Practical NOx reduction techniques using CWS fuels

Conference · Thu Dec 31 04:00:00 EST 1998

OSTI ID:349119

Ashworth, R A ^[1]

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1. Advanced Systems, Energy and Environmental Research Corp. (United States)

Waste coal fines from coal preparation plants, cleaned and formulated as a low cost coal water slurry (CWS) fuel, can be fired with coal in electric utility boilers to reduce NOx emissions. The CWS fuel produced is a low tech 50/50 coal/water slurry that requires no additives. Several CWS firing options are available depending on the NOx reduction desired. For example, if a utility has wall or tangentially-fired units, the CSW may be co-fired with coal through existing burners to reduce NOx emissions. Using this option to replace coal with a lower cost CWS, NOx emissions may be reduced some 15 to 25%. Unprocessed lower cost coal pond fines may be co-fired in CWS form in a cyclone-fired boiler. However, the NOx reduction potential ({approximately} 10%) is less than that for tangential and wall-fired units. If the NOx reduction using the straight co-fire option discussed above is not great enough to meet a certain station`s regulatory limit then a close-coupled air staging technique may be used. Since CWS co-firing adds a new fuel delivery system to the utility furnace, in many cases, the pulverized coal mill(s) feeding the top row of burners on a furnace may be taken out of service. With this option, the upper row of burners are used to supply close-coupled overfire air. Using this air staging technique, NOx emissions may be reduced by some 35 to 40% below baseline levels. If the second technique is still not adequate to meet a station`s regulatory limits, CWS Reburning with a separate overfire air system may be used to reduce NOx emissions some 60 to 70% below baseline conditions. A fourth option may be used to co-fire low cost unprocessed coal pond fines. With this approach, staged combustors would be retrofitted to the boiler to co-fire both coal and CWS. A staged combustor retrofit, although higher in capital cost, offers several operational/environmental advantages: (1) 70 to 80% of the ash is removed in the combustor proper; (2) NOx emissions are low, 0.30 lb/10{sup 6} Btu w/combustor alone and 0.15 lb/10{sup 6} Btu w/combustor plus overfire air; and (3) if the CAIRE{trademark} staged combustor is used, sulfur may also be removed in the combustor proper (70%+ reductions in SO{sub 2} emissions are projected). The technical aspects and economics of using these four CWS firing options are discussed in this paper. The Energy and Environmental Research Corporation has participated in CWS co-firing demonstrations on wall-fired, tangentially-fired and cyclone-fired units. Also, CWS Reburning tests have been completed on a 10 million Btu/hr pilot plant. The CAIRE combustor has been tested at the 12 million Btu/hr pilot scale, and a 25 to 50 million Btu/hr prototype demonstration is currently planned.

• OSTI ID: 349119
• Report Number(s): CONF-980985--; ISBN 1-890977-15-2
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
20 FOSSIL-FUELED POWER PLANTS
AIR POLLUTION ABATEMENT
BOILERS
COAL
COAL FINES
COCOMBUSTION
FUEL SLURRIES
MATERIALS RECOVERY
NITROGEN OXIDES
SETTLING PONDS
STAGED COMBUSTION
WATER