Anti-scaling method for evaporation process of drilling and production wastewater

Abstract

The invention provides an anti-scaling method for a drilling and production wastewater evaporation process, which relates to the technical field of oil and gas field wastewater treatment, and comprises the following steps: adding a sodium hydroxide solution into wastewater to adjust the pH value, and adding a sodium carbonate solution into the wastewater after adjusting the pH value to preliminarily reduce the concentration of calcium and magnesium ions in the wastewater; adding phosphate into the wastewater subjected to primary hardness removal to further remove calcium and magnesium ions, then adding polyaluminum chloride and polyacrylamide for flocculation and precipitation, adding hydrochloric acid into effluent of a precipitation tank to adjust the pH value to 8-9, and then carrying out evaporation treatment. According to the method, calcium, magnesium and strontium ions in the wastewater can be efficiently removed, the removal rate of the calcium and magnesium ions is higher compared with that of a traditional dual-alkali method for removing hardness, and meanwhile cooperative treatment of ammonia and nitrogen is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field wastewater treatment, in particular to an anti-scaling method in the evaporation process of drilling wastewater. Background Art

[0002] During the wastewater evaporation process, the calcium, magnesium and strontium ions contained in the wastewater will form scale in the heat exchanger and process pipelines of the multiple-effect evaporator, causing problems such as reduced heat exchange efficiency and local blockage.

[0003] The existing technology mainly uses the conventional double alkali method to remove the concentration of calcium and magnesium ions in wastewater to reduce the scaling effect of wastewater during evaporation: that is, the pH value of the wastewater is mainly adjusted by adding lime or sodium hydroxide to remove the magnesium ion concentration in the wastewater, and then the calcium ion concentration is removed by adding sodium carbonate, thereby controlling the total hardness and reducing the scale formed by calcium and magnesium salt crystals during the evaporation of wastewater.

[0004] When the double alkali method is used to reduce the hardness of wastewater, it cannot effectively remove residual calcium, magnesium and strontium ions in the wastewater, and the removal efficiency is low. Under high temperature and high concentration conditions, wastewater will still form scale in the heat exchanger and process pipelines of the multiple-effect evaporator. Therefore, it is necessary to develop more efficient wastewater hardness removal technology to prevent scaling of the evaporator. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preventing scaling in the evaporation process of drilling wastewater, which solves the problem that the prior art method for removing calcium and magnesium ions in wastewater cannot effectively remove them, and calcium, magnesium and strontium ions will still remain in the wastewater, and the removal efficiency is low. Under high temperature and high concentration conditions, wastewater will still form scaling in the heat exchanger and process pipeline of the multiple-effect evaporator.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preventing scale in a drilling wastewater evaporation process, comprising the following steps: S1. Determine the calcium hardness CaH and total alkalinity TAC in the wastewater. The units of calcium hardness CaH and total alkalinity TAC are mg / L. S2. Add sodium hydroxide to the wastewater to adjust the pH value of the wastewater to 13±0.2; S3, first-level hardness removal reaction Sodium carbonate is added to the wastewater in an amount of g, which is 1 to 2 times the difference between the calcium hardness CaH and the total alkalinity TAC per cubic meter of wastewater. After adding sodium carbonate, the reaction is stirred at a speed of 80 to 90 rpm for 25 to 40 minutes. S4, secondary hardness removal reaction Add phosphate reagents to the wastewater at an amount of 1-2 kg per cubic meter of wastewater, and stir and react at a speed of 80-90 rpm for 10-20 minutes after adding the phosphate reagents; S5, coagulation, flocculation Add polyaluminium chloride to the wastewater at a mass ratio of 0.05% to 0.1% for coagulation, and add polyacrylamide at a mass ratio of 0.01% for flocculation; S6, precipitation; S7. Adjust the pH value to 8~9.

[0007] Preferably, the phosphate agent is at least one of sodium phosphate, sodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0008] Preferably, the precipitation in step S6 is carried out in a high-efficiency sedimentation tank; The coagulation in step S5 is carried out in a coagulation tank; It also includes: returning the sludge in the high-efficiency sedimentation tank in step S6 to the flocculation tank in step S5, and controlling the return flow rate to be 4% to 8% of the process water flow rate.

[0009] Preferably, the high-efficiency sedimentation tank and coagulation tank both have a sludge discharge system.

[0010] Preferably, after treatment in steps S1-S7, the total hardness of the wastewater is reduced to below 20 mg / L, the strontium ion concentration is reduced to below 30 mg / L, and the ammonia nitrogen is reduced to below 15 mg / L.

[0011] Preferably, the adding of sodium hydroxide into the wastewater in step S2 is completed in a pipeline mixer.

[0012] Preferably, in S7, hydrochloric acid is used to adjust the pH value to 8-9.

[0013] Preferably, the primary hardness removal reaction in step S3 is carried out in a primary hardness removal reaction tank; The secondary hardness removal reaction in step S4 is carried out in a secondary hardness removal reaction tank.

[0014] The present invention provides a method for preventing scale in the evaporation process of drilling wastewater. It has the following beneficial effects: 1. The present invention adopts the method of adding sodium hydroxide solution to wastewater to adjust the pH value, and then adding sodium carbonate solution to the wastewater to preliminarily reduce the concentration of calcium and magnesium ions in the wastewater after adjusting the pH value of the wastewater to 13±0.2 (higher alkalinity), adding phosphate to the wastewater after the preliminary hardness removal to further remove the calcium and magnesium ions, and then adding polyaluminum chloride and polyacrylamide for flocculation and precipitation. Under alkaline conditions, the effect of removing calcium and magnesium ions in each step is more obvious, and the effluent from the sedimentation tank is added with hydrochloric acid to adjust the pH value to 8-9 and then evaporated to effectively remove the concentration of calcium, magnesium and strontium ions in the wastewater. The removal rate of calcium and magnesium ions is higher than that of the traditional double alkali method for removing hardness, and the coordinated treatment of ammonia nitrogen is achieved at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention provides a flow chart of a method for preventing scale in the evaporation process of drilling wastewater. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Embodiment 1: A method for preventing scale in a drilling wastewater evaporation process, comprising the following steps: S1. Determine the calcium hardness CaH and total alkalinity TAC in wastewater (the numerical units of calcium hardness CaH and total alkalinity TAC are consistent, both in mg / L); Specifically, relevant measuring instruments or sampling instruments for calcium hardness CaH and total alkalinity TAC are installed on the pipeline system through which the wastewater flows. If it is a sampling instrument, the sample is taken out and accurately measured in the laboratory to obtain the calcium hardness CaH and total alkalinity TAC.

[0018] S2. Add sodium hydroxide to the wastewater to adjust the pH value of the wastewater to 13±0.2; The addition of sodium hydroxide to the wastewater in step S2 is completed in the pipeline mixer, that is, by installing a sodium hydroxide addition branch pipe system on the pipeline system, pumping sodium hydroxide into the pipeline system in a quantitative manner, and performing detection feedback based on the pH value detection instrument inside the pipeline mixer, thereby controlling the pumping amount of sodium hydroxide.

[0019] In step S2, magnesium ions in the wastewater combine with hydroxide ions to form magnesium hydroxide, bicarbonate ions in the wastewater react with hydroxide ions to form carbonate ions, and carbonate ions react with calcium ions in the wastewater to form calcium carbonate.

[0020] S3, first-level hardness removal reaction Sodium carbonate was added to the wastewater at an amount of 1 to 2 times (CaH-TAC) g per cubic meter of wastewater, and then stirred at a speed of 80-90 rpm for 25 to 40 minutes. The amount of (CaH~TAC) refers to the difference between calcium hardness CaH and total alkalinity TAC. The units of CaH and TAC are both mg / L (calculated as CaCO3).

[0021] The primary hardness removal reaction of step S3 is carried out in a primary hardness removal reaction tank; During the S3 reaction, carbonate ions in sodium carbonate react with calcium ions and strontium ions to form calcium carbonate and strontium carbonate crystals. The stirring equipment is external or built-in in the first-level hardness removal reaction tank to accelerate the mixing of sodium carbonate reagent and wastewater.

[0022] S4, secondary hardness removal reaction Add phosphate reagents to the wastewater at an amount of 1-2 kg per cubic meter of wastewater, and stir and react at a speed of 80-90 rpm for 10-20 minutes after adding the phosphate reagents; The secondary hardness removal reaction of step S4 is carried out in a secondary hardness removal reaction tank.

[0023] The phosphate agent is at least one of sodium phosphate, sodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0024] During the S4 reaction, the residual calcium and magnesium ions in the reaction wastewater react with the phosphate ions in the phosphate reagent to form calcium phosphate and magnesium phosphate precipitates. At the same time, phosphate reacts with magnesium ions and ammonium ions to form ammonium magnesium phosphate precipitates, which also have the effect of removing ammonia nitrogen.

[0025] S5, coagulation, flocculation Add polyaluminium chloride to the wastewater at a mass ratio of 0.05% to 0.1% for coagulation, and add polyacrylamide at a mass ratio of 0.01% for flocculation; The coagulation in step S5 is carried out in a coagulation tank; the flocculation in step S5 is carried out in a flocculation tank.

[0026] S6, precipitation; The precipitation in step S6 is carried out in a high-efficiency sedimentation tank, that is, the solution in the flocculation tank is introduced into the high-efficiency sedimentation tank for precipitation treatment.

[0027] The sludge in the high-efficiency sedimentation tank of step S6 is returned to the flocculation tank of step S5, and the return flow rate is 4%~8% of the process water flow rate. S7, adjust the pH value to 8~9; In S7, hydrochloric acid is used to adjust the pH value to 8-9.

[0028] Both the high-efficiency sedimentation tank and the coagulation tank are equipped with a sludge discharge system. The sedimentation sludge can be discharged from the coagulation tank during the coagulation process, and the sedimentation sludge also needs to be discharged from the high-efficiency sedimentation tank.

[0029] After treatment in steps S1-S7, the total hardness of the wastewater is reduced to below 20 mg / L, the strontium ion concentration is reduced to below 30 mg / L, and the ammonia nitrogen is reduced to below 15 mg / L.

[0030] Embodiment 2: The produced water of a gas field has a calcium hardness of 1200±50mg / L, a total alkalinity of 1000±100mg / L, an ammonia nitrogen content of 30±5mg / L, and a strontium ion concentration of 75±5mg / L. The pH value is adjusted to 13 by adding sodium hydroxide solution, and sodium carbonate solution is added at a dosage of 0.04g / L. The reaction lasts for 30 minutes, and then sodium dihydrogen phosphate is added at a dosage of 1g / L. The reaction lasts for 15 minutes, and then 0.1% polyaluminium chloride and 0.01% polyacrylamide are added for flocculation and precipitation. The total hardness and suspended concentration of the effluent are both lower than 20mg / L, the strontium ion concentration is lower than 30mg / L, and the ammonia nitrogen concentration is lower than 12mg / L.

[0031] Embodiment three: After treatment with steps S1-S7 of a method for anti-scaling in the evaporation process of drilling wastewater in Example 1, the total hardness of the wastewater was reduced from 1200-1500 mg / L to below 20 mg / L, the strontium ion concentration was reduced from 60-80 mg / L to below 30 mg / L, and the ammonia nitrogen was reduced from 30-40 mg / L to below 15 mg / L, thereby effectively reducing the scaling of the evaporator and achieving coordinated treatment of ammonia nitrogen.

[0032] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preventing scale in the evaporation process of drilling wastewater, characterized in that: The following steps are involved: S1. Determine the calcium hardness CaH and total alkalinity TAC in the wastewater. The units of calcium hardness CaH and total alkalinity TAC are mg / L. S2. Add sodium hydroxide to the wastewater to adjust the pH value of the wastewater to 13±0.2; S3, first-level hardness removal reaction Sodium carbonate is added to the wastewater in an amount of g, which is 1 to 2 times the difference between the calcium hardness CaH and the total alkalinity TAC per cubic meter of wastewater. After adding sodium carbonate, the reaction is stirred at a speed of 80 to 90 rpm for 25 to 40 minutes. S4, secondary hardness removal reaction Add phosphate reagents to the wastewater at an amount of 1-2 kg per cubic meter of wastewater, and stir and react at a speed of 80-90 rpm for 10-20 minutes after adding the phosphate reagents; S5, coagulation, flocculation Add polyaluminium chloride to the wastewater at a mass ratio of 0.05% to 0.1% for coagulation, and add polyacrylamide at a mass ratio of 0.01% for flocculation; S6, precipitation; S7. Adjust the pH value to 8~9.

2. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: The phosphate agent is at least one of sodium phosphate, sodium hydrogen phosphate, and sodium dihydrogen phosphate.

3. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: The precipitation in step S6 is carried out in a high-efficiency sedimentation tank; The coagulation in step S5 is carried out in a coagulation tank; It also includes: returning the sludge in the high-efficiency sedimentation tank in step S6 to the flocculation tank in step S5, and controlling the return flow rate to be 4% to 8% of the process water flow rate.

4. The anti-scaling method for drilling wastewater evaporation process according to claim 3 is characterized by: The high-efficiency sedimentation tank and coagulation tank are both provided with a sludge discharge system.

5. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: After treatment in steps S1-S7, the total hardness of the wastewater is reduced to below 20 mg / L, the strontium ion concentration is reduced to below 30 mg / L, and the ammonia nitrogen is reduced to below 15 mg / L.

6. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: The addition of sodium hydroxide to the wastewater in step S2 is completed in a pipeline mixer.

7. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: In S7, hydrochloric acid is used to adjust the pH value to 8-9.

8. The anti-scaling method for drilling wastewater evaporation process according to claim 1, characterized in that: The primary hardness removal reaction of step S3 is carried out in a primary hardness removal reaction tank; The secondary hardness removal reaction in step S4 is carried out in a secondary hardness removal reaction tank.

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