CN110642334A - Electrochemical treatment system and method for high-viscosity fracturing flow-back fluid - Google Patents
Electrochemical treatment system and method for high-viscosity fracturing flow-back fluid Download PDFInfo
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Abstract
The invention discloses an electrochemical treatment system of high-viscosity fracturing flow-back fluid, which comprises a pH adjusting unit, an electrocatalytic oxidation unit and an electric flocculation unit which are sequentially arranged, wherein the pH adjusting unit is used for adjusting the pH value of the fracturing flow-back fluid to 4-7, the electrocatalytic oxidation unit comprises electrocatalytic oxidation equipment, and the electric flocculation unit comprises electric flocculation equipment connected with the effluent of the electrocatalytic oxidation equipment. The invention also discloses a method for treating the fracturing flow-back fluid, which comprises the following steps: 1) adjusting the pH value of the fracturing flow-back fluid to be treated to 4-7; 2) carrying out electrocatalytic oxidation treatment on the fracturing flow-back fluid in the step 1); and 3) performing electric flocculation treatment on the effluent in the step 2). The treatment system and the treatment method mainly adopt electric energy to realize the treatment of the fracturing flow-back fluid, accord with the category of clean production, do not need to enter a large amount of organic or inorganic polymer agents in the treatment process, have no secondary pollution, have stable effluent quality, and save resources and cost.
Description
Technical Field
The invention relates to an electrochemical treatment system and a corresponding treatment method for high-viscosity fracturing flow-back fluid, and belongs to the technical field of sewage treatment in petrochemical industry.
Background
Fracturing flowback fluid refers to residual fracturing fluid remaining after a fracturing construction operation and flowback from a wellhead. As a plurality of additives are added during fracturing, guar gum, suspended matters, crude oil, partial saline water in a stratum brought out during flowback, other organic additives and other substances which are toxic, harmful and difficult to degrade remain in fracturing waste liquid, so that the fracturing waste liquid has complex and variable components and high chloride content and often has the characteristics of three-high (high viscosity, high stability and high COD value). If the fracturing flow-back fluid is directly sent into the existing sewage treatment system for treatment, strong impact can be generated on the existing equipment, so that the fracturing flow-back fluid needs to be treated independently to reduce the subsequent treatment difficulty.
The oil and gas field fracturing flow-back fluid is mainly industrialized by adopting the traditional processes, such as chemical oxidation, medicament flocculation and filtration; or oxidation-flocculation-iron-carbon micro-electrolysis/Fenton oxidation-filtration process, but because the viscosity of the fracturing flow-back fluid is high, the amount of the required oxidant in the treatment process is very large, the gel breaking and viscosity reducing effects are poor, the subsequent flocculation efficiency is very low, a large amount of flocculating agents, coagulant aids and the like are required, the direct operation cost is increased, the amount of hazardous waste sludge is greatly increased, and the secondary pollution treatment cost is increased. For example, CN107417017 discloses a method for treating oil and gas field fracturing flow-back fluid sewage, which adopts KMnO4 and Fenton method oxidation, etc.; CN104556493A discloses a method for recycling fracturing flowback fluid, in which the fracturing fluid is very stable in the early stage, almost settles in layers, and is directly flocculated without oxidation, so the requirement of chemicals is large, and the treatment effect is poor.
In addition, there are also some prior art methods which use electrochemical methods, such as electrocatalytic oxidation or electroflocculation or electro-fenton, alone. Or the electrochemistry and the medicament oxidation flocculation are adopted for use, but the process flow is long, and the medicament consumption and the sludge production are also large. For example, CN106315934A discloses an experimental apparatus for treating a fracturing flow-back fluid, which integrates various process units such as chemical oxidation, ozone oxidation, chemical flocculation, electric flocculation, and the like, and has the defects of long process, large floor area, and the like; the CN107235580A discloses a method for treating the fracturing flow-back fluid of the oil field drilling, which adopts a process combining pretreatment, electric flocculation and electrocatalytic oxidation, but the process route is low in efficiency, and the process units are long and repetitive.
In addition, according to statistics, most of domestic oilfield fracturing flow-back fluid water is generally stored nearby at the periphery of a well site, has the characteristics of dispersion and discontinuity, and is difficult to uniformly and centrally treat. The development of the skid-mounted processing equipment can meet the requirements of decentralized and centralized processing at the same time, and has a certain market. Therefore, in combination with market demands, based on the principle of simplicity, high efficiency and convenience, it is necessary to develop a skid-mounted treatment technology for treating the fracturing flow-back fluid.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an electrochemical treatment system for high-viscosity fracturing flow-back fluid, which can achieve the green, environment-friendly, efficient and economic treatment effect on the fracturing flow-back fluid. In addition, the invention also aims to provide an electrochemical treatment method of the high-viscosity fracturing flow-back fluid.
In order to achieve the purpose, the invention adopts the following technical scheme:
the electrochemical treatment system comprises a pH adjusting unit, an electrocatalytic oxidation unit and an electric flocculation unit which are sequentially arranged, wherein the pH adjusting unit is used for adjusting the pH value of the fracturing flow-back fluid to 4-7, the electrocatalytic oxidation unit comprises electrocatalytic oxidation equipment, and the electric flocculation unit comprises electric flocculation equipment connected with effluent of the electrocatalytic oxidation equipment.
Further: the device also comprises a filtering unit connected with the effluent of the electric flocculation equipment; and the effluent of the filtering unit can be reinjected or recycled after being collected, and the cleaning wastewater generated in the filtering process returns to the electric flocculation unit.
Further: the pH adjusting unit comprises a pH adjusting tank, and the pH value adjusting comprises adding concentrated sulfuric acid or concentrated hydrochloric acid into the pH adjusting tank to adjust the pH value of the fracturing flow-back fluid to 4-7; or the pH value adjustment comprises adding concentrated sulfuric acid or concentrated hydrochloric acid to a water inlet pipeline of the electrocatalytic oxidation unit to adjust the pH value of the fracturing flow-back fluid to 4-7.
Further: the anode electrode of the electrocatalytic oxidation equipment is a titanium-based lead dioxide electrode or a titanium ruthenium-coated iridium electrode with a nanocrystalline film coating, the cathode of the electrocatalytic oxidation equipment is stainless steel, a titanium plate or graphite, and the shell structure of the electrocatalytic oxidation equipment is made of PP or PE materials.
Further: the electric flocculation equipment is high-frequency pulse electric flocculation equipment, a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz is adopted as the power supply, and the high-frequency pulse electric flocculation equipment has an automatic electrode reversing function.
Further: the upper parts of the electrocatalytic oxidation equipment and the electrocoagulation equipment are respectively provided with an oil scraper, a slag scraper or a foam scraper, and the upper parts of the electrocatalytic oxidation equipment and the electrocoagulation equipment are respectively provided with a tail gas collecting system.
Further: the pH adjusting unit, the electrocatalytic oxidation unit, the electric flocculation unit and the filtering unit are integrally arranged on a prying frame.
Another object of the present invention is an electrochemical treatment method for treating high viscosity frac flowback fluid using the electrochemical treatment system as described above, comprising the steps of:
1) adjusting the pH value of the fracturing flow-back fluid to be treated to 4-7;
2) the fracturing flow-back fluid treated by the acid regulation in the step 1) enters an electrocatalytic oxidation device for electrocatalytic oxidation treatment, wherein an anode electrode of the electrocatalytic oxidation device is a titanium-based lead dioxide electrode or a titanium ruthenium-coated iridium electrode with a nanocrystalline film coating, a cathode of the electrocatalytic oxidation device is stainless steel, a titanium plate or graphite, and the shell structure of the device is made of PP or PE materials; and
3) and (3) carrying out electric flocculation treatment on the effluent subjected to the electric catalytic oxidation treatment in the step 2) by using electric flocculation equipment, wherein the electric flocculation equipment is high-frequency pulse electric flocculation equipment, a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz is adopted as the power supply, and an electrode of the high-frequency pulse electric flocculation equipment can have an automatic electrode reversing function.
Further: the treatment time of the electrocatalytic oxidation treatment in the step 2) is 10-120min, and the voltage isIs 0V-12V, and has a current density of 50A/m2～1000A/m2(ii) a The effective treatment time of the electric flocculation treatment in the step 3) is 20min to 60min, the voltage is 0V to 380V, and the current density is 10A/m2～500A/m。
Further: the electrochemical treatment method also comprises the step of filtering the effluent of the electroflocculation treatment, and the filtered produced water can be reinjected or recycled, and the cleaning wastewater generated in the filtering treatment is returned to the step 3).
The treatment system and the treatment method have the beneficial effects that the treatment system and the treatment method adopt a sequential coupling process of pH adjustment, electrocatalysis, electrocoagulation and filtration, and do not need any high-risk chemical oxidant, flocculant, coagulant aid and the like. Moreover, the treatment system and the method mainly adopt clean energy-electric energy to realize the treatment of the fracturing flow-back fluid, accord with the category of clean production, and compared with the traditional medicament method, the scum obtained by electrocatalysis and the sludge obtained by electrocoagulation are both obviously reduced, the sludge yield is only 1/2-1/3 of the traditional process, the secondary treatment cost of the sludge and the scum is greatly reduced, no secondary pollution is caused, the effluent quality is stable, the resources and the cost are saved, the process is simple, the automation degree is high, and the method has better application prospect.
Drawings
FIG. 1 shows a process block diagram of a high viscosity frac flowback fluid electrochemical treatment system according to the present invention;
figure 2 shows a comparative picture of the appearance of water produced after treatment by the treatment units of the electrochemical treatment system of the invention.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings.
According to one aspect of the present invention, there is provided an electrochemical treatment system for high viscosity (typically greater than 5mpa.s) frac flowback fluid, as shown in fig. 1, comprising an electrocatalytic oxidation unit, an electroflocculation unit and a filtration unit arranged in sequence. The pH adjusting unit comprises a corrosion-resistant pH adjusting tank, the fracturing flow-back fluid enters the pH adjusting tank, and meanwhile, sulfuric acid or hydrochloric acid can be added into the pH adjusting tank to adjust the pH value of the fracturing flow-back fluid to 4-7 and then enters the electrocatalytic oxidation unit. Alternatively, the pH adjustment process may be performed on the water inlet pipe of the electrocatalytic oxidation unit, that is, the pH of the fracturing flow-back fluid is adjusted to 4 to 7 by adding sulfuric acid or hydrochloric acid to the water inlet pipe of the electrocatalytic oxidation unit, and then the fracturing flow-back fluid enters the electrocatalytic oxidation unit.
The electrocatalytic oxidation unit comprises electrocatalytic oxidation equipment, so that the fracturing flow-back fluid subjected to the acid regulation treatment is subjected to treatments such as oxidation gel breaking, viscosity reduction, emulsion breaking, air flotation and the like, the stability of colloids such as oil water and the like is damaged, and the operation efficiency of subsequent equipment is improved. The anode electrode of the electrocatalytic oxidation equipment is a titanium-based lead dioxide electrode with a nanocrystalline thin film coating, and has the characteristics of long service life, high efficiency and thin coating, or the anode electrode can also adopt a titanium-coated ruthenium iridium electrode, and has the characteristics of oxidation, wide pH range, electrode reversal, efficient air flotation separation and the like; the cathode is stainless steel, titanium plate or graphite, and the equipment shell is made of PP or PE material. In particular, the electrocatalytic oxidation unit may further comprise an oil scraper, a slag scraper or a foam scraper arranged above the electrocatalytic oxidation device to collect scum generated during the treatment process. In addition, the electrocatalytic oxidation unit can further comprise a tail gas collecting system arranged at the upper part of the electrocatalytic oxidation device. The effluent of the electrocatalytic oxidation equipment enters an electric flocculation unit. The electric flocculation unit comprises electric flocculation equipment, the electric flocculation equipment preferably adopts high-frequency pulse electric flocculation equipment of a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz, and an electrode of the high-frequency pulse electric flocculation equipment can have an automatic electrode reversing function. In particular, the electric flocculation unit can further comprise an oil scraper, a slag scraper or a foam scraper which is arranged at the upper part of the electric flocculation device to collect sludge generated in the treatment process, and in addition, the electric flocculation unit can further comprise a tail gas collection system which is arranged at the upper part of the electric flocculation device. The produced water treated by the electric flocculation treatment unit can be sent to a filtering unit. The filter unit comprises a filter device, and the filter material of the filter device is one or a combination of walnut shells, modified fiber balls and ceramic particles. The effluent of the filtering unit can be collected by a water production tank and then reinjected or recycled, and the cleaning wastewater generated in the filtering process can be returned to the electric flocculation unit. In particular, the pH adjusting unit, the electrocatalytic oxidation unit, the electrocoagulation unit and the filtration unit may be integrally disposed on a skid-mounted frame, wherein the skid-mounted frame may adopt any structure known in the art, and detailed description thereof is omitted. In addition, the electrochemical treatment system of the invention can also comprise a connecting pipeline and a lift pump which are arranged among the treatment units. Moreover, the electrochemical treatment system can also comprise a PLC control unit for automatically controlling each unit.
According to another aspect of the invention, there is also provided a method of treating a high viscosity frac flowback fluid using a clean treatment system as described above, comprising the treatment steps of:
1) and (3) pH adjustment: adding concentrated sulfuric acid or concentrated hydrochloric acid into the fracturing flow-back fluid to be treated to adjust the pH value to 4-7, and then sending the mixture into electro-catalytic oxidation equipment;
2) electrocatalytic oxidation treatment: the fracturing flow-back fluid subjected to the acid adjustment treatment in the step 1) is lifted by a pump to enter an electrocatalytic oxidation device for electrocatalytic oxidation treatment, so that oxidation gel breaking, viscosity reduction, emulsion breaking and air flotation are performed under the action of electrification, the stability of colloids such as oil water and the like is damaged, and the operation efficiency of subsequent equipment is greatly improved; wherein the treatment time of the electrocatalytic oxidation treatment is 10-120min, preferably 20-40 min; the voltage is 0V-12V, and the current density is 50A/m2～1000A/m2Preferably 50A/m2～300A/m2. The produced water after the electrocatalytic oxidation treatment enters an electric flocculation unit for treatment;
3) electric flocculation treatment: the effluent generated by the electrocatalytic oxidation treatment is lifted by a pump to enter into an electric flocculation device for electric flocculation treatment, and most of petroleum, suspended matters, COD (chemical oxygen demand) and the like in the wastewater are removed by generating a flocculating agent in situ under the action of an electrode and an electric field; the electric flocculation device is preferably high-frequency pulse electric flocculation equipment, a power supply of the electric flocculation device adopts a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz, and an electrode of the electric flocculation device has an automatic electrode reversing function. In the invention, the effective treatment time of the electric flocculation treatment is 20 min-60 min, preferably 20min to 50 min; the voltage is 0V to 380V, preferably 0V to 100V; the current density is 10A/m2～500A/m2Preferably 10A/m2～200A/m2. In addition, the pH value of the effluent after the electric flocculation treatment is adjusted back to 8-10 by adding 32 wt% of sodium hydroxide solution at the effluent of the electrode so as to form the optimal environment of flocculation precipitation, and the produced water after the electric flocculation treatment can enter a filtering unit;
4) and (3) filtering treatment: and filtering the produced water after the electric flocculation treatment, wherein the filtered produced water can be reinjected or recycled after being collected by a water production tank, and the cleaning wastewater generated in the filtering treatment can be returned to the electric flocculation treatment step.
In particular, in the present invention, the above-mentioned filtration unit and the corresponding filtration process steps can be present as a standby solution, which can be started and stopped according to the water production requirements.
Example 1
The treatment system and the method are used for treating the fracturing flow-back fluid with certain high viscosity, wherein the viscosity of the fracturing flow-back fluid is 10.5mPa & s, the oil content is about 150mg/L, the suspended matter content is about 500mg/L, and the COD content is about 1800 mg/L. The whole treatment process comprises the following steps:
1) the fracturing flow-back fluid is lifted by a pump to enter an electrocatalytic oxidation device, the pH value of the fracturing flow-back fluid is adjusted to 6 by adopting concentrated sulfuric acid on a water inlet pipeline, the effective reaction time is 45min under the action of electrification, and the current density is 30mA/cm2Carrying out oxidation gel breaking, viscosity reduction, emulsion breaking and air flotation on the fracturing flow-back fluid, and lifting the effluent into high-frequency pulse electrocoagulation equipment through a pump;
2) the produced water after the electrocatalytic oxidation treatment is subjected to high-frequency pulse electrocoagulation at the voltage of 100V and the voltage of 10mA/m2The reaction is carried out for 30min under the current density, polymeric flocculants such as PAC (polyaluminium chloride), PFS (polymeric flocculant) and the like are not required to be introduced in the treatment process, and meanwhile, the double functions of an electric field and an electrode ensure that the in-situ flocculation efficiency is high and the sludge yield is low. Adjusting the pH value of the effluent of the electric flocculation treatment back to 9 at the effluent position of the electrode to form the optimal environment of flocculation precipitation, removing petroleum and suspended matters, and removing the petroleum and suspended matters in an inclined tube sedimentation and suspended sludge layer filtering part in the electric flocculation integrated equipment, wherein the sludge passes through the equipmentThe bottom sludge collecting hopper is discharged to the existing sludge treatment system in the yard, cleaner sewage obtained in the middle layer is sent to the filtering unit, and the floating slag on the upper layer and the electrocatalytic floating slag can be sent to the existing sludge treatment system in the yard together;
3) filtering the middle layer sewage in the step 2), wherein the effluent formed by filtering can be collected and reinjected or recycled, and the cleaning wastewater generated in the filtering process can be returned to the electrocoagulation treatment step.
Fig. 2 shows a color photograph of produced water after the fracturing flow-back fluid is treated in each step, wherein black raw water, transparent electroflocculation effluent and transparent final produced water are sequentially arranged from right to left in the color photograph.
Example 2
The treatment system and the method are used for treating the fracturing flow-back fluid with certain high viscosity, wherein the fracturing flow-back fluid has the viscosity of 80.2mPa & s, the oil content of about 1000mg/L, the suspended matter of about 1140mg/L and the COD of about 6300 mg/L. The whole treatment process of the fracturing flow-back fluid is similar to that of example 1 and will not be described in detail.
Table 1 shows the results of treatment of the frac flowback fluids in examples 1 and 2:
table 1 results of treatments of example 1 and example 2
As can be seen from the processing results in Table 1, the effluent obtained by the process of the invention combining pH adjustment, electrocatalytic oxidation and high-frequency pulse electrocoagulation can achieve good treatment effect, and petroleum, suspended solids and COD can meet the requirements of subsequent biochemical units or reinjection in oil fields. Moreover, each processing device in the invention can be skid-mounted, is simple and practical and has high automation degree.
The present invention has been described in detail with reference to the preferred embodiments. However, variations and additions to the embodiments will become apparent to those of ordinary skill in the art upon a reading of the foregoing description. It is the intention of the applicants that all such variations and additions fall within the scope of the claims. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Any modification and improvement of this product, and the substitution and use of the same or similar substances within the scope or range of patents, shall fall within the scope of protection of this invention.
Claims (10)
1. The utility model provides an electrochemical treatment system of high viscosity fracturing flowback fluid which characterized in that: including pH adjusting unit, electrocatalytic oxidation unit and the electric flocculation unit that sets gradually, wherein, pH adjusting unit is used for returning the pH value of flowing back to 4-7 with the fracturing, the electrocatalytic oxidation unit includes the electric catalytic oxidation equipment, the electric flocculation unit includes the electric flocculation equipment that links to each other with the play water of electric catalytic oxidation equipment.
2. The electrochemical processing system of claim 1, wherein: the device also comprises a filtering unit connected with the effluent of the electric flocculation equipment; and the effluent of the filtering unit can be reinjected or recycled after being collected, and the cleaning wastewater generated in the filtering process returns to the electric flocculation unit.
3. The electrochemical processing system of claim 1 or 2, wherein: the pH adjusting unit comprises a pH adjusting tank, and the pH value adjusting comprises adding concentrated sulfuric acid or concentrated hydrochloric acid into the pH adjusting tank to adjust the pH value of the fracturing flow-back fluid to 4-7; or the pH value adjustment comprises adding concentrated sulfuric acid or concentrated hydrochloric acid to a water inlet pipeline of the electrocatalytic oxidation unit to adjust the pH value of the fracturing flow-back fluid to 4-7.
4. The electrochemical processing system of claim 1, wherein: the anode electrode of the electrocatalytic oxidation equipment is a titanium-based lead dioxide electrode or a titanium ruthenium-coated iridium electrode with a nanocrystalline film coating, the cathode of the electrocatalytic oxidation equipment is stainless steel, a titanium plate or graphite, and the shell structure of the electrocatalytic oxidation equipment is made of PP or PE materials.
5. The electrochemical processing system of claim 1, wherein: the electric flocculation equipment is high-frequency pulse electric flocculation equipment, a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz is adopted as the power supply, and the high-frequency pulse electric flocculation equipment has an automatic electrode reversing function.
6. The electrochemical processing system of claim 1 or 2, wherein: the upper parts of the electrocatalytic oxidation equipment and the electrocoagulation equipment are respectively provided with an oil scraper, a slag scraper or a foam scraper, and the upper parts of the electrocatalytic oxidation equipment and the electrocoagulation equipment are respectively provided with a tail gas collecting system.
7. The electrochemical processing system of claim 2, wherein: the pH adjusting unit, the electrocatalytic oxidation unit, the electric flocculation unit and the filtering unit are integrally arranged on a prying frame.
8. An electrochemical treatment method for treating high viscosity frac flowback fluid using the electrochemical treatment system of any one of claims 1 to 7, comprising: the method comprises the following steps:
1) adjusting the pH value of the fracturing flow-back fluid to be treated to 4-7;
2) the fracturing flow-back fluid treated by the acid regulation in the step 1) enters an electrocatalytic oxidation device for electrocatalytic oxidation treatment, wherein an anode electrode of the electrocatalytic oxidation device is a titanium-based lead dioxide electrode or a titanium ruthenium-coated iridium electrode with a nanocrystalline film coating, a cathode of the electrocatalytic oxidation device is stainless steel, a titanium plate or graphite, and the shell structure of the device is made of PP or PE materials; and
3) and (3) carrying out electric flocculation treatment on the effluent subjected to the electric catalytic oxidation treatment in the step 2) by using electric flocculation equipment, wherein the electric flocculation equipment is high-frequency pulse electric flocculation equipment, a single-pulse or double-pulse direct-current power supply with the frequency of more than 1000Hz is adopted as the power supply, and an electrode of the high-frequency pulse electric flocculation equipment can have an automatic electrode reversing function.
9. The electrochemical treatment method according to claim 8, characterized in that: the treatment time of the electrocatalytic oxidation treatment in the step 2) is 10-120min, the voltage is 0V-12V, and the current density is 50A/m2～1000A/m2(ii) a The effective treatment time of the electric flocculation treatment in the step 3) is 20min to 60min, the voltage is 0V to 380V, and the current density is 10A/m2～500A/m2。
10. The electrochemical treatment method according to claim 7 or 8, characterized in that: the electrochemical treatment method also comprises the step of filtering the effluent of the electroflocculation treatment, and the filtered produced water can be reinjected or recycled, and the cleaning wastewater generated in the filtering treatment is returned to the step 3).
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