FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: COMBUSTION TECHNOLOGY FOR MINIMIZING NOX EMISSIONS BURNING ILLINOIS COALS

ICCI Project Number: 96-1/5.1A-2

Principal Investigator: Murray F. Abbott, CONSOL Inc.

Other Investigators: Jamal B. Mereb, CONSOL Inc.

Project Manager: Ronald H. Carty, ICCI

ABSTRACT

The objective of this project is to demonstrate the combined application of low-NOxburner and pulverized coal reburning technologies as a low-cost option to reduce NOxemissions (possibly as low as 0.15 lb/MM Btu) while firing Illinois coal in dry-bottom pulverized coal steam generators. A successful demonstration may help to maintain or increase Illinois coal use for power generation in the face of economically and environmentally driven competition from both Powder River Basin coal and natural gas.

The project was conducted in the CONSOL 1.5 MM Btu/h combustion pilot plant. Both wall-fired and tangentially-fired burner configurations were investigated firing two commercial high-volatile (36-40% dry volatile matter) Illinois Basin bituminous coals from two CONSOL mines. Pulverized coal was used as both primary and reburn fuels. The impact of the furnace operating variables on NOx emissions and fly ash loss on ignition (LOI) was assessed.

There were significant differences in NOx emissions between the two burner configurations and minor differences between the two test coals. Specifically, NOxemissions were 0.08-0.16 lb/MM Btu lower in the tangentially-fired configuration than in the wall-fired configuration, with larger differences at higher reburn stoichiometries. Pulverized coal reburning reduced NOx emissions from 0.77 (baseline) to 0.23 lb/MM Btu (70% reduction) in the wall-fired configuration, and from 0.61 (baseline) to 0.15 lb/MM Btu (75% reduction) in the tangentially-fired configuration. There were significant differences in LOI between the two test coals and minor differences between the two burner configurations. Pulverized coal reburning increased LOI from less than 1% (baseline) to 10-13% for the higher heating value coal and 2-4% for the lower heating value coal.

The reburn stoichiometry was the dominant operating variable affecting NOx emissions and LOI. An optimum reburn stoichiometry of about 0.84 was identified for low NOxemissions. Changes in the firing rate, the primary stoichiometry and the final stoichiometry produced relatively minor changes in NOx emissions and LOI.

EXECUTIVE SUMMARY

The objective of this project is to demonstrate the combined application of low-NOxburner and pulverized coal reburning technologies as a low-cost option to reduce NOxemissions while firing Illinois coal in dry-bottom pulverized coal steam generators. A successful demonstration of low NOx emissions (near or below 0.15 lb/MM Btu) may help to maintain or increase Illinois coal use for power generation in the face of economically and environmentally driven competition from both Powder River Basin coal and natural gas.

The project was carried out in the CONSOL 1.5 MM Btu/h combustion pilot plant. A pulverized coal reburn system and an over fire air system were independently designed, constructed, tested and installed. Pulverized coal was used as both primary and reburn fuels.

The CONSOL combustion pilot plant is a multi-burner coal combustion test facility with typical feed rates of 100 lb/h for high heating value bituminous coals. It is demonstrated that the combustion pilot plant provides a realistic simulation of virtually any commercial pulverized coal-fired steam generator furnace. It is the only test facility which provides for pulverized coal-fired furnace testing in multiple firing configurations, i.e., wall-fired or tangentially-fired. The project takes advantage of this feature by investigating the application of pulverized coal reburning to both commonly used pulverized coal firing configurations.

In this study, CONSOL investigated both opposed wall-fired and tangentially-fired burner configurations firing two commercial high-volatile (36-40% dry volatile matter) Illinois Basin bituminous coals from two CONSOL mines: one containing 0.9% sulfur, 1.6% nitrogen and 12,300 Btu/lb heating value, the other, lower in rank, containing 3.2% sulfur, 1.2% nitrogen and 11,000 Btu/lb heating value. CONSOL also investigated the impact of four furnace operating variables on NOx emissions and fly ash loss on ignition (LOI): firing rate, primary combustion zone stoichiometry, reburn combustion zone stoichiometry and final stoichiometry.

There were significant differences in NOx emissions between the two burner configurations and minor differences between the two test coals. Specifically, NOxemissions were 0.08-0.16 lb/MM Btu lower in the tangentially-fired configuration than in the wall-fired configuration, with larger differences at higher reburn stoichiometries. Pulverized coal reburning reduced NOx emissions from 0.77 (baseline) to 0.23 lb/MM Btu (70% reduction) in the wall-fired configuration, and from 0.61 (baseline) to 0.15 lb/MM Btu (75% reduction) in the tangentially-fired configuration. However, NOxemissions as low as 0.20 and 0.13 lb/MM Btu were obtained in the two burner configurations, respectively. There were significant differences in LOI between the two test coals and minor differences between the two burner configurations. Pulverized coal reburning increased LOI from less than 1% (baseline) to 10-13% for the higher heating value coal and 2-4% for the lower heating value coal.