Reactor pressure drop

A summary of the nine batch reactor emulsion polymerizations and fifteen tubular reactor emulsion polymerizations are presented in Tables III IV. Also, many tubular reactor pressure drop measurements were performed at different Reynolds numbers using distilled water to determined the laminar-turbulent transitional flow regime. 

Reactor type Wide fxed-bed reactor Pressure-drop channels number, width, depth 256 40 pm 20-25 pm... 

In addition to experiments performed with pretreated silver, experiments were also conducted with preoxidized silver samples. The preoxidized samples were prepared by exposing a clean silver sample to 650 Torr of oxygen at 473 K for 1 hour. Oxygen adsorption was determined by measuring the reactor pressure drop over the 1 hour exposure period. For a typical sample, the pressure drop corresponded to an oxygen uptake of 1x10 0-atoms/gram of silver. 

The more expensive the catalyst, the higher the optimum recycle flowrate (and reactor pressure drop). We are trading off recycle costs with reactor costs. No bypass flow is needed when the inlet temperature is 475 K or higher. The optimum y A/y B ratio decreases as recycle flowrate increases because the costs associated with heat transfer and compression are lower with more B in the gas because of its higher molar heat capacity. 

Pressure Drop, Mass and Heat Transfer Pressure drop is more important in reactor design than in analysis or simulation. The size of the compressor is dictated by pressure drop across the reactor, especially in the case of gas recycle. Compressor costs can be significant and can influence the aspect ratio of a packed or trickle bed reactor. Pressure drop correlations often may depend on the geometry, the scale, and the fluids used in data generation. Prior to using literature correlations, it often is advisable to validate the correlation with measurements on a similar system at a relevant scale. 

The response variables included virtually everything that one might observe in a real reactor — reactor maximum and outlet temperatures, reactor outlet concentrations of butyraldehyde, butanol, and byproducts, inlet and outlet dewpoint temperatures, catalyst productivity, reactor pressure drop, and so on. 

The constraints changed from one trial configuration of the reaction system to the next, but typically included things like the minimum coolant temperature to permit efficient utilization of the heat of reaction as process steam, the maximum allowable aldehyde concentration in the condensed crude product to avoid refining and product specification problems, and a prescribed reactor pressure drop to insure adequate flow distribution among the reactor tubes at a minimum energy cost. All of these are implicit constraints — they establish the maximum or minimum levels for certain response variables. Explicit constraints comprise the ranges for search variables. 

Calculate the reactor pressure drop, Ap, from Equation 7.11.2. 

All the three systems employed graded bed in order to tackle the reactor pressure drop, especially at the front end where the operating temperatures are lower and catalyst encounters the virgin stock. 

As expected, the behavior of Catalyst System-C was similar to that of Catalyst System-B in view of similar HDM catalyst guard at the front end. However, the reactors pressure drop was much higher from the SOR itself, enforcing a lower Gas/Oil ratio that resulted in enhanced catalyst fouling and deactivation. The higher pressure drop was related to the characteristics (i.e. size and shape) of the catalyst. The products yield was, as expected, similar to that of Catalyst System-B. 

Eixure 13. Typical reactor pressure drop for catalyst particles. 

A reasonable starting point for design equations relevant to tubular reactors (pressure drop, heat transfer coefficients, standard pipe and tubing sizes) remains ... 

In catalytic applications, monoliths can provide better control of the contact time of reactants and products with the catalyst. This leads to a potential increase in selectivity. Together with the advantages over conventional trickle-bed reactors (pressure-drop surface area, short diffusion lengths), this makes the monohth reactor very suitable for use in consecutive reaction schemes, such as selective oxidation or hydrogenation. Literature dealing with carbon monolith structures is not yet extensive, however, and a limited number of applications have been reported, as shown in Table 11.2. 

Besides the physical concepts leading to eqs. (15) to (18), we need one more concept, and that is the law of conservation of mass. Applied to porous catalyst in a steady state of reaction, this law says that the total mass of matter which flows into a pellet or pore (or any region thereof) must equal the mass that flows out. For example, in Fig. 4 the mass of reactants plus products which flows across the plane at M must equal the mass of these which flows across the plane at N. The most important special case is the usual one encountered for catalysts of small pore size in reactors operating at low pressure drops across the reactor. For such catalysts the Poiseuille flow forced through the pellet by the reactor pressure drop will be negligible so that there will be no net transport of mass... 

We note that under Knudsen flow conditions (small pores, moderate pressures) the forced flow through pores due to reactor pressure drop cannot ever be important. This is because the available Knudsen diffusion gradient due to reaction is of the order of 1000 times larger than the very small concentration gradient caused by reactor pressure drop, and the Knudsen diffusion coefficient is identical with the Knudsen forced flow coefficient. 

Reactor Pressure Drop (Fixed/Packed Beds)... 

Reactor pressure drop is a best estimate (calculated) value, and... 

Table 2.2 presents the evolutions of these quantities for three types of scale dependence of the operation time m = 0, 1 and 2. For heterogeneous reaction and heat/mass transfers, maintaining either the channels number or their length while reducing the radius induces systematically an increase in the reactor pressure drop that can even become prohibitive. However, by choosing an appropriate channel number and channel length, the pres sure drop for these reactors can be maintained or even reduced. However, this is generally combined with an increase in the reactor cross-section. 

Figure 5—9 illustrates one method to mitigate this problem. Baskets, partially filled with catalyst support balls, are inserted in the Claus plant catalyst bed. The depths of the baskets are sufficient to double the exposed surface area at the lop of the bed. While the effect on the initial reactor pressure drop is small, during the course of a one-year run, the average reduction in pressure drop was estimated to be 30%. The baskets shown in Figure 5-9 were only installed in the first reactor, as encrustation at the top of the second and third reactors is less of a problem. 

The loss in overall conversion of H2S to liquid sulfur due to the shorter average catalyst bed depth of the first reactor was loo small to observe. Also, no shift in reactor temperature rise from the first to second reactors was observed. This loo indicated that the shorter average reactor bed did not adversely affect conversion. The average 30% reduction in the first reactor pressure drop resulted in an approximate increase in Claus capacity of 2%. 

Because of the low gas and liquid mass velocities in pilot plant reactors, pressure drop is low and generally difficult to measure. In commercial reactors, however, it is usually important and computations of pressure drop are usually needed to set pump and compressor designs. Several pressure drop correlations are available in the literature. One poDular one is that by Larkins, White and Jeffrey [39] modified by Reiss [58] which applies to both the trickle gas continuous regime and the pulse flow regime. The correlation is represented below. 

Problems 12-16 investigate the performance of the reactor section for a noncatalytic process for the hydrodeallg lation of toluene to produce benzene. Reactor R-101 in Figure 20.4Vbl operated at the flow conditions shown represents a base case (inlet pressure is 25 bar). Kinetics are given in Table 20.1. Ignore reactor pressure drop. Reactor volume for base case is 4.76 m. ... 

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