CONSOL R&D, PPL, Lechler, and Martin Marietta propose to conduct a field trial of the Low-Temperature Mercury Control (LTMC) process at Unit 1 of the PPL Martins Creek Station. LTMC has the ability to reduce mercury emissions by over 90% as was recently demonstrated by CONSOL R&D on a slip-stream pilot plant at the Allegheny Energy Mitchell Station under DOE Cooperative Agreement DE-FC26-01NT41181. The next step is to demonstrate the performance, operability, and economics on a full-scale utility boiler. In addition this project will demonstrate that magnesium hydroxide (Mg(OH)₂ ) slurry injection into the flue gas reduces SO₃ concentration sufficiently to avoid corrosion at the low-temperature conditions, and will demonstrate that water spray humidification can maintain ESP performance under low-SO₃ conditions.

The LTMC process, controls mercury by cooling the flue gas temperature to about 220°F and absorbing the mercury on the carbon inherent in the fly ash. The host site will be the PPL Martins Creek Unit 1, which is a nominal 130 MWe bituminous coal-fired unit. Martins Creek fly ash, with an LOI between 20 to 25%, is ideally suited for mercury capture. The flue gas exiting the boiler from this unit is divided into two ducts, each equipped with its own air heater and ESP. The LTMC process will be installed on one of the two ducts, leaving the other duct untreated as a control. On the treated side, the flue gas temperature will be reduced from a nominal 300°F to 220°F using water sprays inserted into the existing duct work. To prevent corrosion, magnesium hydroxide slurry will be sprayed into the flue gas before it enters the air heater. A 2 to 6 month test will collect operating data on mercury removal and balance of plant impacts from the process. The project will include an economic analysis, including estimates of capital costs, and fixed and variable O&M costs.

This technology has the potential to remove over 90% of the flue gas mercury at a cost at least an order of magnitude lower (on a $/lb Hg removed basis) than activated carbon injection. The technology is suitable for retrofitting to existing and new plants, and, although it is best suited to bituminous coal-fired plants, it may have some applicability to the full range of coal types. Another benefit is the reduction of SO₃ emissions; SO₃ is a precursor of secondary fine particulate matter and a cause of visible plume problems, and forms ammonium bisulfate air heater deposits when NOx control technologies are in use.

The short-term tests at the Mitchell pilot plant achieved 90+% SO₃ removal at a Mg/SO₃ mole ratio of 4, and >90% mercury reduction at 220 °F with fly ash containing 10 to 15% LOI. The field trial at Martins Creek will prove the concept of deep control of mercury by capture on fly ash via flue gas cooling accompanied by corrosion protection.

Other participants are PPL (the host utility), Lechler, Inc. (the spray nozzle manufacturer), and Martin Marietta (supplier of the magnesium hydroxide).