IN SITU SHALE OIL RETORT WASTEWATER PRETREATMENT USING
COAGULATION AND OXIDATION
Frederic C. Blanc, Associate Professor
James C. O'Shaughnessy, Associate Professor
Irvine W. Wei, Associate Professor
Department of Civil Engineering
Northeastern University
Boston, Massachusetts 02115
Paul E. MacNevin, Project Manager
Universal Engineering Corporation
Boston, Massachusetts 02101
INTRODUCTION
Shale oil is being considered as one of the most significant alternative energy resources
to aleviate the present petroleum shortage. Large quantities of oil shale exist in the United
States. Most of the high grade deposits are located in the western states of Colorado.
Wyoming and Utah. It is estimated that the United States has 100 to 800 billion barrels
of shale oil reserves or roughly ten times its conventional crude oil reserves [ 1 ]. Private
industry and government agencies are sponsoring research programs to develop the technology required to make some of this energy available for consumption. The technology sought
includes mining of the material, extraction of the oil from the shale, refining processes
and treatment for process wastes.
Shale oil exists as a waxy solid substance called kerogen found in marl, a type of limestone formation. Three different methods of mining and extracting the oil are currently
being emphasized. The first process is an above ground process where marl is removed from
the mine, crushed and heated in a surface retort structure. Water must be mixed with the
shale in this process. An expanded rock and a left-over slag must then be dumped. The
shale rock must be heated to 900 F so that kerogen can be vaporized and extracted. This
is the process which uses the most water and produces the most waste. A second method
involves mining and heating the shale underground. This method is called in situ. Large
underground chambers are created by digging a series of horizontal shafts at two different
elevations, and blasting the layer between the shafts. After removing about 25% of the
rock, leaving a large pile of shale rubble, each chamber is sealed and fired to heat the rock.
Kerogen released from the rock flows to the bottom of the chamber and is pumped from a
sump to the surface. The third method is referred to as modified in situ. It is a combination
of the first two methods in which a greater percentage of the ore is mined and retorted
above ground to create enough void space for the remainder to be successfully retorted
underground. More complete description of the mining and retorting processes may be
found in the literature [2].
There are several types of waters and wastewaters associated with oil shale production.
Jackson et al. [3] have summarized some of the earlier analyses of such waters. They
separate the waters into five categories. The first is "conventional industrial water" which
is generated in the normal petroleum industry. This includes domestic, boiler, cooling
wastewaters and process waters similar to wastewaters generated in a petroleum processing
refinery. "Retort water" is^ the second type. It is produced during the retorting process
as a result of the underground combustion and is decanted from the oil at the surface.
A third type of water is "bound water," a dissolved, adsorbed or emulsified water which
travels with the oil. "Natural ground water" intercepted during the underground development of oil shale deposits is a fourth type of water. It could be of high quality or low
quality with high inorganic content. "Backflood water" is the fifth type, a combination
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