When the process fluid is a nonflammable liquid, the simplest means of pressurizing the solid is to slurry it into the process liquid and then pump the resulting slurry to the desired pressure. This is the same concept as the hydraulic conveying system shown in Figure 18.17(a). If the process fluid is flammable, it can still be used to slurry the solids, but a closed atmospheric-pressure slurrying tank must be used and the solids must be fed through a rotary vane feeder or rotary valve that mini-mizes backflow of vapor. The head space in the mixing tank should also be vented with inert gas, as shown in Figure 18.19. Additional treatment of the vent gas may be needed to control particulate (dust) and volatile organic compound (VOC) emissions.