The accurate monitoring of particulate emissions from medium-scale, decentralized biomass combustion units is a major challenge for the deployment of this technology in the framework of the current energy transition. More specifically, the experimental characterization of the size of the emitted particles, i.e., using impactors, is still subject to discussions about the impact of the methodology on the measurement results. To meet these challenges, particulate emissions from a mediumscale biomass boiler (4.5 MW th ) were measured with the Electrical Low Pressure Impactor (ELPI+) using two different dilution systems-one containing a single stage and the other, dual stages-to examine the effect of dilution and the performance of the ELPI+. No statistically significant correlation was found with either system between the dilution ratio (DR) and the total particle number concentration, N tot , or between the DR and the mass concentration, m tot . However, a significant positive correlation was observed with both systems between the DR and the concentration of particles with a diameter, D p , below 0.01 µm due to measurement artefacts. With the one-stage dilution system, the condensation appeared to be enhanced when the DR was reduced. When the ELPI+ impactor was not overloaded, the number concentrations of the N <0.01 and N 0.01-0.1 size fractions decreased over time due to the premature measurement of particles. However, when the impactor was overloaded, the N <0.01 concentration was overestimated, whereas the N 0.01-0.1 and N 0.1-1 concentrations were underestimated, due to the change in the cut-off diameter.

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Despite their obvious benefit in terms of energy efficiency and their potential benefit on pollutant emissions, Flue Gas Condensers (FGCs) are still not widely spread in biomass combustion plants. Although their costs have significantly decreased during the last decade, the economic viability of FGC retrofits is not straightforward and their return on investments is mainly dependent on the temperature of the available heat sink and the moisture content of the fuel. Based on a new techno-economic model of a FGC validated with recent industrial data, this paper presents a methodology to assess the economic viability of an FGC retrofitting in a medium-scale biomass combustion plant. The proposed methodology is applied to the case of a typical District Heating plant for which real data was collected. For the first time, the usual assumptions of constant process data generally used are challenged by considering the variability of the return temperature and heat demand over the year. Furthermore, a new concept of optimal configurations in terms of energy savings is introduced in this paper and compared to a strictly economic optimum. The economic feasibility is mainly evaluated by means of the Net Present Value (NPV), Discounted Payback Period (DPP), and the Modified Internal Rate of Return (MIRR). As expected, results show that the higher the humidity level and the lower the return temperature, the higher the economic profitability of a project. The NPV is, however, increased when considering variable inputs: Even with an average return temperature of 60 °C, a mixed operation of the FGC as a condenser and an economizer along the year is predicted, which results in an increased profitability assessment. Considering a constant return temperature over the year can lead to a 20% underestimation of the project NPV. An alternative averaging method is proposed, where two distinct temperature zones are considered: above and below the flue gas dew point. The discrepancy with a detailed temperature variation is reduced to a few percents. Our results also show that increasing the FGC surface beyond the highest NPV can lead to substantial energy savings at a reasonable cost, up to a certain level. The energetic optimum we defined can lead to an increase in energy savings by 17% for the same relative decrease of the NPV.

Industrial denitrification catalyst monoliths are regularly tested in controlled lab-scale conditions to quantify their activity. As mass transfer phenomena occurring inside the channels of the monoliths have an important impact on the global denitrification kinetics, activity measurements must be conducted in wellknown conditions in terms of sample geometry and gaseous flow regimes, among others. The lack of accurate mass transfer correlations for the complex flows at stake however prevents any accurate generalisation of the test results. In this paper, we propose a semi-empirical method for the quantification of contribution of mass transfer to the global denitrification kinetics for any given test bench. It is based on the experimental adjustment of mass transfer correlations presenting a suitable form. Mass transfer can therefore be decoupled from the intrinsic kinetics and large ranges of conditions can be covered by conducting a limited number of measurements.