JPH11197453A - Dry removing process for hydrogen chloride in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize efficiently sodium bicarbonate used for the treatment of hydrogen chloride in exhaust gas. SOLUTION: Hydrogen chloride contained in exhaust gas is absorbed by sodium bicarbonate 28 and removed therefrom, and then desalted residue 18 containing a reaction formation composed of a sodium compound reacted hydrogen chloride, unreacted sodium bicarbonate and sodium carbonate varied from sodium bicarbonate is fed as a raw material in a manufacturing process 40 of sodium bicarbonate using saline solution 25 and regenerated as sodium bicarbonate or sodium carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dry removal of hydrogen chloride from exhaust gas, and more particularly to a method for removing chlorine from exhaust gas, which is suitable for treating exhaust gas generated by combustion of general waste such as municipal waste and industrial waste. An object of the present invention is to provide a method for recycling sodium bicarbonate used in a method for dry removal of hydrogen.

[0002]

2. Description of the Related Art Chlorine-containing compounds contained in wastes are used in waste treatment in which general waste such as municipal waste and industrial waste such as waste plastic are burned or thermally decomposed. It is known to generate hydrogen chloride during combustion. Hydrogen chloride is a toxic substance,
2. Description of the Related Art Hydrogen chloride has been removed from exhaust gas discharged from waste treatment equipment. The removal of hydrogen chloride is carried out by utilizing the fact that hydrogen chloride is an acidic gas, and a wet and semi-dry method by a contact reaction with an alkaline aqueous solution such as an aqueous sodium hydroxide solution or an alkaline slurry such as a calcium hydroxide slurry. It is removed by a method such as treatment or dry treatment by a contact reaction with solid sodium bicarbonate or calcium hydroxide.

[0003] In particular, the removal method using solid sodium bicarbonate uses sodium bicarbonate, which has gentle properties and is easy to handle as compared with sodium hydroxide or the like, and removes reaction products containing reaction products. Salt residue is also solid,
It has the feature that it is easy to handle. When sodium bicarbonate is used, solid sodium bicarbonate that has reacted with hydrogen chloride in the exhaust gas generated from the waste treatment equipment is recovered as sodium chloride and a desalted residue containing unreacted sodium bicarbonate. Is done.

[0004] A method of reusing the recovered desalted residue has been proposed in Japanese Patent Publication No. 7-504880.
In this proposal, the recovered desalting residue was dissolved in water to form an aqueous solution, the aqueous solution was made alkaline, and then fly ash and insoluble polyvalent metal hydroxides were separated by filtration through a filter, and then contained in the aqueous solution. After removing the polyvalent metal component by treating it with a chelating resin, it is used in a process of producing sodium carbonate by the ammonia-soda method, or sodium bicarbonate and sodium carbonate are combined with sodium chloride by further adding hydrochloric acid or the like. After that, it has been proposed to use it as a raw material in a production process of chlorine and sodium hydroxide by electrolysis of saline.

However, since the above-mentioned method aims at recovering high-purity sodium, it is essential to separate the polyvalent metal component with a chelate resin after filtering and separating the polyvalent metal hydroxide with a filter. There is a problem that the treatment process becomes complicated, and there is a problem that the recycling efficiency of the recovered sodium salt such as sodium bicarbonate is low.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for recycling a desalted residue containing a reaction product produced by dry removal of hydrogen chloride in exhaust gas as sodium bicarbonate in a small number of steps. Is the subject.

[0007]

According to the present invention, there is provided a method for dry-removing hydrogen chloride from exhaust gas, the method comprising reacting an exhaust gas containing hydrogen chloride with sodium bicarbonate to remove hydrogen chloride from the exhaust gas. A desalted residue containing a reaction product reacted with hydrogen chloride, and the desalted residue is supplied as a raw material in a sodium bicarbonate production process using sodium chloride as a raw material, and is regenerated into either sodium bicarbonate or sodium carbonate. This is a dry removal method for hydrogen chloride in exhaust gas. Further, a method for dry-removing hydrogen chloride in exhaust gas, which is obtained by supplying a desalted residue as a raw material salt in a process for producing sodium carbonate and purifying it in a brine purification process, and then regenerating it into either sodium bicarbonate or sodium carbonate. . Further, the present invention is a dry removal method of hydrogen chloride in exhaust gas in which either regenerated sodium bicarbonate or sodium carbonate is reused for removing hydrogen chloride in exhaust gas. Further, after the exhaust gas containing hydrogen chloride separates the pyrolysis residue generated by the pyrolysis of the waste into a combustible component and a non-combustible component, the pyrolysis gas and the combustible component are separated by a combustion furnace. A dry removal method of hydrogen chloride in the exhaust gas, which is the exhaust gas generated together with the molten slag obtained by combustion in the above. And, the production process of sodium carbonate using saline as a raw material includes an ammonia-soda method, a salt and soda method,
The dry removal method described above, wherein the method is regenerated to either sodium bicarbonate or sodium carbonate using any of the methods using organic amines.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reaction between hydrogen chloride in exhaust gas and sodium bicarbonate when the hydrogen chloride in the exhaust gas discharged from an incinerator of waste or the like is dry-removed with sodium bicarbonate. The present invention provides a method for recycling sodium bicarbonate, which makes effective use of a desalted residue composed of a sodium compound such as sodium chloride, unreacted sodium bicarbonate, sodium carbonate, etc. produced by the above method.

The method of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of a waste incinerator using the method for dry-removing hydrogen chloride in exhaust gas of the present invention. The waste a supplied from the waste receiving tank 1 to the crusher 2 is crushed to a desired size, for example, 150 mm or less. The crushed waste a is charged by the conveyor 3 and passed through the screw feeder 4 to the pyrolysis reactor 5.
Supplied to The thermal decomposition reactor 5 uses, for example, a horizontal rotary drum, and its interior is kept in a low oxygen concentration atmosphere by a sealing mechanism (not shown), and is arranged on the downstream side of a combustion melting furnace 6 which is a combustor. The heated air heated by the heat exchanger (hot air heater) 7
Supplied from 1.

The waste a supplied into the pyrolysis reactor 5 by the heated air is kept at 300 to 600 ° C., usually 45 ° C.
Heated to about 0 ° C. As a result, the waste a is thermally decomposed to generate a pyrolysis gas G1 and a mainly non-volatile pyrolysis residue b. And this thermal decomposition reactor 5
The pyrolysis gas G1 and the pyrolysis residue b generated in
The pyrolysis gas G1 separated by the discharge device 8 is supplied to the burner 9 of the combustion melting furnace 6 via a line L2 which is a pyrolysis gas pipe.

Since the pyrolysis residue b is discharged at a relatively high temperature of about 450 ° C., it is cooled to about 80 ° C. by the cooling device 10 and then guided to the separation device 11 where the combustible component c And a non-combustible component d. Separation device 11
A well-known sorter, such as a magnetic separation type, a centrifugal type, or a wind separation type, is used. The combustible component c from which the non-combustible component d has been separated and removed as described above is supplied to the pulverizer 12. The crusher 12 is suitably of a roll type, a tube mill type, a rod mill type, a ball mill type or the like, and is appropriately selected depending on the properties of the waste to be treated.

The combustible component c pulverized by the pulverizer 12 is supplied to the burner 9 of the combustion / melting furnace 6 via a line L3, and the pyrolysis gas G1 is supplied by the combustion air supplied from an air line L4 by a blower 13. At the same time, it is burned in the combustion melting furnace 6 at a high temperature range of about 1300 ° C. The ash is melted by this combustion to produce a molten slag e. The molten slag e falls into the water tank 15 from the slag discharge port 14 and becomes granulated slag. The granulated slag is blocked into a predetermined shape by a device (not shown) or formed into a granular shape, and can be reused as a building material, a pavement material, or the like.

The exhaust gas G2 from the combustion and melting furnace 6 is heat-recovered in a heat exchanger 7 for heating air, and then comes into contact with sodium bicarbonate in a reactor 16 to which sodium bicarbonate 28 is supplied. And other acidic gases are removed by reaction and discharged from the chimney 17. In the reaction device 16, the exhaust gas G2 and the sodium bicarbonate 28 come into contact, and the hydrogen chloride gas in the exhaust gas is absorbed by sodium bicarbonate and removed by the neutralization reaction. The reaction product of the reaction and fly ash in the exhaust gas are separated from the exhaust gas in the reactor 16 and removed. Further, a dust collector, for example, an electric dust collector, a bag filter, or the like may be used instead of the reaction device. In the case of a bag filter, by fixing sodium bicarbonate for removing hydrogen chloride gas on the filter cloth,
An efficient reaction can be performed.

The sodium bicarbonate used in the reactor 16 is preferably 70 μm or less, more preferably 2 to 10 μm. 7
If it is larger than 0 μm, the reactivity with hydrogen chloride becomes worse and the absorption efficiency decreases. On the other hand, when the particle size of sodium bicarbonate is small, it may solidify and hinder the handling as a powder, so that a caking inhibitor may be added to increase the flowability of sodium bicarbonate. . As the anti-caking agent, those having a low bulk specific gravity and a large surface area are preferable, and examples thereof include diatomaceous earth and perlite. Further, the mixing amount of the anti-caking agent is preferably 3 to 20% by weight, more preferably 5 to 10% by weight of the weight of sodium bicarbonate.

The desalting residue 18 having absorbed the hydrogen chloride in the exhaust gas by the reactor 16 is converted into water 2 by a dissolving tank 19.
Dissolved in 0. The solution 21 of the desalted residue contains sodium chloride and sodium bicarbonate that has not reacted, sodium carbonate in which sodium bicarbonate has changed, sodium sulfate generated by the reaction with sulfur oxides in the exhaust gas, and the like. In the method of the present invention, the solution 21 is directly supplied to the sodium bicarbonate production process 40 using the salt 22 as a raw material. The solution 21 of the desalted residue is added to a salt solution tank 23 in the step of producing sodium carbonate, and purified in a step 24 of purifying saline. In the salt solution refining step 24, sodium hydroxide, calcium chloride, and the like are added to precipitate and remove polyvalent metal components contained in the raw material salt and desalted residue. The purified brine 25 dissolves the ammonia 26 and is sent to the carbonation step 27.

The carbonation step 27 can be carried out by a known method for producing sodium bicarbonate from salt, such as an ammonia-soda method, a salt and soda method, and an organic amine method. After the carbonation step 27, sodium bicarbonate is separated by crystallization. After the obtained sodium bicarbonate 28 is dried by the drying device 29, it is circulated and used for removing hydrogen chloride in the exhaust gas. In the case of the ammonia-soda method, the mother liquor 30 from which sodium bicarbonate is separated by crystallization is used for ammonia recovery in an ammonia recovery device 31, and the recovered ammonia is circulated and used. In the case of the salt and salt soda method, ammonium chloride is separated from the mother liquor 30 in an ammonium chloride separating device 32 and then circulated for use after separating ammonium chloride.

Generally, fly ash contains heavy metals, and when treated as solid waste, it is essential to fix the heavy metals by adding a chelating agent so that the heavy metals do not elute from the wastes. However, in the case of the present invention, as described later, there is no need to provide a step of immobilizing heavy metals, and a fixing agent such as a chelating agent is not required.

In the method of the present invention, since the desalting residue in which sodium bicarbonate remains is directly dissolved and circulated,
The use efficiency of sodium bicarbonate can be improved as compared with a method in which hydrochloric acid or the like is added to the remaining sodium bicarbonate to make it into salt and then reused. Further, even when the dissolving solution 21 is added to the path of the purified saline and the polyvalent metal component is mixed in the process, in the process of producing sodium bicarbonate, the circulating mother liquor is circulated for dissolving the salt. Since it is used, the polyvalent metal component contained in the purification step of the saline solution is also removed. In addition, when a large amount of the polyvalent metal component is contained in the solution 21, the solution is supplied to a tank for dissolving the salt, and then, in the salt solution refining step 24,
It may be separated from the solution. Further, the dissolving solution 21 was introduced into a precipitation layer (not shown), and the polyvalent metal component was sedimented and separated in the precipitation layer, and the supernatant was filtered to remove impurities by a known means such as a centrifuge. Salt dissolution tank 2
3 or purified saline 25.

Further, if the apparatus for producing sodium carbonate is specified as a dedicated apparatus for producing sodium bicarbonate which is circulated and used for removing hydrogen chloride from exhaust gas, the polyvalent metal component will be contained in the produced sodium bicarbonate. There is no problem if mixed. Then, the polyvalent metal component is contained in sodium bicarbonate and circulates through the system, so that the polyvalent metal component can be closed. In addition, although the production of sodium bicarbonate has been described with respect to the ammonia-soda method and the sodium salt soda method, a method using an organic amine can also be used. In the above description, as an incinerator, exhaust gas treatment in an incinerator having a combustion-melting furnace with an excellent waste volume reduction rate has been described as an example, but the method for removing hydrogen chloride gas in exhaust gas of the present invention has been described. Can also be used in other incinerators, such as a fluidized bed of waste and a waste incinerator burning in a fixed bed.

[0020]

According to the method of the present invention, hydrogen chloride in the exhaust gas is reacted with sodium bicarbonate, and the obtained desalting residue is directly recycled as a raw material in the sodium carbonate production process for effective use. be able to.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

[Explanation of symbols]

1. Waste receiving tank, 2. Crusher, 3. Conveyor, 4.
... screw feeder, 5 ... pyrolysis reactor, 6 ... combustion melting furnace, 7 ... heat exchanger, 8 ... discharger, 9 ... burner, 10
... Cooling device, 11 ... Separation device, 12 ... Pulverizer, 13 ... Blower, 14 ... Slag outlet, 15 ... Water tank, 16 ... Reactor, 17 ... Chimney, 18 ... Desalination residue, 19 ... Solution tank, 20
... water, 21 ... solution, 22 ... salt, 23 ... salt dissolving tank, 24 ... salt water purification process, 25 ... purified salt water, 26 ...
Ammonia, 27: carbonation step, 28: sodium bicarbonate, 29: drying apparatus, 30: mother liquor, 31: ammonia recovery apparatus, 32: ammonium chloride separation apparatus, 40: sodium bicarbonate production step, a: waste, b: pyrolysis residue, c: combustible component, d: non-combustible component, e: molten slag, G1: pyrolysis gas, G2: exhaust gas from combustion melting furnace, G
3: Exhaust gas, L2: Pyrolysis gas line, L3: Combustible component supply line, L4: Air line

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Kenzo Yamaguchi 5-6-4 Tsukiji, Chuo-ku, Tokyo Concept Engineers Co., Ltd.

Claims (4)

[Claims] 1. A method for dry-removing hydrogen chloride from an exhaust gas, the method comprising reacting an exhaust gas containing hydrogen chloride with sodium bicarbonate to remove the hydrogen chloride from the exhaust gas and reacting the reaction product with the hydrogen chloride. Characterized in that the desalting residue is supplied as a raw material in a process for producing sodium carbonate using sodium chloride as a raw material, and is regenerated into either sodium bicarbonate or sodium carbonate. Dry hydrogen removal method. 2. The method according to claim 1, wherein the desalting residue is supplied as a raw material salt in a process for producing sodium carbonate, purified in a brine purification process, and then regenerated into either sodium bicarbonate or sodium carbonate. Or the dry removal method of hydrogen chloride in exhaust gas according to any one of the above items. 3. The method of claim 1, wherein the recycled sodium bicarbonate or sodium carbonate is reused for removing hydrogen chloride in the exhaust gas. Dry removal method. 4. An exhaust gas containing hydrogen chloride separates a pyrolysis residue generated by pyrolysis of waste into a combustible component and a non-combustible component, and then separates the pyrolysis gas with the combustible component. 4. The method for dry-removing hydrogen chloride in exhaust gas according to claim 1, wherein the exhaust gas is generated together with molten slag obtained by burning in a combustion melting furnace.