Experimental measurements and modeling have been performed in the chimney of a biomass boiler to study the gaseous and particulate matter (PM) emissions during the combustion of wood pellets. A 10 kW boiler with an underfeed burner is equipped with different sensors located in the chimney (anemometer, thermocouples). The PM emissions were measured in the chimney through the engine exhaust particle sizer (EEPS) technique. Moreover, the gaseous emissions (CO₂, CO, total hydrocarbons THC, O₂) were obtained through infrared (IR) spectroscopy and flame ionization detector (FID). The emissions were recorded during the steady phase of the boiler and averaged over several tests. Four locations were investigated in the chimney to evaluate the evolution of the particle size and the potential deposition on the surface. The experimental results were compared with a CFD model with particle transportation. The modeling of turbulent flow in the chimney is based on a Reynolds-averaged Navier–Stokes (RANS) approach with turbulent viscosity closure. To account for flow anisotropy, the $\overline{v^2}-f$ turbulence model was selected for this study. The effect of turbulent fluctuations on the discrete phase is considered by the discrete random walk (DRW) turbulent dispersion model. The results obtained provide access to the topology of the carrier phase flow as well as the complete distribution of the particle field within the chimney enclosure. Advanced measurement of pollutant emissions and modeling of the PM transportation are developed for the first time in a domestic biomass boiler operating in real conditions. Experimental results demonstrate several relevant information. The CO and THC emissions show a similar evolution versus time. The PM granulometric distribution measured along the chimney highlights the particle agglomeration phenomena. Moreover, the CFD model and experimental results give similar results in terms of flow characteristics and PM granulometry.

The paper presents an experimental study and a 0D dynamic modeling of a biomass boiler based on the Bond Graph formalism from mass and energy balance. The biomass boiler investigated in this study is an automatic pellet boiler with a nominal power of 30 kW with a fixed bed. The balances allow to model as time function the flue gas enthalpy flux variation and the thermal transfers between the flue gas and the walls of the boiler subsystems. The main objective is to build a model to represent the dynamic thermal behavior of the boiler. Indeed, small domestic boilers have discontinuous operating phases when the set temperature is reached. The global thermal transfer coefficients for the boiler subsystems are obtained according to an iterative calculation by inverse method. The boiler has an average efficiency of 67.5% under our operating conditions and the radiation is the dominant thermal transfer by reaching 97.6% of the total thermal transfers inside the combustion chamber. The understanding of the dynamic behavior of the boiler during the operating phases allows to evaluate its energy performances. The proposed model is both stimulated and validated using experimental results carried out on the boiler.

Biomass is a key energy resource in the current context of climate and energy crises, due to its lower carbon footprint compared to fossil fuels. However, wood-based energy presents several drawbacks: public health concerns related to pollutant emissions from combustion, and questions about the sustainability of the resource given the increasing demand for cleaner fuels. This study investigates the combustion of mixtures of wood pellets (WPs) and barley straw pellets (BSPs) in a domestic biomass boiler, with the aim of evaluating how such blends affect pollutant emissions and energy production under standard boiler operation, without modifications. Pellets were characterized using a bomb calorimeter and thermogravimetric analysis (TGA), while gaseous and particulate emissions were measured at the chimney using gas analyzers and an Engine Exhaust Particle Sizer (EEPS), respectively. The results show that high BSP proportions (>50%) are not compatible with domestic biomass boilers, as they led to a significant increase in gaseous pollutant emission. However, blends with moderate BSP shares (10 and 25%) can be successfully used, offering benefits in terms of reduced pollutant emissions and improved sustainability. Additionally, infrared and high-speed cameras were installed above the boiler furnace, equipped with an optical window, to provide new insights into the combustion process.