Mercury PAC optimization

Powdered activated carbon (PAC) is injected to remove mercury from combustion gas. The carbon is costly, and it can hurt other parts of the system, especially stack opacity. Griffin’s Hg PAC optimization application weighs those objectives in real time so the unit keeps a high mercury-removal rate while using less PAC.

How it works

Meeting a mercury limit is a priority for many coal-fired processes. A common method injects pulverized activated carbon just after combustion so the carbon adsorbs mercury from the flue gas. Injecting more than necessary wastes carbon and drives opacity up. The useful target is the smallest PAC rate that holds mercury under the limit.

Ordinary PAC controls move slowly, because adsorption is slow and mercury concentrations are extremely low. Opacity, by contrast, can rise quickly and pass an acceptable limit, which forces a manual correction. Plants then cycle between too much carbon and too much opacity, and the whole process runs inefficiently.

There is room to balance those priorities. Griffin’s application considers long-term and short-term objectives for more than one measurement at once, and it respects process limits. The installation uses few I/O points and is typically in place in less than a week. Plants have achieved a 15% to 20% reduction in PAC injection, fewer high-opacity events, and mercury emissions that stay the same or improve.

Contact us to talk about mercury removal on your unit. Hg PAC brief (PDF).