| 1. |
- Larsson, Anton, 1984, et al.
(författare)
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Zero-dimensional modeling of indirect fluidized bed gasification
- 2010
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Ingår i: 13th International Conference on Fluidization.
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Konferensbidrag (refereegranskat)abstract
- Zero-dimensional models has been developed to investigate mass balance and fuel (biomass) conversion in Chalmers 2-4 MWfuel indirect fluidized bed gasifier. The input to the model is measured concentrations and flows. The model shows that the conversion factor of the water gas shift reaction is around 40 %.
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| 2. |
- Maggiolo, Dario, 1985, et al.
(författare)
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Self‐Cleaning Surfaces for Heat Recovery During Industrial Hydrocarbon‐Rich Gas Cooling: An Experimental and Numerical Study
- 2019
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 65:1, s. 317-325
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Tidskriftsartikel (refereegranskat)abstract
- The cooling of hydrocarbon-rich gases in industrial processes often leads to severe fouling, which impedes heat recovery, restricts operative conditions and increases maintenance costs. In the present work, we investigate whether self-cleaning surfaces represent a possible solution to overcome this technological bottleneck. Hydrophilic and hydrophobic treatments of compact heat exchanger plates are experimentally and numerically investigated during cooling of syngas produced from biomass gasification. The experimental evidences related to the operation of heat exchanger plates are assessed first, and a deeper insight into the relevant phenomena is thereafter obtained by performing numerical simulations. Our analysis identifies the hydrophobic treatment as the most promising solution and unveils the induced self-cleaning mechanism: the formation of small-sized and movable condensed droplets that enhance the collection and removal of gas impurities. These findings open up new routes towards the development of cheaper, more efficient and sustainable gas cooling systems.
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| 3. |
- Maggiolo, Dario, 1985, et al.
(författare)
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Two-phase flow patterns and condensation on wetted surfaces for innovative self-cleaning heat exchangers: experiments and numerics
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fouling is a common and pervasive problem in industrial processes that involve the cooling of hydrocarbon-rich gas mixtures and and it is considered responsible for 1%÷2.5% of the global anthropogenic emissions of CO2. One of the major drawbacks related to fouling is that it impedes heat recovery and thereby it considerably limits the efficiency of many industrial processes. We experimentally and numerically have investigated whether self-cleaning surfaces of heat exchangers represent a possible solution to overcome this technological bottleneck. Hydrophilically and hydrophobically treated corrugated plates of heat exchangers have been experimentally tested in a 2 MW th research-gasifier and their capabilities to resist fouling have been evaluated. Results revealed that hydrophobically treated surfaces exhibit good anti-fouling and self-cleaning properties. By means of numerical Lattice-Boltzmann-based simulations we then unveiled the self-cleaning phenomenon induced by the wetted surfaces: with a similar mechanism to lotus-leaves, small and motile condensed water droplets are able to collect and remove impurities present in the gas and prevent surfaces fouling. Condensation, two-phase flows patterns formation and droplets coalescence all contribute to promote or weaken the self-cleaning effects. Therefore, numerical simulations have been finally used to identify the main mass and heat transport mechanisms that affect self-cleaning and the optimal operative conditions of the heat exchangers.
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| 4. |
- Larsson, Anton, 1984, et al.
(författare)
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Evaluation of Performance of Industrial-Scale Dual Fluidized Bed Gasifiers Using the Chalmers 2–4-MWth Gasifier
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:1, s. 6665-6680
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Tidskriftsartikel (refereegranskat)abstract
- 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-MWth 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.
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| 5. |
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| 6. |
- Larsson, Anton, 1984, et al.
(författare)
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Steam gasification of biomass – Typical gas quality and operational strategies derived from industrial-scale plants
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- Steam gasification enables the thermochemical conversion of solid fuels into a medium calorific gas that can be utilized for the synthesis of advanced biofuels, chemicals or for heat and power production. Dual fluidized bed (DFB) gasification is at present the technology applied to realize gasification of biomass in steam environment at large scale. Few large-scale DFB gasifiers exist, and this work presents a compilation and analysis of the data and operational strategies from the six DFB gasifiers in Europe. It is shown that the technology is robust, as similar gas quality can be achieved despite the differences in reactor design and operation strategies. Reference con-centrations of both gas components and tar components are provided, and correlations in the data are in-vestigated. In all plants, adjusting the availability and accessibility to the active ash components (K and Ca) was the key to control the gas quality. The gas quality, and in particular the tar content of the gas, can conveniently be assessed by monitored the concentration of CH4 in the produced gas. The data and experience acquired from these plants provide important knowledge for the future development of the steam gasification of biomass.
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| 7. |
- 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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| 8. |
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| 9. |
- Neves, Daniel Santos Felix, 1982, et al.
(författare)
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Method for online measurement of the CHON composition of raw gas from biomass gasifier
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 113, s. 932-945
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Tidskriftsartikel (refereegranskat)abstract
- For unattended biomass gasification processes, rapid methods for monitoring the elemental composition (CHON) of the raw gas leaving the gasifier are needed. Conventional methods rely on time-consuming and costly laboratory procedures for analysing the condensable part of the raw gas. An alternative method, presented in this work, assesses the CHON composition of raw gas in a "one step" analysis without the need to previously characterise its chemical species composition. Our method is based on the quantitative conversion of a raw gas of complex chemical composition into CO2, H2O, and N2 in a small combustor. The levels of these simple species can be measured with high accuracy and good time resolution, and the CHON composition of the raw gas can be determined from the mass balance across the combustor. To evaluate this method, an online combustion facility was built and used to analyse the raw gas from the Chalmers 2-MWth dual fluidised bed steam gasifier. Test runs of the developed facility demonstrated complete combustion of the raw gas and the measurements were both fast and reliable. The new method used in combination with zero-dimensional reactor modelling provides valuable data for the operational monitoring of gasification processes, such as the degree of fuel conversion, composition of the char exiting the gasifier, oxygen transport by catalytic bed material, and amount of condensables in raw gas.
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| 10. |
- Neves, D., et al.
(författare)
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Volatile gases from biomass pyrolysis under conditions relevant for fluidized bed gasifiers
- 2017
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Ingår i: Journal of Analytical and Applied Pyrolysis. - : Elsevier BV. - 0165-2370. ; 127, s. 57-67
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Tidskriftsartikel (refereegranskat)abstract
- The pyrolytic volatiles released from a converting biomass particle are investigated in this work through laboratorial fluidized bed experiments simulating conditions typical of large-scale gasifiers. Two types of wood (eucalyptus and pine) and two types of pellets (forest residues and wood) with particles of 6-8 mm in diameter are fed over the hot bubbling bed at temperatures within 600-975 degrees C. The resultant major pyrolytic products (char, soot, liquids and permanent gas) are collected to verify the overall mass balance, and the composition of the permanent gas is resolved in C3H8, C2H6, C2H4, CH4, CO2, CO, and H-2. Primary pyrolysis of the parent fuel particles is essentially complete at 600 degrees C and further increase of the temperature mainly leads to a progressive change in the composition of the volatile gas mixture. Although the gas release does not attain thermodynamic equilibrium under the conditions tested, our results show that the yields of CO2 and light hydrocarbons go through maxima as temperature increases to give rise to CO and H-2 as the preferable species at high temperatures. As a whole, the gas composition evolves in such a way that the corresponding lower heating value steadily increases with temperature increase, from about 11 MJ/kg at 600 degrees C to above 17 MJ/kg at 950 degrees C. Furthermore, the yields of key gas species were found well correlated to each other (C2H4 vs. CH4, CH4 vs. CO and H-2 vs. CO), with the relation between the yields of H-2 and CO being slightly dependent on the composition of fuel.
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