JP2000328070A - Waste gasification method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When performing primary gasification with a low-temperature gasifier and secondary gasification with a high-temperature gasifier, surplus low-pressure steam heat is recovered and generated during waste plastic processing. Neutralizes and removes hydrogen chloride, improving overall system efficiency and economy. SOLUTION: A low-temperature gasification step in which organic waste is supplied to a low-temperature gasifier for primary gasification, and the obtained gaseous substance is introduced into a high-temperature gasifier to be secondary-gasified at high temperature. A high-temperature gasification dust-removing step of removing and cleaning the obtained synthesis gas with a gas cleaning tower, a gas cooling-purifying step of cooling and purifying the cleaning gas, and a slag collecting step of collecting slag discharged from the high-temperature gasification step. In the waste gasification treatment including a wastewater treatment step of treating wastewater from the slag recovery step,
An ammonium chloride recovery facility was provided during the wastewater treatment step, and the wastewater was evaporated under reduced pressure using low-pressure steam as a main heat source to concentrate and crystallize ammonium chloride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for gasification of waste by a low-temperature gasifier and a high-temperature gasifier, and particularly to municipal solid waste, sewage sludge, waste plastic, waste FRP, biomass waste, and automobile waste. Gasification and combustion of waste oil and other organic waste, and discharges the metals contained in the waste in an unoxidized state that can be recycled, and converts gaseous substances into useful gases to convert them into resources. At the same time, improving the method of discharging slag from high-temperature gasifiers, and recovering ammonium chloride using low-pressure steam generated in the treatment plant in the wastewater treatment process, resulting in efficient and economical waste The present invention relates to a waste gasification processing method capable of processing.

[0002]

[Prior Art] Municipal waste, sewage sludge, waste plastic,
Organic waste typified by waste FRP, biomass waste, automobile waste, waste oil, etc. is generally reduced in volume by incineration or landfilled untreated and recycled. The amount used is negligible overall. In the above incineration process, stoker furnaces and fluidized bed furnaces have been used until now, but the high air ratio during combustion causes a large amount of exhaust gas, and the metals discharged from the furnace are oxidized. Therefore, it was not suitable for recycling. Although an increasing number of ash melting facilities are being added to such incineration facilities, the construction and operating costs of the entire system have been increased.

In order to solve such a problem, Japanese Patent Application Laid-Open No. Hei 7-332614 was invented, in which organic waste was supplied to a fluidized-bed gasification furnace and gasified at a relatively low temperature.
Along with taking out valuable metals, the generated gas is supplied to the subsequent melting combustion furnace and completely burned at a temperature higher than the melting temperature of the ash. It has been proposed to use slag to extend the life of landfill sites and to recycle them as construction materials. In the above method, a flammable gas containing unburned char is generated from waste by a fluidized bed gasifier at the former stage, supplied to a melting furnace at the latter stage, and completely baked at a high temperature, whereby dioxins of dioxins are produced. It is expected to completely decompose and convert ash to molten slag.

[0004]

By the way, chlorine derived from polyvinyl chloride and the like in waste plastics becomes hydrogen chloride in a low-temperature gasification furnace and a high-temperature gasification furnace, and hydrogen chloride in a generated gas is neutralized with ammonia. It is fixed and enters the wastewater treatment process in the form of ammonium chloride. Therefore, in order to fix hydrogen chloride, it is conceivable to use an alkali such as caustic soda, slaked lime, etc. However, if these are used, they are finally treated so as not to cause environmental deterioration and discharged out of the system. Since it is necessary, there is a problem that the equipment becomes complicated.

The present invention solves the above-mentioned problems when performing primary gasification using a low-temperature gasifier and secondary gasification using a high-temperature gasifier, and can reduce equipment costs and operation costs. It is an object of the present invention to provide a waste gasification treatment method capable of efficiently generating synthesis gas.

[0006]

In order to achieve the above object, a waste gasification treatment method according to the present invention firstly supplies an organic waste to a low temperature gasification furnace using a fluidized bed. A low-temperature gasification step of primary gasification by gasification, a high-temperature gasification and dust removal step of secondary gasification of the obtained gaseous matter in a high-temperature gasification furnace and dusting of the obtained synthesis gas in a gas cleaning tower, and a gas cleaning tower. A gas cooling / purifying step of cooling and purifying the cleaning gas of the present invention and sending it to a subsequent step; a slag collecting step of collecting slag discharged from the high-temperature gasification furnace; and a wastewater treatment of treating wastewater from the slag collecting step. In the method of gasifying waste by using the step, the low-pressure steam generated when wastewater is gasified in the wastewater treatment step is evaporated under reduced pressure as a main heat source to remove ammonium chloride from the system. I took it out It is a wastes gas treatment method. Secondly, in the first waste gasification treatment method, concentrated ammonia water is recovered by heating and dispersing the ammonia component in the condensate of the evaporating water generated by the reduced pressure evaporation of the ammonium chloride recovery equipment, and recovering the concentrated ammonia water. Water is recycled as neutralizing ammonia to the high-temperature gasification furnace and / or the gas scrubbing tower to neutralize hydrogen chloride in the gas generated from the high-temperature gasification furnace and keep the circulating water in the system to be slightly alkaline. It was decided to. Third, ammonia water obtained by recovering by washing / absorbing the ammonia content accompanying the synthesis gas from the cooling and refining step with ammonia-free washing water obtained by heating and dispersing the ammonia gas is used as the ammonia water. The second waste gasification treatment method is characterized in that the waste gasification treatment method is used as at least a part of the aqueous ammonia. Fourthly, in the second or third waste gasification method, the ammonia generated in the low-temperature gasification furnace and the high-temperature gasification furnace is also recovered and used for neutralization by the above method. is there. Fifth
In the first or second waste gasification treatment method, an electrodialysis method (EO method) using an ion exchange membrane before treating wastewater flowing into a wastewater treatment step with an ammonium chloride recovery facility. Alternatively, the wastewater is pre-concentrated by a reverse osmosis method (RO method) using a reverse osmosis membrane. Sixth, in any one of the first to fifth waste gasification treatment methods, at least a part of the slurry water extracted from the gas washing tower is recycled to the high-temperature gasification furnace and used as quenching water. I decided that.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Organic waste is contacted with an oxygen-containing gas at a relatively low temperature (550 to 850 ° C.) by a low-temperature gasification furnace, and pyrolyzed into gas to convert the waste into primary gas. The obtained gaseous matter and a small amount of solid matter are introduced into a high-temperature gasification furnace, where a high temperature (1200 to 1600 ° C.)
By making it contact with the oxygen-containing gas again below, it is converted into a secondary gas to generate a synthesis gas mainly composed of H ₂ (hydrogen) and CO (carbon monoxide) as a synthesis gas. The gasification pressure is usually from normal pressure to 90 atm, preferably from 10 to 40 atm.
Atmospheric pressure. In this case, by using a low-temperature gasification furnace as an internal circulation type fluidized bed furnace, organic waste can be supplied in a pretreatment of roughly crushing degree, and by using oxygen gas as a gasifying agent. The oxygen concentration in the fluidizing gas can be adjusted arbitrarily. This lowers the oxygen concentration in the fluidized gas to prevent agglomeration (agglomeration) of the contents of the fluidized bed, and reduces the metal contained in the waste to an unoxidized state by using a reducing atmosphere in the furnace. It becomes possible to collect it.

Hereinafter, specific embodiments of the waste gasification treatment according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow sheet of the ammonium chloride recovery facility. A first embodiment of the present invention will be described with reference to FIG. In the gasification treatment apparatus, chlorine derived from polyvinyl chloride and the like in waste plastics becomes hydrogen chloride in a low-temperature gasification furnace and a high-temperature gasification furnace, and hydrogen chloride in the generated gas is neutralized and fixed with ammonia to form ammonium chloride. In the form of wastewater treatment process. On the other hand, the gasification processing apparatus is a heating system,
Excess heat comes out as low-pressure steam mainly in the gas cooling and refining process and the slag recovery process. The pressure of this steam is 0
Since it is about ² kg / cm ² G, effective heat recovery cannot be expected by a normal method. In the method of the present invention, an ammonium chloride recovery facility is provided in the wastewater treatment step, and wastewater flowing from the slag recovery step to the wastewater treatment step is evaporated under reduced pressure using the recovered low-pressure steam as a heat source, and the ammonium chloride is crystallized out of the system as a crystal. By taking it out, the heat of the recovered low-pressure steam can be used effectively, avoiding the accumulation of ammonium chloride in the system,
In addition, ammonium chloride is extracted to the outside as a valuable product.

The evaporation under reduced pressure is carried out, for example, in the step shown in FIG. 65 ° C. wastewater containing 0.66% ammonium chloride is heat-exchanged by low-pressure steam (about 100 ° C.) coming from the gas cooling and refining step in the circulation heater 210,
Evaporate at 355 Torr at 80 ° C. under reduced pressure to concentrate ammonium chloride to a concentration of about 1%. Since the aqueous ammonium chloride solution becomes highly corrosive when the temperature exceeds 80 ° C.,
It is desirable to evaporate at a temperature of 0 ° C. or less.
The concentrated solution is further concentrated and crystallized in a crystallizer 214 at 100 Torr and 50 ° C. to obtain a slurry water having a concentration of 36%, and a product (ammonium chloride crystal) is separated and collected by a centrifuge 216. The separated liquid from the centrifugal separator 216 is diluted to a concentration of about 10% with a part of the concentrated liquid (concentration of about 1%) from the evaporator 212 and sent back to the crystallization can 214. And / or blow into the high temperature gasifier combustion chamber. This prevents impurities such as heavy metals dissolved in the liquid from accumulating in the ammonium chloride recovery step, and evaporates entrained water in the gasification furnace to remove impurities such as heavy metals remaining in the molten slag in the high-temperature gasification furnace. In order to fix it.

FIG. 2 is a block process diagram showing each process of the entire gasification treatment apparatus. A second embodiment of the present invention will be described with reference to FIG. Wastewater treatment process In the ammonium chloride recovery equipment, excess ammonia is entrained in the evaporative water generated during the ammonium chloride concentration process and low-pressure steam generated by the two-stage flash in the slag recovery process used as a heat source. The excess ammonia is recovered as concentrated aqueous ammonia by subjecting the condensate to heat dissipation. The concentrated ammonia water is recycled to a high-temperature gasifier and / or a gas washing tower, and is reused for neutralizing and fixing hydrogen chloride in the generated gas. The ammonia that accompanies the synthesis gas from the gas cooling and refining step is also washed and absorbed with the washing water from which the ammonia from the heat dissipation is removed, collected, recycled to a high-temperature gasification furnace and / or a gas washing tower, and similarly. Reuse. Also, in order to prevent corrosion of the apparatus and piping, the concentrated ammonia water is added in excess of the theoretical amount required for fixing hydrogen chloride, and the excess is recycled to maintain the circulating water in the system at a weak alkalinity (pH 7 to 9). I do.

In a conventional synthesis gas production apparatus using fossil fuel or the like as a raw material, nitrogen in fuel reacts with hydrogen in a furnace in a reducing atmosphere to synthesize ammonia. Since it was necessary to extract this ammonia out of the system, it was necessary to separately provide an ammonia removing device. In the method of the present invention, since organic wastes such as waste plastics are used as raw materials, ammonia, which was conventionally unnecessary, is only effective for neutralizing and fixing hydrogen chloride generated from chlorine-based plastics. In addition to that, it is possible to prevent the corrosion of the apparatus by supplying ammonia in a slightly excess amount necessary for the neutralization fixation and circulating the excess ammonia to keep the reaction system weakly alkaline. The effect was obtained. That is, in the prior art, the ammonia generated in the gasification furnace was treated as "a troublesome substance", and it was necessary to provide a special separation / extraction facility to prevent the accumulation in the system. According to the method, the "complicated objects" are also collected and used effectively.

For fixing hydrogen chloride, there is a method using an alkali other than ammonia, such as caustic soda and slaked lime.
When these are used, they need to be treated and discharged out of the system so as not to eventually cause environmental deterioration, so that the equipment for this is complicated. In the method of the present invention, since ammonia, which is a volatile alkali, is used, excess ammonia in the wastewater can be volatilized and recovered and rationally recycled. When ammonia is produced from the synthesis gas generated in the gasification plant, a part of the product can be used as the neutralizing ammonia, so that there is no need to supply ammonia from outside.

FIG. 3 is a flow chart showing a pre-concentration step of wastewater by the electrodialysis method. A third embodiment of the present invention will be described with reference to FIG. The undiluted solution (waste water from the slag recovery process) is collected in a tank 410, where the concentration of ammonium chloride is adjusted to, for example, 5,000 mg / L with water if necessary, and then the cation exchange membrane and the anion exchange membrane are used. 1 to 3 kg / cm ^{2 by the} pump 414 to the electrodialyzer 412 to be used.
It is fed at a pressure of Chloride and ammonium ions are concentrated in anode water and cathode water, respectively, and collected in tank 416. The concentrated solution (ammonium chloride concentration: about 20,000 mg / L) extracted from the tank 416 is sent to a vacuum evaporation crystallization facility. The treatment liquid (ammonium chloride concentration 500 mg / L) is returned to the system as circulating water and reused. By inserting this equipment into the ammonium chloride recovery equipment and pre-concentrating it, the concentration of ammonium chloride can be concentrated up to four times, so that the amount of the processing solution can be reduced to about 1/4. The scale of the crystallization equipment can be greatly reduced. A similar effect can be obtained by using a reverse osmosis method using a reverse osmosis membrane instead of the above electrodialysis method.

FIG. 4 is a flow chart showing slurry water circulation between the high temperature gasifier and the gas scrubber. A fourth embodiment of the present invention will be described with reference to FIG. The gaseous matter flowing from the low-temperature gasifier into the high-temperature gasifier 100 is converted into a secondary gas by a partial oxidation reaction in the high-temperature gasifier, and H ₂ (hydrogen), CO 2
(Carbon monoxide) -based synthesis gas is generated, and the gas cleaning tower 5
Washed at 10. High temperature gasifier 100 and gas cleaning tower 5
The slurry water extracted from 10 is sent to a wastewater treatment step through a slag collection step, and ammonium chloride is collected. In terms of the material balance, the amount of this withdrawn is set such that the concentration of ammonium chloride in the circulating water can be adjusted to a level acceptable for using inexpensive carbon steel, for example, 5,000 ppm to 6,000 ppm.
In order to maintain the concentration at 0 ppm or less, the amount may be appropriate to the concentration of ammonium chloride (for example, about 20 m ³ / H).

In the high-temperature gasification furnace, the reaction is performed at a high temperature of 1200 to 1600 ° C., so that the generated gas and slag descending through the downcomer pipe 111 are cooled. For example, 70 m ³ / H) of cooling water is required. Therefore, in the conventional method, it is necessary to bring extra water from the low-pressure system outside the high-temperature gasification and dedusting process in an amount more than necessary in terms of the material balance. It was extremely uneconomical in this respect.

On the other hand, the method of the present invention circulates a large amount (eg, 70 m ³ / H) of slurry water between the high temperature gasifier 100 and the gas cleaning tower 510 as shown by a dotted line in FIG. It is to be. That is, the gas cleaning tower 5
Slurry water 1 (70 m ³ /
H) is recirculated to the high-temperature gasification furnace 100 as the slurry water 2 for cooling the downcomer 111 and the slurry water 3 for quench spray. From the bottom of the high-temperature gasifier 100, for example, 50 m ³
/ H slurry water 4 is withdrawn and circulated to the gas cleaning tower 510 using its own pressure. At this time, the gas cleaning tower 51
The supply circulating water 5 to 0 and the slurry water 6 extracted in the slag recovery step may be, for example, 20 m ³ / H.

As described above, according to the method of the present invention, most of the cooling water required by the high-temperature gasifier can be covered by the circulating slurry water, and the amount of cooling water supplied can be greatly reduced. And the heat balance and boost energy can be greatly improved. The circulating slurry water system is a system in which a high carbon conversion rate can be obtained by a two-stage gasification method using organic waste raw materials with a small amount of slag, that is, unburned carbon and slag content accompanying the high-temperature gasification furnace generated gas. It is effective when there are few.

[0018]

As described above, an ammonium chloride recovery facility is provided in the wastewater treatment step, and the wastewater flowing from the slag recovery step to the wastewater treatment step is evaporated under reduced pressure using the recovered low-pressure steam as a heat source to remove ammonium chloride. By taking out the crystals as crystals outside the system, it is possible to effectively utilize the heat of the recovered low-pressure steam, avoid the accumulation of ammonium chloride in the system, and extract ammonium chloride as valuable products to the outside. The efficiency and economy of the whole processing system can be improved.

In order to fix hydrogen chloride, there is a method using an alkali other than ammonia, such as caustic soda and slaked lime. However, when these are used, they are treated so as not to eventually cause environmental deterioration, and are thus treated outside the system. However, there is a problem that the equipment for this purpose is complicated.
On the other hand, in the method of the present invention, since ammonia, which is a volatile alkali, is used, excess ammonia in the wastewater can be volatilized and recovered and rationally recycled.

[Brief description of the drawings]

FIG. 1 is a flow sheet of an ammonium chloride recovery facility according to an embodiment of the present invention.

FIG. 2 is a block process diagram showing each process of the entire gasification processing apparatus according to the embodiment of the present invention.

FIG. 3 is a flowchart showing a wastewater preconcentration step by an electrodialysis method according to an embodiment of the present invention.

FIG. 4 is a flow chart showing slurry water circulation between a high temperature gasifier and a gas cleaning tower according to an embodiment of the present invention.

[Explanation of symbols]

 100 high temperature gasifier 111 downcomer 114 slag lock hopper 118 slag pot 122 vibrating sieve 210 circulation heater 212 evaporator 214 crystallizer 216 centrifuge 318 pump 410 tank 412 electrodialyzer 414 pump 416 tank 510 gas washing tower

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/44 C02F 1/44 E1 / 469 C10K 1/02 C10K 1/02 1/12 1/12 F23G 5/027 ZABZ F23G 5/027 ZAB F23J 1/00 B F23J 1/00 1/08 1/08 C02F 1/46 103

Claims (6)

[Claims] 1. A low-temperature gasification step in which organic waste is supplied to a low-temperature gasifier using a fluidized bed to convert it into a primary gas, and the obtained gaseous substance is converted into a secondary gas in a high-temperature gasifier. A high-temperature gasification and dust removal step of removing the synthesized gas by a gas cleaning tower, a gas cooling and purification step of cooling and refining the cleaning gas from the gas cleaning tower and sending it to a post-process, and discharging from the high-temperature gasification furnace In a method of gasifying waste using a slag collection step of collecting slag to be collected and a wastewater treatment step of treating wastewater discharged from the slag collection step, the wastewater is gasified by the wastewater treatment step. A waste gasification method characterized in that low-pressure steam generated at that time is used as a main heat source and evaporated under reduced pressure to extract ammonium chloride out of the system. 2. A concentrated ammonia water is recovered by heating and dispersing an ammonia component in a condensate of the evaporating water generated by the reduced pressure evaporation in the ammonium chloride recovery step, and the concentrated ammonia water is used as the neutralizing ammonia in the high-temperature gasification. 2. The method according to claim 1, wherein the recirculation to the furnace and / or the gas washing tower neutralizes the hydrogen chloride in the gas generated from the high-temperature gasification furnace and keeps the circulating water in the system to be slightly alkaline. Waste gasification method. 3. Ammonia water obtained by recovering by washing and absorbing ammonia contained in the synthesis gas from the cooling and refining step with ammonia-free washing water obtained by heating and dispersing the ammonia gas, The waste gasification treatment method according to claim 2, wherein the waste gasification treatment is used as at least a part of the aqueous ammonia. 4. The waste according to claim 2, wherein the ammonia generated in the low-temperature gasification furnace and the high-temperature gasification furnace is recovered and used as at least a part of the neutralizing ammonia. Gasification method. 5. An electrodialysis method (EO method) using an ion exchange membrane or a reverse osmosis method (RO method) using a reverse osmosis membrane before treating wastewater flowing into the wastewater treatment step with an ammonium chloride recovery facility. The method according to any one of claims 1 to 2, wherein the wastewater is pre-concentrated by the method (1). 6. The method according to claim 1, wherein at least a part of the slurry water extracted from the gas cleaning tower is recirculated to the high-temperature gasification furnace and used as quenching water. Waste gasification method.