Reduction of ash content of biomass feedstock
Taipale, Lauri (2018)
2018
Ympäristö- ja energiatekniikka
Teknis-luonnontieteellinen tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2018-02-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201801261161
https://urn.fi/URN:NBN:fi:tty-201801261161
Tiivistelmä
Biomass ash content is a significant factor to the operational availability of biomass conversion processes and often affects the product quality of bioproducts. High temperature corrosion and fouling of the flue gas ducts due to alkali metals and chlorides are typical issues especially in combustion processes. Some alkali metals can also reduce the preferred liquid yields in pyrolysis and result in biomass degradation to light gases instead. Other products, such as activated carbon, can also be produced from biomass. The quality of the activated carbon product is dependant on the ash content. It is often necessary to include feedstock de-ashing as a pretreatment process, to produce high quality activated carbon with active surface of 1000 m2/g.
The aim of this thesis was to study and analyse the ash content found in biomasses used in the Nordic countries. From these feedstocks, peat was selected as the raw material for further studies. Peat is a promising feedstock, not only for combustion, but for the production of biomaterials such as technical carbons. Typically peat harvested from peatlands in Finland has an ash content in the range of 3-10% on a dry basis. This ash content is comprised of inorganic mineral nutrients, alluvial sediments and chemical sediments. The minerals are typically in finely grained form and include quartz, feldspar, amphiboles and mica [5]. The removal of these grained solid particles was set as the goal of the peat de-ashing.
Methods to separate and remove the grained inorganic compounds from peat were studied during the experimental phase of this thesis. Settlement, flotation and air classification were selected after researching separation techniques used for similar media in industrial scale. Good separation efficiency was achieved with settlement and flotation. The challenge was to improve the recovery efficiency of the low-ash float. Finally, suggestions were made on how to proceed to pilot scale testing using dissolved air flotation and a draft for industrial scale operation was illustrated.
The aim of this thesis was to study and analyse the ash content found in biomasses used in the Nordic countries. From these feedstocks, peat was selected as the raw material for further studies. Peat is a promising feedstock, not only for combustion, but for the production of biomaterials such as technical carbons. Typically peat harvested from peatlands in Finland has an ash content in the range of 3-10% on a dry basis. This ash content is comprised of inorganic mineral nutrients, alluvial sediments and chemical sediments. The minerals are typically in finely grained form and include quartz, feldspar, amphiboles and mica [5]. The removal of these grained solid particles was set as the goal of the peat de-ashing.
Methods to separate and remove the grained inorganic compounds from peat were studied during the experimental phase of this thesis. Settlement, flotation and air classification were selected after researching separation techniques used for similar media in industrial scale. Good separation efficiency was achieved with settlement and flotation. The challenge was to improve the recovery efficiency of the low-ash float. Finally, suggestions were made on how to proceed to pilot scale testing using dissolved air flotation and a draft for industrial scale operation was illustrated.