In addition, wide commercial acceptance of the new system could contribute to significant reductions in national emissions and help extend the life of more than 400 power plants with capacities of 50–300 megawatts, enabling them to continue to produce reliable electricity. These smaller existing units are a valuable part of the Nation's energy infrastructure, constituting almost 60 gigawatts, which is roughly 20 percent of the country's coal-based capacity. Continued operation of such plants would enable utilities and ratepayers to avoid the higher costs of building new plants to replace them.
The goal of the Greenidge Multi-Pollutant Control Project was to show that the multi-pollutant control system could substantially reduce emissions of nitrogen oxides, sulfur dioxide, sulfur trioxide, hydrochloric acid, and mercury, while affording lower capital and maintenance costs and smaller space requirements than leading conventional technologies. The project succeeded in all respects. It began startup and testing in early 2007 and concluded in October of this year.
Many smaller coal-fired units such as AES Greenidge Unit 4 do not have sufficient land area to install conventional pollution control equipment. These units are also penalized by economies of scale, making it difficult to justify the large capital investment required to retrofit them with technologies such as selective catalytic reduction (SCR) and wet flue gas desulfurization (FGD).
The new system required only 0.4 acres of land, significantly less than would have been required for these conventional systems. Moreover, it had a total plant cost roughly 40 percent less than the estimated cost to retrofit the same unit with conventional SCR and wet FGD.
Greenidge's 107-megawatt, 1953-vintage Unit 4 is a tangentially-fired boiler that primarily burns eastern bituminous coal. The unit's new multi-pollutant control equipment includes: (1) a hybrid SCNR/SCR (selective noncatalytic reduction/selective catalytic reduction) system for nitrogen oxide control; and, (2) a circulating fluidized bed dry-scrubbing system for control of sulfur dioxide, mercury, acid gas, and particulate matter. An activated carbon injection system was also installed, but it proved unneccesary to meet the project's mercury removal goal.
Operating data collected through June 2008 revealed average pollutant reductions of 96 percent for sulfur dioxide, 95 percent for sulfur trioxide, 97 percent for hydrochloric acid, and 98 percent for mercury—all of which meet or exceed target values. In addition, the nitrogen oxides emission rate goal of less than or equal to 0.1 pounds per million British thermal units was demonstrated during short-term testing. Although not an original project goal, the system reduced emissions of particulate matter by more than 98 percent relative to the emission rate achieved by the unit's particulate control equipment prior to the project.
A part of the Energy Department's Power Plant Improvement Initiative, the project was conducted by CONSOL Energy Inc., AES Greenidge LLC, and Babcock Power Environmental Inc. The Office of Fossil Energy's National Energy Technology Laboratory was responsible for project oversight through a financial assistance cooperative agreement with CONSOL.