How to choose sludge treatment equipment for oil refinery

The sludge in oil refinery

sludge source

The sludge in the sewage treatment plant of the oil refinery is composed of oil sludge, scum and residual activated sludge, which is usually called "three sludges". Oil sludge includes sewage tank bottom sludge and pool bottom sludge. Tank bottom sludge is a mixture of oil, water, mud, etc. produced when the sewage tank is heated and dehydrated; After the three phases of oil, solid and water are separated, sludge is deposited on the bottom of the pool. The scum comes from the flotation tank of the oily sewage treatment in the refinery, and the remaining activated sludge comes from the secondary sedimentation tank of the oily sewage biochemical treatment system.

sludge properties

Oil sludge is generally a stable suspending emulsion system composed of oil, water and solid substances. Most of the sludge at the bottom of the pool is naturally settled oil particles, mud, slag, ash, etc., with good settling performance; scum contains more Slop oil, chemicals and air bubbles; residual activated sludge contains more microorganisms, bacteria and less oil, and the volatile solid content accounts for about 80% of the total solid content. The scum produced in the process of oil refining sewage treatment in my country accounts for a large proportion of the "three sludges". In fact, it is residual activated sludge, and the proportion of oil sludge is only about 10%. In oil refinery sludge treatment, oil sludge and scum are generally mixed and treated, and the main component is scum.

How to choose sludge treatment equipment for oil refinery

Due to the relatively high moisture content of sludge in the refinery, direct discharge will increase the number of subsequent sludge conveying equipment and the cost of sludge drying or incineration. Therefore, dewatering of sludge is required. At present, the centrifugal dewatering process is widely used in the sludge dewatering treatment in the refinery. The application time of the screw press dewatering technology is short, but due to its advantages in operating costs and other aspects, it is being gradually promoted and used.

The screw press dewatering machine

The screw press dewatering machine uses the principle of screw extrusion, the strong extrusion force generated by the change of screw diameter and pitch, and the small gap between the fixed ring and the floating ring. A new type of solid-liquid separation equipment for sludge dewatering.

more about working principle of screw press dewatering machine,you can read this >>multi disc screw press

The horizontal screw centrifuge

The horizontal screw centrifuge is a sludge treatment equipment that uses the centrifugal force generated by the high-speed rotation of the drum for solid-liquid separation.

more about working principle of horizontal screw centrifuge,you can read this >>horizontal screw centrifuge

multi disc screw press VS Horizontal screw centrifuge 

process comparison

Oily sludge in refineries is generally formed by mixing the bottom sludge produced by the grease trap and the scum produced by the air flotation tank. Compared with the horizontal screw centrifuge, the screw press dehydrator has lower requirements on the inlet pressure. Under normal conditions, the sludge treated by the sludge thickening tank only needs to flow into the flocculation mixing box by itself, while the horizontal screw centrifugal The machine requires a certain inlet pressure, so the sludge transfer pump is indispensable in the process flow of the horizontal screw centrifuge, which will increase the cost of sludge treatment; compared with the screw press dehydrator, the horizontal screw centrifuge In the treatment of refinery sludge, it is necessary to add a specific gravity agent to increase the density difference between the mud and water, thereby improving the separation efficiency of the mud and water, which will also increase the cost of sludge treatment.

Running Cost Comparison

The two dehydrators differ greatly in terms of drug consumption and water consumption; the power consumption of the horizontal screw centrifuge is about 10 times that of the screw press dehydrator. The screw press dehydrator has great advantages in saving energy consumption. Compared with the horizontal screw centrifuge, the screw press dehydrator is simple to operate, manage and maintain, and the sludge transfer pump can be omitted in the sludge treatment process, reducing operating costs. 

Comparison of advantages and disadvantages

The treatment effect of the two sludge dewatering machines is basically the same. Compared with the horizontal screw centrifuge, the concentration of SS filtered by the screw press dewatering machine is slightly lower, and the recovery rate of solids by the surface screw pressing dewatering machine is slightly higher. In view of the large increase in sludge volume in the refinery sewage treatment plant, especially the significant increase in the proportion of scum, the use of horizontal screw centrifuges to treat refinery sludge will not only increase operating costs, but also difficult to guarantee the treatment effect. The use of a screw press dehydrator can save energy, reduce operating costs and improve the working environment on the premise of ensuring the treatment effect. As a newly developed sludge treatment equipment, the current investment cost of screw press dehydrator is slightly higher than that of horizontal screw centrifuge.

Summary

1. Both the screw press dehydrator and the horizontal screw centrifuge are suitable for the dehydration treatment of oily sludge (the main component is scum) and residual activated sludge, but the former is not suitable for larger hardness particles, especially those containing a large amount of sand and gravel. , sludge dewatering of large metal substances.

2. The horizontal screw centrifuge mainly relies on the centrifugal force generated by the high rotating speed of the drum to separate the sludge, while the screw press dehydrator mainly relies on the extrusion of the screw to achieve sludge dewatering. The operating cost of a screw press dewatering machine in sludge treatment is significantly lower than that of a horizontal screw centrifuge.

3. The screw press dewatering machine adopts a fully enclosed box with a reserved odor gas treatment interface, which can effectively reduce the pollution of the odor gas in the sludge to the surrounding working environment.

4. The treatment effect of the two sludge dehydrators is basically the same. Compared with the horizontal screw centrifuge, the concentration of SS after the filtration of the screw press dehydrator is slightly lower, and the effect is slightly better.

5. After the oily sludge in the oil refinery is dewatered, the filtrated liquid contains a large amount of oil, and the main component is emulsified oil. Direct discharge into the sewage treatment system may have an impact on the entire system, so it needs to be treated with caution.