Wiley & Associates conducted full-scale field-testing of a Dense Phase Reburn Combustion System (DPRCS). DPRCS controls combustion stoichiometry from the bottom to the top of the furnace using dense phase injection of micronized coal at a particle size of 80% minus 325 mesh. The testing was conducted at Progress Energy's 150 MW Cape Fear Unit No. 5 that burns a low sulfur bituminous coal in a tangentially-fired furnace. The DPRCS was used in conjunction with Mobotec's rotating overfire air (ROFA™) and ROTAMIX™ systems. Baseline NOx emission rates with the ROFA system ranged from 0.17 to 0.26 lb/MMBtu. During DPRCS testing the micronized coal feed rate averaged 13% of total fuel input and the unit operated at approximately 75% capacity. Tests were conducted with micronized coal injection at four elevations ranging from the lower furnace to below the ROFA injection level in the upper furnace. NOx control performance during the DPRCS testing was mixed depending on injection location. Injection below the ROFA resulted in a 14% increase in the NOx emission rate. Various combinations of DPRCS injection points from the bottom to top coal burner elevations resulted in NOx emission rate reductions ranging from 10% to 30%.

In addition to the reburn studies, furnace sorbent injection (FSI), using finely powdered limestone and Trona, was examined in combination with the NOx reduction capabilities of the ROFA to achieve SO₂ and mercury reductions with relatively low capital and operating costs. These two sorbents were chosen to compare the impact of calcium carbonate versus sodium carbonate in a highly reactive environment. Significant SO₂ reductions of 69% were achieved with Trona and 64% with limestone. Mercury reductions of 89% were achieved with limestone and 67% with Trona. However, slagging in the superheater section was a major operational concern and will need to be addressed by more frequent soot blowing in future applications.