| 1. |
- 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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| 2. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Bed material as a catalyst for char gasification: The case of ash-coated olivine activated by K and S addition
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 224, s. 85-93
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the ability of an ash-coated olivine to catalyze the steam gasification of biomass-derived char is investigated in a laboratory reactor. The olivine investigated is a sample from the Chalmers dual fluidized bed gasifier and it has been activated by the in-bed addition of S and K 2 CO 3 . The char and bed material samples were analyzed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). It is shown that the ash layer coating of the olivine can catalyze the steam gasification of char by transferring catalytic potassium (K) to the char particles. The mobilities of the catalytic species from the olivine ash-layer are discussed. This work furthers the current understanding of the catalytic activities of ash-coated bed material particles during the thermochemical conversion of carbonaceous feedstocks in fluidized beds. In addition, it complements the existing literature on catalytic bed materials, which to date have focused on tar removal and improving gas quality.
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| 3. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Behaviour of biomass particles in a large scale (2-4MWth) bubbling bed reactor
- 2015
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Ingår i: WIT Transactions on Engineering Sciences- Computational methods in multiphase flow VIII. - 9781845649463 ; 89, s. 151-160
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is regarded as an interesting fuel for energy-related processes owing to its renewable nature. However, the high volatile content of biomass adds a number of difficulties to the fuel conversion and process operation. In the context of fluidized bed reactors, several authors have observed that devolatilizing fuel particles tend to float on the surface of a gas-fluidized bed of finer solids. This behaviour, known as segregation, leads to undesired effects such as poor contact between volatiles and bed material. Previous investigations on segregation of gas-emitting particles in fluidized beds are conducted in small units and they are often operated at rather low gas velocities, typically between the minimum fluidization velocity (umf) and 2·umf. Therefore, it is not known to what extent such results are of relevance for industrial scale units and for higher fluidization velocities that are commonly used in large bubbling beds. In this work the behaviour of biomass particles in a large scale bubbling bed reactor is investigated. Tests were conducted at a wide range of fluidization velocities with three different bed materials of varying particle size and density. The fuel was wood pellets and the fluidization medium was steam, which makes the findings relevant for indirect gasification, chemical looping combustion (CLC) and bubbling bed combustion applications. The experiments were recorded by means of a digital video camera and the digital images were subsequently analysed qualitatively. The results show high level of segregation at fluidization velocity up to 3.5umf. Beyond this point fuel mixing was significantly enhanced by increasing fluidization velocities. At the highest fluidization velocity tested (i.e. >8umf), a maximum degree of mixing was achieved.
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| 4. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Comparing Active Bed Materials in a Dual Fluidized Bed Biomass Gasifier: Olivine, Bauxite, Quartz-Sand, and Ilmenite
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4848-4857
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Tidskriftsartikel (refereegranskat)abstract
- Active bed materials are in this work investigated for in situ gas upgrading of biomass-derived gas. Previous research on in situ gas upgrading has focused on assessing gas quality, in terms of the concentrations of tar and permanent gases. Other aspects of fuel conversion, such as char conversion and the impact of oxygen transport on the final gas, are not as well documented in the literature on gasification. In this paper, the overall biomass conversion in a dual fluidized bed biomass gasifier is investigated in the presence of the catalytic material olivine and the alkali-binding material bauxite. The impact of these materials on fuel conversion is described as the combination of four effects, which are induced by the bed material: thermal, catalytic, ash-enhanced catalytic effect, and oxygen transport. Quartz-sand and ilmenite are here used as the reference materials for the thermal and the oxygen transport effects, respectively. Olivine and bauxite show activity toward tar species compared to quartz-sand. After 1 week of operation and exposure to biomass ash, the activities of olivine and bauxite toward tar species increase further, and the water gas shift reaction is catalyzed by both materials. Additionally, bauxite shows a stronger ability to increase char conversion than olivine. Under the conditions tested, olivine and bauxite have some degree of oxygen transport capacity, which is between those of quartz-sand and ilmenite. The oxygen transport effect is higher for bauxite than for olivine; nevertheless, the catalytic activities of the materials result in higher yields of H-2 than in a similar case with quartz-sand. The implications of the findings for the operation of dual fluidized bed gasifiers are discussed.
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| 5. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Experience of more than 1000 h of operation with oxygen carriers and solid biomass at large scale
- 2017
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 190, s. 1174-1183
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an overview of the experience gained from operating a dual fluidized bed system with oxygen carriers and biomass for more than 1000 h. The tests were carried out in the Chalmers boiler/gasifier loop (with inputs of 12 MWth and 2–4 MWth, respectively), which is 2–4 orders of magnitude larger than most existing CLC units. Coarse biomass particles (i.e., commercial wood pellets) were fed as fuel onto the surface of a mild fluidized bed. This limits significantly the contacts between the volatiles and the oxygen carrier particles, as the flotsam fuel tends to remain on the surface of the bed while the volatiles are released. The oxygen carrier materials tested were ilmenite and a manganese ore. The influences on biomass conversion of fluidization velocity, fuel feeding rate, and circulation rate of the bed material were investigated. Both bed materials efficiently transported oxygen between the reactors, achieving up to 60% combustion of the gases released in the reactor at a relatively low temperature, i.e., 830 °C. The ilmenite outperformed the manganese ore under the conditions investigated. With oxygen carriers, the yield of hydrocarbons heavier than benzene was in the range of 10–11 g/N m3, which was 70% (w/w) lower than that obtained in a reference case with silica-sand as the bed material. The conversion of volatile species to CO2 was limited by gas-solids mixing, which could be enhanced by altering the fluidization velocity. The circulation rate of the bed material and the fuel feeding rate were found to have important influences on the rate of char gasification. Given the relatively low operating temperature and the simple reactor design, relatively high conversion of biomass by the oxygen carriers was achieved. There is scope for further optimization of the operating conditions, to achieve higher conversion levels, which would enable the implementation of CLC of biomass on a large scale. © 2017 Elsevier Ltd
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| 6. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Experimental Investigation of Volatiles-Bed Contact in a 2-4 MWth Bubbling Bed Reactor of a Dual Fluidized Bed Gasifier
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 29:10, s. 6456-6464
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Tidskriftsartikel (refereegranskat)abstract
- The use of catalytic bed materials in fluidized bed gasifiers represents a promising primary measure to decrease the tar content of biomass-derived raw gas. For effective application of such in-bed catalysts, extensive contact must be established between the volatile matter released from the fuel particles and the bed material. However, the extent of the contact and, consequently, the potential of in-bed tar removal techniques are not well understood. In this work, the fraction of volatile matter that interacts with the bed in a large (i.e., throughput of 300-400 kg/h biomass) bubbling bed gasifier is quantified experimentally and the effect of fluidization velocity is investigated. The results show that a higher fluidization velocity enhances gas-solid contact, with 48-69% of the volatile matter coming in contact with the bed within the range of 6-10 times the minimum fluidization (umf).
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| 7. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Impact of oxygen transport on char conversion in dual fluidized bed systems
- 2015
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Ingår i: Nordic Flame Days 2015, Copenhagen.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the context of thermochemical conversion of solid fuels in dual fluidized bed (DFB) reactors, oxygen carrier bed materials have been found to enhance the rate of char gasification.Char gasification is typically the rate limiting step in the conversion process, which plays a role on the performance of the overall process and constrains the design of the reactor. The quantity of oxygen carried by the bed material in relation to the fuel feeding rate is likely to influence char conversion. This parameter is commonly characterized in literature by the oxygen-carrier-to-fuel ratio (ϕ), and it can be adjusted by either varying the fuel feed and/or the circulation rate of bed material in the DFB. The residence time of the fuel is typically altered by these changes, which results in an unclear role of the oxygen-carrier-to fuel ratio on the final char conversion. The present work investigates the impact of oxygen transport on char conversion in the 2-4 MWth DFB gasifier at Chalmers University of Technology. An iron ore is used as oxygen carrier and steam as fluidizing agent. A parametric study is conducted, in which a wide range of oxygen-carrier-to-fuel ratio (ϕ=3-12) are achieved by varying fuel flow and bed material circulation. Char conversion is calculated on the basis of gas analysis and mass balance calculations. The results confirm that oxygen transport enhances char conversion, in line with previous research in smaller units. Both fuel feed and circulation of bed material had an impact on the final char conversion under the conditions tested, which differs from previous investigations. For a given residence time of the fuel particles in the reactor, char conversion was found proportional to the oxygen-carrier-to-fuel ratio.
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| 8. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Influence of in-bed catalysis by ash-coated olivine on tar formation in steam gasification of biomass
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:9, s. 9592-9604
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Tidskriftsartikel (refereegranskat)abstract
- The use of catalytic bed materials has become a state-of-the-art solution to control the concentration of tar in fluidized bed biomass steam gasifiers. Ash-coated olivine is commonly applied as bed material, owing to its relatively high catalytic activity towards tar species. However, the mechanisms and conversion pathways influenced by the ash-coated olivine when applied as an in-bed catalyst are still not well understood. The present work aims at proving that the ash-layered olivine prevents the formation of biomass-derived tar at an early stage of their formation. Tests with olivine at different stages of activation and at different temperatures are carried out in the Chalmers 2-4MWth DFB gasifier. Detailed characterization of the tar and light hydrocarbon fractions are presented and discussed in relation to the sources of aromatic species. It is concluded that the ash-coated olivine prevents the formation of aromatic tar species by promoting the steam reforming of early tar precursors. Gas-phase interactions of the early tar precursors and bed material contribute to the tar reduction observed. The results indicate that olivine interferes the cyclization routes involving C2H2 and C3 hydrocarbons.
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| 9. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Mapping the effects of potassium on fuel conversion in industrial-scale fluidized bed gasifiers and combustors
- 2021
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- Potassium (K) is a notorious villain among the ash components found in the biomass, being the cause of bed agglomeration and contributing to fouling and corrosion. At the same time, K is known to have catalytic properties towards fuel conversion in combustion and gasification environments. Olivine (MgFe silicate) used as gasifier bed material has a higher propensity to form catalytically active K species than traditional silica sand beds, which tend to react with K to form stable and inactive silicates. In a dual fluidized bed (DFB) gasifier, many of those catalytic effects are expected to be relevant, given that the bed material becomes naturally enriched with ash elements from the fuel. However, a comprehensive overview of how enrichment of the bed with alkali affects fuel conversion in both parts of the DFB system is lacking. In this work, the effects of ash-enriched olivine on fuel conversion in the gasification and combustion parts of the process are mapped. The work is based on a dedicated experimental campaign in a Chalmers DFB gasifier, wherein enrichment of the bed material with K is promoted by the addition of a reaction partner, i.e., sulfur, which ensures K retention in the bed in forms other than inactive silicates. The choice of sulfur is based on its affinity for K under combustion conditions. The addition of sulfur proved to be an efficient strategy for capturing catalytic K in olivine particles. In the gasification part, K-loaded olivine enhanced the char gasification rate, decreased the tar concentration, and promoted the WGS equilibrium. In the combustion part, K prevented full oxidation of CO, which could be mitigated by the addition of sulfur to the cyclone outlet.
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| 10. |
- Berdugo Vilches, Teresa, 1985
(författare)
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Operational strategies to control the gas composition in dual fluidized bed biomass gasifiers
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Steam gasification of biomass can increase the share of renewable energy and material resources in the energy sector, transportation and different industries. Prior its application, the raw gas produced in biomass gasifiers needs to be cleaned from impurities. In gasifiers operating at mild temperature, such as fluidized bed steam gasifiers, tar is an impurity of major concern due to the operational problems that it can cause. Tar species can condensate at temperatures as high as 300°C, causing the clogging of pipes and coolers, deactivating downstream catalysts, and forcing unplanned shut-downs. Thus, it is necessary to control the tar and gas compositions in gasifiers to ensure the technical reliability of the technology. This work investigates measures to control biomass conversion in dual fluidized bed (DFB) steam gasifiers and, thereby, contribute to the rational operation and design of these types of units. A parametric experimental investigation of the influences of operating conditions on gas and tar compositions is presented. The examined parameters are: fluidization velocity; steam-to-fuel ratio (S/F); circulation rate of the bed material; temperature; and active bed materials. The bed materials tested include silica sand, olivine, bauxite, and feldspar, as well as the oxygen-carrying materials ilmenite and manganese. The work was carried in the Chalmers 2–4-MWth DFB gasifier using woody biomass as the fuel. The gasification technology applied in this work is similar to that of the existing gasifiers at the Güssing, Senden, Oberwart, and GoBiGas plants. Within the operating window investigated, optimization of the bed material activity was the main tool for controlling tar conversion, which can be improved using additives. The levels of effectiveness of the in-bed catalysts were linked to the destruction of tar precursors. It is proposed that both homogeneous and heterogeneous catalysis of tar reactions occur in systems where alkali is expected in the gas phase. With active bed materials, temperature changes in the range of 700°–830°C were found to affect primarily the composition of the tar, and to a lesser extent, the tar yield. Finally, it is shown that a simple gasifier design with on-bed feeding ensures that at least 50% of the volatiles come in contact with the catalytic bed material when the bed is well-fluidized. Extensive experimental results and their implications for the design and operation of a DFB gasifier are discussed throughout this thesis.
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