Coordinated treatment process of coal slime water and fracturing flowback fluid

Abstract

A process for co-treating coal slurry water and fracturing flowback fluid is disclosed. The fracturing flowback fluid is pre-treated in a regulating tank to stabilize its quality and quantity. The stabilized flowback fluid is then transported to an oil separator for sedimentation, and the separated water is transported to a reaction tank. Ammonium persulfate is added to the reaction tank as a breaker, and the treated flowback fluid is discharged into a flocculation sedimentation tank. PAC and PAM are added to the sedimentation tank, and the mixture is stirred until the particles flocculate. Low-turbidity fracturing flowback fluid is obtained after sedimentation. This low-turbidity flowback fluid is discharged into the circulating water tank of a coal preparation plant, forming a mixture with the circulating water. This mixture is then used for coal separation operations such as desliming, heavy media, and jigging to replenish water and inhibit mud formation. Finally, the low-turbidity flowback fluid is discharged into a coal slurry water flocculant dosing tank, where coal slurry water is added via a dosing pump and thoroughly mixed and flocculated. The coal slurry settles in a thickener and is then discharged to a coal slurry dewatering device, with the overflow flowing back into the circulating water tank. This invention inhibits coal slime slurry formation, replaces the additional water supply in the coal preparation system, and simultaneously realizes the resource utilization of fracturing flowback fluid.

Description

Technical Field

[0001] This invention relates to a process for treating and utilizing fracturing flowback fluid, specifically a process for co-treating coal slurry water and fracturing flowback fluid, belonging to the field of industrial wastewater treatment and resource utilization technology. Background Technology

[0002] Coal slurry is an industrial wastewater generated during coal washing and beneficiation. It is characterized by large volume, limited treatment space, and short treatment time. Its treatment effect directly affects the quality of coal separation products and the operational stability of the separation system. Coal slurry contains a large number of micro- and nano-sized particles with a strong negative charge on their surfaces. Traditional treatment processes require the addition of large amounts of inorganic coagulants and polymeric flocculants (such as polyaluminum chloride (PAC) and polyacrylamide (PAM)) to promote the flocculation and sedimentation of coal slurry particles and achieve internal circulation within the clean water plant. However, coagulants are expensive, and controlling the appropriate dosage is difficult. Insufficient coagulant dosage will result in a large number of coal slurry particles escaping and the circulating water concentration failing to meet standards, while excessive dosage will cause a colloidal protective phenomenon on the surface of the coal slurry particles, hindering further floc aggregation. Therefore, developing a low-cost, easily quantifiable coal slurry treatment technology is currently needed by many coal preparation plants.

[0003] During the staged coal sorting process, coal easily becomes muddy and disperses into micro- and nano-sized coal slime particles. The generation of a large amount of fine coal slime reduces the performance of the sorted products and increases the load on the coal slime water clarification treatment. High-valent cations (such as Ca) 2+ Al 3+ Short-chain organic matter (such as coal slurry and slurry) can reduce the thickness of the hydration film on the surface of coal slime particles, inhibiting their mud-like dispersion. Furthermore, because coal products continuously remove moisture from the circulating coal slime water system, coal preparation plants need to continuously replenish water to maintain water balance. For coal mines with low water volume, continuous water replenishment is also a key issue that needs to be addressed.

[0004] During oil and gas field development, the flowback fluid generated after fracturing operations is a typical example of difficult-to-treat industrial wastewater due to its high oil content, high suspended solids, high chemical oxygen demand (COD), and high mineralization. Currently, the industry mainly uses various physicochemical and biological technologies to treat fracturing flowback fluid, resulting in lengthy treatment processes, large infrastructure investments, and high operation and maintenance costs. Fracturing flowback fluid contains a large amount of polyacrylamide polymers, guar gum derivatives, and high concentrations of monovalent and divalent salts. From a compositional perspective, these substances have a mud-inhibiting effect on coal and promote the coagulation and sedimentation of micro-nano particles; the water can also supplement the water consumed in the coal preparation process. However, existing water treatment processes typically treat these substances in fracturing flowback fluid as pollutants, focusing on achieving water quality standards while neglecting the potential utilization value of these substances as resources. Currently, there is a lack of relevant technical solutions for utilizing high-salt, high-COD fracturing flowback fluid as a coal slurry coagulant, a coal slurry mud-inhibiting agent, and a makeup water source.

[0005] In summary, the existing technologies have the following problems: the cost of coal slurry water treatment agents is high, the treatment of fracturing flowback fluid is difficult, and there is no existing co-treatment technology. Directly introducing fracturing flowback fluid into coal slurry water will cause secondary pollution and interfere with coal sorting, which are application obstacles. Summary of the Invention

[0006] The purpose of this invention is to provide a co-treatment process for coal slurry water and fracturing flowback fluid. This process is simple to operate and can co-treat fracturing flowback fluid and coal slurry water. After degumming, oil removal, and coagulation treatment, the fracturing flowback fluid can be used in the coal preparation process. This not only solves the problem of fracturing flowback fluid disposal, but also inhibits coal slurry mudification, replenishes the circulating water required for coal preparation, and replaces the flocculant in coal slurry water, realizing waste treatment and water resource recycling.

[0007] To achieve the above objectives, the present invention provides a process for the synergistic treatment of coal slurry water and fracturing flowback fluid, comprising the following steps: S1: Water quality and quantity adjustment: The fracturing flowback fluid is sent to the equalization tank for water quality and quantity adjustment. The equalization tank is equipped with a stirring device to stir the water in the tank and stabilize the quality and quantity of the effluent. S2: Static oil and slag removal: The fracturing flowback fluid after S1 water quality and quantity adjustment is transported to the oil separator for static stratification, collecting the floating oil on the liquid surface and discharging the bottom sludge. The separated middle layer water is transported to the oxidation debonding reaction tank. S3: Oxidative De-gelling: The fracturing flowback fluid after S2 oil removal and slag discharge is pumped into the reaction tank, and ammonium persulfate de-gelling agent is added to the reaction tank. The treated fracturing flowback fluid is then discharged into the flocculation sedimentation tank. S4: Flocculation and sedimentation: Add 5‰ polyaluminum chloride (PAC) and 0.5‰ polyacrylamide (PAM) to the flocculation and sedimentation tank, stir until the particles flocculate and settle, and the flocs at the bottom are discharged through the sludge discharge pipe. The supernatant is a low-turbidity fracturing flowback fluid. S5: Coal slime mudification inhibition: Low turbidity fracturing flowback fluid is discharged into the coal preparation plant's circulating water pool, where it mixes with the circulating water to form a mixed liquid. The mixed liquid is then added to coal separation operations such as desliming, heavy media, and jigging. S6: Coal slurry water flocculation: Low turbidity fracturing flowback fluid is discharged into the coal slurry water flocculant dosing tank, and then added to the coal slurry thickener feed pipe by the dosing pump to fully mix and flocculate with the coal slurry water. S7: Coal slime settling: The well-mixed low-turbidity fracturing flowback fluid and coal slime water settle in the thickener, with the underflow discharged to the coal slime dewatering equipment and the overflow discharged to the circulating water tank.

[0008] Preferably, in step S4, the mass ratio of the added 5‰ polyaluminum chloride (PAC) solution to the fracturing flowback fluid is 4-6:1000, and the mass ratio of the added 0.5‰ polyacrylamide (PAM) solution to the fracturing flowback fluid is 1-3:1000.

[0009] Preferably, in step S6, the volume ratio of the low-turbidity fracturing flowback fluid to the coal slurry water added to the coal slurry thickener is 2-4:1000.

[0010] Preferably, in step S1, the stirring equipment is a low-speed stirring equipment with a stirring speed controlled at 15-30 rpm; the hydraulic residence time of the fracturing flowback fluid in the regulating tank is 4-8 hours.

[0011] Preferably, in step S2, the fracturing flowback fluid is left to stand in the oil separator for 1.5-2.5 hours.

[0012] Preferably, in step S2, an oil collection pipe is provided at the top of the oil separator to collect floating oil on the liquid surface, and a sludge discharge pipe is provided at the bottom to discharge settled sludge.

[0013] Preferably, in step S3, the ratio of the added ammonium persulfate breaker to the fracturing flowback fluid after degreasing and slag removal is 5:1500-3000.

[0014] Preferably, in step S3, the stirring time in the reaction vessel is controlled at 30-40 minutes, and the stirring speed is set at 200-400 rpm.

[0015] Preferably, in step S5, the mixture is used to suppress coal slime formation and maintain the water balance of the coal preparation plant.

[0016] Preferably, in step S6, a jet mixer is installed inside the feed pipe of the coal slime thickener.

[0017] Compared with existing technologies, this invention can achieve the co-treatment of two types of wastewater, with high resource utilization rate and significant environmental benefits, compared with existing single fracturing flowback fluid treatment processes and conventional coal slurry water treatment processes.

[0018] This invention integrates low-turbidity fracturing flowback fluid, which has undergone multi-stage pretreatment, into a coal slurry water treatment system. It utilizes the existing coal slurry water treatment dosing and concentration equipment in the coal preparation plant to achieve joint treatment, eliminating the need to build separate fracturing flowback fluid disposal facilities. This not only completes the harmless treatment of fracturing flowback fluid and completely eliminates environmental pollution caused by wastewater discharge, but also makes full use of industrial wastewater to achieve waste-to-waste treatment, which can significantly improve the water resource recycling rate and reduce the wastewater treatment cost for enterprises.

[0019] This invention employs a series of steps for treating fracturing flowback fluid: water quantity and quality adjustment, static oil separation, ammonium persulfate degelatinization, and composite flocculation with polyaluminum chloride and polyacrylamide. By adjusting the flowback fluid's quality and quantity through low-speed stirring and a suitable residence time in the regulating tank, fluctuations in water quality and quantity are effectively mitigated, providing stable feedwater for subsequent processes. Natural stratification in the oil separator achieves initial separation of floating oil and sludge. The oxidation effect of ammonium persulfate degrades residual high-molecular-weight thickeners in the water, reducing viscosity and eliminating the inhibitory effect of colloids on subsequent flocculation reactions. Furthermore, the synergistic effect of inorganic and organic flocculants causes fine suspended particles to aggregate into dense flocs, enhancing sedimentation and separation. Ultimately, this invention yields qualified water with low turbidity, low oil content, and low colloid residue, meeting the requirements for coal slurry water treatment agents and coal preparation water.

[0020] This invention limits the addition ratio of ammonium persulfate, polyaluminum chloride, and polyacrylamide, and sets corresponding stirring speed and stirring time. On the one hand, it can ensure that the agents can play a full role and achieve complete debinding, coagulation, and flocculation reactions. On the other hand, it can effectively avoid problems such as insufficient agent addition leading to substandard treatment, or excessive agent addition causing increased water viscosity and flocculation failure.

[0021] The low-turbidity fracturing flowback fluid of this invention is connected to the coal slurry flocculant dosing tank and then pumped to the feed pipe of the coal slurry thickener. An in-pipe jet mixer facilitates rapid mixing and flocculation with the coal slurry. Compared to traditional independent stirred reaction tanks, this invention requires no additional space, resulting in a more compact process. The strong turbulence generated by the jet mixer achieves instantaneous and uniform mixing of the fracturing flowback fluid and the coal slurry, resulting in a fast and thorough flocculation reaction. This effectively improves the density and settling efficiency of the coal slurry flocs, ensuring stable operation of the coal slurry thickening unit.

[0022] By strictly limiting the mixing ratio of the low-turbidity fracturing flowback fluid and coal slurry water in this invention, the invention maximizes the utilization of fracturing flowback fluid while avoiding excessive mixing that could alter the ionic environment and physicochemical properties of the coal slurry water, thus preventing problems such as decreased flocculation effect and poor coal slurry settling. Introducing the low-turbidity fracturing flowback fluid into core coal preparation processes such as desliming, heavy media, and jigging effectively inhibits coal slurry formation and replenishes dissipated water, maintaining the water balance of the entire plant's water circulation system. This ensures the continuous and efficient operation of coal preparation and separation, achieving the organic integration of wastewater treatment and main production processes.

[0023] This invention mainly relies on the existing facilities of coal preparation plants, such as water tanks, dosing equipment, conveying pipelines, and thickeners, to integrate the process. The equipment modification is small and the infrastructure investment is low. The whole process operates under mild conditions and is easy to operate. It can be adapted to fracturing flowback fluid and coal slurry water of different water qualities, has a wide range of applications, and is easy to promote and apply in coal and oil and gas co-production enterprises. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the processing technology of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments.

[0026] A process for the co-treatment of coal slurry water and fracturing flowback fluid includes the following steps: S1: Water quality and quantity adjustment: The fracturing flowback fluid is sent to the equalization tank for water quality and quantity adjustment. The equalization tank is equipped with a stirring device to stir the water in the tank and stabilize the quality and quantity of the effluent. The stirring device of the present invention is a low-speed stirring device, with the stirring speed controlled at 15-30 rpm; the hydraulic residence time of the fracturing flowback fluid in the regulating tank is 4-8 hours.

[0027] Main functions: buffering fluctuations in incoming water volume and reducing the impact load on subsequent equipment; at the same time, relying on low-speed stirring and long-term retention, it fully mixes wastewater of different time periods and concentrations, keeping the effluent quality uniform, eliminating the problem of unstable incoming water from the source, and providing stable incoming water for subsequent processes.

[0028] S2: Static oil and slag removal: The fracturing flowback fluid after S1 water quality and quantity adjustment is transported to the oil separator for static stratification, collecting the floating oil on the liquid surface and discharging the bottom sludge. The separated middle layer water is transported to the oxidation debonding reaction tank. The present invention has an oil collection pipe at the top of the oil separator to collect floating oil on the liquid surface, and a sludge discharge pipe at the bottom to discharge settled sludge.

[0029] This invention utilizes natural gravity settling and the density difference between oil and water to achieve three-phase separation: the upper layer is floating oil, the middle layer is clear water, and the bottom layer is silt and sediment.

[0030] This invention collects the upper layer of floating oil through an oil collection pipe to remove most of the oil pollutants from the wastewater; it periodically discharges the bottom layer of sludge through a sludge discharge pipe to remove fine sand and other particulate matter; and the middle layer of clear water is sent as qualified pre-treated effluent to the downstream reaction tank.

[0031] The fracturing flowback fluid of this invention has a settling time of 1.5-2.5 hours in the oil separator, which provides sufficient time for oil-water and solid-liquid separation. It is a low-cost and efficient physical oil and slag removal process. It first separates the easily removable oil and slag, reduces the consumption of downstream oxidation and gel breaking agents, and reduces the risk of equipment wear and blockage.

[0032] S3: Oxidative De-gelling: The fracturing flowback fluid after S2 oil removal and slag discharge is pumped into the reaction tank, and ammonium persulfate de-gelling agent is added to the reaction tank. The treated fracturing flowback fluid is then discharged into the flocculation sedimentation tank. This invention adds ammonium persulfate as a breaker to the fracturing flowback fluid. The oxidation effect of ammonium persulfate degrades the high-molecular-weight thickener in the fracturing flowback fluid, destroying the colloidal structure and reducing the viscosity of the water. On the one hand, it can eliminate the adverse effects of colloids on the flocculation and sedimentation processes in the pretreatment of fracturing fluid and improve the solid-liquid separation effect. On the other hand, it can avoid problems such as insufficient mixing with coal slurry water caused by excessively high viscosity of fracturing flowback fluid, and ensure the effect of mud inhibition and coal slurry flocculation and sedimentation.

[0033] The ratio of ammonium persulfate breaker to the fracturing flowback fluid after oil and slag removal in this invention is 5:1500-3000. This is to precisely control the dosage. If the proportion of ammonium persulfate breaker is too low, the breaker effect will be insufficient, affecting flocculation and sedimentation, and residual solid particles will increase the sedimentation load on the thickener. If the proportion of ammonium persulfate breaker is too high, it will not only increase processing costs, but excessive oxidant may also damage the coal separation reagents, which is detrimental to the stable operation of the coal preparation system. This ratio can ensure sufficient breaker action and viscosity reduction while avoiding process defects caused by excessive or insufficient reagents, adapting to fluctuations in on-site water quality, and ensuring continuous and efficient operation of the entire process.

[0034] After adding ammonium persulfate as a breaker, this invention controls the stirring time in the reaction tank to 30-40 minutes and the stirring speed to 200-400 rpm. A suitable stirring speed ensures rapid and uniform mixing of the ammonium persulfate solution and the fracturing flowback fluid, avoiding excessively high or low concentrations of the agent in certain areas, ensuring synchronous degradation of the colloids throughout, and preventing incomplete breaker formation or agent overload in certain areas. Setting a reasonable stirring time ensures complete degradation of the polymer colloids, achieving breaker formation and viscosity reduction. Ammonium persulfate requires a certain reaction time to degrade polymer colloids; insufficient time results in incomplete reaction, leaving colloid residues, high water viscosity, and potential problems for subsequent processes. Excessive stirring time increases equipment energy consumption and operating time, reducing processing efficiency.

[0035] S4: Flocculation and sedimentation: Add 5‰ polyaluminum chloride (PAC) and 0.5‰ polyacrylamide (PAM) to the flocculation and sedimentation tank and stir until the particles flocculate. After stirring, the fracturing flowback fluid is discharged from the flocculation and sedimentation tank. The hydraulic retention time is set to 2 hours so that the flocs settle to the bottom and are discharged through the sludge discharge pipe. The supernatant overflow is low-turbidity fracturing flowback fluid. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the fracturing flowback fluid after rupture. PAC destabilizes and aggregates suspended fine particles and residual colloids in the water through charge neutralization, forming small flocs. Then, PAM utilizes its high-molecular-weight adsorption and bridging effect to aggregate these small flocs into large, dense flocs. These flocs rapidly settle and separate in a flocculation sedimentation tank and are discharged through a sludge discharge pipe, effectively removing suspended solids and trace amounts of oil from the water, further reducing effluent turbidity, and ensuring the water quality requirements for subsequent reuse in coal preparation processes.

[0036] In this invention, the mass ratio of 5‰ polyaluminum chloride (PAC) solution to fracturing flowback fluid is 4-6:1000, and the mass ratio of 0.5‰ polyacrylamide (PAM) solution to fracturing flowback fluid is 1-3:1000. This is to achieve precise reagent dosing. Insufficient PAC solution will result in ineffective destabilization of particles and poor coagulation; excessive PAC solution will cause particle restabilization and waste reagents. Insufficient PAM solution will prevent the formation of dense flocs, leading to low solid-liquid separation efficiency; excessive PAM solution will increase water viscosity, and residual polymers may cause coal slime formation, affecting coal preparation operations. This ratio range ensures optimal coagulation and flocculation effects while balancing operating costs and the stability of subsequent processes.

[0037] S5: Coal slime mudification inhibition: Low turbidity fracturing flowback fluid is discharged into the coal preparation plant's circulating water pool, where it mixes with the circulating water to form a mixed liquid. The mixed liquid is then added to coal separation operations such as desliming, heavy media, and jigging. The desliming process involves washing and screening a large amount of fine coal slime from the raw coal with water to separate the fine coal slime from the raw coal and prevent the fine slime from interfering with subsequent sorting operations.

[0038] Heavy media separation uses high-density suspension as the separation medium to separate coal and gangue based on density differences. The entire process relies on circulating water to mix the medium and transport materials.

[0039] Jigging operations utilize the up-and-down pulsation of water flow to cause raw coal to stratify according to density in the water, thus separating coal from gangue. This process cannot be separated from continuous water supply.

[0040] This invention delivers the mixed liquid to the core washing and beneficiation processes of the coal preparation plant, such as desliming, heavy media separation, and jigging. The cations and small molecule organic matter in the mixed liquid are adsorbed on the surface of coal particles, thus thinning the hydration layer and inhibiting the mudding and dispersion of raw coal during the separation process, while meeting the water needs of each working unit.

[0041] S6: Coal slurry water flocculation: The low-turbidity fracturing flowback fluid is discharged into the coal slurry water flocculant dosing tank, and introduced into the coal slurry water in the feed pipe of the coal slurry thickener by the dosing pump, so that the low-turbidity fracturing flowback fluid and the coal slurry water are fully mixed and flocculated. The treated low-turbidity fracturing flowback fluid is transported to the flocculant dosing tank and then pumped into the feed pipe of the coal slime thickener by the dosing pump. The feed pipe is equipped with a jet mixer. With the help of the hydraulic mixing action of the jet mixer, the low-turbidity fracturing flowback fluid and the coal slime water are fully mixed and the flocculation reaction is completed in the pipeline. In this invention, the volume ratio of low-turbidity fracturing flowback fluid to coal slurry water added to the coal slurry thickener is 2-4:1000. If the proportion of low-turbidity fracturing flowback fluid is too low, the wastewater absorption capacity will be insufficient, the flocculation effect of the coal slurry water will be poor, and the synergistic treatment and resource utilization cannot be fully realized. If the proportion of low-turbidity fracturing flowback fluid is too high, it will change the ionic environment and physicochemical properties of the coal slurry water, interfere with the flocculant's action, and lead to poor coal slurry floc formation, decreased settling efficiency, and an inability to maintain the balance of circulating water in the coal preparation plant. By limiting the reasonable ratio range, the flocculation reaction and coal slurry thickening process can be carried out normally while fully absorbing the fracturing flowback fluid, maintaining the stable operation of the entire production system.

[0042] S7: Coal slime settling: The well-mixed low-turbidity fracturing flowback fluid and coal slime water settle in the thickener, with the underflow discharged to the coal slime dewatering equipment and the overflow discharged to the circulating water tank.

[0043] Example 1

[0044] S1: The fracturing flowback fluid is introduced into the equalization tank. The speed of the low-speed stirring equipment in the tank is controlled at 15 rpm, and the hydraulic retention time is 4 hours to achieve homogenization and equalization, and to suppress fluctuations in water quality and quantity. S2: The adjusted wastewater is transported to the oil separator and left to stand for 1.5 hours; the oil collection pipe on the liquid surface collects the floating oil, the bottom sludge discharge pipe discharges the sediment, and the middle layer of water is sent to the oxidation and de-gelling reaction tank. S3: Add the breaker to the reaction vessel at a volume ratio of 5:1500 (ammonium persulfate solution: fracturing flowback fluid); control the stirring speed at 200 rpm and the stirring time at 30 min to allow the agent to fully react with the water, oxidize and degrade the residual polymer colloids, and complete the breaker and viscosity reduction. S4: Add 5‰ polyaluminum chloride (PAC) solution and 0.5‰ polyacrylamide (PAM) solution sequentially, so that the mass ratio of 5‰ PAC solution to fracturing flowback fluid is 4:1000 and the mass ratio of 0.5‰ PAM solution to fracturing flowback fluid is 1:1000; stir until the suspended particles in the water are fully flocculated to form flocs, and then send the water into the flocculation sedimentation tank; S5: The wastewater is left to stand in the flocculation sedimentation tank. The flocs settle to the bottom of the tank and are discharged through the sludge discharge pipe to obtain low-turbidity fracturing flowback fluid. S6: The low-turbidity fracturing flowback fluid is discharged into the coal slurry water flocculant dosing tank of the coal preparation plant, and then added to the coal slurry thickener feed pipe by the dosing pump to fully mix and flocculate with the coal slurry water. The volume ratio of the low-turbidity fracturing flowback fluid to the coal slurry water is 2:1000. The two are fully mixed with the flocculant and flocculated again by the in-pipe jet mixer. S7: The mixed flocculated material enters the coal slime thickener to complete solid-liquid concentration. The resulting mixture is added to coal separation operations such as desliming, heavy media, and jigging, effectively inhibiting coal slime sludge formation. At the same time, it replenishes the system water and maintains the water balance of the coal preparation plant.

[0045] In this embodiment 1, the fracturing flowback fluid showed good removal of colloids, floating oil, and suspended solids, and the turbidity of the effluent met the standards. The coal slurry water flocculation and sedimentation efficiency was normal, the coal slurry mudification phenomenon was significantly suppressed, and the operation of each coal preparation process was stable, achieving zero wastewater discharge.

[0046] Example 2

[0047] S1: The fracturing flowback fluid is introduced into the equalization tank. The speed of the low-speed stirring equipment in the tank is controlled at 22 rpm, and the hydraulic retention time is 6 hours to achieve homogenization and equalization, and to suppress fluctuations in water quality and quantity. S2: The adjusted wastewater is transported to the oil separator and left to stand for 2 hours; the oil collection pipe on the liquid surface collects the floating oil, the bottom sludge discharge pipe discharges the sedimented sludge, and the middle layer of water is sent to the oxidation and de-gelling reaction tank. S3: Add the breaker to the reaction vessel at a volume ratio of 5:2250 (ammonium persulfate solution: fracturing flowback fluid); control the stirring speed at 300 rpm and the stirring time at 35 min to allow the agent to fully react with the water, oxidize and degrade the residual polymer colloids, and complete the breaker and viscosity reduction. S4: Add 5‰ polyaluminum chloride (PAC) solution and 0.5‰ polyacrylamide (PAM) solution sequentially, so that the mass ratio of 5‰ PAC solution to fracturing flowback fluid is 5:1000 and the mass ratio of 0.5‰ PAM solution to fracturing flowback fluid is 2:1000; stir until the suspended particles in the water are fully flocculated to form flocs, and then send the water into the flocculation sedimentation tank; S5: The wastewater is left to stand in the flocculation sedimentation tank. The flocs settle to the bottom of the tank and are discharged through the sludge discharge pipe to obtain low-turbidity fracturing flowback fluid. S6: The low-turbidity fracturing flowback fluid is discharged into the coal slurry water flocculant dosing tank of the coal preparation plant, and then added to the coal slurry thickener feed pipe by the dosing pump to fully mix and flocculate with the coal slurry water. The volume ratio of the low-turbidity fracturing flowback fluid to the coal slurry water is 3:1000. The two are fully mixed with the flocculant and flocculated again by the in-pipe jet mixer. S7: The mixed flocculated material enters the coal slime thickener to complete solid-liquid concentration. The resulting mixture is added to coal separation operations such as desliming, heavy media, and jigging, effectively inhibiting coal slime sludge formation. At the same time, it replenishes the system water and maintains the water balance of the coal preparation plant.

[0048] In this Example 2, the process reaction is sufficient, the reagent utilization rate is high, the fracturing flowback fluid is thoroughly purified, the coal slurry water settles quickly, the coal slurry mudification inhibition effect is optimal, the whole system operates continuously and stably, and the overall operating cost is the lowest.

[0049] Example 3

[0050] S1: The fracturing flowback fluid is introduced into the equalization tank. The speed of the low-speed stirring equipment in the tank is controlled at 30 rpm, and the hydraulic retention time is 8 hours to achieve homogenization and equalization, and to suppress fluctuations in water quality and quantity. S2: The adjusted wastewater is transported to the oil separator and left to stand for 2.5 hours; the oil collection pipe on the liquid surface collects the floating oil, the bottom sludge discharge pipe discharges the sediment, and the middle layer of water is sent to the oxidation and de-gelling reaction tank. S3: Add the breaker to the reaction vessel at a volume ratio of 5:3000 (ammonium persulfate solution: fracturing flowback fluid); control the stirring speed at 400 rpm and the stirring time at 40 min to allow the agent to fully react with the water, oxidize and degrade the residual polymer colloids, and complete the breaker and viscosity reduction. S4: Add 5‰ polyaluminum chloride (PAC) solution and 0.5‰ polyacrylamide (PAM) solution sequentially, so that the mass ratio of 5‰ PAC solution to fracturing flowback fluid is 6:1000 and the mass ratio of 0.5‰ PAM solution to fracturing flowback fluid is 3:1000; stir until the suspended particles in the water are fully flocculated to form flocs, and then send the water into the flocculation sedimentation tank; S5: The wastewater is left to stand in the flocculation sedimentation tank. The flocs settle to the bottom of the tank and are discharged through the sludge discharge pipe to obtain low-turbidity fracturing flowback fluid. S6: Discharge the low-turbidity fracturing flowback fluid into the coal slurry water flocculant dosing tank of the coal preparation plant, and transport it together to the feed pipe of the coal slurry thickener; so that the volume ratio of the low-turbidity fracturing flowback fluid to the coal slurry water is 4:1000, and rely on the in-pipe jet mixer to achieve full mixing and further flocculation of the two with the flocculant; S7: The mixed flocculated material enters the coal slime thickener to complete solid-liquid concentration. The resulting mixed liquid is added to the desliming, heavy media, and jigging operations to effectively inhibit coal slime sludge formation. At the same time, it replenishes the system water and maintains the water balance of the coal preparation plant.

[0051] In Example 3, the fracturing flowback fluid was thoroughly treated and the water quality indicators were qualified. When the water mixing ratio was at the upper limit, the coal slime water flocculation condition remained stable, and no problems such as loose flocs, poor sedimentation, or aggravated coal slime mudification occurred, indicating a large process tolerance range.

[0052] Comparative Example 1 Process flow: The ammonium persulfate degelatinization step is omitted, and the remaining steps and parameters are completely consistent with those in Example 2.

[0053] Results: In Comparative Example 1, a large amount of high molecular weight colloids remained in the fracturing flowback fluid, resulting in high water viscosity. Subsequently, the flocculation effect of PAC and PAM decreased significantly, the flocs were small and loose, and the turbidity of the sedimentation tank effluent exceeded the standard. After the water entered the coal slurry water system, the coal slurry became severely muddy, and the coal preparation and separation efficiency decreased.

[0054] Comparative Example 2 Process flow: Same as in Example 2, except that the volume ratio of ammonium persulfate solution to fracturing flowback fluid is adjusted to 8:3200 (exceeding the upper limit).

[0055] Operating results: Excessive oxidant destroyed the activity of subsequent flocculants, preventing the formation of effective flocs and causing solid-liquid separation failure; abnormal physicochemical properties of the water body affected coal preparation production.

[0056] Comparative Example 3 Process flow: Same as in Example 2, except that the volume ratio of low-turbidity fracturing flowback fluid to coal slurry water is 2:1200.

[0057] Operating results: The water ion environment of coal slime was altered, the flocculation reaction was hindered, the turbidity of the thickener overflow increased, the coal slime settling efficiency decreased, and the operating conditions of the coal preparation system fluctuated significantly.

[0058] In summary, this invention can operate stably throughout the entire parameter range, achieves good harmlessness and resource utilization of fracturing flowback fluid, and ensures stable coal preparation production conditions.

[0059] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A process for the synergistic treatment of coal slurry water and fracturing flowback fluid, characterized in that, Includes the following steps: S1: Water quality and quantity adjustment: The fracturing flowback fluid is sent to the equalization tank for water quality and quantity adjustment. The equalization tank is equipped with a stirring device to stir the water in the tank and stabilize the quality and quantity of the effluent. S2: Static oil and slag removal: The fracturing flowback fluid after S1 water quality and quantity adjustment is transported to the oil separator for static stratification, collecting the floating oil on the liquid surface and discharging the bottom sludge. The separated middle layer water is transported to the oxidation debonding reaction tank. S3: Oxidative De-gelling: The fracturing flowback fluid after S2 oil removal and slag discharge is pumped into the reaction tank, and ammonium persulfate de-gelling agent is added to the reaction tank. The treated fracturing flowback fluid is then discharged into the flocculation sedimentation tank. S4: Flocculation and sedimentation: Add 5‰ polyaluminum chloride and 0.5‰ polyacrylamide to the flocculation and sedimentation tank, stir until the particles flocculate and settle, and the flocs at the bottom are discharged through the sludge discharge pipe. The supernatant is low-turbidity fracturing flowback fluid. S5: Coal slime mudification inhibition: Low turbidity fracturing flowback fluid is discharged into the coal preparation plant's circulating water pool, where it mixes with the circulating water to form a mixed liquid. The mixed liquid is then added to the desliming, heavy media, and jigging coal separation operations. S6: Coal slurry water flocculation: Low turbidity fracturing flowback fluid is discharged into the coal slurry water flocculant dosing tank, and then added to the coal slurry thickener feed pipe by the dosing pump to fully mix and flocculate with the coal slurry water. S7: Coal slime settling: The well-mixed low-turbidity fracturing flowback fluid and coal slime water settle in the thickener, with the underflow discharged to the coal slime dewatering equipment and the overflow discharged to the circulating water tank.

2. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 1, characterized in that, In step S4, the mass ratio of the added 5‰ polyaluminum chloride solution to the fracturing flowback fluid is 4-6:1000, and the mass ratio of the added 0.5‰ polyacrylamide solution to the fracturing flowback fluid is 1-3:1000.

3. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 2, characterized in that, In step S6, the volume ratio of the low-turbidity fracturing flowback fluid to the coal slurry water added to the coal slurry thickener is 2-4:1000.

4. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 2, characterized in that, In step S1, the stirring equipment is a low-speed stirring equipment, and the stirring speed is controlled at 15-30 rpm; the hydraulic residence time of the fracturing flowback fluid in the equalization tank is 4-8 hours.

5. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 2, characterized in that, In step S2, the fracturing flowback fluid is allowed to stand in the oil separator for 1.5-2.5 hours.

6. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 2, characterized in that, In step S2, an oil collection pipe is installed at the top of the oil separator to collect floating oil on the liquid surface, and a sludge discharge pipe is installed at the bottom to discharge settled sludge.

7. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 4, characterized in that, In step S3, the ratio of the added ammonium persulfate breaker to the fracturing flowback fluid after oil removal and slag discharge is 5:1500-3000.

8. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 6, characterized in that, In step S3, the stirring time in the reaction vessel is controlled at 30-40 minutes, and the stirring speed is set at 200-400 rpm.

9. The co-treatment process for coal slurry water and fracturing flowback fluid according to claim 4, characterized in that, In step S5, the mixture is used to suppress coal slime formation and maintain the water balance in the coal preparation plant.

10. The synergistic treatment process of coal slurry water and fracturing flowback fluid according to claim 4, characterized in that, In step S6, a jet mixer is installed inside the feed pipe of the coal slime thickener.

Images