Introduction of solid-liquid separation technology

The ultimate intention of liquid separation, theoretically speaking, should be to completely separate the two phases of solid and liquid to obtain their respective pure components: solid and liquid. According to the current development, solid-liquid separation is fundamentally two methods, namely sedimentation separation and filtration. The sedimentation separation can be divided into two kinds, namely gravity sedimentation and centrifugal sedimentation.

I. Methods of solid-liquid separation

In the solid-liquid suspension system, the solid is the dispersed phase and the liquid is the continuous phase. From the point of view of the separation process, the solid is excessive from a highly dispersed state to a concentrated state. In sedimentation separation, the movement of solid particles is required, and the lower the solid concentration, the more conducive to this process. On the contrary, filtration moves in the liquid phase, so it is advantageous for separation when the liquid phase is small, that is, the solid concentration is high.

1. Sedimentation

When the effect of sedimentation separation and filtration is not ambitious, filter AIDS can generally be added to improve the power. These filter AIDS are composed of rigid, porous, highly permeable powder particles, which are added to the slurry to improve its filtration function.

Gravity sedimentation principle:

The use of gravitational sedimentation properties for interliquid separation is theoretically the most economical method, because it relies on gravity without the need for external energy. Of course, in order to achieve useful separation, it is first necessary to provide a satisfactory settling area, and secondly in order to accelerate the terminal settling rate of solid particles, it is necessary to choose coagulation and flocculation skills. Generally to participate in flocculant. For the suspension composed of smaller particles and higher viscosity solution, when it is still difficult to reach the request of solid-liquid separation only by flocculation skills, it is necessary to introduce centrifugal force to enhance the driving force of solid particle settlement, that is, centrifugal sedimentation.

Principle of centrifugal sedimentation:

The centrifugal technique is the use of strong centrifugal force when the object is rotating at high speed, so that the suspended particles placed in the rotating body can settle or float, and then some particles reach the intention of concentration or separation from other particles. Suspended particles here generally refer to the cells, organelles, viruses and biomacromolecules that make up the suspended state. When the centrifuge rotor rotates at high speed, when the density of suspended particles is greater than the density of the surrounding medium, the particles move away from the axis direction and settle. If the particle density is lower than the density of the surrounding medium, the particles move in the direction of the axis and float.

(1) centrifugal force; If the solid liquid suspension is in the centrifugal force field, the solid particles will be subjected to the sedimentation force many times larger than the gravity force, which will accelerate the sedimentation along the direction of the centrifugal force field. Solid particles with a mass of m suspended in liquid are in a centrifuge rotating at high speed.

(2) Separation factor. The ratio of the centrifugal force on the solid particles in the centrifugal force field to the force in the gravitational field is called the separation factor.

(3) Sedimentation separation in the centrifugal force field: the sedimentation of particles in the centrifugal force field and the settlement in the gravitational field have the same three flow patterns, such as laminar flow, transitional flow and turbulent flow. However, the difference is that in the gravitational field, the particles are settled at the same speed, while in the centrifugal force field, they are accelerated in the radial direction.

3. Membrane separation

The membrane separation process is mostly carried out at ambient temperatures, and the principle is not messy: by applying a push force on both sides of the membrane, it can be a concentration difference, pressure difference or voltage difference, and then the material transfer between the mixture moving on both sides of the membrane can be carried out in the desired direction. Separation equipment in the petroleum industry

1. Hydrocyclone

Hydrocyclone is a device that uses centrifugal force field effects, in addition to a pump, it does not require mechanical transmission parts, and is cheap, compact, and widely used in solid-liquid separation processes. It operates like a centrifuge, but with a much larger separation factor. The primary activities in the cyclone are the fundamental vortex and the secondary vortex. The primary vortex is located outside the secondary vortex and carries the suspended matter down the cyclone axis. The secondary vortex carries the material along the axial upward movement into the overflow outlet at the top.

Operation principle of hydrocyclone: Under the effect of pressure, the slurry enters the shell along the tangential direction of the cylinder through the feed pipe, and does rotary movement in the shell. The coarse particles (or dense particles) in the slurry enter the periphery of the rotary flow due to the larger centrifugal force, and move with the slurry flow downward, eventually discharged from the bottom settling nozzle into settling sand; The small centrifugal force of the fine particles is in the base of the revolving flow and moves upward with the flow direction, and finally the overflow is discharged from the overflow pipe.

It is a developing trend in recent years to use hydrocyclone technique to remove oil from oilfield wastewater and pre-dehydrate produced liquid in high water cut period.