Reactor dilute-phase

The initial application of fluidized beds in the petroleum industry was the upflow dilute-phase reactor (M45). The obvious disadvantage of this design is that all of the flowing catalyst passes overhead and must be removed in dust-removal equipment. Later, the basic design which finds widest application is the downflow dense-bed reactor (M2), which has the following major advantages (K26) ... 

Pressurized Hydrogasification of Raw Coal In a Dilute-Phase Reactor... 

The hydrocarbon feed rate to the reactor also affects the burning kinetics in the regenerator. Increasing the reactor feed rate increases the coke production rate, which in turn requires that the air rate to the regenerator increase. Because the regenerator bed level is generally held constant, the air residence time in the dense phase decreases. This decrease increases the O2 content in the dilute phase and increases afterbum (Fig. 5). 

Reactor dilute phase (dome) pressure Reactor catalyst dilute phase bed level Reactor-stripper catalyst bed level Reactor-stripper catalyst density Spent catalyst standpipe elevation Pressure above the spent catalyst slide valve Spent catalyst slide valve AP ( 55% opening)... 

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

Short contact time in the riser and in the reactor dilute phase... 

Thermal reactions are a function of time and temperature yields are proportional to (time) (exp " ). Figure 9-1 shows the typical elfects of vapor residence time and temperature on dilute phase cracking. For example, at 5 seconds residence time, the dry-gas yield increases 8% when the reactor temperature increases from 960°F to 9S0 "F. increasing the residence time to 10 seconds increases the dry gas yield another 8%. 

Eliminating long dilute-phase residence time downstream of the riser to prevent recracking of hydrocarbon vapors in the reactor housing. 

In a fluidized bed reactor, entrained particles leaving in a dilute phase stream are conventionally and desirably either partially or wholly condensed into a bulk stream and returned to the bed via a centrifugally driven cyclone system. At equilibrium, or when steady state operation is attained, any particle loss rate from the cyclones, as well as the remaining bed particle size distribution, are functions of (a) the rate of any particle attrition within the system and (b) the smallest particle size that the cyclone system was designed to completely collect (i.e., with 100% efficiency), or conversely the largest size which the system cannot recover. These two functions result in an interdependency between loss rate and bed particle size distribution, eventually leading to an equilibrium state (Zenz Smith, 1972 Zenz, 1981 Zenz Kelleher, 1980). 

Radioactive tracers [14] are a useful tool to measure unit parameters such as residence times and distribution of the catalyst and vapors in the reactor, stripper, or regenerator. Bypassing can be detected, slip factors calculated and dilute phase residence times are examples of useful calculations that can point the way to future modifications. This technology is also useful for detecting and analyzing equipment malfunctions. Plugged distributors, erratic standpipes, and main fractionator problems such as salt deposits or flooding can be detected with tracers. 

Use reaction mix sampling to determine amount dry gas made in the reactor dilute phase 9. Increase catalyst additions 10% or more and observe yield changes... 

In operation, preheated feedstock meets a controlled stream of hot. regenerated catalyst. Vaporized oil and catalyst ascend in the riser, such that the catalyst particles are suspended in a dilute phase. Essentially all of the cracking occurs in the riser. The catalyst particles are separated from the cracked vapors at the end of the riser and the catalyst containing a coke deposit is relumed in the regenerator. The cracked vapors puss through one or more cyclones located in the upper portion of the reactor and proceed to Ihe fractionator (main column) thai produces the side streams indicated. 

If the solid particles can be maintained in the fluidised state without problems of agglomeration or attrition, the fluidised bed reactor Fig. 1.45c is likely to be preferred. For short contact times at high temperatures the dilute phase transfer line reactor (Fig. 3.37[Pg.187]

Qader, et al., (4) reported work on hydrogenation in a dilute phase free fall reactor at temperatures in the order of 515°C, pressures of 2000 psi and with a heavy dose of catalyst, 15% stannous chloride by weight of coal. Up to 75% conversion was reported with a product distribution of 43% oil, 32% gas and 25% char. The residence time of the coal feed particles was estimated to be in the order of seconds, however, no measurement was made and aromatics were reported after further hydrorefining in a second stage hydrogenation. 

The concept is a dilute-phase hydrogasification process in which coal is directly reacted with hydrogen to produce maximum yield of methane in the reactor. We are not, as an organization, competitive with industry either in hardware or in process work. 

A schematic diagram of the reactor system of the 100 B/D plant is shown in Figure 13. There are three major vessels reactor, regenerator, and external cooler. The reactor consists of a dense fluid-bed section (60 cm ID x 13.2 m height) located above a dilute phase riser. Two modes will be studied to remove reaction heat ... 

C designates the non-reactive elemental carbon contained in the char product The chemical reaction is assumed to be the rate controlling step. This assumption is justified in the Discussion of Results. The reactions are considered to be first order with respect to fraction of carbon remaining in coal as well as converted to hydrocarbons and m 1 order with respect to H2 partial pressure. The details of the development of the model is reported elsewhere ( ). The experimental data correlated was obtained from dilute phase operation in an excess of hydrogen atmosphere, so the partial pressure of hydrogen was considered to be approximately equal to the total system pressure and was assumed constant along the length of the reactor. 

Viscosity. Dense phase solid-gas mixtures may be required to flow in transfer line catalytic crackers, between reactors and regenerators and to circulate in dryers such as Figures 9.13(e), (f). In dilute phase pneumatic transport the effective viscosity is nearly that of the fluid, but that of dense phase mixtures is very much... 

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