No single technology will work for every coal-fired power plant. The mercury control options under investigation can be classified into six broad categories:
• Sorbent injection involves injecting a material, usually in powdered form, that adsorbs mercury upstream of a particulate collector such as a baghouse or electrostatic precipitator (ESP). Activated carbon injection currently represents one of the most promising controls on the horizon. It is the only technology that is close to being commercialized.
• Wet and dry scrubbers collect soluble and condensable oxidized mercury species such as mercuric chloride. Both types are usually installed to remove a gas—such as SO%—that contributes to the formation of acid rain. However, a few wet scrubbers are used primarily to capture particulate matter (fly ash).
• Catalysts or chemicals can be added to coal or flue gas to oxidize elemental mercury to soluble mercury or convert all forms of vapor-phase mercury to particulate form. This enables the downstream particulate and/or 862 control to capture the mercury.
• Fixed or fluid beds have been used in Europe for mercury polishing in waste incineration plants. Circulating fluidized beds that use fly ash and limestone placed upstream of the primary particulate collector for SOx control may reduce mercury through the introduction of mercury sorbents into the bed.
• Mercury adsorption by fixed structures such as honeycombs and plates is being investigated as part of the development of EPRI’s MerCAP process.