Characteristic Properties and Applications of Fine Particles in Biomass Gasification

Abstract: Popular Abstract in Swedish Many of the energy needs in today’s modern society are fulfilled by sources based on fossil fuels, including non-domestic oil and coal. It is well known that the increase in CO2 emission is the result of human activities, mostly fossil fuel consumption. The use of such fuels is unsustainable and has led to the phenomena such as climate change, political instability in some parts of the world and, most important of all, an imbalance in the natural environment – in which we humans live with other organisms. The shift to a sustainable way of living is much needed if we wish to safeguard the environment for future generations and still enjoy a modern and conscious living. There is growing public awareness of alternative energy sources, and bioenergy is one of the options that can help us combat global warming, reduce the emission of harmful gases, and exploit local energy sources. The thermochemical conversion of biomass has emerged as a suitable technology of choice. It has attracted a great deal of interest from the research and development community due to its potential to help meet energy demands in a sustainable way, mainly through the possibility of producing liquid and gaseous fuels. Further exploitation of this technology will result in a reduction of net greenhouse gas emissions and hence counteract global warming effect. The thermochemical conversion of biomass consists of combustion (to produce energy) and gasification (to produce heat, power, chemicals and vehicle fuel). This thesis deals with biomass gasification and the impact of the emitted impurities on downstream cleaning systems and catalytic upgrading processes. As with any other energy conversion process, biomass gasification is not without challenges and technical obstacles that must be overcome. The gaseous and particulate contaminants present in the produced gas threaten the performance of catalytic processes of producing biofuels, and integrated heat and power generation. There is a reasonable understanding and technological development available to handle gaseous poisonous compounds but the removal of contaminants in particulate form in the harsh environment inside the gasifier remains as serious problem. The high-temperature cleaning devices available do not optimally meet the requirements for the level of contaminants in the producer gas suitable for most applications. The research presented in this thesis describes the efforts made to understand the post-gasification handling of producer gas to remove particle contaminants, and the study of different mechanisms of particle formation in order to develop efficient filtration devices. Effects on the upgrading process have been studied, demonstrating a loss of catalytic activity due to the presence of harmful particulates in the post-gasifier streams. A method has been developed to characterize the particles in producer gas which can be used to evaluate the filtration efficiency of particle removal systems. The initial testing of developed method at a lab-scale gasifier has shown its ability to sample representative particles, from which useful information on their characteristic properties can be obtained. The developed soot-particles generator was also utilized in the application of soot sensor for online detection of soot in high-temperature processes, e.g. in a vehicle exhaust diesel particulate filter and combustion boilers. This scientific work constitutes a step forward in our understanding of the formation of particles, their impact on downstream technological systems, and the development of gas cleaning devices for biomass gasification applications. The knowledge gained through this work will aid the further development of gasification technology for bioenergy, and hence the shift towards a more sustainable society.