An analytical study of pressure-gradient data from laboratory oil shale retorts is described. A review of the flow-pressure equation shows it to have the same form for transitional as for laminar and turbulent flow, provided that Reynolds number variation is small. Comparison of measured with calculated vertical-pressure differences in a small retort reveals good agreement above the level where maximum temperature is reached. Below this level, values differ by at least 30% because of retained oil, which reduces the gas flow space. Methods for calculating total pressure difference across a retort and implications for in situ oil shale processing are also suggested.
Laboratory experience in the operation of oil shale retorts shows that, for a constant mass flow rate, the pressure difference across the retort increases greatly as retorting proceeds. The two oil shale retorts at the Lawrence Livermore Laboratory have been described by Sandholtz and Ackerman'. Figure 1 shows pressure difference as a function of time for run S-16 in the small (125 kg) retort. The shape of this curve is typical. Both capital costs and operating costs for gas flow equipment could be important if the pressure difference continues to increase as retorting proceeds in a tall in situ retort. A study of flow and pressure data gives some insight into the reason for the increases in pressure difference. In addition, such data aid in estimating the amount of oil retention that occurs in the lower, cool part of an operating retort.