Particle Emissions from District Heating Units Operating on Solid Biofuels
Författare
Summary, in English
With the increasing interest in the use of biofuels for heat and energy generation there is a growing concern about emissions from their combustion. It has been shown that biofuel furnaces emit relatively high quantities of particulate matter in comparison to natural gas and light fuel oil furnaces. Majority of the emitted particulates are smaller than 10 μm with high contribution of fine (< 2.5 μm) and submicron (< 1 μm) particles. These fine particles tend to be the most troublesome; in ambient air they have been associated with adverse health effects. Submicron particles are difficult to capture in the available particle removal technologies.
The aim of this study was to characterise particle emissions from district heating units operating on three commonly used biofuels, namely sawdust, pellets and forest residues. Boilers were of moving grate type, with the maximum thermal output between 1 and
1.5 MW. The measurements were done after multicyclones, the only particle removal devices installed, therefore the direct emissions to ambient air were characterised. Influence of type of the fuel and operation load on particle emissions was investigated. Furthermore collection efficiencies of electrostatic precipitator (ESP) and flue gas condenser, used particle separation devices in 6 MW unit, were investigated.
It has been shown that in all cases large amounts of fine particles containing heavy metals are being emitted to the atmosphere, even though the studied district heating units meet the current mass concentration emission limit requirements. Total number concentration of emitted particles with aerodynamic diameter smaller than 5 μm ranged from 3 to
8 x 107 particles /cmn3 with the slightly higher values from combustion of forest residues. Both mass and total number concentrations were dominated by submicron particles contribution.
Elements determined by Particle Induced X-rays Emission (PIXE) analysis (Z > 12) contributed to 21 – 34 % of PM1 mass, of which K, S, Cl and Ca contributed to 18 –33% of PM1 mass, and Zn, Mn, Fe, Cr, Pb and Cd to 1 – 3 %. Emitted concentrations of heavy metals depended on type of the fuel and operating load. Forest residues gave relatively high emissions of Zn, Cr, Cd and Pb, while pellets gave high emissions of Zn and Cd. The lowest emissions of heavy metals came from the combustion of sawdust.
Particulate organic (OC) and elemental (EC) carbon contribution to PM1 ranged from
1 - 19% and 0 - 56%, respectively. Particulate OC concentrations strongly depended on the operation load regardless the type of the fuel, while EC concentrations seemed to depend both on load and the type of the fuel.
Both ESP and flue gas condenser showed size dependant particle separation efficiency. ESP proved to remove 96% of particle number concentration and 83% of mass concentration, whereas flue gas condenser did not alter the particle number concentration to a significant degree but reduced the mass concentration by half.
Obtained results characterise particle emission from combustion of commonly used solid biofuels. This type of data is useful for assessment of biofuels combustion impact on environment and human health. It can also be used, together with the presented results on collection efficiencies of ESP and flue gas condenser, for optimisation of combustion technologies and development of efficient and cost effective emission control measures.
The aim of this study was to characterise particle emissions from district heating units operating on three commonly used biofuels, namely sawdust, pellets and forest residues. Boilers were of moving grate type, with the maximum thermal output between 1 and
1.5 MW. The measurements were done after multicyclones, the only particle removal devices installed, therefore the direct emissions to ambient air were characterised. Influence of type of the fuel and operation load on particle emissions was investigated. Furthermore collection efficiencies of electrostatic precipitator (ESP) and flue gas condenser, used particle separation devices in 6 MW unit, were investigated.
It has been shown that in all cases large amounts of fine particles containing heavy metals are being emitted to the atmosphere, even though the studied district heating units meet the current mass concentration emission limit requirements. Total number concentration of emitted particles with aerodynamic diameter smaller than 5 μm ranged from 3 to
8 x 107 particles /cmn3 with the slightly higher values from combustion of forest residues. Both mass and total number concentrations were dominated by submicron particles contribution.
Elements determined by Particle Induced X-rays Emission (PIXE) analysis (Z > 12) contributed to 21 – 34 % of PM1 mass, of which K, S, Cl and Ca contributed to 18 –33% of PM1 mass, and Zn, Mn, Fe, Cr, Pb and Cd to 1 – 3 %. Emitted concentrations of heavy metals depended on type of the fuel and operating load. Forest residues gave relatively high emissions of Zn, Cr, Cd and Pb, while pellets gave high emissions of Zn and Cd. The lowest emissions of heavy metals came from the combustion of sawdust.
Particulate organic (OC) and elemental (EC) carbon contribution to PM1 ranged from
1 - 19% and 0 - 56%, respectively. Particulate OC concentrations strongly depended on the operation load regardless the type of the fuel, while EC concentrations seemed to depend both on load and the type of the fuel.
Both ESP and flue gas condenser showed size dependant particle separation efficiency. ESP proved to remove 96% of particle number concentration and 83% of mass concentration, whereas flue gas condenser did not alter the particle number concentration to a significant degree but reduced the mass concentration by half.
Obtained results characterise particle emission from combustion of commonly used solid biofuels. This type of data is useful for assessment of biofuels combustion impact on environment and human health. It can also be used, together with the presented results on collection efficiencies of ESP and flue gas condenser, for optimisation of combustion technologies and development of efficient and cost effective emission control measures.
Avdelning/ar
Publiceringsår
2004
Språk
Engelska
Dokumenttyp
Licentiatavhandling
Ämne
- Production Engineering, Human Work Science and Ergonomics
Nyckelord
- district heating
- particle emissions
- biomass combustion
Status
Published
Handledare