Mercer Station Cuts NOx With Reburn Experiments
THE 1999 OZONE season is fast approaching and utilities in the Ozone Transport Region are facing requirements for cuts in NOx emissions. The Gas Research Institute (GRI) is sponsoring field experiments at Mercer Station in Hamilton Township, N.J. to establish the commercial viability of Amine-Enhanced Fuel-Lean Gas Reburn (AEFLGR) technology to assist utilities in meeting emissions requirements.
The technology involves injecting a stream of amine-enhanced natural gas into the upper furnace flue gas with high-velocity turbulent jets. The process results in chemical reactions that reduce NO to molecular nitrogen within the proper temperature window. The amount of natural gas is controlled to maintain an overall fuel-lean stoichiometry in the upper furnace, eliminating the need for additional air injection above the gas injection zone.
Experiments using the new technology have been conducted since January 1998 in the reheat furnace of a Foster Wheeler wall-fired, wet-bottom boiler at Mercer Station. Unit 2 burns low-sulfur, Eastern bituminous coal as a primary fuel with natural gas as a start-up and secondary fuel. This unit was considered an appropriate site for the first full-scale demonstration of the technology. The unit is equipped with selective noncatalytic reduction. The AEFLGR process is a combination of the urea-based Fuel Tech`s SNCR process, called NOxOUT, and the fuel-lean gas reburn process developed by Energy Systems Associates with GRI support.
“Laboratory results repeatedly showed that the combination of FLGR and SNCR could be synergistic. The amine essentially doubles the gas effectiveness at constant dollars per ton of NOx removed,” said Roy Johnson, Fuel Tech vice president of business development.
The Mercer experiments use existing boiler openings for the SNCR injectors at the front and back walls of the furnace, which were modified for co-injection of gas and urea.
“We are attempting to use the Linear Integral Moment advanced modeling U to guide us in optimizing the co-injection of gas and urea to achieve our NOx goals across the load range of 60 MW to 320 MW,” said John Pratapas, GRI team leader. “So far the test results are promising. We`ve been able to reach or exceed our goals at 200 MW or less.”
Goals for the experiment include NOx reductions of more than 60 percent across all loads, less than 8 percent natural gas heat input and a urea non-stoichiometric ratio of 1.5 or less, and CO emissions below 100 ppm.
The chemical reactions of SNCR are efficient NOx reducers within a temperature window of 1,700 to 1,900 F. Using natural gas as a carrier widens the acceptable temperature window, allows urea injection at higher temperatures, and improves the kinetic rates of the critical chemical reduction mechanisms. Reaction completion at higher temperatures also decreases the chance of ammonia slip. Installed capital costs for the Mercer project were around $25/kW.
GRI has filed a patent application for the technology and has plans to automate and expand the AEFLGR process to the entire Mercer plant this year.