Spontaneous
emission intensities of Na*, Ca*, and K* during the combustion of
single wood and straw pellets doped with known concentrations of Na,
Ca, and K were measured using optical bandpass filters mounted on
an intensified charge-coupled device camera. The impregnated biomass
pellets were suspended in a natural gas flat flame at 750 and 1000
°C. Before the pellets were made, the biomass samples were washed
and soaked to demineralize and doped with different
concentrations of Na, Ca, and K (0.5, 2, and 5 wt %). During the experiments,
the temperature at the center of the pellets was measured with a thermocouple
and the combustion stages were identified with the help of the temperature
derivative. The results reveal that, at the lower gas temperature,
the emission of the selected alkalis is marginal, in agreement with
previous studies. At the higher gas temperature, the emission profiles
reveal that K and Na are released distinctively in
the volatile combustion and char combustion stages. The presence of
large amounts of silica and alumina may trap the alkalis in the solid
phase, leading to a reduced emission of these species during the char
combustion. Calcium does not evaporate at the tested temperature conditions,
but the temperature is high enough to promote the decomposition of
calcium oxalate in the outer layer of the pellet, leading to a flat
emission profile during the combustion stages. Finally, the total
integrated emission increased proportionally with the increase of
the doping concentration for all species.
In this research carbon monoxide (CO), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC), ammonia (NH3) and total suspended particles (TSP) were measured, and national emission factors (EF) were determined. Although biomass is commonly used in the residential sector and releases a large part of pollutants in the atmosphere, due to lack of well-documented investigations on air pollutants EFs of wood burning it is difficult to set up representative country-specific emission factors in Lithuania. This study is focused on biomass combustion in the residential sector in order to provide data for country- and technology-specific national EFs. The study has estimated EFs of CO, NOx, NMVOC, TSP and NH3 from biomass burning in the residential and agriculture sectors, respectively, using four-step methodology according to the exhaust gas analysis.
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