Method for treating chlorination furnace tail gas in chlorination process titanium dioxide production

Abstract

The invention provides a method for treating chlorination furnace tail gas in chlorination process titanium dioxide production, which is characterized in that primary filtrate obtained by dissolving dust collection slag generated by a chlorination furnace with water and then filtering is used for selectively absorbing chlorine in the chlorination furnace tail gas, the concentration percentage of Fe < 2 + > in the primary filtrate is 0.5%-12%, the concentration percentage of HCl is 0.1%-10%, and the concentration percentage of Cl is 0.1%-10%. Ferric chloride and chlorine in the primary filtrate react to generate ferric trichloride, chlorine in the tail gas of the chlorination furnace is removed, meanwhile, the primary filtrate is acidic and is prevented from reacting with carbon dioxide contained in the tail gas of the chlorination furnace to generate low-solubility carbonate, the output of waste is reduced, and the production cost is reduced. The problem that low-solubility carbonate generated in the chlorine gas absorption process through traditional alkali washing is separated out in a leaching tower and a pipeline, and consequently the leaching tower and the pipeline are blocked is solved. Meanwhile, the waste liquid is recycled, the treatment cost of the tail gas of the chlorination furnace is reduced, the ferric chloride solution generated after the chlorine gas is absorbed by the primary filtrate can be recycled, and the subsequent environmental protection problem is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chlorination furnace tail gas treatment, more particularly to a method for treating chlorination furnace tail gas in the production of titanium dioxide by chlorination process. BACKGROUND

[0002] Titanium tetrachloride is produced by carbon boiling chlorination of high-titanium slag, which is an efficient titanium resource extraction process and is used as a method for preparing titanium tetrachloride by most titanium dioxide production plants by chlorination process and sponge titanium production plants. The method can realize the reaction of titanium tetrachloride generated by 80% to 90% TiO2-containing titanium raw material, Cl2 and petroleum coke in a boiling chlorination furnace at 950℃, and the following chemical reactions mainly occur: TiO2+2C+2Cl2→TiCl4+2CO; TiO2+C+2Cl2→TiCl4+CO2.

[0003] In the production of titanium dioxide by chlorination process, the raw ore used in the chlorination furnace mainly contains TiO2, and also contains some elemental metals such as iron, calcium, magnesium, manganese, chromium and aluminum and oxides thereof, among which the content of iron is relatively high. In the chlorination process, these metal elements react with chlorine to produce corresponding chlorides, forming TiCl4 high-temperature gas containing FeCl2, MnCl2, VOCl2 and carbon powder. After gas-solid separation, solid phase and high-temperature gas are obtained. The solid phase is dissolved with water and then filtered to obtain a first filter cake containing carbon powder and slag and a first filtrate mainly containing FeCl2. The high-temperature gas is cooled to obtain crude TiCl4, which is refined to obtain refined TiCl4. The refined TiCl4 can be used as an important raw material for the production of sponge titanium and titanium dioxide by chlorination process.

[0004] The chlorination furnace tail gas generated after the collection of titanium tetrachloride enters the chlorination furnace tail gas treatment system. The conventional chlorination furnace tail gas treatment system is composed of a four-stage water spray washing tower and a two-stage alkali spray washing tower. The washing medium in the water washing tower is H2O, which can dissolve HCl and metal chlorides in the chlorination furnace tail gas, and can wash most of the chlorides in the chlorination tail gas. The washing medium in the alkali washing tower is NaOH solution or lime milk, which mainly removes Cl2 from the tail gas to make the chlorination tail gas meet the emission standard.

[0005] In the chlorination furnace tail gas treatment process, the liquid produced by water washing can be reused as hydrochloric acid, and the sodium hypochlorite or calcium hypochlorite produced by alkali washing can be sold as a byproduct. For example, the invention patent with the publication number CN103432867A discloses a comprehensive utilization method of waste hydrochloric acid generated in the chlorination leaching tail gas process in the production of titanium dioxide by chlorination process. The acid tail gas generated in the production process by chlorination method is directly passed through the water washing tower, the tail gas after water washing is then passed through the alkali washing tower, and then it is discharged after meeting the standard. Then the acid wastewater and waste residue generated in the water washing process are treated to obtain chlorides and high-purity hydrochloric acid.

[0006] But the chlorination furnace tail gas also contains a large amount of carbon dioxide, and the carbon dioxide and hydroxide in the alkali washing tower form low-solubility sodium carbonate or calcium carbonate, which is easy to precipitate on the wall of the alkali spray washing tower and the pipe wall, causing the alkali spray washing tower to be blocked, resulting in abnormal operation of the alkali spray washing tower; at the same time, the reaction of a large amount of carbon dioxide in the chlorination furnace tail gas and the alkali solution causes the alkali consumption of the alkali washing process to be higher than expected, increasing the production cost; in addition, the by-product sodium hypochlorite obtained by the process has the problem of many impurities, which is not conducive to the sale of the product and cannot be effectively recycled. Therefore, a low-cost method for treating chlorination furnace tail gas is needed to overcome the problem of blocking the washing tower and the pipe. SUMMARY

[0007] In view of the above, the present application provides a method for treating chlorination furnace tail gas in the production of chlorination method titanium dioxide, selectively absorbing chlorine in the chlorination furnace tail gas, solving the problem of blocking the washing tower and the pipe caused by the formation of low-solubility substances in the traditional alkali washing process.

[0008] The present application provides a method for treating chlorination furnace tail gas in the production of chlorination method titanium dioxide, which uses a primary filtrate obtained by dissolving the dust collection residue generated by the chlorination furnace with water and filtering to selectively absorb chlorine in the chlorination furnace tail gas, wherein the concentration percentage of Fe 2+ in the primary filtrate is 0.5% to 12%, and the concentration percentage of HCl is 0.1% to 10%.

[0009] FeCl2 contained in the primary filtrate can react with Cl2 to generate FeCl3, which can effectively absorb chlorine in the chlorination furnace tail gas, and at the same time, the primary filtrate is acidic, and the metal ions therein will not react with CO2, having the property of selectively absorbing chlorine in the chlorination furnace tail gas, and will not form low-solubility carbonate substances during the absorption of chlorine, avoiding the problem of blocking the washing tower and the pipe; wherein the concentration percentage of Fe 2+ is 0.5% to 12% and the concentration percentage of HCl is 0.1% to 10% is a suitable concentration range; wherein the concentration of Fe 2+ should not be too large, and a too large concentration will cause saturation and precipitation of crystals, and a too small concentration of Fe 2+ will not achieve the expected effect of chlorine absorption; and a too small concentration of HCl will cause the reaction of basic substances to generate low-solubility substances, and a too large concentration of HCl will cause FeCl2 crystals to precipitate due to the common ion effect.

[0010] The solid content in the primary filtrate is 0.01% to 5%, and a small amount of solid substances is allowed to exist in the filtrate, but it should not be higher than 5%, otherwise it will cause the system to be blocked and the pump to run poorly.

[0011] The total concentration percentage of other metal elements in the primary filtrate is 0.01% to 20%, and the other metal elements include Mn, Al, V, Cr, Ca, Mg and Ti.

[0012] The specific steps of the method for treating the tail gas of a chlorination furnace in the production of titanium dioxide by chlorination method include:

[0013] (1) collecting a primary filtrate obtained by dissolving dust collection residues generated by the chlorination furnace in water and filtering, and then pouring into an alkali storage tank of an alkali leaching tower of a chlorination furnace tail gas treatment system;

[0014] (2) the primary filtrate in the alkali storage tank is pumped into the top of the alkali leaching tower by a circulating pump, mixed with the tail gas of the chlorination furnace in the alkali leaching tower, and absorbs chlorine in the tail gas of the chlorination furnace, and the primary filtrate after absorbing chlorine is an absorption liquid;

[0015] (3) when the concentration percentage of Fe 3+ in the absorption liquid reaches 0.5% to 12%, the absorption liquid is discharged into an absorption liquid storage tank, and the post-treatment of the absorption liquid is reused; wherein the content of Fe 3+ is controlled because a too high content of Fe 3+ will reduce the efficiency of Cl2 absorption and is not conducive to the subsequent absorption of chlorine;

[0016] (4) the qualified tail gas of the chlorination furnace after absorbing chlorine by the primary filtrate is discharged into the atmosphere through a chimney.

[0017] The concentration of chlorine in the qualified tail gas of the chlorination furnace is ≤0.5 mg / m 3 .

[0018] The alkali leaching tower is a packed tower or an empty tower.

[0019] The alkali leaching tower is a primary tower or a multi-stage tower.

[0020] The primary filtrate is atomized by a nozzle after being pumped from the alkali storage tank to one or more positions in the upper part of the alkali leaching tower by a circulating pump and mixed with the tail gas.

[0021] The post-treatment of the absorption liquid includes adding an alkali substance, evaporation crystallization and evaporation concentration to obtain reusable products; the reusable products are used for the production of water treatment agents, the alkali substance includes ammonia water, sodium hydroxide and calcium hydroxide; the reusable products can also be used as additives for the production of iron oxide pigments or ironmaking raw materials, and the iron oxide pigments include iron oxide red, iron oxide yellow and yellow iron black.

[0022] The present application has the following beneficial effects:

[0023] The application uses the primary filtrate obtained by dissolving the dust collection residue generated by the chlorination furnace in water and filtering to selectively absorb chlorine in the tail gas of the chlorination furnace, generates ferric chloride by the reaction of the ferrous chloride in the primary filtrate and chlorine, removes chlorine in the tail gas of the chlorination furnace, and at the same time, the primary filtrate is acidic, can avoid the reaction of a large amount of carbon dioxide contained in the tail gas of the chlorination furnace to generate carbonates with low solubility, avoids the generation of carbonates waste, reduces the amount of waste generated, solves the problem that the low-solubility carbonates generated in the traditional alkali washing process to absorb chlorine precipitate in the leaching tower and pipeline, causing the leaching tower and pipeline to be blocked; at the same time, the waste liquid is recycled, the treatment cost of the tail gas of the chlorination furnace is reduced, and the ferric chloride solution generated after the primary filtrate absorbs chlorine can be used as a water treatment agent or to produce iron oxide pigments such as red iron oxide, yellow iron oxide, yellow iron black, etc., without subsequent environmental problems. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in more detail below. The present application can be implemented in various forms, and should not be interpreted as being limited to the embodiments set forth herein, but rather, the embodiments are provided to make the present application more thoroughly and completely understood. It should be understood that the embodiments of the present application are only for exemplary purposes, and are not intended to limit the scope of protection of the present application.

[0025] The embodiments of the present application are implemented according to the following technical solutions, and the specific steps include:

[0026] (1) collecting the primary filtrate obtained by dissolving the dust collection residue generated by the chlorination furnace in water and filtering, wherein the concentration percentage of Fe 2+ in the primary filtrate is 0.5% to 12%, the concentration percentage of HCl is 0.1% to 10%, the total concentration percentage of other metal elements is 0.01% to 20%, and the solid content is 0.01% to 5%;

[0027] (2) then, the primary filtrate is punched into the alkali storage tank of the alkali leaching tower of the chlorination furnace tail gas treatment system, wherein the main components of the chlorination furnace tail gas are Cl2, N2, CO2, CO, and N2;

[0028] (3) the primary filtrate in the alkali storage tank is punched into the top of the alkali leaching tower by a circulating pump, mixed with the chlorination furnace tail gas in the alkali leaching tower, and absorbs chlorine in the chlorination furnace tail gas, wherein the flow rate of the chlorination furnace tail gas is 2000 to 2500 m 3 / h, the Cl2 concentration in the chlorination furnace tail gas is 2 to 3 g / m 3 , and the primary filtrate after absorbing chlorine is the absorption liquid; wherein the alkali leaching tower is a packed tower or an empty tower, the alkali leaching tower is a primary tower or a multi-stage tower, the primary filtrate is punched into one or more positions in the upper part of the alkali leaching tower from the alkali storage tank by the circulating pump, and is atomized by a spray head to mix with the chlorination tail gas;

[0029] (4) When the concentration percentage of Fe in the absorption liquid reaches 0.5% to 12%, the absorption liquid is discharged to the absorption liquid storage tank while being supplemented with new filtrate, and the absorption liquid is reused after post-treatment; 3+

[0030] (5) The qualified chlorination furnace tail gas after absorbing chlorine in the primary filtrate, and the chlorine concentration of the qualified chlorination furnace tail gas is ≤0.5 mg / m 3 , and is discharged into the atmosphere through a chimney.

[0031] The alkali liquid leaching tower used in Example 1 is a packed tower, a two-stage leaching device, and the primary filtrate is sprayed into the leaching tower from the top of the leaching tower; the alkali liquid leaching tower used in Examples 2 to 5 is a packed tower, a one-stage leaching device, and the primary filtrate is sprayed into the leaching tower from the top of the leaching tower.

[0032] The specific implementation conditions and results of the examples are shown in Table 1.

[0033] Table 1 Specific implementation conditions and results of examples

[0034]

[0035] The post-treatment of the absorption liquid for reuse specifically includes:

[0036] Examples 1 to 2: Sodium hydroxide is added to the absorption liquid to adjust the pH value to 5.9, and neutralized slurry is obtained, and the neutralized slurry is pressure filtered, and the filtrate is used for caustic soda electrolysis, and the filter cake is washed and used for cement production.

[0037] Example 3: Sodium hydroxide is added to the absorption liquid to adjust the pH value to 7, and neutralized slurry is obtained, and the neutralized slurry is pressure filtered, and the filtrate is used for caustic soda electrolysis, and the filter cake is washed and used for cement production.

[0038] Example 4: The absorption liquid is heated to 80℃, sodium hydroxide is added to the absorption liquid to adjust the pH value to an appropriate value, when the color of the suspension changes to yellow, the suspension is filtered, and the filter cake is washed and low-temperature dried to obtain yellow iron oxide, and the filtrate is used for chlor-alkali electrolysis process.

[0039] Example 5: The absorption liquid is heated to 80℃, sodium hydroxide is added to the absorption liquid to adjust the pH value to an appropriate value, when the color of the suspension changes to yellow, the suspension is filtered, and the filter cake is washed and high-temperature dried to obtain red iron oxide, and the filtrate is used for chlor-alkali electrolysis process.

[0040] Examples 6 to 7: Sodium hydroxide is added to the absorption liquid to adjust the pH value to 7, the suspension is filtered, and the filter cake is washed and calcined to obtain red iron oxide, and when the impurities in the primary filtrate are many, the calcined ash can be used as sintered raw ore in ironworks.

[0041] ​Experiments prove that the method can effectively absorb the chlorine in the tail gas of the chlorination furnace, so that the emission standard is less than or equal to 0.5 mg / m 3 , waste is treated by waste, at the same time, low-solubility carbonates are not generated, the blockage of the leaching tower and the pipeline is avoided, the generated absorption liquid can be recycled, and the production cost and the environmental protection cost are reduced.

[0042] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application, therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process, characterized in that: The dust residue produced by the chlorination furnace is dissolved in water and filtered to obtain a primary filtrate to selectively absorb chlorine in the tail gas of the chlorination furnace, wherein the Fe 2+ The concentration percentage of isocyanate is 0.5% to 12%, and the concentration percentage of HCl is 0.1% to 10%.

2. A method for treating the tail gas of a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 1, characterized in that: The solid content in the primary filtrate is 0.01% to 5%.

3. A method for treating chlorination furnace tail gas in the production of titanium dioxide by chloride process according to claim 1, characterized in that: The total concentration percentage of other metal elements in the primary filtrate is 0.01% to 20%, and the other metal elements include Mn, Al, V, Cr, Ca, Mg, and Ti.

4. A method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process according to any one of claims 1 to 3, characterized in that: The specific steps include: (1) collecting the primary filtrate obtained by dissolving the dust residue generated by the chlorination furnace in water and filtering it, and then pumping it into the alkali liquid storage tank of the alkali liquid washing tower of the chlorination furnace tail gas treatment system; (2) The primary filtrate in the alkali solution storage tank is pumped into the top of the alkali solution washing tower through a circulation pump, mixed with the tail gas of the chlorination furnace in the alkali solution washing tower, and absorbs the chlorine in the tail gas of the chlorination furnace. The primary filtrate after absorbing the chlorine is the absorption liquid; (3) When Fe 3+ When the concentration percentage reaches 0.5% to 12%, the absorption liquid is discharged into the absorption liquid storage tank and reused after post-treatment; (4) The qualified chlorination furnace tail gas after the primary filtrate absorbs chlorine is discharged into the atmosphere through the chimney.

5. A method for treating the tail gas of a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 4, characterized in that: The chlorine concentration in the qualified chlorination furnace tail gas is ≤0.5mg / m 3 .

6. A method for treating chlorination furnace tail gas in the production of titanium dioxide by chloride process according to claim 4, characterized in that: The alkali solution elution tower is a packed tower or an empty tower.

7. A method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 4, characterized in that: The alkali solution washing tower is a single-stage tower or a multi-stage tower.

8. A method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 4, characterized in that: The primary filtrate is transported from the alkali solution storage tank to one or more locations on the upper part of the alkali solution washing tower via a circulation pump, and is atomized by a nozzle and then mixed with the chlorinated tail gas.

9. A method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 4, characterized in that: The post-treatment of the absorption liquid includes adding alkaline substances to the absorption liquid, evaporating and crystallizing, and evaporating and concentrating to obtain a reusable product; the reusable product is used for the production of water treatment agents, wherein the alkaline substances include ammonia water, sodium hydroxide, and calcium hydroxide.

10. The method for treating tail gas from a chlorination furnace in the production of titanium dioxide by the chloride process according to claim 9, wherein: The recyclable product is used as an additive for the production of iron oxide pigments or ironmaking raw materials, wherein the iron oxide pigments include iron oxide red, iron oxide yellow, and iron oxide black.

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