Evaluation of aged woodstove catalysts

Abstract

Woodstove emission of atmospheric pollutants has been a growing concern in the last two decades, and catalytic combustors have been used in woodstoves to reduce emissions. Field tests of EPA-certified catalytic stoves have demonstrated that emission factors increase substantially after a few seasons of use, and catalyst degradation is a suspected cause. Previously, an in-field test developed to assess catalyst condition was performed on a group of catalytic stoves in field use. In the current study, a laboratory test apparatus and procedure for the evaluation of woodstove catalysts was developed to verify the accuracy of the field test. Bench tests were performed on 24 aged catalysts retrieved from the field-tested stoves. In the bench test, steady-state conversions of CO and propene were measured at discrete temperatures ranging from 100°C to 400°C. At a temperature of 400°C, the average CO conversion of the aged catalysts was 94.8% and the average propene conversion was 83.1%. Comparison of individual catalyst data did not show a strong correlation between field measurements and bench test data. It is concluded that inaccuracies in the field test are responsible for the lack of correlation, and modifications to the field tests are recommended. In addition to the experimental work, a flow model of a catalytic woodstove was developed to better understand the interaction between the combustion process and the fluid mechanics within a woodstove. Evaluations of a catalytic woodstove under a set of baseline operating conditions show that the catalyst is not a significant source of frictional pressure loss in a catalytic stove-flue system. The model also predicts that increasing the flue crosswind velocity from 0 to 5 m/s will increase the mass flow rate through the stove by 21%.