Development and evaluation of highly-loaded coal slurries. Phase I summary report, October 15, 1977-December 31, 1978

Abstract

Slurry fuels comprised of either bituminous, subbituminous, or lignite coal, and either aqeuous media or emulsions of No. 6 oil in water as the carrier were developed and evaluated at solids loadings up to 70% by weight. Emphasis was placed on aqueous slurries of bituminous coal. These slurries were developed for use in place of No. 6 oil in oil-fired burners. High solids loadings were attained by use of bimodal particle size distributions, which are blends of coarse-grind coal (approx. 50 to 85% -50 mesh) and fine-grind coal (generally 90% -200 mesh). The effect of the blends on slurry viscosity was determined to find the blends that minimize viscosity. The effect of mill conditions on particle size distribution was determined for each coal, using a hammermill pulverizer. A large number of water-soluble resins were evaluated for effect on slurry stability and viscosity. The best of these was found to be hydroxypropylated corn starch. Slurries based on the use of 3% solutions of the starch in water were prepared with up to 70% by weight bituminous coal and up to 65% subbituminous coal. The slurries are pourable pseudo-plastic fluids having room-temperature viscosities in the range of 550 to 1100 cp atmore » a shear rate of 3000 sec/sup -1/, depending on the type of coal, solids loading, and particle size distribution. None of the slurries exhibited hard pack settling, even after room-temperature storage up to 74 days. Oil-in-water emulsions made with polyethylene glycol (23) lauryl ether as an emulsifier were found to be stable with respect to phase separation when stored at 160/sup 0/F. Slurries made with these emulsions do not exhibit hard pack settling after one week storage at 160/sup 0/F.« less