Effect of substitution of old coal boilers with new biomass boilers on the concentration of particulate matter in ambient air: A case study Mionica

Abstract

Residential and commercial solid fuel burning in stoves, small and medium combustion plants have been designated as the largest sources of fine particles with serious impacts on air quality, climate and human health. Having in mind the age and condition of the plant, as well as domestic raw lignite of poor quality which is widely used in these plants, this problem becomes even more pronounced in Serbia during the heating season. An additional reason for such high dust emissions certainly lies in the fact that most of these combustion units, in addition to being in very poor condition, work without any flue gas system for dedusting, also the mentioned lignite is low in calorific value with high ash and moisture content. Replacement of such combustion units with modern biomass boiler units is certainly appropriate, and in places where natural gas is not available, this energy source is the best solution. In this paper and for the case study of Mionica town, the influence on the concentration of PM in ambient air will be presented by replacing two old coal boilers with new biomass boilers. Namely, two old boilers (2x950 kWth) covered the heat demand of the sports centre as well as primary and secondary school, these boilers were replaced with two new biomass boilers of the same installed thermal capacity. In order to analyse the influence of boilers substitution on PM concentration in ambient air, the regulatory air dispersion model, recommended by the US Environmental Protection Agency (US EPA) AERMOD, is used, which is based on the Gaussian model. Air dispersion modeling within this Study includes only sources which are associated with this Case Study. Other sources of emissions and background pollution are not included. The aim of this Study is not to show the air quality in the domain, but rather to provide a representative assessment of the impact of boilers substitution on PM concentration in the model domain. For the purpose of this Study NASA digital maps SRTM1 - Shuttle Radar Topography Mission (resolution ~ 30m, or 1 arc-sec) are used and processed by the AERMAP, while meteorological, data processed by the AERMET, are site specific MM5 (Grid Cell 12 km x 12 km), giving an hourly-modelled meteorological data set for full five consecutive calendar years. The results presented in this paper were obtained using a model which includes the emissions of TSP, PM10 and PM2.5 from the old and new boilers. An emission inventory has been prepared based on combustion calculations and emission factors (EMEP/EEA, 2019) for old coal fired boilers, while for new biomass boilers, site-specific measurements and PM size distribution factors (US EPA, AP 42, 2003) have been used. Modelling results consist of graphical (isopleth diagrams) ground level concentrations for TSP, PM10 and PM2.5 and various average periods.