Analysis of Oilfield Wastewater Treatment Technology

With the acceleration of oilfield development, oilfield wastewater is increasing, which seriously pollutes the ecological environment. The oilfield wastewater is complex in water quality and contains environmental pollutants such as petroleum demulsifier, salt, phenol and sulfur. Briefly describe the source and composition of high-concentration alkali slag wastewater in the petrochemical industry, the selection of high-concentration alkali slag wastewater treatment process and process flow, and focus on the engineering design examples and the process characteristics and application in the design and transformation process for the majority of peers. Learn from and reference. Oilfield wastewater mainly includes oilfield produced water, drilling wastewater and other types of oily sewage in the station. The treatment of oilfield wastewater can be carried out in various ways depending on factors such as oilfield production and environment. When the oilfield needs water injection, the oilfield sewage will be reinjected into the formation after treatment. At this time, a number of indicators such as suspended solids and oil in the water should be strictly controlled to prevent damage to the formation. Most of the oil production units are concentrated in arid areas, and water resources are seriously lacking. How to turn waste water generated in the oil production process into treasure is of great practical significance. 1 Oilfield wastewater treatment technology The water treatment process of oilfields generally has the following processes: “oil-filtering” and “oil-floating-flotation (or cyclone degreasing)-filtration”, commonly known as “old” Three sets, the process is mainly to remove oil and suspended solids from wastewater. For a long time, this process has been widely used in the treatment of produced water in various oil fields, and the effect is good. The treated water quality can generally meet the requirements of refilling water.

1.1 Technical Classification

According to the different treatment levels and water quality requirements of oilfields, sewage treatment technology is usually divided into primary treatment, secondary treatment and tertiary treatment. Generally, the primary treatment is a pretreatment, and the secondary treatment can remove about 90% of the solid suspended matter of the degradable organic matter by 90% to 95%. However, for heavy metals and toxic organic carbon compounds difficult to degrade biologically and nitrogen appear biochemical process, difficult to completely remove the phosphorus, tertiary treatment remains to be done. The treatment technologies at various levels mainly include gravity separation, coarse granulation, flotation, filtration, membrane separation and biological methods. The primary and secondary treatments mainly use the over-consideration, sedimentation and flotation methods to remove suspended solids from the sewage. Remove minerals from the wastewater and most of the solid suspended solids, oils, etc. The main methods include gravity separation, centrifugation, filtration, coarse granulation, neutralization, biological treatment and the like. These technologies are relatively mature at home and abroad.

1.2 General Process of Oilfield Wastewater Treatment

The composition of oilfield wastewater is complex, the oil content and the form of oil in water are different, and in most cases, it is often mixed with other wastewaters. Therefore, single treatment is often ineffective. At the same time, due to various limitations of the force method, in practical applications, two or three methods are usually used in combination to make the effluent water quality meet the discharge standard. In addition, the production methods, environmental requirements and the use of treated water in different oil fields make the oilfield wastewater treatment process different. In these processes, common primary treatments include gravity separation, flotation and centrifugal separation. Mainly remove oil and oil wet solids; secondary treatment has filtration, coarse granulation, chemical treatment, etc., mainly demulsification and removal. Dispersed oil; advanced treatment with ultrafiltration, activated carbon adsorption, biochemical treatment, etc., mainly to remove dissolved oil.

1.3 Membrane Bioreactor Process

Membrane bioreactor is a new water treatment technology that combines membrane separation unit and biological treatment unit. The membrane module replaces the secondary sedimentation tank to maintain high activated sludge concentration in the bioreactor to reduce the occupation of sewage treatment facilities. Reduce the amount of sludge by keeping the sludge load low. Compared with traditional biochemical water treatment technology, MBR has the following main features: high processing efficiency, good effluent quality; compact equipment, small footprint; easy to achieve automatic control, simple operation and management. Since the 1980s, this technology has received more and more attention and has become one of the research hotspots. At present, membrane bioreactors have been used in more than ten countries such as the United States, Germany, France and Egypt, ranging in size from 6m3/d to 13000m3/d. In China, membrane bioreactors are a high-tech of wastewater recycling, and their development and research are getting deeper and deeper. Although the practical application of membrane bioreactors in China is still rare, however, in the case of increasingly scarce water resources, with the development of membrane technology, the development of new membrane materials and the gradual decline of membrane material costs, membrane bioreactors There will be better application prospects.

2 Analysis of sewage treatment technology

At present, the alkali slag wastewater treatment methods in the petrochemical industry mainly include direct treatment, chemical treatment and biological oxidation.

Direct treatment methods include sale, dilution, deep well injection, and incineration. Among them, incineration is the main method. Direct treatment is prone to pollution transfer (atmosphere) or transfer (other places), so it is subject to certain restrictions.

The chemical treatment method usually adopts the wet air oxidation technology, that is, under the condition of 150~200 ° C and 1.5-10 MPa, the direct oxidation of oxygen to remove the sulfide in the alkali residue to achieve the purpose of pretreatment of the alkali residue. The treatment effect of alkali slag is subject to the temperature and pressure of the oxidation reaction system. The higher the pollutant removal efficiency, the higher the temperature and pressure required by the corresponding system. The high equipment investment quota and operating cost of the WAO method limit its application. . Incineration and wet catalytic oxidation are processing technologies that are very expensive to invest and operate. In contrast, the use of biochemical technology for processing, its investment, operating costs are only a fraction of a wet catalytic, incineration method or a few tens of ones, simple operation and management, stable treatment.

The biological oxidation method is to first moderately dilute the alkali residue (10 to 20 times) and control the sulfide to be 1000 to 3000 mg. L-1, and after neutralization, using a special bioreactor, the sulfur bacteria form a biological oxidation bed in the bioreactor, and the action of the organism utilizes the oxygen in the air to oxidize the sulfide and the phenol, thereby achieving the alkali residue pretreatment. purpose. The biological oxidation method has better technical and economic value, and the internal circulation fixed biological oxidation bed technology, that is, the IRBAF treatment process, is for the waste alkali residue (gasoline, diesel, liquid hydrocarbon, etc.) generated in the petroleum refining and petrochemical product refining process. The development of alkali slag has greatly reduced the influent load of the sewage treatment plant, and can effectively oxidize and treat high-concentration wastewater such as catalytic gasoline waste lye and liquid hydrocarbon waste lye, ensuring the normal operation and compliance of existing sewage treatment systems. .

3 IRBAF treatment process introduction

Enternal Recurrence Fixed Biological Bed (IRBAF) is a high-activity biological enzyme catalytic oxidation bed that promotes the oxidation of pollutants in water by using a special process environment of special microorganisms under normal temperature and normal pressure conditions. . When the BAF reaction tank is operated for a certain period of time, a large amount of biomass will be produced in the packing. When the biomass bed is added too much, the operation of the water inside the packing will be affected, and the treatment efficiency will be reduced. Excess biomass in the biological bed is removed. The backwashing of the BAF can be done by a backflushing or semi-automatic system. The backwash cycle is determined by the influent COD load. The higher the COD load, the shorter the backwash cycle. Conversely, the longer the backwash cycle of the BAF. The backwashing adopts a new pulse gas-water combined backwashing technology, the backwashing wind adopts the non-purifying wind of the refinery, the backwashing water adopts the secondary internal circulating BAF purification water, and the flushed high-concentration muddy water mixture flows into the muddy water separation tank. After separation by precipitation, the supernatant is recycled. The process has less mud production and can be retained in the mud water separation tank, and is discharged into the existing sludge treatment system of the purification water plant from time to time. Characteristics of IRBAF process: (1) High-quality filler: The biological bed adopts clay ceramsite, which has large specific surface area and total pore volume, high mechanical abrasion resistance, rough surface and strong chemical stability. (2) Isolated aeration technology: using the unique isolation aeration technology to oxygenate the reactor, lift the sewage along the aeration pipeline, and then pass through the reactor biological bed to form a cycle, avoiding the traditional aeration. The method is to wash the filter material, and at the same time, the reactor water body is in an internal circulation state, and can be cycled 10 to 20 times per hour, which increases the water flow speed in the filter material, enhances the exchange of the medium between the sewage and the living body, and improves the reactor. The treatment efficiency has the characteristics of a fully mixed reactor, which improves the reactor's ability to withstand toxic substances and impact resistance. The isolated aeration technology changes the volume utilization rate of the traditional aeration method and is easy to form a short circuit of water flow. Increases the volumetric efficiency and processing efficiency of the reactor. (3) Unique gas-water combined backwashing method: IRBAF's backwashing technology is an improvement of traditional backwashing technology, which improves the strength of the filter layer disturbance, increases the additional shear stress in the system stress, and improves the intergranularity. Collision opportunities, thereby improving the backwashing effect of the system, avoiding the bondage of the filter material, maintaining the activity of the reactor, and achieving the purpose of stable treatment. (4) High degree of automation: Backwashing is the key to ensure the normal operation of the system. It has a great influence on the effluent quality, operating cycle and operating conditions. The entire backwashing process of the design system is controlled by the program, and the valves on the pipeline are automatically controlled in sequence. Reduce manpower and facilitate operation. For the alkali slag high-concentration sewage that has been plaguing the refinery and chemical industry sewage treatment field, after physicochemical treatment such as oil separation and air floatation, it enters the internal circulation fixed biological oxidation bed IRBAF process for biochemical pretreatment, which can effectively and most remove most COD. To reduce the processing load of the subsequent common biochemical treatment process, improve the impact resistance of the entire sewage treatment plant, stable effluent quality, easy operation, low engineering cost and low operating cost, and will surely be in the field of high-concentration sewage treatment of alkali slag in the refining and petrochemical industry. It is widely used.

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