CN101481186A - Process and apparatus for treating oil-gas field wastewater - Google Patents

Abstract

The invention discloses an oil and gas field wastewater treatment process and device. The wastewater treatment process includes a pretreatment step and an advanced treatment step. The pretreatment step adopts electric floating treatment + coagulation sedimentation treatment method; the advanced treatment step includes oxidation treatment and secondary coagulation. Precipitation treatment, filtration, conditioning treatment. The wastewater treatment device includes a sequentially arranged pretreatment device and an advanced treatment device, and the pretreatment device includes a sequentially arranged electrical floating treatment device and a first-stage coagulation and sedimentation device. Beneficial effects: the wastewater treatment effect is good. Under normal circumstances, the effluent index of oil (gas) wastewater treatment can reach the first-class standard of GB8978-1996, and the effluent index of drilling and workover and downhole operation wastewater can reach the second-class standard of GB8978-1996 . This wastewater treatment device has strong processing capacity, low energy consumption, and high degree of automation. Under the normal operation of the whole set of devices, only 2 people are required to cooperate with the operation.

Description

Oil and gas field wastewater treatment process and device

technical field

The invention relates to wastewater treatment technology, in particular to an oil and gas field wastewater treatment process and device.

Background technique

Oil and gas field wastewater is mainly composed of oil and gas field produced water, well washing wastewater, drilling wastewater, and downhole operation wastewater. Contains petroleum, SS, demulsifier, drilling fluid additives, soluble minerals, polymer treatment agent, organic matter, residual acid, alkali, heavy metal ions, etc., the composition is complex, generally with high COD, high petroleum, high SS, high mineral It has high pollution load, strong environmental hazards, and difficult treatment.

Oil and gas field wastewater treatment process includes two steps, namely wastewater pretreatment and advanced treatment.

At present, the pretreatment of oil and gas field wastewater is usually carried out by chemical demulsification, oil separation, (dissolved air) air flotation, coagulation, sedimentation, etc. Stability, poor degreasing effect, large amount of chemical dosage, low pollutant removal rate and other disadvantages bring great difficulties to the subsequent deep standard treatment of wastewater.

There are many methods of advanced wastewater treatment, which can be divided into physical chemical method and biochemical method according to the treatment type. Physical and chemical methods include chemical redox, electrochemical redox, catalytic oxidation, adsorption, extraction, membrane separation and other processes; biochemical methods include aerobic and anaerobic processes.

In addition to using biochemical treatment process for advanced treatment, methods such as Fenton reagent method, O ₃ method, O ₃ +H ₂ O ₂ method, Fenton reagent + O ₃ and other methods can be used for advanced treatment of wastewater according to different water quality conditions, especially The Fenton+O ₃ method has the best treatment effect, but the COD removal rates of these methods are all low. Taking the Fenton+O ₃ method as an example, because O ₃ is a slightly soluble gas in water, in the current treatment process or device, O 3 is generally added by the aeration _{head or aeration tube, and the gas between O 3 and} the wastewater The liquid mass transfer effect is poor, and the absorption efficiency of O ₃ is low, which affects the oxidative degradation effect of Fenton+O ₃ on organic pollutant components.

In addition, in southern my country, oil and gas field wells are scattered, and the well sites are remote, far away from wastewater treatment plants and stations. At present, most of them are transported to wastewater treatment plants and stations by tank trucks, and the transportation cost is very high, thus increasing the treatment cost. Although some mobile oil and gas field wastewater treatment equipment have appeared in recent years, their technology is relatively backward, and most of them use different combinations of unit processes such as chemical stabilization, coagulation, air flotation, sedimentation, and filtration to achieve different treatment requirements and purposes. There are disadvantages such as poor treatment effect, difficulty in reaching the standard, small treatment capacity, unstable operation, low degree of automation, and high treatment cost, making it difficult to popularize and use it on a large scale.

Contents of the invention

The object of the present invention is to overcome the shortcomings of the existing oil and gas field wastewater treatment process and devices, and provide a kind of oil and gas field wastewater treatment process up to standard, and a mobile wastewater treatment device with large processing capacity, stable operation, high degree of automation, low processing cost.

Technical solution of the present invention is:

An oil and gas field wastewater treatment process includes a pretreatment step and an advanced treatment step, and the pretreatment step adopts electric floatation treatment + coagulation sedimentation treatment method.

The step of deep processing comprises the following sub-steps:

1). Oxidation treatment

Adding an oxidizing agent to the supernatant after coagulation and precipitation to carry out oxidation treatment;

2).Secondary coagulation and sedimentation treatment

Add flocculants and coagulation aids to the oxidized wastewater, coagulate with the dirt in it to form a precipitate, and send the supernatant to the next process for treatment;

3). Filter

The supernatant after secondary coagulation and precipitation is filtered with activated carbon, and the filtrate is sent to the next process for processing;

4).Quenching and tempering treatment

Add a pH regulator to the filtrate to adjust the pH of the filtrate to meet the discharge requirements.

The oxidation step adopts a composite catalytic oxidation method, adding an Fe ²⁺ catalyst to the supernatant.

The oxidizing agent is O ₃ or O ₃ +H ₂ O ₂ .

The filtration step adopts a composite filtration method, adding O ₃ to the supernatant after secondary coagulation and precipitation, and then filtering by activated carbon.

An oil and gas field wastewater treatment device includes a pretreatment device and an advanced treatment device arranged in sequence, and the pretreatment device includes an electrical floating treatment device and a first-stage coagulation and sedimentation device arranged in sequence.

The advanced treatment device includes an oxidation device, a secondary coagulation sedimentation device, a filter device, and an adjustment and monitoring device arranged in sequence.

The oxidation device adopts a sieve plate oxidation tower.

The filter device is an O ₃ +activated carbon composite filter device.

The oil and gas field wastewater treatment device is fixed on the ground, or the oil and gas field wastewater treatment device is arranged on a mobile vehicle.

Technical effect of the present invention:

(1) The treatment effect is good. Under normal circumstances, the effluent index after treatment of oil (gas) wastewater can meet the first-class standard of GB8978-1996, and the effluent index after treatment of drilling and workover and downhole operation wastewater can reach the second-class standard of GB8978-1996.

(2) The processing capacity of the device is strong. The treatment speed can be adjusted according to the water pollution load, and the adjustment range is between 5 and 10m ³ /h.

(3) Low energy consumption. The total power used by the whole set of equipment under normal operation is ≤40kw.

(4) High degree of automation. Under the normal operation of the whole set of equipment, only 2 people are required to cooperate with the operation.

(5) Mobility and flexibility. The device is skid-mounted, and can be pulled to the field for mobile use by transport vehicles, or placed in a fixed station for wastewater treatment.

Description of drawings

Fig. 1 is a process flow diagram of the present invention

Figure 2 is a structural block diagram of the oil and gas field wastewater treatment device

Figure 3 is a schematic structural view of the electrical floatation pretreatment device (3-1 top view, 3-2 front view)

Figure 4 is a schematic structural view of the sieve plate oxidation tower

Figure 5 is a schematic structural view of the coagulation settling device

Fig. 6 is the schematic structural view of filtering device

Fig. 7 is a structural schematic diagram of the adjustment monitoring device (7-1 front view, 7-2 top view)

Detailed ways

See Figure 2: The oil and gas field wastewater treatment device includes an electric floating treatment device I, a primary coagulation sedimentation device II, an oxidation device III, a secondary coagulation sedimentation device IV, a filter device V, and a regulating monitoring device VI arranged in sequence. The structure of each part is described as follows.

Refer to Fig. 3-1 and Fig. 3-2: the electrical floating treatment device I includes a power source 1, an electrolytic tank 2, and a slag overflow tank 3. In the electrolytic cell 2, a plurality of pole plates 4 are vertically dispersed and arranged. The pole plates 4 are divided into two groups, one group is the anode, and the other is the cathode. Connection, bus 5 is connected to power supply 1.

The pole plate 4 is made of ordinary carbon steel, installed in parallel on the pole plate fixing card 6 in the electrolytic cell 2, and supported by the Cao steel bracket 14; the bus bar 5 uses copper bars, and is connected in a unipolar manner. The power supply 1 adopts a low-voltage high-frequency pulse power supply, the voltage is continuously adjustable from 0 to 18V, and the current is continuously adjustable from 0 to 6000A.

The pole plates 4 are divided into several groups by the separators 7; one end of the separators 7 is fixed and closed, and the adjacent separators 7 are staggered from each other, so that the water flows back and forth in the electrolytic cell 2, forming a tumbling type. The water inlet 8 of the electrolytic cell 2 is arranged at the bottom, and the water outlet 9 is arranged at the waist, forming a bottom inlet and an upper outlet. The water inlet 8 inputs waste water through a water inlet pipe 10 , and the water outlet 9 discharges waste water through a drain pipe 11 .

The upper edge of the slag overflow tank 3 is slightly higher than the liquid level in the electrolytic tank 2 , and its bottom outflow pipe 12 is connected with the slag discharge pipe 13 of the electrolytic tank 2 .

See Figure 4: Oxidation device III adopts a sieve-plate oxidation tower, including a tower body A, an upper head B, and a lower head C; the tower body A has a multi-layer missing circular sieve plate 15, and the missing sides of the multi-layer sieve plates are staggered Arranged to form a baffle structure; the missing side of the sieve plate 15 is provided with an overflow weir 16; the gap between the overflow weir 16 and the inner wall of the tower forms a downflow channel 17, and the wastewater from the upper sieve plate flows down to the lower sieve plate through this channel; The upper part of the tower body A is provided with a waste water inlet 18, which is higher than the uppermost sieve plate 15, and the waste water inlet 18 has a catalyst addition port. The lower part of the tower body A is provided with an oxidant inlet 19 which is lower than the bottom sieve plate 15 . The upper head B is provided with an exhaust gas outlet 20, and the lower head C is provided with a waste water outlet 21.

The oxidizing agent adopts ozone, or a mixture of ozone and hydrogen peroxide.

Catalyst adopts Fe ²⁺ reagent.

Referring to FIG. 5 : the coagulation and sedimentation devices II and IV have the same structure, including a coagulation tank 22 and a sedimentation tank 23 . Coagulation tank 22 has waste water inlet 24, flocculant agent automatic feeding hopper 25, agitator 26 is arranged in coagulation tank 22, the outlet of coagulation tank 22 is connected with lifting pump 27, and the outlet of lifting pump 27 has pipeline mixer 28 , for adding flocculation aids. There is an outlet weir plate 29 in the sedimentation tank 23, which isolates the space in the tank into an upstream section and a downstream section. The upstream section is arranged with inclined pipes 30, mud buckets 31, and rectifying plates 32 in sequence from top to bottom. The inclined pipes 30 are inclined downward. The inclination angle is 60 ⁰ , and it is fixed on the inclined pipe support 33, and there is a mud discharge pipe 34 at the bottom of the pool. A deflector 35 is arranged on the downstream section, and an outlet overflow port 36 is arranged on the vertical wall. There is a mud bucket 31 at the bottom of the groove, and the mud bucket 31 is connected with a mud discharge pipe 34.

Referring to FIG. 6 : the filtering device V includes an ozone generator 37 , a waste water booster pump 38 , and a filter tank 39 . The outlet of the wastewater booster pump 38 is connected to the water inlet at the bottom of the filter tank 39 through the pipeline 40. The pipeline 40 is provided with a jet 41, and the ozone from the ozone generator 37 is added from the jet 41 to mix with the waste water. Filtration tank 39 is filled with filtering medium activated carbon 42, and waste water is filtered by activated carbon 42 and discharged from outlet 43 on the top of filter tank 39. The top of the filter tank 39 is provided with a pressure relief valve 44 for discharging exhaust gas, and the tank body 39 is provided with a manhole 45 for filling activated carbon 42 . In addition, a backwash pump 46 is also provided for regularly washing the filter residue in the filter medium.

Refer to Fig. 7-1 and Fig. 7-2: the adjustment and monitoring device VI includes a pH controller 47, a metering pump 48, an acid mixing tank 49, an acid mixing tank 50, and a monitoring tank 51. A pipeline 52 is connected between the monitoring tank and the acid distribution tank (the water used for acid distribution can recycle the clear water in the monitoring tank). The acid delivery pipeline 54 is transported to the water inlet 55 of the mixed acid tank 50. A group of baffles 56 are installed in the mixed acid tank 50. The number of baffles 55 depends on actual needs. The waste water in the mixed acid tank 50 enters the monitoring system through the water inlet 57. The tank 51 and the sensing electrode 58 of the pH controller 47 are fixed in the monitoring tank 51 by a fixing card 59 , and the clear water in the monitoring tank 51 is discharged through the water outlet 60 .

Referring to Fig. 1, the workflow and principle of the method are as follows:

The wastewater is pumped into the electric floating treatment device for electrolysis, flocculation, and air flotation treatment. The electric floating device is powered by a low-voltage high-frequency pulse power supply. Under the action of direct current, the plate material loses electrons due to the forced oxidation-reduction reaction to generate metal ions into the wastewater, and interacts with ^OH in the water to form a variety of hydroxyl complexes, polynuclear hydroxyl complexes and hydroxides. These products have strong activity and can strongly condense and adsorb colloidal particles, suspended solids, and heavy metal ions in wastewater to form a large number of flocs that settle to the bottom of the pool to purify water; at the same time, O ₂ and H are released from the surface of the plate during electrolysis. ₂ , CO ₂ , Cl _{2 ,} etc., form a large number of micro-bubbles with a diameter of 10-30 μm. Due to the large surface area of the micro-bubbles, they are easy to adhere to colloidal particles, suspended solids, heavy metal ions, oil and flocs in the wastewater to form floating Slag; scum is discharged through the overflow tank. In addition, OH free radicals with strong oxidizing ability will be generated during electrolysis, so it also has the ability to oxidize, decolorize, deodorize, and disinfect. Depending on the conductivity of the wastewater, a small amount of salt can be added to the wastewater to improve the conductivity of the wastewater, usually [C1 ^- ] ≥ 1000mg/l without adding. Compared with the traditional electric floating treatment device, this unit device can save energy by more than 30%, the working voltage is ≤12V, the treatment process is safe and reliable, the unit power consumption of wastewater is ≤1KW per ton of wastewater, the consumption of plate materials is reduced by more than 30%, and the supporting power supply is small in size , weighing only a few hundred kilograms.

The effluent treated by the electric floatation device enters the first-stage coagulation and sedimentation device, and the automatic device is used to quantitatively add an appropriate amount of flocculant and coagulation aid for coagulation reaction, and the coagulated mixed solution enters the inclined tube sedimentation tank for rapid settlement. The final supernatant enters the next advanced treatment unit, and the sediment at the bottom of the sedimentation tank is discharged from the bottom slag discharge pipe. The first-stage coagulation and sedimentation device mainly precipitates a large amount of flocs and metal ions produced by the electric floating unit to make the water clear and create favorable conditions for subsequent advanced treatment. After electric flotation and first-stage coagulation and sedimentation treatment, the removal rate of SS, petroleum and metal ions in wastewater can reach 80% to 95%, and the removal rate of COD can reach 40% to 70%.

The supernatant of the first-stage coagulation and sedimentation tank is pumped into the self-developed wastewater oxidation treatment device for compound catalytic oxidation after adding a small amount of catalytic additives with a metering pump. The oxidation treatment device adopts Fenton + O ₃ + sieve plate oxidation tower. The gas oxidant O ₃ produced by the oxidant generating equipment enters the device from the bottom of the oxidation tower for reverse mixing of gas and liquid, and a homogeneous composite catalytic oxidation reaction occurs. After the reaction, the wastewater from The exhaust gas is discharged from the bottom of the device, and the exhaust gas is discharged from the exhaust port on the top of the device. Since the oxidation device is equipped with a multi-layer baffle full of micropores, the waste water is in contact with the oxidant for a long time when it flows through the oxidation device, and at the same time, the gas oxidant is fully in contact with the waste water after passing through the micropores. High COD removal rate, fast chroma removal speed and high processing efficiency. Compared with the traditional aeration head or aeration tube, the gas-liquid mass transfer efficiency is higher when the sieve plate oxidation tower is used, and the O ₃ absorption efficiency can reach more than 70%. After oxidation treatment, 10% to 20% of COD in wastewater can be further removed.

Since the waste water still contains a small amount of divalent metal ions after primary coagulation and sedimentation, and a small amount of Fe ²⁺ is also added to the oxidation treatment unit, the divalent ions are converted into trivalent ions after oxidation treatment to make the waste water have a certain color. Further coagulation and sedimentation treatment is carried out to remove metal ions and reduce the color of wastewater. Therefore, after putting a small amount of flocculant and additives into the effluent treated by the oxidation device, it enters the secondary coagulation and sedimentation device for coagulation and sedimentation, and the working principle is the same as that of the coagulation and sedimentation device.

The supernatant from the secondary coagulation and sedimentation device enters the filter device for fine filtration. This step adopts O ₃ + activated carbon composite filtration process, O ₃ is added by jet device, mixed with wastewater and enters the activated carbon filter together. Because _O3 continuously oxidizes and desorbs the adsorption points inside the activated carbon during filtration, compared with purely using activated carbon for filtration, the saturation period of activated carbon is prolonged and the service life is increased by more than 30%. Therefore, the consumption of filter material is reduced and the cost is saved. At the same time, O ₃ can also further oxidatively degrade and decolorize the organic matter in the filtered wastewater, that is, COD, so as to ensure that the COD value of the filtered water meets the requirements of the second-level standard of GB8978-1996.

Since the primary and secondary coagulation and sedimentation processes have added an excessive amount of alkaline precipitation agents, the filtered water is alkaline and needs to be entered into a monitoring device for pH adjustment. The PH controller in the monitoring tank automatically controls the amount of acid added by the metering pump according to the pH value of the water quality. The acid liquid and the water in the acid mixing tank are automatically mixed by hydraulic impact, and the mixed wastewater enters the monitoring tank through the water inlet of the monitoring tank for storage. Realize the closed-circuit cycle of automatic pH detection-acid addition-mixing-storage-PH detection, and discharge the wastewater after the pH value reaches the standard.

Claims (10)

1. an oil gas field waste water technology comprises pre-treatment step and advanced treatment step, it is characterized in that: described pre-treatment step adopts electric floating processing+coagulating sedimentation facture.

2. oil gas field waste water technology according to claim 1 is characterized in that described advanced treatment step comprises following substep:

1). oxide treatment

Add oxygenant in the supernatant liquor behind coagulating sedimentation, it is carried out oxide treatment;

2). the two-stage coagulation precipitation process

To in the waste water of oxide treatment, adding flocculation agent and coagulation auxiliary agent, carry out coagulating with wherein dirt, form precipitation, supernatant liquor send down the operation processing;

3). filter

With the supernatant liquor activated carbon filtration of two-stage coagulation post precipitation, filtrate send down operation to handle;

4). modifier treatment

Add the pH value conditioning agent to filtrate, regulate the filtrate pH value, make it to meet emission request.

3. oil gas field waste water technology according to claim 2 is characterized in that: described oxidation step adopts the composite catalytic oxidation method, adds Fe in supernatant liquor ²⁺Catalyzer.

4. oil gas field waste water technology according to claim 2 is characterized in that: described oxygenant is O ₃Or O ₃+ H ₂O ₂

5. oil gas field waste water technology according to claim 2 is characterized in that: described filtration step adopts the combined filtration method, to the supernatant liquor adding O of two-stage coagulation post precipitation ₃, again by activated carbon filtration.

6. an oil gas field waste water treatment device comprises the pretreatment unit and the advanced treatment apparatus that are disposed in order, it is characterized in that: described pretreatment unit comprises electric floating treatment unit and the one-level coagulating sedimentation device that is disposed in order.

7. oil gas field waste water treatment device according to claim 6 is characterized in that: described advanced treatment apparatus comprises oxidation unit, two-stage coagulation settler, filtration unit, the adjusting monitor device that is disposed in order.

8. oil gas field waste water treatment device according to claim 7 is characterized in that: described oxidation unit adopts the sieve-board type oxidizing tower.

9. oil gas field waste water treatment device according to claim 7 is characterized in that: described filtration unit is O ₃+ gac composite filtering equipment.

10. oil gas field waste water treatment device according to claim 6 is characterized in that: this oil gas field waste water treatment device lands fixed and arranged, or is arranged on the carrier loader that flows.

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