Reactor design, improvements

There exists a considerable literature on CVD (2) but relatively few attempts have been made to combine chemical and physical rate processes to give a complete representation of the deposition process. Most CVD studies have focused on demonstrating the growth of a particular material or crystal structure. However, the combined analysis is necessary in order to design CVD reactors where it is possible to deposit thin films of constant thickness and uniformity across an entire wafer. This is particularly important in the realization of submicron feature sizes for Very Large Scale Integrated Circuits. The further development of devices based on III-V compounds also depends on CVD reactor design improvements since the composition and thus the electronic properties of these materials vary considerably with process conditions. 

The use of excess reactants, diluents, or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes the recycling of unwanted byproduct to the reactor can inhibit its formation at the source. If this can be achieved, it improves the overall use of raw materials and eliminates effluent disposal problems. Of course, the recycling does in itself reuse some of the other costs. The general tradeoffs are discussed in Chap. 8. 

Evolving Reactor Design to Improve Heat Integration... 

Nuclear power has achieved an excellent safety record. Exceptions are the accidents at Three Mile Island in 1979 and at Chernobyl in 1986. In the United States, safety can be attributed in part to the strict regulation provided by the Nuclear Regulatory Commission, which reviews proposed reactor designs, processes appHcations forUcenses to constmct and operate plants, and provides surveillance of all safety-related activities of a utiUty. The utiUties seek continued improvement in capabiUty, use procedures extensively, and analy2e any plant incidents for their root causes. Similar programs intended to ensure reactor safety are in place in other countries. 

National Nuclear Corporation, New advanced gas-eooled reactors incorporate design improvements, Nud. Engr. Int., March 1981,27 36. 

Tubular reactors often offer the greatest potential for inventory reduction. They are usually simple, have no moving parts, and a minimum number of joints and connections that can leak. Mass transfer is often the rate-limiting step in gas-liquid reactions. Novel reactor designs that increase mass transfer can reduce reactor size and may also improve process yields. 

According to Wisseroth, the agitator design was quite important, and was very similar to those shown in reference 1. The speed was adjustable from 0-360 rpm and a gland packing seal was used. For special operations, metallic balls were added to the reactor to improve temperature stability (10). 

Some reactants in atmospheric-pressure reactors must be highly diluted with inert gases to prevent vapor-phase precipitation, while generally no dilution is necessary at low pressure. However, atmospheric pressure reactors are simpler and cheaper. They can operate faster, on a continuous basis and, with recent design improvements, the quality of the deposits has been upgraded considerably and satisfactory deposits of many materials, such as oxides, are obtained. 

Besides improvements in catalyst characteristics [28], the low productivity of a photocatalytic process can also be improved by reactor design. In photocatalytic research on a laboratory scale, the most widely applied reactors are the top illumination or annular reactors containing a suspended catalyst [29]. This type of... 

Minimization goes much further than storage, however. For many processes the largest inventory of hazardous materials is in the reactor. If, through radical reactor design, inventories and equipment size can be reduced whilst throughput is maintained, then this presents opportunities for improved safety and possibly reduced capital costs. This is the concept behind Process Intensification which is discussed more fully below. 

EVOLVING REACTOR DESIGN TO IMPROVE HEAT INTEGRATION... 

Tong, L. S., 1988, Principles of Design Improvement for Light Water Reactors, Hemisphere, New York. 

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