Four Different Approaches to Removing the Mercury Presented in Hot Topic Hour August 2
Dr. Behrooz Ghorishi, R&D Director for Albemarle’s Environmental Division, made a case for using a concrete friendly activated carbon. The economic benefits of using flyash to replace a fraction of the cement in concrete include increased revenue from the sale of the ash and reduced costs for flyash disposal. The main concern for power plants that sell their flyash for cement replacement is that powdered activated carbons (PAC)-based sorbents used for mercury control make the flyash incompatible with concrete. PAC adsorbs the air-entraining admixtures (AEAs) that are added to the concrete slurry. These surfactants enable incorporation of the precise amount of air bubbles needed to create the air voids required for concrete workability and freeze-thaw capabilities.
Albemarle, using an innovative one-step process, commercialized a Concrete-Friendly™ mercury sorbent, C-PAC™, which is currently used in several power plants across the U.S. Flyash containing C-PAC demonstrates equally high strength concrete as flyash without any activated carbon. The cost of C-PAC is slightly higher than the standard product but for a utility which wants to sell its flyash it is cost effective solution. Three cement plants have also have successfully utilized C-PAC. In these plants C-PAC is added ahead of the kiln baghouse. Most of the dust with the C-PAC returns to the kiln but a portion is directed to use in the final product.
Kyle Neidig, Manager of SCR Catalyst Products at Hitachi Power Systems America, reported on a new catalyst (TRAC®) which achieves NOx reduction, minimizes SO3 creation and has substantially improved conversion of elemental mercury to an oxidized form. These catalyst improvements present significant cost savings for compliance by either reducing or eliminating the need for new air pollution controls on utility coal-fired generating units. Full scale units have demonstrated good performance. A Northern U.S. power plant was achieving 35 percent mercury removal. After installing TRAC to replace just one of the four catalyst layers the efficiency improved to 70 percent. NOx removal was 90 percent. The HCl content was 0.5 ppm. This is a plant burning PRB coal with an ESP and a wet FGD. At plant Miller the replacement of one layer increased Hg capture from 30 to 60 percent.
Jonas Klingspor, Vice-President of Business Development at URS, reported on development of the Gore/URS mercury control technology. This technology utilizes a fixed bed technology installed after the mist eliminator and has some interesting characteristics: It is not sensitive to mercury speciation, not sensitive to the concentration of mercury, does not rely on injection of activated carbon or bromides, does not contaminate flyash, has a lifetime of between three to nine years between replacement, has a very low pressure drop, and achieves 90 percent plus mercury removal and 60 percent SO2 removal.
A number of pilot tests are proceeding in parallel. The expectation is to offer the system commercially in the fourth quarter of 2012. The system is applicable to any plant exhaust which contains at least 2 ppm SO2. The SO2 is converted to sulfuric acid, which functions to keep the membrane clean. Tests have been conducted at a cement plant where promising results were achieved. The fact that it is placed downstream of the scrubber allows it to function in a complementary rather than competitive manner with other technologies. So a scrubber with 80 percent total mercury removal can be complimented by a Gore module with 50 percent removal to achieve 90 percent total removal.
By contrast the TRAC/scrubber and activated carbon technologies are competitive. If the scrubber is achieving 80 percent total mercury removal with an inlet of 100 lbs/yr, then it is removing 80 pounds. Then an activated carbon injection system is installed upstream for 50 percent removal or 50 pounds. The scrubber now only sees 50 lbs of mercury and removes 80 percent. So it is now only removing 40 pounds per year.
Jon Lehmkuhler, Commercial Manager of Great Lakes Solutions (a Chemtura business), reviewed the bromine-based products which are available for mercury reduction. Both calcium bromide and sodium bromide are available in liquid form. The company can advise users relative to storage and transfer. Railcars with transfer from dip-tube and trucks from bottom valve are proven delivery modes. Storage tanks should be properly insulated or liquid should be circulated in colder regions. The crystallization temperature is a function of the pressure and other factors. It can vary from 10°F to 27°F depending on these variables. The company maintains an inventory at multiple strategic locations. It can provide onsite support and service for delivery by drum, truck or rail car.
The Bios, Abstracts and Photos information is linked below.
BIOS, ABSTRACTS, PHOTOS - AUGUST 2, 2012.htm