| OCR Text |
Show a) Gas injection at the 6th floor elevation will give better NOx removal efficiency that at the 5th floor A 2 4 % relative improvement in NOx reduction is predicted i f gas is injected at the 6th floor elevation. b) Gas should be injected through the six front wall injectors, as well as through the two foremost sidewall injectors, since these introduce gas into the fuel-rich zone near the furnace front wall. Up to 3 3 % relative improvement in NOx reduction is predicted when using this inector configuration. c) Gas injectors should be modified to introduce gas at the largest downward angle possible while avoiding significant wall interference effects. An additional 16% relative improvement in NOx reduction is predicted if 60° injector inclinations are used in place of the existing 45° injectors. d) Injector holes should be enlarged to 5/8-in. to avoid over-penetration of the reburn gas past the oxygen mixing layer Certain of these recommendations are currently under consideration for possible implementation to improve the reburn system performance at Elrama Unit 2. 4. LIM SIMULATIONS OF GAS REBURNING AT JOLIET UNIT 6 Commonwealth Edison's (ComEd) Joliet Unit 6 is a 327 M W e cyclone-fired coal-burning utility boiler manufactured by Babcock & Wilcox and placed in service in 1959. A schematic of the facility is shown in Fig. 15. The unit is fired by nine horizontal cyclone furnaces, with four cyclones on the front wall and five on the back wall. The primary furnace is 60-ft. wide. 20-ft. deep, and 25-ft. high, and the secondary furnace is nearly 90-ft. high. Combustion gases move upward from the primary furnace through the split secondary furnace, the secondary superheater, the primary superheater and reheater, and the economizer. A fuel-lean gas reburn system for Joliet Unit 6 was designed by ESA and ComEd, in collaboration with the Gas Research Institute (GRI), prior to the simulation work described here. This system consists of a total of 36 gas injectors within the secondary furnace. 26 of which are located at the 208-ft. elevation and 10 located at the 229-ft. elevation. These locations are. respectively. 56 feet and 35 feet below the entrance to the secondary superheater. Half of the injectors are located on each of the front and back walls of the furnace. The nozzles were designed to allow gas injection perpendicular to the wall via high velocity jets. 4.1 LIM simulation geometry and initial conditions As was the case for Elrama Unit 2. the Joliet Unit 6 furnace and the reburn gas injection system developed for it are reasonably well suited to the two-dimensional modeling currently accessible to LIM simulations. However, unlike Elrama Unit 2, Joliet Unit 6 is a much more homogeneous furnace. For this reason, it is possible to avoid modeling the primary coal combustion process that results in the cyclones and in the primary furnace, and instead take the primary combustion product stream entering the secondary furnace as being uniform. As in the previous case, all surfaces with the exception of inflows and outflows are represented by zero flow-through |
