Types and working principles of mechanical dewatering equipment for oily sludge

In recent years, PetroChina has continuously expanded its overseas business in the Iran-Iraq region (Iran and Iraq), and its oilfield surface engineering construction projects have grown rapidly. The sewage treatment system occupies a very important position in the construction of ground engineering, and the oily sludge treatment system is an indispensable part of it. Oily sludge is generally composed of water-in-oil and oil-in-water emulsions and suspended solids. The particles of oily sludge are small and flocculated; the density difference with water is small, the water content is high, and the water holding capacity is strong. In addition, due to the use of a large number of chemicals in the sewage treatment system, the oily sludge has complex composition, serious sludge emulsification, and is difficult to settle; and it is easily corrupted, produces foul odors, pollutes the air, and causes great harm to the environment. With the increasingly strict environmental protection requirements, the innocence, reduction and recycling of oily sludge have become an inevitable development trend, and sludge dewatering is the premise of sludge disposal. Reducing the moisture content of the sludge can reduce the equipment load and processing difficulty of the subsequent sludge treatment, and significantly reduce the subsequent disposal costs. The research of the environmental protection department in Orange shows that when the moisture content of the sludge is below 78%, the subsequent treatment of each ton of sludge is reduced by more than 1 dollar for every percentage point reduction. sludge dewatering technology and equipment are very important.

At present, the commonly used mechanical dewatering equipment for oily sludge at home and abroad mainly includes plate and frame filter presses, belt filter presses, centrifugal dewatering machine and multi disc screw press dewatering machine. In this paper, through the in-depth analysis and comparison of commonly used sludge dewatering equipment, combined with the investigation of the status quo of sludge treatment in Daqing Oilfield, Hailar Oilfield and Liaohe Oilfield, according to the properties of oily sludge in an oilfield in Iraq, several types of common in the market are analyzed. sludge dewatering equipment.

1. Plate and frame filter press

The plate and frame filter press mainly uses the pressure difference on both sides of the filter medium as the driving force, so that the water in the sludge is forced to pass through, and the solid particles are trapped on the filter cloth, so as to achieve the purpose of dehydration. The plate and frame filter press is mainly composed of a concave filter plate, a frame, an automatic-pneumatic closing system, a side plate suspension system, an aluminum plate vibration system, an air compression device, a filter cloth high-pressure washing device, and a photoelectric protection device on one side of the fuselage. The work flow of the plate and frame filter press includes pressing the filter plate, feeding, pressing the filter cake, washing the filter cake, purging the filter cake and discharging. First, the sludge enters each filter chamber from the feed hole under a certain pressure through the sludge pump, and the filter plate is compressed by the hydraulic-pneumatic device, the sludge is trapped in the filter chamber, and gradually forms a filter cake on the surface of the filter cloth ; The filtrate is discharged through the water outlet hole on the plate frame; as the filtration progresses, the filter cake filtration starts, and the thickness of the mud cake gradually increases until it fills the entire filter chamber; Compress the air to remove the remaining washing liquid; then open the filter press to remove the filter cake, clean the filter cloth, re-compress the plate frame, and start the next working cycle.

The plate and frame filter press can filter suspensions with solid phase particle size above 5μm and solid phase mass fraction of 0.1%-60.0%, difficult-to-filter materials with high viscosity or colloidal shape, and substances with high quality requirements for filter residues. The sludge concentration has strong adaptability, and the moisture content of the sludge is generally between 65% and 75%. Compared with other types of sludge dewatering machines, the solid content of the filter cake is higher. The dosage of flocculant is small, and even no chemicals are added.

The Daqing Oilfield Combined Station adopts an automatic box-type plate-and-frame filter press, which has a simple structure and is suitable for sludge of various properties(≤ 70%). However, it can only run intermittently, which is troublesome in operation and management, and the filter cloth is easily blocked and needs to be cleaned and replaced regularly, especially when the oil content is high, it is not easy to form a filter cake. Huansilian Sewage Station of Liaohe Oilfield also adopts box-type plate and frame filter press. According to the on-site investigation, the equipment runs for 4 hours a day, the sludge discharge volume is 1-2m³, and the filter cloth is replaced every 2 months. Although the box type is adopted, the working environment is still poor.

2. Belt filter press

The belt filter press is mainly composed of filter belt, roller pressing cylinder, filter belt tensioning system, filter belt deviation adjustment system, filter belt washing system and filter belt driving system. The dehydration process of the belt filter press is divided into three stages: gravity dehydration, wedge dehydration, pressing and shearing dehydration. The flocculated sludge is transported to the filter belt in the gravity dehydration zone, and free water is removed under the action of gravity to form a non-flowing sludge; the sludge dewatered by gravity relies on the tension of the upper and lower filter belts to form a countermeasure against the sludge. The squeezing and shearing of the mud layer gradually squeezes the sludge and removes the capillary water in the sludge layer to achieve a greater degree of separation of mud and water, and then forms a filter cake for discharge. The filter belt deviation adjustment system is composed of air cylinder, adjustment roller signal back pressure, and electrical system. It is used to adjust the deviation of the filter belt caused by the uneven tension of the filter belt, the installation error of the roller, and the uneven feeding, so as to ensure the smooth operation of the filter press. Continuity and stability; the filter belt cleaning system is mainly composed of a sprayer, a cleaning water contact box and a cleaning cover, which are used to clean the filter belt under high pressure and prepare for the next dehydration process. The moisture content of the incoming mud of the belt filter press is generally below 97.5%, and the moisture content of the outgoing mud is generally below 82%. The belt filter press entered the country earlier and is widely used.

3. Centrifugal dewatering machine

The centrifugal dewatering machine is mainly composed of a drum and a screw conveyor with a hollow shaft. The centrifugal force is generated by the high-speed rotation of the drum, and the solid-liquid separation is realized by using the solid-liquid density difference. After the sludge is sent into the drum by the hollow shaft, it is thrown into the drum cavity under the action of the centrifugal force generated by the high-speed rotation. Due to the high density of the sludge, it sticks to the inner wall of the drum during the rotation to form a solid layer; the water with lower density forms a liquid layer inside the solid. The sludge in the solid layer is transported to the outlet for continuous discharge under the slow push of the screw conveyor, and the liquid is discharged from the dewatering from the overflow of the weir. The centrifugal dewatering machine has the integrated processing function of sludge concentration and dehydration, and can realize the fully enclosed continuous dehydration operation. It is less affected by the change of the sludge concentration, and the sludge has a high solid content, and the moisture content of the sludge is generally 75%-80%.

4. Multi-disc screw press dewatering machine

Multi-disc screw press dewatering machine is a new type of sludge dewatering equipment, which has been rapidly developed, innovated and popularized in my country. Because the multi-disc screw press dewatering machine has the characteristics of easy separation of mud and water and no blockage, it has been successfully applied in Shanxi Yanchang Petroleum, Shandong Shengli Oilfield, Daqing Hailar Oilfield, etc.

The multi-disc screw press dewatering machine uses the screw extrusion principle to complete the sludge concentration and filter press dewatering in one cylinder. After the sludge enters the filter BODy, the rotation of the screw shaft drives the fixed ring and the floating ring to move and squeeze relative to each other, so that the filtrate flows out from the lamination gap quickly, and realizes rapid concentration; With the passage of the dewatering zone, as the filter seam and screw pitch gradually become smaller, the space in the filter cavity is continuously reduced, and the internal pressure of the sludge is continuously increased. Coupled with the blocking effect of the back pressure plate, it can achieve dehydration, and form a mud cake after dehydration. The water content of the multi-disc screw press dewatering machine is generally 95.0%-99.5% in the mud, and the water content in the mud is generally 75%-80%.

The multi-disc screw press dewatering machine adopts the movable fixed ring to replace the filter cloth. Under the rotation of the screw shaft, the movable plate is constantly displaced relative to the fixed plate, thus realizing the continuous self-cleaning process and avoiding the common existence of traditional dewatering machines. clogging problem. The multi-disc screw press dewatering machine has strong oil resistance, easy separation of mud and water, clean and environmentally friendly, no odor, no secondary pollution, especially suitable for the dewatering of viscous sludge in the petrochemical industry.

Final summary:

The multi-disc screw press dewatering technology was originally used in the fishery and food industries, and has been gradually developed and applied in the petroleum and chemical fields in recent years, and has been continuously improved and innovated for the corrosive operating environment of oily sludge with high viscosity and high chlorine content.

The application results of Hailar Oilfield show that the dosage of sludge is 300mg/L, the moisture content of sludge before dewatering is 97%-99%, and the moisture content of mud cake is 71%-86%. After the sludge treatment, the emulsified mud layer in the sewage disappears, which reduces the difficulty of sewage treatment, the effluent quality is obviously improved, and the environmental pollution is reduced at the same time.

The above engineering applications show that the multi-disc screw press dewatering machine is suitable for the sludge with high viscosity or oily that is difficult to handle by conventional dewatering machines. equipment.

Being a solid liquid separation solution provider, Bioetp is with rich experience in design and manufacturing the sludge dewatering machine. More important, Bioetp is able to provide overall solution for separation and conveying with the rich product line and strong fabrication and assembly capabilities.

So,if you have any industrial solid liquid separation requirement aroused, please feel free to contact Bioetp. You can find our contact on Bioetp official website www.bioetp.com.