Paper details

Title:

Multi-fuel Boiler Combustion System Upgrade and Controls Optimization

Author(s):

Pethe, S.J., Tebbetts, R.G., Porter, T.J., Britt, M.L., Frasca, M.C.

Document(s):

Abstract:

Wheelabrator Technologies Inc. (WTI) operates an energy generating station in Auburndale, Florida, where a single 664.7 GJ/hr multi-fueled steam power boiler generates 50 MW of electrical power. During a typical day, the boiler operates at a peak load steaming rate of 156.5 tons/hr for about 11 hours while firing a mixture of landfill gas, wood waste, and municipal solid waste consisting of tires and yard waste. For six hours at night, the steaming rate is lowered to 90.7 tons/hr while firing wood waste only. The unit is subject to a carbon monoxide (CO) emission limit of 90.7 kg/hr on a 30-day rolling average equivalent to 339 ppm (dry at 7% oxygen (O2)). The boiler was to be classified as a Refuse Derived Fuel stoker boiler under the United States Environmental Protection Agency’s Large Municipal Waste Combustor requirements in 40 CFR 60, Subparts Ea/Cb. With the new classification, the boiler would become subject to a lower CO emission limit of 150 ppm (dry at 7% O2) on a 24-hour block average. WTI contracted Jansen Combustion and Boiler Technologies, Inc. to assess the boiler combustion system and following this assessment received a contract to engineer/implement combustion improvements to meet the 150 ppm CO limit. Historical operation showed that measured CO levels on a continuous basis were well below the 90.7 kg/hr limit, but they were below the 150 ppm limit for less than 60% of the time. CO would elevate and become variable during peak load. The analyses revealed that significantly lower CO emissions could be achieved by improving combustion conditions. Current and new combustion system arrangements were evaluated with Computational Fluid Dynamics modeling. The modeling revealed the primary cause of high CO was an ineffective overfire air (OFA) system which resulted in limited penetration and mixing. This system consisted of multiple rows of small ports on the front and rear walls. Combustion modeling with larger and fewer interlaced side wall OFA nozzles was shown to significantly improve CO burnout. Limited combustion air flow metering instrumentation prevented cascade mode boiler operation. This was a challenge as manual adjustments to air damper outputs would be required to adjust the airflows through the daily change in steaming rate and fuel mix transitions. The boiler upgrade included installation of a new OFA system, air metering instrumentation, and a reconfiguration of the combustion controls. Subsequent testing shows a 50% reduction in CO at peak load and the unit confidently achieves the 150 ppm 24-hour block average limit. The controls now automatically modulate the air flows to adjust for the daily changes in boiler load and the fuel mix between the landfill gas, wood waste, and tires without requiring operator intervention.

Keywords:

carbon monoxide, computational fluid dynamics (CFD), combustion optimization, boiler upgrade, emissions control, overfire air, waste-to-energy

Topic:

Industry Sessions

Subtopic:

Power & Heat processes and systems

Event:

27th European Biomass Conference and Exhibition

Session:

IBO.16.2

Pages:

1902 - 1909

ISBN:

978-88-89407-19-6

Paper DOI:

10.5071/27thEUBCE2019-IBO.16.2

Price:

FREE