Pressure drop across reactor

A catalyst manufactured using a shaped support assumes the same general size and shape of the support, and this is an important consideration in the process design, since these properties determine packing density and the pressure drop across the reactor. Depending on the nature of the main reaction and any side reactions, the contact time of the reactants and products with the catalyst must be optimized for maximum overall efficiency. Since this is frequendy accompHshed by altering dow rates, described in terms of space velocity, the size and shape of the catalyst must be selected carehiUy to allow operation within the capabiUties of the hardware. 

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

The riser pressure drop is related mainly to the catalyst circulation rate and the slip factor. Catalyst circulation rate is largely a function of the oil feed rate, the reactor temperature, and the feed temperature. Increasing the feed rate, reactor temperature, or lowering the feed temperature will increase the pressure drop across the riser. 

The pressure drop across the reactor cyclones, reactor vapor line, main fractionator, and main column overhead condensing/cooling system can be too high. The pressure drop is primarily a function of vapor velocity. Any plugging can increase the pressure drop. 

High pressure drop across the reactor overhead vapor line... 

Four pilot plant experiments were conducted at 300 psig and up to 475°C maximum temperature in a 3.07-in. i.d. adiabatic hot gas recycle methanation reactor. Two catalysts were used parallel plates coated with Raney nickel and precipitated nickel pellets. Pressure drop across the parallel plates was about 1/15 that across the bed of pellets. Fresh feed gas containing 75% H2 and 24% CO was fed at up to 3000/hr space velocity. CO concentrations in the product gas ranged from less than 0.1% to 4%. Best performance was achieved with the Raney-nickel-coated plates which yielded 32 mscf CHh/lb Raney nickel during 2307 hrs of operation. Carbon and iron deposition and nickel carbide formation were suspected causes of catalyst deactivation. 

At first glance, these results seem fantastic. Look at the case where S = 100. When the pressure drop across the pilot reactor is large, a mere 47% increase in length gives a 100-fold increase in inventory The pressure and the density increase by a factor of about 69. Multiply the pressure increase by the length increase and the factor of 100 in inventory has been found. The reactor volume increases by a factor of only 1.47. The inventory and the throughput scale as S. The scaling factor for volume is much lower, 1.47 instead of 100 in this example. 

Photomicrographs obtained following the second oxidation showed the appearance of small cracks throughout the pellets. In actual use, these cracks would be detrimental since they are the precursor to pellet fracture and subsequent compaction, which would result in increased pressure drop across the reactor. 

Weisman, J., A. Husain, and B. Harshe, 1978, Two-Phase Pressure Drop Across Abrupt Changes and Restriction, in Two-Phase Transport and Reactor Safety, T. N. Vezetroglu and S. Kakac, Eds., Taylor Francis, Inc., Washington, DC. (3)... 

If one desires to design a pilot scale tubular reactor to operate isothermally at 500 °C, what length of 6-in. pipe will be required to convert 90% of the raw feedstock to methyl acrylate The feedstock enters at 5 atm at a flow rate of 500 lb/hr. Ideal gas behavior may be assumed. A 6-in. pipe has an area of 0.0388 ft2 available for flow. Pressure drop across the reactor may be neglected. 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

Pressure drop across the reactor is negligible compared to the total pressure of the systeiri. 

Hollow cylindrical catalyst pellets are sometimes employed in commercial chemical reactors in order to avoid excessive pressure drops across a packed bed of catalyst. A more complex expression for the effectiveness factor is obtained for such geometry. This case was first discussed by Gunn [4]. Figure 2 illustrates the effectiveness factor curves obtained for the slab, sphere and cylinder. 

A differential pressure sensor monitors the pressure drop across the reactor, giving also an indication of the coke formation. The outside shell of the reactor is thermally insulated to limit heat loss. 

For many applications, like chemical-vapor-deposition reactors, the semi-infinite outer flow is not an appropriate model. Reactors are often designed so that the incoming flow issues through a physical manifold that is parallel to the stagnation surface and separated by a fixed distance. Typically the manifolds (also called showerheads) are designed so that the axial velocity u is uniform, that is, independent of the radial position. Moreover, since the manifold is a solid material, the radial velocity at the manifold face is zero, due to the no-slip condition. One way to fabricate a showerhead manifold is to drill many small holes in a plate, thus causing a large pressure drop across the manifold relative to the pressure variations in the plenum upstream of the manifold and the reactor downstream of the manifold. A porous metal or ceramic plate would provide another way to fabricate the manifold. 

As mentioned, the aim of the study is to develop desulfurization equipment of industrial interest so understanding its general performance is important. Several sets of typical operation data measured under stable operations are listed in Table 7.5. The comparable data are depending on coal type, S02 content in flue gas ranges from 1400 to 11400 mg/m while the permitted discharge level in China is normally 1200 mg/m3. The data show that the designed equipment exhibits satisfactory global performance and meets the requirements for desulfurization by wet process. Under moderate operation conditions, the content of S02 in the cleaned gas can achieve a much lower level than that permitted. Even if the mole ratio of Ca/S is as low as 1.0, a sulfur-removal efficiency of nearly 90% can be achieved (see the fourth row in Table 7.5) while the pressure drop across the reactor is very small, ca. 400 Pa only. 

The impinging stream gas-liquid reactor has low hydraulic resistance. In the range of operation conditions tested, the pressure drop across the reactor, Ap, is round 400 Pa only. 

In industrial fluidized bed reactors, the bed height is commonly fixed by an overflow weir. Thus, as the gas velocity, U, increases from Umf, the apparent bed density decreases. An important design principle for the gas distributor is to ensure its sufficient pressure drop for a uniform gas distribution, i.e., without gas channeling, and stable bed operation. Specifically, the total pressure drop across both the distributor and the bed should be in an increasing trend with an increase in the gas velocity. Suppose that the pressure drop across a perforated distributor, Apdistnbuior, with a total orifice area of Ao can be expressed by... 

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