Catalyst fluidization

Catalyst circulation is like blood circulation to the human body. Without proper catalyst circulation, the unit is dead. Troubleshooting circulation problems requires a good understanding of the pressure balance around the reactor-regenerator circuit and the factors affecting catalyst fluidization. The fundamentals of fluidization and catalyst circulation are discussed in Chapter 5. 

Optical fiber measurement of local solids concentrations of FCC catalyst fluidized in a 9-cm-i.d. column gave the results shown typically in Fig. 26. Analysis of these data showed that the radial voidage profile could be described solely by the cross-section-average voidage e, calculated as shown in Sec. 5.1, and the reduced radial coordinate r/R ... 

As practiced today, FCC is a fluidized-bed process with continuous catalyst regeneration which reUes on short contact in a riser reactor between the feed and catalyst, fluidized with an inert gas, followed by disengagement and catalyst regeneration to burn off coke deposits and return the catalyst to near-fresh activity. 

Chapter 20 Reactors with Suspended Solid Catalyst, Fluidized Reactors of Various Types /447... 

In the Riser Simulator, an impeller rotating at very high speed on the top of the reaction chamber keeps the catalyst fluidized between two metal porous plates, inducing the internal circulation of the reacting mixture in an upward direction through the chamber. When the reactor is at the desired experimental conditions, the reactant is fed through an injection port, and immediately after the set reaction time is attained, products are evacuated and analyzed by gas chromatography. Of particular importance to the experiments performed was the ability to extend reaction... 

The experiments of Stewart (S20) show (Fig. 53) that the radius of an observed bubble cloud at 0 = 0 falls between Eqs. (6-1) and (6-2). Figure 54 shows the thickness of the cloud-overlap region estimated by Eqs. (6-1) and (6-2) for a flne microspherical catalyst fluidized by ambient air, where the minimum fluidization velocity Vmt is calculated by Wen and Yu s equation (W4). The cloud-overlap region is seen as being limited to at most a few layers of fine particles (M30). Rieke and Pigford (R8) observed experimentally for a two-dimensional fluidized bed that the gas in the... 

CO is an especially powerful poison if added directly to a divalent chromium catalyst prior to its placement into the reactor [377], Added in this way, it does not need to displace ethylene in order to poison a site. The result of a titration done in this way is shown in Figure 36. Gaseous injections of CO were made sequentially into a bed of Cr(II) catalyst fluidized by N2 [377]. A small sample of the bed was then taken from the fluidized bed and used for polymerization. The most highly coordi-natively unsaturated sites (the Turin group s Cr, ) should chemisorb CO that would thus kill the site. Indeed, addition of CO to the bed was found to lower the activity of the sample. Because the catalyst was already reduced, CO did not affect the shape of the rate profile of the Cr(II) catalyst, only the overall rate. 

Amination by ammonolysis, G, solid catalyst, fluidized bed [-650 MJ/kmol] 440 °C, 4 s (acrylontrile, 5 data) rate doubles 30 °C for the range 400-550 °C multitube fixed catalyst bed [-650 MJ/kmol] 230 °C, 4 s (acrylonitrile, ethyl amine, 4 data) rate doubles in 25 °C for the range 150-250 °C. 

FFB Reactors. The two 5-m i.d. FT reactors in the Brownsville, Texas, plant were FFB units. They, initially, were plagued by low conversion attributed to poor catalyst fluidization. These problems were apparently overcome, but the plant was shut down in the mid 1950s. It took more than 30 years before this type of reactor was again used commercially. Improved versions of the FFB reactors were developed by Sasol R D (see the section The Order of Development of FT Reactors at Sasol R D ) and installed at the Secunda plant. Over the period 1995-1999, 16 second-generation CFB reactors were replaced by 8 FFB reactors, 4 of 8-m i.d. with capacities of 0.47 Mt per year each and 4 of 10.7-m i.d. each with a capacity of 0.85 Mt per year. This increased the Secunda plant s capacity from about 5.1 Mt to about 7.5 Mt per year. These units were named SAS (Sasol Advanced Synthol) reactors. 

Results on fluidized-bed-reactor performance when using a La203-Ca0 catalyst fluidizable over a wide range of operating conditions up to 400 h without any problems. 

---