METHANE de-NOX for Utility PC Boilers
The overall project objective is the development and validation of an innovative combustion system, based on a novel coal preheating concept prior to combustion, that can reduce NO{sub x} emissions to 0.15 lb/million Btu or less on utility pulverized coal (PC) boilers. This NO{sub x} reduction should be achieved without loss of boiler efficiency or operating stability, and at more than 25% lower levelized cost than state-of-the-art SCR technology. A further objective is to ready technology for full-scale commercial deployment to meet the market demand for NO{sub x} reduction technologies. Over half of the electric power generated in the U.S. is produced by coal combustion, and more than 80% of these units utilize PC combustion technology. Conventional measures for NOx reduction in PC combustion processes rely on combustion and post-combustion modifications. A variety of combustion-based NO{sub x} reduction technologies are in use today, including low-NO{sub x} burners (LNBs), flue gas recirculation (FGR), air staging, and natural gas or other fuel reburning. Selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) are post-combustion techniques. NO{sub x} reduction effectiveness from these technologies ranges from 30 to 60% and up to 90-93% for SCR. Typically, older wall-fired PC burner units produce NO{sub x} emissions in the range of 0.8-1.6 lb/million Btu. Low-NO{sub x} burner systems, using combinations of fuel staging within the burner and air staging by introduction of overfire air in the boiler, can reduce NO{sub x} emissions by 50-60%. This approach alone is not sufficient to meet the desired 0.15 lb/million Btu NO{sub x} standard with a range of coals and boiler loads. Furthermore, the heavy reliance on overfire air can lead to increased slagging and corrosion in furnaces, particularly with higher-sulfur coals, when LNBs are operated at sub-stoichiometric conditions to reduce fuel-derived NOx in the flame. Therefore, it is desirable to minimize the need for overfire air by maximizing NO{sub x} reduction in the burner. The proposed combustion concept aims to greatly reduce NO{sub x} emissions by incorporating a novel modification to conventional or low-NO{sub x} PC burners using gas-fired coal preheating to destroy NO{sub x} precursors and prevent NO{sub x} formation. A concentrated PC stream enters the burner, where flue gas from natural gas combustion is used to heat the PC up to about 1500 F prior to coal combustion. Secondary fuel consumption for preheating is estimated to be 3 to 5% of the boiler heat input. This thermal pretreatment releases coal volatiles, including fuel-bound nitrogen compounds into oxygen-deficient atmosphere, which converts the coal-derived nitrogen compounds to molecular N{sub 2} rather than NO. Design, installation, shakedown, and testing on Powder River Basin (PRB) coal at a 3-million Btu/h pilot system at RPI's (Riley Power, Inc.) pilot-scale combustion facility (PSCF) in Worcester, MA demonstrated that the PC PREHEAT process has a significant effect on final O{sub x} formation in the coal burner. Modifications to both the pilot system gas-fired combustor and the PC burner led to NO{sub x} reduction with PRB coal to levels below 0.15 lb/million Btu with CO in the range of 35-112 ppmv without any furnace air staging.
- Research Organization:
- Gas Technology Institute, Des Plaines, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-00NT40752
- OSTI ID:
- 895024
- Country of Publication:
- United States
- Language:
- English
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