material that basically comprises substantial amounts of material of biological origin, but may also contain minor amounts of other combustible materials.
• a particularly suitable biofuel is waste wood scrapped from building sites. The use of refuse-derived fuel reduces the loading of dumping sites and, in some cases, even a compensation may be enjoyed from the incineration of such waste.
• the particle size of material to be burned may be substantially larger than what is required in burners specifically designed for firing with particulate wood-derived material, because the wood-derived fuel need not sustain the flame, but rather, wood particles are ignited in the main fuel flame and subsequently serve to enhance the combustion of the main fuel.
• the moisture content of the particulate fuel may be much higher, which means that the quality of fuel to be burnt need not be as high as in conventional arrangements. Resultingly, wider resources of biofuels become available, whereupon the threshold limiting the use of biomaterials as fuel is lowered, since the common problem of insufficient volume and poor availability of biofuels close to the energy-generating plant as a factor in investment decision-making loses its prior weight.
• One essential factor in the evaluation of the profitability of the method is that it can burn a substantially higher percentage of biofuel in regard to the fossil fuel, whereby according to present experiences it is possible to substitute at least 30 % of fossil fuel by biofuel using the method in accordance with the invention.
• the arrangement according to the invention makes combustion of materials derived from municipal waste and the like refuse particularly advantageous inasmuch the waste being burned passes through the high-temperature fireball zone of the boiler, whereby organic hydrocarbon compounds are disintegrated.
• Addition of wood also reduces the amount of oxides of sulfur and nitrogen occurring in the combustion of coal.
• Such improvement of the combustion process by co-firing with wood or other biofuel is a remarkable benefit by way of allowing a wider latitude in the selection of fuels.
• the reduced emissions of sulfur compounds permits firing with fuels of a higher sulfur content without resorting to pretreatment of the fuel or increase in the capacity of the flue gas cleaning system.
• FIG. 1 shows an embodiment of the biofuel feed arrangement
• FIG. 2 shows an embodiment of the biofuel feed arrangement
• FIG. 2 shows another embodiment of the biofuel feed arrangement.
• the main fuel may as well be brown coal or peat
• the co- fired fuel can be selected from the group of other like biofuels already mentioned above, such as straw, bagasses refuse or the like material readily available in suffi- cient quantities, as well as municipal waste, particularly the combustible components thereof that may contain other than organic waste.
• peat is counted as a fossil fuel, while in certain cases it is considered to be a renewable biofuel.
• coal In a coal-fired energy-generating plant, coal is first fetched from a storage and fed into a coal mill, wherein it is comminuted into particles of a sufficiently small size for firing. All the different coal grades are generally fragile and, hence, easily grindable, for which purpose a ball mill is used. Each plant has typically a plurality of coal mills and feed lines for passing the milled coal into the combustion chamber of the boiler. Coal is fed into the combustion chamber pneumatically conveyed along a line exiting at a coal nozzle.
• the carrier gas of coal conventionally air, forms a portion of the required combustion air, while the rest of combustion air is today generally fed stagewise into the burner flame and the combustion chamber.
• the biofuel is mixed with the fossil fuel prior to the igni- tion of the fossil main fuel, which in practice must take place prior to the exit of the burner's fuel feed line into the combustion chamber.
• An alternative arrangement might be contemplated such that has the biofuel feed is arranged to exit from a separate nozzle or other like feed means just in front of the main fuel nozzle tip, preceding the ignition point of the main fuel.
• the mixing point of the biofuel in the upstream direction of the main fuel flow should advantageously take place not earlier than after the milling of the main fuel.
• FIG. 1 therein is shown schematically the co-use of a biofuel in the firing of a coal-fired boiler 1.
• the invention is applicable to all types of boilers fired with particulate solid fuel.
• the biofuel is received at a hauling terminal 2, wherefrom the fuel is transferred by conveyors 3 in proper amounts to processing into fuel.
• the fuel is driven over a magnet drum 4, where possible magnetic tramp metal is separated from the fuel.
• the fuel is passed to a screen 5, where larger clumps are separated and conveyed to a precrusher 6.
• the material may also be dried.
• this predrying stage is primarily helpful in making the grinding of the fuel easier.
• the biomaterial is passed to a grinder that can be an impact mill 7 in an advantageous and simple arrangement.
• Boiler flue gases can be passed into the impact mill along a line 9 to help drying the fuel in the impact mill and the precrusher.
• the particle size of the crushed material should be smaller than 8 mm and the moisture content should advantageously be not greater than 25 %.
• the particle size may be allowed to be this large inasmuch the combustion process with the main fuel in a common flame is very effective. Even a higher moisture content can be allowed for the comminuted fuel, depending on the composition of the received material.
• the fuel moisture content is 10 % to 40 %.
• the biofuel is passed along a line 8 to one of the burner groups 11 of a coal-fired boiler.
• a burner group 1 1 is formed by burners operating at the same height on the boiler wall.
• One possible location of the burners of a given burner group 1 1 is at the corners of the boiler, for instance.
• Pulverized coal serving as the main fuel is passed to the burners along lines 10.
• the biofuel is fed to one coal burner group only, but with the provision of a sufficiently ample supply of biomaterial, it is possible to feed biofuel to plural burners, even to all of them.
• FIG. 2 shows a possible arrangement for biofuel feed.
• the biofuel is mixed with the main fuel flow prior to the burner by way of connecting the biofuel line 8 to the main fuel line 10.
• the biofuel particles undergo mixing with the pulverized main fuel, whereupon the ignition and burning of the fuel mix- ture take place in a conventional manner in the burner flame.
• the embodiment according to the invention uses the burner type which is schematically illustrated in the diagram and achieves ignition of the fuel flow by means of a stabilizing ring 12. With the help of such a stabilizing ring 12, the flame can be ignited efficiently even under air-deficient conditions so that the flame always ignites at the burner tip and burns under all conditions in a stable manner.
• the fuel flow contains less air than is needed for complete combustion of the fuel, whereby more combustion air is stagewise added to the flame via secondary-air and tertiary-air nozzles 13, 14.
• this kind of fuel feed arrangement might be feasible as such, a problem may be encountered from sideflow of pulverized coal into the biofuel line or from backflow effects in the biofuel line due to pressure variations in the feed system.
• Neither one of these feed arrangements needs a separate ignition system, and the completed combustion of coal is aided, among other factors, by the volatile components imported by the biofuel.
• the invention is particularly suited for use in conjunction with this kind of modern burners in which the combustion process can be readily controlled. Nevertheless, the use of the invention may also be contemplated in other types of burners.
• Burners of the above kind are described, e.g., in US Pat. Nos. 5,799,594, 5,431 ,1 14, 4,907,962 and 5,263,426.
• the test results support the concept that the biofuel should be mixed with coal that is already pulverized, particularly when large amounts of biofuel or coarse biomaterial is being used.
• the biofuel is mixed with coal only after the milling of the coal.
• This arrangement gives the benefit that the expensive coal mill need not be used for processing the biofuel, but instead, its comminution may be carried out using less costly grinding equipment can be used such as an impact mill.
• the volumetric amount of wood in the mixed fuel was 17 vol.-% which corresponds to approx. 4-5 wt.-% and approx. 1-2 % of the overall heat content of the mixed fuel.
• the amount of wood was raised to 20 vol.-% corresponding to approx. 6-7 wt.-%. Due to uneven mixing and changes in the heat content of the fuel components, the actual mixing percentage varied.
• the amount of wood in the mixed fuel was further raised to 25 vol.-% which corresponds to 9-10 wt.-% and 3-4 % of the overall heat content of the mixed fuel.
• the flame ignition and burning process was normal. Also the formation of fly ash and soot was normal.

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• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Combustion Of Fluid Fuel (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=8555342

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (12)

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• 1999
  • 1999-09-23 FI FI992046A patent/FI119124B/fi active
• 2000
  • 2000-09-22 AU AU72944/00A patent/AU7294400A/en not_active Abandoned
  • 2000-09-22 CZ CZ20020999A patent/CZ303811B6/cs not_active IP Right Cessation
  • 2000-09-22 HU HU0203046A patent/HU229926B1/hu unknown
  • 2000-09-22 EP EP00960746A patent/EP1214549A1/en not_active Withdrawn
  • 2000-09-22 PL PL00353990A patent/PL195937B1/pl unknown
  • 2000-09-22 WO PCT/FI2000/000818 patent/WO2001025689A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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