| 1. |
- Berguerand, Nicolas, 1978, et al.
(författare)
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Use of Nickel Oxide as a Catalyst for Tar Elimination in a Chemical-Looping Reforming Reactor Operated with Biomass Producer Gas
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 51:51, s. 16610-16616
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Tidskriftsartikel (refereegranskat)abstract
- A secondary tar-cleaning process based on Chemical-Looping Reforming (CLR) was investigated for upgrading biomass producer gas, derived from the Chalmers University of Technology 2-4 MW indirect gasifier. The experiments were conducted in a bench-scale CLR reactor using a manufactured nickel oxide (NiO) catalyst. Although Ni is a well-documented and efficient steam-reforming catalyst, it is susceptible to rapid deactivation under tar-rich conditions. The aim of this study was to explore the advantages of CLR as a gas-cleaning application, a process which offers continuous regeneration of the carbon deposits on catalysts. The tar-reforming performance of this Ni material and its influence on the gas composition and in particular its potential to increase the H2/CO ratio, were studied. The system was tested at reforming temperatures that ranged from 700°C to 880°C and at oxygen concentrations of 1.0% and 2.2% in the inlet feed to regenerator section. The results confirm the strong ability of the catalyst to reform tars. Higher process temperatures clearly promoted tar conversion, with 96% overall conversion at 880°C (99% if benzene is excluded), as compared with 45% conversion at 700°C. The hydrogen production was favored when temperature was raised. Though, a maximum ratio H2/CO of 2.2 was observed at 750°C. Finally, no time-on-stream deactivation of the catalyst in the CLR was observed during the test, which lasted almost 7 hours.
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| 2. |
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| 3. |
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| 4. |
- Israelsson, Mikael, 1985, et al.
(författare)
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Assessment of the Solid-Phase Adsorption Method for Sampling Biomass-Derived Tar in Industrial Environments
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:12, s. 7569-7578
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature gasification of biomass is a primary process step for production of biofuels or electricity using gas-fired engines or turbines. In addition to the desired product gas, the raw gas produced through gasification inevitably contains condensable hydrocarbons, known collectively as tar. The amount and composition of the tar have relevance for the efficiencies of the downstream processes. Tar can be measured using both online and off-line methods. However, many of these methods currently lack information regarding their implementation and accuracy levels for large-scale systems. In this work, the Solid-Phase Adsorption (SPA) method for measuring tar in industrial applications is evaluated. The individual steps of the method were examined for their effects on the overall performance of the analysis. Sample collection was found to be the most prominent source of error, and this was mainly due to human factors. Omitting to determine the temperature and pressure of the sampled gas contributed to this error, as the sampled volume of gas under normal conditions could not be correctly calculated. Inconsistencies in the treatment and storage of the collected samples were shown to affect the more volatile species with boiling points similar to that of benzene. The gas chromatography (GC) analysis was performed with satisfying accuracy. However, the reliability of the estimations of the average composition and dew-point of the tar mixture were dependent upon the amount of the identified species. The current implementation of the SPA method yields values with a relative standard deviation within 10% for the majority of the compounds in a given sample. However, in line with the result of previous studies, the tar species with boiling points between those of benzene and xylene (i.e., the BTX compounds) were measured with a lower accuracy than those of heavier tars.
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| 5. |
- Israelsson, Mikael, 1985, et al.
(författare)
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Conversion of Condensable Hydrocarbons in a Dual Fluidized Bed Biomass Gasifier
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 29:10, s. 6465-6475
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Tidskriftsartikel (refereegranskat)abstract
- Biomass gasification is a primary process in the thermochemical conversion of biomass into biofuels, chemicals, and electricity. The produced raw gas consists of permanent gas species, such as hydrogen (H2) and carbon monoxide (CO), with variable amounts of heavier/larger species, depending on the gasification technique and process conditions employed. These heavier species are often referred to as tar, which is herein defined as all species with boiling points that lie between the boiling points of benzene and coronene. In this work, experiments were conducted in the Chalmers 2-4-MW dual fluidized bed gasifier utilizing equipment that allows for simultaneous quantification of the cold gas and the tar species, together with the total raw gas yields of C, H, O, and N. The obtained results are used to describe the effects of temperature, steam-to-fuel ratio, residence time, and active materials on both the gas composition and the carbon balance of the system. Furthermore, as the carbon balance is fulfilled, the char conversion, oxygen transport, and amounts of carbon in unidentified condensable species can be determined. The unidentified condensable species comprise a group of compounds that are not measured as part of the other groups [cold gas and SPA tar, measured using the solid phase adsorption (SPA) method]. In addition, this group is shown to be readily converted into SPA tar, and cold gas as the severity of the gasifier, in terms of temperature and residence time, was increased.
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| 6. |
- Israelsson, Mikael, 1985, et al.
(författare)
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Gasification Reaction Pathways of Condensable Hydrocarbons
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4951-4959
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Tidskriftsartikel (refereegranskat)abstract
- Dual fluidized bed (DFB) gasification of biomass generates numerous species with large differences in-size and boiling point. At the heavier (tar) end, the produced species range from benzene to coronene: In this work, a method for elucidating the pathways of tar evolution is, applied to previously presented measurements that satisfy the carbon, balance of the Chalmers 2-4-MW DFB gasifier. In addition to quantifying the cold gas and tar, the measurements yield information regarding the amount and C, O, H composition of unknown condensable species (UCS). The reaction pathways were identified by means of fitting a model to the performed measurements. The employed solver varies freely the reaction rate coefficients of three global reactions (mimicking dissociation and reactions with hydrogen and steam) per modeled group, as well as the carbon distribution coefficients within a predefined reaction scheme. The mature tar (excluding primary tar) spectrum is divided into phenols, furans, benzene, naphthalene, pyrene, and one-, two-, and three-ring aromatic components. In addition, UCS that are considered to contain primary tar are divided into four subgroups, to encompass two levels of reactivity with varying composition. Ultimately, the solver converges, yielding a reaction scheme that is based on the findings of earlier works and that describes the creation of mature tar from UCS. Furthermore, the importance of individual reaction routes is discerned for the pertinent measurements. Thus, it is demonstrated that the maturation of secondary tar species (e.g., toluene and phenol) is not in itself sufficient to describe the formation of the tar spectrum.
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| 7. |
- Israelsson, Mikael, 1985, et al.
(författare)
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Online Measurement of Elemental Yields, Oxygen Transport, Condensable Compounds, and Heating Values in Gasification Systems
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:9, s. 5892-5901
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Tidskriftsartikel (refereegranskat)abstract
- Biomass gasification produces a wide range of species, from permanent gases to condensable hydrocarbons, with different composition and boiling points. This complicates the mass balance of the system, as multiple techniques are needed to quantify the various components of the produced raw gas. In this study, a high-temperature reactor for thermal conversion of raw gas at 1700°C was developed to generate a gas stream that consisted primarily of CO, CO2, H2, and H2O. The reactor was experimentally evaluated, and subsequently used for measurements of the raw gas from theChalmers 2-4–MW dual fluidized bed gasifier. The gas stream that exits the reactor is analyzed to obtain the total elemental flows of C, H, O, N, which facilitate determinations of the fuel conversion and oxygen transport in a dual fluidized bed reactor. The proposed system was operated in parallel with a gas-cleaning system, to determine the yield of condensable species, including tar and GC-undetectable species. A simplified approach is proposed for quantifying the average energy content of the condensable species, thereby allowing the wet raw gas efficiency and lower heating value (LHV) to be calculated.
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| 8. |
- Israelsson, Mikael, 1985
(författare)
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Tar and Condensable Hydrocarbons in Indirect Gasification Systems
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass gasification, which is a primary process step in the production of biofuels, yields a combustible gas mixture (raw gas). This raw gas consists of a wide range of species, from permanent gases to condensable hydrocarbons, which are collectively known as tar. Considered as the Achilles heel of biomass gasification, tar starts to condense at temperatures of around 350°C, causing blockage and fouling of downstream equipment. In addition to creating operational difficulties, tar is responsible for a loss of efficiency if it is not successfully converted into permanent gases. Consequently, there is a need to understand the concepts underlying tar formation and evolution, so as to guide efforts towards reducing its yield, as well as towards facilitating its removal once formed. This requires accurate quantification of all the components of the produced raw gas to evaluate the behavior of the tar. However, as the produced gas comprise such a wide range of species, several different measurement techniques are required. In this work, the effects of catalytic materials on tar were investigated in two different systems. The observed responses motivated the development of improved measurement systems, directed to fulfilling the mass balance of the gasifier. These systems were subsequently implemented to map the behaviors of the various species of the raw gas, for a range of process parameters, and to derive a reaction scheme for all the condensable species.The concepts of primary and secondary measures were studied by introducing a catalytic material directly into the Chalmers dual fluidized bed (DFB) gasifier (primary measure) and by utilizing an additional reactor for catalytic reforming of the raw gas (secondary measure). Overall, both measures resulted in significantly decreased levels of tar. However, the composition of the remaining tar differed for the two measures, as did the added amounts of oxygen.The SPA method for tar measurement was evaluated for reproducibility, which was found to be well within 10% for the majority of the measured species. In addition, the detection limits of the SPA method have been extended throughout this work and currently extend from benzene to coronene. A high-temperature reactor, for thermal cracking of all the gas species into CO, CO2, H2, and H2O, was constructed to measure the total elemental yields of C, H, O, and N in the raw gas. This measurement allowed a mass balance for the system to be constructed, which combined with the cold gas and tar measurements, was used to obtain information regarding the yields and composition of previously unmeasured condensable species. This group contained a level of carbon similar to that found in the SPA-measured tar, thereby underlining the need for quantification through standard measurements.iiThe developed measurement equipment was used to map the behavior of the gasifier under various temperatures, residence times, and steam-to-fuel ratios. The performed measurements showed that not only are the previously unmeasured species important for fulfilling the mass balance of the gasifier, but also for describing the formation of SPA-measureable tar. Subsequent modeling of the tar formation and evolution for the measured cases revealed that a substantial fraction of these species tends to form tertiary SPA tar directly, as these species are reformed. Furthermore, it was shown that additional factors, presumably related to the aging of the bed material, can significantly affect the reactivity of the gasifier and should be quantified to improve the functionality of the model.
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| 9. |
- Jareteg, Adam, 1989, et al.
(författare)
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Packed-Bed Reactor Characterization of Steam-Regenerated Solvent Adsorbers for Raw-Gas Cleaning
- 2017
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Ingår i: Proceedings of the 14th International Conference Multiphase Flow in Industrial Plant.
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Konferensbidrag (refereegranskat)abstract
- Packed beds with activated carbon is a commonly used technology for removing unwantedsubstances from a process stream. To better understand how such beds operate and in orderto optimize their design and operation, one-dimensional models are typically employed.The multiphase aspects of these systems are typically neglected due to their complexity,even though regeneration with steam creates a liquid phase that may trickle through thebed, thereby effectively transporting heat and mass. This paper investigates andcharacterizes the differences in transport of gas and liquid in a representative packed bedthrough comprehensive three-dimensional numerical simulations. In addition, the effect ofheterogeneities in the packing of the bed on the transport of both phases is also investigated.It is confirmed that the dispersion of air may be well described by a conventional one-dimensional model, but that the dispersion of water requires an additional effort. It is alsofound that the system orientation significantly influences the water flow and that non-idealpacking has strong effects on the residence time distribution for both phases.
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| 10. |
- Jurca, Manuela, et al.
(författare)
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ZEITLUPE Promotes ABA-Induced Stomatal Closure in Arabidopsis and Populus
- 2022
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Ingår i: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Plants balance water availability with gas exchange and photosynthesis by controlling stomatal aperture. This control is regulated in part by the circadian clock, but it remains unclear how signalling pathways of daily rhythms are integrated into stress responses. The serine/threonine protein kinase OPEN STOMATA 1 (OST1) contributes to the regulation of stomatal closure via activation of S-type anion channels. OST1 also mediates gene regulation in response to ABA/drought stress. We show that ZEITLUPE (ZTL), a blue light photoreceptor and clock component, also regulates ABA-induced stomatal closure in Arabidopsis thaliana, establishing a link between clock and ABA-signalling pathways. ZTL sustains expression of OST1 and ABA-signalling genes. Stomatal closure in response to ABA is reduced in ztl mutants, which maintain wider stomatal apertures and show higher rates of gas exchange and water loss than wild-type plants. Detached rosette leaf assays revealed a stronger water loss phenotype in ztl-3, ost1-3 double mutants, indicating that ZTL and OST1 contributed synergistically to the control of stomatal aperture. Experimental studies of Populus sp., revealed that ZTL regulated the circadian clock and stomata, indicating ZTL function was similar in these trees and Arabidopsis. PSEUDO-RESPONSE REGULATOR 5 (PRR5), a known target of ZTL, affects ABA-induced responses, including stomatal regulation. Like ZTL, PRR5 interacted physically with OST1 and contributed to the integration of ABA responses with circadian clock signalling. This suggests a novel mechanism whereby the PRR proteins—which are expressed from dawn to dusk—interact with OST1 to mediate ABA-dependent plant responses to reduce water loss in time of stress.
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| 11. |
- Karlsson, Johannes, 1977-, et al.
(författare)
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Efficient P2P mobile service for live media streaming
- 2006
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Ingår i: Proceedings of the Australian Telecommunication Networks and Applications Conference (ATNAC 2006). 4-6 December 2006, Melbourne, Australia..
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Konferensbidrag (refereegranskat)abstract
- Mobile TV is a new interesting area in the telecommunication industry. The technology for sending live video to mobile clients is characterized by relatively low CPU processing power, low network resources, and low display resolution. In this paper we discuss a solution to all of these problems by using application layer multicasting. This can significantly reduce the needed bitrate and required computing resources for each client. At the same time the received video quality is increased. Several different methods for splitting the video into substreams are discussed. Simulations for the local wireless ad-hoc network are performed. A system for application layer multicasting using layered H.264 is also presented.
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| 12. |
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| 13. |
- Karlsson, Mikael, et al.
(författare)
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Chemical Sensors Generated on Wafer-Scale Epitaxial Graphene for Application to Front-Line Drug Detection
- 2019
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Ingår i: Sensors. - : MDPI. - 1424-8220. ; 19:10
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Tidskriftsartikel (refereegranskat)abstract
- Generation of large areas of graphene possessing high quality and uniformity will be a critical factor if graphene-based devices/sensors are to be commercialized. In this work, epitaxial graphene on a 2" SiC wafer was used to fabricate sensors for the detection of illicit drugs (amphetamine or cocaine). The main target application is on-site forensic detection where there is a high demand for reliable and cost-efficient tools. The sensors were designed and processed with specially configured metal electrodes on the graphene surface by utilizing a series of anchors where the metal contacts are directly connected on the SiC substrate. This has been shown to improve adhesion of the electrodes and decrease the contact resistance. A microfluidic system was constructed to pump solutions over the defined graphene surface that could then act as a sensor area and react with the target drugs. Several prototypic systems were tested where non-covalent interactions were used to localize the sensing components (antibodies) within the measurement cell. The serendipitous discovery of a wavelength-dependent photoactivity for amphetamine and a range of its chemical analogs, however, limited the general application of these prototypic systems. The experimental results reveal that the drug molecules interact with the graphene in a molecule dependent manner based upon a balance of -stacking interaction of the phenyl ring with graphene (p-doping) and the donation of the amine nitrogens lone pair electrons into the *-system of graphene (n-doping).
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| 14. |
- Larsson, Anton, 1984, et al.
(författare)
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Using Ilmenite To Reduce the Tar Yield in a Dual Fluidized Bed Gasification System
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:4, s. 2632-2644
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Tidskriftsartikel (refereegranskat)abstract
- Biomass gasification plays an important role in the emerging production of second-generation biofuels. One of the major challenges facing biomass gasification is to find simple and efficient ways to reform tar components. While the tar causes operational problems, it can be reformed to increase the chemical efficiency of the gasification process. With respect to tar reforming, catalytic materials are of special interest. Many of the materials that have been proposed as promising catalysts are metal oxide-based materials. However, metal oxides also have the ability to transport oxygen when subjected to alternating oxidizing and reducing atmospheres, similar to that which occurs in a dual fluidized bed gasification system. In this work, ilmenite was used as the catalytic material in the Chalmers 2-4 MWth dual fluidized bed gasifier to decrease the yield of tar. The ilmenite was mixed with the silica sand, which was used as the bed material, to investigate how the level of ilmenite affected chemical efficiency and tar yield. Furthermore, energy balance calculations were established to elucidate the general aspects of oxygen transport in dual fluidized bed gasification systems. The results presented in this paper reveal that adding low levels of ilmenite reduces the tar yield by similar to 50%(mass). However, the oxygen transport induced by ilmenite caused a reduction in the chemical efficiency of the gasifier and the heating value of the gas, compared to using 100% silica sand as the bed material. The impact of adding ilmenite was found to be dependent upon the operational conditions of the gasifier; a low fluidization velocity gave the highest reduction of the tar yield, whereas higher fluidization velocities led to increased levels of heavy components. Overall, the use of ilmenite as a catalyst for reduction of the yield of tar appears promising, provided that the level of oxygen transport can be restricted.
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| 15. |
- Leion, Henrik, 1976, et al.
(författare)
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Solid fuels in chemical-looping combustion using oxide scale and unprocessed iron ore as oxygen carriers
- 2009
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Ingår i: Fuel. - 0016-2361. ; 88:10, s. 1945-1954
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a novel technology that can be used to meet demands on energy production without CO2 emissions. The CLC-process includes two reactors, an air and a fuel reactor. Between these two reactors oxygen is transported by an oxygen carrier, which most often is a metal oxide. This arrangement prevents mixing of N2 from the air with CO2 from the combustion. The combustion gases consist almost entirely of CO2 and H2O. Therefore, the technique reduces the energy penalty that normally arises from the separation of CO2 from other flue gases, hence, CLC may make capture of CO2 cheaper.Iron ore and oxide scale from steel production were tested as oxygen carriers in CLC batch experiments with solid fuels. Petroleum coke, charcoal, lignite and two bituminous coals were used as fuels.The experiments were carried out in a laboratory fluidized-bed reactor that was operating cyclically with alternating oxidation and reduction phases. The exhaust gases were led to an analyzer where the contents of CO2, CO, CH4 and O2 were measured. Gas samples collected in bags were used to analyze the content of hydrogen in a gas chromatograph.The results showed that both the iron ore and the oxide scale worked well as oxygen carrier and both oxygen carriers increased their reactivity with time.
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| 16. |
- Lind, Fredrik, 1978, et al.
(författare)
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Manganese oxide as catalyst for tar cleaning of biomass-derived gas
- 2012
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Ingår i: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6815 .- 2190-6823. ; 2:2, s. 133 - 140
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Tidskriftsartikel (refereegranskat)abstract
- The possibilities to upgrade raw gas with the use of a manganese oxide have been investigated in an application for secondary tar cleaning of biomass derived gas. Experiments were conducted in a reactor system where a novel technique that combines tar cleaning with catalyst regeneration is applied. Raw gas from the Chalmers non-catalytic steam biomass gasifier - containing roughly 32 gtar/Nm3gas - was fed to the tar cleaning reactor. The tar reforming qualities of the manganese oxide were evaluated in the reactor system using a mixture of 23 wt% catalysts in silica sand at the temperatures 700 and 800°C. Experiments showed that the catalyst was continuously regenerated from carbon deposits and that the total amount of tars was decreased by as much as 44,5% at a gas residence time of 0.4 s in the bed. The catalyst showed activity in water-gas shift reaction and the H2/CO-ratio increased from 0.6 in the raw gas to a peak value of 1 in the reformed gas at 800°C. Only a slight decrease in methane and acetylene content was observed for both operating temperatures.
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