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The combustion of a char in the 41 mm ID riser of a laboratory circulating fluidized bed combustor has been investigated at different air excesses and rates of solids (char and sand) circulating in the loop. Riser performance was characterized by an axial oxygen concentration profile as well as by the overall carbon content and particle size distribution. The proposed model accounts for carbon surface reaction, intraparticle and external diffusion, and attrition. External diffusion effects were relevant in the riser dense region where char was potentially entrapped in large clusters of inert solids. Experimental data and results of the model calculations are in satisfactory agreement.

The general conditions for gel formation by phenolformaldehyde polymer solutions have been examined in studies with three acrylamide polymers, Contrary to an earlier repom polymer crosslinking is found to take place over a wide interval of PH. While the gelation time is relatively insensitive to the concentrations of phenol and formaldehyde or pH, it is strongly influenced by the temperature and the nature of the polymer. l%ese getants display good injectivity in coreflood and slim-tube experiments at temperatures'upto 140"C. On the other hant he partitioning of phenol into crude oil is found to be a significant issue for the propagation of these gelants< The use of a phenol pre-flush of the formation is shown by numerical modeling to be a potentially viable solution for this problem.

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