Single reactors

The inlet and outlet molar flow rates are related through the extents of reaction. If R independent reactions take place, and if the extents of reaction are zero in the Stream that enters the reactor. 

Energy balance— whole reactor— multiple reactions 

We wiU assume that the feed and product Streams are ideal solutions, so that the partial molar enthalpies, Hi, can be replaced by pure component enthalpies. Hi. The ideal solution assumption usually is reasonably good for gas-phase reactions, provided that the pressure is not too high. Moreover, this assumption may be necessary for reactiois in solutioi, at least for preliminary calculations, until a sound Ihermocfynamic description of non-ideaKties is available. Thus, 

The term is just the enthalpy change on reaction, i.e., the heat ofreaction, for Reaction 

If the pressure difference between the feed and product Streams is not substantial, and if there are no phase changes 

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Wetox uses a single-reactor vessel that is baffled to simulate multiple stages. The design allows for higher destmction efficiency at lower power input and reduced temperature. Its commercial use has been limited to one faciHty in Canada for treatment of a complex industrial waste stream. Kenox Corp. (North York, Ontario, Canada) has developed a wet oxidation reactor design (28). The system operates at 4.1—4.7 MPa (600 to 680 psi) with air, using a static mixer to achieve good dispersion of Hquid and air bubbles. 

The entire QSL process takes place in a single reactor as shown in Figure 6 (15). The reactor consists of an almost horizontal, refractory-lined cylinder, which can be tilted by 90° when operation is intermpted. Concentrates, fluxes, recirculated flue dust, and normally a small amount of coal, depending on the type of concentrate, are pelletized. The pelletizer ensures that the raw materials are mixed to the required degree of uniformity. 

In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

The optimum pH for both enzymes was 7.5-8.0. For practical production it is desirable to carry out a reaction in a single reactor at optimum pH. Therefore, it is most advantageous to carry our the two step enzyme reaction at pH 8.0. 

D. Blum Just going a bit further, the liquid-phase methanation process now uses one reactor. You can or you cannot use a polishing reactor as the economics dictate. You can actually go right to pipeline quality gas in one reactor, which is equivalent to about 99.8% conversion of a 20% CO feed gas. We envision at this moment that combined shift-methanation could be done in the same single reactor. It would obviously require lower feed gas rates so you may need two of these reactors. We don t exactly have the numbers yet. I think that s one of the areas that deserves future work. 

So far, consideration has been limited to chemistry physical constraints such as heat transfer may also dictate the way in which reactions are performed. Oxidation reactions are highly exothermic and effectively there are only two types of reactor in which selective oxidation can be achieved on a practical scale multitubular fixed bed reactors with fused salt cooling on the outside of the tubes and fluid bed reactors. Each has its own characteristics and constraints. Multitubular reactors have an effective upper size limit and if a plant is required which is too large to allow the use of a single reactor, two reactors must be used in parallel. 

A parallel reactor system has an extra degree of freedom compared with a series system. The total volume and flow rate can be arbitrarily divided between the parallel elements. For reactors in series, only the volume can be divided since the two reactors must operate at the same flow rate. Despite this extra variable, there are no performance advantages compared with a single reactor that has the same total V and Q, provided the parallel reactors are at the same temperature. When significant amounts of heat must be transferred to or from the reactants, identical small reactors in parallel may be preferred because the desired operating temperature is easier to achieve. 

The general rule is that combinations of isothermal reactors provide intermediate levels of performance compared with single reactors that have the same total volume and flow rate. The second general rule is that a single, piston flow reactor will give higher conversion and better selectivity than a CSTR. Autocatalytic reactions provide the exception to both these statements. 

Example 4.10 Consider a reactor train consisting of a CSTR followed by a piston flow reactor. The total volume and flow rate are fixed. Can series combination offer a performance advantage compared with a single reactor if the reaction is autocatalytic The reaction is... 

Determine the minimum operating cost for the process of Example 6.2 when the reactor consists of two equal-volume CSTRs in series. The capital cost per reactor is the same as for a single reactor. 

The process can be operated under moderate conditions (50-130 °C and 3-10 bar) in a single reactor. Regeneration of cupric chloride occurs in a separate oxidizer. 

The whole system is constructed from two silicon wafers, fabricated using photoresist by deep reactive ion etching (DRIB) [21]. The wafers were thermally bonded. Thereafter, inlet and outlet ports were machined and the single reactors isolated by DRIB. 

Figure 4.24 Modular micro-reactor system. Left single reactor module with (length 60 mm). Right mounted system of four single reactors (overall length 24 cm) [51].

OS 68] [R 19] [P 50] A numbering-up of five mini mixers, tested at the pilot stage, was used [134]. Automation of the entire process was required liquid-flow splitting to the single reactors was ... by no means trivial... [134]. The capacity of one mini reactor was 30 ml s , i.e. 1081 h . The complete setup hence should be operated close to 5001 h . The micro-reactor plant was operated at intervals as the preceding step was carried out batchwise. The operation of the micro-reactor plant started in August 1998 after a period of only about 1.5 years for development. 

Table VIII demonstrates the inverse relationship of conversion to S02 concentration in the feed that is a consequence of applying flow reversal to S02 oxidation using a single reactor. As the S02 concentration in the table moves from 0.8 to over 8 vol%, the conversion drops from 96-97% down to 85%. At the same time, the maximum bed temperature changes from 450 to 610°C. For an equilibrium-limited, exothermic reaction, this behavior is explained by variation of the equilibrium conversion with temperature.

Thus j plug flow reactors in series with a total volume Ik, totai give the same conversion as a single reactor of volume VRttota]. 

For the case where the cascade consists of only a single reactor, only a single straight line of the form of equation 8.3.31 is involved in the graphical solution. One merely links the point on curve M corresponding to the effluent concentration of benzoquinone with the point on the abscissa corresponding to the feed concentration. The slope of this line is equal to ( — 1/t) or — io/VR). In the present instance the slope is equal to... 

The selectivity of a catalyst is typically optimized towards a reaction type, but some operations required a high level of removal for more than one contaminant. In fact, the treatment of a VGO, for instance, involves the removal of metals, S and N. Depending on the quality of the feed and on the specifications of the desired product, the hydrotreatment may require more than one catalyst. The catalyst can be stacked in a single reactor or disposed in sequential stages, when more than one reactor is available. Stacked-bed reactors with more than one catalyst type are a common practice in HDT. 

In Section 2.2 (this Chapter), we mentioned the difficulties in trying to comply with the new specifications by using single reactor units. From the above discussion, it appears that a second (high-pressure) reactor, with H2S (inter-reactor) scrubbing facilities is the way to go. 

The Syn technology is oriented to the production of ULSD, to the saturation of aromatics and to the improvement of cetane number. These processes can be run in a single reactor unit, in which case, the initial part of the reactor is fed in a co-current way,... 

UOP offers a family of technologies to conform the MQD Unionfining. It can be applied in a single reactor or in a two reactor systems, in different arrangements to process VGO, as well as SR distillates and cracked distillates. More than one reactor combined-systems also incorporate inter-reactor stripping (Fig. 13). 

Heavy fractions (e.g., vacuum gas oils) and residues HDP might involve both, hydrotreatment and hydrocracking operations. HDT, in this case, is a feed pretreatment, for preparation to another process unit, which might be a HCK unit. This process combination, HDT-HCK can be used on Cycle Oil (FCC, coker), VGO (SR and coker) and SR residues (atmospheric and vacuum). It can be carried out in a single reactor with more than one catalyst, or in more than one reactor. 

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