Sequencing reactors

Conversion arid Reactor Sfeing Chap. 2 Example Z-7 Companng the Order of Sequencing Reactors... 

As was described in the review of previous work, over the last ten years MINLP optimization models have been reported for the synthesis of process flowsheets, heat-exchanger networks, separation sequences, reactor networks, utility plants, and design of batch processes. Rather than describing in detail each of these works, we will briefly highlight several examples from our research group at Carnegie Mellon to illustrate the capabilities and the current limitations of the MINLP approach. 

The choice of configuration is usually made on the basis of the requirements of the two processes and the expected advantages to be gained. The conventional sequence reactor-separator shown in scheme 1 represents the trivial case of no integration. If the two processes are really interrelated, their coexistence affects the rate or the yield of the reaction and/or separation. Both schemes 2 and 3 could be used in this circumstance. Scheme 3 offers the possibility to operate both processes in the same equipment, thus making a saving of space and investment costs in comparison to scheme 2. Catalytic membranes are just a particular case of scheme 3. 

The problem with this approach is obvious. It involves a considerable amount of work to generate a measure of the quality of the sequence, the total vapor load, which is only a guideline. There are many other factors to be considered. Indeed, as we shall see later, when variables such as reactor conversion are optimized, the sequence might well need readdressing. 

Also, if there are two separators, the order of separation can change. The tradeoffs for these two alternative flowsheets will be different. The choice between different separation sequences can be made using the methods described in Chap. 5. However, we should be on guard to the fact that as the reactor conversion changes, the most appropriate sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

We should be on guard for the fact that as the reactor conversion changes, the most appropriate separation sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

If a fluid is placed between two concentric cylinders, and the inner cylinder rotated, a complex fluid dynamical motion known as Taylor-Couette flow is established. Mass transport is then by exchange between eddy vortices which can, under some conditions, be imagmed as a substantially enlranced diflfiisivity (typically with effective diflfiision coefficients several orders of magnitude above molecular difhision coefficients) that can be altered by varying the rotation rate, and with all species having the same diffusivity. Studies of the BZ and CIMA/CDIMA systems in such a Couette reactor [45] have revealed bifiircation tlirough a complex sequence of front patterns, see figure A3.14.16. 

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

The raw material for nuclear reactor fuel, uranium, exits the mining—milling sequence as uranium oxide. Because of its color, it is called yellow cake. The yellow cake is converted to uranium hexafluoride and enriched in 235u... 

Shift Conversion. Carbon oxides deactivate the ammonia synthesis catalyst and must be removed prior to the synthesis loop. The exothermic water-gas shift reaction (eq. 23) provides a convenient mechanism to maximize hydrogen production while converting CO to the more easily removable CO2. A two-stage adiabatic reactor sequence is normally employed to maximize this conversion. The bulk of the CO is shifted to CO2 in a high... 

The sequencing batch reactor (SBR) or intermittent process is a combination of complete mix and plug dow, and usually controls filamentous bulking. The nature of the process eliminates the need for an external clarifier. 

The Catofin process, which was formerly the property of Air Products (Houdry Division), uses a proprietary chromium catalyst in a fixed-bed reactor operating under vacuum. There are actually multiple reactors operating in cycHc fashion. In sequence, these reactors process feed for about nine minutes and are then regenerated for nine minutes. The chromium catalyst is reduced from Cr to Cr during the regeneration cycle. 

This is the equation for a plug flow reactor. It can be derived directly from the rate equations with the aid of Laplace transforms. The sequences of second-order reactions of Figs. 7-5n and 7-5c required numerical integrations. 

Flexible batch. Both the formula and the processing instructions can change from batch to batch. Emulsion polymerization reactors are a good example of a flexible batch facility. The recipe for each produc t must detail Both the raw materials required and how conditions within the reac tor must be sequenced in order to make the desired product. 

Process equipment function changes with different steps in process sequence (e.g., same vessel used as feed tank, reactor, crystallizer pump... 

Process equipment function changes with different steps in process sequence (e.g., same vessel used as feed tank, reactor, crystallizer pump used to pump in/out). Instrumentation and controls not kept in phase with the current process step (e.g., control set points, interlocks etc.). 

Sequence errors refer to situations when a person performs a task, or an individual step in a task, out of sequence. For example, charging the reactor before starting the cooling water flow. 

Initiating Event Feed Shuts Off Reactor Dump Works Accident Sequence Number Frequency (events/yr) Consequence (impacts/event)... 

The two main principles involved in establishing conditions for performing a reaction are chemical kinetics and thermodynamics. Chemical kinetics is the study of rate and mechanism by which one chemical species is converted to another. The rate is the mass in moles of a product produced or reactant consumed per unit time. The mechanism is the sequence of individual chemical reaction whose overall result yields the observed reaction. Thermodynamics is a fundamental of engineering having many applications to chemical reactor design. 

Fan, L. T., Erickson, L. E., Sucher, R. W., and Mathad, G. S. (1965). Optimal design of a sequence of continuous-flow stiired-tank reactors with product recycle. Ind Eng Chem., 4, 432—440. 

When used to identify and evaluate significant risk contributors, as well as to assess the consequences of accident sequences, the PSA provides a comprehensive framework for making many types of decisions regarding reactor design, operation, and siting. These and other appi ications can be facilitated by the rational evaluation of the risks associated with a particular installation. 

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