The use of biomass as a renewable fuel source can help the United States reduce its dependence on fossil fuels, especially in providing affordable heat for many middle- and low-income households. However, residential wood combustion (RWC) releases pollutants that can negatively impact the environment and human health, especially for those living in the vicinity of wood-burning locations. Current compliance testing methods are insufficient in capturing the actual in-use emissions of residential wood heaters because they do not represent real-life use, leading to higher emissions during actual use.
This thesis investigates emissions during realistic operations of wood-fired heaters to identify and quantify the majority of emissions and ways to minimize such emissions. The study focuses on investigating eight different woody biomass fired heaters, including three pellet stoves, a pellet boiler, two wood chip-fired hydronic heaters, and two outdoor cordwood fired hydronic heaters. This research contributes a new knowledge on the impact of combustion strategies, fuel type, and control strategies to minimize emissions. The obtained data can provide information to manufacturers, policy makers, and consumers, guiding low-emission and more efficient use of wood-fired heating devices.
In all chapters, variability was evident due to burn phase, fuel type, and operation. The results from the pellet stoves showed that even while using a homogeneous fuel, different burn phases produce different emissions than the overall period. For the pellet boiler studies, the highest efficiencies were achieved during the high load, steady state tests. The burn phase also affects emissions from woodchip boilers, where low output periods are significantly higher in terms of emissions compared to high output periods. Each individual burn phase of the duty cycle produced different emissions in cordwood testing, with steady-state phases having the lowest emissions and highest efficiency. The variability in emissions from different burn phases is a crucial factor in evaluating the performance of wood-burning appliances.
Lower moisture content fuels were found to have better performance in terms of PM emissions and efficiency. Fuel type can impact emissions, but it may be overshadowed by burn phase and technology. Relatively high emissions were often related to low or incorrect air-to-fuel ratios. Gasification techniques used in some woodchip boilers during low output periods significantly increased efficiency and reduced CO emissions. Additionally, gasification techniques used during high burn steady states with wet fuel chips resulted in a 77% reduction in PM emissions. Comparing all the primary heaters studied in this thesis, in terms of PM emission output, showed the units that used gasification, integrated catalysts, or thermal storage had the lowest emissions.
The results of the study are compiled into data sets that give a more accurate picture of real-world operation of wood-fired heaters that will benefit air quality modelers and policy makers. Such emission data for various biomass heaters in EPA’s AP-42, under realistic operating conditions, currently either does not exist or is limited. Additionally, this research identifies the most important parameters that need to be included in the development of high-resolution models, optimizing the performance of wood-fired devices and supporting the transition from current compliance testing to more realistic testing.
In conclusion, this work provides new insights into the performance and emissions of wood-fired heaters during realistic operation. The results of the study can help manufacturers optimize their products for real-life performance and help policy makers and consumers make informed decisions regarding low-emission and more efficient use of wood-fired heating devices. The study highlights the importance of capturing transient phases and the impact of fuel type and control strategies on minimizing emissions.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/4ce9-j192 |
| Date | January 2023 |
| Creators | Trojanowski, Rebecca Ann |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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