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Carbon Capture and Storage Program(CCSP) Final report 1.1.2011–31.10.2016

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A new 10-50 kWth scale dual fluidized bed (DFB) chemical looping combustion (CLC) process development unit (PDU) applicable for biomass was constructed during 2015-16, located in VTT’s new piloting center Bioruukki in Finland. The DFB-CLC test rig consists of a circulating fluidized bed (CFB) air reactor interconnected with a bubbling fluidized bed (BFB) fuel reactor. A set of tests were carried out with ilmenite as oxygen carrier, using white and black wood pellets as fuels. The main targets were to study main operational and process parameters for CLC using biomass-based fuels with a high volatile content. Another interest was to assess the risk for high-temperature corrosion in the flue gas path of the air reactor to evaluate the possibility for improving power generation efficiency by using enhanced steam values. The DFB-PDU was operated with biofuel in total for 16 h for 9 tests. The main challenge encountered was an insufficient bed temperature of the fuel reactor (900-950ºC targeted, 840-860ºC achieved) causing a relatively high oxygen demand (29-41%). The main reason for this was that the DFB-PDU was originally designed for gasification. A clear dependency of the fluidization velocity on the CO2 capture efficiency and oxygen demand was found and explained. As the fuel is fed and gasified in the fuel reactor, fuel leakage to the air reactor was low and alkaline components were not accumulated to the surface of oxygen carrier particles, it can be concluded that concentrations of vaporized alkali chlorides components in air reactor flue gas are much lower than in conventional biomass combustion applications. The results indicate that the risk of high-temperature corrosion of superheater tubes is lower in bio-CLC than conventional biomass combustion, making it possible to to use higher steam values (temperature, pressure) in bio-CLC improving the power generation efficiency from biomass.
Conference Paper
In chemical looping combustion CLC solid metal oxides are used to burn organic fuels. Typically the metal oxide serving as oxygen carrier is oxidized in separate air reactor and reduced in separate fuel reactor. The oxygen carrier suffers repeated oxidation and reduction cycles, and the chemical cycling affects the oxygen carrier’s physical and chemical characters. In order to run CLC-process economically oxygen carrier degradation should be as low as possible by minimizing the oxygen carrier make up together with maintained fluidity. Small scale fluidized bed reactor was constructed to tests as pure chemical cycling resistance of oxygen carriers as possible. Fe2O3-Al2O3 type granulated oxygen carrier, sintered at 1100ºC, was tested in repeated 50% CH4- CO2 mixture and air for 100 cycles. Tests revealed that repeated reduction and oxidation has clear effect on oxygen carrier and that the test arrangement can be used to tests chemical cycling resistance and to develop the long term durability of oxygen carriers. The test revealed that very fine dust was formed in chemical cycling, indicating degradation, which did not occur in tests conducted in air for the same time. The fine particles formed coated the surface of the oxygen carrier granules.
Article
The study presents a path for selecting the reaction and reactor parameters of a process applying thermo-catalytic decomposition of methane (TDM). Temperature and catalyst are the main reaction parameters affecting the type of TDM carbon and defining the reaction’s theoretical heat requirement. Secondly, the reaction parameters affect the reactor design including the selection of reactor type and heating source as well as the reactor dimensioning. The reactor dimensioning is discussed by highlighting the methane residence time requirement at different reaction conditions. Finally, the economic value of the TDM products is analyzed. According to the analyses, the reaction temperature and catalyst have a significant effect on reactor design and on the value and utilization possibilities of the TDM carbon. The prices of carbon products vary greatly as does the global demand of those. The utilization possibilities of carbon highly affect the overall viability of the TDM process and therefore should be carefully considered during process design.
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Extraction of magnesium from minerals serpentinite, amphibolite and diopside for mineral carbonation in Finland are compared. In part two of this study, extraction in an aqueous solution reactor is the main focus, using solvents such as ammonium bisulphate (ABS), ammonium sulphate (AS) and hydrochloric acid. The advantage of using a mixture of ABS and AS as solvent is analysed. A process suggested containing an aqueous solution extraction reactor is compared to a mineral carbonation process with a thermal solid/solid extraction step. Extracted elements, mainly magnesium, are measured with atomic absorption spectroscopy (AAS). The two serpentines tested in the study showed sufficient reactivities required for an efficient carbonation process, while the two other minerals' reactivities were insufficient. The best extraction results obtained for the two serpentines give a binding capacity of CO2 that is 292 and 260kg CO2/ton rock. Reactivity with a minimal amount of water, and recirculating and regenerating solvent salts is analysed.
Article
The only option for carbon capture and storage (CCS) in Finland is mineral carbonation, which has been extensively researched at Åbo Akademi University (ÅA). Finding suitable minerals for mineral carbonation in different regions of Finland will keep transportation of either CO2 or the actual mineral at a lowest possible level. Four different rocks from different regions in Finland have been compared with respect to composition and possibility to extract magnesium. This paper presents experiments applying thermal solid/solid extraction. It was found that a mixture of ammonium sulphate (AS) and ammonium bisulphate (ABS) could extract a significant part of magnesium compared to tests using only AS or ABS. Serpentinite rock is also the best option for magnesium extraction while diopside and magnesiohornblende are much less reactive. Continuous mixing during the experiment in a rotary tube and adding some water to the solid/solid mixture gives better extraction results. The binding capacities of CO2 in the serpetinites with respect to the magnesium extractions achieved in this study are 240kg CO2/ton rock (Serp-A) and 207kg CO2/ton rock (Serp-B).
Article
Ca-Looping technology has experienced a substantial development in the technical readiness level in the last years, especially in its application as post-combustion CO2 capture technology in power plants. Experimental results from MW-scale power plants worldwide have confirmed post-combustion Ca-Looping process using interconnected circulating fluidised bed reactors as a promising technology for CO2 capture. Among the different fields of research having contributed to this breakthrough, modelling activity aiming at assessing sorbent properties, interpreting results from experimental reactors or assessing technology scale-up through large-scale reactors and process integration have played a crucial role. This paper aims at reviewing and discussing findings obtained by different research groups worldwide about post-combustion Ca-Looping process modelling. Assumptions made with respect to sorbent performance, reactor operating conditions and process integration between different components are crucial when evaluating the performance of the Ca-Looping process as a post-combustion technology for CO2 capture. With the aim of understanding the importance of these assumptions, this paper covers particle reaction and reactor models for carbonation and calcination steps, assessing the impact of the conditions used for their determination into their reactivity predictions, as well as process modelling works that assess performance obtained when integrating a Ca-Looping process into a power plant. Indications on the research needs detected among the reviewed works have also been highlighted in this work to contribute to the advancement of the knowledge on the Ca-Looping technology.