Fluidized beds heating process

The CO2 Acceptor process, also developed under AGA/DOE sponsorship, by the ConsoHdation Coal Co., uses steam to gasify lignitic coal. Heat is supphed by the exothermic reaction between CO2 and calciaed dolomite [17069-72-6]. The dolomite is calciaed ia a separate fluidized bed. This process operates ia a 40 t/d pilot plant, but there are no plans for commercialization as of this writing. 

The heat input into the fluidized bed granulation process is controlled with a steam control valve. The settings for the sensors and controls used in the Glatt unit are listed (Table V). 

Therefore, product temperature should be monitored closely to control the fluidized bed drying process. During fluid-bed drying, the product passes through three distinct temperature phases (Fig. 21). At the beginning of the drying process, the material heats up from the ambient temperature to approximately the wet-bulb temperature of the air in the dryer. This temperature is maintained until the granule moisture content is reduced to the critical level. At this point, the material holds no free surface water, and the temperature starts to rise further. 

In this contribution a novel fluidized-bed coating process is introduced to encapsulate heat-sensitive materials with particle sizes below 100 pum. Supercritical carbon dioxide is used as solvent for the coating material as well as carrier fluid for the core material. The behaviour of the high pressure fluidized-bed was investigated for different process parameters and materials. It is shown that the fluidization starts at lower fluid velocities if the pressure is increased and it was possible to fluidized particles with a mean size below 10 xm. The coating of glass beads with stearyl alcohol was carried out and layers with a thickness of 1-8 xm were achieved. 

Fluidized-bed Coating of an Article A rectangular metal article with dimensions of 0.5 x 5.0 x 10.0 cm is to be coated with PVC powder to a uniform coat thickness of 0.01 cm, using the fluidized-bed coating process. The fluidized-bed temperature is 20°C and the initial metal temperature is 150°C. (a) Assuming no convective losses to the fluidized bed, what would the metal temperature decrease need to be to form the desired coat thickness (b) Estimate the effect of convective heat losses on the temperature decrease of the metal. 

In US Patent 5,569,785 an attrition-resistant zeolite catalyst is described that can be used for the production of methylamines in fluidized bed reactors. The technology claims to provide improved temperature control because of better heat transfer and more efficient solids handling in the fluidized bed. The process also offers more precise temperature control to maintain the activity of the catalyst and eliminate the formation of hot spots that lead to catalyst deactivation. 

Advantages of three-phase fluidized beds over trickle beds and other fixed bed systems are temperature uniformity, high heat transfer, ability to add and remove catalyst particles continuously, and limited mass transfer resistances (both external to the particles and bubbles, because of turbulence and limited bubble size, and inside the particles owing to relatively small particle diameters). Disadvantages include substantial axial dispersion (of gas, liquid, and particles), causing substantial deviations from plug flow, and lack of predictability because of the complex hydrodynamics. There are two major applications of gas-liquid-solid-fluidized beds biochemical processes and hydrocarbon processing. 

Recently, a steam-fluidized bed drying process being implemented at a plant operated by the State Electricity Commission of Victoria (SECV), Australia, uses a heat exchanger supplied by an external high-pressure steam source to dry finely ground brown coal. A tube network immersed... 

Many factors affect optimum fluidized bed reactor performance, including hydrodynamics, heat and mass transfer of interparticles and intraparticles, and complexities of reaction kinetics. The design of fluidized bed reactor processes follows the general approach for multiphase reactor processes. Krishna (1994) and Jazayeri (1995) outlined the general procedure for this process development. The design of the processes can be described by considering various factors as illustrated in Fig. 3. 

Within these four generic types of boilers, specific types of boilers emerge, with their classification based on their use. An example would be a heat-recovery boiler (Fig. 6.1) which recovers normally unused energy and converts it into usable heat. Likewise, a fluidized-bed boiler is one which utUizes a fluidized-bed combustion process. In this type of process, fuel is burned in a bed of granulated particles which are maintained in a mobile suspension by an upward flow of air and combustion products. This technology, in use for over 40 years, is currently being adapted as a combustion process to be installed within a boiler. 

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