Nowadays we are quite familiar with decanter centrifuges because we can see them almost everywhere in different industry sectors. Many people also think them a very simple machine, they just generate high centrifugal forces which is in turn applied to solids so as to separate them from liquids.

However in real application there are many factors affecting the performance of decanter centrifuges and we have to take into consideration many influences to achieve optimized performance of decanter centrifuges.

We discuss about flocculants application. During the operation of decanter centrifuge we need to use flocculants to speed up the separation of solids from liquids. In field application we encounter the following situation from time to time.

• The centrate has a lot of solids. If this happens the solids concentration in the incoming flow must be checked. For GN Solids Control, its decanter centrifuges are designed to work with highest efficiency when solids concentration is around 20%. If decanter centrifuges are overloaded, they will never work well;
• Differential speed. Three is a slight difference between the rotation speed of centrifugal bowl and auger, usually between a few RPM to less than 20RPM. The lower the differential speed, the longer solids stay in the rotating bowl. There is a very important consideration in this differential speed, the breaking of flocculants, as they intend to break if exposed pressure for long, making them lose the ability to coagulate find particle, and having them discharged with liquid. A trial and error test can determine the optimum differential speed for that particular type of solids;
• Another consideration on flocculants is its strength. When flocculants come into decanter centrifuge, there is a big difference speed between flocculants and the solids. Once flocculants falls on to the wall of rotating wall, there is a huge shearing force exerted on them, and they need to be strong enough to withstand the shearing force to remain as integral particles so as to attract fine particles onto them and move out of decanter centrifuge along with bigger particles.

Decanter centrifuge is everywhere in the industry, it is so important that it is used almost in every corner of the industry.

Because we are familiar with centrifugal force, we take for granted that decanter centrifuge is a simple machine. To some extent it is true as it is a long barrel on a pair of bearings rotating at high speed. However, it is not that simple. Designing and application of decanter centrifuges require a lot careful planning and coorindation.

The first consideration is the inlet zone, where slurry to be separated enters into rotation bowl. The most important consideration of this part is to minimize the degradation of solids, because degradation can disturb the settlement of solids on bowl wall. Many manufacturers have particular design for specific application to make this purpose.

The second and the most important consideration is the rotation bowl. On one site it needs to be strong enough to withstand the huge centrifugal force being exerted on bowl wall. Just remember G force on the rotation bowl can be as high as 3000 G. In other words one KG of solids can becomes 3 tons heavy. If there is 500KG of solids in the rotating bowl, it would be 1500 ton heavy. The rotating bow need to be extremely strong to undertake this force. GN Solids Control uses duplex stainless steel to make rotating bowl, which is much stronger than regular 304 and 316 stainless steel.

The other consideration of rotating bowl is its resistance of erosion and corrosion. There exists big speed difference between solids and rotating bowl thus there will be potential of big erosion. Also there are numerous number of materials to be separated including some very corrosive material. Rotating bowl needs to be able to resist such erosion and corrosion to provide long service life of the decanter centrifuge.

30 years ago decanter centrifuge was considered high tech equipment due the challenge to cast high strength rotating bowl and control of erosion from high abrasion solids. At that time decanter centrifuge could cost up to 1 million US dollars. Any enterprises which manufactured decanter centrifuge were considered high tech company.

With advancement of technology, there is no longer mysteries in decanter centrifuge, and many people take them as granted. However one need to have at least some basic knowledge about decanter centrifuge before he can understand and operate them in a proper and safe manner.

Let us have a look at rotating bowl.

First there is an inlet tube, which dumps slurry into the rotating bowl. Please note, the material inside the rotating bowl is spinning at very high speed with the rotating bowl. Once slurry from inlet tube drops down to the wall of rotating bowl. On one side the slurry will produce erosion to bowl wall, and it also damage solids settlement on bowl wall. A properly designed decanter centrifuge can minimize this disturbing effect.

Second component is screw conveyor. This device plays instrumental role for the performance of decanter centrifuge. The more effective the screw conveyor is, the more efficient the decanter centrifuge is. Therefore it is very important to have proper design of screw conveyor. Extensive industrial experience about the pitch, angle and differential speed are the foundations for successful design of screw conveyor.

Third consideration of solids discharge section. The biggest challenge here is erosion, as there is huge centrifugal force on the solids. Depending on the feature of solids, they can be very dry like powder, or they can be like paste, sticky and viscous. Discharge ports withstand tremendous erosion and all measures should be taken to protect discharge portion to maximize their service life.

Crude oil exploration and production has been in existence for over 100 years. It revolutionized industry and how people live in this planet, and greatly improve the quality of life. However, it also bring many side effect on the earth, oil contamination is one of them.

Oil contamination is a frequently encountered in the exploration and production of crude oil, such us drilling process, oil well workover,  well tesingt and other operations performed on oil wells. Once the land is contaminated, it will take centuries for the land to remediate. Oil contamination is a big challenge to environment protection.

GN Solids Control is mindful of this thread to lives on the earth and has been performing R&D work to resolve this problem. The result is the oil sludge treatment system.

The major achieve of this system is the effectively separation of oil from water and solids, turning contaminated land into arable, and recovered oil can be used again.

The treatment process is to mix the contaminated soil with chemicals and water, properly stirred, then send it to a GN shale shaker, which separate big solids particles from the liquid. Then the liquid is sent to a secondary mixing tank to be treated with chemicals. After that the liquid is sent to GN decanter centrifuge to further separate solids from liquid employing the super strong separation force of GN decanter centrifuge. Liquid from the decanter centrifuge is sent to GN three phase disc separator to segregate oil, water and solids. The oil can be re-utilized while the water can be used to treat fresh contaminants.

The advantage of such system is its speed. The maximum capability of GN oil sludge treatment system is 30m³/h, and bigger process capability system can be customized. In other words, it can clean an entire well site in one day.

As more and more stringent environment protection policies are implemented, oil contamination job will be increased, the market is promising.

GN Solids Control is continuing its effort to put into the market more efficient oil sludge treatment system to make its contribution to the society.