Reduction of Water Use in Wet FGD Systems

Abstract

Cooperative Agreement DE-FC26-06NT42726 was established in January 2006, and is current through Amendment 2, April 2006. The current reporting period, April 1, 2008 through June 30, 2008, is the eighth progress-reporting period for the project. However, this report will be the final report (instead of a quarterly report) because this project is being terminated. Efforts to bring this project to a close over the past several months focused on internal project discussions, and subsequent communications with NETL, regarding the inherent difficulty with completing this project as originally scoped, and the option of performing an engineering study to accomplish some of the chief project objectives. However, NETL decided that the engineering study did indeed constitute a significant scope deviation from the original concepts, and that pursuit of this option was not recommended. These discussions are summarized in the Results and Discussion, and the Conclusion sections. The objective of this project by a team lead by URS Group was to demonstrate the use of regenerative heat exchange to reduce flue gas temperature and minimize evaporative water consumption in wet flue gas desulphurization (FGD) systems on coal-fired boilers. Furthermore, the project intended to demonstrate that regenerative heat exchange to cool flue gas upstreammore » of the electrostatic precipitator (ESP) and reheat flue gas downstream of the FGD system would result in the following benefits to air pollution control (APC) systems on coal-fired power plants: (1) Improve ESP performance due to reduced gas volume and improved ash resistivity characteristics, (2) Control SO3 emissions through condensation on the fly ash, and (3) Avoid the need to install wet stacks or to provide flue gas reheat. Finally, operation at cooler flue gas temperatures offered the potential benefit of increasing mercury (Hg) removal across the ESP and FGD systems. This project planned to conduct pilot-scale tests of regenerative heat exchange to determine the reduction in FGD water consumption that can be achieved and assess the resulting impact on APC systems. An analysis of the improvement in the performance of the APC systems and the resulting reduction in capital and operating costs were going to be conducted. The tests were intended to determine the impact of operation of cooling flue gas temperatures on FGD water consumption, ESP particulate removal, SO{sub 3} removal, and Hg removal, and to assess the potential negative impact of excessive corrosion rates in the regenerative heat exchanger. Testing was going to be conducted on Columbian coal (with properties similar to low-sulfur Eastern bituminous coal) and SO{sub 3} will be spiked onto the flue gas to simulate operation with higher SO{sub 3} concentrations resulting from firing a higher sulfur coal, or operating with a selective catalytic reduction (SCR) unit. The project was also going to include associate planning, laboratory analytical support, reporting, and management activities. The URS project team finalized a conceptual alternative approach to demonstrate, via an engineering study, the use of regenerative heat exchange to reduce flue gas temperature and minimize evaporative water consumption. This idea was presented in summary format to NETL for consideration. NETL determined that this alternative approach deviated from the original project objectives, and that it would be in the best interest of all parties involved to cancel the project.« less