Particle Emissions from Small Wood-fired District Heating Units

Abstract

Particle and gaseous emissions of four different wood chip-fired district heating units in the size range 5−15 MW were studied. Three of the units were fire-tube boilers based on rotating grate combustion technology, and one was a gasification combustion boiler. All of the units were equipped with cyclones to remove coarse particles from the flue gas. In addition, two of the rotating grate boilers were equipped with single field electrostatic precipitators (ESP), and one with a condensing flue gas scrubber. The particle filtration efficiencies of these particle removal appliances were measured. The grate boilers produced on average 211−483 mg/MJ of total suspended particles (TSP) and 55−92 mg/MJ of fine particles (PM1) upstream of the secondary particle filters. These levels of TSP and PM1 were clearly higher than those produced by the gasification combustion boiler (on average 50 mg/MJ TSP and 13 mg/MJ PM1). The ESPs were found to remove around 95% of the PM1s and 93% of TSP, leading to relatively low particle emissions. The lowest collection efficiency (for particles below 10 μm) was achieved in the size range 0.2−1 μm. The condensing flue gas scrubber removed on average 44% of PM1 and 84% of TSP. In all of the plants, the fine particles mainly consisted of potassium salts. In addition, they contained small amounts of organic material and various metals, of which zinc was the most abundant. In general, the study shows that small (<20 MW) biomass-fired boilers, not equipped with effective particle filters, are an important source of fine particles introduced into ambient air and they have a high potential for reducing the emissions with currently available flue gas cleaning technology.

Solid Particle Emission Abatement from Biomass-Fired Boilers at District Heating Plants

“…It is known that, wood bark has the highest ash content directly influencing the ash concentration of biomass fuel. The major part of wood ash is typically composed of calcium (Ca) and potassium (K), part of which volatilizes during the combustion and forms fine particles [5]. According to the data in Ref.…”

“…Multicyclones are often used for pre-cleaning of the flue gas in front of the flue gas condensation unit [5]. Multicyclones are known as simple-design units with low to moderate gas side pressure drop, inexpensive and working in a wide range of temperatures.…”

Solid Particle Emission Abatement from Biomass-Fired Boilers in District Heating Plants

“…According to the data collected in [7], the mass concentration of fly ash particles behind the boiler is in the range of 60-3000 mg/nm 3 . The major part of wood ash is typically composed of calcium (Ca) and potassium (K), part of which volatilizes during the combustion and forms fine particles [11].…”

“…Multicyclones are often used for pre-cleaning of the flue gas before the flue gas condensation unit. [11].…”

Characterization of Chemical and Microbial Species from Size-Segregated Indoor and Outdoor Particulate Samples

“…In addition, the concentrations of Ni and Fe were clearly highest in the summer outdoor samples. The elevated concentrations of these five metals during summer were likely to be attributable to the wildfire smoke plumes, especially K, Zn and Pb are known to be efficiently released in fine particles during biomass combustion (Sippula et al, 2007, Sippula et al, 2009a while during the winter the main emission sources were probably biomass combustion for heating in the area. This is supported by the data from winter time ultrafine fractions showing clearly the highest fractions of K (Fig.…”