CN106915841A - A kind of oil gas field mercury-containing waste water New Process for Treatment - Google Patents

Abstract

The present invention relates to a kind of oil gas field mercury-containing waste water New Process for Treatment, belong to improvement waste water technology field.First, waste water is through impurity such as suspension, floating object, the amount of grease in gravity settler and coagulation-flocculation device removal waste water.Then, an air-floating apparatus are entered after being reacted through dosing, oil removal, grease and part Elemental Mercury is removed；Remaining waste water enters pH and adjusts tank by overflow pipe, regulation pH to 8~9 (in alkalescence), sulfide is added simultaneously, and the waste water then adjusted pH in tank is promoted to secondary air floatation device through pump, and effluent reaches national grade one discharge standard after being adsorbed through mercury adsorbent equipment.Rational technology of the invention, treatment effeciency are high, good reliability, and can process the traditional handicraft pollutant to be removed, and the mercury-containing waste water produced during exploitation, production, treatment and transport etc. mainly for oil gas field is processed.

Description

A new process for the treatment of mercury-containing wastewater from oil and gas fields

technical field

The invention relates to a new process for treating mercury-containing wastewater in oil and gas fields, and belongs to the technical field of wastewater treatment.

Background technique

Mercury (Hg), commonly known as mercury, is the only metal that exists in a liquid state at normal temperature and pressure. It is chemically stable and insoluble in acids and alkalis. However, mercury can evaporate at room temperature, and mercury vapor and mercury compounds are highly toxic. Mercury and its compounds can enter the human body through the respiratory tract, digestive tract, and skin, and mainly harm the human nervous system. Due to the slow discharge of mercury, it can be enriched in the body, and long-term intake will cause mercury poisoning. Among them, metallic mercury is mainly absorbed through the respiratory tract in the form of vapor. Mercury vapor can also pass through the blood-brain barrier, causing damage to the nervous system, digestive system and kidneys. In severe cases, it can cause mercury poisoning encephalopathy and even death; its compounds invade Human respiratory tract, digestive tract, skin and mucous membranes, and in severe cases, it can be distributed in various organs of the whole body, with the highest content in the kidney. For the high permeability of mercury, the mercury content in the gas, water and solid waste produced and discharged from oil and gas fields should be limited to the maximum content allowed by the country before it can be discharged.

A large amount of mercury-containing wastewater will be generated in the process of exploitation, production, treatment and transportation of oil and gas fields, such as: oil-water separator devices, three-phase separator devices and filters in oil and gas treatment plants will generate a large amount of mercury-containing wastewater . Mercury-containing wastewater from oil and gas fields may contain elemental mercury (Hg ⁰ ), mercury-containing suspended solids (HgS), mercury ions (Hg ²⁺ ) and a small amount of organic mercury.

At present, there are relatively many studies on the treatment system of oily sewage in oil and gas fields. The treatment process of oil and gas field sewage has been developed to a certain extent at home and abroad, and a variety of relatively mature treatment methods have been studied, such as hydrocyclone, flocculation, gas Float method, electrocoagulation method, biological method, membrane separation method, etc. However, there are not many research results on mercury-containing gas field sewage treatment technology and its application. Especially in China, the research on mercury-containing oil and gas field sewage treatment technology is still in its infancy. The commonly used treatment technology is chemical precipitation, including sulfide Mercury removal by precipitation and mercury removal by coagulation precipitation. The treatment of mercury-containing sewage in foreign countries generally adopts precipitation method, sedimentation/flocculation method, adsorption method and ion exchange method. Adsorption and ion exchange methods are suitable for treating low-mercury sewage, and foreign manufacturers have successively developed some new high-efficiency multifunctional composite flocculants and adsorbents. Membrane filtration is in the experimental stage and has no large-scale industrial application. Therefore, in summary, there is an urgent need for a stable and efficient new process for the treatment of mercury-containing wastewater from oil and gas fields in China.

Contents of the invention

The purpose of the present invention is to provide a new process for the treatment of mercury-containing wastewater in oil and gas fields, which is mainly aimed at treating the mercury-containing wastewater produced in the process of mining, production, treatment and transportation in oil and gas fields.

In order to achieve the above object, technical scheme of the present invention is:

A new process for treating mercury-containing wastewater in oil and gas fields, the specific process flow is:

(1) Mercury-containing wastewater from oil and gas fields is collected into the sewage collection tank, enters the gravity settling tank, and is treated by adding a demulsifier to remove the sludge with a larger particle size in the wastewater, and the sludge enters the sludge thickening tank;

(2) The wastewater after primary treatment enters the coagulation and flocculation device, and the solid particles and some oils are condensed into large molecular groups by adding coagulant and flocculant, and the wastewater in the coagulation and flocculation device is lifted to the primary air by the lift pump floating device;

(3) The wastewater treated by the primary air flotation device enters the pH adjustment tank through the overflow pipe for pH adjustment and sulfide precipitation, and adjusts pH=8 to 9. Add sulfide, coagulant, and flocculant to the pH adjustment tank , the added amount of sulfide is 50wt% more than the theoretically calculated amount;

(4) The wastewater treated by the pH adjustment tank is lifted to the secondary air flotation device by the pump. The secondary air flotation device adopts a reversible fiber ball filter, and the water quality oil and SS are detected to meet the discharge standard; the secondary air flotation device Sludge is transported to the sludge thickening tank through pipelines;

(5) The overflow wastewater after being treated by the secondary air flotation device reaches the discharge standard after being adsorbed by the mercury adsorption device, in which Hg≤0.05mg/L, COD<100mg/L, ammonia nitrogen<15mg/L, SS≤70mg /L, oil content ≤ 5mg/L, pH = 6.0-9.0, flow into the external drainage tank for external discharge of purified water; the sludge in the mercury adsorption device is transported to the sludge concentration tank through pipelines;

(6) The sludge generated during the treatment process is stored in the sludge thickening tank. The sludge is lifted to the plate and frame filter press by the sludge screw pump to separate the solid from the liquid. The liquid phase filter water produced by the solid-liquid separator Back to the sewage collection tank, the dehydrated mud cake is transported outside.

In the new process for treating mercury-containing wastewater from oil and gas fields, in step (1), the sludge with larger particle size is suspended solids, floating solids or part of grease.

In the new process for the treatment of mercury-containing wastewater from oil and gas fields, in step (2), the primary air flotation device adopts the combination of advection air flotation tank, inclined plate air flotation tank and filter integration. The flocs in the floating tank are fully mixed and contacted with the air bubbles released by the micro-bubble releaser, so that the tiny air bubbles in the water adhere to the flocs, and the flocs form scum and float to the water surface. After the scum gathers, it is scraped by the scum scraper. Enter the air flotation mud tank, and then transport it to the sludge thickening tank through the pipeline; after the filter filters the waste water, part of the clear water in the lower layer of the primary air flotation device is pumped by the dissolved air pump for the use of dissolved air water, and the primary air flotation device can remove 90wt% Suspended solids, 40-50wt% oil and some elemental mercury, organic mercury.

In the new process for treating mercury-containing wastewater from oil and gas fields, in step (3), when excess S ^2- ions are present in the wastewater, ferrous sulfate is added to form iron sulfide precipitates with excess S ^2- ions.

In the new process for treating mercury-containing wastewater from oil and gas fields, in step (4), Thiol-SAMMS is used as the adsorbent.

Design principle of the present invention is:

The present invention adopts the combined treatment process of chemical precipitation + flocculation and adsorption, which involves gravity settling tank, coagulation and flocculation device, primary air flotation device, pH adjustment tank, secondary air flotation device, Thiol-SAMMS mercury adsorption device, etc. Mercury in wastewater is mainly removed through air flotation devices and mercury adsorption devices, and finally meets the discharge standard. First, the wastewater goes through a gravity settling tank and a coagulation and flocculation device to remove impurities such as suspended solids, floating solids, and some oils in the wastewater. Then, after the dosing reaction, it enters an air flotation device to remove suspended solids, grease and some elemental mercury; the remaining waste water enters the pH adjustment tank through the overflow pipe, and adjusts the pH to 8-9 (alkaline), and at the same time adds sulfur Then the wastewater in the pH adjustment tank is pumped to the secondary air flotation device, and the overflow wastewater is absorbed by the mercury adsorption device to meet the national first-level discharge standard.

Advantage of the present invention and beneficial effect are:

1. Compared with the original chemical precipitation method, sedimentation/flocculation method, adsorption method, and ion exchange method, the present invention provides a new process for the treatment of mercury-containing wastewater in oil and gas fields with reasonable process, high treatment efficiency and good reliability, and It can handle pollutants that cannot be removed by traditional processes.

2. The present invention can treat high-concentration mercury-containing wastewater from oil and gas fields, and adopts a combined treatment process of chemical precipitation + flocculation adsorption. The treatment process does not produce waste residue, waste gas, and does not cause secondary pollution. The external drainage can reach the national first-level discharge standard Require.

Description of drawings

Fig. 1 is the process flow chart of the present invention for the treatment of mercury-containing wastewater in oil and gas fields.

detailed description

The following is further described in conjunction with the accompanying drawings and specific embodiments, but does not limit the present invention.

Example:

The indicators of mercury-containing wastewater in an oil and gas field in the west are as follows (Table 1):

Table 1

pollution factor Hg SS oil content pH value 600～7500μg/L 200～500mg/L 100～1000mg/L 6.0～9.0

As shown in Figure 1, after adopting the new processing technology of the present invention to handle, discharge out after reaching the national first-class discharge standard, its specific technological process is:

(1) Mercury-containing wastewater from oil and gas fields is collected into sewage collection tanks, enters gravity settling tanks, and is treated by adding chemicals (commonly used demulsifiers) to remove sludge with larger particle sizes (suspended solids, floating solids, and some grease) in wastewater and other impurities), the sludge enters the sludge thickening tank.

(2) The wastewater after primary treatment enters the coagulation and flocculation device, and the solid particles and some oils are condensed into large molecular groups by adding drugs (commonly used coagulants and flocculants), and the wastewater in the coagulation and flocculation device is lifted The pump lifts to the primary air flotation unit.

The primary air flotation device adopts the combination of advection air flotation tank, inclined plate air flotation tank and filter integration. The flocs in the advection air flotation tank and inclined plate air flotation tank are fully mixed with the bubbles released by the microbubble releaser. , so that the tiny air bubbles in the water adhere to the flocs, so that the flocs form scum and float to the water surface. After the scum gathers to a certain thickness, it is scraped into the air flotation mud tank by the scum scraper, and then transported to the sludge through the pipeline Concentration tank; after the waste water is filtered by the filter, part of the clear water in the lower layer of the primary air flotation device is pumped by the dissolved air pump for the use of dissolved air water. The primary air flotation device can remove 90wt% of suspended solids, 40-50wt% of grease and part of elemental mercury , Organic mercury.

(3) The wastewater treated by the primary air flotation device enters the pH adjustment tank through the overflow pipe, and performs pH adjustment and sulfide precipitation, adjusts pH = 8 to 9 (alkaline), and adds medicine (commonly used) in the pH adjustment tank. sulfide, coagulant, flocculant), the amount of sulfide added is 50wt% more than the theoretically calculated amount, the chemical principle: ①Hg ²⁺ +S ^2- ＝HgS↓; ②2Hg ⁺ +S ^2- ＝Hg ₂ S;

The solubility product of the sulfide produced by the reaction is very small, such as: K _sp of HgS = 4×10 ^-53 , K _sp of Hg ₂ S = 1.0×10 ^-45 .

If there are excessive S ^2- ions in the wastewater, ferrous sulfate (FeSO ₄ ) can be added to form iron sulfide precipitation with excess S ^2- ions. Chemical principle: FeSO ₄ +S ^2- ＝FeS↓+SO ₄ ^2- ;

After adding FeSO ₄ , it will not affect the precipitation of HgS. Since the solubility product of HgS is 34 orders of magnitude smaller than that of FeS (K _sp =3.7×10 ⁻¹⁹ ), HgS will preferentially form precipitates.

(4) The wastewater treated by the pH adjustment tank is pumped to the secondary air flotation device. The secondary air flotation device adopts the combination of flat flow air flotation tank, inclined plate air flotation tank and reversible fiber ball filter. The effluent quality oil and SS meet the emission standards. The sludge in the secondary air flotation device is transported to the sludge thickening tank through pipelines.

(5) After being treated by the secondary air flotation device, the overflowing wastewater is adsorbed by the mercury adsorption device (using Thiol-SAMMS as the adsorbent) and reaches the discharge standard, in which Hg≤0.05mg/L, COD<100mg/L, ammonia nitrogen <15mg/L, SS≤70mg/L, oil content≤5mg/L, pH=6.0~9.0, flow into the external drainage tank for external discharge of purified water. The sludge in the mercury adsorption device is transported to the sludge thickening tank through pipelines.

(6) The sludge generated during the treatment process is stored in the sludge thickening tank. The sludge is lifted to the plate and frame filter press by the sludge screw pump to separate the solid from the liquid. The liquid phase filter water produced by the solid-liquid separator Back to the sewage collection tank, the dehydrated mud cake is transported outside.

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

Claims (5)

1. A new process for the treatment of mercury-containing wastewater from oil and gas fields, characterized in that the concrete process flow is: (1) Mercury-containing wastewater from oil and gas fields is collected into the sewage collection tank, enters the gravity settling tank, and is treated by adding a demulsifier to remove the sludge with a larger particle size in the wastewater, and the sludge enters the sludge thickening tank; (2) The wastewater after primary treatment enters the coagulation and flocculation device, and the solid particles and some oils are condensed into large molecular groups by adding coagulant and flocculant, and the wastewater in the coagulation and flocculation device is lifted to the primary air by the lift pump floating device; (3) The wastewater treated by the primary air flotation device enters the pH adjustment tank through the overflow pipe for pH adjustment and sulfide precipitation, and adjusts pH=8 to 9. Add sulfide, coagulant, and flocculant to the pH adjustment tank , the added amount of sulfide is 50wt% more than the theoretically calculated amount; (4) The wastewater treated by the pH adjustment tank is lifted to the secondary air flotation device by the pump. The secondary air flotation device adopts a reversible fiber ball filter, and the water quality oil and SS are detected to meet the discharge standard; the secondary air flotation device Sludge is transported to the sludge thickening tank through pipelines; (5) The overflow wastewater after being treated by the secondary air flotation device reaches the discharge standard after being adsorbed by the mercury adsorption device, in which Hg≤0.05mg/L, COD<100mg/L, ammonia nitrogen<15mg/L, SS≤70mg /L, oil content ≤ 5mg/L, pH = 6.0-9.0, flow into the external drainage tank for external discharge of purified water; the sludge in the mercury adsorption device is transported to the sludge concentration tank through pipelines; (6) The sludge generated during the treatment process is stored in the sludge thickening tank. The sludge is lifted to the plate and frame filter press by the sludge screw pump to separate the solid from the liquid. The liquid phase filter water produced by the solid-liquid separator Back to the sewage collection tank, the dehydrated mud cake is transported outside. 2. The new process for treating mercury-containing wastewater from oil and gas fields according to claim 1, characterized in that, in step (1), the sludge with larger particle size is suspended matter, floating matter or part of grease. 3. According to the new process for treating mercury-containing wastewater in oil and gas fields according to claim 1, it is characterized in that, in step (2), the primary air flotation device adopts the combination of flat-flow air flotation tank, inclined plate type air flotation tank, and filter integration , the flocs in the flat-flow air flotation tank and inclined plate air flotation tank are fully mixed and contacted with the air bubbles released by the micro-bubble releaser, so that the tiny air bubbles in the water adhere to the flocs, and the flocs form scum and float to the water surface. After the scum gathers, it is scraped into the air flotation mud tank by the scum scraper, and then transported to the sludge concentration tank through the pipeline; after the filter is used to filter the waste water, part of the clear water in the lower layer of the primary air flotation device is pumped by the dissolved air pump to supply the dissolved air water When used, the primary air flotation device can remove 90wt% of suspended solids, 40-50wt% of grease and part of elemental mercury and organic mercury. 4. according to claim 1 described oil and gas field mercury-containing waste water treatment new technology, it is characterized in that, in step (3), in waste water, when there is excessive S ^2- ion, add ferrous sulfate, and excessive S ^2- ions to form iron sulfide precipitates. 5. According to the new process for treating mercury-containing wastewater in oil and gas fields according to claim 1, it is characterized in that, in step (4), Thiol-SAMMS is used as adsorbent.