Equipment sizing chemical reactors

All chemical reactions are accompanied by some heat effects so that the temperature will tend to change, a serious result in view of the sensitivity of most reaction rates to temperature. Factors of equipment size, controllability, and possibly unfavorable product distribution of complex reactions often necessitate provision of means of heat transfer to keep the temperature within bounds. In practical operation of nonflow or tubular flow reactors, truly isothermal conditions are not feasible even if they were desirable. Individual continuous stirred tanks, however, do maintain substantially uniform temperatures at steady state when the mixing is intense enough the level is determined by the heat of reaction as well as the rate of heat transfer provided. 

Chemical reactors are the most important features of a chemical process. A reactor is a piece of equipment in which the feedstock is converted to the desired product. Various factors are considered in selecting chemical reactors for specific tasks. In addition to economic costs, the chemical engineer is required to choose the right reactor that will give the highest yields and purity, minimize pollution, and maximize profit. Generally, reactors are chosen that will meet the requirements imposed by the reaction mechanisms, rate expressions, and the required production capacity. Other pertinent parameters that must be determined to choose the correct type of reactor are reaction heat, reaction rate constant, heat transfer coefficient, and reactor size. Reaction conditions must also be determined including temperature of the heat transfer medium, temperature of the inlet reaction mixture, inlet composition, and instantaneous temperature of the reaction mixture. 

The rate equation is fundamental to the design of any chemical reactor. PI This equation describes the rate at which a chemical process takes place with respect to the physical dimensions of the reactor and, therefore, the size of the equipment needed to reach the desired level of cleaning for a given solvent throughput. PI... 

For industrial production of chemical compounds, it is obvious that faster reactions are better than slower reactions as long as they are controllable. With faster reactions, a greater quantity of compounds can be produced per unit time. The productivity per unit volume of a reactor also increases with increase in the reaction rate. The use of extremely fast reactions in conjunction with flow systems may lead to a smaller size of reactor in chemical plants, which leads to lower cost for investment in plants and equipment. In addition, faster synthesis leads to lower cost of labor because the working hour per unit weight of products is shorter. 

Mapping Results. After Aspen IPE has mapped and sized the equipment items, it is prudent to check the results, especially for major equipment items such as towers, compressors, and chemical reactors. These items are usually very expensive, and consequently, it is a good practice to estimate equipment sizes independently for comparison with the Aspen IPE results. To view the Aspen IPE results for an equipment item, double click on the item on the IPE Workbook window or on its icon in the Process Flow Diagram. For example, the following component specification form, which contains some of the sizing results, is obtained for the depropanizer tower. 

Since high levels of heat transfer are required, as well as a reaction scheme with the main aim of reducing the equipment size to be used in an automotive vehicle, an integrated chemical reactor and compact heat exchanger (Brown et al., 2(X)4) appears to be the most promising process intensification technology suitable for this task. 

To ensure flexibility the size of the reaction and separation units and the feed and side-drawn points in column are changeable. The construction idea was to couple all equipment with quick connectors so that all devices are easy to reconnect when needed. The main facility consists of separation units connected to a series of chemical reactors. The reactors can be used as traditional prereactors followed by separation and recycle, or as side reactors closely connected to the column. The design pressure range is 0-20 bar(g) and the design temperature range is from -30°C up to 200°C. The capacity range is 5-20 litres per day. 

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