Synfuel systems. A review of letdown devices and other multiphase flow problems

Abstract

In an effort to develop domestic sources of energy, a number of processes to convert coal to clean fuels have been investigated. Products of these processes span the range from clean coal substitutes, to synthetic crude oil, to synthetic natural gas. Some of these processes, after successful operation in the laboratory, are now operating on a pilot plant scale to determine the feasibility of further scale up. These pilot plants range in capacity from 1/1000 to 1/10 of that projected for commercial operation [1]. At the pilot plant scale, problem areas which are generic to the conversion process have come to light. These problem areas include: handling of highly abrasive slurries, three phase heat transfer, high temperatures, high pressure, and high pressure slurry letdown. In this report the problems associated with high pressure slurry letdown from the reactor/dissolver to the fractionating section will be discussed. The operating experience and the current state of the art for high pressure letdown valves in the coal conversion industry and the process industry will be examined. Also, the commonly used valve sizing techniques will be examined in relation to the problem of sizing for high pressure letdown. A summary of the instrumentation needed to monitor the letdown process for valve development, and ultimately for process control, is also included.