Reactor choice design

Before the details of a particular reactor are specified, the biochemical engineer must develop a process strategy that suits the biokinetic requirements of the particular organisms in use and that integrates the bioreactor into the entire process. Reactor costs, raw material costs, downstream processing requirements, and the need for auxiliary equipment will all influence the final process design. A complete discussion of this topic is beyond the scope of this chapter, but a few comments on reactor choice for particular bioprocesses is appropriate. 

Besides the classical engineering question of reactor choice, the most important point in enzyme reactor design is the aspect of enzyme reuse, either by immobilization or by separation from the product stream. Batch processes without enzyme reuse are only possible if the costs of the biocatalyst are negligible. Different reactor techniques addressing the aspect of enzyme reuse are discussed in the following sections. 

Nuclear reactors are designed for production of heat, mechanical and electric power, radioactive nuclides, weapons material, research in nuclear physics and chemistry, etc. The design depends on the purposes, e.g. in the case of electric power production the design is chosen to provide the cheapest electricity taking long term reliability in consideration. This may be modified by the availability and economy of national resources such as raw material, manpower and skill, safety reasons, etc. Also the risk for proliferation of reactor materials for weapons use may influence the choice of reactor type. Many dozois of varying reactor concepts have been formulated, so we must limit the discussion in this chapter to a summary of the main variables, and the most common research and power reactors. Fast reactors and some other designs are discussed in Chapter 20. 

Prismatic graphite-block fuel with traditional refueling. The LS-VHTR would be fueled with prismatic fiiel and refueled when shut down. This particular fuel geometry provides a large latitude for the reactor core designer in the choice of (1) fuel-moderator-coolant ratios and (2) core geometry. 

Neither choice would present incremental nuclear safety vulnerability - because the reactor is designed to passively accommodate a loss of heat sink accident and, therefore, a flibe pipe break or freeze-up is expected to present no hazard to the reactor. A decision is yet to be made between the two approaches. 

There are some problems encountered such as residential time distribution and deposition on the wall. The residential time distribution can induce widening of the particle size distribution. This can be solved by proper design of the reactor or designing the operation such that the reaction time is reduced or by introducing segmented flow. The deposition of reactant on the wall can cause critical problems because it can induce clogging, uncontrollable flow, particle size distribution widening, and reduction of product yields. To solve these problems, proper choice of reaction systems and wall materials is necessary. Furthermore,... 

Since process design starts with the reactor, the first decisions are those which lead to the choice of reactor. These decisions are among the most important in the whole design. Good reactor performance is of paramount importance in determining the economic viability of the overall design and fundamentally important to the environmental impact of the process. In addition to the desired products, reactors produce unwanted byproducts. These unwanted byproducts create environmental problems. As we shall discuss later in Chap. 10, the best solution to environmental problems is not elaborate treatment methods but not to produce waste in the first place. 

Having made a choice of the reaction path, we need to choose a reactor type and make some assessment of the conditions in the reactor. This allows assessment of reactor performance for the chosen reaction path in order for the design to proceed. 

In the design of a fine chemicals plant equally important to the choice and positioning of the equipment is the selection of its size, especially the volume of the reaction vessels. Volumes of reactors vary quite widely, namely between 1,000 and 10,000 L, or ia rare cases 16,000 L. The cost of a production train ready for operation iacreases as a function of the 0.7 power. The personnel requirement iacreases at an even lower rate. Thus a large plant usiag large equipment would be expected to be more economical to mn than a small one. 

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