Process for extracting sodium thiocyanate from coking desulfurization and decyanation waste liquid
By adding dilute sulfuric acid and evaporation condensate to the desulfurization and decyanation wastewater after coking, adjusting the pH and controlling the content of the three salts, combined with double-effect concentration and equipment modification, the problem of sodium sulfate blockage was solved, and efficient and low-energy sodium thiocyanate extraction was achieved.
Patent Information
- Application Number
- CN202511903302.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-03-03
AI Technical Summary
In the existing post-desulfurization processes of coking plants, sodium sulfate is prone to clogging pipes during the catalytic oxidation stage, resulting in long process flow, high energy consumption and low automation.
By adding dilute sulfuric acid and evaporating condensate to the catalytic oxidation unit to adjust the pH to weakly acidic, the proportion of sodium thiocyanate in the original solution is increased by using sodium thiocyanate mother liquor, the content of the three salts is controlled to be ≤30%, and a double-effect concentration and closed-loop equipment modification are adopted to prevent sodium sulfate precipitation.
It effectively prevents sodium sulfate blockage, simplifies the process, reduces energy consumption, improves automation, and enables continuous production.
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Figure BDA0005743789740000061 
Figure BDA0005743789740000071
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium thiocyanate extraction technology, specifically relating to a process for extracting sodium thiocyanate from desulfurization and decyanation waste liquid after coking. Background Technology
[0002] Currently, coke oven gas desulfurization in coking plants primarily uses the HPF method with ammonia as the alkali source for pre-desulfurization, while the ADA method with sodium carbonate as the alkali source for post-desulfurization is rare. Therefore, in the treatment of desulfurization wastewater, most enterprises use pre-desulfurization processes for salt extraction, with post-desulfurization processes being relatively less common. Currently, the industry's most common post-desulfurization process is: catalytic oxidation – plate and frame filtration for sulfur – plate and frame filtration for activated carbon – single-reactor concentration for primary sodium sulfate removal – single-reactor secondary sodium sulfate removal – plate and frame filtration for activated carbon – single-reactor concentration to produce sodium thiocyanate. This method has a long process flow, high energy consumption, and very low automation.
[0003] A major obstacle in existing post-desulfurization processes is that sodium sulfate is generated from the reaction of sodium thiosulfate in the early catalytic oxidation stage, which causes sodium sulfate to precipitate and block the pipeline. Therefore, how to overcome the blockage defect of sodium sulfate in post-desulfurization processes is a technical problem that urgently needs to be solved in this field.
[0004] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention
[0005] This disclosure provides at least one process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking.
[0006] In a first aspect, embodiments of this disclosure provide a process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking, comprising the following steps: S1, the desulfurization wastewater is transported to a catalytic oxidation device, dilute sulfuric acid is added, air is blown in to blow out sulfur dioxide from the solution, and after the reaction is complete, an appropriate amount of liquid alkali is added to adjust the pH to weakly acidic, thereby obtaining the material; S2, the material is pumped into a sulfur centrifuge to separate the sulfur solids, which fall into a sulfur slurrying kettle, and evaporation condensate is added to form a slurry, which is then pumped into a coking sulfur foaming high-level tank and into a sulfur melting kettle to obtain sulfur, with the remaining slurry yielding activated carbon; S3, sodium sulfate and / or sodium thiocyanate are prepared; wherein the slurry treated in S2 is... The solution enters a double-effect concentration unit, where water is evaporated under vacuum and steam heating conditions until the sodium thiocyanate content is 48-55%. It is then placed in a sodium sulfate centrifuge to obtain solid sodium sulfate. The solid sodium sulfate is then placed in a sodium sulfate drying unit to obtain the product sodium sulfate. Alternatively, the liquid after centrifugation is decolorized again with activated carbon, filtered to separate the activated carbon, and then enters a single-effect concentration unit. Under vacuum and steam heating conditions, water is evaporated until the sodium thiocyanate content is 72-80%. The liquid is then placed in a crystallization kettle and cooled to 80-85°C to precipitate sodium thiocyanate. The material is then pumped into a sodium thiocyanate centrifuge for separation and drying to obtain the product sodium thiocyanate.
[0007] In an optional embodiment, step S1 further includes sampling and analyzing the content of three salts in the original desulfurization waste liquid to obtain the consumption of dilute sulfuric acid; the three salts include sodium thiocyanate, sodium thiosulfate, and sodium sulfate.
[0008] In one optional embodiment, the addition of dilute sulfuric acid in step S1 specifically includes first adding an appropriate amount of dilute sulfuric acid to react with sodium carbonate and sodium bicarbonate in the desulfurization waste liquid, and then adding the remaining dilute sulfuric acid to react with sodium thiosulfate to generate sodium sulfate, elemental sulfur and sulfur dioxide.
[0009] In one alternative embodiment, the pH range of weak acidity in step S1 is 6 to 7.
[0010] In one optional embodiment, the single-tank operating volume of the catalytic oxidation device in step S1 is 10–100 m³. 3 .
[0011] In one optional embodiment, the method for preparing activated carbon in step S2 includes: adding the remaining slurry to a decolorizing kettle, adding a quantitative amount of powdered activated carbon, pumping it into an activated carbon filter, and filtering to obtain activated carbon.
[0012] In one optional embodiment, the sodium sulfate content in the product is not less than 97%.
[0013] In one optional embodiment, the sodium thiocyanate content in the product is not less than 92%.
[0014] Secondly, embodiments of this disclosure also provide sodium thiocyanate extracted using the process described above.
[0015] Thirdly, embodiments of this disclosure also provide sodium sulfate extracted using the process described above.
[0016] The beneficial effects of this invention are that the process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking utilizes the ratio of sodium thiocyanate mother liquor and evaporation condensate in the early stage of the catalytic oxidation unit. Its main core is to increase the proportion of sodium thiocyanate in the raw liquid by utilizing the sodium thiocyanate content of 48-55% in the sodium thiocyanate mother liquor. Then, evaporation condensate is added to the catalytic oxidation unit to make the content of tri-salts ≤30% in the catalytic oxidation, so as to prevent sodium sulfate from being generated by the reaction of sodium thiosulfate in the catalytic oxidation unit, which would cause sodium sulfate to precipitate and block the pipeline, thus overcoming the existing defects of the post-desulfurization process.
[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description.
[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.
[0021] In this document, as used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.
[0022] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.
[0023] The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.
[0024] This disclosure provides a process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking, comprising the following steps: S1, the desulfurization wastewater is transported to a catalytic oxidation device, dilute sulfuric acid is added, air is blown in to blow out sulfur dioxide from the solution, and after the reaction is complete, an appropriate amount of liquid alkali is added to adjust the pH to weakly acidic, thereby obtaining the material; S2, the material is pumped into a sulfur centrifuge to separate the sulfur solids, which fall into a sulfur slurrying kettle, and evaporation condensate is added to form a slurry, which is then pumped into a coking sulfur foaming high-level tank and into a sulfur melting kettle to obtain sulfur, with the remaining slurry yielding activated carbon; S3, sodium sulfate and / or sodium thiocyanate are prepared; wherein the slurry after S2 is fed into a double-stage catalytic oxidation device. In a single-effect concentration unit, under vacuum and steam heating conditions, water is evaporated until the sodium thiocyanate content is 48-55%. The solution is then placed in a sodium sulfate centrifuge to obtain solid sodium sulfate. The solid sodium sulfate is then placed in a sodium sulfate drying unit to obtain the product sodium sulfate. Alternatively, the liquid treated by the sodium sulfate centrifuge is decolorized again with activated carbon, filtered to separate the activated carbon, and the liquid enters a single-effect concentration unit. Under vacuum and steam heating conditions, water is evaporated until the sodium thiocyanate content is 72-80%. The solution is then placed in a crystallization kettle and cooled to 80-85°C to precipitate sodium thiocyanate. The material is then pumped into a sodium thiocyanate centrifuge for separation and drying to obtain the product sodium thiocyanate.
[0025] In some embodiments, specifically, step S1 further includes sampling and analyzing the content of three salts in the original desulfurization waste liquid to obtain the consumption of dilute sulfuric acid; the three salts include sodium thiocyanate, sodium thiosulfate, and sodium sulfate.
[0026] In some embodiments, specifically, the addition of dilute sulfuric acid in step S1 includes first adding an appropriate amount of dilute sulfuric acid to react with sodium carbonate and sodium bicarbonate in the desulfurization waste liquid, and then adding the remaining dilute sulfuric acid to react with sodium thiosulfate to generate sodium sulfate, elemental sulfur and sulfur dioxide.
[0027] Specifically, the chemical formulas for the reactions involved in S1 are as follows:
[0028] Na₂CO₃ + H₂SO₄ = Na₂SO₄ + H₂O + CO₂
[0029] 2NaHCO3+H2SO4=Na2SO4+H2O+CO2
[0030] Na2S2O3+H2SO4=Na2SO4+S+SO2+H2O
[0031] H₂SO₄ + 2NaOH = Na₂SO₄ + H₂O
[0032] In some embodiments, specifically, the pH range of weak acidity in step S1 is 6 to 7.
[0033] In some embodiments, specifically, the single-reactor operating volume of the catalytic oxidation device in step S1 is 10–100 m³. 3 .
[0034] In some embodiments, specifically, the method for preparing activated carbon in step S2 includes: adding the remaining slurry to a decolorizing kettle, adding a quantitative amount of powdered activated carbon, pumping it into an activated carbon filter, and filtering to obtain activated carbon.
[0035] In some embodiments, specifically, the sodium sulfate content in the product is not less than 97%.
[0036] In some embodiments, specifically, the sodium thiocyanate content in the product is not less than 92%.
[0037] Specifically, in the past, the post-desulfurization process involved three concentration steps, but after optimization, it only requires two concentration steps, eliminating one sodium sulfate concentration stage.
[0038] Specifically, in the past, the concentration process used a single-reactor concentration, which consumed ≥1.2 tons of steam per ton of waste liquid. This time, the desulfurization liquid ratio was optimized and adjusted, and a double-effect concentration was adopted in the first step of sodium sulfate removal, which consumed ≤0.85 tons of steam per ton of waste liquid.
[0039] Specifically, this solution features a high degree of automation, allows for adjustment of the catalytic oxidation volume, and employs a combined catalytic oxidation tank, increasing the single-reactor operating volume to 10m³. 3 Change to 100m 3 The process is streamlined by replacing the plate and frame filter press with a closed sulfur centrifuge to achieve continuous closed production. Additionally, the two single-stage concentration steps are replaced with a single double-effect concentration, automating the process. Sodium thiocyanate single-stage concentration is replaced with a single-effect concentration, enabling continuous material input and output. The previous intermittent open-top hanging bag centrifuge is replaced with a closed, automated scraper-operated bag-pulling unloading and continuous horizontal screw centrifuge.
[0040] Example
[0041] This process has been applied to a coking plant in Shanxi Province. The results after the process improvement are shown in Table 1 below.
[0042] Table 1
[0043]
[0044] During the initial operation, the desulfurization liquid parameters are shown in Table 2 below:
[0045] Table 2
[0046] Sodium carbonate g / L Sodium bicarbonate / g / L Sodium thiocyanate / g / L Sodium thiosulfate / g / L Sodium sulfate g / L <![CDATA[Density g / cm 3 > 5.57 10.94 156 111 72 1.22
[0047] The desulfurization liquid is pumped into the catalytic unit, where dilute sulfuric acid is added to react with sodium thiosulfate. The pH is then adjusted using liquid alkali. At this point, the tri-salt content is approximately 26%, including 10.25% sodium thiocyanate, 0.8% sodium thiosulfate, and 15.01% sodium sulfate. When this material enters the double-effect concentration unit, some water is evaporated, bringing the thiocyanate content to 48-55%. At this point, sodium sulfate is almost completely precipitated, and the sodium sulfate solids content in the material is 42.28%. At this solids content, the pipeline becomes completely blocked, and production cannot proceed.
[0048] After adding 12t of sodium thiocyanate mother liquor and 15t of evaporated condensate, the tris(tris) content of the material during catalytic oxidation was 28%. After adding dilute sulfuric acid and liquid alkali to adjust the concentration, the tris(tris) content was 25.5%. After double-effect concentration, the sodium sulfate solids content was 28.51%. At this point, there was no blockage in the pipelines and equipment, meeting the process requirements.
[0049] In summary, the process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking utilizes the ratio of sodium thiocyanate mother liquor and evaporation condensate in the initial catalytic oxidation unit. Its core is to increase the proportion of sodium thiocyanate in the raw liquid by using the sodium thiocyanate content of 48-55% in the mother liquor. Then, evaporation condensate is added to the catalytic oxidation unit to ensure that the content of tri-salts in the catalytic oxidation is ≤30%. This prevents sodium sulfate from being generated by the reaction of sodium thiosulfate in the catalytic oxidation unit, which would cause sodium sulfate to precipitate and block the pipeline, thus overcoming the existing defects of the post-desulfurization process.
[0050] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.
Claims
1. A process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking, characterized in that, Includes the following steps: S1, the desulfurization waste liquid is transported to the catalytic oxidation unit, dilute sulfuric acid is added, and air is blown in to blow out the sulfur dioxide in the solution. After the reaction is complete, an appropriate amount of liquid alkali is added to adjust the pH to weakly acidic, and the material is obtained. S2, the material is pumped into the sulfur centrifuge to separate the sulfur solids and drop them into the sulfur slurry kettle. Evaporated condensate is added to form a slurry, which is pumped into the coking sulfur foam high-level tank and then into the sulfur melting kettle to obtain sulfur. The remaining slurry is used to obtain activated carbon. S3, to prepare the product sodium sulfate and / or the product sodium thiocyanate; in The slurry after S2 treatment is fed into a double-effect thickener. Under vacuum and steam heating conditions, water is evaporated until the sodium thiocyanate content is 48-55%. It is then placed in a sodium sulfate centrifuge to obtain solid sodium sulfate. The solid sodium sulfate is then placed in a sodium sulfate drying unit to obtain the product sodium sulfate; and / or, The liquid treated by the sodium sulfate centrifuge is decolorized again by activated carbon, and the activated carbon is separated by filtration. The liquid enters a single-effect concentration device, where water is evaporated under vacuum and steam heating conditions until the sodium thiocyanate content reaches 72-80%. Then it is placed in a crystallization kettle and cooled to 80-85°C to precipitate sodium thiocyanate. The material is pumped into a sodium thiocyanate centrifuge for separation and drying to obtain the product sodium thiocyanate.
2. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, Step S1 also includes taking samples of the desulfurization waste liquid to analyze the content of the three salts in the original liquid and obtaining the amount of dilute sulfuric acid consumed. The trisalts include sodium thiocyanate, sodium thiosulfate, and sodium sulfate.
3. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 2, characterized in that, The addition of dilute sulfuric acid in step S1 specifically includes first adding an appropriate amount of dilute sulfuric acid to react with sodium carbonate and sodium bicarbonate in the desulfurization waste liquid, and then adding the remaining dilute sulfuric acid to react with sodium thiosulfate to generate sodium sulfate, elemental sulfur and sulfur dioxide.
4. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, In step S1, the pH range of weak acidity is 6 to 7.
5. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, The single-reactor operating volume of the catalytic oxidation device in step S1 is 10 to 100 m³.
6. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, The method for preparing activated carbon in step S2 includes: adding the remaining slurry to a decolorizing kettle, adding a quantitative amount of powdered activated carbon, pumping it into an activated carbon filter, and filtering to obtain activated carbon.
7. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, The sodium sulfate content in the product is not less than 97%.
8. The process for extracting sodium thiocyanate from desulfurization and decyanation wastewater after coking as described in claim 1, characterized in that, The sodium thiocyanate content in the product is not less than 92%.
9. Sodium thiocyanate extracted using the process described in any one of claims 1-8.
10. Sodium sulfate extracted using the process described in any one of claims 1-8.