CN106915841B - Novel process for treating mercury-containing wastewater of oil and gas field - Google Patents

Abstract

The invention relates to a novel process for treating mercury-containing wastewater of an oil-gas field, belonging to the technical field of wastewater treatment. Firstly, the wastewater is treated by a gravity settling tank and a coagulation flocculation device to remove impurities such as suspended matters, floating matters, partial grease and the like in the wastewater. Then, after the chemical addition reaction, the mixture enters a primary air flotation device to remove suspended matters, grease and partial elemental mercury; and the residual wastewater enters a pH adjusting tank through an overflow pipe, the pH is adjusted to 8-9 (alkaline), sulfide is added at the same time, then the wastewater in the pH adjusting tank is lifted to a secondary air flotation device through a pump, and the overflow wastewater reaches the national first-level emission standard after being adsorbed by a mercury adsorption device. The method has the advantages of reasonable process, high treatment efficiency and good reliability, can treat pollutants which cannot be removed by the traditional process, and mainly treats the mercury-containing wastewater generated in the processes of exploitation, production, treatment, transportation and the like of the oil-gas field.

Description

Novel process for treating mercury-containing wastewater of oil and gas field

Technical Field

The invention relates to a novel process for treating mercury-containing wastewater of an oil-gas field, belonging to the technical field of wastewater treatment.

Background

Mercury (Hg), commonly known as mercury, is the only metal present in a liquid state at ambient temperature and pressure, is chemically stable, and is insoluble in acid and also insoluble in alkali. However, mercury can be evaporated at normal temperature, and mercury vapor and mercury compounds are often highly toxic. Mercury and its compounds can enter human body through respiratory tract, digestive tract and skin, and mainly harm human nervous system, and mercury is discharged slowly, can be enriched in human body, and can cause mercury poisoning after long-term intake. Wherein, the metallic mercury is mainly absorbed through the respiratory tract in a vapor form, and the mercury vapor can also pass through the blood brain barrier to cause the damage of the nervous system, the digestive system and the kidney, and can cause the mercury poisoning encephalopathy even death in serious cases; the compound can invade respiratory tract, digestive tract and skin mucosa of human body in the form of dust, and can distribute organs of the whole body under severe conditions, with the highest kidney content. For high permeability of mercury, the mercury content in the gas, water and solid waste generated and discharged by oil and gas fields is limited to the highest content allowed by the state.

In the process of exploitation, production, treatment, transportation and the like of oil and gas fields, a large amount of mercury-containing wastewater is generated, such as: oil-water separator devices, three-phase separator devices, filters, etc. in oil-gas treatment plants all produceA large amount of mercury-containing wastewater. The mercury-containing wastewater of the oil and gas field may contain elemental mercury (Hg)⁰) Mercury-containing suspension (HgS), mercury ions (Hg)²⁺) And a small amount of organic mercury.

At present, relatively more researches are carried out on oil-containing sewage treatment systems of oil and gas fields, the treatment process of the oil and gas field sewage at home and abroad is developed to a certain extent, and various relatively mature treatment methods are researched, such as: hydrocyclone, flocculation, air flotation, electroflocculation, biological, membrane separation, etc. However, the research on the mercury-containing gas field sewage treatment technology and the application thereof is not many, especially in China, the research on the mercury-containing gas field sewage treatment technology is still in the beginning stage, and the commonly adopted treatment technology is a chemical precipitation method, including sulfide precipitation demercuration and coagulating precipitation demercuration. The treatment of foreign mercury-containing sewage generally adopts precipitation method, sedimentation/flocculation method, adsorption method and ion exchange method. The adsorption method and the ion exchange method are suitable for treating low-mercury-containing sewage, and foreign manufacturers also successively develop novel high-efficiency multifunctional composite flocculating agents and adsorbents. The membrane filtration process is in the experimental stage and has not been applied industrially on a large scale. Therefore, in summary, a new process for treating mercury-containing wastewater in oil and gas fields, which is stable and efficient, is urgently needed in China.

Disclosure of Invention

The invention aims to provide a novel process for treating mercury-containing wastewater of an oil and gas field, which is mainly used for treating mercury-containing wastewater generated in the processes of exploitation, production, treatment, transportation and the like of the oil and gas field.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a new process for treating mercury-containing wastewater of oil and gas fields comprises the following specific process flows:

(1) collecting mercury-containing wastewater of an oil-gas field into a wastewater collection tank, allowing the wastewater to enter a gravity settling tank, adding a demulsifier for treatment, removing sludge with larger particle size in the wastewater, and allowing the sludge to enter a sludge concentration tank;

(2) the wastewater after primary treatment enters a coagulation and flocculation device, solid particles and partial grease are coagulated into large molecular groups by adding a coagulant and a flocculant, and the wastewater in the coagulation and flocculation device is lifted to a primary air flotation device by a lift pump;

(3) the wastewater treated by the primary air floatation device enters a pH adjusting tank through an overflow pipe to carry out pH adjustment and sulfide precipitation, wherein the pH is adjusted to be 8-9, sulfide, coagulant and flocculant are added into the pH adjusting tank, and the addition amount of the sulfide is 50 wt% more than the theoretical calculation amount;

(4) the wastewater treated by the pH adjusting tank is lifted to a secondary air flotation device by a pump, the secondary air flotation device adopts a reversible fiber ball filter, and the quality of the effluent, namely oil and SS, reaches the discharge standard; conveying the sludge in the secondary air flotation device to a sludge concentration tank through a pipeline;

(5) the wastewater overflowing after being treated by the secondary air flotation device reaches an external discharge standard after being absorbed by a mercury absorption device, wherein Hg is less than or equal to 0.05 mg/L, COD is less than 100 mg/L, ammonia nitrogen is less than 15 mg/L, SS is less than or equal to 70 mg/L, oil content is less than or equal to 5 mg/L, and pH is 6.0-9.0, and the wastewater flows into an external discharge water tank to be discharged for water purification;

(6) sludge generated in the treatment process is stored in a sludge concentration tank, the sludge is lifted to a plate-and-frame filter press through a sludge screw pump to realize the separation of solid and liquid, liquid-phase filter pressing water generated by a solid-liquid separator returns to a sewage collecting tank, and the dewatered sludge cake is transported outwards.

In the new process for treating the mercury-containing wastewater in the oil and gas field, in the step (1), the sludge with larger particle size is suspended matters, floaters or partial grease.

In the step (2), a primary air floating device adopts a mode of integrally combining a horizontal flow type air floating tank, an inclined plate type air floating tank and a filter, flocculating constituents in the horizontal flow type air floating tank and the inclined plate type air floating tank are fully mixed and contacted with bubbles released by a micro-bubble releaser, so that micro bubbles in water are adhered to the flocculating constituents, the flocculating constituents form floating slag to float to the water surface, the floating slag is scraped into an air floating mud tank by a slag scraper after being gathered, and the floating slag is conveyed to a sludge concentration tank through a pipeline; after the filter filters the wastewater, part of clear water at the lower layer of the primary air floating device is pumped by the dissolved air pump to be used by the dissolved air water, and 90 wt% of suspended matters, 40-50 wt% of grease, part of simple substance mercury and organic mercury can be removed by the primary air floating device.

The new process for treating the mercury-containing wastewater of the oil and gas field comprises the step (3) of adding excessive S into the wastewater^2-When the ion is generated, ferrous sulfate is supplemented, and excessive S is added^2-The ions form iron sulfide precipitates.

The novel process for treating the mercury-containing wastewater in the oil and gas field comprises the step (4) of adopting Thiol-SAMMS as an adsorbent.

The design principle of the invention is as follows:

the invention adopts a treatment process combining chemical precipitation and flocculation adsorption, and relates to a gravity settling tank, a coagulation flocculation device, a primary air floatation device, a pH adjusting tank, a secondary air floatation device, a Thiol-SAMMS mercury adsorption device and the like. The mercury in the wastewater is mainly removed through an air floatation device and a mercury adsorption device, and finally reaches the discharge standard. Firstly, the wastewater is treated by a gravity settling tank and a coagulation flocculation device to remove impurities such as suspended matters, floating matters, partial grease and the like in the wastewater. Then, after the chemical addition reaction, the mixture enters a primary air flotation device to remove suspended matters, grease and partial elemental mercury; and the residual wastewater enters a pH adjusting tank through an overflow pipe, the pH is adjusted to 8-9 (alkaline), sulfide is added at the same time, then the wastewater in the pH adjusting tank is lifted to a secondary air flotation device through a pump, and the overflow wastewater reaches the national first-level emission standard after being adsorbed by a mercury adsorption device.

The invention has the advantages and beneficial effects that:

1. compared with the original chemical precipitation method, sedimentation/flocculation method, adsorption method and ion exchange method, the invention provides a novel process for treating mercury-containing wastewater in an oil-gas field, which has reasonable process, high treatment efficiency and good reliability, and can treat pollutants which can not be removed by the traditional process.

2. The invention can treat the mercury-containing wastewater of high-concentration oil-gas fields, adopts the combined treatment process of chemical precipitation and flocculation adsorption, does not produce waste residue and waste gas in the treatment process, does not bring secondary pollution, and the discharged water can reach the national first-level emission standard requirement.

Drawings

FIG. 1 is a flow chart of the process for treating the mercury-containing wastewater of the oil and gas field.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments, but is not limited thereto.

Example (b):

the mercury-containing wastewater indexes of a certain western oil-gas field are as follows (table 1):

TABLE 1

Contamination factor	Hg	SS	Oil content	pH
					Numerical value	600～7500μg/L	200～500mg/L	100～1000mg/L	6.0～9.0

As shown in figure 1, after the novel treatment process is adopted, the waste water is discharged after reaching the national first-level emission standard, and the specific process flow is as follows:

(1) the mercury-containing wastewater in the oil-gas field is collected into a wastewater collection tank, enters a gravity settling tank, is treated by adding a commonly-used demulsifier, and then is treated to remove sludge (suspended matters, floaters, partial grease and other impurities) with larger particle size in the wastewater, and the sludge enters a sludge concentration tank.

(2) The wastewater after primary treatment enters a coagulation and flocculation device, solid particles and partial grease are coagulated into large molecular groups by adding drugs (common coagulant and flocculant), and the wastewater in the coagulation and flocculation device is lifted to a primary air flotation device by a lifting pump.

The primary air flotation device adopts a mode of integrally combining an advection type air flotation tank, an inclined plate type air flotation tank and a filter, flocculants in the advection type air flotation tank and the inclined plate type air flotation tank are fully mixed and contacted with bubbles released by a micro-bubble releaser, micro-bubbles in water are adhered to the flocculants, the flocculants form floating slag and float to the water surface, and the floating slag is scraped into an air flotation mud tank by a slag scraper after being gathered to a certain thickness and is conveyed to a sludge concentration tank through a pipeline; after the filter filters the wastewater, part of clear water at the lower layer of the primary air floating device is pumped by the dissolved air pump to be used by the dissolved air water, and 90 wt% of suspended matters, 40-50 wt% of grease, part of simple substance mercury and organic mercury can be removed by the primary air floating device.

(3) The wastewater treated by the primary air floatation device enters a pH adjusting tank through an overflow pipe to carry out pH adjustment and sulfide precipitation, the pH is adjusted to be 8-9 (alkaline), chemicals (commonly used sulfide, coagulant and flocculant) are added into the pH adjusting tank, the addition amount of the sulfide is 50 wt% more than the theoretical calculation amount, and the chemical principle is that ① Hg is used as a chemical principle²⁺+S^2-＝HgS↓；②2Hg⁺+S^2-＝Hg₂S；

The solubility product of sulfide generated by the reaction is very small, such as: k of HgS_sp＝4×10^-53，Hg₂K of S_sp＝1.0×10^-45。

If there is an excess of S in the wastewater^2-When the ion is generated, ferrous sulfate (FeSO) can be supplemented₄) With an excess of S^2-The ions form iron sulfide precipitates. The chemical principle is as follows: FeSO₄+S^2-＝FeS↓+SO₄ ^2-；

FeSO is added₄After that, precipitation of HgS was not affected. Because the solubility product of HgS is greater than that of FeS (K)_sp＝3.7×10^-19) By 34 orders of magnitude, HgS preferentially forms a precipitate.

(4) And the wastewater treated by the pH adjusting tank is lifted to a secondary air flotation device by a pump, and the secondary air flotation device adopts a mode of integrally combining a horizontal flow type air flotation tank, an inclined plate type air flotation tank and a reversible fiber ball filter to detect that the quality of the effluent, namely oil and SS (suspended solid) reaches the discharge standard. And conveying the sludge in the secondary air flotation device to a sludge concentration tank through a pipeline.

(5) The wastewater overflowing after being treated by the secondary air flotation device reaches an external discharge standard after being adsorbed by a mercury adsorption device (taking Thiol-SAMMS as an adsorbent), wherein Hg is less than or equal to 0.05 mg/L, COD is less than 100 mg/L, ammonia nitrogen is less than 15 mg/L, SS is less than or equal to 70 mg/L, oil content is less than or equal to 5 mg/L, and pH is 6.0-9.0, and the wastewater flows into an external discharge water tank to be discharged for water purification.

(6) Sludge generated in the treatment process is stored in a sludge concentration tank, the sludge is lifted to a plate-and-frame filter press through a sludge screw pump to realize the separation of solid and liquid, liquid-phase filter pressing water generated by a solid-liquid separator returns to a sewage collecting tank, and the dewatered sludge cake is transported outwards.

The results of the examples show that the process of the invention is reasonable, the treatment efficiency is high, the reliability is good, and the invention can treat the pollutants which can not be removed by the traditional process, and is mainly used for treating the mercury-containing wastewater generated in the production process of oil and gas fields.

Claims (1)

1. A novel process for treating mercury-containing wastewater of oil and gas fields is characterized by comprising the following specific process flows:

(1) collecting mercury-containing wastewater of an oil-gas field into a wastewater collection tank, allowing the wastewater to enter a gravity settling tank, adding a demulsifier for treatment, removing sludge with larger particle size in the wastewater, wherein the sludge with larger particle size is suspended matters, floaters or partial grease, and allowing the sludge to enter a sludge concentration tank;

(2) the wastewater after primary treatment enters a coagulation and flocculation device, solid particles and partial grease are coagulated into large molecular groups by adding a coagulant and a flocculant, and the wastewater in the coagulation and flocculation device is lifted to a primary air flotation device by a lift pump;

in the step (2), the primary air flotation device adopts a mode of integrally combining a horizontal flow type air flotation tank, an inclined plate type air flotation tank and a filter, flocculants in the horizontal flow type air flotation tank and the inclined plate type air flotation tank are fully mixed and contacted with bubbles released by a micro-bubble releaser, so that micro bubbles in water are adhered to the flocculants, scum is formed by the flocculants and floats to the water surface, and after the scum is gathered, the scum is scraped into an air flotation mud tank by a scum scraper and then is conveyed to a sludge concentration tank through a pipeline; after the filter filters the wastewater, part of clear water at the lower layer of the primary air floating device is pumped by a dissolved air pump to be used by dissolved air water, and the primary air floating device can remove 90 wt% of suspended matters, 40-50 wt% of grease, part of simple substance mercury and organic mercury;

(3) the wastewater treated by the primary air floatation device enters a pH adjusting tank through an overflow pipe for pH adjustment and sulfide precipitation, wherein the pH is adjusted to be 8-9, sulfide, coagulant and flocculant are added into the pH adjusting tank, the addition amount of the sulfide is 50 wt% more than the theoretical calculation amount, and the chemical principle is ① Hg²⁺+S^2-＝HgS↓；②2Hg⁺+S^2-＝Hg₂S；

The solubility product of sulfide generated by the reaction is very small, and the K of HgS_sp＝4×10^-53，Hg₂K of S_sp＝1.0×10^-45；

If there is an excess of S in the wastewater^2-When the ion is generated, ferrous sulfate is supplemented, and excessive S is added^2-Generating iron sulfide precipitate by ions; the chemical principle is as follows: FeSO₄+S^2-＝FeS↓+SO₄ ^2-；

FeSO is added₄Then, the precipitation of HgS is not affected; because the solubility product of HgS is greater than the solubility product K of FeS_sp＝3.7×10^-19By 34 orders of magnitude, HgS preferentially forms precipitates;

(4) the wastewater treated by the pH adjusting tank is lifted to a secondary air flotation device by a pump, the secondary air flotation device adopts a reversible fiber ball filter, and the quality of the effluent, namely oil and SS, reaches the discharge standard; conveying the sludge in the secondary air flotation device to a sludge concentration tank through a pipeline;

(5) the wastewater overflowing after being treated by the secondary air flotation device adopts Thiol-SAMMS as an adsorbent, and reaches an external discharge standard after being adsorbed by a mercury adsorption device, wherein Hg is less than or equal to 0.05 mg/L, COD is less than 100 mg/L, ammonia nitrogen is less than 15 mg/L, SS is less than or equal to 70 mg/L, oil content is less than or equal to 5 mg/L, and pH is 6.0-9.0, and the wastewater flows into an external discharge water tank to be discharged and purified;

(6) sludge generated in the treatment process is stored in a sludge concentration tank, the sludge is lifted to a plate-and-frame filter press through a sludge screw pump to realize the separation of solid and liquid, liquid-phase filter pressing water generated by a solid-liquid separator returns to a sewage collecting tank, and the dewatered sludge cake is transported outwards.

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