Page 197 - Synthetic Fuels Handbook

FUELS FROM OIL SHALE 183

Oil shale can be mined using one of two methods: (a) underground mining using the
room and pillar method or (b) surface mining. Room and pillar mining has been the pre-
ferred underground mining option in the Green River formations. Technology currently
allows for cuts up to 90 ft in height to be made in the Green River formation, where ore-
bearing zones can be hundreds of meters thick. Mechanical continuous miners have also
been selectively tested in this environment.
After mining, the oil shale is transported to a facility for retorting after which the oil must
be upgraded by further processing before it can be sent to a refinery, and the spent shale must
be disposed of, often by putting it back into the mine. Eventually, the mined land is reclaimed.
Both mining and processing of oil shale involve a variety of environmental impacts, such as
global warming and greenhouse gas emissions, disturbance of mined land, disposal of spent
shale, use of water resources, and impacts on air and water quality. The development of a
commercial oil shale industry in the United States would also have significant social and
economic impacts on local communities. Other impediments to development of the oil shale
industry in the United States include the relatively high cost of producing oil from oil shale
(currently greater than $60 per barrel) and the lack of regulations to lease oil shale.
Surface retorting involves transporting mined oil shale to the retort facility, retorting
and recovering the raw kerogen oil, upgrading the raw oil to marketable products and dis-
posing of the spent shale (Fig. 6.1). Retorting processes require mining more than a ton of
shale to produce 1 bbl oil. The mined shale is crushed to provide a desirable particle size,
injected into a heated reactor (retort), where the temperature is increased to about 450°C
(842°F). At this temperature, the kerogen decomposes to a mixture of liquid and gas. One
way the various retorting processes differ is in how the heat is provided to the shale by hot
gas, a solid heat carrier, or conduction through a heated wall.

Mining and Retorting Oil Oil to
crushing upgrading refinery

Spent shale
disposal Reclamation
on-site

FIGURE 6.1 Process steps in mining and surface retorting.
(Source: Bartis, J. T., T. LaTourrette, and L. Dixon: “Oil Shale Development in the United
States: Prospects and Policy Issues,” Prepared for the National Energy Technology of the
United States Department of Energy, Rand Corporation, Santa Monica, Calif., 2005.)

Advances in mining technology continue in other mineral exploitation industries,
including the coal industry. Open-pit mining is a well established technology in coal, tar
sand, and hard rock mining. Furthermore, room and pillar and underground mining have
previously been proven at commercial scale for oil shale in the western United States. Costs
for room and pillar mining will be higher than for surface mining, but these costs may be
partially offset by having access to richer ore.
Current mining advances continue to reduce mining costs, lowering the cost of shale
delivered to conventional retort facilities. Restoration approaches for depleted open-pit
mines are demonstrated, both in oil shale operations and other mining industries.
The fundamental issue with all oil shale technologies is the need to provide large
amounts of heat energy to decompose the kerogen to liquid and gas products. More than 1 t
of shale must be heated to temperatures in the range 425 to 525°C (797–977°F) for each
barrel of oil generated, and the heat supplied must be of relatively high quality to reach