PERFORMANCE OF A SMALL-SCALE INJECTOR FOR ATOMIZATION OF COAL-WATER AND PETCOKE-WATER SLURRIES

摘要

The University of Utah operates a 1 ton/day pressurized, slurry-fed, oxygen-blown entrained flow gasifier. Coal or petcoke slurry isintroduced into the top of the reactor through an injector, which atomizes the slurry with high-pressure oxygen. An atomizer beingdeveloped for this system is a two-stream, coaxial, micro-hole atomizer that functions similar to the airblast design. This atomizerdesign offers prompt phase contact, with the atomizing gas meeting the liquid approximately 1 mm from the liquid exit orifice.Atomizers of this design are commonly used in slurry-fed combustion and gasification systems. To understand the operation andbehavior of these systems, and to help with design of other, larger atomizers, thorough characterization of the spray is needed.This manuscript describes the characterization of sprays resulting from the atomization of coal-water slurries and petcoke-waterslurries. Two solids loadings were explored for both CWS and PCWS. Atomization of water was performed for a baseline. Theatomizing gas was air for all conditions, and all tests were performed in atmospheric pressure. Two levels of liquid flow were exploredalong with three levels of gas flow. Two spray sections were examined: the edge of the spray and a position along the central axis.As the liquids being evaluated often have very different physical properties, each slurry was analyzed over a range of shear rates (upto 500 s–1) using a viscometer. This provides insight into how these commonly non-Newtonian liquids will respond while undergoingthe high shear rates typically associated with this type of atomizer.The spray was quantitatively characterized using particle shadow velocimetry (PSV), which provides in-line illumination of a portionof the spray paired with imaging equipment. The region captured by PSV was roughly 10.5 mm by 10.5 mm. This allows the detectionof drop diameters on the order of 10 micron. This characterization provides drop sizes, a drop size distribution, and a vector fieldassociated with the identified drops. Patternation was also performed, which provides a spatial distribution of the spray.During gasifier operation, this atomizer design has been shown to offer very stable operation. While the system conditions aredifferent from those existing during spray characterization, this spray characterization offers much into the behavior of fuelsuspensions during atomization.