Environmental Engineering Reference
In-Depth Information
make use of waste heat while steam turbines do not. Reciprocating engines and
emerging microturbine and fuel-cell technologies are also strong technologies for
cogeneration on smaller scales, including commercial and apartment buildings.
Coal gasification by partial oxidation with oxygen to make synthetic gases (mainly
carbon oxide and hydrogen), usually called “syngas,” makes it possible to pro-
duce electricity via integrated gasifier combined cycle plants, at high efficiencies
and with air pollutant emissions nearly as low as for natural gas combined cycles.
These plants are branded integrated gasifier combined cycle (IGCC). Today, power
from IGCC cogeneration plants would often be competitive with power from coal
or steam electric plants in either cogeneration or power-only configurations.
Very clean syngas-derived synthetic fuels such as synthetic middle distillates
and dimethyl ether can soon play significant roles by supplementing conventional
liquid fuels (for transportation, cooking, peak power generation, etc.). They can al-
leviate oil supply security concerns and facilitate the implementation of tougher
air pollution regulations. Such fuels can often be produced for global markets at
competitive cost from huge low-cost natural gas supplies that would otherwise be
stranded assets at remote sites. In natural gas-poor, coal-rich regions, a promising
strategy for producing such fuels is via coal gasification and “polygeneration”—the
coproduction of various combinations of clean fuels, chemicals, and electricity.
Such systems might include production of extra syngas for distribution, by
pipelines, to small-scale cogeneration systems in factories and buildings, thereby
enabling clean and efficient use of coal on small as well as large scales. Rapidly
growing polygeneration activity is already under way in several countries based on
gasification of low-quality petroleum feedstocks.
Carbon Capture and Storage (CCS) is a technology to capture the CO
2
gases emit-
ted from power stations and bury them into the ground at high pressures, either in
depleted gas, oil, or coal deposits, naturally occurring caverns, saline aquifers, or
the deep ocean. If no leaking occurs, these could be considered permanent reser-
voirs.
Such technology has been used in the past for enhanced oil recovery, in which
CO
2
is pumped into reservoirs to bring to the surface oil that would not naturally
gush out. There are almost 40 years of experience in enhanced oil recovery (EOR),
and presently approximately 40 million tons of CO
2
are being used for this pur-
pose.
