Browsing by Subject "torrefaction"

Carbonization is thermochemical conversion, where biomass is thermally degraded in the absence of oxygen. Solid char, pyrolysis oil and non-condensable gases are produced from the biomass. Torrefaction is early phase of the carbonization in temperatures of 220–300 °C. Torrefied wood is promising as a renewable fuel for industrial use in coal co-combustion and gasification-combustion. Torrefaction and carbonization increase the higher heating value and fuel properties of wood compared to untreated wood. There’s a lack of knowledge in torrefaction and carbonization effects to higher heating value, carbon content and turn from endothermic to exothermic reaction of conifer zone wood species. Raw material was stemwood of birch (Betula pubescens) and pine (Pinus sylvestris) including bark. Trees were harvested from the Helsinki district and chipped, particle size 16 ? 8 mm. Samples were torrefied and carbonized at 250, 300, 350, 400 and 450 ?C without nitrogen flow. Carbon content (%), higher heating value (MJ/kg), mass yield (%) and turn of endothermic to exothermic reaction were inspected. Carbon content of untreated birch and pine increased from 47 % to 82 % (at 450 ?C). Higher heating value exceeded 26 MJ/kg at 300 ?C and 28 MJ/kg at 400 ?C, reaching bituminous coal’s values. Mass yield declined to 45–54 % of the initial mass at 300 °C. In low temperature, gradual exothermic peak was observable. In higher temperatures peak was evident. Carbonization and torrefaction improved the higher heating value and carbon content of wood but decreased the solid char yield.

The objective of this thesis is to study the climate impacts and the social returns and social desirability of torrefied wood pellet production and use as an alternative fuel to coal. The raw material of torrefied pellets is forest chips and production and use are assumed to take place in Finland. Climate impacts are assessed with focus on the full fuel chain, or the torrefied pellet life cycle. A brief review of other environmental impacts of the fuel chain is also provided. A socio-economic model is then developed for analyzing how desirable torrefied pellet production and use would be from society’s viewpoint when both private profits and climate benefits are taken into account. The model is applied to a hypothetical case where torrefied pellets are produced in Northern Finland and co-fired with coal at Helsingin Energia’s cogeneration plant. The purpose of this study is thus to analyze whether co-firing torrefied pellets with coal in combined heat and power production generates social surplus and is socially desirable when both net climate benefits and the private revenue and costs of torrefied pellet production and use are taken into account. Results show that co-firing torrefied pellets and coal in combined heat and power production leads to a reduction in greenhouse gas emissions compared to a coal-only situation when the life cycle of both fuels is taken into account. In the case studied, torrefied pellet production and use also generates positive social returns. The energy producer’s private profits proved to have the greatest impact on net social benefits.