Sulfur-containing sewage treatment method

Abstract

The invention relates to a sulfur-containing sewage treatment method, and belongs to the technical field of oil and gas field sulfur-containing sewage treatment. According to the sulfur-containing sewage treatment method, the gas stripping gas mainly composed of nitrogen and carbon dioxide is adopted to perform gas stripping desulfurization on the sulfur-containing sewage, and the content of sulfide in the sewage can be effectively reduced, so that the dosage of a subsequent desulfurization flocculant is reduced, and the treatment cost of the sulfur-containing sewage can be effectively reduced.

Description

Technical Field

[0001] The invention relates to a method for treating sulfur-containing sewage, and belongs to the technical field of sulfur-containing sewage treatment in oil and gas fields. Background Art

[0002] During the exploitation of sulfur-containing gas fields, a large amount of sulfur-containing wastewater is generated. The pH value of sulfur-containing wastewater is above 8, and the sulfide content is generally 1000-3000 mg / L, mainly HS - , S 2- , H2S. These sulfur-containing wastewaters are extremely toxic and pose a great threat to human health and the surrounding environment; secondly, the sulfides in the water are highly corrosive and can cause serious damage to metal pipelines and gas field development; at the same time, the hardness of the desulfurized wastewater needs to meet the standard when it is reused as a resource. Therefore, the sulfur-containing wastewater generated by gas field mining must be desulfurized and hardened.

[0003] The main methods for removing hardness from sewage include lime soda method, caustic soda method, membrane technology, etc. The high-sulfur sewage hardness removal treatment process usually adopts the caustic soda method, which includes the following steps: adding caustic soda and soda reagents to the sewage, adjusting the pH value of the sewage to 10-11, adding coagulants and flocculants at the same time, and performing sedimentation reaction, and then using hydrochloric acid to adjust the pH value to 6-9. In the above-mentioned hardness removal process, a large amount of caustic soda and soda reagents are required, and the adjustment of the effluent pH value also requires the addition of hydrochloric acid, resulting in a high cost for the treatment of high-sulfur sewage hardness removal.

[0004] The desulfurization treatment of high-sulfur wastewater in oil and gas fields generally adopts gas stripping desulfurization. Based on Henry's law and the low solubility of hydrogen sulfide gas in water, an inert gas (nitrogen or natural gas) that does not react with hydrogen sulfide gas is used in the gas stripping tower to continuously countercurrently contact the wastewater, so that the partial pressure of hydrogen sulfide in the gas phase is lower than the partial pressure when the gas-liquid phase is in equilibrium. The hydrogen sulfide in the liquid phase will continue to enter the gas phase, thereby achieving the purpose of desulfurization from the wastewater. However, when the pH value of the wastewater is high, the sulfide in the wastewater is HS - , S 2- The gas stripping tower cannot remove the ionic sulfide. In actual production, a large amount of hydrochloric acid is needed to adjust the pH value of the sewage to 5.0-5.5. When the hydrochloric acid is insufficient, the sulfide in the sewage cannot be completely resolved, causing the sulfide in the effluent to exceed the standard. When the hydrochloric acid is excessively added, it will have an impact on the smooth operation of the subsequent water treatment system, resulting in water quality exceeding the standard. At the same time, it will also aggravate the corrosion of the water treatment system, and the use of hydrochloric acid will increase the treatment cost.

[0005] Therefore, there is an urgent need to develop a low-cost method for treating sulfur-containing wastewater. Summary of the invention

[0006] The purpose of the present invention is to provide a method for treating sulfur-containing wastewater, which can solve the problem of high cost in treating sulfur-containing wastewater generated in the process of exploiting sulfur-containing gas fields.

[0007] In order to achieve the above object, the technical solution adopted by the method for treating sulfur-containing wastewater of the present invention is:

[0008] A method for treating sulfur-containing wastewater comprises the following steps:

[0009] (1) conditioning the sulfur-containing wastewater to adjust the pH of the sulfur-containing wastewater to 6 to 7 to obtain pretreated wastewater;

[0010] (2) The pretreated sewage and the stripping gas are countercurrently contacted to perform stripping desulfurization on the pretreated sewage to obtain desulfurized sewage; the stripping gas is mainly composed of nitrogen and carbon dioxide; the volume ratio of nitrogen to carbon dioxide is (1-4):1.

[0011] The method for treating sulfur-containing wastewater of the present invention uses a stripping gas mainly composed of nitrogen and carbon dioxide to perform gas stripping desulfurization on the sulfur-containing wastewater, which can effectively reduce the sulfide content in the wastewater, thereby reducing the amount of subsequent desulfurization flocculant used, and can effectively reduce the treatment cost of the sulfur-containing wastewater.

[0012] Generally, the method of the present invention is suitable for general oilfield sulfur-containing wastewater. For example, the method of the present invention is suitable for sulfur-containing wastewater that meets the following conditions: sulfide content ≤3000 mg / L, pH ≤9, hardness ≤1000 mg / L.

[0013] Before gas lift desulfurization, the pH of the sulfur-containing wastewater is adjusted to 6-7 to facilitate the analysis of sulfides in the subsequent gas lift process; adjusting the pH of the sulfur-containing wastewater to below 6 will increase the amount of acid used and increase the treatment cost; adjusting the pH of the sulfur-containing wastewater to above 7 will reduce the gas lift desulfurization efficiency and cause the sulfide content in the effluent to exceed the standard.

[0014] When the pretreated sewage and the stripping gas are in countercurrent contact, the carbon dioxide in the stripping gas dissolves in the sewage, ionizes to produce hydrogen ions, and converts the sulfide in the sewage into hydrogen sulfide gas, while the nitrogen in the stripping gas decomposes the hydrogen sulfide gas in the sewage and is taken away by the stripping gas. The relationship between the volume ratio of nitrogen and carbon dioxide in the stripping gas and the content of sulfide in the pretreated sewage is: as the sulfide content in the pretreated sewage increases, the volume ratio of nitrogen and carbon dioxide in the stripping gas decreases.

[0015] In the present invention, sulfur-containing wastewater refers to sulfur-containing wastewater generated during the exploitation of oil and gas fields.

[0016] Preferably, the volume ratio of the stripping gas to the pretreated wastewater during the gas stripping desulfurization is (5-20):1.

[0017] Preferably, the working pressure of the gas stripping desulfurization is 5 to 15 kPa. The greater the working pressure of the gas stripping desulfurization, the more conducive it is for the gas stripping gas to dissolve into the pretreated sewage and take out the hydrogen sulfide. However, if the working pressure of the gas stripping desulfurization is too high, it will make it difficult for the hydrogen sulfide in the liquid phase to escape. At the same time, in order to increase the solubility of carbon dioxide and promote the generation of hydrogen ions by carbon dioxide, the working pressure of the gas stripping desulfurization should be controlled within an appropriate range.

[0018] In the present invention, the index parameters of the desulfurized wastewater are as follows: pH value is 6-9, and sulfide content is ≤300 mg / L.

[0019] In the present invention, the pretreated sewage and the stripping gas are in countercurrent contact in a packed tower, the pretreated sewage flows from top to bottom in the packed tower, and the stripping gas flows from bottom to top in the packed tower. The pretreated sewage and the stripping gas are in countercurrent contact during the flow process to complete the stripping desulfurization.

[0020] It is understood that the packing in the packed tower used for gas lift desulfurization is a structured packing, for example, a structured pulse corrugated packing. The pulse corrugated packing is a disc-shaped or block-shaped packing body assembled according to certain rules by pulse corrugated sheets with pulse units of specific shapes made of plastic or metal thin strips.

[0021] Preferably, in step (1), the conditioning treatment is to first remove solid particles in the sulfur-containing wastewater, and then adjust the pH of the sulfur-containing wastewater to 6-7. Removing solid particles can prevent particles in the wastewater from clogging the gas stripping tower filler and affecting the gas stripping desulfurization effect. Removing solid particles first and then adjusting the pH to 6-7 can avoid dissolving some particles when adjusting the pH, and is conducive to the stable operation of pH adjustment.

[0022] Preferably, in step (1), the solid particles in the sulfur-containing wastewater are removed by filtration.

[0023] Preferably, the method for treating sulfur-containing wastewater also includes the following steps: desulfurizing the desulfurized wastewater using a chemical desulfurizer to convert the sulfide in the wastewater into elemental sulfur, then adding a coagulant and a flocculant to carry out a coagulation and flocculation reaction, and performing solid-liquid separation to obtain secondary desulfurized wastewater, and then performing a hardness removal treatment on the secondary desulfurized wastewater, and finally adjusting the pH of the wastewater after the hardness removal treatment to a set value to obtain purified water.

[0024] It can be understood that chemical desulfurizers, coagulants, and flocculants suitable for treating sulfur-containing wastewater are all suitable for the present invention. For example, the chemical desulfurizer is hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide flocculant.

[0025] The dosage of chemical desulfurizer, coagulant and flocculant can be determined according to the sulfide content of desulfurized wastewater. Preferably, the mass ratio of sulfide in desulfurized wastewater to chemical desulfurizer is 1:(50-80); the mass ratio of sulfide in desulfurized wastewater to coagulant is 100:(20-25); the mass ratio of sulfide in desulfurized wastewater to flocculant is 100:(0.5-1).

[0026] Preferably, the hardness removal treatment method comprises the following steps: using an alkaline pH regulator to adjust the pH of the secondary desulfurization wastewater to 7.0-8.5 to obtain a first alkaline treatment liquid, then absorbing carbon dioxide in the first alkaline treatment liquid to obtain an acidic treatment liquid, then using an alkaline pH regulator to adjust the pH of the acidic treatment liquid to 10-11, performing a first solid-liquid separation to obtain a second alkaline treatment liquid, and finally subjecting the second alkaline treatment liquid to an electrocoagulation treatment, a second solid-liquid separation, and completing the hardness removal treatment. In the hardness removal treatment method, the role of first using an alkaline pH regulator to adjust the pH of the secondary desulfurization wastewater to 7.0-8.5 is to improve the efficiency of wastewater absorbing carbon dioxide. In this step, if the pH is less than 7, insufficient carbon dioxide will be dissolved in the wastewater, and the calcium ion in the system effluent will exceed the standard. If the pH is greater than 8.5, calcium ion precipitation will cause the filler to be blocked, affecting the absorption of carbon dioxide. The purpose of adjusting the pH of the acidic treatment liquid to 10-11 with an alkaline pH adjuster is to cause cations such as calcium and magnesium in the liquid to undergo precipitation reaction with hydroxide to remove cations such as calcium and magnesium. In this step, if the pH is less than 10, insufficient precipitation will result, and cations such as calcium and magnesium cannot be effectively removed. If the pH is greater than 11, excessive liquid alkali will be added, increasing the treatment cost.

[0027] Preferably, the first alkaline treatment liquid absorbs carbon dioxide by countercurrently contacting the first alkaline treatment liquid with carbon dioxide, so that the first alkaline treatment liquid absorbs carbon dioxide. For example, the first alkaline treatment liquid and carbon dioxide are countercurrently contacted in a packed tower to achieve the first alkaline treatment liquid absorbing carbon dioxide.

[0028] Preferably, in the hardness removal method, the pH of the acidic treatment liquid is 6.0 to 7.5. The pH of the acidic treatment liquid is controlled at 6.0 to 7.5 to ensure that sufficient carbonate ions enter the system, thereby forming carbonate precipitation with cations such as calcium and magnesium. When the pH is too low, carbonate ions form bicarbonates and cannot form precipitation with cations such as calcium and magnesium.

[0029] Preferably, during the electrocoagulation treatment, the electrocoagulation anode is made of aluminum and / or iron. During the electrocoagulation treatment, the energized plates in the electrocoagulation device undergo an electrochemical reaction to dissolve Al 3+ or Fe 2+The plasma is hydrolyzed in the water to produce flocculation reaction. The external electric field of the electric flocculation device will also cause the anions and cations in the sewage to move in a directional manner in the electric field, so that cations such as calcium and magnesium are enriched near the cathode and combined with the high concentration of hydroxide ions produced by the cathode to produce hydroxide precipitation, thereby achieving the purpose of hardness removal.

[0030] Preferably, the voltage of the electro-flocculation treatment is 2.0-4.0V, and the current is 800-1200A.

[0031] Preferably, the pH of the treated sewage after hardness removal is adjusted to a set value by using carbon dioxide. Further preferably, the pH of the treated sewage after hardness removal is adjusted to a set value by using carbon dioxide to make countercurrent contact with the treated sewage after hardness removal.

[0032] Preferably, the set value is 6 to 9. The purpose of adjusting the pH of the sewage after hardness removal treatment to 6 to 9 is to facilitate the subsequent resource utilization of the sewage.

[0033] Preferably, the step of adjusting the pH of the treated sewage to a set value using carbon dioxide comprises subjecting the carbon dioxide and the treated sewage to countercurrent contact to adjust the pH of the treated sewage to the set value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic flow chart of the method for treating sulfur-containing wastewater according to Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0036] 1. The specific embodiment of the method for treating sulfur-containing wastewater of the present invention is as follows:

[0037] Example 1

[0038] The method for treating sulfur-containing wastewater of this embodiment is as follows: Figure 1 As shown, the specific steps include:

[0039] (1) filtering the sulfur-containing wastewater (sulfide content of 3000 mg / L, pH=9, hardness of 1000 mg / L) generated in the exploitation of the sulfur-containing gas field to remove solid particles in the sulfur-containing wastewater, and then mixing the filtered liquid with an acid solution (the acid solution is hydrochloric acid with a mass fraction of 30%) to obtain pretreated wastewater with a pH of 6.0;

[0040] (2) The pretreated sewage is introduced into the upper part of the gas stripping desulfurization tower (the gas stripping desulfurization tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, a packing thickness of 8000 mm, and a regular pulse corrugated packing), and at the same time, the gas stripping gas composed of nitrogen and carbon dioxide in a volume ratio of 1:1 is introduced into the bottom of the gas stripping desulfurization tower. The pretreated sewage and the gas stripping gas are in countercurrent contact in the gas stripping desulfurization tower to achieve gas stripping desulfurization of the pretreated sewage. The volume ratio of the gas stripping gas to the pretreated sewage is 20:1. The working pressure in the gas stripping desulfurization tower is controlled at 15 kPa. The sewage after gas stripping desulfurization (desulfurized sewage) flows out from the bottom of the gas stripping desulfurization tower;

[0041] (3) The desulfurized wastewater is transported to a flocculation tank, and then a chemical desulfurizer is added to the flocculation tank. After stirring for 10 seconds, the desulfurized wastewater reacts with the chemical desulfurizer to generate elemental sulfur. Then, a coagulant and a flocculant are added to the flocculation tank. After coagulation and flocculation, a precipitate is generated. The supernatant is the secondary desulfurized wastewater. The chemical desulfurizer is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide. The mass ratio of sulfide in the desulfurized wastewater to the chemical desulfurizer is 100:50; the mass ratio of sulfide in the desulfurized wastewater to the coagulant is 100:20; and the mass ratio of sulfide in the desulfurized wastewater to the flocculant is 100:0.5.

[0042] (4) The secondary desulfurization wastewater is adjusted to a pH of 8.5 using an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) to obtain a first alkaline treatment liquid, and then the first alkaline treatment liquid is introduced into the upper inlet of the first absorption tower (i.e., except for the hard absorption tower, the first absorption tower is a packed tower with a diameter of 800 mm, a height of 12,000 mm, a packing thickness of 8,000 mm, and a regular pulse corrugated packing). At the same time, carbon dioxide gas is introduced into the first absorption tower from the bottom inlet of the first absorption tower. The first alkaline treatment liquid and carbon dioxide are in countercurrent contact in the first absorption tower. During the countercurrent contact process, the first alkaline treatment liquid absorbs carbon dioxide to form an acidic treatment liquid, and the acidic treatment liquid flows out from the bottom outlet of the first absorption tower. The pH of the acidic treatment liquid is 6.0;

[0043] Then, the acidic treatment liquid is passed into the electrocoagulation tank, and at the same time, an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) is added into the electrocoagulation tank. The acidic treatment liquid and the alkaline pH regulator are mixed under stirring to obtain a second alkaline treatment liquid with a pH of 10.5; the anode of the electrocoagulation tank has an aluminum plate with adjustable current, the voltage of the electrocoagulation is 4V, and the current is 1200A. The aluminum plate reacts chemically under the action of the current to produce aluminum ions. In an alkaline environment, the aluminum ions are hydrolyzed and a flocculation reaction occurs. The cations such as calcium and magnesium in the second alkaline treatment liquid are enriched at the cathode and combined with the hydroxide ions near the cathode to produce precipitation, which is then filtered to complete the hardness removal treatment. The filtered liquid is the wastewater after hardness removal;

[0044] (5) The de-hardened sewage is introduced into the upper inlet of the second absorption tower (the second absorption tower is a packed tower with a diameter of 800 mm, a height of 12,000 mm, a packing thickness of 8,000 mm, and a regular pulse corrugated packing). At the same time, the carbon dioxide gas is introduced into the second absorption tower from the bottom inlet. The de-hardened sewage and the carbon dioxide are in countercurrent contact in the second absorption tower. During the countercurrent contact process, the de-hardened sewage absorbs the carbon dioxide to form purified water with a pH of 6 to 9. The purified water flows out from the bottom outlet of the second absorption tower.

[0045] Example 2

[0046] The method for treating sulfur-containing wastewater in this embodiment specifically comprises the following steps:

[0047] (1) filtering the sulfur-containing wastewater (sulfide content of 2000 mg / L, pH=8, hardness of 800 mg / L) generated in the exploitation of the sulfur-containing gas field to remove solid particles in the sulfur-containing wastewater, and then mixing the filtered liquid with an acid solution (the acid solution is hydrochloric acid with a mass fraction of 30%) to obtain pretreated wastewater with a pH of 7.0;

[0048] (2) The pretreated sewage is introduced into the upper part of the gas stripping desulfurization tower (the gas stripping desulfurization tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, and a packing thickness of 8000 mm), and at the same time, the gas stripping gas composed of nitrogen and carbon dioxide in a volume ratio of 3:1 is introduced into the bottom of the gas stripping desulfurization tower. The pretreated sewage and the gas stripping gas are in countercurrent contact in the gas stripping desulfurization tower to achieve gas stripping desulfurization of the pretreated sewage. The volume ratio of the gas stripping gas to the pretreated sewage is 10:1. The working pressure in the gas stripping desulfurization tower is controlled at 10 kPa, and the sewage after gas stripping desulfurization (desulfurized sewage) flows out from the bottom of the gas stripping desulfurization tower;

[0049] (3) The desulfurized wastewater is transported to a flocculation tank, and then a chemical desulfurizer is added to the flocculation tank. After stirring for 10 seconds, the desulfurized wastewater reacts with the chemical desulfurizer to generate elemental sulfur. Then, a coagulant and a flocculant are added to the flocculation tank. After coagulation and flocculation, a precipitate is generated. The supernatant is the secondary desulfurized wastewater. The chemical desulfurizer is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide. The mass ratio of sulfide in the desulfurized wastewater to the chemical desulfurizer is 100:80; the mass ratio of sulfide in the desulfurized wastewater to the coagulant is 100:25; and the mass ratio of sulfide in the desulfurized wastewater to the flocculant is 100:1.

[0050] (4) The secondary desulfurization wastewater is adjusted to a pH of 8.5 using an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) to obtain a first alkaline treatment liquid, and then the first alkaline treatment liquid is introduced into the upper inlet of a first absorption tower (the first absorption tower is the same as the first absorption tower in Example 1), and at the same time, carbon dioxide gas is introduced into the first absorption tower from the bottom inlet of the first absorption tower. The first alkaline treatment liquid and carbon dioxide are in countercurrent contact in the first absorption tower. During the countercurrent contact process, the first alkaline treatment liquid absorbs carbon dioxide to form an acidic treatment liquid, and the acidic treatment liquid flows out from the bottom outlet of the first absorption tower. The pH of the acidic treatment liquid is 7.0;

[0051] Then, the acidic treatment liquid is passed into the electrocoagulation tank, and at the same time, an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) is added into the electrocoagulation tank. The acidic treatment liquid and the alkaline pH regulator are mixed under stirring to obtain a second alkaline treatment liquid with a pH of 10; the anode of the electrocoagulation tank has an aluminum plate with adjustable current, the voltage of the electrocoagulation is 3V, and the current is 1000A. The aluminum plate reacts chemically under the action of the current to produce aluminum ions. In an alkaline environment, the aluminum ions are hydrolyzed and a flocculation reaction occurs. The cations such as calcium and magnesium in the second alkaline treatment liquid are enriched at the cathode and combined with the hydroxide ions near the cathode to produce precipitation, which is then filtered to complete the hardness removal treatment. The filtered liquid is the wastewater after hardness removal;

[0052] (5) The de-hardened sewage is introduced into the upper inlet of the second absorption tower (the second absorption tower is the same as the second absorption tower in Example 1), and the carbon dioxide gas is introduced into the second absorption tower from the bottom inlet of the second absorption tower. The de-hardened sewage and the carbon dioxide are in countercurrent contact in the second absorption tower. During the countercurrent contact process, the de-hardened sewage absorbs the carbon dioxide to form purified water with a pH of 6 to 9, and the purified water flows out from the bottom outlet of the second absorption tower.

[0053] Example 3

[0054] The method for treating sulfur-containing wastewater in this embodiment specifically comprises the following steps:

[0055] (1) filtering the sulfur-containing wastewater (sulfide content of 1000 mg / L, pH=8, hardness of 500 mg / L) generated in the exploitation of the sulfur-containing gas field to remove solid particles in the sulfur-containing wastewater, and then mixing the filtered liquid with an acid solution (the acid solution is hydrochloric acid with a mass fraction of 30%) to obtain pretreated wastewater with a pH of 6.5;

[0056] (2) The pretreated sewage is introduced into the upper part of the gas stripping desulfurization tower (the gas stripping desulfurization tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, and a packing thickness of 8000 mm), and at the same time, the gas stripping gas composed of nitrogen and carbon dioxide in a volume ratio of 4:1 is introduced into the bottom of the gas stripping desulfurization tower. The pretreated sewage and the gas stripping gas are in countercurrent contact in the gas stripping desulfurization tower to achieve gas stripping desulfurization of the pretreated sewage. The volume ratio of the gas stripping gas to the pretreated sewage is 5:1. The working pressure in the gas stripping desulfurization tower is controlled at 5 kPa, and the sewage after gas stripping desulfurization (desulfurized sewage) flows out from the bottom of the gas stripping desulfurization tower;

[0057] (3) The desulfurized wastewater is transported to a flocculation tank, and then a chemical desulfurizer is added to the flocculation tank. After stirring for 10 seconds, the desulfurized wastewater reacts with the chemical desulfurizer to generate elemental sulfur. Then, a coagulant and a flocculant are added to the flocculation tank. After coagulation and flocculation, a precipitate is generated. The supernatant is the secondary desulfurized wastewater. The chemical desulfurizer is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide. The mass ratio of sulfide in the desulfurized wastewater to the chemical desulfurizer is 100:60; the mass ratio of sulfide in the desulfurized wastewater to the coagulant is 100:22; and the mass ratio of sulfide in the desulfurized wastewater to the flocculant is 100:0.8.

[0058] (4) The secondary desulfurization wastewater is adjusted to a pH of 7.0 using an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) to obtain a first alkaline treatment liquid, and then the first alkaline treatment liquid is introduced into the upper inlet of a first absorption tower (the first absorption tower is the same as the first absorption tower in Example 1), and at the same time, carbon dioxide gas is introduced into the first absorption tower from the bottom inlet of the first absorption tower. The first alkaline treatment liquid and carbon dioxide are in countercurrent contact in the first absorption tower. During the countercurrent contact process, the first alkaline treatment liquid absorbs carbon dioxide to form an acidic treatment liquid, and the acidic treatment liquid flows out from the bottom outlet of the first absorption tower. The pH of the acidic treatment liquid is 7.5;

[0059] Then, the acidic treatment liquid is passed into the electrocoagulation tank, and at the same time, an alkaline pH regulator (the alkaline pH regulator is a sodium hydroxide solution with a mass fraction of 20%) is added into the electrocoagulation tank. The acidic treatment liquid and the alkaline pH regulator are mixed under stirring to obtain a second alkaline treatment liquid with a pH of 11; the anode of the electrocoagulation tank has an aluminum plate with adjustable current, the voltage of the electrocoagulation is 2V, and the current is 800A. The aluminum plate reacts chemically under the action of the current to produce aluminum ions. In an alkaline environment, the aluminum ions are hydrolyzed and a flocculation reaction occurs. The cations such as calcium and magnesium in the second alkaline treatment liquid are enriched at the cathode and combined with the hydroxide ions near the cathode to produce precipitation, which is then filtered to complete the hardness removal treatment. The filtered liquid is the wastewater after hardness removal;

[0060] (5) The de-hardened sewage is introduced into the upper inlet of the second absorption tower (the second absorption tower is the same as the second absorption tower in Example 1), and the carbon dioxide gas is introduced into the second absorption tower from the bottom inlet of the second absorption tower. The de-hardened sewage and the carbon dioxide are in countercurrent contact in the second absorption tower. During the countercurrent contact process, the de-hardened sewage absorbs the carbon dioxide to form purified water with a pH of 6 to 9, and the purified water flows out from the bottom outlet of the second absorption tower.

[0061] Comparative Example 1

[0062] The only difference between the method for treating sulfur-containing wastewater in this comparative example and the method for treating sulfur-containing wastewater in Example 1 is that in step (1) of the method for treating sulfur-containing wastewater in this comparative example, the filtered liquids are mixed to obtain pretreated wastewater with a pH of 7.5, and in step (2) of the method for treating sulfur-containing wastewater in this comparative example, the volume ratio of the stripping gas to the pretreated wastewater is increased to 30:1 to allow more carbon dioxide to dissolve into the pretreated wastewater.

[0063] Comparative Example 2

[0064] The difference between the method for treating sulfur-containing wastewater in this comparative example and the method for treating sulfur-containing wastewater in Example 1 is that in step (2) of the method for treating sulfur-containing wastewater in this comparative example, the pretreated wastewater is first introduced into the upper part of the first packed tower, and carbon dioxide is introduced into the bottom of the first packed tower at the same time. The pretreated wastewater and carbon dioxide are in countercurrent contact in the first packed tower, and the pretreated wastewater absorbs carbon dioxide to convert sulfide in the wastewater into hydrogen sulfide. After the pretreated wastewater absorbs carbon dioxide, second pretreated wastewater is formed and flows out from the bottom of the first packed tower. The second pretreated wastewater is then introduced into the upper part of the second packed tower, and nitrogen is introduced into the bottom of the second packed tower. The second pretreated wastewater and nitrogen are in countercurrent contact in the second packed tower. The second pretreated wastewater absorbs carbon dioxide. Nitrogen is collected to allow hydrogen sulfide in the sewage to escape, and desulfurized sewage is obtained, and the desulfurized sewage flows out from the bottom of the second packed tower; the volume ratio of carbon dioxide to pretreated sewage in the first packed tower is the same as the volume ratio of the stripping gas to pretreated sewage in step (2) of Example 1, and the working pressure in the first packed tower is the same as the working pressure in the packed tower in step (2) of Example 1; the volume ratio of nitrogen to the second pretreated sewage in the second packed tower is the same as the volume ratio of the stripping gas to pretreated sewage in step (2) of Example 1, and the working pressure in the second packed tower is the same as the working pressure in the packed tower in step (2) of Example 1, and the first packed tower and the second packed tower are the same as the stripping desulfurization tower in step (2) of Example 1.

[0065] Comparative Example 3

[0066] The difference between the method for treating sulfur-containing wastewater in this comparative example and the method for treating sulfur-containing wastewater in Example 1 is that in step (2) of the method for treating sulfur-containing wastewater in this comparative example, the working pressure in the gas lift desulfurization tower is controlled at 18 kPa.

[0067] Comparative Example 4

[0068] The difference between the treatment method of the sulfur-containing wastewater of this comparative example and the treatment method of the sulfur-containing wastewater of Example 1 is that in step (2) of the treatment method of the sulfur-containing wastewater of this comparative example, the working pressure in the gas lift desulfurization tower is controlled at 3 kPa.

[0069] Comparative Example 5

[0070] The method for treating sulfur-containing wastewater in this comparative example specifically comprises the following steps:

[0071] (1) filtering the sulfur-containing wastewater (sulfide content of 1000 mg / L, pH=8, hardness of 500 mg / L) generated in the exploitation of the sulfur-containing gas field to remove solid particles in the sulfur-containing wastewater, and then mixing the filtered liquid with an acid solution (the acid solution is hydrochloric acid with a mass fraction of 30%) to obtain pretreated wastewater with a pH of 5;

[0072] (2) The pretreated sewage is introduced into the upper part of the gas stripping desulfurization tower (the gas stripping desulfurization tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, and a packing thickness of 8000 mm), and nitrogen is introduced into the bottom of the gas stripping desulfurization tower at the same time. The pretreated sewage and the gas stripping gas are in countercurrent contact in the gas stripping desulfurization tower to achieve gas stripping desulfurization of the pretreated sewage. The volume ratio of the gas stripping gas to the pretreated sewage is 20:1. The working pressure in the gas stripping desulfurization tower is controlled at 15 kPa. The sewage after gas stripping desulfurization (desulfurized sewage) flows out from the bottom of the gas stripping desulfurization tower;

[0073] (3) The desulfurized wastewater is transported to a flocculation tank, and then a chemical desulfurizer is added to the flocculation tank. After stirring for 10 seconds, the desulfurized wastewater reacts with the chemical desulfurizer to generate elemental sulfur. Then, a coagulant and a flocculant are added to the flocculation tank. After coagulation and flocculation, a precipitate is generated. The supernatant is the secondary desulfurized wastewater. The chemical desulfurizer is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide. The mass ratio of sulfide in the desulfurized wastewater to the chemical desulfurizer is 100:50; the mass ratio of sulfide in the desulfurized wastewater to the coagulant is 100:20; and the mass ratio of sulfide in the desulfurized wastewater to the flocculant is 100:0.5.

[0074] (4) using sodium carbonate and sodium hydroxide to remove the hardness of the secondary desulfurization wastewater, and then mixing the hardness-removed system with a coagulant and a flocculant to perform a coagulation and flocculation reaction, and the supernatant after precipitation is the hardness-removed wastewater; the coagulant is polyaluminium chloride, and the flocculant is polyacrylamide;

[0075] (5) The wastewater after hardness removal is adjusted to purified water with a pH of 6 to 9 using 30% hydrochloric acid.

[0076] Comparative Example 6

[0077] The difference between the treatment method of sulfur-containing wastewater in this comparative example and the treatment method of sulfur-containing wastewater in comparative example 5 is that the sulfide content of the sulfur-containing wastewater in step (1) of the treatment method of sulfur-containing wastewater in this comparative example is 2000 mg / L, pH=8, and hardness is 800 mg / L, and the volume ratio of the stripping gas and the pretreated wastewater in step (2) is 10:1, the working pressure in the stripping desulfurization tower is controlled at 10 kPa, and the mass ratio of the sulfide in the desulfurized wastewater and the chemical desulfurizer in step (3) is 100:80; the mass ratio of the sulfide in the desulfurized wastewater and the coagulant is 100:25; and the mass ratio of the sulfide in the desulfurized wastewater and the flocculant is 100:1.

[0078] Comparative Example 7

[0079] The difference between the treatment method of sulfur-containing wastewater in this comparative example and the treatment method of sulfur-containing wastewater in comparative example 5 is that the sulfide content of the sulfur-containing wastewater in step (1) of the treatment method of sulfur-containing wastewater in this comparative example is 1000 mg / L, pH=8, and hardness is 500 mg / L, and the volume ratio of the stripping gas and the pretreated wastewater in step (2) is 5:1, the working pressure in the stripping desulfurization tower is controlled at 5 kPa, and the mass ratio of the sulfide in the desulfurized wastewater and the chemical desulfurizer in step (3) is 100:60; the mass ratio of the sulfide in the desulfurized wastewater and the coagulant is 100:22; and the mass ratio of the sulfide in the desulfurized wastewater and the flocculant is 100:0.8.

[0080] Experimental example

[0081] In order to evaluate the desulfurization effect of the treatment method of sulfur-containing wastewater in Examples 1-3 and Comparative Examples 1-4, the sulfide content of the desulfurized wastewater obtained in step (2) of the treatment method of sulfur-containing wastewater in Examples 1-3 and Comparative Examples 1-4 was detected, and the hardness of the purified water obtained by the treatment method of sulfur-containing wastewater in Examples 1-3 and Comparative Examples 1-4 was detected. At the same time, according to the initial sulfide content and hardness of the sulfur-containing wastewater, the corresponding sulfide removal rate and hardness removal rate were calculated, and the results are shown in Table 1. Among them, the sulfide removal rate of desulfurized wastewater = (sulfide content of sulfur-containing wastewater - sulfide content of desulfurized wastewater) / sulfide content of sulfur-containing wastewater × 100%, and the hardness removal rate of purified water = (hardness of sulfur-containing wastewater - hardness of purified water) / hardness of sulfur-containing wastewater × 100%.

[0082] Table 1 Sulfide removal rate of sulfur-containing wastewater and hardness removal rate of purified water in different treatment methods

[0083]

[0084] In order to evaluate the cost difference between the treatment method of sulfur-containing wastewater of the present invention and the conventional treatment method of sulfur-containing wastewater, the reagent costs (including hydrochloric acid, sodium hypochlorite, polyaluminum chloride, polyacrylamide, sodium hydroxide, sodium carbonate, etc. used in the treatment process) and operating costs (including electricity costs and sludge disposal costs, etc.) in the treatment methods of Examples 1-3 and Comparative Examples 5-7 are summarized, and the results are shown in Table 2.

[0085] Table 2 Comparison of costs required for different treatment methods

[0086]

[0087]

Claims

1. A method for treating sulfur-containing wastewater, characterized in that: The following steps are involved: (1) conditioning the sulfur-containing wastewater to adjust the pH of the sulfur-containing wastewater to 6 to 7 to obtain pretreated wastewater; (2) The pretreated sewage and the stripping gas are countercurrently contacted to perform stripping desulfurization on the pretreated sewage to obtain desulfurized sewage; the stripping gas is mainly composed of nitrogen and carbon dioxide; the volume ratio of nitrogen to carbon dioxide is (1-4):

1.

2. The method for treating sulfur-containing wastewater according to claim 1, wherein: The volume ratio of the stripping gas to the pre-treated sewage during the stripping desulfurization is (5-20):

1.

3. The method for treating sulfur-containing wastewater according to claim 1, characterized in that: The working pressure of the gas stripping desulfurization is 5 to 15 kPa.

4. The method for treating sulfur-containing wastewater according to claim 1, characterized in that: In step (1), the conditioning treatment is to first remove solid particles in the sulfur-containing wastewater, and then adjust the pH of the sulfur-containing wastewater to 6-7.

5. The method for treating sulfur-containing wastewater according to any one of claims 1 to 4, characterized in that: The method for treating sulfur-containing wastewater also includes the following steps: desulfurizing the desulfurized wastewater with a chemical desulfurizer to convert the sulfide in the wastewater into elemental sulfur, then adding a coagulant and a flocculant to perform a coagulation and flocculation reaction, and performing solid-liquid separation to obtain secondary desulfurized wastewater, and then performing a hardness removal treatment on the secondary desulfurized wastewater, and finally adjusting the pH of the wastewater after the hardness removal treatment to a set value to obtain purified water.

6. The method for treating sulfur-containing wastewater according to claim 5, characterized in that: The hardness removal treatment method comprises the following steps: using an alkaline pH regulator to adjust the pH of the secondary desulfurization wastewater to 7.0-8.5 to obtain a first alkaline treatment liquid, then absorbing carbon dioxide into the first alkaline treatment liquid to obtain an acidic treatment liquid, then using an alkaline pH regulator to adjust the pH of the acidic treatment liquid to 10-11, performing a first solid-liquid separation to obtain a second alkaline treatment liquid, and finally subjecting the second alkaline treatment liquid to an electric flocculation treatment, a second solid-liquid separation, and completing the hardness removal treatment.

7. The method for treating sulfur-containing wastewater according to claim 6, characterized in that: In the hardness removal method, the pH of the acidic treatment solution is 6.0 to 7.

5.

8. The method for treating sulfur-containing wastewater according to claim 6, characterized in that: The first alkaline treatment liquid absorbs carbon dioxide by bringing the first alkaline treatment liquid and carbon dioxide into countercurrent contact, so that the first alkaline treatment liquid absorbs carbon dioxide.

9. The method for treating sulfur-containing wastewater according to claim 6, characterized in that: During the electro-flocculation treatment, the electro-flocculation anode is made of aluminum and / or iron; the voltage of the electro-flocculation treatment is 2.0-4.0V, and the current is 800-1200A.

10. The method for treating sulfur-containing wastewater according to claim 5, characterized in that: The pH of the wastewater after hardness removal treatment is adjusted to a set value using carbon dioxide; the set value is 6 to 9.

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