A method and system for separating and recycling elemental sulfur from sulfur-containing sludge

Abstract

A method and system for separating and recycling elemental sulfur from sulfur-containing sludge. First, the sulfur-containing sludge, sulfide solution and strong alkali solution are mixed in proportion, sealed and stirred, and then filtered or centrifuged to separate the non-sulfur sludge and the sulfur-containing mixed solution after standing. Then, the sulfur-containing mixed solution is added with an acid solution to adjust the pH value of the sulfur-containing mixed solution to 3.0-7.0, and then filtered or centrifuged to separate the elemental sulfur after standing again. The filtrate is added with a strong alkali solution and reused as a sulfide solution and a strong alkali solution. The method is simple to operate, low in operating cost, wide in applicability, and has the advantages of environmental protection and high efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge resource disposal and utilization, and specifically relates to a method and a system for separating and recycling elemental sulfur from sulfur-containing sludge. Background Art

[0002] Sludge is a product of sewage treatment. It is an extremely complex heterogeneous body composed of organic debris, bacterial cells, inorganic particles, colloids, etc. Sludge will become corrupt and produce foul odors during storage, polluting the environment. The content of elemental sulfur in sulfur-containing sludge is very high. Taking biogas biological desulfurization as an example, studies have found that the content of elemental sulfur in biological desulfurization sludge is 51.2%, protein 5%, and Na + 8.32%, K + 7.47%, Mg 2+ 4.82%, SO4 2- 10.5%, Cl - 4.45% and ash content 8.24%, so sludge treatment after biological desulfurization is a difficult problem.

[0003] There are several main methods for separating and recovering elemental sulfur from sulfur-containing sludge:

[0004] Extraction method: Patent CN101481091 B provides a method for recovering and purifying elemental sulfur from flue gas biological desulfurization sludge, using halogenated hydrocarbons, alkyl or aryl disulfides as extractants, recovering elemental sulfur from biological desulfurization sludge by heating extraction, and then purifying elemental sulfur by cooling crystallization; this method has a high elemental sulfur recovery rate (>90%), but the extraction system requires heating (80-100℃) and cooling (20-25℃), a temperature difference of 60-80℃, high energy consumption, and the volatilization of the extractant will cause harm to human health and the environment.

[0005] Melting method: Patent CN1304869 A proposes a method for producing insoluble sulfur (insoluble in CS2) using sulfur as raw material and adopting a melting anhydrous method; this method does not involve the process of separating sulfur from the material, but focuses on the conversion of the sulfur microstructure.

[0006] Gravity separation method: Patent CN201610775168 discloses a method for separating sulfur from solid sediments in a high-sulfur gas field gathering and transportation system. Two liquids of high density and low density are prepared using zinc chloride solutions with different mass percentages. Substances of different densities in the solid sediments are subjected to secondary separation according to gravity to achieve separation and recovery of sulfur. This method is simple to operate and has low operating costs. However, considering that the solid sediments are not a simple mixture of pure components, there may be mutual aggregation and combination of the components. The density of the aggregates is affected by their internal components. It is difficult to obtain sulfur of higher purity by gravity separation based on density, and the residues after treatment will still contain a considerable proportion of sulfur.

[0007] Microbial conversion method: Patent CN110438164A discloses a resource-based treatment method for preparing dilute sulfuric acid by biological oxidation of sulfur-containing sludge. The method utilizes autotrophic sulfur / iron oxidizing strains (bacteria) to grow at high density and oxidize at high rate in a membrane bioreactor to complete the desulfurization of sulfur-containing sludge and the preparation of dilute sulfuric acid. The advantages of this method are that it is green and efficient, but the disadvantages are that it has high requirements on the corrosion resistance of the reaction system, and the generated sulfuric acid concentration is relatively low (pH 0.75-1.0), which is not conducive to long-distance transportation.

[0008] Patent CN202011173177 discloses a treatment process for sulfur-containing sludge from high-sulfur gas fields, in which sulfides in the sludge are transferred to the liquid phase through alkaline extraction, and the sulfides are converted into sulfates and thiosulfates by catalytic oxidation. The sludge phase after alkaline extraction is demulsified to recover the corrosion inhibitor / diesel in the original sulfur-containing sludge, and the elemental sulfur in the residual sludge is converted into sulfuric acid by microbial oxidation. This method provides an overall treatment technology route for sulfur-containing sludge from high-sulfur gas fields, but the process is complicated. Considering that sulfides can also be converted into sulfuric acid by microorganisms, whether the complex alkali, acid, and catalytic oxidation are necessary is questionable. In addition, this technology also has the problem that dilute sulfuric acid is not convenient for long-distance transportation, similar to Patent CN110438164A.

[0009] At present, the conventional sulfur-containing sludge treatment process in industry (Wang Hongchun, Xiong Juanjuan, Xi Junlan, Huo Haizhou. Comparison of treatment and disposal processes for sulfur-containing sludge in high-sulfur gas fields [J]. Oil and Gas Field Environmental Protection, 2019, 29(04): 17-20+24.) is to remove sulfur by artificially adding chemical agents such as H2O2 before filtration, but the desulfurization effect is not good and there is a risk of poisoning for operators; at the same time, the demand for sulfur is very large and sulfur resources are scarce. Therefore, it is of great practical significance to recover elemental sulfur from sulfur-containing sludge in an environmentally friendly and efficient manner. Summary of the invention

[0010] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method and system for separating and recycling elemental sulfur from sulfur-containing sludge, which has the advantages of simple operation, low operating cost, wide applicability, environmental protection and high efficiency.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for separating and recycling elemental sulfur from sulfur-containing sludge comprises the following steps:

[0013] 1) First, sulfur-containing sludge, sulfide solution and strong alkaline solution are mixed in proportion, sealed and stirred, and then allowed to stand and then filtered or centrifuged to separate the sulfur-free sludge and the sulfur-containing mixed solution;

[0014] 2) then adding the sulfur-containing mixed solution obtained in step 1) into an acid solution, adjusting the pH of the sulfur-containing mixed solution to 3.0-7.0, and separating the elemental sulfur by filtering or centrifugation after standing again; adding a strong alkaline solution to the filtrate, and reusing it as a sulfide solution and a strong alkaline solution in step 1).

[0015] The sulfur-containing sludge in step 1) is biogas biological desulfurization sludge, flue gas biological desulfurization sludge, sulfur autotrophic denitrification sludge and high-sulfur gas field sludge; the sulfide solution is sodium sulfide solution, potassium sulfide solution, ammonium sulfide solution or other solutions or mixtures containing sulfides, such as waste alkali liquor after treating H2S-containing waste gas by alkali liquor absorption method; the strong alkali solution is sodium hydroxide or potassium hydroxide.

[0016] The reaction in step 1) needs to be carried out in a closed environment.

[0017] In the step 1), the molar ratio of elemental sulfur contained in the sulfur-containing sludge to sulfur element contained in the sulfide solution is 1-8:1; the molar ratio of sulfide (negative divalent sulfur) in the sulfur-containing sludge to the strong alkaline solution is 1.1-1.5.

[0018] The stirring and dissolving time of elemental sulfur in the sulfur-containing sludge in step 1) is 1 to 12 hours.

[0019] The sulfur-containing mixed liquid obtained in step 1) is directly recovered and used as an electron donor sulfur source for sulfur autotrophic denitrifying bacteria, and is used for denitrification of nitrate-containing wastewater; the sulfur-free sludge obtained in step 1) is treated as solid waste.

[0020] The acid solution in step 2) includes strong acid solutions such as concentrated sulfuric acid and concentrated hydrochloric acid.

[0021] The elemental sulfur obtained in step 2) is further processed, including washing and drying, to obtain elemental sulfur with higher purity.

[0022] The filtrate obtained by filtration or centrifugation in step 2) needs to be reused after adding a strong alkaline solution to adjust the pH to above 12.5.

[0023] A system for separating and recycling elemental sulfur from sulfur-containing sludge to implement the above method comprises a first reactor 2, sulfur-containing sludge, sulfide solution and strong alkali solution are added to the first reactor 2 through a first pipeline 1, the sulfur-containing sludge, sulfide solution and strong alkali solution are stirred and mixed in the first reactor 2, and after the reaction is completed, the elemental sulfur in the sludge dissolves into the sulfide solution to form a sulfur-containing mixed liquid; the sulfur-containing mixed liquid enters a filtering or centrifugal device 4 through a second pipeline 3 for filtering and separation, and the residue after filtering and separation is sent to a sludge dehydration device 6 through a third pipeline 5 for dehydration, and then the dehydrated sulfur-free sludge is discharged from a fourth pipeline 7; and the sulfur-containing mixed liquid separated by filtering or centrifuging device 4 enters a second reactor 13 through a fifth pipeline 8, and then the acid solution is added to the second reactor 13 through a sixth pipeline 11 The pH is adjusted in the reaction kettle 13, a pH probe 12 is provided in the second reaction kettle 13, the hydrogen sulfide gas generated by the reaction is introduced into the gas absorption device 20 through the seventh pipeline 19 for absorption, and the sulfide-containing solution after absorbing the hydrogen sulfide gas is reused through the eighth pipeline 23; then the pH-adjusted mixture solution is sent to the centrifuge 15 through the ninth pipeline 14 for centrifugation to separate the solid and the liquid, and the obtained solid is sent to the cleaning and drying device 17 through the tenth pipeline 16, and then the elemental sulfur is discharged through the eleventh pipeline 18; the liquid obtained by centrifugation is added with an alkaline solution through the twelfth pipeline 21 to adjust the pH, and then refluxed into the first reaction kettle 2 through the thirteenth pipeline 22 for reuse; the sulfur-containing mixed liquid separated by filtration or centrifugation device 4 enters the liquid storage tank 10 through the fourteenth pipeline 9 and is directly used as an electron donor sulfur source for sulfur autotrophic denitrifying bacteria.

[0024] The beneficial effects of the present invention are:

[0025] (1) Low energy consumption: Since the present invention uses sulfide solution to recover elemental sulfur in sulfur-containing sludge, compared with melting treatment and extraction treatment of sulfur-containing sludge, no heat energy is consumed, energy is saved, and thus it has the advantage of low energy consumption.

[0026] (2) Low cost: Since the present invention only requires repeated consumption of acid and alkali to recover elemental sulfur, it has a lower cost than thermal or extraction methods, and the sulfide and strong alkaline solution can be recycled, so it has the advantage of low cost. In addition, the present invention converts sulfur-containing hazardous waste into general solid waste, significantly reducing the cost of subsequent waste treatment and disposal.

[0027] (3) Environmental protection and high efficiency: Since the present invention adopts the method of adding acid solution to adjust the pH to recover the elemental sulfur in the sulfur-containing sludge, compared with the method of adding organic extractants or other organic reagents, there is no risk of volatile organic matter harming the human body and the environment, and the recovered elemental sulfur has a higher purity, so it has the advantages of environmental protection and high efficiency.

[0028] (4) Simple operation: Since the present invention has no complicated operating unit and can be operated at room temperature, no temperature control unit is required, so it has the advantage of simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0031] Reference Figure 1 A system for separating and recycling elemental sulfur from sulfur-containing sludge, comprising a first reactor 2, sulfur-containing sludge, sulfide solution and strong alkaline solution are added to the first reactor 2 through a first pipeline 1, and the molar ratio of the added sulfur-containing sludge to the sulfur element in the sulfide solution is 1 to 8:1; the sulfur-containing sludge, sulfide solution and strong alkaline solution are fully stirred and mixed in the first reactor 2, and the reaction time is 1 to 12 hours. A closed environment is ensured during the reaction process. After the reaction is completed, the elemental sulfur in the sludge dissolves into the sulfide solution to form a sulfur-containing mixed liquid; after stopping stirring, the sulfur-containing mixed liquid enters a filtering or centrifugal device 4 through a second pipeline 3 for filtering and separation, and the residue after filtering and separation is sent to a sludge dehydrating device 6 through a third pipeline 5 for dehydration, and then the dehydrated sulfur-free sludge is discharged from a fourth pipeline 7; and the sulfur-containing mixed liquid separated by the filtering or centrifugal device 4 is sent to a fifth pipeline 5 for filtering and separation. The mixture solution is introduced into the second reactor 13 through the sixth pipeline 11, and then the acid solution is added into the second reactor 13 through the sixth pipeline 11 to adjust the mixture solution to 3.0-7.0. The second reactor 13 is provided with a pH probe 12 for observing the pH value of the mixture solution in the second reactor. A small amount of hydrogen sulfide gas generated by the reaction is introduced into the gas absorption device 20 through the seventh pipeline 19 for absorption. The sulfide-containing solution after absorbing the hydrogen sulfide gas can be reused through the eighth pipeline 23; then the mixture solution after adjusting the pH value is sent to the centrifuge 15 through the ninth pipeline 14 for centrifugation to separate the solid and the liquid. At this time, the obtained solid is sent to the cleaning and drying device 17 through the tenth pipeline 16, and then the elemental sulfur is discharged through the eleventh pipeline 18; the liquid obtained by centrifugation is added with an alkaline solution through the twelfth pipeline 21 to adjust the pH, and then refluxed into the first reactor 2 through the thirteenth pipeline 22 for reuse;

[0032] Another alternative approach is to directly use the sulfur-containing mixed liquid separated by filtering or centrifuging device 4 into liquid storage tank 10 through fourteenth pipeline 9 as an electron donor sulfur source for sulfur autotrophic denitrifying bacteria for denitrification of nitrate-containing wastewater.

[0033] The present invention is described in detail below in conjunction with embodiments

[0034] Embodiment 1, as Figure 1 As shown, sulfur autotrophic denitrification sludge with a sulfur content of 30% is mixed with sodium sulfide solution at a sulfur element molar ratio of 1:1, and a strong alkaline solution is added, and the molar ratio of sulfide (negative divalent sulfur) in the sulfur-containing sludge to the strong alkaline solution is 1.1; the mixed solution is stirred for 4 hours and then filtered, and then the filtrate, i.e., the sulfur-containing mixed solution, is adjusted to pH 7.0 with concentrated sulfuric acid solution, and the mixed solution is filtered and centrifuged at room temperature to obtain high-purity elemental sulfur. In this embodiment, the recovery rate of elemental sulfur is 87.99%, and the purity of elemental sulfur is 91.5%.

[0035] Example 2, other steps are the same as Example 1, except that: the sludge in this example is high-sulfur gas field sludge with a sulfur content of 42%. In this example, the recovery rate of elemental sulfur is 88.33%, and the recovery purity of elemental sulfur is 92.7%.

[0036] In Example 3, the other steps are the same as those in Example 1, except that the sludge in this example is biogas biological desulfurization sludge with a sulfur content of 17%. In this example, the recovery rate of elemental sulfur is 82.37%, and the recovery purity of elemental sulfur is 84.42%.

[0037] In Example 4, the other steps are the same as those in Example 1, except that the source of the sulfide solution and the strong alkali solution in this example is that the filtrate obtained after adjusting the pH with the concentrated acid solution in Example 1 and filtering is adjusted to pH 12.5 with a high concentration of strong alkali, and then reused as the sulfide solution and the strong alkali solution. In this example, the recovery rate of elemental sulfur is 81.33%, and the recovery purity of elemental sulfur is 85.65%.

[0038] In Example 5, the other steps are the same as those in Example 1, except that the stirring reaction time in this example is 12 hours. In this example, the recovery rate of elemental sulfur is 95.58%, and the recovery purity of elemental sulfur is 95.2%.

[0039] In Example 6, the other steps are the same as those in Example 1, except that the molar ratio of sulfur sludge to sulfur in the sodium sulfide solution in this example is 8: 1. In this example, the recovery rate of elemental sulfur is 72.16%, and the recovery purity of elemental sulfur is 81.9%.

[0040] In Example 7, the other steps are the same as those in Example 1, except that the molar ratio of the sulfur-containing sludge to the sulfur element in the sodium sulfide solution in this example is 6:1, and the pH is adjusted to 6.0 using a concentrated sulfuric acid solution. In this example, the recovery rate of elemental sulfur is 82.20%, and the recovery purity of elemental sulfur is 86.7%.

[0041] Example 8, other steps are the same as Example 1, except that: the molar ratio of sulfur-containing sludge to sulfur in sodium sulfide solution in this example is 5:1, and concentrated hydrochloric acid is used to adjust the pH value to 3.0. In this example, the recovery rate of elemental sulfur is 84.39%, and the recovery purity of elemental sulfur is 90.5%.

[0042] Example 9, other steps are the same as Example 1, except that the molar ratio of sulfur-containing sludge to sulfur in sodium sulfide solution in this example is 5:1, the stirring reaction time is 10 hours, and concentrated hydrochloric acid is used to adjust the pH value to 6.0. In this example, the recovery rate of elemental sulfur is 83.69%, and the recovery purity of elemental sulfur is 87.4%.

[0043] Example 10, other steps are the same as Example 1, except that: the molar ratio of sulfur-containing sludge to sulfur in sodium sulfide solution in this example is 4:1, the stirring reaction time is 10 hours, and concentrated hydrochloric acid is used to adjust the pH value to 4.4. In this example, the recovery rate of elemental sulfur is 86.01%, and the recovery purity of elemental sulfur is 91.1%.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for separating and recycling elemental sulfur from sulfur-containing sludge, characterized in that: The following steps are involved: 1) First, sulfur-containing sludge, sulfide solution and strong alkaline solution are mixed in proportion, sealed and stirred, and then filtered or centrifuged to separate the sulfur-free sludge and sulfur-containing mixed solution after standing; The reaction in step 1) must be in a closed environment; In the step 1), the molar ratio of elemental sulfur contained in the sulfur-containing sludge to the sulfur element contained in the sulfide solution is 1-8:1; the molar ratio of negative divalent sulfur of the sulfide in the sulfur-containing sludge to the strong alkaline solution is 1.1-1.5; 2) Then, the sulfur-containing mixed solution obtained in step 1) is added with an acid solution, and the pH of the sulfur-containing mixed solution is adjusted to 3.0-7.

0. After standing again, the elemental sulfur is separated by filtration or centrifugation; the filtrate is added with a strong alkaline solution and reused as a sulfide solution and a strong alkaline solution in step 1).

2. The method according to claim 1, characterized in that: The sulfur-containing sludge in step 1) is biogas biological desulfurization sludge, flue gas biological desulfurization sludge, sulfur autotrophic denitrification sludge or high-sulfur gas field sludge; The sulfide solution is sodium sulfide solution, potassium sulfide solution, ammonium sulfide solution or a mixture thereof; the strong alkali solution is sodium hydroxide solution or potassium hydroxide solution.

3. The method according to claim 1, characterized in that: The stirring and dissolving time of elemental sulfur in the sulfur-containing sludge in step 1) is 1 to 12 hours.

4. The method according to claim 1, characterized in that: The sulfur-containing mixed liquid obtained in step 1) is directly recovered and used as an electron donor sulfur source for sulfur autotrophic denitrifying bacteria, and is used for denitrification of nitrate-containing wastewater; the sulfur-free sludge obtained in step 1) is treated as solid waste.

5. The method according to claim 1, characterized in that: The acid solution in step 2) includes concentrated sulfuric acid solution or concentrated hydrochloric acid solution.

6. The method according to claim 1, characterized in that: The elemental sulfur obtained in step 2) is further processed, including washing and drying, to obtain elemental sulfur with higher purity.

7. The method according to claim 1, characterized in that: The filtrate obtained by filtration or centrifugation in step 2) needs to be reused after adding a strong alkaline solution to adjust the pH to above 12.

5.

8. A system for separating and recycling elemental sulfur from sulfur-containing sludge according to any one of claims 1 to 7, characterized in that: The invention comprises a first reactor (2), wherein sulfur-containing sludge, sulfide solution and strong alkali solution are added into the first reactor (2) through a first pipeline (1), the sulfur-containing sludge, sulfide solution and strong alkali solution are stirred and mixed in the first reactor (2), and after the reaction is completed, the elemental sulfur in the sludge is dissolved into the sulfide solution to form a sulfur-containing mixed liquid; the sulfur-containing mixed liquid enters a filtering or centrifugal device (4) through a second pipeline (3) for filtering and separation, and the residue after filtering and separation is sent to a sludge dehydration device (6) through a third pipeline (5) for dehydration, and then the dehydrated sulfur-free sludge is discharged through a fourth pipeline (7); and the sulfur-containing mixed liquid separated by the filtering or centrifugal device (4) enters a second reactor (13) through a fifth pipeline (8), and then an acid solution is added into the second reactor (13) through a sixth pipeline (11) to adjust the pH value, and the second reactor (13) is A pH probe (12) is provided. The hydrogen sulfide gas generated by the reaction is introduced into the gas absorption device (20) through the seventh pipeline (19) for absorption. The sulfide-containing solution after absorbing the hydrogen sulfide gas is recycled through the eighth pipeline (23). The pH-adjusted mixed solution is then sent to the centrifuge (15) through the ninth pipeline (14) for centrifugation to separate the solid and the liquid. The obtained solid is sent to the cleaning and drying device (17) through the tenth pipeline (16), and then the elemental sulfur is discharged through the eleventh pipeline (18). The liquid obtained by centrifugation is added with an alkaline solution through the twelfth pipeline (21) to adjust the pH, and then refluxed into the first reaction kettle (2) through the thirteenth pipeline (22) for recycling. The sulfur-containing mixed solution separated by the filtration or centrifugal device (4) is sent to the liquid storage tank (10) through the fourteenth pipeline (9) and directly used as an electron donor sulfur source for sulfur autotrophic denitrifying bacteria.

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