Technical Transformation and Application of Horizontal Spiral Discharge Centrifuge

Abstract: This article introduces the working principle and existing problems of the sc800h horizontal spiral discharge centrifuge during the expansion and renovation of a 50kt/a ABS production unit. In response to the current situation where the working condition of the centrifuge is still insufficient after the renovation, the lwl450x300-n horizontal spiral discharge centrifuge is used to replace it, thus solving the need for continuous production.

Keywords: Horizontal spiral discharge centrifuge; Renovation; application

In the production process, with the requirements of dehydration, clarification, concentration, classification, and separation processes, separation equipment becomes the key equipment to complete such processes. Compared with other separation machinery, centrifuges can not only obtain solid phases with low moisture content and high-purity liquid phases, but also have advantages such as small volume, good sealing, continuous operation, and automatic remote control. Therefore, they are widely used in various industries such as chemical, petrochemical, petroleum refining, light industry, and medicine.

1 sc800h horizontal spiral discharge centrifuge

The SC800h horizontal spiral discharge centrifuge mainly consists of a high-speed rotating drum, a spiral feeder and differential with the same rotation direction as the drum and slightly higher speed than the drum. After the suspension that needs to be separated enters the centrifuge drum, the high-speed rotating drum generates a strong centrifugal force. After the centrifuge drum, the high-speed rotating drum generates a strong centrifugal force to settle solid particles with a higher density than the liquid phase onto the inner wall of the drum. Due to the different rotational speeds of the drum and the screw feeder, there is relative motion (i.e. speed difference) between the two. The relative motion of the screw feeder and the drum is used to push the solid particles deposited on the inner wall of the drum towards the outlet of the large end of the drum and discharge them. The separated clear liquid is discharged from the centrifuge drum through the channel between the outer drum and the shell.

1.2 Main technical parameters

Drum inner diameter 800mm

Working length of drum 800mm

Cone angle 15 degrees

Speed 2 150r/min

Separation factor 1650

Main motor power 75kw

Material selection volume 6.0m3/h

Filter mesh size 120 mesh

1.3 Main components

1.3.1 Drum

The drum of the SC800h horizontal spiral discharge centrifuge is a conical cylinder (with a large end diameter of 800mm and a length of 900mm), with uniformly distributed holes of 5mm on the cone. The outer surface is equipped with ribs (20mm x 3mm, 24 pieces), which are welded to the outer surface of the drum by intermittent welding. This is beneficial for increasing the length to diameter ratio and improving the dehydration efficiency. The inner surface is covered with a 120 mesh filter screen, which is fixed on the inner wall of the drum by end face pressure rings. Due to the small cone angle (15 degrees) of the drum, the material stays in the drum for a longer time, which can improve the washing effect of the filter cake.

1.3.2 Spiral feeder

The spiral feeder is one of the important components of the SC800h horizontal spiral discharge centrifuge, with three continuous integral spiral blades on the outer surface. When pushing the material, the blades of the screw feeder are prone to wear and tear, so high hardness tungsten carbide alloy is sprayed on the surface of the blades. At the same time, the top of the blades is made into a 10mm radius arc and a 45 degree x 3mm chamfer is poured out to reduce the centrifugal vibration caused by wear and viscous resistance. The gap between the screw feeder and the drum should not be less than 0.2mm, which can prevent friction between the screw feeder and the drum and cause vibration of the unit.

1.3.3 Differential

In a horizontal spiral discharge centrifuge, the axial movement of the filter cake between the screw feeder and the drum is achieved through the relative motion (speed difference) between the screw feeder and the drum, and the speed difference is achieved through the differential. The speed difference between the screw feeder and the drum also determines the residence time of the product in the drum to a certain extent, which is conducive to improving the separation effect of solid-liquid two-phase. The SC800h horizontal spiral discharge centrifuge adopts a circular arc cycloidal pinwheel drive differential, with the differential housing connected to the drum and the output shaft connected to the screw feeder to achieve a differential speed ratio of 15r/min.

1.3.4 Overload protection device

In a horizontal spiral discharge centrifuge, when the feed rate or concentration suddenly increases and changes the filter cake amount, the screw pushing torque and main motor current will increase. If there are no protective measures at this time, it is inevitable to damage the differential. The SC800h horizontal spiral discharge centrifuge adopts a trig-o maric anti overload coupling. If the torque is overloaded, the hydraulic coupling will attract the motor installed at the rear end of the differential to start, driving the differential planetary gear and sun gear to rotate at the same speed.

1.4 Problems during the test drive process

When the 50kt/a ABS expansion unit entered the material testing stage, the SC800h horizontal spiral discharge centrifuge was first loaded with an empty load vehicle. When the centrifuge is driven, the body produces periodic vibration and shows an upward trend, and the vibration value seriously exceeds the standard. After the action balance test of the screw feeder and drum, it is found that there is indeed dynamic imbalance phenomenon, and the deviation is large. After debugging and processing, the dynamic imbalance of the screw feeder and drum was controlled within the allowable range. After installation, the test was conducted, and the periodic vibration was weakened and the vibration value decreased.

The SC800h horizontal spiral discharge centrifuge was tested under load with a feed rate of 6.0m3/h and a slurry concentration of about 15%. The moisture content in the discharge was 36%, and the moisture content was unstable. After about 1 hour of testing, the centrifuge suddenly experienced a vibration chain shutdown. Upon opening and inspection, it was found that the filter screen was damaged due to excessive vibration and rubbing against the centrifuge rotor, and there was a layer of adhesive scale on the screen.

1.5 is mainly caused by the following reasons

1.5.1 The feed overflows through the high-level tank, causing significant fluctuations in the feed volume.

1.5.2 The filter mesh size of the centrifuge is too small when it is effective

The failure to remove the internal mother in a timely manner causes vibration, which in turn leads to screw feeding

The scraping vibration between the feeder and the drum intensifies.

1.5.3 After measurement, the speed of the centrifuge is 2150r/min, which is close to and exceeds the second critical speed of the machine, which is the main reason for periodic vibration.

In response to the above issues, the centrifuge has been modified multiple times, and the specific work is as follows:

a. The centrifuge spiral feeder and drum were dynamically balanced and recalibrated.

b. Increase the mesh size of the centrifuge filter to 150 mesh.

c. Replace the pulley and reduce the speed of the spiral discharge centrifuge to 1570r/min.

d. Change the original high-level tank feeding to using a Nitz screw pump to stabilize the feeding amount.

After renovation, although the centrifuge and feeding system meet production needs, their output cannot meet the requirements.

2 lwl450 × 300-n horizontal spiral discharge centrifuge

2.1 Working principle

The drum of the lwl450 × 300-n horizontal spiral discharge centrifuge and the spiral feeder rotate at a certain speed difference (completed through a gear differential) in the same direction at high speed. The material is continuously introduced into the conveying inner drum through the feeding pipe, accelerated, and then enters the drum. Under the action of the centrifugal force field, the liquid phase passes through the filtering medium and is discharged outside the machine. The solid phase is trapped inside the drum to form a filter cake. The filter cake continuously moves towards the large end of the drum under the combined action of the conical force of the centrifugal force and the spiral feeder, and is discharged outside the machine through the discharge groove.

2.2 Main technical parameters

Drum inner diameter 450mm

Drum working length 300mm

Cone angle 10 degrees

Speed 2096r/min

Separation factor 1105

Main motor power 22kw

Feed volume 4.5m3/h

2.3 Characteristics and Application Situation

The lwl450 × 300-n horizontal spiral discharge centrifuge can continuously feed, separate, wash, and discharge at full speed. It has the characteristics of compact structure, small volume, continuous operation, smooth operation, strong adaptability, large processing capacity, and low moisture content of filter cake.

At an average feed concentration of 15%, the single machine wet based production capacity is 3.375t/h and can meet 80% of the production load. In terms of mechanical structure, the centrifuge adopts a gear differential, which has a small volume, smooth operation, long cycle, convenient maintenance, and low labor intensity, greatly alleviating the passive situation of ABS wet powder production.

3 Conclusion

The lwl450 × 300-n horizontal spiral discharge centrifuge has completely overcome various unfavorable factors of the original centrifuge, eliminated the bottleneck of long-term stable operation of the ABS device, and provided a reference basis for the selection of similar equipment in domestic similar devices.