Reactor sizing

Pilot plants utilizing a single-full-sized reactor tube from a commercial plant are generally used to assess the quaUty and performance of individual catalyst lots and to perform plant or customer ordered process tests. A weU-designed pilot unit is capable of simulating the performance of a commercial plant with great accuracy. 

If the downtime is 45 min per batch, what size reactor is needed for 90% conversion ... 

In previous studies, the main tool for process improvement was the tubular reactor. This small version of an industrial reactor tube had to be operated at less severe conditions than the industrial-size reactor. Even then, isothermal conditions could never be achieved and kinetic interpretation was ambiguous. Obviously, better tools and techniques were needed for every part of the project. In particular, a better experimental reactor had to be developed that could produce more precise results at well defined conditions. By that time many home-built recycle reactors (RRs), spinning basket reactors and other laboratory continuous stirred tank reactors (CSTRs) were in use and the subject of publications. Most of these served the original author and his reaction well but few could generate the mass velocities used in actual production units. 

The scheme of commercial methane synthesis includes a multistage reaction system and recycle of product gas. Adiabatic reactors connected with waste heat boilers are used to remove the heat in the form of high pressure steam. In designing the pilot plants, major emphasis was placed on the design of the catalytic reactor system. Thermodynamic parameters (composition of feed gas, temperature, temperature rise, pressure, etc.) as well as hydrodynamic parameters (bed depth, linear velocity, catalyst pellet size, etc.) are identical to those in a commercial methana-tion plant. This permits direct upscaling of test results to commercial size reactors because radial gradients are not present in an adiabatic shift reactor. 

Viable operating eonditions were identified experimentally for maximising the produetion of ethylene, propylene, styrene and benzene from the pyrolysis of waste produets. Data are given for pyrolysis temperature, produet reaetion time, and quench time using a batch microreactor and a pilot-plant-sized reactor. 26 refs. CANADA... 

Therefore, there is a maximum size reactor for each set of reaction conditions. This size will now be calculated. The maximum rate of heat production will be determined first. 

All the previous calculations have been done using GPPS. It will be assumed that the same conditions apply MIPS and HIPS except that the reaction times are different. For economic purposes the same size reactor will be used for each product. For MIPS the reaction takes 0.5 hr longer however, only one-third as much product is planned. 

Together we need 3 reactors for MIPS and HIPS, making a total of 7 reactors needed. An eighth will be installed as a spare. This will allow full production to continue if cleaning out the reactors becomes more of a problem than expected. Obviously a standard size reactor will be chosen it may be somewhat below the size calculated. (A similar statement can be made for each piece of equipment listed.)... 

Batch reactors are often used for liquid phase reactions, particularly when the required production is small. They are seldom employed on a commercial scale for gas-phase reactions because the quantity of product that can be produced in reasonably sized reactors is small. Batch reactors are well suited for producing small quantities of material or for producing several different products from one piece of equipment. Consequently they find extensive use in the pharmaceutical and dyestuff industries and in the production of certain specialty chemicals where such flexibility is desired. When rapid fouling is encountered or contamination of fermentation cultures is to be avoided, batch operation is preferable to continuous processing because it facilitates the necessary cleaning and sanitation procedures. 

The size reactor needed to perform a specified task under specified operating conditions may be determined. 

As Levenspiel points out, the optimum size ratio is generally dependent on the form of the reaction rate expression and on the conversion task specified. For first-order kinetics (either irreversible or reversible with first-order kinetics in both directions) equal-sized reactors should be used. For orders above unity the smaller reactor should precede the larger for orders between zero and unity the larger reactor should precede the smaller. Szepe and Levenspiel (14) have presented charts showing the optimum size ratio for a cascade of two reactors as a function of the conversion level for various reaction orders. Their results indicate that the minimum in the total volume requirement is an extremely shallow one. For example, for a simple... 

For the case of multiple equal-sized reactors in series, the problem of determining the reactor sizes necessary to achieve a specified degree of... 

For a first-order reaction, we showed that for a cascade composed of equal-sized reactors, equation 8.3.42 governed the effluent composition from the nth reactor. 

One of the first things that should be done in the analysis is to determine if pressure variations along the length of a reasonable-size reactor will be significant for the specified operating conditions. This will require a knowledge of the superficial mass velocity through the tubes. This quantity may be calculated from the tube dimensions and the inlet flow rate and... 

When scaling a conventional centimetre-sized reactor down to the micron scale, the surface-to-volume ratio significantly increases to the point where the container walls can effectively become an active or influential part of the reaction or process occurring in the fluidic channel. Clearly this attribute of micro-reactors can be viewed in a positive way and leads to the opportunity of exploiting surface-dependent performance including electrokinetic driven flow, surface functionalisation and mass transfer, and heat transfer. 

Equations (2) and (1) together with the appropriate temperature equation, (3) or (4) or (5), are solved by POLYMATH. The full flow and the split flow operations give the same conversion in the same size reactors. At half flowrate, the values are x2 = 0.5 and T2 = 1521 at the midpoint, the same as the final values of the full stream. 

A 95% conversion of reactant A is required in a tubular reactor for which we anticipate DluL will be 0.5. The reaction is first order with rate coefficient, k, equal to 0.16 min and there is no change in volume on reaction 107 dm min of feed must be treated. What size reactor is required ... 

What size reactor is needed for 50% decomposition of ozone This problem is a modification of a problem given by Corcoran and Lacey (1970). 

Now the space-time t (or mean residence time t) is the same in all the equal-size reactors of volume V,. Therefore,... 

The optimum size ratio for two mixed flow reactors in series is found in general to be dependent on the kinetics of the reaction and on the conversion level. For the special case of first-order reactions equal-size reactors are best for reaction orders n > 1 the smaller reactor should come first for n < 1 the larger should come first (see Problem 6.3). However, Szepe and Levenspiel (1964) show that the advantage of the minimum size system over the equal-size system is quite small, only a few percent at most. Hence, overall economic consideration would nearly always recommend using equal-size units. 

We want to design a commercial-sized reactor to treat large amounts of feed to 80% conversion at the above temperature and pressure. Our choice... 

One can begin to diagnose the performance of a catalytic reactor very quickly with very limited knowledge of its properties by considering the effects of (1) temperature, (2) stirring, and (3) pellet size. Reactor engineers should always be aware of these effects in any catalytic process. 

Another factor which contributes most to the high cost of the alkylation process is the necessity of having a large excess of isobutane in the reaction zone. This requirement results in increased capital costs for over-sized reactors, settlers, fractionators, and accessories, as well as in increased operating costs of this equipment. Process developments which would allow satisfactory operations at considerably lower isobutane-to-olefin ratios would help reduce these costs. Such developments might again involve improvements in reactors or in catalysts. 

The effect of plant capacity on investment can be seen from Fig. 8.2-3. Costs of around 245 million DM, or only 817 DM/t on the 1997 basis, are required for plants equipped with maximum-stream-size reactors of 300,000 t/a. The data can be extrapolated to actual (1998) costs by means of the price index of 1.01 published in [1], These plants with large design capacities have significantly reduced specific investment costs. 

The multiplication factor for an infinite sized reactor core is given by the four-factor formula ... 

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