JP2006213535A - Method of and apparatus for producing salt from salt water generated when waste materials are treated in gasification-melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a high-quality mixed salt from the waste water of a gasification-melting furnace. <P>SOLUTION: This method comprises producing salt from the salt water which is generated in an exhaust gas treatment system when waste materials are subjected to melting/gasifying treatment or incineration or when the incineration ash of the waste materials is melt-treated, and contains respective ions of Na, NH<SB>4</SB>, Ca and Cl. The method is characterized by including at least the processes of salt water concentration, NH<SB>4</SB>removal and salt crystallization, and dehydrating salt slurry obtained from the salt crystallization process through a dehydrating process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention is a salt water containing each ion of Na, NH ₄ , Ca, and Cl generated in an exhaust gas treatment system when waste gasification treatment or incineration treatment or waste incineration ash is fusion treatment. The present invention relates to a salt production method and apparatus for producing a salt from the same.

  Conventionally, incineration treatment of industrial waste or general waste has been carried out in various types, but in recent years, emission standards for trace hazardous substances such as dioxins in exhaust gas at incineration plants have been strengthened, The remaining amount of landfills mainly for stable landfills that incinerate incinerated main ash, and the amount of landfilled landfills for landfills after intermediate treatment of incinerated fly ash by one of the four methods stipulated by law is tight. The number of cases where it is difficult to renew and follow the conventional incineration treatment type is increasing. Also, from the viewpoint of creating a resource recycling society, rather than simply incinerating waste, a system that recovers fuel gas or chemical raw material gas by gasifying the waste and reforming it at a high temperature (non- Patent Document 1) is desired.

As such a gasification reforming-type incineration facility, a waste gasification and melting process based on the Kawatetsu thermoselect method having a process flow as shown in FIG. 1 has been developed (see Non-Patent Document 2).
This process consists of the following four steps.

(1) Press and degassing channels (a) Waste (waste) compression, (b) Drying and pyrolysis (2) High temperature reactor and homogenization furnace (c) Gasification and melting, (d) Slag homogenization, (E) Gas reforming (3) Gas purification (f) Gas quenching (quenching, acid cleaning, alkali cleaning), (g) Gas purification (dust removal, desulfurization, dehumidification)
(4) Water treatment (h) Water treatment / salt production equipment

The outline of each step is as follows.
(1) Press / degas channel (a) First, the waste transferred from pit 1 is compressed to about 1/5 of the initial volume by press 2. Thereby, the distribution of moisture in the waste is made uniform, air is excluded, and the degassing efficiency is improved.
(B) Next, the compressed waste is degassed in the degassing channel 3 which is an indirect heating furnace (evaporation of moisture, generation of volatile components by thermal decomposition), and then radiant heat from the high temperature reactor 4 etc. Is further thermally decomposed. There are the following reaction examples (formulas (1) and (2)) as thermal decomposition reactions of hydrocarbons and cellulose contained in waste, and pyrolytic carbon is obtained by these reactions.
CnHm → xCH ₄ + yH ₂ + zC (1)
3C ₆ H ₁₀ O ₅ → 8H ₂ O + C ₆ H ₈ O + 2CO ₂ + 2CO
+ CH ₄ + H ₂ + 7C (2)

(2) High-temperature reactor / homogenization furnace (c) The gas generated in the degassing channel 3 flows into the high-temperature reactor 4, and the pyrolysate is pushed out by charging new compressed waste, and the high-temperature reactor 4 Deposit at the bottom. Oxygen produced by PSA (Pressure Swing Adsorption) 6 is blown into the lower part of the high temperature reactor 4 and the temperature of the lower part is determined by the reaction of the oxygen and carbon in the pyrolyzate (equations (3) and (4)). Reaches a maximum of about 2000 ° C. in the center, and the metal and inorganic components in the waste melt.
C + O ₂ ＣＯ CO ₂ + ΔQ (3)
C + 1 / 2O ₂ ⇔CO + ΔQ (4)

The carbon component remaining in the lower part of the high temperature reactor 4 and O ₂ react exothermically to become CO ₂ . The generated CO ₂ is reduced to CO when it passes through the pyrolyzate containing C (formula (5)).
C + CO ₂ ⇔ 2CO-ΔQ (5)
In the presence of excess hot water vapor molecules, a water gasification reaction occurs. In this case, carbon and water vapor are converted into CO and H ₂ (formula (6)).
C + H ₂ O ＣＯ CO + H ₂ −ΔQ (6)
The organic compound is thermally decomposed into CO and H ₂ (formula (7)).

CnHm + nH ₂ O → nCO + (n + ½ m) H ₂ −ΔQ (7)
(D) The melt flows from the high temperature reactor 4 to the soaking furnace 5 maintained at about 1600 ° C., and a small amount of carbon is gasified. In the homogenization furnace 5, the metal melt (metal) has a high density and therefore accumulates in the lower part of the inorganic melt (slag). These continuously flow through the overflow weir and flow down to the granulation system 7 to be cooled and solidified. The recovered mixture cooled and solidified is separated into slag and metal by magnetic separation.

(E) The gas generated in the lower part of the high temperature reactor 4 and the pyrolysis gas generated in the degassing channel merge and stay in the reforming part in the upper part of the high temperature reactor 4 at about 1200 ° C. for 2 seconds or longer. Under these conditions, the tar content, dioxins and their precursors in the gas are completely decomposed and reformed into a crude synthesis gas mainly composed of H ₂ , CO, CO ₂ and H ₂ O. At a temperature of about 1200 ° C., the equilibrium of equation (8) shifts to the right side, and the amount of methane gas becomes extremely small.
CH ₄ + H ₂ O⇔CO + 3H ₂ (8)

(3) Gas purification (f) The crude synthesis gas reformed in the high-temperature reactor 4 was rapidly water-cooled from about 1200 ° C. to about 70 ° C. with the quenching device 8 to prevent re-synthesis of dioxins by de novo synthesis. Thereafter, in the washing tower 11, heavy metals are removed by acid washing, and acid gases are removed by alkali washing.
Here, heavy metal components such as Zn and Pb having a low boiling point are mainly transferred from the high temperature reactor 4 in a gas state. Further, chlorine contained in the waste is mainly present in the synthesis gas as HCl, and HCl is dissolved in the cooling / cleaning liquid. The crude synthesis gas is washed with the acidic water (pH 2 to 3) containing HCl, and heavy metal components are removed (for example, formulas (9) and (10)). Therefore, fly ash is not generated in this process.
Zn + 2HCl → H ₂ + ZnCl ₂ (9)
Pb + 2HCl → H ₂ + PbCl ₂ (10)

  Thus, in this process, the chlorine content in the waste is effectively utilized. The cleaning liquid is sent to the settling tank 12 to remove the carbon fine particles, indirectly cooled by the heat exchanger 15A, and then circulated and used again for rapid cooling of the gas. The water derived from the garbage becomes surplus water in the settling tank 12 and is sent to the water treatment device 13 for processing.

The acid-cleaned synthesis gas is alkali-cleaned, and an acidic gas such as hydrogen chloride gas is neutralized and removed (formula (11)). The produced NaCl is finally recovered as a mixed salt by the salt production device 14.
HCl + NaOH → NaCl + H ₂ O (11)

  (G) Further, the gas is sent from the washing tower 11 to the multi scrubber 9 to be dedusted, desulfurized and washed, dehumidified and dried to become a clean refined synthetic gas from which harmful substances have been removed. Used as fuel gas.

(4) Water treatment (h) H ₂ O produced until the gas reforming process is condensed in the gas quenching / refining process, and heavy metals and salts contained in the exhaust gas as fly ash in the conventional incineration system Move all into the wash water. Therefore, fly ash is not generated, and water containing metals such as Fe, Zn, Pb, Na, and K is generated, but the metal is recovered by the water treatment device 13 as useful substances such as hydroxides and mixed salts. The
Moreover, NaCl produced | generated by reaction of (11) Formula is sent to the salt manufacturing apparatus 14 from the water treatment apparatus 13, is refine | purified, and is collect | recovered as mixed salt.

By the way, in order to reuse the above mixed salt as a valuable material, the amount of metals such as NH _{4 and} Al contained in the mixed salt must be reduced.
However, general waste contains about 0.5 to 2% (5000 to 20000 mg / kg) of nitrogen in combustibles, and this nitrogen content is in the case of thermal decomposition performed in a reducing atmosphere with less air. Is partly converted into ammonia, which is contained in the crude synthesis gas, reacts with hydrogen chloride in the gas during quenching to acid cleaning to produce ammonium chloride, which dissolves in the cleaning solution and is washed In the case of recovering the mixed salt from the waste liquid (cleaning liquid after being used for cleaning), there has been a problem that the grade (NaCl concentration) of the mixed salt is lowered and its use is restricted.

Ministry of Health and Welfare: Ministry of Health and Welfare Ordinance No. 14, March 3, 1999 "Gasification reforming system" Kawasaki Steel Technical Report 32 (2000) 4, 287-291

  An object of the present invention is to produce a high-quality mixed salt from the waste water of a gasification melting furnace and to collect water as reused water in a plant.

In the waste treatment system that solves these problems, gasifies and reforms waste, and cleans and purifies to obtain purified synthesis gas, the quality of the waste waste liquid is reusable as a resource. As a result of intensive investigations to find a treatment method for producing a mixed salt with improved quality, it was found that the above problem can be solved by combining a salt water concentration step, a de-NH ₄ step, and a salt crystallization step. Has been reached.
That is, the configuration of the present invention is as described below.

(1) From salt water containing each ion of Na, NH ₄ , Ca, Cl generated in an exhaust gas treatment system when waste is melted and gasified or incinerated, or when waste incinerated ash is melted A salt production method for producing a salt, comprising at least a salt water concentration step, a de-NH ₄ step, and a salt crystallization step, wherein the salt slurry obtained in the salt crystallization step is dehydrated by a dehydration step. Production method.
(2) The salt production method according to the above (1), wherein the dehydration step is performed by centrifugation.
(3) The salt production method according to the above (1) or (2), wherein the salt crystallization step is performed by vacuum evaporation.
(4) The salt production method according to the above (3), wherein a salt content accompanying the evaporated vapor during the vacuum evaporation is removed by a cyclone or a demister.

(5) The method for producing a salt according to the above (1) to (4), wherein the de-NH ₄ step is performed by adding NaOH to the liquid to be treated and performing a vacuum evaporation treatment.
(6) The salt production method according to the above (5), wherein the vacuum evaporation treatment in the de-NH ₄ step is performed by vacuum evaporation using a multi-effect can.
(7) The method for producing a salt according to (5) or (6) above, wherein the vacuum evaporation treatment in the de-NH ₄ step is performed with the pH of the liquid to be treated being alkaline of 10 to 13.5.
(8) The salt production method according to any one of (1) to (7) above, wherein each of the salt water concentration step, the de-NH ₄ step, and the salt crystallization step proceeds in this order.

(9) The method for producing a salt according to (1) to (8) above, further comprising a Ca removing step of removing Ca contained in the salt water.
(10) the Ca removal step, the method of salt preparation above (9), characterized in that it is performed prior to de-NH ₄ steps.
(11) The method for producing a salt according to (9) or (10) above, wherein the steps of the Ca removal step, the salt water concentration step, the de-NH ₄ step, and the salt crystallization step proceed in this order.
(12) From salt water containing each ion of Na, NH ₄ , Ca, Cl generated in an exhaust gas treatment system when waste gasification or incineration treatment or waste incineration ash is melt treatment in the salt producing apparatus for producing salt, said apparatus, comprising at least, brine concentration means, de-NH ₄ means includes ShioAkira析means, and a dewatering means for dewatering the salt slurry obtained by ShioAkira析means The salt manufacturing apparatus characterized by having performed.

(13) From salt water containing each ion of Na, NH ₄ , Ca, Cl generated in an exhaust gas treatment system when waste is melted and gasified or incinerated or when incinerated ash of waste is melted in the salt producing apparatus for producing salt, the apparatus is, at least, Ca removal means, brine concentration means, de-NH ₄ means includes ShioAkira析means, and, dewatering the salt slurry obtained by ShioAkira析means A salt production apparatus comprising a dehydrating means.
(14) A salt produced by the salt production method of (1) to (11) above, wherein the impurity concentration is NH ₄ ≦ 10 mg / kg (dry).

  According to the present invention, when waste is gasified or incinerated, a high-quality mixed salt that can be reused as raw materials for caustic soda industry is produced from salt water containing a salt generated in a gas treatment system. be able to.

Salt is valuable from salt water containing each ion of Na, NH ₄ , Ca, Cl generated in the exhaust gas treatment system when waste is melted and gasified or incinerated, or when waste incineration ash is melted. In order to reuse it as a product, the amount of NH ₄ contained in the mixed salt must be reduced.
For example, in order to reuse salt as a caustic soda industry raw material, it is preferable to reduce the impurity concentration to the extent shown in Table 1 below.

In order to remove the impurities, the salt production method of the present invention includes at least a salt water concentration step, a de-NH ₄ step, a salt crystallization step, and further includes a Ca removal step.
An example of a process chart for carrying out the method of the present invention is shown in FIG. 2, and the present invention will be described based on this figure.

The salt raw water is sent to the coagulation sedimentation apparatus A. Coagulating agents (FeCl ₃ , NaOH, Na ₂ CO _3, etc.) are supplied to the coagulating sedimentation apparatus A, where Ca is coagulated and separated and discharged as sludge (a1). This is because Ca is likely to generate a scale in the next ammonia evaporation step, and therefore Ca is previously removed here.

  The separated liquid (a2) separated from the precipitate in the coagulating sedimentation apparatus A is preheated and then sent to the vacuum evaporation apparatus B, where ammonia (b2) is removed by evaporation. As the evaporation apparatus, it is preferable to use a vacuum evaporation apparatus that can perform an evaporation operation at a low temperature, requires a small amount of heat, and is advantageous in terms of material, and more preferably a vacuum evaporation apparatus using a multi-effect can.

  When evaporating, the treatment liquid is preferably made alkaline with a pH of 10 to 13.5. In order to remove ammonia, about pH 12.5 is necessary, and if it is less than pH 10, the removal efficiency of ammonia is poor. Moreover, since it will have a bad influence on the material of an evaporator when pH13.5 is exceeded, it is unpreferable. The evaporated ammonia is condensed in a condenser together with water vapor to become condensed water (another water) in which ammonia (b2) is dissolved. After being stored, the ammonia gas is appropriately diffused from the aqueous solution by an ammonia stripper (not shown). Part of this is decomposed into nitrogen gas and water vapor in the ammonia decomposition step, and then released to the outside of the system, and the remainder is supplied to an ammonia-free catalytic denitration reactor as required.

  The salt water (b1) concentrated by the vacuum evaporator is sent to the crystallizer C. As the crystallization apparatus, a heating evaporation apparatus, a vacuum heating evaporation apparatus, or the like can be used.

  The salt slurry (c1) discharged from the crystallizer C is sent to the dehydrator D and dehydrated to obtain a mixed salt (d1). The obtained mixed salt is carried out of the system as a product, and the separated water (d2) is returned to the crystallizer C. As the dehydrator D, a centrifuge, a filter press, or the like can be used.

  The evaporated vapor (c2) discharged from the crystallizer C is condensed and then used as reused water in the system. Since the evaporated vapor (c2) discharged from the crystallizer C is used as reused water as described above, the salt content accompanying the evaporated vapor may be removed by a cyclone or demister to reduce the salt concentration. preferable.

Salt water generated in the gas treatment system of the gasification melting furnace (salt concentration of 1 to 5% in the salt raw water, flow rate of 350 m ³ / day) was treated by the flow shown in FIG. In the deammonification step, the pH was controlled at about 12.5.
The impurity concentration in the salt raw water and the impurity concentration in the obtained mixed salt were as shown in Table 2. As shown in Table 2, the mixed salt obtained by the method of the present invention has an impurity concentration reduced to such an extent that it can be reused as a raw material for the caustic soda industry.

  According to the method of the present invention, a salt with a low impurity concentration and high quality can be produced from raw water containing a salt such as Na discharged from a waste treatment apparatus, so that the obtained salt can be used as a raw material for caustic soda industry, etc. Can be reused.

It is a figure which shows an example of the process flowchart in the case of processing a waste material by a gasification reforming system. It is a figure which shows each process for enforcing the salt manufacturing method of this invention.

Explanation of symbols

1 Pit 2 Press 3 Degassing Channel 4 High Temperature Reactor 5 Homogenizing Furnace 6 PSA (Pressure Swing Adsorption)
7 Water cooling system 8 Quenching device 9 Multi scrubber
10 Gas engine generator
11 Washing tower
12 Settling tank
13 Water treatment equipment
14 Salt production equipment
15 Heat exchanger

Claims (14)

Manufactures salt from salt water containing Na, NH ₄ , Ca, Cl ions generated in exhaust gas treatment system when waste is melted or gasified or incinerated, or waste incinerated ash is melted A salt production method comprising: at least a salt water concentration step, a de-NH ₄ step, and a salt crystallization step, wherein the salt slurry obtained in the salt crystallization step is dehydrated by a dehydration step.   The salt production method according to claim 1, wherein the dehydration step is performed by centrifugation.   The salt production method according to claim 1 or 2, wherein the salt crystallization step is performed by vacuum evaporation.   The salt production method according to claim 3, wherein a salt content accompanying the evaporated vapor during the vacuum evaporation is removed by a cyclone or a demister. The method of salt preparation according to claim 1, wherein the de-NH ₄ step is performed by adding a vacuum evaporation process the NaOH liquid to be treated. The de-NH ₄ method of salt preparation according to claim 5, wherein the vacuum evaporation process in the step is characterized by being performed by vacuum evaporation using multiple-effect evaporator. The method for producing a salt according to claim 5 or 6, wherein the vacuum evaporation treatment in the de-NH ₄ step is performed with the pH of the liquid to be treated being alkaline of 10 to 13.5. The salt production method according to any one of claims 1 to 7, wherein each of the salt water concentration step, the de-NH ₄ step, and the salt crystallization step proceeds in this order.   The salt production method according to claim 1, further comprising a Ca removal step of removing Ca contained in the salt water. The Ca removal step, the method of salt preparation according to claim 9, characterized in that it is performed prior to de-NH ₄ steps. The method for producing a salt according to claim 9 or 10, wherein each of the Ca removal step, the salt water concentration step, the de-NH ₄ step, and the salt crystallization step proceeds in this order. Manufactures salt from salt water containing Na, NH ₄ , Ca, Cl ions generated in exhaust gas treatment system when waste is melted or gasified or incinerated, or waste incinerated ash is melted In the salt producing apparatus, the apparatus includes at least a salt water concentrating means, a de-NH ₄ means, a salt crystallization means, and a dehydrating means for dehydrating the salt slurry obtained by the salt crystallization means. A salt production apparatus. Manufactures salt from salt water containing Na, NH ₄ , Ca, Cl ions generated in exhaust gas treatment system when waste is melted or gasified or incinerated, or waste incinerated ash is melted In the salt manufacturing apparatus, the apparatus includes at least a Ca removing unit, a salt water concentrating unit, a deNH ₄ unit, a salt crystallization unit, and a dehydrating unit that dehydrates the salt slurry obtained by the salt crystallization unit. A salt production apparatus characterized by comprising. A salt produced by the method for producing a salt according to claim 1, wherein the impurity concentration is NH ₄ ≦ 10 mg / kg (dry).

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