Fluid beds, heat removal

The gas, along with entrained ash and char particles, which are subjected to further gasification in the large space above the fluid bed, exit the gasifier at 954—1010°C. The hot gas is passed through a waste-heat boiler to recover the sensible heat, and then through a dry cyclone. SoHd particles are removed in both units. The gas is further cooled and cleaned by wet scmbbing, and if required, an electrostatic precipitator is included in the gas-treatment stream. 

A fluid-bed incinerator uses hot sand as a heat reservoir for dewatering the sludge and combusting the organics. The turbulence created By the incoming air and the sand suspension requires the effluent gases to be treated in a wet scrubber prior to final discharge. The ash is removed from the scrubber water by a cyclone separator. The scrubber water is normally returned to the treatment process and diluted with the total plant effluent. The ash is normally buried. 

One of the most important considerations in designing a process for converting methanol to olefins was to find the best way to remove the considerable heat of reaction. Despite the fact that we are stopping the reaction at the intermediate olefin product, the reactions leading to these intermediates give off almost 90% of the heat released in the overall MTG reaction scheme (49 vs. 56 kJ/mole of methanol converted for MTO vs. MTG). Efficient removal of the heat of reaction is one of the main reasons a fluid-bed reactor was selected for scale-up demonstration. A second advantage of the fluid-bed is that product composition can be kept constant, since optimum catalyst activity can be maintained by continuous make-up and regeneration. 

The fluid bed operation allows the continuous removal of a portion of deactivated catalyst and continuous replacement of catalyst during operation. This results in a steady state performance. In addition, a fluid bed reactor is nearly isothermal by design, which minimizes catalyst deactivation due to exposure to excessive heat. 

Afterwards, the PP powder is fluidized by a mixture of ethylene, propylene and inert gas (propane) in the fluid bed reactor, FBR, which is cooled by convective gas flow. The monomer conversion per gas circulation is limited to a few percent, because of the adiabatic temperature rise of more than 10 K per % conversion. Neglecting the heat loss through the reactor wall and through the product withdrawal, and assuming a well mixed reactor, the heat removal capacity of a steady-state FBR limits the productivity and can be expressed by... 

The heat exchanger removes generated heat from or adds required heat to the fluidized bed by a cooling fluid or heating fluid. Heat exchangers can either be immersed in the dense bed or be placed both in the dense bed and in the freeboard, which is the region above the dense bed. Possible erosion and corrosion of heat exchangers require special attention. 

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 ... 

Fig. 7.9. Batch fluid bed spray granulator used to produce tablet granulations in the pharmaceutical industry. Air-flow necessary for fluidization is generated by a suction-fan (2) mounted in the top portion of the unit, directly driven by an electric motor. The air being used is heated to the desired temperature by an air heater (5). Prefilters remove all impurities at the air inlet (6). The material to be processed has been loaded into the material container (1). The container bottom consists of a perforated plate above which a fine mesh stainless steel retaining screen is fitted. Exhaust filters (7) mounted above the product container retain fines and dust. The granulating liquid (3) is sprayed as a fine mist through a mechanical or pneumatically actuated nozzle (4) onto the finely dispersed, fluidized material to form the desired agglomerates. (Courtesy Aeromatic AG.)...

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