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Mercury Removal by Activated Carbon Injection

• Yes, Simon, PRB refers to Powder River Basin coal. The Powder River Basin is an area in southeast Montana and northeast Wyoming known for its rich coal deposits. Mines in this area supply around 40% of the coal fired power plants in the U.S. It is known for its low sulfur and ash content, but it also has a low chlorine content which leads to more of the mercury being emitted in the elemental form. The elemental form is harder to capture which is why the activated carbon used for adsorption is commonly treated with a halogen.

• The table below shows how much carbon is typically needed for different removal efficiencies.
Target Hg Removal Efficiency(%)--------Predicted Injection Concentration(lbs/MMacf)------Predicted Injection Ratea(lbs/h)
....................50..............................................................0.5...................................................................<30
....................75..............................................................1.5.....................................................................45
....................90..............................................................3.0.....................................................................90
a. Injection rate based on nominal flow at full load of 500, 000 acfm.

• The activated carbon mercury removal technology has been implemented at a number of sites where variable testing has been done. These include but are not limited to PG & E National Energy Group sites in Salem Harbor, MA and Braton Point, MA, Wisconsin Electric in Pleasant Prairie, WI, Alabama Power in Glaston, AL, and also Ontario Power Generation. Presque Isle Power Plant in Marquette, MI is projected to be the first to implement this technology on a full scale in 2009.

• The mercury emitted in the taconite process comes mainly from stack gases. It is important to note that the taconite mercury emissions are mostly a regional problem. In Northeast MN, taconite processing is a sufficiently large industry that it is one of the biggest emitters of mercury in the state of Minnesota and to the Lake Superior Basin. However, it is not so large as to significantly impact national and international mercury atmospheric budgets.

• Carbon injection as a sorbent normally occurs after the main particulate collection has already occurred. Studies have shown that this increases efficiency of mercury removal. Below is a schematic which illustrates particulates being collected by an electrostatic precipitator, after which a baghouse collects the mercury adsorbed onto the injected carbon.

schematic.bmp

Comments

The formatting is tricky on this thing. The values for projected injection rate did not show up. They are <30, 45, and 90.

Looks like an interesting process to remove Mercury. I wonder what will happen if it is put into full scale all the time. Do you guys think that this would be a good solution in the future to remove mercury on a large scale?

How do they remove the carbon/ mercury from the stack gas if it is done after the ESP? Do thay add in another particle removal (like a cyclone). What happens to the carbon after it is collected - can the mercury be removed or is off to a landfill? If landfill, how much mass is generated in a typical day? Can it be mixed with the other solid wastes? Oh, too many questions...

As Steve mentioned what happens to the carbon after it is used to adsorb the mercury. Does this process result in an increase in particulates coming from the stack? What size activated carbon particles are used? Does the this process reduce other pollutants at the same time?

As Steve mentioned what happens to the carbon after it is used to adsorb the mercury. Does this process result in an increase in particulates coming from the stack? What size activated carbon particles are used? Does the this process reduce other pollutants at the same time?

It was not mentioned in the post, but the carbon is collected in a baghouse as shown on the diagram.