• Energy Research

AbstractThe present work describes the results achieved during a study aiming at the full replacement of the natural gas demand of an integrated hot metal production. This work implements a novel approach using a biomass gasification plant combined with an electrolysis unit to substitute the present natural gas demand of an integrated hot metal production. Therefore, a simulation platform, including mathematical models for all relevant process units, enabling the calculation of all relevant mass and energy balances was created. As a result, the calculations show that a natural gas demand of about 385 MW can be replaced and an additional 100 MW hydrogen-rich reducing gas can be produced by the use of 132 MW of biomass together with 571 MW electricity produced from renewable energy. The results achieved indicate that a full replacement of the natural gas demand would be possible from a technological point of view. At the same time, the technological readiness level of available electrolysis units shows that a production at such a large scale has not been demonstrated yet.

AbstractChemical looping combustion is a highly efficient CO2 separation technology without direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier in dual fluidized beds to generate clean CO2. The use of biomass is the focus of current research because of the possibility of negative CO2 emissions and the utilization of biogenic carbon. The most commonly proposed OC are natural ores and residues, but complete combustion has not yet been achieved. In this work, the direct utilization of CLC exhaust gas for methane synthesis as an alternative route was investigated, where the gas components CO, CH4 and H2 are not disadvantageous but benefit the reactions in a methanation step. The whole process chain, the coupling of an 80 kWth pilot plant with gas cleaning and a 10 kW fluidized bed methanation unit were for this purpose established. As OC, ilmenite enhanced with limestone was used, combusting bark pellets in autothermal operation at over 1000 °C reaching high combustion efficiencies of up to 91.7%. The fuel reactor exhaust gas was mixed with hydrogen in the methanation reactor at 360 °C and converted with a methane yield of up to 97.3%. The study showed especially high carbon utilization efficiencies of 97% compared to competitor technologies. Based on the experimental results, a scale-up concept study showed the high potential of the combination of the technologies concerning the total efficiency and the adaptability to grid injection. Graphical Abstract

AbstractChemical-looping combustion (CLC) is a highly efficient CO2 separation technology with no direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier (OC) and acts in a dual fluidized bed as a separation tool and supplies the fuel with oxygen, which as an oxidation medium causes combustion to CO2 and H2O. The use of solid fuels, especially biomass, is the focus of current investigations. The OC plays a key role, because it must meet special requirements for solid fuels, which are different to gaseous fuels. The ash content, special reaction mechanisms, and increased abrasion make research into new types of OC essential. Preliminary testing of OC before their use in larger plants regarding their suitability is recommended. For this reason, this work shows the design and the results of a laboratory reactor, which was planned and built for fundamental investigation of OC. Designed as a transient fluidized bed, the reactor, equipped with its own fuel conveying system and an in situ solid sampling, is intended to be particularly suitable for cheap and rapid pre-testing of OC materials. During the tests, it was shown that the sampling device enables non-selective sampling. Different OC were tested under various operating conditions, and their ability to convert different fuels could be quantified. The results indicate that OC can be sufficiently investigated to recommend operation in larger plants.

Mit Chemical Looping Combustion (CLC) wird eine effiziente CO2-Abscheidetechnologie erforscht. Durch eine atmosph��rische Trennung der Luft und des Brennstoffes ��ber ein Metalloxid, auch genannt der Sauerstofftr��ger, finden kaum Wirkungsgradverluste statt. Obwohl die Technologie mit gasf��rmigen Brennstoffen schon weit entwickelt ist, steht CLC mit festen Brennstoffen noch vor verschiedensten Herausforderungen. Hierbei spielt das Metalloxid eine zentrale Rolle. Dieses transportiert ��ber ein Zweibettwirbelschichtsystem den ben��tigten Sauerstoff f��r eine Verbrennung von der Verbrennungsluft zum Brennstoff. Das Produkt der Reaktion enth��lt je nach Brennstoff ausschlie��lich CO2 und Wasserdampf. Durch das Auskon-densieren von Wasser wird hochkonzentriertes CO2 gewonnen. In dieser Arbeit wurden Versuche an einer Laborwirbelschicht durgef��hrt, welche gr����entechnisch das Bindeglied zwischen Pilotanlagen und kleineren Laboreinheiten bilden soll. Das schnelle Testen neuer Brennstoffe und Sauerstofftr��ger erweist sich in gro��en Anlagen als teuer und aufwendig. So ist der verwendete Reaktor im Batchbetrieb als einfache Wirbelschicht ausgef��hrt und es ist m��glich das Zweibettwirbelschichtsystem zu simulieren. Hier k��nnen Versuchsparameter und Eigenschaften von Sauerstofftr��gern kosteng��nstiger erforscht werden. Zu diesem Zweck werden bei dem Batchreaktor Adaptionen durchgef��hrt und geeignete Betriebsbedingungen ermittelt, die eine ��bertragung der Ergebnisse auf gr����ere Anlagen zulassen. Die Versuche zeigen unter anderem, dass die Fluidisierung, die Temperatur sowie die Wahl des Brennstoffes und des Sauerstofftr��gers den gr����ten Einfluss auf den Reaktionsverlauf haben. Mit den verwendeten Sauerstofftr��gern Braunit (Manganerz) und Ilmenit (Eisen-Titan-erz) werden ohne Nachverbrennung bis zu 80% des Kohlenstoffs im Brennstoff zu CO2 umgesetzt. ��ber die Versuchsergebnisse im Batchreaktor werden Trends auf eine 80kW-Pilotanlage f��r feste Brennstoffe umgelegt. Im Zuge dieser Arbeit wurden in ��ber 200 Betriebsstunden des Batchreaktors die wichtigsten Einflussparameter und deren Auswirkungen untersucht. Ein Umlegen der Ergebnisse auf eine gr����ere Anlage ist m��glich, jedoch sind f��r ein genaues Scale-up mehr Versuchsdaten notwendig. Chemical Looping Combustion (CLC) is an efficient CO2 capture technology. There is hardly any efficiency penalty, because of the atmospheric separation of air and combustion via metal oxides. Although the gas-fuelled technology is high developed, there are still major challenges with solid-fuels. The metal oxide, which is also called the oxygen carrier, is at the centre of interest. He delivers oxygen through a dual-fluidized bed, which is required for combustion free of interfering gases. The product of the reaction contains only CO2 and water vapour de-pending on the fuel. While condensing the water vapour, highly concentrated CO2 could be generated. In terms of size, the experimental reactor for CLC treated in this work, forms the missing link between pilot plants and smaller laboratory units. Rapid testing of new fuel and oxygen carri-ers proves to be expensive and costly in large plants. The adopted reactor is running in batch mode as a simple fluidized bed. Experimental parameters and characteristics of oxygen carriers can be researched at lower costs. For this purpose, there will be adaptations for the new operating Batch-reactor and also research for suitable operating conditions to approximate the results to large-scale units. The experiments show that the fluidization and the choice of fuel and oxygen carriers are most influencing to the progress of the reaction. There are CO2 conversion rates up to 80% achieved by using Braunit and Ilmenite as oxygen carriers. The experimental results in the Batch-reactor allow trends to be transferred to an 80kW solid fuel plant. In summary, in over 200 operating hours, the most important parameters and their effects can be identified. A transfer of results to a large plant is possible, but for an exact scale-up more experimental data is necessary.

Chemical looping combustion (CLC) of biogenic fuels offers significant potential for achieving negative CO2 emissions by capturing CO2 during energy production. However, ensuring high purity of captured CO2 for compression, transport, and storage applications poses challenges, particularly due to potential impurities in biomass such as ash, phosphorus (P), sulfur (S), nitrogen (N), and chlorine (Cl). The distribution of these impurities among transport to the air reactor, binding to cyclone ash, or conversion to the gas phase, as well as their impact on reaction pathways, remains largely uncertain, varying greatly depending on the reactor system, fuel used, and oxygen carrier employed. This study focused on establishing impurity balances during pilot plant operation (80 kWth) using a synthetic manganese-iron-copper oxygen carrier with bark as fuel. Through detailed analysis of gas components in the fuel reactor (FR) exhaust gas, as well as examination of bed material after the FR and the FR cyclone, nitrogen and sulfur mass balances were determined. Approximately 90 wt% of the fuel's nitrogen was converted to gaseous N2, with the remainder mainly transported with the bed material to the air reactor (AR). Concentrations of unwanted nitrogen compounds such as NH3, NO, and N2O were each below 1 wt% of the fuel's nitrogen. The SO2 concentration of the gas was low due to separation during gas analysis via water condensation and washing with rapeseeds methyl ester. A discussion of possible gas cleaning routes to meet storage requirements is based on the measured impurity levels.