OCR Text |
Show In the COM combustion tests, COM's were prepared with coal concentrations ranging from 30 to 50 percent by weight; the coal particle size consists varied from 90-percent minus 325 mesh to 60-percent minus 200 mesh; and three coal types (Pittsburgh seam coal, Montana subbituminous coal, and Illinois No. 6 coal) were used. In the CWM and CMM combustion tests, mixtures were prepared with the highest coal concentrations that resulted in acceptable mixing and transport characteristics. The CWM's generally contained approximately 60-percent dry coal, pulverized to a nominal size consist of 90-percent minus 200 mesh, and 0.5-percent Lomar-D* (a viscosity-reducing agent); the balance was water. Three types of coal with different ash levels (11.4-percent-ash Pittsburgh seam coal, 7.3-percent-ash Virginia coal, and 2.7-percent-ash beneficiated Eastern Kentucky coal) have been used. The CMM's contained from 46- to 60-percent dry coal, depending upon coal type, and methanol with variable levels of water. Three types of coal (Pittsburgh seam, Montana subbituminous, and Texas lignite) are being used in the CMM tests. For slurry recirculation or transfer, rotary gear pumps are effective for continuous service with COM's at up to 100-psig pump discharge pressures. When operating with CWM or CMM, the pump cavities tended to foul with coal particles, causing total flow blockage ; compressed-air-powered diaphragm pumps are now being used at PETC. For pump discharge pressures in excess of 100 psig and for minimum fuel flow fluctuations, progressing cavity pumps have been used as feed pumps for all three types of coal slurries at PETC. During earlier COM tests in the 700-hp boiler, excess wear of the tool steel rotor and stator in the progressing cavity pump was noted. When a Buna-N stator and a 10-mil-undersized chromed-faced tool steel rotor were used, pump performance was considerably improved. Some *Reference in this paper to any specific commercial product, process, or service is to facilitate understanding and does not necessarily imply its endorsement or favoring by the United States Department of Energy. 14-6 |