Attrition rate, carbon

Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others.

Table 3. Summary of attrition rate constants for activated carbon at different gas velocities.

Activated carbon in solvent recovery service will have a useful service life of 1 to 10 years, depending on the attrition rate and reduction in adsorption capacity. 

Attrition rates are usually less than 1 -3% per year. The actual rate will depend on carbon hardness. Particle abrasion and the resulting bed compaction leads to an increased pressure loss after several years of service. After 3-5 years of service screening to its original size is necessary. 

Coal particle fragmentation and attrition during combustion has been extensively studied. For bubbling fluidized bed combustion, the attrition rate has been typically assumed proportional to the excess gas velocity above minimum fluidizing conditions, carbon... 

They find that the rate of attrition is proportional to the energy dissipation rate in the bed, which is proportional to uQ -i f, and that it is much higher during oxidation than pyrolysis. They postulate that asperities are produced on the surface of the char during combustion and that these are abraded by collisions with the bed solids. The rate of the carbon surface regression due to attrition is approximately given by... 

To design and implement systems for water treatment, it is not only the adsorption charaeteristics of the activated carbon that must be considered but also the effect that the carbon may have on the practical operation of the unit. In this context, the pressure drop generated across a GAC bed is one of the most important factors, as it also is for gas phase applications. The particle size distribution should be optimized to attain an acceptable pressure drop commensurate with the desired rate of adsorption. The carbon attrition resistance is another important parameter. Part of the operating cost of adsorbers is due to the loss of carbon fines during transport, handling, and regeneration. 

In addition, workers were exposed to mean average concentrations of 3.2-8 ppm carbon disulfide. If carbon disulfide exerts effects through an arteriosclerotic process, this duration of exposure may not have been adequate to observe cardiovascular effects. Also, the study does not include the turnover rate due to death or attrition among workers, some of which could be attributable to cardiovascular effects. 

Classical analysis has demonstrated that a given quantity of active material should be deposited over the thinnest layer possible in order to minimize diffusion limitations in the porous support. This conclusion may be invalid for automotive catalysis. Carbon monoxide oxidation over platinum exhibits negative order kinetics so that a drop in CO concentration toward the interior of a porous layer can increase the reaction rate and increase the effectiveness factor to above one. The relative advantage of a thin catalytic layer is further reduced when one considers its greater vulnerability to attrition and to the deposition of poisons. 

In a turbulent bed the char-burning rate is dictated by its kinetic rate of combustion, and the mass transfer rate of oxygen from the bulk of the bed to the particle surface. In parallel with combustion, a small fraction of carbon undergoes attrition from the carbon surface. In a comprehensive study of combustion in turbulent fluidized beds, account must be taken of all of these interacting mechanisms. 

Shrinkage of each coal particle occurs both by combustion and attrition. The attrition contribution to the shrinkage rate of a burning carbon particle may be obtained from Equation 18 as [22],... 

Attrition of activated carbon can be minimized by proper design of the adsorption vessels. The air-flow rate should be below 100 ft/min., preferably below 60 ft/min., and good air distribution to the top of the bed should be provided. Plugging of activated carbon beds can be prevented by eliminating any sources of carbon attrition and providing an adequate screen or filter ahead of the adsorption vessel. 

Size distributions of solids (coal and limestone) in the feed and in the bed shoiald be considered in the evaluation of attrition and elutriation loss. Standard correlations for elutriation rate constants have been found to be inadequate for the calcijlation of solids elutriation. Data obtained from large pilot-scale FBC show large disagreement from those calciilated based on existing elutriation rate correlations. Recently, correlations for attrition and elutriation of bed particles have been proposed by Merrick and Highley (106). For larger particles, this correlation underestimates the carbon loss. 

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