Question

explain the working principle of disc stack centrifuge and operating condition for downstream process of protein

Answer 1

Functional principle of a self cleaning disc stack centrifuge
The product to be separated enters the inside of the bowl through a stationary inlet pipe (1) into the distributor (2). The separation takes place in the disc stack (3). The product flow is divided into multiple thin layers by the disk stack and a large surface area is created. From the disk stack, the clarified liquid flows to the impeller (5) to be discharged.

Depending on the process, the liquid can be discharged under pressure or unpressurized. A distinction is drawn between a clarifier and a purifier version with a single or double impeller. Separated solids are packed in the solids chamber (4) and discharged periodically.

Bowl The bowl of a self-cleaning disc stack centrifuge consists of a bowl bottom (6) including the hydraulic discharge system and the bowl top.

The solid discharge (9) is opened and closed by vertical sliding of the piston (7) and controlled by the bowl valves (8). Using a hydraulic system in the bowl bottom, the separated solids are discharged at full speed.The hydraulic system of the FLOTTWEG AC centrifuges enables exactly reproducible partial discharges as well as total discharges in any combination.

Disc stack The disc stack (3) consists of the discs and the distributor. The purifier and concentrator versions are equipped with additional separation discs (10). The product is introduced to the center of the distributor through the inlet pipe (1). A specially-designed distributor ensures the smooth acceleration of the product. The impact of sheer forces on the particles has to be avoided. This would lead to emulsification and therefore be counterproductive for the separation process. Passing the distributor through holes at the bottom, the product enters the disc stack. Through the rising channels, the product is fed into the space between the discs. An additional separation disc on top of the disc stack (purifier and concentrator) ensures the separated or concentrated liquid to flow into the corresponding collection chamber.

Liquid discharge The separated liquids leave the disc stack centrifuge through the liquid discharge. The design varies depending on whether it is a clarifier, purifier or concentrator version. Using a clarifier version, the liquid is discharged under pressure via a stationary impeller. There are three options for the purifier and concentrator version: – Both separated liquids are discharged by means of a double impeller (11). – The light phase is discharged by a single impeller. The heavy phase is discharged unpressurized and leaves through a stationary regulating ring.– The heavy phase is discharged by a single impeller (5). The light phase is discharged unpressurized and leaves through a stationary regulating ring.

Drive The required drive power is transmitted directly to the bowl shaft using a standard threephase AC motor with frequency drive control via a V-ripped or flat belt. The motor is controlled by a frequency drive enabling a smooth acceleration and limiting the inrush current. Furthermore, there is the possibility to vary the bowl speed. Compared with other drive systems, the FLOTTWEG drive offers lower maintenance and increased efficiency

Materials of construction All product-wetted parts are made of stainless Cr-Ni-Steel. Depending on the requirements, the components of the bowl are made of stainless steel or duplex alloys. The sealing materials are made of perbunan (NBR) and polyamide. Other materials such as PEEK, Viton (FKM) and EPDM are available.

Disc stack centrifuges are able to apply a force from 4000 to 14,000 times gravitational force , thus reducing separation time. These are the most common industrial centrifuges and are widely used in commercial plants for high-value microalgal products and in microalgal biofuel pilot plants.

Disc stack centrifuges are ideally suited for separating particles 3–30 μm in concentrations of 0.02%–0.05% of microalgal cells . However, they generally exhibit high energy consumption.

Downstream Process of Protein

A widely recognized heuristic for categorizing downstream processing operations divides them into four groups which are applied in order to bring a product from its natural state as a component of a tissue, cell or fermentation broth through progressive improvements in purity and concentration.

Removal of insolubles is the first step and involves the capture of the product as a solute in a particulate-free liquid, for example the separation of cells, cell debris or other particulate matter from fermentation broth containing an antibiotic. Typical operations to achieve this are filtration, centrifugation, sedimentation, precipitation, flocculation, electro-precipitation, and gravity settling. Additional operations such as grinding, homogenization, or leaching, required to recover products from solid sources such as plant and animal tissues, are usually included in this group.

Product isolation is the removal of those components whose properties vary considerably from that of the desired product. For most products, water is the chief impurity and isolation steps are designed to remove most of it, reducing the volume of material to be handled and concentrating the product. Solvent extraction, adsorption, ultrafiltration, and precipitation are some of the unit operations involved.

Product purification is done to separate those contaminants that resemble the product very closely in physical and chemical properties. Consequently, steps in this stage are expensive to carry out and require sensitive and sophisticated equipment. This stage contributes a significant fraction of the entire downstream processing expenditure. Examples of operations include affinity, size exclusion, reversed phase chromatography, ion-exchange chromatography, crystallization and fractional precipitation.

Product polishing describes the final processing steps which end with packaging of the product in a form that is stable, easily transportable and convenient. Crystallization, desiccation, lyophilization and spray drying are typical unit operations. Depending on the product and its intended use, polishing may also include operations to sterilize the product and remove or deactivate trace contaminants which might compromise product safety. Such operations might include the removal of viruses or depyrogenation.