A waste acid treatment process for co-producing sodium metabisulfite

Abstract

The invention relates to the technical field of nitroaniline wastewater treatment, and discloses a waste acid treatment process for co-producing sodium pyrosulfite, comprising the following steps: (1) waste acid stripping, (2) absorption reaction, (3) centrifugal separation, (4) drying and packaging, and (5) tail gas treatment, wherein the alkali solution for absorbing tail gas in step (5) is saturated and then mixed into the sodium sulfite solution for absorbing sulfur dioxide in step (2); the process uses the waste acid generated in the dye production process as a raw material for sodium pyrosulfite production, and after passing through a sodium pyrosulfite production section, the waste acid is neutralized and can be directly sent to a subsequent wastewater treatment section, and the process of the invention uses sodium sulfite to replace the liquid alkali in the traditional process to neutralize the waste acid.

Description

Technical Field

[0001] The invention relates to the technical field of nitroaniline wastewater treatment, and in particular to a waste acid treatment process for co-producing sodium pyrosulfite. Background Art

[0002] Acid is an important raw material in the dye industry. A large amount of waste acid is generated during the production of various dyes and intermediates. The existing waste acid treatment process generally requires pretreatment before entering the wastewater device to neutralize the acid to neutrality. This process consumes a large amount of alkali, which increases the cost of waste acid treatment.

[0003] At present, the process of producing sodium metabisulfite generally uses sulfur or sulfur ore. The specific method is: first crush the sulfur into powder, send it into a combustion furnace with compressed air, and self-ignite at 600-800°C to obtain a gas containing 10%-13% SO2 concentration. The gas is passed into a multi-stage reactor to react with liquid alkali. When the content of sodium bisulfite in the solution reaches saturation concentration, sodium sulfate is crystallized and centrifuged, dried, and packaged to obtain sodium metabisulfite products. The traditional production process of sodium metabisulfite requires sulfur or sulfur ore as raw materials, and the production process using waste acid as raw materials has not been reported. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a waste acid treatment process for the co-production of sodium metabisulfite. The process uses the waste acid generated in the dye production process as a raw material for the production of sodium metabisulfite. After passing through the sodium metabisulfite production section, the waste acid is neutralized and can be directly sent to the subsequent wastewater treatment section. The process of the present invention uses sodium sulfite instead of liquid alkali in the traditional process to neutralize the waste acid.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A waste acid treatment process for co-producing sodium metabisulfite comprises the following steps:

[0007] (1) Spent acid stripping: The dye waste acid, the absorption section mother liquor and the sodium sulfite solid are transported to the waste acid stripping device. The waste acid stripping device is a stripping tower. The mixture of the waste acid, the absorption section mother liquor and the sodium sulfite enters the stripping tower from the top of the tower. The waste acid reacts with the sodium sulfite to produce sulfur dioxide. Hot air is introduced into the bottom of the stripping tower. The liquid and the air are in reverse contact. The sulfur dioxide resolved from the liquid enters the absorption reaction device along with the air. The waste acid in the liquid phase is neutralized by reacting with the sodium sulfite. The neutralized waste acid flows out from the bottom of the stripping tower to obtain a sulfur dioxide-containing gas and a neutralized waste acid. The neutralized waste acid enters other wastewater treatment devices for treatment.

[0008] (2) Absorption reaction: the sulfur dioxide-containing gas obtained in step (1) is introduced into a sodium sulfite solution for absorption, the tail gas is sent to a tail gas treatment section, the sodium sulfite solution is crystallized to precipitate sodium metabisulfite, and the mother liquor containing sodium metabisulfite extraction is sent to a centrifugal separation section;

[0009] (3) Centrifugal separation: The mother liquor containing sodium metabisulfite extracted from step (2) is centrifuged to obtain sodium metabisulfite which is then sent to a drying and packaging workshop. The mother liquor is then sent to a waste acid stripping section to further neutralize the waste acid or to be mixed with a sodium sulfite solution for absorbing sulfur dioxide.

[0010] (4) Drying and packaging: drying and packaging the wet sodium metabisulfite separated in step (3) to obtain the product, and sending the generated waste gas to the tail gas treatment section;

[0011] (5) Tail gas treatment: The waste gas from the absorption reaction section and the drying and packaging section is sprayed with alkali solution and passed into the tail gas absorption device for tail gas absorption treatment.

[0012] As a preferred option, the alkali solution used to absorb the tail gas in step (5) is saturated and then mixed into the sodium sulfite solution used to absorb sulfur dioxide in step (2), thereby achieving the reuse of the alkali solution.

[0013] As a preferred option, the alkaline solution for absorbing tail gas in step (5) is a sodium hydroxide solution with a molar concentration of 10%-30%.

[0014] As a preferred method, the dye waste acid is a dye waste acid with an acidity of 7%; the mass ratio of the dye waste acid added in step (1), the absorption section mother liquor and the sodium sulfite solid is 30:10:1.

[0015] As a preferred embodiment, the sodium sulfite solution in step (2) is prepared from sodium sulfite solid and deionized water, and the molar concentration of the sodium sulfite solution is 20-40%.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The process of the present invention uses waste acid generated in the dye production process as a raw material for sodium pyrosulfite production. After passing through the sodium pyrosulfite production section, the waste acid is neutralized and can be directly sent to a subsequent wastewater treatment section. The process of the present invention uses sodium sulfite instead of liquid alkali in the traditional process to neutralize the waste acid, thereby reducing the treatment cost of the waste acid and playing a role in resource saving.

[0018] The invention uses waste acid as raw material, and the sulfur dioxide gas generated does not contain dust like the sulfur dioxide gas generated by burning sulfur or sulfur ore, thereby avoiding the gas washing process required in the traditional production process, shortening the sodium pyrosulfite process, and reducing the operating workload. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the waste acid treatment process for the co-production of sodium metabisulfite. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Embodiment 1:

[0022] A waste acid treatment process for co-producing sodium metabisulfite comprises the following steps:

[0023] (1) Spent acid stripping: Dye waste acid with an acidity of 7% is transported into a stripping tower with a mass ratio of 30:10:1 with the mother liquor of the absorption section and sodium sulfite solid. The mixture of the waste acid, the mother liquor of the absorption section and sodium sulfite enters the stripping tower from the top of the tower. The waste acid reacts with sodium sulfite to produce sulfur dioxide. Hot air is introduced into the bottom of the stripping tower. The liquid and the hot air are in reverse contact. The sulfur dioxide resolved from the liquid enters the absorption reaction device along with the air. The waste acid in the liquid phase is neutralized by reacting with sodium sulfite. The neutralized waste acid flows out from the bottom of the stripping tower to obtain a gas containing sulfur dioxide and neutralized waste acid. The neutralized waste acid enters other wastewater treatment devices for treatment.

[0024] (2) Absorption reaction: the sulfur dioxide-containing gas obtained in step (1) is introduced into a sodium sulfite solution prepared from sodium sulfite solid and deionized water for absorption, wherein the molar concentration of the sodium sulfite solution is 20-40%; the tail gas is sent to a tail gas treatment section, the sodium sulfite solution is crystallized to precipitate sodium metabisulfite, and the mother liquor containing sodium metabisulfite extraction is sent to a centrifugal separation section;

[0025] (3) Centrifugal separation: The mother liquor containing sodium metabisulfite extracted from step (2) is centrifuged to obtain sodium metabisulfite which is then sent to a drying and packaging workshop. The mother liquor is then sent to a waste acid stripping section to further neutralize the waste acid or to be mixed with a sodium sulfite solution for absorbing sulfur dioxide.

[0026] (4) Drying and packaging: drying and packaging the wet sodium metabisulfite separated in step (3) to obtain the product, and sending the generated waste gas to the tail gas treatment section;

[0027] (5) Tail gas treatment: The waste gas from the absorption reaction section and the drying and packaging section is sprayed with a sodium hydroxide solution with a molar concentration of 10%-30% to the tail gas absorption device for tail gas absorption treatment; after the alkali solution is saturated, it is mixed into the sodium sulfite solution used to absorb sulfur dioxide in step (2), thereby achieving the reuse of the alkali solution.

[0028] In this example, 1400 kg of dye waste acid with an acidity of 7% consumes 450 kg of sodium sulfite solid to carry out the above process operation, and finally obtains 346 kg of sodium pyrosulfite product with a purity of 95%. After neutralization, the acidity of the waste acid is reduced to 1%, so that the waste acid is neutralized, the treatment cost of the waste acid is reduced, and the effect of resource saving is achieved;

[0029] By utilizing the process of the present invention, for every 1000kg of sodium sulfite input, the amount of 190kg of 30% liquid caustic soda can be reduced, and 247kg of sodium metabisulfite can be produced. Excluding operating costs, an economic benefit of 216 yuan is generated. Assuming that the process of the present invention replaces the 200,000 tons of sodium metabisulfite market, 180 million yuan of waste acid treatment costs can be saved.

[0030] At the same time, the sulfur dioxide gas produced by using waste acid as raw material will not contain dust like the sulfur dioxide gas produced by burning sulfur and sulfur ore, avoiding the gas washing process required in the traditional production process, shortening the sodium metabisulfite process and reducing the operating workload.

[0031] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A process for treating waste acid for co-production of sodium metabisulfite, characterized in that: The following steps are involved: (1) Waste acid stripping: The dye waste acid, the absorption section mother liquor and the sodium sulfite solid are transported to the waste acid stripping device, and air is used for stripping to obtain sulfur dioxide-containing gas and neutralized waste acid. The neutralized waste acid is then sent to other wastewater treatment devices for treatment; (2) Absorption reaction: the sulfur dioxide-containing gas obtained in step (1) is introduced into a sodium sulfite solution for absorption, the tail gas is sent to a tail gas treatment section, the sodium sulfite solution is crystallized to precipitate sodium metabisulfite, and the mother liquor containing sodium metabisulfite extraction is sent to a centrifugal separation section; (3) Centrifugal separation: The mother liquor containing sodium metabisulfite extracted from step (2) is centrifuged to obtain sodium metabisulfite which is then sent to a drying and packaging workshop. The mother liquor is then sent to a waste acid stripping section to further neutralize the waste acid or to be mixed with a sodium sulfite solution for absorbing sulfur dioxide. (4) Drying and packaging: drying and packaging the wet sodium metabisulfite separated in step (3) to obtain the product, and sending the generated waste gas to the tail gas treatment section; (5) Tail gas treatment: The waste gas from the absorption reaction section and the drying and packaging section is sprayed with alkali solution and passed into the tail gas absorption device for tail gas absorption treatment.

2. A waste acid treatment process for co-producing sodium metabisulfite according to claim 1, characterized in that: The alkali solution used to absorb the tail gas in step (5) is saturated and then mixed into the sodium sulfite solution used to absorb sulfur dioxide in step (2).

3. A waste acid treatment process for co-producing sodium metabisulfite according to claim 2, characterized in that: The alkali solution for absorbing tail gas in step (5) is a sodium hydroxide solution with a molar concentration of 10%-30%.

4. A waste acid treatment process for co-producing sodium metabisulfite according to claim 1, characterized in that: The dye waste acid is dye waste acid with an acidity of 7%.

5. A waste acid treatment process for co-producing sodium metabisulfite according to claim 4, characterized in that: The mass ratio of the dye waste acid, the absorption section mother liquor and the sodium sulfite solid added in step (1) is 30:10:

1.

6. A waste acid treatment process for co-producing sodium metabisulfite according to claim 1, characterized in that: In step (2), the sodium sulfite solution is prepared from sodium sulfite solid and deionized water, and the molar concentration of the sodium sulfite solution is 20-40%.

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