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Three portable dilution devices (a two-stage dilutor, a one-stage dilutor and an axial dilutor) and a stationary dilution tunnel were compared by employing them in an experimental setup for particle emission measurements from a 40 kW pellet boiler. Total concentrations and number size distributions of particles were detected by an ELPI + analyzer. Averaged values of total particle emission per MJ received from measurements with available dilution devices were within the range between 3.14 × 1013 and 1.15 × 1014 for the full power regime, and between 1.54 × 1013 and 5.03 × 1013 for the reduced power regime. Measured particle concentrations decreased by using dilution devices in the following order: a two-stage dilutor, a one-stage dilutor, a dilution tunnel and an axial dilutor. The number size distributions of particles for the majority of cases are qualitatively similar for all devices for similar combustion regimes of the boiler. Applying dilution air with or without heating did not significantly affect the results of measurements. During multiple series of measurements the degree of dilution was varied when possible for different devices within a range between 8 and 102. No dependence of particle concentrations on the degree of dilution could be determined from these experiments. Applying a method of one-way analysis of variance revealed the statistically significant difference in particle concentrations measured with different dilution devices. Implementing this method to CO, and CO2 gas emission components of different series it was determined that the boiler operation was stable as the measured data belong to the same distribution. Thus, the statistical differences in particle concentrations most likely relate to the varied measuring equipment, i.e., dilution devices. Copyright © 2021 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Abstract: Biomass combustion in pulverized-fuel boilers is a growing way to produce electricity from a renewable source of energy. Slagging and fouling limit however the reliability of the units that were initially designed for coal combustion. Computational Fluid Dynamics (CFD) codes aiming at studying those phenomena include simplified models of biomass particle pyrolysis, of which the pertinence has already been questioned for the typical conditions of interest. A comprehensive model has been developed to investigate pyrolysis of particles in pulverized-fuel boilers, with sizes ranging from 17μm to 2.5mm. The detailed model accounts for internal heat conduction, internal gaseous convection, moisture evaporation and particle shrinkage. It includes a competitive, multi-component kinetic scheme, improved for high temperatures. The discrepancy between the simplified models integrated in most CFD applications and the detailed simulations is highlighted. The simplified isothermal models underestimate pyrolysis time for the largest particles. Moreover, such models delay and shorten the volatiles release. The flame lengths, the local temperature fields and the pollutant emissions might be importantly impacted in global combustion simulations. Apparent kinetic parameters have been derived from the detailed simulations. Their use in existing simplified models improves the behavior of the biomass particles during pyrolysis, and offers therefore an efficient alternative to the integration of complex pyrolysis models in CFD codes. [ABSTRACT FROM AUTHOR]

Electrostatic precipitators (ESP) are an effective means of reducing particulate matter emissions from biomass combustion. This study presents a comprehensive evaluation of the performance of an ESP integrated in a 240 kW wood chip boiler. The boiler-integrated ESP is commercially available and is evaluated in-situ using two types of wood chips, unlike previous studies, which mainly focuses on prototypes or lab-based constructions. The obtained results indicate a mass-based ESP efficiency of 94%–96%, surpassing previously reported values for small-scale boiler-integrated ESPs. Furthermore, the number-based ESP efficiency is 83%–92%, which is in line with values reported in literature. Despite the promising performance, the widespread adoption of integrated ESPs in small-scale appliances faces challenges due to the lack of financial, regulatory and energetic incentives. Nevertheless, the application of ESPs in this context remains crucial in addressing local air pollution and reducing the overall environmental impact of small-scale biomass combustion. To facilitate broader implementation, further research and policy initiatives are necessary. This study provides valuable insights into the true effectiveness of a small-scale ESP in mitigating particulate matter emissions. • Study of commercially available ESP in real-world use. • Particle mass-based ESP collection efficiency is 94–96%. • Particle number-based ESP collection efficiency is 83–92%. • ESP effectively reduces particulate emissions from small-scale biomass combustion. • Lack of financial, regulatory and energetic incentives to invest in small-scale ESP. [ABSTRACT FROM AUTHOR]

Flue Gas Condensers (FGC) are used to increase the thermal output of biomass boilers. This reduces the emissions per unit of produced energy but furthermore, fine dust particles will be collected in the condenser. These condensers therefore have a double effect on the specific particulate matter emissions. In addition to the mechanisms that cause particle capture such as thermophoresis and diffusiophoresis, other agglomeration or condensation growth mechanisms also influence the size of the emitted particles. Due to the combination of these mechanisms, the capture efficiency depends on particle size. A size range presenting a lower capture efficiency, called a penetration window, is generally observed. Measurements on a 5 MW th boiler showed that this penetration window is in size range 0.07–0.49 μm where the capture efficiency is reduced by around 20%. Measurements on an 18 kW th boiler showed that the penetration window is in the size range 0.04–0.49 μm and the capture efficiency can even be negative in this window. For the medium-scale boiler, the condenser reduces the overall particulate emissions by 64% in number and 62% in mass per m3, and 70% in number and 69% in mass per MJ. For the small-scale boiler, the condenser reduces the overall particulate emissions by 4% in number and 50% in mass per m3, and 14% in number and 55% in mass per MJ. • FGC particle collection efficiency has a penetration window with reduced efficiency. • Overall FGC particle collection efficiency is positive in both mass and number. • Minimum FGC collection efficiency occurs at peak of accumulation mode. • Maximum baghouse collection efficiency occurs at peak of accumulation mode. [ABSTRACT FROM AUTHOR]