July 15, 2008

New strategies for conquering environmental challenges

Angela Neville, JD

Advances in mercury control technologies

Under the Clean Air Mercury Rule (CAMR), many coal-fired power plants in the U.S. would have been mandated to cut their mercury emissions below current levels by 2010, and additional reductions were scheduled to take place by 2018. In February 2008, however, the U.S. District of Columbia Circuit Court of Appeals dismissed CAMR and reinstated a more stringent regime as set out under the Clean Air Act Section 112. Currently, the EPA is regrouping and evaluating the impact from that decision. This regulatory rollercoaster underscores the need for utilities to develop more effective mercury capture systems as soon as feasible. (See “Future of national mercury rule now uncertain” in POWER, May 2008 for an in-depth review of the status and prospects of new mercury rules.)

1. Take a powder. Lawrence Bool, III, senior development associate at Praxair, presented “Production of Powdered Activated Carbon for Mercury Capture Using Hot Oxygen.” Source: POWER

In the session that focused on mercury control technologies, Lawrence Bool, III, senior development associate at Praxair, discussed the production of powdered activated carbon (PAC), which is used for mercury capture from coal-fired power plants. He talked about the use of the new patented hot oxygen burner developed by his company. PAC is an often-used sorbent that can be effective for both elemental and oxidized mercury capture (Figure 1).

Bool explained how a patented burner is used as the basis of the multistage PAC production process. First, the hot, oxygen-rich gas mixes with pulverized coal feedstock and reacts in an entrained flow reactor. The oxidizing gas reacts with the carbon to open pores. Then a quench is introduced to cool the gas and solids. Cooled carbon particles and syngas are separated in a cyclone. Next, the syngas is returned to the utility boiler as fuel and the PAC is further cooled and sent to a storage silo. According to Bool, the process yields PAC with good mercury capture characteristics with a number of different coals.