CN110745980B - Shale gas fracturing flowback fluid pretreatment process and system - Google Patents

Shale gas fracturing flowback fluid pretreatment process and system Download PDF

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Publication number
CN110745980B
CN110745980B CN201810812821.3A CN201810812821A CN110745980B CN 110745980 B CN110745980 B CN 110745980B CN 201810812821 A CN201810812821 A CN 201810812821A CN 110745980 B CN110745980 B CN 110745980B
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clear liquid
treatment
shale gas
ion exchange
gas fracturing
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CN110745980A (en
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杨杰
彭锋
王兴睿
向启贵
雷宇
胡金燕
杨平
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Petrochina Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/50—Treatment of water, waste water, or sewage by addition or application of a germicide or by oligodynamic treatment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
    • C02F1/56—Macromolecular compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/70—Treatment of water, waste water, or sewage by reduction
    • C02F1/705—Reduction by metals
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
    • C02F2001/425—Treatment of water, waste water, or sewage by ion-exchange using cation exchangers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/02—Softening water by precipitation of the hardness
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Separation Of Suspended Particles By Flocculating Agents (AREA)

Abstract

The invention discloses a shale gas fracturing flowback fluid pretreatment process and a shale gas fracturing flowback fluid pretreatment system, and belongs to the field of sewage treatment. The method comprises the steps of sequentially adding a descaling agent, a coagulant and a flocculating agent to remove scaling ions and particle impurities in the shale gas fracturing flowback fluid to obtain primary clear liquid. And adding a bactericide into the primary clear liquid for sterilization treatment to obtain a secondary clear liquid. And the three filtering and combining modes of sand filtering, activated carbon filtering and ultrafiltration treatment are sequentially carried out on the secondary clear liquid, so that suspended matters, soluble organic matters, inorganic scale precipitates and bacteria in the secondary clear liquid are reduced, and the tertiary clear liquid is obtained. Through carrying out ion exchange treatment to tertiary clear liquid, having got rid of the multivalent cation in the tertiary clear liquid, only contained monovalent cation in the reverse osmosis membrane influent water that makes up to standard that obtains, reached the follow-up requirement of carrying out reverse osmosis membrane desalination treatment influent water quality of water, reduced the contaminated risk of reverse osmosis membrane among the reverse osmosis membrane desalination treatment process, prolonged reverse osmosis membrane's life.

Description

Shale gas fracturing flowback fluid pretreatment process and system
Technical Field
The invention belongs to the field of sewage treatment, and relates to a shale gas fracturing flow-back fluid pretreatment process and a shale gas fracturing flow-back fluid pretreatment system.
Background
In the shale gas fracturing process, shale gas fracturing fluid injected into the stratum by a pump is returned to the ground to form shale gas fracturing flow-back fluid. Because shale gas fracturing flowback fluid contains a large amount of chemical additives, formation ions, mechanical impurities and the like, the shale gas fracturing flowback fluid needs to be treated and then discharged. The treatment process of the shale gas fracturing flowback fluid mainly comprises pretreatment and desalination treatment of a reverse osmosis membrane which are sequentially carried out.
The related art preprocessing process includes: lime and sodium carbonate are added into shale gas fracturing flowback fluid to reduce water hardness, then suspended matters are removed through flocculation and precipitation, finally micromolecular substances are removed through ultrafiltration treatment, and the solution after ultrafiltration enters a reverse osmosis membrane for desalination treatment.
The inventors found that the related art has the following technical problems:
in the related technology, lime and sodium carbonate are adopted to reduce the hardness of water, so that a large amount of precipitates can be generated, and scale-forming calcium ions can be generated, and more scale-forming ions can be remained after treatment, so that a reverse osmosis membrane in the subsequent reverse osmosis membrane desalination treatment is polluted, the membrane flux is reduced, the service life of the membrane is shortened, and the treatment cost is increased.
Disclosure of Invention
The embodiment of the invention provides a shale gas fracturing flowback fluid pretreatment process and a system, which can solve the technical problems. The specific technical scheme is as follows:
in one aspect, a shale gas fracturing flowback fluid pretreatment process method is provided, and the method comprises the following steps:
step a, sequentially adding a scale remover, a coagulant and a flocculant into the shale gas fracturing flow-back fluid to remove scale forming ions, particle impurities, insoluble colloid and organic matters in the shale gas fracturing flow-back fluid to obtain primary clear liquid;
b, adding a bactericide into the primary clear liquid, and performing sterilization treatment to obtain a secondary clear liquid;
c, sequentially carrying out sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid to remove soluble organic matters to obtain a tertiary clear liquid;
and d, carrying out ion exchange treatment on the third-level clear liquid to remove multivalent cations in the third-level clear liquid so as to obtain qualified reverse osmosis membrane inlet water.
In one possible implementation, in the step a, the detergent is a mixture of sodium hydroxide and sodium carbonate.
In a possible implementation manner, in the step a, the coagulant is polyaluminium chloride or aluminium sulfate, and the addition amount of the coagulant is 80-100 mg/L.
In a possible implementation manner, in the step a, the flocculating agent is one of anionic polyacrylamide, sodium acrylate, polyacrylic acid and acrylic acid, and the dosage of the flocculating agent is 1-1.5 mg/L.
In one possible implementation, the biocide comprises: sodium hypochlorite;
adding a reducing agent to the secondary clear liquid after the activated carbon filtration and before the ultrafiltration treatment, and then adjusting the pH value of the secondary clear liquid to 5-8.
In one possible implementation, the reducing agent is sodium bisulfite.
In one possible implementation manner, in the step d, the ion exchange process includes: sequentially carrying out primary ion exchange treatment and secondary ion exchange treatment;
the aperture of the ion exchange resin adopted by the primary ion exchange treatment is larger than that of the ion exchange resin adopted by the secondary ion exchange treatment.
On the other hand, a shale gas fracturing flow-back fluid pretreatment system is provided, and is used for any one shale gas fracturing flow-back fluid pretreatment process, and comprises a dosing unit, a filtering unit and an ion exchange unit which are sequentially communicated through pipelines;
the chemical adding unit is used for adding the descaling agent, the coagulant, the flocculating agent and the bactericide into the shale gas fracturing flow-back fluid;
the filtering unit is used for sequentially carrying out sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid to obtain a tertiary clear liquid;
the ion exchange unit is used for carrying out ion exchange treatment on the tertiary clear liquid to remove the multivalent cations in the tertiary clear liquid.
In one possible implementation, the medicated unit includes: a first dosing tank and a second dosing tank which are sequentially communicated through a pipeline;
the first dosing pool is used for adding the descaling agent, the coagulant and the flocculating agent into the shale gas fracturing flow-back fluid;
the second dosing pool is used for adding the bactericide into the shale gas fracturing flow-back fluid;
the filter unit includes: a sand filtration unit, an active carbon filtration unit and an ultrafiltration unit which are sequentially communicated through pipelines;
the ion exchange unit comprises a primary cation exchange resin and a secondary cation exchange resin which are sequentially communicated through a pipeline;
the pore diameter of the primary cation exchange resin is larger than that of the secondary cation exchange resin.
In one possible implementation, the primary cation exchange resin and the secondary cation exchange resin are both weak acid sodium type ion exchange resins.
The technical scheme provided by the embodiment of the invention has the following beneficial effects: according to the pretreatment process of the shale gas fracturing flow-back fluid, provided by the embodiment of the invention, the scale forming ions, particle impurities, insoluble colloid and organic matters in the shale gas fracturing flow-back fluid are removed by sequentially adding the scale remover, the coagulant and the flocculant, so that primary clear liquid is obtained. And adding a bactericide into the primary clear liquid for sterilization treatment to obtain a secondary clear liquid. And the three filtration modes of sand filtration, active carbon filtration and ultrafiltration treatment are sequentially carried out on the secondary clear liquid, so that suspended matters, soluble organic matters, inorganic scale precipitates, bacteria and the like in the secondary clear liquid are reduced, and the tertiary clear liquid is obtained. Through carrying out ion exchange treatment to tertiary clear liquid, having got rid of the multivalent cation in the tertiary clear liquid, only contained monovalent cation in the reverse osmosis membrane influent water that makes up to standard that obtains, reached the follow-up requirement of carrying out reverse osmosis membrane desalination treatment influent water quality of water, reduced the contaminated risk of reverse osmosis membrane among the reverse osmosis membrane desalination treatment process, prolonged reverse osmosis membrane's life, reduced treatment cost.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic view of a shale gas fracturing flowback fluid pretreatment system according to an embodiment of the present invention.
The reference numerals denote:
1-a medicine adding unit, wherein the medicine adding unit is connected with a medicine adding unit,
101-a first dosing tank, wherein the first dosing tank is provided with a first dosing tank,
102-a second dosing tank, wherein the second dosing tank is provided with a first dosing tank,
2-a filtering unit, wherein the filtering unit is provided with a filter,
201-a sand filtration unit, wherein,
202-an activated carbon filter unit, wherein,
203 an ultrafiltration unit, wherein the ultrafiltration unit is provided with a membrane,
3-an ion exchange unit, wherein,
301-a primary cation exchange resin,
302-secondary cation exchange resin.
Detailed Description
Unless defined otherwise, all technical terms used in the examples of the present invention have the same meaning as commonly understood by one of ordinary skill in the art. In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The embodiment of the invention provides a shale gas fracturing flowback fluid pretreatment process, which comprises the following steps:
step 1, sequentially adding a scale remover, a coagulant and a flocculant into the shale gas fracturing flow-back fluid to remove scale forming ions, particle impurities, insoluble colloid and organic matters in the shale gas fracturing flow-back fluid, and obtaining primary clear liquid.
And 2, adding a bactericide into the primary clear liquid, and performing sterilization treatment to obtain a secondary clear liquid.
And 3, sequentially carrying out sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid to remove soluble organic matters to obtain a tertiary clear liquid.
And 4, carrying out ion exchange treatment on the obtained tertiary clear liquid, removing multivalent cations in the tertiary clear liquid, and obtaining the qualified reverse osmosis membrane inlet water.
According to the pretreatment process of the shale gas fracturing flow-back fluid, provided by the embodiment of the invention, the scale forming ions, particle impurities, insoluble colloid and organic matters in the shale gas fracturing flow-back fluid are removed by sequentially adding the scale remover, the coagulant and the flocculant, so that primary clear liquid is obtained. And adding a bactericide into the primary clear liquid for sterilization treatment to obtain a secondary clear liquid. And the three filtration modes of sand filtration, active carbon filtration and ultrafiltration treatment are sequentially carried out on the secondary clear liquid, so that suspended matters, soluble organic matters, inorganic scale precipitates, bacteria and the like in the secondary clear liquid are reduced, and the tertiary clear liquid is obtained. Through carrying out ion exchange treatment to tertiary clear liquid, having got rid of the multivalent cation in the tertiary clear liquid, only contained monovalent cation in the reverse osmosis membrane influent water that makes up to standard that obtains, reached the follow-up requirement of carrying out reverse osmosis membrane desalination treatment influent water quality of water, reduced the contaminated risk of reverse osmosis membrane among the reverse osmosis membrane desalination treatment process, prolonged reverse osmosis membrane's life, reduced treatment cost.
The above steps are summarized below:
for the step 1, a scale remover, a coagulant and a flocculant are sequentially added into the shale gas fracturing flow-back fluid to remove scale forming ions and particle impurities in the shale gas fracturing flow-back fluid, so as to obtain primary clear liquid.
Wherein the particle diameter of the particulate impurities means particle impurities having a particle diameter of more than 5 μm. For example, 5 μm, 10 μm, 15 μm, 25 μm, 35 μm, 45 μm, 55 μm, 65 μm, etc.
As an example, the detergent is a mixture of sodium hydroxide and sodium carbonate. It can be understood that the dosage of sodium hydroxide in the mixture is Mg in the shale gas flowback fluid2+Twice the content of (c). To make the scaling ion Mg2+The total removal, the amount of sodium hydroxide added may be three times, four times, etc. the magnesium ion content. The dosage of the sodium carbonate in the mixture is Ca in the shale gas fracturing flowback fluid2+、Ba2+、Sr2+Sum of contents of in order to add Ca2+、Ba2+、Sr2+All the sodium carbonate is removed, and the dosage of the sodium carbonate can beCa2+、Ba2+、Sr2+One, two or three times the ion content.
The mixture of sodium hydroxide and sodium carbonate is used for carrying out precipitation treatment on scaling ions in shale gas fracturing flowback fluid, and the sodium hydroxide and the sodium carbonate do not contain the scaling ions, such as: ca2+、Mg2+、Ba2+、Sr2+And the sodium hydroxide is easy to dissolve in water and can be prepared into solution, and the solution can be continuously prepared in the dosing process, so that the precipitation process is continuous, and the descaling rate is stable.
Wherein the dosage of the sodium hydroxide is 102-110 percent of the theoretical dosage, the dosage of the sodium carbonate is 102-115 percent of the theoretical dosage, the dosage of the coagulant is 80-100mg/L, and the dosage of the flocculating agent is 1-2.0 mg/L.
The descaling agent is a mixture of sodium hydroxide and sodium carbonate. The descaling reaction formula is as follows:
Mg2++2OH-＝Mg(OH)2↓
Ca2++CO3 2-＝CaCO3↓
Ba2++CO3 2-＝BaCO3↓
Sr2++CO3 2-＝SrCO3↓
it is understood that the theoretical addition amount of sodium hydroxide and the theoretical addition amount of sodium carbonate are the addition amount of sodium hydroxide and the addition amount of sodium carbonate calculated according to the above reaction formulae. The dosage of the sodium hydroxide and the sodium carbonate is larger than the dosage theoretically required by the sodium hydroxide and the sodium carbonate, so that the scaling ions completely react to generate precipitates.
The dosage of the sodium hydroxide is 102-110% of the theoretical dosage, and the dosage of the sodium carbonate is 102-115% of the theoretical dosage. For example, the dosing amount of sodium hydroxide may be 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, etc. of the theoretical dosing amount. The amount of sodium carbonate added may be 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 112%, 114%, 115% or the like of the theoretical amount added.
The coagulant can be polyaluminium chloride, aluminum sulfate and the like.
As an example, the coagulant is polyaluminium chloride, also called basic aluminium chloride, the English code is PAC, the polyaluminium chloride has strong bridging adsorption function, the flocculating settling speed is high, the good settling effect is achieved, and the coagulant is non-corrosive to equipment. The addition amount of the coagulant is 80-100mg/L, and can be 80mg/L, 85mg/L, 90mg/L, 91mg/L, 95mg/L, 100mg/L and the like.
It can be understood that the added polyaluminium chloride can change the electrical property of particles in the shale gas fracturing flowback fluid, so that the repulsion among the particles and the distance among the particles are reduced, and the flocculation after the flocculant is added is facilitated. The particles subjected to the action of the polyaluminium chloride are polymerized into large particles by adding a flocculating agent and are precipitated.
The flocculating agent can be anionic polyacrylamide, sodium acrylate, polyacrylic acid, acrylic acid and the like.
As an example, the flocculant is anionic polyacrylamide and the english code is PAM. The adsorption and bridging action of polyacrylamide enables polyacrylamide molecular chains to be fixed on the surfaces of different particles, polymer bridges are formed among the particles, and the particles form aggregates to be settled. The addition amount of the flocculant is 1 to 1.5mg/L, and may be, for example, 1mg/L, 1.1mg/L, 1.3mg/L, 1.5mg/L, 1.7mg/L, 1.8mg/L, 1.9mg/L, 2.0mg/L or the like.
It can be understood that the dosage units of the scale remover, the coagulant and the flocculant are mg/L, wherein L refers to the volume of the shale gas fracturing flowback fluid.
For step 2, a bactericide is added to the primary clear liquid for sterilization treatment. Bacteria in the primary clear liquid can be removed to obtain a secondary clear liquid. As an example, the biocide may be sodium hypochlorite. The sodium hypochlorite is used as a common bactericide, is low in price, and is used in the embodiment of the invention, so that the introduction of other scaling foreign ions is avoided.
And 3, performing sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid in sequence to obtain a tertiary clear liquid.
In order to reduce the damage of the treated tertiary clear liquid to the reverse osmosis membrane in the subsequent reverse osmosis membrane desalting treatment process, a reducing agent is added after the active carbon filtration and before the ultrafiltration treatment, and the pH value is adjusted to 5-8.
And (3) performing sand filtration on the secondary clear liquid treated in the step (2) to remove the sediments in the step (1) and suspended matters, impurity dirt, colloid and the like in the secondary clear liquid after sterilization in the step (2). Filtering with sand, filtering with active carbon to remove soluble organic substances, and removing clean bacteria and chromaticity in step 2. Filtering with active carbon, adding reducing agent into the clear liquid, and reducing hypochlorite ions in the added bactericide. And adjusting the pH value to 5-8, and then carrying out ultrafiltration treatment to further remove small molecular soluble organic matters and remove clean small particle colloids which are not removed by sand filtration and active carbon filtration.
The pH value can be adjusted to 5-8 by hydrochloric acid so as to reduce the damage to the reverse osmosis membrane in the subsequent reverse osmosis membrane desalination treatment. Illustratively, the pH may be 5, 6, 7, 8, and the like.
It can be understood that the ultrafiltration treatment adopts an ultrafiltration membrane to remove small molecule soluble organic matters and small particle colloids in the secondary clear liquid, and in order to achieve the filtering effect of the ultrafiltration membrane, the pore diameter of the ultrafiltration membrane is smaller than the particle diameters of the small molecule soluble organic matters and the small particle colloids. For example, the pore size of the ultrafiltration membrane can be selected from 2-50nm according to the particle size of the soluble organic matter and the small particle colloid. For example, ultrafiltration membranes having pore diameters of 2nm, 10nm, 15nm, 20nm, 30nm, 35nm, 40nm, and 50nm may be used.
As an example, the reducing agent may be sodium bisulfite. Sodium bisulfite reacts with sodium hypochlorite serving as a bactericide to generate sodium chloride and sodium sulfate, scaling ions are not introduced during reduction, the sodium bisulfite is a common reducing agent and is low in price, and the cost of the treatment process is reduced.
For step 4, the obtained tertiary clear liquid is subjected to ion exchange treatment to remove multivalent cations in the tertiary clear liquid.
To remove polyvalent cations in the tertiary clear liquidIons, e.g. Ca2+、Mg2+、Ba2+、Sr2+And removing ions and the like to ensure that the discharged reverse osmosis membrane inlet water only contains monovalent cations, and performing primary ion exchange treatment and secondary ion exchange treatment sequentially. As shown in FIG. 1, the primary ion exchange treatment is carried out by using a primary cation exchange resin 301, and the secondary ion exchange treatment is carried out by using a secondary cation exchange resin 302.
In order to achieve the effect of removing multivalent cations, the pore diameter of the primary cation exchange resin 301 is larger than that of the secondary cation exchange resin 302, and the clear solution which is not completely treated by the primary cation exchange resin 301 is subjected to secondary ion exchange treatment by the secondary cation exchange resin 302, so that multivalent cations in the third clear solution are completely treated.
As an example, the primary cation exchange resin 301 and the secondary cation exchange resin 302 may be weakly acidic sodium type ion exchange resins. The weak acid sodium type ion exchange resin can be adsorbed with other multivalent cations in the third-level clear liquid to generate cation exchange effect. The two-stage weak acid sodium ion exchange resin can deeply remove multivalent cations including scale forming ions, such as Ca, from the three-stage clear liquid2+、Mg2+、Ba2+、 Sr2+The pollution risk to the reverse osmosis membrane in the subsequent reverse osmosis treatment is reduced, the service life of the reverse osmosis membrane is prolonged, and the cost of the reverse osmosis treatment is reduced.
The inlet water of the reverse osmosis membrane which is treated by the shale gas fracturing flow-back fluid treatment process provided by the embodiment of the invention and reaches the standard only contains monovalent cations, such as sodium ions. The fresh water can be discharged after reaching the standard after subsequent reverse osmosis treatment, and the treated concentrated water can be used for preparing high-quality salt by evaporative crystallization, so that the optimal utilization of resources is achieved.
The embodiment of the present invention further provides a shale gas fracturing flow-back fluid pretreatment system, which is used in any one of the above shale gas fracturing flow-back fluid pretreatment processes, as shown in fig. 1, and the system includes: a dosing unit 1, a filtering unit 2 and an ion exchange unit 3 which are sequentially communicated through pipelines. The dosing unit 1 comprises a first dosing tank 101 and a second dosing tank 102 which are sequentially communicated through a pipeline. The filtering unit 2 comprises a sand filtering unit 201, an activated carbon filtering unit 202 and an ultrafiltration unit 203 which are sequentially communicated through pipelines. The ion exchange unit 3 includes a primary cation exchange resin 301 and a secondary cation exchange resin 302 which are in communication with each other in this order through a pipeline.
With the treatment system provided by the embodiment of the invention, as shown in fig. 1, shale gas fracturing flow-back fluid is injected into the first dosing tank 101, a scale remover, a coagulant and a flocculant are sequentially added into the first dosing tank 101, scale forming ions in the shale gas fracturing flow-back fluid are subjected to precipitation treatment by adding the scale remover, and particles in the shale gas fracturing flow-back fluid are subjected to flocculation precipitation treatment by adding the coagulant and the flocculant to obtain primary clear liquid. And sending the primary clear liquid into a second medicine adding pool 102, and adding a bactericide for sterilization to obtain a secondary clear liquid.
The second-level clear liquid is sent into the filtering unit 2 and sequentially passes through a sand filtering unit 201, an active carbon filtering unit 202 and an ultrafiltration unit 203. Suspended matters, impurity dirt, colloid and the like in the secondary clear liquid are removed through the sand filtering unit 201, for example, the completely precipitated particulate matters, the impurity dirt and the like carried in the original solution are not precipitated through the precipitation treatment of the first dosing tank 101 and the second dosing tank 102. Soluble organic matter is removed by the activated carbon filtering unit 202, and clean bacteria and color, etc. are not removed through the step 2. Further removing small molecule soluble organic matters through the ultrafiltration unit 203, and filtering the small molecule soluble organic matters through sand filtration and active carbon filtration without removing clean small particle colloids to obtain third-level clear liquid.
The three filtration combination modes reduce suspended matters, soluble organic matters, inorganic scale precipitates, bacteria and the like in the primary clear liquid, and obtain the tertiary clear liquid. After being filtered by the activated carbon filtering unit 202, the reducing agent is added into the clear liquid to reduce hypochlorite ions in the added bactericide.
In order to reduce the damage to the reverse osmosis membrane in the subsequent reverse osmosis membrane desalination treatment, the pH value of the secondary clear liquid filtered by the activated carbon filtering unit 202 is adjusted to 5-8, and then the secondary clear liquid is sent to the ultrafiltration unit 203 for ultrafiltration treatment, so that small molecular soluble organic matters are further removed, and clean small particle colloids are not removed by sand filtration and activated carbon filtration. As an example, the pH can be adjusted to 5-8 with hydrochloric acid, and as an example, the pH can be 5, 6, 7, 8, and the like.
As an example, the reducing agent may be sodium bisulfite. The sodium bisulfite is used as a reducing agent for reduction, does not introduce scaling ions, is a common reducing agent, has low price and reduces the cost of the treatment process.
The treatment system provided by the embodiment of the invention can deeply reduce suspended matters, soluble organic matters, inorganic scale precipitates, bacteria and the like in secondary clear liquid by combining the three filtering modes of the sand filtering unit 201, the activated carbon filtering unit 202 and the ultrafiltration unit 203. The water quality of the three-level clear liquid is improved, the pollution risks to the reverse osmosis membrane when the reverse osmosis membrane is subjected to reverse osmosis membrane desalination treatment in the follow-up process, including organic pollution, bacterial pollution, inorganic scale pollution, suspended matter pollution and the like, are reduced, the service life of the reverse osmosis membrane is prolonged, and the treatment cost is reduced.
As shown in the attached figure 1, the third-level clear liquid is sent into a cation exchange unit 3 and passes through a first-level cation exchange resin 301 and a second-level cation exchange resin 302 in sequence to obtain the inlet water of the reverse osmosis membrane reaching the standard.
The shale gas fracturing flowback fluid treated by the system provided by the embodiment of the invention, namely the qualified reverse osmosis membrane inlet water, only contains univalent cations, such as sodium ions. The fresh water can be discharged after reaching the standard after subsequent reverse osmosis treatment, and the treated concentrated water can be used for preparing high-quality salt by evaporative crystallization, so that the optimal utilization of resources is achieved.
In order to completely treat multivalent cations in the tertiary supernatant, the system provided by the embodiment of the invention adopts a primary cation exchange resin 301 and a secondary cation exchange resin 302 which are communicated in sequence. It will be appreciated that, in order to achieve the above treatment effect, the pore size of the primary cation exchange resin 301 is larger than that of the secondary cation exchange resin 302. The multivalent cations in the three-level clear liquid are treated by the first-level cation exchange resin 301 and the second-level cation exchange resin 302 which are connected in series, so that the reverse osmosis membrane inlet water subjected to reverse osmosis membrane desalination treatment only contains monovalent cations, the damage to the reverse osmosis membrane is reduced, the risk of fouling and blocking of the reverse osmosis membrane is reduced, and the treatment cost is reduced.
As an example, the primary cation exchange resin 301 and the secondary cation exchange resin 302 may be weak acid sodium type ion exchange resins. The weak acid sodium type ion exchange resin can be adsorbed with other cations in the third-level clear liquid to generate cation exchange effect. The two-stage weak acid sodium ion exchange resin can deeply remove multivalent cations including scale forming ions, such as Ca, from the three-stage clear liquid2+、Mg2+、Ba2+、Sr2+The pollution risk to the reverse osmosis membrane in the subsequent reverse osmosis membrane desalination treatment is reduced, the service life of the reverse osmosis membrane is prolonged, and the cost of the reverse osmosis membrane desalination treatment is reduced.
In an implementation manner, shale gas fracturing flowback fluid flowing back from a wellhead at 165 th day after certain shale gas well fracturing construction is treated by a pretreatment system adopted in the related art and the pretreatment system provided by the embodiment of the invention.
The specific processing process of the pretreatment system provided by the embodiment of the invention is as follows:
the shale gas fracturing flowback liquid firstly enters a first dosing tank 101, sodium hydroxide, sodium carbonate and coagulant polyaluminium chloride are sequentially added, a flocculant anion polyacrylamide is precipitated, the supernatant of the first dosing tank 101 enters a second dosing tank 102, a bactericide sodium hypochlorite is added for sterilization, the obtained supernatant sequentially enters a sand filtering unit 201 and an active carbon filtering unit 202, a reducing agent sodium bisulfite is added into the supernatant from the active carbon filtering unit 202, HCl is added for adjusting the pH to 6, the supernatant after pH adjustment sequentially enters an ultrafiltration unit 203, and the supernatant after the pH adjustment sequentially enters a primary cation exchange resin 301 and a secondary cation exchange resin 302 for treatment. Wherein the dosage of the sodium hydroxide is 106 percent of the theoretical dosage, the dosage of the sodium carbonate is 108 percent of the theoretical dosage, the dosage of the polyaluminium chloride is 90mg/L, and the dosage of the anionic polyacrylamide is 1.5 mg/L.
The water quality after the two pretreatment systems and the water quality standard of reverse osmosis membrane inlet are shown in table 1.
TABLE 1 Water quality after treatment by two systems and reverse osmosis membrane influent Water quality Standard
Figure BDA0001739591100000101
As can be seen from Table 1, after the shale gas fracturing flowback fluid is treated by the pretreatment system, the total number of bacterial colonies, total organic carbon, chemical oxygen demand, total silicon and scale forming ions in the reverse osmosis inlet water quality index are obviously reduced, so that the pollution risk of the reverse osmosis membrane is reduced, the service life of the membrane is prolonged and the economic benefit is increased when the reverse osmosis membrane is treated.
The above description is only an illustrative embodiment of the present invention, and should not be taken as limiting the scope of the invention, and any modifications, equivalents, improvements and the like that are within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. The shale gas fracturing flowback fluid pretreatment process is characterized by comprising the following steps of:
step a, sequentially adding a scale remover, a coagulant and a flocculant into the shale gas fracturing flow-back fluid to remove scale forming ions, particle impurities, insoluble colloid and organic matters in the shale gas fracturing flow-back fluid to obtain primary clear liquid;
b, adding a bactericide into the primary clear liquid, and performing sterilization treatment to obtain a secondary clear liquid;
c, sequentially carrying out sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid to further reduce the contents of suspended matters, colloids, inorganic scale precipitates and soluble organic matters so as to obtain a tertiary clear liquid;
d, carrying out ion exchange treatment on the tertiary clear liquid to remove multivalent cations in the tertiary clear liquid to obtain qualified reverse osmosis membrane inlet water;
the descaling agent is a mixture of sodium hydroxide and sodium carbonate, the dosage of the sodium hydroxide is 102-110% of the theoretical dosage, and the dosage of the sodium carbonate is 102-115% of the theoretical dosage;
the coagulant is polyaluminium chloride or aluminum sulfate, and the dosage of the coagulant is 80-100 mg/L;
the flocculant is one of anionic polyacrylamide, sodium acrylate, polyacrylic acid and acrylic acid, and the dosage of the flocculant is 1-1.5 mg/L;
the ultrafiltration treatment adopts an ultrafiltration membrane with the aperture of 2-50 nm;
the bactericide comprises: sodium hypochlorite;
adding a reducing agent to the secondary clear liquid after the activated carbon filtration and before the ultrafiltration treatment, and then adjusting the pH value of the secondary clear liquid to 5-8;
in the step d, the ion exchange treatment includes: sequentially carrying out primary ion exchange treatment and secondary ion exchange treatment;
the aperture of the ion exchange resin adopted by the primary ion exchange treatment is larger than that of the ion exchange resin adopted by the secondary ion exchange treatment.
2. The shale gas fracturing flowback fluid pretreatment process of claim 1, wherein the reducing agent is sodium bisulfite.
3. The shale gas fracturing flow-back fluid pretreatment system is used for the shale gas fracturing flow-back fluid pretreatment process according to any one of claims 1-2, and is characterized by comprising a dosing unit (1), a filtering unit (2) and an ion exchange unit (3) which are sequentially communicated through pipelines;
the dosing unit (1) is used for adding the descaling agent, the coagulant, the flocculant and the bactericide into the shale gas fracturing flow-back fluid;
the filtering unit (2) is used for sequentially carrying out sand filtration, activated carbon filtration and ultrafiltration treatment on the secondary clear liquid to obtain a tertiary clear liquid;
the ion exchange unit (3) is used for carrying out ion exchange treatment on the tertiary clear liquid to remove the multivalent cations in the tertiary clear liquid;
the medicine adding unit (1) comprises: a first dosing pool (101) and a second dosing pool (102) which are communicated in sequence through pipelines;
the first dosing pool (101) is used for adding the descaling agent, the coagulant and the flocculant into the shale gas fracturing flow-back fluid;
the second chemical adding pool (102) is used for adding the bactericide into the shale gas fracturing flowback fluid;
the filtration unit (2) comprises: a sand filtration unit (201), an active carbon filtration unit (202) and an ultrafiltration unit (203) which are communicated in sequence through pipelines;
the ion exchange unit (3) comprises a primary cation exchange resin (301) and a secondary cation exchange resin (302) which are sequentially communicated through a pipeline;
the pore diameter of the primary cation exchange resin (301) is larger than that of the secondary cation exchange resin (302).
4. The shale gas fracturing flowback fluid pretreatment system of claim 3, wherein the primary cation exchange resin (301) and the secondary cation exchange resin (302) are both weak acid sodium type ion exchange resins.
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