Decanter centrifuge separation

Centrifugal separators are used in many modem processes to rapidly separate the hydrocarbon and used acid phases. Rapid separation greatly reduces the amounts of nitrated materials in the plant at any given time. After an explosion in a TNT plant (16), decanters (or gravity separators) were replaced with centrifugal separators. In addition, rapid separation allows the hydrocarbon phase to be quickly processed for removal of the dissolved nitric acid, NO, etc. These dissolved materials lead to undesired side reactions. The organic phase generally contains some unreacted hydrocarbons in addition to the nitrated product. 

Separation of two liquid phases, immiscible or partially miscible liquids, is a common requirement in the process industries. For example, in the unit operation of liquid-liquid extraction the liquid contacting step must be followed by a separation stage (Chapter 11, Section 11.16). It is also frequently necessary to separate small quantities of entrained water from process streams. The simplest form of equipment used to separate liquid phases is the gravity settling tank, the decanter. Various proprietary equipment is also used to promote coalescence and improve separation in difficult systems, or where emulsions are likely to form. Centrifugal separators are also used. 

A continuous decanter centrifuge may be acceptable for the operation. The separation of solids is controlled by the centrifugal force, the bowel radius, and the effective length. The specification depends on the desired products maximum clarification, classification, or solids dryness. 

The next step in the process is removal of remaining soluble and insoluble protein. Starch slurry discharging from the primary centrifugal separator must be diluted with process water to a slurry density of 10-12° Baume (18-21% dry solids). The starch may then be further purified in a second centrifugal separator to a final insoluble protein level of <0.38% dry basis (preferably 0.27-0.32% dry basis). However, since solubles content of the slurry must next be reduced by filtration of centrifugal decantation, the second step currently preferred is to utilize 8 to 14 stages of liquid cyclones which simultaneously remove residual gluten and wash the starch.207-209... 

Decanter centrifuges are well suited to high solids concentrations at feed rates between 1 and 100 m3/hr. They cannot achieve such high standards of separation as a disc stack machine, and are more difficult to engineer as truly hygienic or contained units. They are suitable for continuous operation and can discharge solids continuously. 

Two major types of centrifugal separators are used in press-type oil/fat extractions and wet rendering horizontal decanters and vertical stacked conical disk centrifuges. A drawing of a... 

Isolation and purification of substances filtration, decantation, centrifugation, magnetic separation, crystallization, distillation. 

FIG. 18-155 Two-phase decanter centrifuge—gravity liquid discharge. Flottweg Separation Technology,... 

FIG. 18-158 Three-ph ase decanter centrifuge. FloUweg Separation Techiwlogy.)... 

As in a decanter, an accelerated feed is introduced to the separation pool. The denser solids settle toward the bowl wall and the effluent escapes through the ports at the large end of the machine. The sediment is scrolled toward the beach, typically with a steeper angle compared to the decanter centrifuge. As the solids are conveyed to the... 

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