Two full-scale power-plant demonstrations, using the MinPlus mineral sorbent, were discussed by Joep Biermann, MinPlus, Inc. The MinPlus sorbent was injected into the open radiant furnace at flue-gas temperatures exceeding 2000° F with promising results. MinPlus produces mineral sorbents for the capture of metals at high (in-furnace) temperatures. Since 1995, the company has studied metal sorption for elements such as mercury, sodium, lead and cadmium.

MinPlus Sorbent is produced in Europe in amounts of about 50,000 tons/year. The thermally-produced material is based on meta-kaoline and calcium compounds. The sorbent is a white powder that looks a bit like flyash, except that it is very reactive with metals, even capturing elemental mercury. The sorbent doesn’t burn in hoppers and preserves the flyash for cement quality applications.

The MinPlus sorbent technology was demonstrated at Richmond Power & Light’s Whitewater Valley power plant 65-MW unit 2 and at a 154-MW power plant in North Carolina. Both power plants are equipped with a rotating opposed fired air system (ROFA) supplied by Mobotec USA. This patented system generates a rotation of the flue gas by the application of asymmetrically placed air nozzles, resulting in highly turbulent mixing. The turbulent mixing allows for the effective in-furnace mixing of injected materials, like the MinPlus sorbent.

Injection of the MinPlus sorbent had no noticeable effects on the operational performance of both power plants. Neither the plant personnel nor the plant data could identify the periods during which the sorbent injection was started or halted, indicating the non-intrusive character of the MinPlus mercury sorption technology.

In-furnace injection of MinPlus resulted in good removal of mercury. The Whitewater Valley demonstration yielded 95 percent mercury removal to yield a very low residual mercury emission of below 0.2 µg/Nm³ at 3 percent O₂. The North Carolina power plant demonstration yielded 70-80 percent mercury removal. The observed difference in mercury removal rate for both power plants is considered to be caused by sub-optimal dispersion of the sorbent at the second power plant. Sorbent dosage rates of 2 lb/MW-hr are considered adequate for effective mercury removal, provided good sorbent dispersion in the upper furnace is achieved.

The mercury removal by the MinPlus sorbent probably occurred at temperatures of more than 1200° F. This implies that the mercury capture occurred while in its elemental form, which in turn implies that the plant-load variations that normally influence the ratio of elemental and oxidized forms of mercury have little effect on this sorbent’s efficiency. This is an advantage over mercury removal systems such as scrubbers or activated carbon. In both demonstrations, the sorbent injection was transparent to the operation of the power plant and had no effects on sootblowing frequency, opacity, ash quality or ESP performance.

Ash quality measurements on physical mixtures of the MinPlus sorbent and a saleable flyash from We Energies Pleasant Prairie power plant revealed that the flyash quality remained unaltered in terms of cementitious applicability of the flyash, when compared to alternative (activated carbon) mercury sorbents. The removed mercury was found to be chemically and strongly bound to the sorbent. The amount of mercury in the sorbent was about eight times higher than that on the ash. Measured TCLP and SCLP leachability of mercury from the spent sorbent plus ash mixture was less than 1/1000^th of the EPA threshold for landfilling.