JPH10192820A - Treatment of ash in waste disposal by gasification fusion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating ashes in waste disposal conforming to gasificating fusion in which secondary amount of waste necessitating land reclamation is made zero. SOLUTION: In the method for treating ashes in waste disposal by gasification fusion, waste is thermally cracked at low temperature and gasified by using a gasification furnace and thereafter burned at high temperature by using a melting furnace. Collection ashes (h) are obtained from at least one process of respective processes of cooling, heat exchange and dust removal for exhaust gas discharged from the melting furnace. Collection ashes (h) are suspended 19 in an acidic solution to elute contained heavy metals and salts. Thereafter, solid matter is separated as dehydrated sludge 1 and again supplied to the fluidized bed gasification furnace or the melting furnace and changed into slag. An alkali agent (n) is added to an aqueous solution in which heavy metals and salts have been eluted and solid matter has been separated. Thereby, heavy metals are made insoluble and recovered (p).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating ash in waste treatment, and more particularly to municipal solid waste, solidified fuel, slurried fuel, waste plastic, waste FRP, biomass waste, automobile waste, and low quality. Waste such as charcoal and waste oil,
The present invention relates to an ash treatment method in an environmental protection type waste treatment in which gasification and melting completely burn without generating dioxins and convert ash contained in the waste into molten slag. The solidified fuel (= RDF) in the waste is
After crushing and sorting municipal solid waste, it is subjected to compression molding by adding quicklime and the like. The slurry fuel is obtained by crushing municipal solid waste and the like into a water slurry, and then converting the municipal solid waste to water by hydrothermal decomposition under high pressure.

[0002]

2. Description of the Related Art As a new waste treatment technology that replaces conventional incineration, companies are competing for the development of a "gasification and melting system" that combines gasification and melting and combustion, and has already reached the level of practical use. In the “gasification and melting system”, a fluidized bed gasification furnace (preferably an internal swirling type fluidized bed furnace)
A combination of a rotary melting furnace and a rotary melting furnace is currently regarded as the most promising in that it has the following features. Due to the low air ratio combustion, the amount of exhaust gas is greatly reduced. Dioxins and furans are hardly generated by high-temperature combustion. Ash in the waste is recovered as harmless and non-bulky slag from which heavy metals do not elute. Therefore, the life of the landfill can be prolonged, and it can be used for roadbed materials and the like. The retained energy of gas, tar, and carbide generated by gasification can be effectively used as a high-temperature source for melting ash. Since the functions of dioxin treatment and ash melting are incorporated in the system, the entire apparatus is made compact, and the construction cost is lower than that of a conventional incineration facility.

In a combination of a fluidized-bed gasification furnace (preferably, an internal swirling type fluidized-bed furnace) and a swirling melting furnace, a high-speed swirling flow formed in the swirling melting furnace requires 80% in one pass.
High slag recovery up to ９０90% is shown. However, the remaining 10 to 20% accompany the exhaust gas as fly ash,
It is collected by equipment that performs cooling, heat exchange, and dust removal at the subsequent stage.
When the gas temperature is lowered, heavy metals and salts having a low boiling point are deposited on fly ash, so that there is a problem in treating collected ash containing a large amount of these metals and salts. On the other hand, of the incombustibles discharged from the gasifier, iron,
Since copper, aluminum, and the like are recovered in an unoxidized and clean state, they can be recycled as bullion by metal type. Non-combustible materials other than metals, such as rubble and stone, can be used as backfill materials. The slag discharged from the melting furnace has applications in civil engineering and construction materials, horticultural materials, or ecocement. Therefore, if the collected ash can be recycled, it is possible to completely eliminate the amount of secondary waste requiring a landfill disposal site. Although this collected ash has a small absolute amount, if it is stabilized using conventional ash treatment methods such as the cement solidification method, the kneading method with the addition of a chemical (chelate resin), and the acid extraction method, a new landfill site will be created. Required. The method of returning the entire amount of ash to the gasification furnace or the melting furnace is not feasible due to accumulation of heavy metals and salts.

[0004]

In view of the fact that dioxins are not contained in the collected ash in the gasification and melting, a processing method different from that of the collected ash in an ordinary incinerator becomes possible. In view of the above-mentioned conventional technology, the present invention can recover most of the collected ash by converting it to slag, and no landfill disposal site is required.
Moreover, an object of the present invention is to provide an ash treatment method in waste treatment suitable for gasification and melting.

[0005]

In order to solve the above-mentioned problems, in the present invention, waste is gasified by pyrolysis and gasification using a gasification furnace, followed by high-temperature combustion using a melting furnace. In the ash treatment method in waste treatment, the collected ash obtained from at least one of the cooling, heat exchange, and dust removal steps of the exhaust gas from the melting furnace is suspended in an acidic solution. After eluting the contained heavy metals and salts,
The solid content is separated as dewatered sludge and supplied again to the fluidized bed gasification furnace or melting furnace to form slag. In the ash treatment method, the heavy metal can be insolubilized and recovered by adding an alkali agent to the aqueous solution after the heavy metal and salts are eluted and the solid content is separated. The recovered heavy metals can be recycled and, if necessary, salts can be recovered. In the present invention, high-temperature combustion in a melting furnace does not necessarily mean complete combustion, but includes a case where a char or the like entrained by a pyrolysis gas from a gasification furnace is gasified by partial combustion. In this case, the pyrolysis gasification in the gasification furnace is preferably performed at a low temperature.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an overall configuration diagram of a gasification and melting system. In FIG. 1, 1 is a refuse pit, 2 is a refuse crane, 3 is a refuse hopper, 4 is a dust supply device, 5 is a gasifier, 6 is a noncombustibles discharge device, 7 is a vibrating sieve, 8 is a rotary melting furnace, 9 Is a slag conveyor, 10 is a waste heat boiler, 11
Is an air preheater, 12 is a economizer, 13 is a bag filter,
14 is an induction blower, 15 is a chimney, 16 is a steam turbine,
a is waste, b is air, c is silica sand, d is incombustible, e is slag, f is water, g is steam, h is ash, i is slaked lime, j
Is exhaust gas.

[0007] The waste a carried in by truck is stored in the garbage pit 1. Next, the waste is supplied to the waste hopper 3 by the waste crane 2. The waste a cut out by the dust supply device 4 provided below the waste hopper is supplied to the gasification furnace 5 by a screw feeder via a lock hopper having a gas sealing function. In the gasification furnace, a fluidized bed of silica sand is formed on the air distribution plate by the air b sent into the furnace bottom. Waste a is 450-650 ° C
Is dropped into the fluidized bed held in the furnace, and is quickly pyrolyzed into gas in the fluidized bed of the heated silica sand c while being in contact with the air b, thereby producing gas, tar, and solid carbon.
The solid carbon is pulverized and pulverized by the disturbance motion of the fluidized bed. Air b is also blown into the free board of the gasification furnace 5, and gasification of tar and solid carbon is performed at 650 to 850 ° C. At the furnace bottom, the silica sand c and the incombustible material d are discharged by the incombustible material discharge device 6, and then the incombustible material d is recovered by classification. The incombustibles d include valuable metals such as iron, copper, and aluminum, but can be recovered in an unoxidized and clean state.

The gas exiting the gasification furnace 5 accompanied by the fine solid carbon is supplied to the primary combustion chamber of the swirling melting furnace 8 and mixed with the preheated air b in a swirling flow while being mixed with the preheated air b.
Burns fast at 200-1500 ° C. The combustion is completed in the inclined secondary combustion chamber. The ash in the solid carbon becomes slag mist due to the high temperature, and is captured by the molten slag phase on the furnace wall of the primary combustion chamber by the centrifugal force of the swirling flow. Next, it flows down the furnace wall, enters the secondary combustion chamber, and is discharged from the bottom of the slag separation section. The exhaust gas j exiting the swirling melting furnace 8 is supplied to the waste heat boiler 10, and the generated high-temperature, high-pressure steam g is guided to the steam turbine 16 to generate power. Exhaust gas j exiting the waste heat boiler 10 is supplied with air b by an air preheater 11,
In the economizer 12, the condensate f from the steam turbine 16 is preheated, and the temperature of the condensate itself drops. Next, after the dust is removed by the bag filter 13, the dust is released to the atmosphere from the chimney 15 via the induction blower 14.

FIG. 2 shows a process chart of an ash treatment method using an acidic solution according to the present invention. In FIG. 2, 17 is an ash hopper, 18 is an ash feeder, 19 is a dissolution tank, 20 is an ash sedimentation tank, 21 is a centrifugal separator, 22 is a pH adjustment tank, 23 is a heavy metal sedimentation tank, k is acid, and l is Dewatered sludge of ash, m is separated water, n is an alkaline agent, o is drainage, and p is heavy metal. The ash h collected by the waste heat boiler 10, the economizer 11, the air preheater 12, and the bag filter 12 in FIG. 1 is supplied to an ash hopper 17 after being pulverized as necessary. Next, the ash cut by the ash feeder 18 is supplied to the melting tank 19.
And suspended in an acidic solution into which an acid k such as hydrochloric acid or sulfuric acid is injected by stirring. In this way, heavy metals and salts contained in the ash dissolve into the solution side and are ionized.

The suspension in the dissolution tank 19 is transferred to an ash sedimentation tank 20, where the ash is settled and separated. The concentrated ash slurry discharged from the lower part of the ash sedimentation tank is supplied to a screw decanter type centrifugal separator 21 and dewatered. The flocculant is supplied to the centrifuge 21 as needed. The ash dewatered sludge discharged from the centrifugal separator 21 is supplied to the gasification furnace 5 or the rotary melting furnace 8 for the purpose of forming molten slag. On the other hand, the separated water m discharged from the centrifuge 21
Is slightly returned to the ash sedimentation tank 20.
The supernatant water of the ash sedimentation tank 20 is supplied to the pH adjustment tank 22. An alkaline agent n such as sodium hydroxide or sodium carbonate is supplied to the pH adjusting tank 22, and while being slowly stirred, insolubles such as hydroxides and sulfides of heavy metals are generated. Next, it is supplied to the heavy metal sedimentation tank 23, and the heavy metal insolubilized product is settled and concentrated to be separated. The recovered heavy metal insolubilized material is recycled and the supernatant water is discharged. If the salts in the supernatant water are recovered, it can be completely closed by reuse.

[0011]

By employing the ash treatment method according to the present invention, a stabilization treatment of the collected ash, which is always a problem in ordinary incineration or gasification and melting, is completely unnecessary here. As a result, an ideal environmental protection type waste treatment technology that does not generate secondary waste was established.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a gasification and melting system.

FIG. 2 is a process diagram of the ash treatment method according to the present invention.

[Explanation of symbols]

1: refuse pit, 2: refuse crane, 3: refuse hopper, 4: dust supply device, 5: gasifier, 6: incombustible discharger, 7: vibrating sieve, 8: swirling melting furnace, 9: slag conveyor, 10: waste heat boiler, 11: air preheater, 12: economizer, 13: bag filter, 14: induction blower, 15:
Chimney, 16: steam turbine, 17: ash hopper, 18:
Ash feeder, 19: dissolution tank, 20: ash settling tank, 21: centrifugal separator, 22: pH adjustment tank, 23: heavy metal settling tank a: waste, b: air, c: silica sand, d: noncombustible, e: slag, f: water, g: steam, h: ash, i: slaked lime,
j: exhaust gas, k: acid, l: ash slurry, m: separated water,
n: alkaline agent, o: drainage, p: heavy metal

Claims (2)

[Claims] An ash treatment method in waste treatment by gasification and melting in which a waste is pyrolyzed and gasified using a gasification furnace and then burnt at a high temperature using a melting furnace. The collected ash obtained from at least one of the steps of cooling, heat exchange and dust removal of the exhaust gas is suspended in an acidic solution to elute heavy metals and salts contained therein. An ash treatment method in waste treatment by gasification and melting, wherein the ash is separated as dewatered sludge and supplied again to the fluidized bed gasifier or melting furnace to form slag. 2. The disposal by gasification melting according to claim 1, wherein the heavy metal is insolubilized and recovered by adding an alkali agent to the aqueous solution from which the heavy metals and salts are eluted and the solids are separated. Ash treatment method in material processing.