School of Water, Energy and Environment (SWEE)

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Browsing School of Water, Energy and Environment (SWEE) by Supervisor "Anthony, Edward J."

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    Enhanced sorbents for the calcium looping cycle and effects of high oxygen concentrations in the calciner
    (2017-05) Erans Moreno, Maria; Anthony, Edward J.; Manovic, Vasilije
    Increasing CO2 emissions from the energy and industrial sectors are a worldwide concern due to the effects that these emissions have on the global climate. Carbon capture and storage has been identified as one of a portfolio of technologies that would mitigate the effects of global warming in the upcoming decades. Calcium looping is a second generation carbon capture technology aimed at reducing the CO2 emissions from the power and industrial sectors. This thesis assesses the improvement of the calcium looping cycle for CO2 capture through enhanced sorbent production and testing at lab-, bench- and pilot-scale, and a new operational mode with high oxygen concentrations in the calciner through experimental campaigns in Cranfield’s 25 kWth pilot unit. Novel biomass-templated sorbents were produced using the pelletisation technique and tested at different conditions in a thermogravimetric analyser (TGA) and a bench-scale plant comprising a bubbling fluidised bed (BFB) reactor. Moreover, the effects of sorbent poisoning by SO2, and the influence of steam were studied in order to explore the effects of real flue gas on this type of material. In addition to the chemical performance, the mechanical strength, i.e. resistance to fragmentation of these materials was tested. In additon, two different kinds of enhanced materials were produced and tested at pilot-scale. Namely, calcium aluminate pellets and HBr-doped limestone were used in experimental campaigns in Cranfield’s 25 kWth pilot plant comprising a CFB carbonator and a BFB calciner. The suitability of these materials for Ca looping was assessed and operation challenges were identified in order to provide a basis for synthetic sorbent testing at a larger scale. Lastly, a new operational mode was tested, which is aimed at reducing the heat provided to the calciner through high oxygen concentration combustion of a hydrocarbon (in this case natural gas) in the calciner. This approach reduces or even eliminates the recirculated CO2 stream in the calciner. In consequence, this results in a lower capital (reduced size of the calciner) and operational cost (less oxygen and less fuel use). Several pilot plant campaigns were performed using limestone as solid sorbent in order to prove this concept, which was successfully verified for concentrations of up to 100% vol oxygen in the inlet to the calciner.
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    Oxy-fuel and chemical-looping combustion for a low-carbon future.
    (Cranfield University, 2020-09) Yan, Yongliang; Clough, Peter T.; Manovic, Vasilije; Anthony, Edward J.
    This thesis is focused on investigating the potential of oxy-fuel and chemical- looping combustion (CLC) for carbon capture, and their integration with sorbent enhanced steam methane reforming (SE-SMR) for low-carbon hydrogen production. Oxy-fuel combustion converts a fuel within a mixture of O₂/CO₂ instead of air, while CLC converts a fuel by reduction of a metal oxide. In both cases, the resulting flue gas is free of N₂, and consist of only CO₂ and steam, and the steam can easily be condensed out. With the use of biomass as the fuel feedstock for the oxy-fuel combustion and CLC, negative CO₂ emissions can be achieved for power and heat generation. Oxy-fuel combustion is also a likely route to decarbonise the calcination of limestone, as used in the calcium looping and SE-SMR processes. SE-SMR combines the conventional steam methane reforming with calcium looping (CaL), which utilises CO₂ sorbents (e.g. CaO) to capture the CO₂ produced during the SMR process and shifts the equilibrium of the reforming and water-gas shift reactions in favour of more H₂ production according to Le Chatelier’s principle. Three main areas of work were conducted within this thesis, which includes 1) a detailed investigation into the effects of various parameters on the reaction kinetics of air and oxy-fuel combustion of woody biomass in a lab-scale fluidised- bed reactor; 2) applying machine learning in estimating the performance of oxygen carriers in chemical-looping processes; and 3) thermodynamic and techno-economic assessment of the integration of SE-SMR with oxy-fuel and chemical-looping combustion for low-carbon hydrogen production. Firstly, combustion rates of the biomass and its char were measured by a lab- scale fluidised-bed reactor. The shirking core model was used to simulate the char conversion during the experiments and under combustion mechanisms. Then, a novel approach that uses machine learning to efficiently screen the suitable oxygen carrier materials for CLC has been proposed. Lastly, the integration of oxy-fuel and CLC within the calciner of SE-SMR has been simulated in the Aspen Plus to understand their thermodynamic limitations and optimal operating conditions. Moreover, a detailed techno-economic analysis of the proposed configurations has been conducted to investigate their feasibility for a large-scare low-carbon hydrogen production. The obtained combustion kinetics and characteristics of air- and oxy-fuel combustion of biomass can provide useful information for retrofit and design of boilers. The framework of applying machine learning in oxygen carriers is expected to accelerate the finding and designing cost-effective oxygen carriers for large-scale CLC. The results of techno-economic analysis of the integration of oxy-fuel combustion and CLC with SE-SMR indicate that it is competitive with conventional steam methane reforming (SMR) with carbon capture and storage (CCS).
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    Oxygen carrier and reactor development for chemical looping processes and enhanced CO2 recovery
    (Cranfield University, 2016-04) Haider, Syed Kumail; Patchigolla, Kumar; Oakey, John; Anthony, Edward J.
    This thesis’s main focus is a CO2 capture technology known as chemical looping combustion (CLC). The technology is a novel form of combustion and fuel processing that can be applied to gas, solid and liquid fuels. By using two interconnected fluidised-bed reactors, with a bed material capable of transferring oxygen from air to the fuel, a stream of almost pure CO2 can be produced. This stream is undiluted with nitrogen and is produced without any direct process efficiency loss from the overall combustion process. The heart of the process is the oxygen carrier bed material, which transfers oxygen from an air to fuel reactor for the conversion of the fuel. Oxygen carrier materials and their production should be of low relative cost for use in large-scale systems. The first part of this research centres on development and investigative studies conducted to assess the use of low-cost materials as oxygen carriers and as supports. Mixed-oxide oxygen carriers of modified manganese ore and iron ore were produced by impregnation. While copper (II) oxide supported on alumina cement and CaO have been produced by pelletisation. These oxygen carriers were investigated for their ability to convert gaseous fuels in a lab-scale fluidised bed, and characterised for their mechanical and chemical suitability in the CLC process. The modified ores and pelletised copper-based oxygen carriers’ mechanical properties were enhanced by their production methods and in the case of the modified iron ore, significant oxygen uncoupling was observed. The copper-based oxygen carriers particularly those containing alumina cement showed high conversion rates of gaseous fuels and improved mechanical stability. The second part of this research thesis focuses on the design philosophy, commissioning and operation of a dual-fast bed chemical looping pilot reactor. Based on the operational experience, recommendations for modifications to the CLC system are discussed. In support, a parallel hydrodynamic investigation has been conducted to validate control and operational strategies for the newlydesigned reactor system. It was determined that the two fast bed risers share similar density and pressure profiles. Stable global circulation rate is flexible and could be maintained despite being pneumatically controlled. Reactor-reactor leakage via the loop-seals is sensitive to loop seal bed-height, and inlet fluid velocity but can be maintained as such to ensure no leakage is encountered.