Scaling fluidized-bed reactors

An advantage of this approach to model large-scale fluidized bed reactors is that the behavior of bubbles in fluidized beds can be readily incorporated in the force balance of the bubbles. In this respect, one can think of the rise velocity, and the tendency of rising bubbles to be drawn towards the center of the bed, from the mutual interaction of bubbles and from wall effects (Kobayashi et al., 2000). In Fig. 34, two preliminary calculations are shown for an industrial-scale gas-phase polymerization reactor, using the discrete bubble model. The geometry of the fluidized bed was 1.0 x 3.0 x 1.0 m (w x h x d). The emulsion phase has a density of 400kg/m3, and the apparent viscosity was set to 1.0 Pa s. The density of the bubble phase was 25 g/m3. The bubbles were injected via 49 nozzles positioned equally distributed in a square in the middle of the column. 

Studies at Mobil Research have shown that light olefins instead of gasoline can be made from methanol by modifying both the ZSM-5-type MTG (Methanol-to-Gasoline) catalyst and the operating conditions. Work carried out in micro-scale fluidized-bed reactors show that methanol can be completely converted to a mixture of hydrocarbons containing about 76 wt% C2-C5 olefins. The remaining hydrocarbons are 9% C1-C5 paraffins, of which the major component is isobutane, and 15% C6+, half of which is aromatic. 

Flow maldistribution of the phases can render the evaluation of RTD data very difficult. In some cases, maldistribution may exist in small units but it may not exist in large-scale units (e g., trickle-bed reactors). While in some other cases, such as three-phase fluidized-bed reactors, nonuniform gas distribution in large-scale units may cause undesirable recirculation and dead zones. Uniform gas distribution can usually be achieved in the small-scale fluidized-bed reactor. 

Catalytic butane dehydrogenation can be successfully carried out in a laboratory scale fluidized bed reactor operating at 310 °C and at atmospheric pressure. The catalytic particles have diameter 310 pm and density 2060 kg/m. Such a reactor is 150 mm in diameter and has a fixed 500 mm long catalytic bed. When the catalyst bed is fluidized with butane blown at a velocity of 0.1 m/s, it becomes 750 mm thick. 

Each test was carried out in an atmospheric bench-scale fluidized bed reactor shown schematically in Figure 1. The main reactor consists of a 321 stainless steel tube with an inside diameter of 73 mm and a length of 1 m. The tube is encased in an electric furnace used to preheat the reactor. At the top, the reactor expands into a 127 mm square section with a cross-sectional area 4 times larger than the main reactor column. This section is used to disengage larger bed and partially reacted fuel particles from... 

Fig. Schematic of the bench-scale fluidized-bed reactor system.

Matsui et compared experimental data on the steam gasification of coal char from a laboratory-scale fluidized-bed reactor with the Kunii and Levenspiel model. Good agreement was reported when the bubble diameter was treated as a fitted constant. 

Methanol to olefins (MTO), which provides a new route to produce light olefins such as ethylene and propylene from abundant natural materials (e.g., coal, natural gas or biomass), has been recently industrialized by the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. In this contribution, the process development of MTO is introduced, which emphasizes the importance of mesoscale studies and focuses on three aspects a mesoscale modeling approach for MTO catalyst pellet, coke formation and control in MTO reactor, and scaling up of the microscale-MTO fluidized bed reactor to pilot-scale fluidized bed reactor. The challenges and future directions in MTO process development are also briefed. 

In the pilot-scale experiments, the continuous reaction-regeneration is also investigated. The details of the results will not be discussed here. However, we wiU focus on the influence of the average residence time and catalyst to methanol on the MTO reaction in pilot-scale fluidized bed reactor. 

Figure 29 shows the average residence time of catalyst in the pilot-scale fluidized bed reactor by adjusting the catalyst circulation rate while keeping other conditions such as reaction temperature, inventory, feed rate, and WHSV unchanged. UrJike that in the fluidized bed reactor without catalyst... 

The design of an industrial scale fluidized bed reactor for a new or existing process can be challenging. Any study of an existing operating unit will immediately justify the basis of this statement. 

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