Coal and pollution controls
A portion of existing plants and all new ones offer some pollution control technologies to reduce their emissions, especially sulfur dioxide and particulates.
Common pollution control methods include scrubbers and filters. Scrubbers use a wet limestone slurry to absorb pollution as it passes through. Filters are collections of large cloth bags that catch particulates as they travel through the cloth. Smaller particulates are less likely to be absorbed, and can pass out the smokestack into the air.
IGCC technology is more expensive than pulverized coal technology, but offers certain environmental advantages. While modern pollution controls for nitrogen oxides, sulfur dioxide, and particulate matter can dramatically reduce emissions from pulverized coal plants (by 90 to 99 percent), IGCC plants are capable of even greater reductions.
It is also easier and less costly to capture and dispose of mercury from an IGCC plant than from a pulverized coal plant, which became increasingly important after mercury restrictions came into effect in 2011.
At the moment, commercially available control technology that can be added to coal plants to reduce their CO2 emissions is expensive. However, carbon capture and storage (CCS) is an emerging technology that may allow plant operators to capture CO2, transport it to a “geologic sequestration” site, and pump it into the ground for permanent storage.
With respect to capturing carbon, IGCC has an additional advantage over pulverized coal technology. Since its gasification process allows for the separation and capture of CO2 before combustion, the gas is still in a relatively concentrated and pressurized form. Pulverized coal plants can only capture CO2 after combustion, when it is far more diluted and harder to separate, increasing the costs of implementing CCS.
Pre- and post-combustion technologies are both expected to capture between 85 and 95 percent of a plant’s CO2. However, capturing and compressing CO2 is a very energy-intensive process, causing large reductions in the amount of net energy the plant is able to produce.
State-of-the-art methods for capturing CO2 from pulverized coal plants are expected to reduce the plant’s energy output by a quarter or more (assuming CCS is built into the original plant design and not added as a retrofit, in which case it would reduce power output even more).
Although the output loss for IGCC plants would be smaller, reductions greater than 15 percent are still expected. When factoring in the likely additional fuel used to power the CO2 removal process, the actual amount of CO2 avoided per unit of electricity would fall to the 80 or 90 percent range.