Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/30—Destroying solid waste or transforming solid waste into something useful or harmless involving mechanical treatment
  • B09B3/38—Stirring or kneading
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/70—Chemical treatment, e.g. pH adjustment or oxidation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/48—Sulfur compounds
  • B01D53/50—Sulfur oxides
  • B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/38—Removing components of undefined structure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/73—After-treatment of removed components
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/20—Agglomeration, binding or encapsulation of solid waste
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
• • 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
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B2101/00—Type of solid waste
  • B09B2101/30—Incineration ashes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J2700/00—Ash removal, handling and treatment means; Ash and slag handling in pulverulent fuel furnaces; Ash removal means for incinerators
  • F23J2700/001—Ash removal, handling and treatment means
• • 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
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/20—Waste processing or separation

Definitions

• the present invention concerns a method for the cleaning of flue gases from the combustion of refuse and the reduction of the volume of environmentally hazardous ash landfills, in which cleaning at least two fractions of ash are bled from the process of combustion and cleaning of flue gases, where the first ash fraction is bled closer to the furnace and has a first level of environmentally hazardous substances and the second ash fraction is bled later from the flue gas passage and has a second level of environmentally hazardous substances.
• Modern boilers for the combustion of solid household refuse often have a fluidised bed or other type of furnace for the combustion, and the flue gases from the furnace of the boiler pass from the boiler and cooling surfaces of the boiler to equipment for the cleaning of flue gases, which may comprise a pre-separator, for example a cyclone, and it may also or alternatively comprise a filter, for example a fabric filter, for the final separation of solid components before the flue gases pass through a flue gas fan out through a chimney, see, for example, US 4 862 813.
• the cleaning of flue gases can in certain cases comprise several stages of flue gas cleaning using either dry, partially dry or wet cleaning technology in one or several stages in various combinations.
• the furnace is equipped with a fluidised bed, it is normal that larger quantities of ash are generated than the quantities generated by conventional grate boilers where the refuse lies on the bottom during the combustion without the intensive mixing that takes place in boilers with a fluidised bed.
• slaked lime and active carbon be added at the stage before the filter in order to neutralise acidic components in the flue gases and in order to reduce further the release of heavy metals, dioxms and organic pollutants, see, for example, US 5 443 022, US 5 220 111 and US 5 220 112
• At least three flows of ash leave the combustion and the cleaning of flue gases. At least one bottom ash is obtained from the combustion in the case in which a flmdised bed is used, or slag in the case in which the combustion of refuse takes place on gratings It is possible subsequently to obtain a second flow of ash, known as "return flue ash" from the return flue of the boiler.
• the cleaning of flue gases commences after this, which often has a cyclone as its first stage, which separates cyclone ash.
• a second separation of ash then normally takes place with the aid of a suitable separator, for example a fab ⁇ c filter, form which filter ash is obtained.
• the principal aim of the current invention is thus to use a method of the type described in the introduction to clean the first ash fraction such that it satisfies the requirements for a normal landfill by a clear margin, not only with respect to reducing the amounts of the environmentally hazardous substances but also with respect to reduced leaching of the residues of environmentally hazardous substances that remain in the ash fraction.
• first ash fraction being leached with a leaching fluid in order to bind a fraction of the environmentally hazardous substances that are present in the first ash fraction in this leaching fluid, and at least a part of this leaching fluid, with its content of environmentally hazardous substances leached from the first ash fraction, is reintroduced into the flue gas passage before the bleeding position for the second ash fraction, whereby a part of the environmentally hazardous substances that are present in the first ash fraction bind to the second ash fraction, whereby the level of environmentally hazardous substances in the first ash fraction is reduced while the level of environmentally hazardous substances in the second ash fraction increases, with the result that the total volume of ash that is bled from the combustion and that requires further treatment or deposition is reduced.
• a leaching process is relatively simple and does not involve significant cost. It can be carried out either batchwise or continuously.
• At least 50%, preferably at least 75%, of at least one of the environmentally hazardous substances in the first ash fraction is leached from this ash fraction. It is also appropriate that at least 50% of at least one of the environmentally hazardous substances in the first ash fraction is leached out from this ash fraction and is bled through the second ash fraction.
• the first ash fraction is in this way cleaned such that it safely satisfies the requirements for it to be placed into a normal landfill, while the second ash fraction, which constitutes hazardous waste in any case, will obtain an increased level of leachable pollutants.
• the flue gases come from a boiler with a fluidised bed for the combustion of refuse, in which boiler flue gases pass from the furnace to a cyclone, after which active carbon and slaked lime are added and the flue gases are led through a filter, whereby bottom ash from the furnace, cyclone ash from the cyclone, and filter ash from the filter leave the boiler while it is in use, and whereby cyclone ash constitutes the first ash fraction and the filter ash constitutes the second ash fraction, the first ash fraction is mixed, according to the invention, with the leaching fluid and is leached, after which the mixture is fed to a fluid separator, where process fluid is separated from the leached ash.
• the boiler is constructed in such a manner that the fluidised bed is a bubbling or circulating fluidised bed, and that the flue gases pass from the furnace into a withdrawal chute, turn in a return flue and pass onwards into superheaters, pass heating surfaces and through an economiser to the cyclone, and that the return flue ash is separated from the flow of gas in the return flue.
• Ash that separates spontaneously from the flue gases, by, for example, the flue gases turning in a return flue are normally denoted “boiler ash” by convention, while the ash that is separated by special equipment (cyclones, electrical filters, etc.) is denoted "ash from pre-separators".
• This return flue ash is added to the cyclone ash and they are leached together, such that both of these ash fractions can be leached and obtain a lower content of, for example, heavy metals.
• the leached ash is preferably formed to a bed in the fluid separator, from which bed leaching fluid is removed by replacement washing with a washing fluid, preferably water. This may take place, for example, batchwise in a pressure filter, or continuously in a centrifuge with the opportunity to wash the filter cake.
• the ash bed that has been washed in a pressure filter is compacted for the removal of the principal part of the washing fluid, preferably to a dryness level that is greater than 80%.
• the dryness level in this way increases and the weight of the leached and washed ash that is to be placed into a normal landfill is reduced.
• the fluid removed from the ash bed is led to a process fluid tank.
• the process water that is separated in the fluid separator contains salts and heavy metals, and it must therefore be cleaned.
• another part of the process fluid is recycled and injected into the gas flow after the cyclone, but before the addition of active carbon and slaked lime, whereby the process fluid that has been injected is converted to vapour, and salts and heavy metals are separated out in the filter.
• the contaminants have been transferred from the return flue ash (if present) and the cyclone ash to the filter ash, and in this way it has become possible to reduce the deposition costs for the return flue ash and cyclone ash.
• the filter ash has become somewhat more highly contaminated, but this is going to end up in a landfill for hazardous waste in any case, and this means that the deposition costs for the filter ash are unchanged.
• the temperature of the flue gases on input to the cyclone should be raised somewhat, in order not to obtain temperatures at the input to the fab ⁇ c filter that are too low, appropriately such that the temperature at input to the fab ⁇ c filter with the preceding fluid injection will be essentially unchanged from the temperature that was obtained without the preceding fluid injection
• the process fluid is taken care of in this manner in a simple way, and the cleaning of the flue gases will become somewhat more efficient.
• the separation of HCl and SO 2 in the filter increases, namely, with increasing moisture levels in the flue gases
• the drawing is a simplified sketch showing the principles of a boiler with flue gases cleaning for the combustion of refuse in a fluidised bed with a block diagram of the subsequent flue gas cleaning and the treatment of ash according to one preferred embodiment of the invention.
• the boiler shown in the drawing is of a conventional design and it comp ⁇ ses a furnace 1 for the combustion of solid refuse in a fluidised bed
• the flue gases pass from the furnace 1 into an withdrawal chute 2, which constitutes the input to a return flue 3, and they pass onwards through a rear chute 4 out of the boiler.
• the flue gases pass in the return flue 3 and the rear draw 4 boiler components that are not shown in the drawing such as superheaters, heating surfaces, and economisers, where they are cooled to approximately 150 0 C
• the flue gases subsequently pass through gas cleaning equipment, which comp ⁇ ses a cyclone 5 and a filter 6, before they are allowed to escape through a chimney 7 with the aid of a flue gas fan, not shown in the drawing
• the filter 6 is normally constituted by a conventional fab ⁇ c filter, but also other types of filter may be used.
• the cleaning of the flue gases comp ⁇ ses in the embodiment shown also the addition of active carbon, denoted by the arrow 18, and slaked lime, denoted by the a ⁇ ow 19, which is carried out either directly in the flue gas channel or in a reactor, which is, in p ⁇ nciple, an expanded part of the flue gas channel.
• the present invention concerns a method for the cleaning of flue gases from the combustion of refuse, and for a reduction in the volume of environmentally hazardous depositions of ash, in which cleaning at least two fractions 15, 16 of ash are bled from the process, where the first ash fraction 15 is bled more closely to the furnace 1 and has a first content of environmentally hazardous substances and the second ash fraction 16 is bled later in the flue gas passage and has a second content of environmentally hazardous substances.
• Table 1 shows typical compositions of the ashes that are obtained during the combustion of solid household refuse.
• a first ash fraction 15 is leached in 20 with a leaching fluid 26 in order to bind a fraction of the environmentally hazardous substances that are present in the first ash fraction 15 in this leaching fluid, and at least a portion 28 of this leaching fluid with its content of environmentally hazardous substances leached from the first ash fraction 15 is reintroduced into the flue gas passage before the bleeding position 6 of the second ash fraction 16, by which means a part of the environmentally hazardous substances that are present in the first ash fraction 15 bind to the second ash fraction 16, whereby the level of environmentally hazardous substances in the first ash fraction 15 is reduced while the level of environmentally hazardous substances in the second ash fraction 16 increases, with the result that the total volume of ash that is bled from the combustion and that requires more stringent handling or deposition is reduced.
• the leaching is carried out in the block that is denoted in Figure 1 by 20.
• the block 20 can comprise, for example, one or more leaching tanks, not shown in the drawing, or it may comprise columns for batchwise or continuous leaching process. Ash sediments easily, such that the ash particles after a sort period will become surrounded by stationary fluid, and it is for this reason appropriate to carry out the leaching du ⁇ ng stirring of the mixture of ash and leaching fluid in order to accelerate the leaching process.
• the stirring may be achieved in many ways, as one skilled m the arts will be aware. It is advantageous, for example, to use propeller stirrers with essentially plane blades located obliquely in tanks, while it is possible to allow the leaching fluid in a column to ascend through a sedimentmg bed of ashes.
• the return flue ash 13 is added to the cyclone ash 15 and they are leached together in the block 20 in order to make it possible to leach both of these fractions in the same treatment step.
• the mixture of ash and leaching fluid denoted by 21 is then fed out to a fluid separator block 23, this is carried out in the embodiment shown via a buffer tank 22, which evens out the flows through the leaching block 20 and through the fluid separator block 23.
• Process fluid is separated in the block 23 from the leached ash. It will be obvious to one skilled in the arts that several different conventional fluid separators can be used. It is preferable that these are of such a type that the leached ash is formed to a bed in the fluid separator, from which bed leaching fluid is removed by replacement washing with water or another suitable fluid, which is denoted in the drawing with reference number 24.
• the bed of ashes that has been washed in a pressure filter is compressed in order to remove the major part of the leaching fluid, preferably to a dryness level that exceeds 80%.
• the dryness level increases in this manner and the weight of the leached and washed ash that is to be deposited in a landfill is reduced.
• the leached and washed ash that emerges from the fluid separator block 23 is denoted in the drawing with the reference number 25.
• the leaching fluid that has been separated in the block 23 is denoted by reference number 26.
• This fluid is led to a process fluid tank 27, from which a part of the fluid is recirculated for use as leaching fluid in the leaching block 20.
• the volume of process fluid is maintained in this manner at a low value, and only a small part of fresh water or other suitable washing fluid is added to the system.
• the consumption of fresh water amounted in trials to less than 1 m 3 per tonne of dry filter cake.
• the process fluid contains salts and heavy metals, denoted here as "environmentally hazardous substances", and must therefore be cleaned.
• another part of the process fluid here denoted with the reference number 28, is recycled and injected into the gas flow after the cyclone 5. It is preferable that the injection take place before the addition of active carbon 18 and slaked lime 19, if these additives are added.
• the process fluid that has been injected will then be converted to vapour, and salts and heavy metals can be easily separated out in the filter 6.
• the contaminants have been transferred from the return flue ash 13 (if present) and the cyclone ash 15 to the filter ash 16, and in this way it has become possible to reduce the deposition costs for the return flue ash 13 and cyclone ash 15.
• the filter ash 16 has become somewhat more highly contaminated, but this is going to end up in a landfill for hazardous waste in any case, and this means that the deposition costs for the filter ash are unchanged.
• process fluid 28 By recirculating process water 26 in the ash leaching 20 and adding only a small amount of fresh water or other suitable washing fluid 24, the amount of process fluid is maintained at a low level and a considerable energy loss when the fluid is converted to vapour is avoided. Injection of process fluid 28 into the gas flow after the cyclone 5 does, however, reduce the temperature of the flue gases, and this temperature reduction can be of the order of 25-50 0 C at the volumes of process fluid that it is required to deal with.
• the temperature of the flue gases on input to the cyclone 5 should be raised somewhat, in order not to obtain temperatures at the input to the fabric filter 6 that are too low, appropriately such that the temperature at input to the fabric filter 6 with the preceding fluid injection will be essentially unchanged from the temperature that was obtained without the preceding fluid injection.
• a further alternative may be to have an auxiliary burner after the addition of the process fluid. It is also possible to use leaching fluid that is advantageous for the cleaning of the flue gases from a purely chemical point of view, or to add such a fluid to the process fluid.
• the process fluid 28 is taken care of in this manner in a simple way, and the cleaning of the flue gases will become somewhat more efficient.
• the separation of HCl and SO 2 in the filter 6 increases, namely, with increasing moisture levels in the flue gases.
• the volume of process fluid, in this case leaching fluid, that is injected into the flue gas passage before the final cleaning in the filter stage amounts to approximately 450-900 kg/h.
• the volume of flue gases generated that passes the final filter stage amounts to approximately 9.8 m 3 /s of moist gas. It is possible by leaching of the return flue ash and the cyclone ash to leach an ash weight of approximately 450 + 450 kg/h to such a degree that this ash can be deposited without high deposition fees. The weight of filter ash is increased marginally, by a few percent. Given deposition fees for hazardous waste (in Sweden in 2005) of SEK 500-1000 per tonne, a saving of approximately SEK 675 SEK per hour is achieved
• the mother fluid (the leaching fluid) that is retained in the filter cake can be efficiently washed out by replacement washing using a washing fluid volume that is twice the volume of mother fluid.
• the invention can be modified in numerous ways within the framework of the patent claims.
• the different leaching processes and the leaching fluid used can be tailored for the different environmentally hazardous substances that are to be leached from the early ash fractions and that are subsequently to be reintroduced into the flue gas passage in order to be bound to later ash fractions.
• the leaching can also take place in more than one step, where the first step can be adapted or optimised in order to leach out certain of the environmentally hazardous substances, while other environmentally hazardous substances can be leached out from the ash fraction in other, subsequent steps.
• several different leaching fluids can be used, tailored according to the substances that are to be either leached out or stabilised, or both, in the ash fraction after leaching.
• acidic leaching fluids for certain of the environmentally hazardous substances.
• Various other combinations of equipment for cleaning flue gases can be used.
• Wet gas cleaning technology can, for example, be used in a flue gas cleaning step between a cyclone and a fabric filter, where fluid from the wet flue gas cleaning step is partially or fully used in order to leach the ash from the cyclone or return flue.
• the leaching fluid can subsequently be inserted into the flue gas passage between the wet flue gas cleaning step and the fabric filter.
• the leaching fluid from ash after leaching can also be inserted into the flue gas passage before a wet flue gas cleaning stage, where the environmentally hazardous substances are bled into the fluid flow from the wet flue gas cleaning stage.
• a further alternative can be to use the leaching fluid that is obtained as a wet medium in a subsequent wet flue gas cleaning step.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Health & Medical Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Biomedical Technology (AREA)
• Analytical Chemistry (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Processing Of Solid Wastes (AREA)
• Treating Waste Gases (AREA)

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• 2005
  • 2005-09-21 SE SE0502099A patent/SE529103C2/sv not_active IP Right Cessation
• 2006
  • 2006-09-19 EP EP20060799806 patent/EP1933971A1/en not_active Withdrawn
  • 2006-09-19 WO PCT/SE2006/050342 patent/WO2007035169A1/en active Application Filing

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