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We are approaching the end of 2017. Many activities in GAFT need to be wrapped up before the year ends. Next year will be the last "official" year of the project which will be accompanied by a large number of deliverables that are awaiting to be finalized. Some of these are related to work that has been going on for the entire project period while others will be completely new. The new year will also witness a high activity level for the entrained flow reactor, as several projects (including GAFT) will be using this experimental installation for R&D purposes. In this context, we are aiming for 2018 to be the highlight year for this project with many new and interesting results which we are hoping that you will find interesting. The newsletter contains a brief summary of the activities that we have worked on this year, presented below for the different subprojects.
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A fruitful ending of Subproject 1, feedstock knowledge & pretreatment
The major objectives of SP1 are to identify biomass resources with proper properties, suitable for entrained flow gasification. In addition, these feedstocks should be further optimized through pretreatment methods. The work in SP1 began by performing a complete characterization of the feedstocks that have been defined as "important" for the project.
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This step made possible the establishment of a solid knowledge foundation that could be used to lay down clever strategies for the following pretreatment step. Two methods for the pretreatment have been applied, fuel mixing helped produce proper ash fusion characteristics and torrefaction helped produce suitable physical properties (particle shape and size distribution). Through these feedstock upgrading methods, an optimized fuel for entrained flow gasification could be produced. In GAFT SP1, the effect of torrefaction on physiochemical properties and thermal decomposition behavior were thoroughly studied.
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It was found that torrefaction reduced substantially the energy required for grinding the woody biomass to fine particles. It also increased the homogeneity of the ground particles which is crucial for both the steady feeding to the gasifier and for the particle entrainment inside the reactor. Particle entrainment is important for increasing the fuel residence time inside the reactor and by that achieve higher conversion rates. The non-torrefied and torrefied feedstocks were ground and fed into the entrained flow gasifier through a vibrating feeder.
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The results showed that torrefaction helped improve the feeding stability of the spruce wood fuel. In GAFT, spruce was chosen as the main feedstock for the experimental work on gasification. Normally such type of feedstock has a low content of ash that melts at a rather high temperature and cause challenges during entrained flow gasification. Therefore, fuel mixing is a necessary step in order to avoid operational challenges during gasification.
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Briefly explained, a low ash content will result in a reactor core exposed to high temperatures which gives a higher chance for corrosion and result in damaging the refractory, while high ash melting point will give challenges in taking the ash out of the reactor (it will stick to the reactor walls and/or outlet instead of flowing freely out of the reactor). Intensive thermodynamic calculations were carried out to study the effect of fuel mixing and gasification operation parameters on important properties of the gasification products such as cold gas efficiency and ash fusion characteristics.
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The thermodynamic calculations provided valuable results for the future design of the gasification experiments. In addition, a numerical tool was developed in order to help choose optimal gasification parameters during the experimental operation of the gasifier. Mixtures of spruce with different additive fuels, such as spruce bark, forest residues and organic waste residues from anaerobic digestion were also tested experimentally. The purpose was to validate the results with the thermodynamic calculations. Ash elements in the additives that contributed to the reduction of the ash melting temperature were identified.
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The results showed that addition of additive fuel reduced the melting temperature of spruce wood ash by 100 – 150 °C. This intensive and detailed experimental and theoretical work that was carried out in SP1, resulted in four journal articles and two conference papers. In addition, the results have been presented in three international conferences through four oral presentations.
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Journal article publications based on results from SP1, these can be found in the GAFT eRoom (internal link, access restricted to project partners)
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Progress update on entrained flow gasification
If syngas could be produced from frustration I know where to source the feedstock!
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It's been a challenging fall concerning commissioning of the gasification reactor. The main reason has not been poor design, discovery of engineering mistakes or other things one might suspect when a new reactor is being commissioned. It has been new parts, sourced from reputable suppliers that has been leaking (thermocouples and rotameters), PID-regulators where the parameters have been set by "experts" which do not regulate and suppliers which cannot provide the necessary correct documentation.
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I have learned a thing or two, for one which suppliers I will not use again. However, the reactor is now gas tight. We have defined gas tight as; when we do not see any indicated pressure drop for half an hour starting from 8 bars of pressure. When we start the gasification campaigns we will see if this criterion is sufficiently tight, especially with regards to CO detection in the vicinity of the reactor.
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Week 50 we will receive the thermocouples back from repair, we will install them and start to heat the reactor. Our ambition is to do this is in two steps. In step one we will heat the reactor to 200 °C to learn the heating and cooling characteristics. In the second step, we will heat to 1200 °C. The system is designed so that no personnel need to be present during heating; the process control system should detect if anything is overheating etc. However, when we do this for the first time we have to be present, just to make sure that the system reacts as it should. We will do this in three shifts (including one night shift), preliminary for three days, although this may be revised depending on the reactor heating characteristics. What we know so far is that we cannot heat the refractory faster than 100 °C/hour, to prevent cracking. If everything works as it should during the heating process we will also operate the gasifier, as a gasifier for roughly 2 hours during this campaign. Things are definitely heating up, and I'm looking forward to the upcoming experimental campaigns, which will be a joint effort between three different projects, says the leader of the gasification SP.
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Pulverized biomass particles are assumed to be spheres in many CFD (Computational Fluid Dynamics) simulations despite the fact that they are non-spherical in reality. A new spheroid model that simulates pulverized biomass particles as needle-like spheroids is implemented into OpenFOAM, an open source CFD platform, to address this issue. A series of simulations are conducted to validate the implementations of the new spheroid model. Simulations results are compared with DNS (Direct Numerical Simulation) and experimental data. It has been found that the implementations of the new spheroid model are valid. It can also be observed that there are noticeable differences when simulating pulverized biomass particles with the spheroid model and the sphere model.
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The above results have been presented by Ph.D. Candidate Ning Guo at the Nordic Flame Days (NFD) in Stockholm, Sweden on October 11th, 2017. NFD is a major platform that brings experts in combustion related research together in the Nordic regions. This year’s conference was organized by the Swedish and Finnish National Committees of the International Flame Research Foundation (IFRF) and the Scandinavian-Nordic Section of the Combustion Institute (CINS). The title of the presentation is “Eulerian-Lagrangian simulations of spheroidal biomass particles in turbulent flows.”
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In addition, attempts are being made to investigate the accuracy of the new spheroid model by comparing experimental data with simulations using the spheroid model or the sphere model. Upon invitation, the results are expected to be orally presented at the 2nd International Workshop on Oxy-Fuel Combustion in Bochum, Germany on February 14-15th, 2018.
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Simulation results of normalized particle centerline velocity decay with the sphere and the spheroid model (aspect ratio 10) in co-flow jet configurations.
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Progress update on Fischer-Tropsch testing
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After testing a variety of cobalt and iron-based Fischer-Tropsch catalyst, a FeCuKSiO2 catalyst was chosen for further studies of the effect of process conditions, relevant for the GAFT project, on product selectivities and catalyst stability. This includes reaction temperatures from 230 - 290 °C, and H2:CO ratios from 0.5 - 2 with and without CO2 in the syngas. Some of this work is summarized in the table below. With increasing H2:CO ratio, C5+ formation decreases while there is a slight shift towards lighter hydrocarbons. The study also shows that adding CO2 in syngas apparently decreases the CO-conversion, but that CO2 has no clear effect on the hydrocarbon distribution. Further studies will include long time catalyst stability testing and gathering of data as input to the kinetic model.
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Effect of H2:CO ratio and CO2 addition on the syngas composition. FeCuKSiO2 catalyst at 270 °C and 20 bars.
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Progress update on value-chain analysis
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Fischer Tropsch synthesis (FTS) is a catalytic process that converts a mixture of CO and H2 (syngas) into a pool of linear hydrocarbons with a wide carbon number range (C1 - C60+) and with ultra-low sulfur and nitrogen content. One of the main technological advantages of using FTS for the production of liquid biofuels come by the fact that the hydrocarbon products from FTS can be easily fractionated and converted to naphtha, kerosene, diesel and heavy fuel oils in conventional refinery processes downstream the oil-crude desalting and distillation processes (see Figure below). Moreover, the absence of sulfur and nitrogen in FTS fractions requires simpler hydro-processing units, with lower energy and hydrogen consumption. In the GAFT project the real economic value of FTS fractionated products for producing liquid biofuels will be evaluated by performing a techno-economic analysis of the production, fractionation and upgrading of FTS products to market fuels.
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Integration of Fisher Tropsch synthesis products into an existing refinery
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Other news
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The second steering committee meeting in 2017, held in Follum
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The second steering committee meeting of the year 2017 was held at Follum at Treklyngen, the former Follum papermill head-office. The meeting extended over a period of 2 days where on the first day a workshop was arranged for the dissemination of project results. The second day combined a formal SC meeting with a midway evaluation of the project which witnessed the participation of Trond Værnes from the Research Council of Norway. We would like to extend our gratitude to Viken Skog and Ole Petter Løbben who took care of us during these 2 days.
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A group photo of industry and R&D partners who participated in the second workshop/steering committee meeting of 2017, arranged October 18th – 19th
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Calendar of events
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Contacts
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Fischer-Tropsch synthesis:
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