Mixing basic tank design

The simple batch reactor generally consists of a cooled, agitated mixing tank designed for operation at ambient pressure. Figure 3.1 shows a type of a simple batch reactor arrangement. There are four basic operating steps for this type of reactor used in alkylphenol service. 

Settlers tend to be less varied in their design. They typically comprise a relatively large, shallow tank, rectangular in shape, with an inlet for the mixed phases at one end and two outlets for the separated phases at the other. Various devices are used to introduce the mixed phases gently into the settler, and to control the flow of the mixed phases while they separate, but these do not change the basic principle of separation under gravity. 

Chemical reactors basically come in the form of tanks, such as for batch reactors or back-mix flow reactors, large cylinders, such as for fluidized-bed or plug-flow reactors, or multiple tubes inside a cylindrical container, such as for plug-flow reactors when special needs exist for temperature control. High pressure and extremes of temperature as well as corrosive action of the materials involved can introduce complications in the design which must be handled by the design engineer. 

We turn now to consider the principal types of reactors and derive a set of equations for each that will describe the transformation 5 of the state of the feed into the state of the product. The continuous flow stirred tank reactor is one of the simplest in basic design and is widely used in chemical industry. Basically it consists in a vessel of volume V furnished with one or more inlets, an outlet, a means of cooling and a stirrer which keeps its composition and temperature essentially uniform. We shall assume that there is complete mixing on the molecular scale. It would be possible to treat of other cases following the work of Danckwerts (1958) and Zweitering (1959), but the corresponding transformation is much less wieldy. If the reactants flow in and out at a constant rate q, the mean residence time T/g is known as the holding time of the reactor. 

The focus of this entry is limited to the design of aerobic fermenters, i.e., stirred tank and concentric tube airlift fermenters, which are commonly utilized in the bioprocessing industries. Design principles and the basic calculations are described with a couple of industrial examples. Readers with a limited background in mixing technology are referred to the gas-liquid contactor entry of this encyclopedia for a more comprehensive understanding of fluid flow and mass transfer characteristics in stirred tank reactors and bubble columns. 

Many elements must be taken into consideration designing mixing devices, basically determining the geometry and size of the tank, what type of impeller to use, the size of the impeller, the size and geometry of heat transfer equipment and if baffles are needed. 

A vessel in which the properties are uniform is called a stirred-tank (or well-mixed) reactor. If there is no mixing in the direction of flow in the cylindrical vessel for hydrocarbon processing, another ideal type is realized the ideal tubular-flow, orpi -flow, reactor. Here the reaction mass consists of elements of fluid that are independent of each oth gpach one having a different composition, temperature, etc. This classification is of basic significance in design, because simplified treatments of the physical processes of mass and energy transfer are applicable for each ideal reactor. We noted in Sec. 

Basic Design ofEnv me Reactors Under Ideal Conditions. Batch Reactor Continuous Stirred Tank Reactor Under Complete Mixing Continuous Packed-Bed Reactor Under Plug Flow Regime... 

---