Page 25 - Synthetic Fuels Handbook

FUEL SOURCES 13

oil shale transportation, and (c) cost and labor effectiveness. However, difficulties are in
the domain of (a) process control and reliability, (b) environmental and ecological impact
before and after the processing, (c) long-term ground water contamination, and (d) process
efficiency. Sites for in situ processing are put back to normal vegetated areas or to the
original forms of the environment as close as possible, upon completion.
There are several advantages associated with oil shale commercialization and they are
(a) worldwide abundance and distribution, (b) surface mining or in situ processing possi-
bilities, (c) source for high-quality crude products, (d) source for aliphatic liquid fuels, and
last but by no means least (e) oil shale is a politically less sensitive fossil fuel resource.
The quality of oil shale can be very simply represented by its oil content in the shale. To
compare the oil contents as recoverable amounts of hydrocarbon from a wide variety of oil
shale, a standardized method of oil content determination is needed. Fischer assay is most
generally used for this purpose and it has definite merits based on its simplicity and use of
a common apparatus (Fischer assay).
The mostly aliphatic nature of the shale oil is very attractive from the environmental
and processing standpoints, since aromatics in liquid fuel are generally viewed negatively
due to the high potential for evaporative and fugitive emission that introduces a high level
of volatile organic compounds (VOCs) into the atmosphere. In fact, there are several issues
that relate to the environmental constraints in exploiting oil shale formations:
1. Water availability and salinity change in water.
2. Availability and development of other energy and mineral resources.
3. Ecology and preservation of natural character of the region.
4. Sources of fugitive dust from such operations as crushing, sizing, transfer conveying,
vehicular traffic, and wind erosion.
5. Gaseous emissions such as H S, NH , CO, SO , NO , and trace metals.
3
2
x
2
6. Nature of the region and the population density.
7. Outdoor recreation in the oil shale region.
8. Environmental permits and regulations.
Oil shale can be ignited and burst into fire, if conditions are met. Depending upon
the shale types and their hydrocarbon contents, the self-ignition temperature (SIT) of dry
shale in the atmosphere varies widely from as low as 135 to 420°C. The finer the particle,
the stronger is the possibility of catching fire spontaneously. However, it is generally too
expensive to grind oil shale to fine meshes for processing. This threshold value is not
generally set for all types of oil shale or processes; however, it is estimated to be about 1 to
3 mm as a minimum. Oozing oils from raw or spent shale can complicate the safety matters
by exposing not only potentially hazardous air pollutants (HAPs) to the environment, but
also highly combustible matters in contact with air. This can be especially true with spent
shale transportation, if the residual hydrocarbons are not burnt off for heat recovery for the
process. Reburial or disposal of spent shale potentially renders an ecological and environ-
mental concern. Since spent shale is the shale that has gone through a thermal treatment
process, it is more likely to become a source for leaching of minerals and organics, that may
be harmful to the ecologic constituents, and contaminating the ground waterway.
For much of the twentieth century, the Naval Petroleum and Oil Shale Reserves served as
a contingency source of fuel for the U.S. military, as the government owned both. However,
in the later part of the twentieth century, the Naval Petroleum and Oil Shale Reserves
were determined to no longer serve the national defense purpose envisioned earlier in
the century. Privatization of these properties followed and commercial exploitation was
prompted, as evidenced by the Elk Hill field (California) operated by Occidental Petroleum