Fluidized beds high tube temperatures

It has to be operated at a steam temperature of around 300°C. We have therefore designed a plant with the tubes installed in the fluidized bed. Though the temperature of the fluidized bed zone is lower than that in the freeboard zone, the concentration of HCl is also lower (about 1/50 of that in the freeboard zone) and the temperature of sand is still high enough to recover energy. Thus we have been able to raise the temperature of the... 

High tube temperature Bed temperature Minimum fluidizing velocity Steam temperature Steam velocity (m/s)... 

Phthalic anhydride Naphthalene is oxidized by air to phthalic anhydride in a bubbling fluidized reactor. Even though the naphthalene feed is in liquid form, the reaction is highly exothermic. Temperature control is achieved by removing heat through vertical tubes in the bed to raise steam [Graham and Way, Chem. Eng. Prog. 58 96 (January 1962)]. 

Circulating Beds These fluidized beds operate at higher velocities, and virtually all the solids are elutriated from the furnace. The majority of the elutriated sohds, still at combustion temperature, are captured by reverse-flow cyclone(s) and recirculated to the foot of the combustor. The foot of the combustor is a potentially very erosive region, as it contains large particles not elutriated from the bed, and they are being fluidized at high velocity. Consequently the lower reaches of the combustor do not contain heat-transfer tubes and the water walls are protected with refractory. Some combustors have... 

Chemical reactors basically come in the form of tanks, such as for batch reactors or back-mix flow reactors, large cylinders, such as for fluidized-bed or plug-flow reactors, or multiple tubes inside a cylindrical container, such as for plug-flow reactors when special needs exist for temperature control. High pressure and extremes of temperature as well as corrosive action of the materials involved can introduce complications in the design which must be handled by the design engineer. 

Fluidized bed combustion. In the temperature range 820 to 870°C, limestone reacts with SO2 and air to give calcium sulfate rather than sulfite, and this product can be safely disposed of or utilized, for example, as roadbed cement. Fennelly describes a two-stage fluidized bed furnace (Fig. 8.2) in which coal fluidized in an airstream is burned at 1100 to 1300°C (the temperature at which combustion is most efficient) around the boiler tubes, giving highly efficient heat transfer without formation of hot spots. The gases then pass to the... 

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