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A general approach to evaluating the performance of industrial-scale dual fluidized bed (DFB) gasifiers was developed in this work. The approach is intended to simplify comprehensive evaluation of DFB gasifiers and to highlight important parameters, some of which are often missed or omitted in the literature. By applying this procedure, experimental results can be generalized, which is verified in this work using the Chalmers 2−4-MW th DFB gasifier. In a DFB gasifier, some of the fuel is converted to the desired calorific gas, while the remaining portion is combusted to meet the heat demands of the process. As shown here, the total heat demands limit the amount of chemical energy that can be restored from the fuel into the produced gas, whereby the main heat demands are from the drying and heating of the fuel, in addition to heating the combustion air and steam. By establishing a heat balance across the system, the chemical efficiency can be estimated. With lower heat demands, higher chemical efficiency is achievable, whereas with higher heat demands, more of the fuel must be burned and a lower chemical efficiency is achieved. It is experimentally complicated to quantify the level of fuel conversion and heat demands of a DFB gasification system. In this work, an experimental procedure is presented and implemented using the Chalmers gasifier to quantify the fuel conversion and heat demands. Furthermore, it was investigated how a variation in the amount of steam used for fluidization of the gasifier affects fuel conversion and other important parameters. To establish a reference case, silica sand was used as bed material and wood pellets was used as fuel to minimize the effects of ash and the bed material. By increasing the level of fluidization steam, the average residence time of the gas was decreased and the gas temperature, gas velocity, and steam-to-fuel ratio were increased, which resulted in increased conversion (up to 36%) of organic compounds (OC). However, limited char conversion was achieved (0%−4%), and the chemical efficiency remained unaffected by the amount of steam added to the process. The chemical efficiency of the Chalmers gasifier was determined to be 74% when using wood pellets as fuel. This is comparable to results from thermo-economic modeling of second-generation biofuels production processes, which, based on the heat demand, report the chemical efficiency of the DFB gasifier as being in the range of 74%−77% to maximize the overall efficiency. This shows that the required chemical efficiency is achieved, even with low char conversion, when using a fuel with a high content of volatiles, such as wood pellets.

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

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SUMMARYThe Gothenburg Biomass Gasification plant (2015) is currently the largest plant in the world producing biomethane (20 MW biomethane ) from woody biomass. We present the experimental data from the first measurement campaign and evaluate the mass and energy balances of the gasification sections at the plant. Measures improving the efficiency including the use of additives (potassium and sulfur), high-temperature pre-heating of the inlet streams, improved insulation of the reactors, drying of the biomass and introduction of electricity as a heat source (power-to-gas) are investigated with simulations. The cold gas efficiency was calculated in 71.7%LHV daf using dried biomass (8% moist). The gasifier reaches high fuel conversion, with char gasification of 54%, and the fraction of the volatiles is converted to methane of 34% mass . Because of the design, the heat losses are significant (5.2%LHV daf ), which affect the efficiency. The combination of potential improvements can increase the cold gas efficiency to 83.5%LHV daf , which is technically feasible in a commercial plant. The experience gained from the Gothenburg Biomass Gasification plant reveals the strong potential biomass gasification at large scale.