A method for treating a sulfur-containing wastewater

Abstract

The present application relates to a kind of sulphur-containing sewage treatment method, belong to oil and gas field sulphur-containing sewage treatment technical field.The sulphur-containing sewage treatment method of the present application, using the stripping gas mainly by nitrogen and carbon dioxide is stripped to sulphur-containing sewage and desulfurization, can effectively reduce the sulfide content in sewage, thereby reducing the amount of subsequent desulfurization flocculant, can effectively reduce the processing cost of sulphur-containing sewage.

Description

TECHNICAL FIELD

[0001] The application relates to a treatment method of sulfur-containing sewage, and belongs to the technical field of sulfur-containing sewage treatment of oil and gas fields. BACKGROUND

[0002] A large amount of sulfur-containing sewage is generated in the exploitation process of a sulfur-containing gas field, the pH value of the sulfur-containing sewage is above 8, the sulfide content is generally 1000-3000 mg / L, and the sulfides mainly exist in the forms of HS - , S 2- and H2S. The sulfur-containing sewage has extremely strong toxicity, can cause great threat to personnel health and the surrounding environment, the sulfides in the water body have strong corrosiveness, can cause serious damage to metal pipelines and gas field development, and the hardness of the desulfurized sewage needs to be up to standard in resource recycling. Therefore, the sulfur-containing sewage generated in the exploitation of the gas field must be subjected to desulfurization and hardness removal treatment.

[0003] The methods for removing the hardness of sewage mainly include a lime and soda method, a caustic soda and soda method, and a membrane technology. The caustic soda and soda method is usually used for the hardness removal treatment of high-sulfur sewage, and includes the following steps: adding caustic soda and soda reagents into the sewage, adjusting the pH value of the sewage to 10-11, adding a coagulant and a flocculant, performing a sedimentation reaction, and then adjusting the pH value to 6-9 by using hydrochloric acid. In the above hardness removal process, a large amount of caustic soda and soda reagents need to be used, and hydrochloric acid needs to be added for adjusting the pH value of the effluent, so that the cost of the hardness removal treatment of high-sulfur sewage is high.

[0004] The desulfurization treatment of high-sulfur sewage of oil and gas fields generally adopts a gas stripping method. Based on Henry's law, the hydrogen sulfide gas has the characteristic of small solubility in water, and the inert gas (nitrogen or natural gas) which does not react with the hydrogen sulfide gas is used to continuously contact the sewage in a gas stripping tower, so that the partial pressure of the hydrogen sulfide in the gas phase is lower than the partial pressure in the gas-liquid phase equilibrium, and the hydrogen sulfide in the liquid phase continuously enters the gas phase, so as to achieve the purpose of desulfurization from the sewage. However, when the pH value of the wastewater is high, the sulfides in the wastewater exist in the forms of HS - , S 2- , and the gas stripping tower cannot remove the ionic sulfides, and a large amount of hydrochloric acid needs to be used to adjust the pH value of the sewage to 5.0-5.5 in actual production. When the hydrochloric acid is insufficiently added, the sulfides in the sewage cannot be completely resolved, and the effluent sulfides are over standard. When the hydrochloric acid is excessively added, the smooth operation of the subsequent water treatment system is impacted, the water quality is over standard, the corrosion of the water treatment system is intensified, and the treatment cost is increased due to the use of the hydrochloric acid.

[0005] Therefore, it is urgent to develop a low-cost treatment method of sulfur-containing sewage. SUMMARY

[0006] The present application aims to provide a sulfur-containing sewage treatment method, which can solve the problem of high cost in treating sulfur-containing sewage generated in the process of exploiting sulfur-containing gas fields.

[0007] To achieve the above-mentioned purpose, the technical scheme of the sulfur-containing sewage treatment method of the present application is as follows:

[0008] A sulfur-containing sewage treatment method, comprising the following steps:

[0009] (1) The sulfur-containing sewage is subjected to conditioning treatment to adjust the pH of the sulfur-containing sewage to 6-7, to obtain pretreated sewage.

[0010] (2) The pretreated sewage is subjected to countercurrent contact with stripping gas to strip and desulfurize the pretreated sewage, to obtain desulfurized sewage; the stripping gas mainly consists of nitrogen and carbon dioxide; the volume ratio of the nitrogen to the carbon dioxide is (1-4):1.

[0011] The sulfur-containing sewage treatment method of the present application can effectively reduce the sulfide content in the sewage by using the stripping gas mainly consisting of nitrogen and carbon dioxide to strip and desulfurize the sulfur-containing sewage, thereby reducing the amount of subsequent desulfurization flocculant and effectively reducing the treatment cost of the sulfur-containing sewage.

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

[0013] Adjusting the pH of the sulfur-containing sewage to 6-7 before stripping and desulfurization is beneficial to the subsequent stripping process of sulfides; adjusting the pH of the sulfur-containing sewage to below 6 will increase the amount of acid liquid and increase the treatment cost, and adjusting the pH of the sulfur-containing sewage to above 7 will reduce the stripping and desulfurization efficiency and cause the effluent sulfide to exceed the standard.

[0014] When the pretreated sewage is subjected to countercurrent contact with the stripping gas, the carbon dioxide in the stripping gas dissolves in the sewage, ionizes to produce hydrogen ions, and converts the sulfides in the sewage into hydrogen sulfide gas, while the nitrogen in the stripping gas strips the hydrogen sulfide gas from the sewage and carries it away. The relationship between the volume ratio of nitrogen to carbon dioxide in the stripping gas and the sulfide content in the pretreated sewage is that as the sulfide content in the pretreated sewage increases, the volume ratio of nitrogen to carbon dioxide in the stripping gas decreases.

[0015] In the present application, the sulfur-containing sewage refers to the sulfur-containing sewage generated in the process of exploiting oil and gas fields.

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

[0017] Preferably, the working pressure of the gas stripping desulfurization is 5-15 kPa. The greater the working pressure of the gas stripping desulfurization, the more beneficial it is for the stripping gas to dissolve into the pretreated sewage and carry out hydrogen sulfide, but the working pressure of the gas stripping desulfurization is too large, which causes the hydrogen sulfide in the liquid phase to be difficult to escape, and in order to improve the amount of carbon dioxide dissolved and promote the hydrogen ion generated by carbon dioxide, the working pressure of the gas stripping desulfurization is controlled in a suitable range.

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

[0019] In the present application, the pretreated sewage and the stripping gas are countercurrently contacted in the packed tower, the pretreated sewage flows from top to bottom in the packed tower, the stripping gas flows from bottom to top in the packed tower, and the pretreated sewage and the stripping gas are countercurrently contacted during the flowing process to complete the gas stripping desulfurization.

[0020] It can be understood that the packing in the packed tower for the gas stripping desulfurization is structured packing, for example, structured pulse wave corrugated packing. The pulse wave corrugated packing is a disc-shaped or block-shaped packing body composed of pulse wave sheet pieces with specific shape pulse units made of plastic or metal thin strips according to certain rules.

[0021] Preferably, in step (1), the conditioning treatment is to remove the solid particles in the sulfur-containing sewage, and then adjust the pH of the sulfur-containing sewage to 6-7. Removing the solid particles can avoid the particles in the sewage from blocking the packing of the stripping tower and affecting the effect of the gas stripping desulfurization. Removing the solid particles first and then adjusting the pH to 6-7 can avoid the dissolution of part of the particles when adjusting the pH and is beneficial to the stable operation of the pH adjustment.

[0022] Preferably, in step (1), the removal of the solid particles in the sulfur-containing sewage is achieved by filtration.

[0023] Preferably, the treatment method of the sulfur-containing sewage further comprises the following steps: desulfurizing the desulfurized sewage by using a chemical desulfurizing agent to convert the sulfide in the sewage into elemental sulfur, then adding a coagulant and a flocculant to perform a coagulation and flocculation reaction, performing solid-liquid separation to obtain secondary desulfurized sewage, then performing a hardness removal treatment on the secondary desulfurized sewage, and finally adjusting the pH of the sewage after the hardness removal treatment to a set value to obtain purified water.

[0024] It can be understood that the chemical desulfurizing agent, the coagulant and the flocculant suitable for the treatment of the sulfur-containing sewage are all suitable for the present application. For example, the chemical desulfurizing agent is hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is a polyacrylamide flocculant.

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

[0026] Preferably, the method for removing hardness comprises the following steps: adjusting the pH of the secondary desulfurization wastewater to 7.0-8.5 by using an alkaline pH regulator to obtain a first alkaline treatment liquid, absorbing carbon dioxide by the first alkaline treatment liquid to obtain an acid treatment liquid, adjusting the pH of the acid treatment liquid to 10-11 by using an alkaline pH regulator, first solid-liquid separation to obtain a second alkaline treatment liquid, and finally performing electrocoagulation treatment on the second alkaline treatment liquid and second solid-liquid separation to complete the hardness removal treatment. In the method for removing hardness, the step of adjusting the pH of the secondary desulfurization wastewater to 7.0-8.5 by using an alkaline pH regulator is to improve the efficiency of absorbing carbon dioxide by the wastewater. In this step, if the pH is less than 7, the dissolved carbon dioxide in the wastewater will be insufficient, and the calcium ion in the system effluent will exceed the standard; if the pH is greater than 8.5, the calcium ion will precipitate and block the filler, affecting the absorption of carbon dioxide. The step of adjusting the pH of the acid treatment liquid to 10-11 by using an alkaline pH regulator is to make the calcium, magnesium and other cations in the liquid react with hydroxyl ions to precipitate, so as to remove the calcium, magnesium and other cations. In this step, if the pH is less than 10, the precipitation will be insufficient, and the calcium, magnesium and other cations cannot be effectively removed; if the pH is greater than 11, the amount of liquid alkali added will be excessive, increasing the treatment cost.

[0027] Preferably, the absorption of carbon dioxide by the first alkaline treatment liquid is achieved by countercurrent contact of the first alkaline treatment liquid and carbon dioxide. For example, the first alkaline treatment liquid and carbon dioxide are countercurrently contacted in a packed column to achieve the absorption of carbon dioxide by the first alkaline treatment liquid.

[0028] Preferably, in the method for removing hardness, the pH of the acid treatment liquid is 6.0-7.5. Controlling the pH of the acid treatment liquid to be 6.0-7.5 can ensure that enough carbonate ions enter the system to form carbonate precipitates with calcium, magnesium and other cations. When the pH is too low, bicarbonate is formed instead of carbonate, and the calcium, magnesium and other cations cannot form precipitates.

[0029] Preferably, in the electrocoagulation treatment, the electrocoagulation anode material is aluminum and / or iron. In the electrocoagulation treatment process, the electrified electrode plate in the electrocoagulation device will undergo an electrochemical reaction to dissolve Al 3+ or Fe 2+The flocculation reaction occurs by plasma and hydrolysis in water. The electric field of the electric flocculation device also makes the anions and cations in the sewage move directionally in the electric field, so that the cations such as calcium and magnesium are enriched near the cathode and combine with the high-concentration hydroxyl ions generated by the cathode to produce hydroxide precipitates, so as to achieve the purpose of hardness removal.

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

[0031] Preferably, carbon dioxide is used to adjust the pH of the sewage after hardness removal treatment to a set value. Further preferably, the carbon dioxide is used to contact the sewage after hardness removal treatment in a countercurrent manner to adjust the pH of the sewage after hardness removal treatment to a set value.

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

[0033] Preferably, the use of carbon dioxide to adjust the pH of the sewage after hardness removal treatment to a set value is to contact the carbon dioxide and the sewage after hardness removal treatment in a countercurrent manner to adjust the pH of the sewage after hardness removal treatment to a set value. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The figure is a flowchart of the treatment method of the sulfur-containing sewage of Example 1 of the present application. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described below in combination with specific examples.

[0036] First, the specific implementation of the treatment method of the sulfur-containing sewage of the present application is as follows:

[0037] Example 1

[0038] The treatment method of the sulfur-containing sewage of the present application is as shown in Figure 1 , and specifically includes the following steps:

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

[0040] (2) the pretreated sewage is introduced into the upper part of a 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 regular pulse corrugated packing), while stripping gas composed of nitrogen and carbon dioxide with a volume ratio of 1:1 is introduced into the bottom of the gas stripping desulfurization tower, the pretreated sewage and the stripping gas are countercurrently contacted in the gas stripping desulfurization tower to realize gas stripping desulfurization of the pretreated sewage, the volume ratio of the stripping gas to the pretreated sewage is 20:1, the working pressure in the gas stripping desulfurization tower is controlled at 15 kPa, and the desulfurized sewage (desulfurized sewage) flows out from the bottom of the gas stripping desulfurization tower;

[0041] (3) the desulfurized sewage is transported into a flocculation tank, then a chemical desulfurizing agent is added into the flocculation tank, after stirring for 10 s, elemental sulfur is generated after the desulfurized sewage reacts with the chemical desulfurizing agent, then a coagulant and a flocculant are added into the flocculation tank, and after coagulation and flocculation, a precipitate is generated, and the supernatant is the secondary desulfurized sewage; the chemical desulfurizing agent is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide; the mass ratio of sulfides in the desulfurized sewage to the chemical desulfurizing agent is 100:50; the mass ratio of sulfides in the desulfurized sewage to the coagulant is 100:20; and the mass ratio of sulfides in the desulfurized sewage to the flocculant is 100:0.5;

[0042] (4) the secondary desulfurized sewage is adjusted to a pH of 8.5 by using an alkaline pH regulator (the alkaline pH regulator is a 20% sodium hydroxide solution), 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 (i.e., a hardness removal absorption tower, the first absorption tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, a packing thickness of 8000 mm, and regular pulse corrugated packing), while 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 the carbon dioxide are countercurrently contacted in the first absorption tower, in the countercurrent contact process, the first alkaline treatment liquid absorbs the carbon dioxide to form an acidic treatment liquid, the acidic treatment liquid flows out from the bottom outlet of the first absorption tower, and the pH of the acidic treatment liquid is 6.0;

[0043] Then the acidic treatment liquid is introduced into an electrocoagulation tank, while an alkaline pH regulator (the alkaline pH regulator is a 20% sodium hydroxide solution) 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 4 V, the current is 1200 A, the aluminum plate undergoes chemical reaction under the action of the current to generate aluminum ions, the aluminum ions undergo hydrolysis in the alkaline environment to generate a flocculation reaction, the calcium, magnesium and other cations in the second alkaline treatment liquid are enriched at the cathode to combine with the hydroxyl ions near the cathode to generate a precipitate, then filtration is performed, the hardness removal treatment is completed, and the liquid obtained by filtration is the sewage after hardness removal.

[0044] (5) the hardening-removed wastewater is introduced into the upper inlet of a second absorption tower (the second absorption tower is a packed tower with a diameter of 800 mm, a height of 12000 mm, and a packing thickness of 8000 mm, and the packing is regular pulse wave packing), and carbon dioxide gas is introduced into the second absorption tower from the bottom inlet of the second absorption tower, so that the hardening-removed wastewater and the carbon dioxide gas are countercurrently contacted in the second absorption tower; in the countercurrent contact process, the hardening-removed wastewater absorbs the carbon dioxide to form purified water with a pH of 6-9, and the purified water flows out from the bottom outlet of the second absorption tower.

[0045] Example 2

[0046] The treatment method of the sulfur-containing wastewater in the embodiment specifically comprises the following steps:

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

[0048] (2) the pretreated wastewater is introduced into the upper part of a 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 stripping gas composed of nitrogen and carbon dioxide with a volume ratio of 3:1 is introduced into the bottom of the gas stripping desulfurization tower, so that the pretreated wastewater and the stripping gas are countercurrently contacted in the gas stripping desulfurization tower to realize gas stripping desulfurization of the pretreated wastewater; the volume ratio of the stripping gas to the pretreated wastewater is 10:1, the working pressure in the gas stripping desulfurization tower is controlled at 10 kPa, and the desulfurized wastewater (desulfurized wastewater) flows out from the bottom of the gas stripping desulfurization tower;

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

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

[0051] Then the acidic treatment liquid is introduced into an electrocoagulation tank, while an alkaline pH regulator (the alkaline pH regulator is a 20% sodium hydroxide solution by mass fraction) is added into the electrocoagulation tank, and the acidic treatment liquid and the alkaline pH regulator are mixed under stirring to obtain a second alkaline treatment liquid with pH 10; the anode of the electrocoagulation tank has an aluminum plate with adjustable current, the voltage of the electrocoagulation is 3V, the current is 1000A, the aluminum plate undergoes chemical reaction under the action of the current to generate aluminum ions, and the aluminum ions undergo hydrolysis to generate a flocculation reaction in the alkaline environment, the calcium, magnesium and other cations in the second alkaline treatment liquid are enriched at the cathode to combine with the hydroxyl ions near the cathode to generate a precipitate, then filtration is performed, the hardening removal treatment is completed, and the liquid obtained by filtration is the wastewater after hardening removal;

[0052] (5) the wastewater after hardening removal is introduced into an upper inlet of a second absorption tower (the second absorption tower is the same as the second absorption tower in Example 1), while carbon dioxide gas is introduced into the second absorption tower from a bottom inlet of the second absorption tower, and the wastewater after hardening removal and the carbon dioxide are countercurrently contacted in the second absorption tower, in the process of countercurrent contact, the wastewater after hardening removal absorbs the carbon dioxide to form purified water with pH 6-9, and the purified water flows out from a bottom outlet of the second absorption tower.

[0053] Example 3

[0054] The treatment method of the sulfur-containing wastewater in the embodiment specifically includes the following steps:

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

[0056] (2) the pretreated sewage is introduced into the upper part of a 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), while stripping gas composed of nitrogen and carbon dioxide with a volume ratio of 4:1 is introduced into the bottom of the gas stripping desulfurization tower, the pretreated sewage and the stripping gas are countercurrently contacted in the gas stripping desulfurization tower to realize gas stripping desulfurization of the pretreated sewage, the volume ratio of the 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 sewage is transported into a flocculation tank, then a chemical desulfurizing agent is added into the flocculation tank, after stirring for 10 s, the desulfurized sewage reacts with the chemical desulfurizing agent to generate elemental sulfur, then a coagulant and a flocculant are added into the flocculation tank, after coagulation and flocculation, a precipitate is generated, and the supernatant is the secondary desulfurized sewage; the chemical desulfurizing agent is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide; the mass ratio of sulfides in the desulfurized sewage to the chemical desulfurizing agent is 100:60; the mass ratio of sulfides in the desulfurized sewage to the coagulant is 100:22; and the mass ratio of sulfides in the desulfurized sewage to the flocculant is 100:0.8;

[0058] (4) the secondary desulfurized sewage is adjusted to pH 7.0 by 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, 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), while 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 the carbon dioxide are countercurrently contacted in the first absorption tower, in the process of countercurrent contact, the first alkaline treatment liquid absorbs the carbon dioxide to form an acid treatment liquid, the acid treatment liquid flows out from the bottom outlet of the first absorption tower, and the pH of the acid treatment liquid is 7.5;

[0059] Then the acid treatment liquid is introduced into an electrocoagulation tank, while 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 acid 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 is an aluminum plate with adjustable current, the voltage of electrocoagulation is 2 V, the current is 800 A, the aluminum plate undergoes chemical reaction under the action of current to generate aluminum ions, the aluminum ions undergo hydrolysis in the alkaline environment to generate flocculation, the calcium, magnesium and other cations in the second alkaline treatment liquid are enriched at the cathode to combine with the hydroxyl ions near the cathode to generate a precipitate, then filtration is performed to complete the hardness removal treatment, and the liquid obtained by filtration is the sewage after hardness removal;

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

[0061] Comparative Example 1

[0062] The difference between the treatment method of the sulfur-containing wastewater of the present comparative example and the treatment method of the sulfur-containing wastewater of Example 1 is that in step (1) of the treatment method of the sulfur-containing wastewater of the present comparative example, the liquid obtained by filtration is mixed to obtain pretreated wastewater with a pH of 7.5, and in step (2) of the treatment method of the sulfur-containing wastewater of the present comparative example, the volume ratio of stripping gas to pretreated wastewater is increased to 30:1 to dissolve more carbon dioxide into the pretreated wastewater.

[0063] Comparative Example 2

[0064] The difference between the treatment method of the sulfur-containing wastewater of the present 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 the present comparative example, the pretreated wastewater is first introduced into the upper part of a first packed tower, and carbon dioxide is introduced into the bottom part of the first packed tower. The pretreated wastewater and the carbon dioxide are countercurrently contacted in the first packed tower. The pretreated wastewater absorbs the carbon dioxide to convert the sulfides in the wastewater into hydrogen sulfide. After the pretreated wastewater absorbs the 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 a second packed tower, and nitrogen is introduced into the bottom part of the second packed tower. The second pretreated wastewater and the nitrogen are countercurrently contacted in the second packed tower. The second pretreated wastewater absorbs the nitrogen to release the hydrogen sulfide in the wastewater to obtain desulfurized wastewater, which flows out from the bottom of the second packed tower. The volume ratio of carbon dioxide to pretreated wastewater in the first packed tower is the same as the volume ratio of stripping gas to pretreated wastewater 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 second pretreated wastewater in the second packed tower is the same as the volume ratio of stripping gas to pretreated wastewater 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. The first packed tower and the second packed tower are the same as the stripping and desulfurization tower in step (2) of Example 1.

[0065] Comparative Example 3

[0066] The difference between the treatment method of the sulfur-containing wastewater of the present 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 the present comparative example, the working pressure in the gas stripping desulfurization tower is controlled at 18 kPa.

[0067] Comparative Example 4

[0068] The difference between the treatment method of the sulfur-containing wastewater of the present 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 the present comparative example, the working pressure in the gas stripping desulfurization tower is controlled at 3 kPa.

[0069] Comparative Example 5

[0070] The treatment method of the sulfur-containing wastewater of the present 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 the solid particles in the sulfur-containing wastewater, and then mixing the filtered liquid with an acid liquid (the acid liquid is a hydrochloric acid with a mass fraction of 30%) to obtain pretreated wastewater with a pH of 5;

[0072] (2) passing the pretreated wastewater into the upper part of a 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 passing nitrogen into the bottom of the gas stripping desulfurization tower at the same time, so that the pretreated wastewater and the stripping gas are countercurrently contacted in the gas stripping desulfurization tower to realize gas stripping desulfurization of the pretreated wastewater, the volume ratio of the stripping gas to the pretreated wastewater is 20:1, the working pressure in the gas stripping desulfurization tower is controlled at 15 kPa, and the desulfurized wastewater (desulfurized wastewater) flows out from the bottom of the gas stripping desulfurization tower;

[0073] (3) delivering the desulfurized wastewater to a flocculation tank, then adding a chemical desulfurizing agent into the flocculation tank, stirring for 10 s, and then generating elemental sulfur after the desulfurized wastewater reacts with the chemical desulfurizing agent, and then adding a coagulant and a flocculant into the flocculation tank, generating a precipitate after coagulation and flocculation, and the supernatant is the secondary desulfurized wastewater; the chemical desulfurizing agent is sodium hypochlorite, the coagulant is polyaluminum chloride, and the flocculant is polyacrylamide; the mass ratio of the sulfide in the desulfurized wastewater to the chemical desulfurizing agent is 100:50; the mass ratio of the sulfide in the desulfurized wastewater to the coagulant is 100:20; and the mass ratio of the sulfide in the desulfurized wastewater to the flocculant is 100:0.5;

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

[0075] (5) The hardening-removed wastewater is adjusted to pH 6-9 with 30% hydrochloric acid to obtain purified water.

[0076] Comparative Example 6

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

[0078] Comparative Example 7

[0079] The difference between the treatment method of the sulfur-containing wastewater of the present comparative example and the treatment method of the sulfur-containing wastewater of Comparative Example 5 is that in step (1) of the treatment method of the sulfur-containing wastewater of the present comparative example, the sulfide content of the sulfur-containing wastewater is 2000 mg / L, pH = 8, and the hardness is 800 mg / L, and in step (2), the volume ratio of stripping gas to pretreated wastewater is 10:1, the working pressure in the stripping desulfurization tower is controlled at 10 kPa, and in step (3), the mass ratio of sulfides in the desulfurized wastewater to the chemical desulfurization agent is 100:80; the mass ratio of sulfides in the desulfurized wastewater to the coagulant is 100:25; and the mass ratio of sulfides in the desulfurized wastewater to the flocculant is 100:1.

[0080] Experimental Example

[0081] To evaluate the desulfurization effect of the treatment methods of the sulfur-containing wastewater of Examples 1-3 and Comparative Examples 1-4, the sulfide content of the desulfurized wastewater obtained in step (2) of the treatment methods of the sulfur-containing wastewater of Examples 1-3 and Comparative Examples 1-4 was detected, and the hardness of the purified water obtained by the treatment methods of the sulfur-containing wastewater of 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 the desulfurized wastewater = (sulfide content of the sulfur-containing wastewater - sulfide content of the desulfurized wastewater) / sulfide content of the sulfur-containing wastewater x 100%, and the hardness removal rate of the purified water = (hardness of the sulfur-containing wastewater - hardness of the purified water) / hardness of the sulfur-containing wastewater x 100%.

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

[0083]

[0084] To evaluate the cost difference between the treatment method of the sulfur-containing wastewater of the present application and the conventional treatment method of the sulfur-containing wastewater, the reagent cost (including hydrochloric acid, sodium hypochlorite, polyaluminum chloride, polyacrylamide, sodium hydroxide, sodium carbonate, etc. used in the treatment process) and the operation cost (including electricity cost and sludge disposal cost, etc.) in the treatment methods of Examples 1-3 and Comparative Examples 5-7 were 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 a sulfur-containing wastewater, characterized by, The method comprises the following steps: (1) conditioning treatment of the sulfur-containing wastewater to adjust the pH of the sulfur-containing wastewater to 6-7 to obtain pretreated wastewater; (2) countercurrent contact of the pretreated wastewater and gas stripping gas to perform gas stripping desulfurization on the pretreated wastewater to obtain desulfurized wastewater; the gas stripping gas mainly comprises nitrogen and carbon dioxide; the volume ratio of the nitrogen to the carbon dioxide is (1-4):1; the working pressure of the gas stripping desulfurization is 5-15 kPa; the desulfurized wastewater is subjected to sulfur removal by using a chemical sulfur removal agent to convert sulfides in the wastewater into elemental sulfur, and then is subjected to coagulation and flocculation by adding a coagulant and a flocculant, followed by solid-liquid separation to obtain secondary desulfurized wastewater, and the secondary desulfurized wastewater is subjected to hardness removal treatment; the hardness removal treatment comprises the following steps: adjusting the pH of the secondary desulfurized wastewater to 7.0-8.5 by using an alkaline pH regulator to obtain a first alkaline treatment liquid, absorbing carbon dioxide by the first alkaline treatment liquid to obtain an acid treatment liquid, adjusting the pH of the acid treatment liquid to 10-11 by using an alkaline pH regulator, first solid-liquid separation to obtain a second alkaline treatment liquid, and finally electrocoagulation treatment of the second alkaline treatment liquid, second solid-liquid separation, and completion of the hardness removal treatment.

2. The method of treating sulfur-laden wastewater of claim 1, wherein, The volume ratio of the gas stripping gas to the pretreated wastewater during the gas stripping desulfurization is (5-20):

1.

3. The method of treating sulfur-laden wastewater of claim 1, wherein, The sulfur-containing wastewater has a sulfide content of ≤3000 mg / L, a pH of ≤9, and a hardness of ≤1000 mg / L.

4. The method of treating sulfur-laden wastewater of claim 1, wherein, In step (1), the conditioning treatment is to 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 by, The method for treating the sulfur-containing wastewater further comprises the following steps: the mass ratio of the sulfides in the desulfurized wastewater to the chemical sulfur removal agent is 1:(50-80); the mass ratio of the sulfides in the desulfurized wastewater to the coagulant is 100:(20-25); and the mass ratio of the sulfides in the desulfurized wastewater to the flocculant is 100:(0.5-1).

6. The method of treating sulfur-laden wastewater of claim 1, wherein, In the hardness removal treatment, the pH of the acid treatment liquid is 6.0-7.

5.

7. The method of treating sulfur-laden wastewater of claim 1, wherein, The absorption of carbon dioxide by the first alkaline treatment liquid is countercurrent contact of the first alkaline treatment liquid and the carbon dioxide to enable the first alkaline treatment liquid to absorb the carbon dioxide.

8. The method of treating sulfur-laden wastewater of claim 1, wherein, In the electrocoagulation treatment, the electrocoagulation anode material is aluminum and / or iron; the voltage of the electrocoagulation treatment is 2.0-4.0 V, and the current is 800-1200 A.

9. The method of treating sulfur-laden wastewater of claim 1, wherein, The pH of the wastewater after the hardness removal treatment is adjusted to a set value by using carbon dioxide; the set value is 6-9.

10. The method of treating sulfur-laden wastewater of claim 9, wherein, The adjustment of the pH of the wastewater after the hardness removal treatment to a set value by using carbon dioxide is countercurrent contact of the carbon dioxide and the wastewater after the hardness removal treatment to adjust the pH of the wastewater after the hardness removal treatment to the set value.

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