Spherical reactor

Advances in multiphase reactors for fuel industry are discussed in this work. Downer reactors have some advantages over riser reactors, but suffer from some serious shortcomings. The coupled reactors can fully utilize the advantages of the riser and the downer. For fuel industry that involves gas-liquid-solid system, slurry bed reactors especially airlift reactors are preferred due to their performance of excellent heat control and ease of seale up. For high-pressure processes, the spherical reactor is promising due to its special characteristics. 

The other limit of real reactors is where the heat removal term is not infinite but instead is neghgible. We call case where Q — 0 the adiabatic reactor. For wall cooling. A, is proportional to for a tube and to for a spherical reactor. Since heat generahon is proportional to V and coohng is proportional to A, cooling becomes more difficult to maintain as the reactor becomes larger, and, as noted, large reactors fiequently must be operated adiabaticaUy. 

The initial conditions are at t = 0, T = To, andp = 0. The parameter n characterizes the dimensions of the volume for a parallel plate reactor n = 0 for a cylindrical reactor n = 1 and for a spherical reactor n = 2. In these equations, x is a space coordinate A. is the coefficient of thermal conductivity r is the characteristic size of the reactor k is the heat transfer coefficient and To is the initial temperature of the initial medium. 

While 8 is somewhat greater than 1, both p and / are somewhat smaller than 1. Therefore, for approximate calculations, epf can be set 1. The fission factor rj varies appreciably with the energy of the neutrons, as shown in Fig. 11.4 for The neutron losses in a reactor of finite dimensions can be taken into account approximately by the sum L +1 , where Ls is the mean slowing-down length of the fission neutrons in the moderator and L the mean diffusion length in the fuel-moderator mixture. For a spherical reactor of radius R the approximate relation is... 

When small catalyst pellets are required, the pressure drop can be signif. icant. In Example 4-6 we saw that significant design flaws can r ult if pressure drop is neglected or if steps are not taken to minimize pressure drop. One type of reactor that minimizes pressure drop and is also inexpensive to build is the spherical reactor, shown in Figure 4-8. In this reactor, called an ultraformer, dehydrogenation reactions such as... 

Another advantage of spherical reactors is that they are the most aco-nonucal shape for high pressures. As a first approximation we will as.sume that the fluid moves down through the reactor in plug flow. Consequently, because... 

Because the cross-sectional area of the reactor is small near the inlet and outlet, the presence of catalyst there would cause substantial pressure drop, thereby reducing the efficiency of the spherical reactor. To solve this problem, screens to hold the catalyst are placed near the reactor entrance and exit (Figures 4-9 and 4-10). Here L is the location of the screen from the center of the... 

Figure 4-9 Sttetnatic drawing of the inside of a spherical reactor.

Figure 4-10 Coordinate system and variables used with a spherical reactor. The initial and final integration values are shown as Zo and Z/.

By using these formulas and the standard pressure drop algorithm, one can solve a variety of spherical reactor problems. Note that Equations (4-38) and... 

Hinr. You could use Equation (P4,23-i), which would include dp and an unknown proportionality constant which you could evaluate from the data. For very small values of the Thiele modulus we know t = 1 and for very large values of the Thiele modulus we know that -n = 3/ = VCd. ] P4-24c Spherical reactor) Because it is readily available from coal, methanol has been investigated as an alternative raw material for producing valuable olefins... 

Because the pressure drop in the spherical reactor is very small, one could increase the reactant flow rate significantly and still maintain adequate pressure at the exit. In fact, Amoco uses a reactor with similar specifications to process 60,000 barrels of petroleum naphtha per day. 

P4-24c (Spherical reactor) Because it is readily available from coal, methanol has bem investi ted as an alternative raw material for producing valuable olefins... 

Let s consider carrying out this reaction in a spherical reactor similar tc one shown in the margin and discussed in detail in the CD-ROM. In a sp. cal reactor, the cross section varies as we move through Che reactor ar greater than in a normal packed-bed reactor. Consequently, the superficial i velocity C = will be smaller. From Equation (4-22). we see th... 

Example 4-6 Calculating X in a Reactor with Pressure Drop Example 4 7 Gas-Phase Reaction in Microreactor—Molar Flow Rate Example 4-8 Membrane Reaeior Example CDR4.1 Spherical Reactor Example 4.3.1 Aerosol Reactor Example 4-9 Isothermal Semibatch Reactor Profe.ssional Reference Shelf R4.1. Spherical Packed-Bed Reactor. ... 

Analysis of a spherical reactor equation along with an example problem carried out on the CD-ROM. 

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