JP4456899B2 - Method and apparatus for producing salt from salt water generated when processing waste or incineration ash of waste - Google Patents

Description

This invention contains each ion of Na, NH ₄ , Ca, heavy metal 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 salt water.

  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 four methods stipulated by law is tight. The number of cases in which 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 thermal decomposition)
(2) High-temperature reactor and homogenization furnace (c) Gasification and melting, (d) Slag homogenization, (e) Gas reforming)
(3) Gas purification (f) Gas quenching (rapid cooling, 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.
Cn Hm → 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 reaction between the oxygen and carbon in the pyrolyzate (equations (3) and (4)) causes the lower temperature 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, and 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. Similarly, metals such as Al remained in the mixed salt, and the quality of the mixed salt (NaCl concentration) was lowered.

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

  The 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 the 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 studies to find a treatment method for producing a mixed salt improved, it has been found that the above problem can be solved by combining a salt water concentration step, a de-NH ₄ step, a heavy metal removal step, and a salt crystallization step. The present invention has been achieved.
That is, the configuration of the present invention is as described below.

(1) Contain each ion of Na, NH ₄ , Ca, heavy metal and Cl generated in the exhaust gas treatment system when the waste is melted and gasified or incinerated or when the incinerated ash of the waste is melted in the salt method for manufacturing the salt from brine, Ca removing step, the step of performing a salt water concentration and de-NH _4, performs heavy metal removing step, the steps of ShioAkira析steps in this order, obtained as the salt crystallization step The salt manufacturing method characterized by dehydrating the salt slurry by a dehydration process.
( 2 ) The method for producing a salt according to (1), wherein the salt crystallization step is performed by heat evaporation or vacuum heat evaporation.
( 3 ) The method for producing a salt according to ( 2 ), wherein a salt content accompanying the evaporated vapor is removed by a cyclone or a demister during the heating evaporation or the vacuum heating evaporation.

( 4 ) The method for producing a salt according to (1) to ( 3 ), wherein the heavy metal removing step is performed in a neutral region of pH 6.5 to 8.
( 5 ) The method for producing a salt according to any one of (1) to ( 4 ), wherein the step of concentrating the salt water and removing NH ₄ is performed by vacuum evaporation.
(6) The method of salt preparation above (5) to be carried out the vacuum evaporation in the step of performing said brine concentration and de-NH ₄ is as alkaline 10 to 13.5 the pH of the liquid undergoing treatment.

( 7 ) Contain each ion of Na, NH ₄ , Ca, heavy metal and Cl generated in the exhaust gas treatment system when waste gasification treatment or incineration treatment or incineration ash of waste is melt treatment in the salt producing apparatus for producing salt from salt water, comprising said apparatus, Ca removing means, evaporation means for carrying out the salt concentration and de-NH _4, heavy metals removal means, the means of the ShioAkira析means in this order, and salts A salt production apparatus comprising a dehydrating unit for dehydrating a salt slurry obtained by a crystallization unit.

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

Salt from salt water containing each ion of Na, NH ₄ , Ca, heavy metal and Cl generated in the exhaust gas treatment system when waste is melted and gasified or incinerated or when waste incinerated ash is melted In order to reuse as a valuable resource, the amount of NH _4, Al and other metals 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 heavy metal removal 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 (a) is sent to the coagulation sedimentation apparatus B. Coagulating agents (FeCl ₃ , NaOH, Na ₂ CO _3, etc.) are supplied to the coagulating sedimentation apparatus B, where Ca is coagulated and separated and discharged as sludge (b2). 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 (b1) separated from the precipitate in the coagulating sedimentation apparatus B is preheated and then sent to the vacuum evaporation apparatus C, where ammonia (c2) 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 form condensed water (an aqueous solution: c2) in which the ammonia gas 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 remaining part is supplied to an ammonia-free catalytic denitration reactor as required.

The salt water (c1) concentrated in the evaporator is sent to the coagulation sedimentation apparatus D. Here, a flocculant (FeCl ₃ or the like) and an acid are added to the salt water to make the pH 6.5 to 8 neutral, so that heavy metals are coagulated and precipitated and removed as sludge (d2). The reason why the pH is 6.5 to 8 is that the heavy metal has the lowest solubility in the neutral region.
The reason for separating the heavy metal after removing the ammonia is that ammonia tends to form a complex salt with the heavy metal, so that coexistence and separation of the heavy metal becomes difficult when ammonia coexists.

  The salt water (d1) from which the aggregate has been separated is sent to the crystallizer E. As the crystallization apparatus, a heating evaporation apparatus, a vacuum heating evaporation apparatus, or the like can be used.

  The salt slurry (e1) discharged from the crystallizer E is sent to the dehydrator F and dehydrated to obtain a mixed salt. The obtained mixed salt is carried out of the system as a product. As the dehydrator F, a centrifuge, a filter press, or the like can be used.

  The evaporated vapor discharged from the crystallizer E is condensed and then used as reused water in the system. Since the evaporated vapor discharged from the crystallizer E is used as reused water as described above, the salinity accompanying the evaporated vapor (e1) may be removed by a cyclone or demister to reduce the salinity 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.

Claims (7)

Salt from salt water containing each ion of Na, NH ₄ , Ca, heavy metal and Cl generated in the exhaust gas treatment system when waste is melted and gasified or incinerated or when waste incinerated ash is melted in the salt method for manufacturing a, Ca removing step, the step of performing a salt water concentration and de-NH _4, heavy metal removal step, performed in this order the steps of ShioAkira析step, salt slurry obtained in about salt crystallization step The salt production method characterized by dehydrating by a dehydration process. The salt production method according to claim 1 , wherein the salt crystallization step is performed by heat evaporation or vacuum heat evaporation. The salt production method according to claim 2, wherein a salt content accompanying the evaporated vapor during the heat evaporation or the vacuum heat evaporation is removed by a cyclone or a demister. The method for producing a salt according to any one of claims 1 to 3 , wherein the heavy metal removing step is performed in a neutral region of pH 6.5 to 8. The method of salt preparation according to any one of claims 1 to 4, characterized in that the step of performing said brine concentration and de-NH ₄ is carried out by vacuum evaporation. The method of salt preparation according to claim 5, wherein the vacuum evaporation in the step of performing said brine concentration and de-NH ₄ is carried out as alkaline 10 to 13.5 the pH of the liquid undergoing treatment. Salt from salt water containing each ion of Na, NH ₄ , Ca, heavy metal and Cl generated in the exhaust gas treatment system when waste is melted and gasified or incinerated or when waste incinerated ash is melted in the salt producing apparatus for producing, said apparatus, Ca removing means, evaporation means for carrying out the salt concentration and de-NH _4, heavy metals removal means, ,, and including the means of the ShioAkira析means in this order, ShioAkira析A salt production apparatus comprising dehydrating means for dewatering the salt slurry obtained by the means.

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