SE529103C2 - Procedure for the purification of flue gases and treatment of ash from waste incineration - Google Patents

Abstract

In a method for the cleaning of flue gases and the treatment of ash from a boiler with a fluidised bed for the combustion of solid household refuse, in which boiler the flue gases pass from the furnace (1) to a cyclone (5), after which active carbon (18) and slaked lime (19) can be added and the flue gases led through a filter (6), for example a fabric filter, bottom ash (11) from the furnace, cyclone ash (15) from the cyclone, and filter ash (16) from the filter, among other residues, leave the boiler during operation. In order to clean the cyclone ash (15) such that it satisfies the requirements for deposition into a normal landfill with a clear margin, the cyclone ash is leached with leaching fluid (26) during the formation of an ash sludge (21), which is fed to a fluid separator (23), for example a pressure filter, where the process fluid (26) is separated from the ash (25) that has been leached. It is preferable that the process fluid is recycled through a part of it being used for the leaching and for the formation of the ash sludge, and through another part (28) of it being injected into the flue gas flow after the cyclone (5) but before the addition, if any, of active carbon (18) and slaked lime (19).

Description

25 30 529 103 2 turning shaft, so-called turning shaft box. Then the flue gas purification takes place, which often as the first step has a cyclone that separates cyclone ash. Thereafter, a second separation of ash normally takes place by means of a suitable separator, for example a hose filter, from which filter ash is obtained.

In order to stabilize heavy metals such as lead and cadmium in the fly ash against leaching when placed in landfill, it is proposed in US 5,220 lll that the ask ash, which has first been subjected to treatment with slaked lime in a scrubber, be calcined in an oxygen-present gas stream at a temperature of 375 ° C. 5 T 5 800 ° C for a period of 170 s 5 t 5 5 h, whereby the heavy metal content of leachate from the landfill shall be below the limit set by the Environmental Protection Agency (EPA) in the USA. The same result is achieved according to US 5,220,112 by mixing the ash gas with a calcium-present material so that the weight ratio between calcium and ash will be between 0.04: 1 and 0.5: 1, after which the calcination is carried out at 475 ° C. ° C for a period of 0.5 h 5 h 5 3 h.

When incinerating waste, the requirements for ash qualities and the handling of different ashes at landfills have gradually increased. EU Directive 2000/76 / EC contains rules for sampling and minimization of ash streams during the incineration of waste. Furthermore, a decision in the EU Council of Ministers (in Swedish 2003/33 / EC, in English 2003/33 / EC) sets out criteria and procedures for assessment when receiving waste at landfills. In general, for ash from waste incineration in an unidentified bed, the bottom ash can be placed in a regular landfill, alternatively used as a filling material, while the cyclone ash is on the verge of clearing a normal landfill and the filter ash must go to a landfill for hazardous waste. The requirements apply not only to the actual content of various environmentally polluting substances, but also to their leachability in the landfill, as they want to limit the amount of the various environmentally polluting substances that can be leached out and get into the surface or groundwater. The pollutants must thus be separated from, or alternatively stabilized in, the ash that is deposited in the landfill.

Since the difference in cost between landfilling at a regular landfill and at a landfill for hazardous waste in Sweden in 2005 amounts to SEK 500-1000 / ton, in addition to the nature conservation aspect, there is also an economic incentive to clean the cyclone ash so that it meets the requirements for ordinary g deponi.

SUMMARY OF THE INVENTION The main object of the present invention is therefore to purify the first ash fraction in a process of the kind mentioned in the introduction so that it meets the requirements for ordinary landfill by a good margin, partly with respect to reduced amounts of the pollutants partly with regard to reduced leaching of the ash fraction remaining residues of the pollutants. This is achieved by leaching the first ash fraction with a leaching liquid to bind in this leaching liquid a part of the environmental pollutants present in the first ash fraction, where at least a part of this leaching liquid, with its content of the environmentally polluting substances leached from the first ash fraction, in the flue gas passage before the soaking position of the second ash fraction, whereby some of the pollutants present in the first ash fraction are bound in the second ash fraction, whereby the content of pollutants is reduced in the first ash fraction while the content of pollutants in the second ash the ash fraction increases, with the result that the total volume of ash which is soaked from the incineration and which requires further handling or landfill is reduced. Such a lacquering process is relatively simple and not appreciably costly and can be carried out batchwise or continuously.

Suitably at least 50%, preferably at least 75% of at least one of the pollutants in the first ash fraction is leached from this ash fraction. It is also suitable that at least 50% of at least one of the environmentally harmful substances in the first ash fraction is leached out of this ash fraction and bled out via the second ash fraction. In this way, the first ash fraction is purified so that it can safely meet the requirements for disposal in an ordinary landfill, while the second ash fraction, which nevertheless constitutes hazardous waste, will have an increased content of leachable pollutants.

According to a preferred embodiment where the flue gases come from a fluidized bed boiler for incineration of waste, in which boiler the flue gases go from the fireplace to a cyclone, after which activated carbon and slaked lime are added and the flue gas is passed through a filter, with bottom ash from the fireplace, cyclone ash from the cyclone and filter ash from the filter leaves the boiler during operation, and the cyclone ash constituting the first ash fraction and the filter ash the second ash fraction, according to the invention the first ash fraction is mixed with SE0508.doc 10 15 20 25 30 529 103 a liquid separator, where process liquid is separated from leached ash.

It is suitable in this case that the boiler is designed in such a way that the fluidized bed is a bubbling or circulating fl uidised bed and the flue gases go from the fireplace into a vacuum, turn in a turning shaft and go further into superheaters, past cooking surfaces and through an economizer to the cyclone, and that reversing shaft ash is separated from the gas stream in the reversing shaft. Ash that separates spontaneously from the flue gases, for example when the flue gases turn in a turning shaft, is usually conventionally called boiler ash, because the ash that is separated with special devices (cyclone, electric filter, etc.) is called ash from pre-separators.

This ash shaft ash is combined with the cyclone ash and they are leached together so that both of these ash fractions can be leached out and have a lower content of, for example, heavy metals.

As the ash settles easily during the leaching, which can be carried out batchwise or continuously in tanks or in columns, it is convenient to keep the ash suspended in the leach liquid by stirring, thereby accelerating the leaching, the ash particles becoming porous, becoming more irregular in shape and decreasing in size. the proportion of larger particles decreases and the proportion of smaller particles increases.

Preferably, the leached ash is formed into a bed of liquid separator, from which bed of liquefied liquid is removed by displacement washing with a washing liquid, preferably water.

This can be done, for example, in batches in a filter press or continuously in a Centrifuge with the possibility of washing the filter cake.

The ash bed washed in a filter press is suitably compacted to remove a major part of the washing liquid, preferably to a dry matter content greater than 80%. This increases the dry content and reduces the weight of the leached and washed ash that is to be placed in a regular landfill.

The liquid removed from the ash bed is suitably transferred to a process liquid tank. The process water separated in the liquid separator contains salts and heavy metals and therefore needs to be purified. In waste incineration plants of the present type, there is normally no liquid purification that can handle this type of contaminated liquid. In order to reduce the emissions of process liquid, it is therefore suitable that a part of the process liquid is recycled for use in the washing and formation of the ash suspension. It is also convenient that another part of the process liquid is recycled and injected into the gas stream after the cyclone but before the addition of activated carbon and slaked lime, whereby the injected process liquid is evaporated and salts and heavy metals are separated in the filter. In simple terms, the contaminants have then been transferred from the possible headland ash and cyclone ash to the filter ash, thus making it possible to reduce the landfill costs for the headland ash and cyclone ash.

The filter ash has become slightly more polluted, but this will in any case end up in a landfill for hazardous waste, which means that the disposal cost for the filter ash is unchanged.

By recycling the process liquid in the ash leaching and adding only a small amount of fresh water or other suitable washing liquid, the amount of process liquid is kept down and a considerable energy loss is avoided when liquid evaporates. Injection of process liquid into the gas stream after the cyclone, however, lowers the flue gas temperature, and at the process liquid quantities that it is relevant to take care of, the temperature drop can be of the order of 25 ~ 50 ° C. Therefore, in order not to get too low temperatures into the hose filter, the flue gas temperature into the cylinders should be raised slightly, preferably so that the temperature into the hose filter during the previous liquid injection becomes substantially unchanged compared to the temperature without the previous liquid injection. In addition to getting rid of your process liquid in a simple way in this way, the flue gas purification will be somewhat more efficient.

Namely, the separation of I-IC1 and SO2 in the filter increases with increasing relative moisture content in the flue gas.

BRIEF DESCRIPTION OF THE ATTENDED DRAWING In the following, the invention will be described in more detail with reference to preferred embodiments and the accompanying drawing.

The figure is a simplified schematic diagram of a flue gas purification boiler for incineration of waste in an unidentified bed with a block diagram for subsequent flue gas purification and treatment of ash according to a preferred embodiment of the invention.

SE0508.doc 10 15 20 25 30 529 103 6 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The boiler shown in the figure is of conventional design and comprises a fireplace 1 for incineration of solid waste in a fluidized bed. From the fireplace 1, the flue gases enter an empty draft 2, which forms the beginning of a turning shaft 3, and continue through a rear draft 4 out of the boiler. In the turning shaft 3 and the rear draft 4, the flue gases pass by boiler components (not shown), such as superheaters, cooking surfaces and economizers, where they are cooled to about 150 ° C. The flue gases then pass through a gas purification equipment, which comprises a cyclone 5 and an filter 6, before they are allowed to escape through a chimney 7 by means of a flue gas fan (not shown). The filter 6 usually consists of a conventional hose filter, but other filter types are also useful. The flue gas purification in the embodiment shown also includes dosing of activated carbon denoted by arrow 18 and slaked lime denoted by arrow 19, which is done either directly in the flue gas duct or in a reactor, which is in principle an expanded part of the flue gas duct.

The present invention relates to a process for purifying flue gases from waste incineration and reducing the volume of environmentally harmful ash landfills, in which purification of at least two fractions 15, 16 of ash is soaked from the process, where the first ash fraction is soaked closer to the fireplace 1 and has a first content of pollutants and the second ash fraction 16 were later bled from the flue gas passage and have a second content of pollutants.

From the boiler and flue gas purification equipment, the shown embodiment departs four arrows marked with arrows, namely bottom ash 11, turning shaft ash 13, cyclone ash 15 and filter ash 16. as filling material.

The cyclone ash 15, which constitutes said first ash fraction, and the filter ash 16, which constitutes said second ash fraction, have been taken out mixed or separate and have been so contaminated that they have to go to a landfill for hazardous waste with stricter rules on ash handling, which high costs. It is therefore desirable to clean the Cyclone Box 15 so that it meets the requirements for a regular landfill by a good margin.

Table 1 below shows typical aggregates of the ashes obtained from the incineration of solid household waste.

SE0508.doc 529 103 7 _ Table 1 Moisture SC C03 C unburned Cl Si Na Ca A1 Fe K Mg åßQåååååââåååååšlåå Ing / kg mg / kg Ing / kg IIIs / kg Bottom ash Reverse shaft ash Cyclone ash Filter ash 0.2 0.245 0.2 0.025 0.2 0.09 31.15 6.95 6.59 4.16 2.93 1.865 0.94 0.36 0.175 0.16 0.07 3125 30 500 74 207.5 3375 1215 2 69 21 0.02 0.2 0.445 0.2 0.17 0.2 0.22 30.15 3.69 7.385 6.71 2.475 1.85 0.795 0.68 0.41 0.165 0.085 5310 35 475 27.5 230 3890 1025 3.85 47 35 0.025 0.2 0.735 1.05 0.94 0.2 1.495 17.6 3.455 15.7 10.945 2.72 1.675 1.615 1.115 0.905 0.345 0.21 5310 54.5 350 41 150 7310 1405 10.5 30 21.5 0.075 0.375 0.815 3.3 1.415 1.85 14.7 3.585 2.175 31.8 2.2 0.675 0.545 0.81 0.645 0.39 0.13 0.065 7540 200 22.5 53.5 4885 4470 49 41.5 17, 6.32 According to the invention, a first ash fraction 15 is leached with a leaching liquid 26 to bind in this leaching liquid a part of the environmental contaminants present in the first ash fraction 15 and at least a part of this leaching liquid. 28 with p The contents of the pollutants leached from the first ash fraction 15 are reintroduced into the flue gas passage before the bleeding position 6 of the second ash fraction 16, whereby some of the pollutants present in the first ash fraction 15 are bound in the second ash fraction 16, whereby the content of mill. Island pollutants are reduced in the first ash fraction 15 while the content of environmental pollutants in the second ash fraction 16 increases, with the result that the total volume of ash that bleeds out from the incineration and which requires greater handling or landfill is reduced.

This can be done as shown in the drawing by mixing the cyclone ash 15 with leach liquid and leaching, after which the mixture is fed to a liquid separator, where process liquid is separated from leached ash. The leaching is carried out in the block which in Figure 1 is denoted by 20. The block 20 may comprise, for example, one or more leaching tanks (not shown) or columns for batch or continuous leaching. Since the ash settles easily, so that the ash particles after KOIT time will be surrounded by stagnant leachate, it is convenient to carry out the leaching while stirring the mixture of ash and leachate to speed up the leaching process. As is known to those skilled in the art, stirring can be accomplished in many ways. For example, propeller agitators with substantially flat, sloping blades can be used to advantage in tanks, while in a column the leachate can be allowed to rise upwards through a sedimentary ash bed.

In the preferred embodiment shown in the figure, the face shaft ash 13 is combined with the cyclone ash 15 and they are leached together in the block 20 to enable leaching of both of these ash fragments in the same treatment step.

The mixture of ash and leach liquor designated 21 is then fed to a liquid separator block 23, in the embodiment shown via a buffer tank 22, which equalizes the fumes through the lacquer block 20 and through the liquid separator block 23. In block 23, process liquid is separated from leached ash. As will be readily appreciated by those skilled in the art, a variety of conventional liquid separators can be used. Preferably, they are of such a type that the leached ash is formed into a bed in the liquid separator, from which bed of liquid is removed by displacement washing with water or other suitable liquid, as the figure is denoted by 24. This can be done, for example, batchwise in a filter press or continuously in a centrifuge with the possibility to wash the filter cake. The basic construction of an presslterpress is shown in SEOS08_b.doc 10 15 20 25 30 529 1039 for example US 3,342,123, but has in recent years been improved to better control the formation of the filter cake, see for example WO 03/057344.

The ash bed washed in a filter press is suitably compacted to remove a major part of the leach liquid, preferably to a dry matter content greater than 80%. This increases the dry content and reduces the weight of the leached and washed ash that is to be placed in the landfill.

The leached and washed ash coming out of the liquid separator block 23 is indicated in Figure by the 25. the amount of process liquid is kept down and only a small amount of fresh water or other suitable washing liquid is added to the system. The consumption of fresh water in experiments amounted to less than 1 m3 per tonne of dry ter lter cake.

The process liquid contains salts and heavy metals, called the environmentally damaging sleeve, and therefore needs to be cleaned. In plants for the incineration of solid household waste with dry or semi-dry flue gas treatment, there is usually no water treatment that can take care of this type of contaminated liquid. To avoid installing a water purifier, it would therefore be desirable to be able to get rid of this liquid in some alternative way. According to a preferred embodiment of the invention, therefore, another part of the process liquid, referred to herein as 28, is recycled and injected into the gas stream after cyclone 5. The injection preferably takes place before the addition of activated carbon 18 and slaked lime 19 if such additives are used. The injected process liquid will then evaporate and salts and heavy metals are separated in the filter 6.

Simply put, the contaminants have then been moved from the possible headland ash box 13 and the cyclone box 15 to the filter box 16 and thus made it possible to reduce the landfill costs for the headland shaft and cyclone box 13 and 15, respectively. The filter box 16 has become slightly more polluted, to end up in a landfill for hazardous waste, which means that the cost of landfilling the filter ash is unchanged.

By recycling the process liquid 26 in the ashtray 20 and adding only a small part of fresh water or other suitable washing liquid 24, the amount of process liquid is kept down and a considerable energy loss is avoided when liquid is evaporated. however, injecting process liquid 28 into the gas stream after cyclone 5 lowers the flue gas temperature, and in the case of the process liquid quantities which it is relevant to take care of, the temperature reduction may be of the order of 25-50 ° C. Therefore, in order not to get too low temperatures into the hose filter 6, the flue gas temperature into the cyclone 5 should be raised slightly, suitably so that the temperature into the hose filter 6 at the previous liquid injection remains substantially unchanged compared to the temperature without the previous liquid injection.

Another option may be to have an additive burner after the addition of the process liquid.

It is also possible to use leachate which is favorable for the flue gas purification chemically or to add such an additive to the process liquid.

In addition to getting rid of your process liquid 28 in a simple manner in this way, the flue gas purification will be somewhat more efficient. Namely, the separation of HCl and SO 2 filter 6 increases with increasing relative moisture content in the flue gas.

TYPICAL OPERATING CASE When operating a waste incinerator with a boiler output of 20 MW, it is possible to incinerate waste in an amount of approximately 7100 kg / h. From this combustion 4 different fractions of ash are obtained in the form of; bottom, shafts, cyclone and filter ash in substantially equal amounts each.

Approximately 450 kg / h each of the fractions - bottom, shafts, cyclone and filter ash are produced.

The amount of process liquid, here leachate, which is sprayed into the flue before the last purification in the filter stage is approximately 450-900 kg / h. The volume of flue gas generated that passes the last filter stage amounts to approximately 9.8 ma / s wet gas.

By leaching headland ash and cyclone ash, it is possible to leach out of an ash load of approximately 450 + 450 kg / h to such an extent that this can be landfilled without high landfill fees. The amount of filter ash is increased marginally by a few single percent.

With landfill fees for hazardous waste (in Sweden 2005) of 500-1000 SEK / ton, a saving of approximately 675 SEK / hour (900 kg / h> <750 SEK / ton) is obtained, which is 16,200 SEK / day and just over 4.8 million on an annual basis (300 operating days). The invention thus results in SIOI savings and a reduction of the total amount of hazardous waste to about one third.

Performed test runs show that: 1. The cyclone ash and the reversible shaft ash undergo physical and chemical changes during leaching.

SEO508_b.doc 10 15 20 25 30 529 103 11 2. Larger ash particles decompose on the mixture with the aqueous leachate, and a fraction of smaller particles increases. 3. Through pore formation, the inner surface of the particles increases markedly. 4. The most soluble salts are leached out within 5 minutes in a tank with stirring at room temperature and the leachate recycled from the liquid separator has a high pH, is strongly alkaline. Filtration is a suitable method for separating the solids from the liquid after the leaching step, which is characterized by low filtration resistance in the range from 9.6E + O8 to 4.3E + 09 m / kg. 6. The mother liquor (leach liquid) retained in the filter cake can be washed out efficiently by displacement washing using a volume of washing liquid which is twice the volume of the mother liquor. 7. The levels of the substances which, in the raw, unpainted ash, were above the EU-established limit values for placing the ash in a regular landfill, were reduced in the leached and washed ash to acceptable levels. In samples, it has been shown that the content of Cl has been reduced well above 90% by about 92% and the leachability of Cl in the leached ash fraction has been reduced by 90-97%. The content of As was not significantly affected, but the residual amount of As remaining in the leached ash fraldion has reduced its leachability by more than 90%. the ash of reckon that ammonia and hydrogen gas can be released from the mixture of ash and leachate.

It will be apparent to those skilled in the art that even though the method of the invention has been described in detail above, numerous modifications of the method are possible within the scope of the appended claims.

The invention can be modified in a number of ways within the scope of the claims. The different leaching processes and used leaching liquid can be tailored to the different environmental pollutants which are to be leached out of the early ash fractions and which are then to be returned to the flue to be bound in later ash fractions. The leaching can also take place in more than one step, where the first step can be adapted / optimized to leach out some of the environmentally damaging scars, SE0508_b.doc 10 15 529 103 12 and in other subsequent steps, others of the environmentally damaging ones are leached out of the ash fracture.

Thus, several different leaching liquids can be used, tailored to the substances to be leached out and / or stabilized in the leached ash fraction. It is thus possible to use acidic leaching liquids for some of the pollutants.

Various other combinations of flue gas cleaning equipment can be used. For example, a wet gas purification technique can be used in a flue gas purification step between a cyclone and a hose filter, where liquid from the wet flue gas purification step is used in whole or in part to leach the ash from the cyclone / reversing shaft. The leach liquid can then be pushed into the flue gas passage between the wet flue gas cleaning stage and the hose filter.

The leachate from leached ash can also be pushed into the flue before a wet flue gas purification step, where the pollutants are bled into the liquid from the wet flue gas purification stage.

Another alternative may be to use the obtained leachate as wet media in a subsequent wet flue gas purification step.

SE0508_b.doc

Claims (1)

1. 0 15 20 25 30 529 103 13 PATENT REQUIREMENTS. Process for purifying flue gases from waste incineration and reducing the volume of environmentally harmful ash landfills, in which purification of at least two fractions (15, 16) of ash is soaked in steps from the combustion, cooling and flue gas purification process, where the first ash fraction (15) is soaked closer to the fireplace (1) and has a first content of environmentally polluting substances and the second ash fraction (16) was later soaked from the flue gas passage and has a second content of environmentally polluting substances, characterized in that the first ash fraction (15) is leached (20) with a leaching liquid (26) for binding in this leaching liquid some of the environmentally polluting substances present in the first ash fraction (15), where at least a part of this leaching liquid (28), with its content of the environmental pollutants leached from the first ash fraction (15) the substances, are reintroduced into the flue gas passage before the bleeding position (6) of the second ash fraction (16), whereby a part of the Irxiljö load present in the first ash fraction (15) The substances are bound in the second ash fraction (16), whereby the content of pollutants is reduced in the first ash fraction (15) while the content of pollutants in the second ash fraction (16) increases. . Process according to Claim 1, characterized in that at least 50%, preferably at least 75% of at least one of the pollutants in the first ash fraction (15) is leached from this ash fraction, and at least one of the remaining pollutants in the first ash fraction stabilized during leaching to reduce the leachability of these environmentally harmful substances in this ash fraction after leaching. . A method according to claim 1, characterized in that at least 50% of at least one of the pollutants in the first ash fraction (15) is leached from this ash fraction and bled out via the second ash fraction (16). . A method according to any one of claims 1-3, wherein the flue gases come from a fluidized bed boiler for incineration of waste, in particular solid waste, in which boiler the flue gases go from the fireplace (1) to a cyclone (S), after which activated carbon (18 ) and slaked lime (19) are added and the flue gas is passed through a filter (6), whereby bottom ash (11) from the fireplace (1), cyclone ash (15) from the cyclone (5) and filter ash (16) from the filter (6) leave the boiler SE0508_b.doc 10 15 20 25 30 10. 11. 529 103 14 during operation, and wherein the cyclone ash (15) constitutes the first ash fraction and the filter ash (16) the second ash fraction, characterized in that the cyclone ash (15) is mixed with leach liquid (26) and leached (in 20), after which the mixture (21) is fed to a liquid separator (23), where process liquid (26) is separated from leached ash (25). A method according to claim 4, wherein the fl uidised bed is a bubbling fl uidised bed and the flue gases go from the fireplace (1) into an empty draft (2), turn into a turning shaft (3) and go further into superheaters, past cooking surfaces and through an economizer to the cyclone (5), and wherein the reversing shaft ash (13) is separated from the gas stream in the reversing shaft (3), characterized in that the reversing shaft ash (13) and the cyclone ash (15) are brought together and leached together. A method according to any one of claims 1-5, characterized in that the leaching (i 20) is carried out with stirring to keep the ash suspended. A method according to any one of claims 4-5, characterized in that the leached ash is formed into a bed in the liquid separator (23), from which bed of leach liquid (26) is removed by displacement washing with washing liquid (24), preferably water. A method according to claim 7, characterized in that the washed ash bed is compacted to remove a main part of the washing liquid to a dry content greater than 50%, preferably to a dry content greater than 80%. Method according to claim 7 or 8, characterized in that the liquid (26) removed from the ash bed is conveyed to a process liquid tank (27). Method according to one of Claims 1 to 9, characterized in that a part of the leach liquid (26) is recycled after separation from the leached ash for reuse in the lacquer ring (in 20). Process according to one of Claims 1 to 10, characterized in that the leachate (28) is returned to the flue gas stream before a position for adding activated carbon (18) and slaked lime (19) between the bleeding positions. (5 and 6) for the first and second ash fractions. Method according to claim 11, characterized in that the flue gas temperature up to the bleed position (5) of the first ash fraction (15) is raised to compensate for the cooling effect of the injected leach liquid (28), so that the flue gas temperature into the bleed position (6) ) for the second ash fraction (16) remains essentially unchanged. SE0508__b.doc