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Characteristic Properties and Applications of Fine Particles in Biomass Gasification

Malik, Azhar LU (2011)
Abstract (Swedish)
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... (More)
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. (Less)
Abstract
The gasification of biomass is a promising route to increase the share of renewable sources in the energy mix. Besides having an overall higher thermal efficiency than combustion, it also offers the possibility of producing gaseous and liquid biofuels that can be used in the transport sector. The use of biomass gasification for energy purposes can help lower the net emissions of greenhouse gases, and hence help counter the global warming. One of the problems impeding the exploitation of this technology is the lack of efficient high-temperature cleaning systems to limit the release of fine particle contaminants after gasification. These contaminants can penetrate through the filters presently in use, and be deposited on the surfaces of... (More)
The gasification of biomass is a promising route to increase the share of renewable sources in the energy mix. Besides having an overall higher thermal efficiency than combustion, it also offers the possibility of producing gaseous and liquid biofuels that can be used in the transport sector. The use of biomass gasification for energy purposes can help lower the net emissions of greenhouse gases, and hence help counter the global warming. One of the problems impeding the exploitation of this technology is the lack of efficient high-temperature cleaning systems to limit the release of fine particle contaminants after gasification. These contaminants can penetrate through the filters presently in use, and be deposited on the surfaces of integrated thermal plants leading to corrosion and on catalysts in downstream upgrading processes. Condensable material may also pass through the high-temperature filters in the gas phase, and form significant amounts of particulate matter if the temperature is decreased for operational reasons.

The overall aim of this work was to develop methodologies to aid the further development of post-gasification high-temperature cleaning systems. It included the high-temperature dilution particle sampling techniques, detection of agglomerated soot particles using a novel sensor concept and the investigation of catalysts deactivation due to particulates present in the producer gas. To accomplish this, a laboratory-based method of generating well-characterized model aerosol particles was developed. These particles were compact KCl particles generated by a nebulizer in order to represent the alkali particles, and soot generated by a flame soot generator to represent agglomerated particles in the gasifier. Di-octyl-sebacate (DOS) was used to model tar forming compounds present in gasifier producer gas. The characteristic properties of the particles, such as size, concentration, morphology and mass fraction of organic coating, were analyzed using sophisticated on-line aerosol characterization techniques, including a Scanning Mobility Particle Sizer (SMPS), and a Differential Mobility Analyzer – heater – Aerosol Particle Mass Analyzer (DMA-heater-APM). This provided useful information regarding the morphology and density of agglomerated particulate with a condensed phase, which is not possible with the SMPS technique.

The soot and KCl particles mixed with DOS were sampled with a probe-denuder setup at 200 °C, and the effects of the concentration of condensable material, the dilution ratio in the probe, and the flow rate through the denuder were investigated. This setup demonstrated the capacity to collect >99% of organics when the denuder inlet concentration of DOS was below 6 mg/m3. The soot sampling was also performed by replacing the denuder with a packed bed, which exhibited an enhanced collection capacity for condensable material for inlet concentrations of up to 15 mg/m3.

The sampling system developed was used to sample particles from a circulating fluidized bed gasifier downstream of an existing filter to assess the filtration performance and to allow characterization of the particulates released from the gasifier. This demonstrated the usefulness of the setup by revealing the presence of coarse particles of calcium and silica from bed material, and fine particles dominated by K and Cl released from biomass feedstock.

In catalytic activity measurements on Ni and Pt/Rh catalysts, it was found that potassium and soot particles could reduce the activity by up to 50% when the catalyst was exposed to very small amounts of model particles (soot 0.5 wt %; potassium 0.0038 wt %). The physical blocking of the active sites, and hence reduced active metal surface area is thought to be the main cause of activity loss. The model soot particles were also used to develop an online detection method for soot particles detection at the high temperatures. The performance of the soot sensor was satisfactory in the soot concentration limits tested, with the possibility of enhancing the sensitivity by improving the design. Such soot sensors could be installed after downstream cleaning devices in thermochemical conversion processes.

The research presented in this thesis contributes to the development of effective cleaning systems in the biomass gasification process by improving our understanding of particle formation, deposition and catalyst deactivation mechanisms. This will help us move towards renewable energy sources in an efficient way. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Pettersson, Jan, University of Gothenburg, Sweden
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Gasification, Biomass, Fine particles, catalyst deactivation, dilution probe sampling, organic
pages
133 pages
defense location
Auditorium, Ingvar Kamprad Design Centre, Sölvegatan 26, Lund University Faculty of Engineering
defense date
2011-06-16 10:15
ISBN
978-91-7473-124-8
language
English
LU publication?
yes
id
a962d428-8890-4da7-9de3-fb3fc3ba5f49 (old id 1962668)
date added to LUP
2011-05-17 10:12:35
date last changed
2016-09-19 08:45:19
@misc{a962d428-8890-4da7-9de3-fb3fc3ba5f49,
  abstract     = {The gasification of biomass is a promising route to increase the share of renewable sources in the energy mix. Besides having an overall higher thermal efficiency than combustion, it also offers the possibility of producing gaseous and liquid biofuels that can be used in the transport sector. The use of biomass gasification for energy purposes can help lower the net emissions of greenhouse gases, and hence help counter the global warming. One of the problems impeding the exploitation of this technology is the lack of efficient high-temperature cleaning systems to limit the release of fine particle contaminants after gasification. These contaminants can penetrate through the filters presently in use, and be deposited on the surfaces of integrated thermal plants leading to corrosion and on catalysts in downstream upgrading processes. Condensable material may also pass through the high-temperature filters in the gas phase, and form significant amounts of particulate matter if the temperature is decreased for operational reasons. <br/><br>
The overall aim of this work was to develop methodologies to aid the further development of post-gasification high-temperature cleaning systems. It included the high-temperature dilution particle sampling techniques, detection of agglomerated soot particles using a novel sensor concept and the investigation of catalysts deactivation due to particulates present in the producer gas. To accomplish this, a laboratory-based method of generating well-characterized model aerosol particles was developed. These particles were compact KCl particles generated by a nebulizer in order to represent the alkali particles, and soot generated by a flame soot generator to represent agglomerated particles in the gasifier. Di-octyl-sebacate (DOS) was used to model tar forming compounds present in gasifier producer gas. The characteristic properties of the particles, such as size, concentration, morphology and mass fraction of organic coating, were analyzed using sophisticated on-line aerosol characterization techniques, including a Scanning Mobility Particle Sizer (SMPS), and a Differential Mobility Analyzer – heater – Aerosol Particle Mass Analyzer (DMA-heater-APM). This provided useful information regarding the morphology and density of agglomerated particulate with a condensed phase, which is not possible with the SMPS technique.<br/><br>
The soot and KCl particles mixed with DOS were sampled with a probe-denuder setup at 200 °C, and the effects of the concentration of condensable material, the dilution ratio in the probe, and the flow rate through the denuder were investigated. This setup demonstrated the capacity to collect &gt;99% of organics when the denuder inlet concentration of DOS was below 6 mg/m3. The soot sampling was also performed by replacing the denuder with a packed bed, which exhibited an enhanced collection capacity for condensable material for inlet concentrations of up to 15 mg/m3.<br/><br>
The sampling system developed was used to sample particles from a circulating fluidized bed gasifier downstream of an existing filter to assess the filtration performance and to allow characterization of the particulates released from the gasifier. This demonstrated the usefulness of the setup by revealing the presence of coarse particles of calcium and silica from bed material, and fine particles dominated by K and Cl released from biomass feedstock.<br/><br>
In catalytic activity measurements on Ni and Pt/Rh catalysts, it was found that potassium and soot particles could reduce the activity by up to 50% when the catalyst was exposed to very small amounts of model particles (soot 0.5 wt %; potassium 0.0038 wt %). The physical blocking of the active sites, and hence reduced active metal surface area is thought to be the main cause of activity loss. The model soot particles were also used to develop an online detection method for soot particles detection at the high temperatures. The performance of the soot sensor was satisfactory in the soot concentration limits tested, with the possibility of enhancing the sensitivity by improving the design. Such soot sensors could be installed after downstream cleaning devices in thermochemical conversion processes.<br/><br>
The research presented in this thesis contributes to the development of effective cleaning systems in the biomass gasification process by improving our understanding of particle formation, deposition and catalyst deactivation mechanisms. This will help us move towards renewable energy sources in an efficient way.},
  author       = {Malik, Azhar},
  isbn         = {978-91-7473-124-8},
  keyword      = {Gasification,Biomass,Fine particles,catalyst deactivation,dilution probe sampling,organic},
  language     = {eng},
  pages        = {133},
  title        = {Characteristic Properties and Applications of Fine Particles in Biomass Gasification},
  year         = {2011},
}