Gas interchange

Bubble Dynamics. To adequately describe the jet, the bubble size generated by the jet needs to be studied. A substantial amount of gas leaks from the bubble, to the emulsion phase during bubble formation stage, particularly when the bed is less than minimally fluidized. A model developed on the basis of this mechanism predicted the experimental bubble diameter well when the experimental bubble frequency was used as an input. The experimentally observed bubble frequency is smaller by a factor of 3 to 5 than that calculated from the Davidson and Harrison model (1963), which assumed no net gas interchange between the bubble and the emulsion phase. This discrepancy is due primarily to the extensive bubble coalescence above the jet nozzle and the assumption that no gas leaks from the bubble phase. 

Davies, L. and Richardson, J. F. Trans. Inst. Chem. Eng. 44 (1966) T293. Gas interchange between bubbles and the continuous phase in a fluidised bed. 

Lbe = the mass transfer coefficient between the bubble and emulsion phase (m3 gas interchange volume/m3 of reactor) (1/s) yb = the volume fraction of the bubble occupied by solids ( rh,vs) = the reaction rate in bubbles per unit volume of solids, based on the reactant... 

K = the mass-transfer coefficient based on the bubble volume, (m3 gas interchange volume/m3 of bubble) (1/s)... 

The definition of phase can be carried further. Depending on temperature and pressure, solids can take on different crystalline forms. These constitute separate phases. The petroleum engineer normally is not concerned with the crystalline forms of solids therefore, we will consider only three phases gas, liquid, and solid. For the purpose of our discussion we will use the words vapor and gas interchangeably. Some authors try to distinguish between these two words, but the difference is unimportant to us. 

Recently two widely divergent process variations of PSA have been commercialized by Union Carbide Corporation The first of these is called POLYBED PSA, which Is used for hydrogen recovery (17-21) Plants with capacities of up to about 1 2 x 10 NM /day of hydrogen have been built Hydrogen recoveries of 86 percent vs 70-75 percent for other PSA processes have been demonstrated, as well as purities of 99 999 mole percent (20) POLYBED PSA involves the use of five or more beds, with extensive gas Interchanges and pressure equalizations between the beds One process embodiment (17) is shown In Figure 3 ... 

Van Deemter (1980) compared the kinetic constant fcc calculated from A and E obtained in the laboratory with the pseudo-kinetic constants k c from several commercial and pilot plants, and found that the values for k c are always lower than those corresponding to kc, as shown in Fig. 13. It appears, therefore, that the process of coke burning is principally controlled by gas interchange and mass transfer in the bubbling or turbulent bed. Fast... 

It is assumed here that the size of the last compartment is determined from the difference between the cummulative compartments size and the height of the expanded bed. However, for consistency, gas interchange coefficients and the linear bubble phase gas velocity are based on a hypothetical bubble diameter predicted from Eqn. (12). The computational scheme also takes into consideration the possibility of only two phases in any compartment. 

Liquid cooling Liquid cooling High-temperature gas interchange... 

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