According to the Intergovernmental Panel on Climate Change (IPCC), scenarios that have a good chance of restricting global warming to less than 2°C involve substantial cuts in anthropogenic greenhouse gas (GHG) emissions, implemented through large-scale changes in energy systems. The use of renewable energy sources and fossil fuels, in combination with carbon capture and storage (CCS), could help to reduce GHG emissions in the AbstractThis paper presents the main experiences gained and conclusions drawn from the demonstration of a first-of-its-kind wood-based biomethane production plant (20-MW capacity, 150 dry tonnes of biomass/day) and 10 years of operation of the 2-4-MW (10-20 dry tonnes of biomass/day) research gasifier at Chalmers University of Technology in Sweden. Based on the experience gained, an elaborated outline for commercialization of the technology for a wide spectrum of applications and end products is defined. The main findings are related to the use of biomass ash constituents as a catalyst for the process and the application of coated heat exchangers, such that regular fluidized bed boilers can be retrofitted to become biomass gasifiers. Among the recirculation of the ash streams within the process, presence of the alkali salt in the system is identified as highly important for control of the tar species. Combined with new insights on fuel feeding and reactor design, these two major findings form the basis for a comprehensive process layout that can support a gradual transformation of existing boilers in district heating networks and in pulp, paper and saw mills, and it facilitates the exploitation of existing oil refineries and petrochemical plants for large-scale production of renewable fuels, chemicals, and materials from biomass and wastes. The potential for electrification of those process layouts are also discussed. The commercialization route represents an example of how biomass conversion develops and integrates with existing industrial and energy infrastructures to form highly effective systems that deliver a wide range of end products. Illustrating the potential, the existing fluidized bed boilers in Sweden alone represent a jet fuel production capacity that corresponds to 10% of current global consumption. 7
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 towards tar species compared to quartz-sand. After one week of operation and exposure to biomass ash, the activities of olivine and bauxite towards tar species increase further, and the WGS reaction is catalyzed by both materials. Additionally, bauxite shows 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
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 (H 2 ) 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.
The aim of this work was to investigate the potential of alkali-feldspar ore [(K, Na)AlSi3O8] as an alternative bed material for indirect gasification of biomass. Experiments conducted in the Chalmers 2-MW gasifier confirmed that alkali-feldspar could withstand stringent fluidizing conditions. Moreover, this material showed strong promise for promoting the water–gas shift reaction and reforming higher hydrocarbons, in particular tars. This activity was enhanced by time-on-stream in the indirect gasifier, and the gas and tar yields were higher than for activated olivine or bauxite used in the same unit. SEM-EDX analysis revealed that the observed activity of alkali-feldspar was due to the formation of active ash layers on the feldspar particles (consisting principally of Ca, Mg, K, and Na) that originated from the woody fuel. At some point, the feldspar showed capacity to transport oxygen from the boiler to the gasifier. Thus, an optimal level of bed regeneration would benefit the reforming reactions in the gasifier, while creating the possibility to improve fuel conversion in the boiler through increased access and distribution of oxygen, which is transported by the bed material throughout the boiler.
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