“Oil is not only an important sector of our industry but also a symbol of the independence of our country, of the hope for a better future”. These were the words of President Nursultan Nasarbayev in September 1999, commemorating the 100th anniversary of the formation of the oil and gas industry. The oil industry in Kazakhstan has existed for more than 100 years, however a significant boom in this sector only started after the declaration of independence of the Republic. Since independence was gained, the economic boom in Kazakhstan has been tightly connected with the success of the oil and gas industry. “Today the Kazakhstanian oil is working for our people” the President continued. Actually, the discovery of huge oil fields in the Kazakhstanian part of the Caspian Sea was a milestone. The oil projects carried out concentrate especially on Makat, Dossor Karazhanbas and Usen. In Usen, approximately 75 mi away from the ocean, there are several sedimentation ponds and lagoons where oil residuals have been settling for decades. The German company Flottweg provided complete systems to effectively handle these lagoons and ponds and recover useful oil.
How a FLOTTWEG DECANTER / TRICANTER® works
The product to be separated is fed through a stationary pipe into the feed zone located in the center of the scroll. The product is then accelerated circumferentially and delivered through distribution ports into the bowl. The bowl has a cylindrical/conical shape and rotates at a pre-set speed optimal for the application. The product rotates with the bowl at the operating speed and forms a concentric layer at the bowl wall. The solids contained in the product are packed against the bowl wall by centrifugal force. The scroll rotates at a slightly different speed than the bowl and conveys the separated solids toward the conical end of the bowl. This differential speed determines the residence time of the solids in the bowl. Residence time is an important variable for cake dryness. It can be adjusted by changing the differential speed of the scroll thus providing optimal separation. Settled solids are ejected through ports at the conical end of the bowl into the solids housing and fall through to the discharge chute.
FLOTTWEG uses high-quality stainless steel for all product wetted areas.
The clarified liquids flow to the cylindrical end of the bowl where they exit over weir plates or impeller. Easily adjustable precision weir plates allow for the accurate adjustment of the pond depth in the bowl. Overflow is then collected and discharged by gravity into a centrate chamber.
The clarified liquid can also be decanted with an impeller and discharged from the bowl under pressure. This eliminates the need for a separate centrate pump. The Flottweg adjustable impeller is an engineering refinement that permits quick and precise adjustment of the pond depth during operation to accommodate changing conditions.
The FLOTTWEG TRICANTER® enables three-phase separation, i.e. the simultaneous separation of two immiscible liquids with different densities and one solid phase, provided that the solid phase is the heaviest phase. The most important difference from a decanter is the separate discharge of the two liquid phases. The FLOTTWEG TRICANTER® discharges the heavy liquid through an adjustable impeller under pressure and the light phase by gravity. The adjustable impeller allows adjusting the separation zone and degree of separation within the machine during operation. This optimizes the purity of the liquids and may possibly eliminate downstream equipment.
For a long period of time, in Usen, the ponds and lagoons where the difficult to separate residuals such as paraffin-containing emulsions and oil sludge generated from technical failures, have been settling continually. To date, the large lagoon has reached a depth of 5 meters and a surface of 500 meters wide and over 1 km in length.
The project was to first process the large lagoon and recover valuable oil, and then move the installation to the smaller ponds. For this purpose, FLOTTWEG delivered two complete systems in containers and on platforms. Currently, the project is in full production.
Part of the FLOTTWEG oil recovery system is an oil-suction unit that enables the extraction of oil sludge from a defined depth below the pond’s surface. The suction pump is mounted on a pontoon that floats on the surface of the pond or lagoon. If the suctioned portion contains high contents of paraffin and asphaltum, the oil sludge is fluidized in the suction pipe using steam operated heater coils. The extracted oil sludge is then processed like slop oil. The slop oil is heated, surfactant and flocculants are added, and finally, oil, water, and solids are separated by means of a FLOTTWEG TRICANTER®.
The first machine, a TRICANTER® Z6E – 3/441 was delivered, set up, and commissioned in 2004. The aim was to gain oil of quality level I, which means that it contains a water content below 0.5 % and a chloride content below 100 ppm. Due to the positive experience with the FLOTTWEG TRICANTERS®, which assured stable operating conditions and high oil quality, a second Usen project was carried out in 2006. FLOTTWEG delivered two additional Z6E -4/441 TRICANTERS®. They also enabled high performance and good oil quality.
At the same time, a TRICANTER® Z4E was delivered as a mobile unit for tank cleaning.
When commissioning the system, the machines and the influencing factors for separation were thoroughly analyzed. Then the machines were optimized by adjustment of the centrifuges and the utilities, and the regulation of the process temperature.
An important influencing factor for success is the demulsifier used. As seen in Figure 1, only the product SP3 met the defined requirements. Demulsifier 2 can be used, but it is not as efficient as SP3. Use of the other tested demulsifiers can not be recommended because the desired oil quality could not be reached, even when using high dosages.
Due to the clear advantages of demulsifier SP 3, only this product was used for further optimization.
High centrifugal force is necessary for the separation because lower speed in the bowl results in a higher amount of residual water in the oil.
Temperature is also essential factor for oil quality. Middle temperatures do not lead to the requested oil quality. Most of the further tests were executed at 175˚ F and it was found that high temperature results in better separation.
The chloride content is reduced by adding water. During the start of the system, there was a relatively low chloride content in the feed of the centrifuge. In order to reduce the higher chloride content in other parts of the pond, more water needed to be added.
There are Tricanters® in two different sizes operating at the plant. In a series of tests, the two types of machines were compared (Figure 2). The machine with the longer bowl offers more capacity – in this case meaning that the requested performance could be reached. It can also clearly be seen that the water content increases disproportionately with higher flow rate.
Due to the extensive tests during the start-up of the system, it was possible to find exact results and a calculated basis for planning installations for oil sludge treatment.
The client was especially satisfied that it was possible to adjust the system exactly to requested parameters.