Oxy-combustion studies into the co -firing of coal and biomass blends: Effects on heat transfer, gas and ash compositions

Oxy-combustion with coal and biomass co-firing is a technology that could revolutionize fossil fuel power generation. It can significantly reduce harmful greenhouse gas emissions and permit the continued use of plentiful coal supplies and thereby secure our future energy needs without the severe environmental impacts expected if fossil fuels are used without CCS. The work presented here was conducted by means of experimental tests co-firing coal and biomass under oxy-firing conditions at the retrofitted 100kWth oxy-combustor facility at Cranfield University. A parametric study was performed with respect to the effect of recycled ratio and fuel variability on gas composition (including SO3), temperatures, heat flux, burn-out and ash deposition. Furthermore, the possible compensation in heat transfer resulting from the higher heat capacity and emissivity of the gases in the oxy-combustion process as compared to the air-firing case was explored. This was done by the use of blends of coal and biomass, and we concluded that this compensation is unlikely to be significant due to the marked differences between heat fluxes reached under air and oxy-firing conditions

Oxy-combustion studies into the co -firing of coal and biomass blends: Effects on heat transfer, gas and ash compositions

Oxy-combustion with coal and biomass co-firing is a technology that could revolutionize fossil fuel power generation. It can significantly reduce harmful greenhouse gas emissions and permit the continued use of plentiful coal supplies and thereby secure our future energy needs without the severe environmental impacts expected if fossil fuels are used without CCS. The work presented here was conducted by means of experimental tests co-firing coal and biomass under oxy-firing conditions at the retrofitted 100kWth oxy-combustor facility at Cranfield University. A parametric study was performed with respect to the effect of recycled ratio and fuel variability on gas composition (including SO3), temperatures, heat flux, burn-out and ash deposition. Furthermore, the possible compensation in heat transfer resulting from the higher heat capacity and emissivity of the gases in the oxy-combustion process as compared to the air-firing case was explored. This was done by the use of blends of coal and biomass, and we concluded that this compensation is unlikely to be significant due to the marked differences between heat fluxes reached under air and oxy-firing conditions

Oxy-fuel Combustion for Carbon Capture and Sequestration (CCS) from a Coal/Biomass Power Plant: Experimental and Simulation Studies

Oxy-fuel combustion is a promising and relatively new technology to facilitate CO2 capture and sequestration (CCS) for power plants utilising hydrocarbon fuels. In this research experimental oxy-combustion trials and simulation are carried out by firing pulverised coal and biomass and co-firing a mixture of them in a 100 kW retrofitted oxy-combustor at Cranfield University. The parent fuels are coal (Daw Mill) and biomass cereal co-product (CCP) and experimental work was done for 100 % coal (w/w), 100 % biomass (w/w) and a blend of coal 50 % (w/w) and biomass 50 % (w/w). The recirculation flue gas (RFG) rate was set at 52 % of the total flue gas. The maximum percentage of CO2 observed was 56.7 % wet basis (73.6 % on a dry basis) when 100 % Daw Mill coal was fired. Major and minor emission species and gas temperature profiles were obtained and analysed for different fuel mixtures. A drop in the maximum temperature of more than 200 K was observed when changing the fuel from 100 % Daw Mill coal to 100 % cereal co-product biomass. Deposits formed on the ash deposition probes were also collected and analysed using the environmental scanning electron microscopy (ESEM) with energy-dispersive X-ray (EDX) technique. The high sulphur, potassium and chlorine contents detected in the ash generated using 100 % cereal co-product biomass are expected to increase the corrosion potential of these deposits. In addition, a rate-based simulation model has been developed using Aspen Plus® and experimentally validated. It is concluded that the model provides an adequate prediction for the gas composition of the flue gas

Towards decarbonisation of sugar refineries by calcium looping: Process integration, energy optimisation and technoeconomic assessment

Data availability: https://doi.org/10.17633/rd.brunel.25864513.v1.Supplementary material is available online at: https://www.sciencedirect.com/science/article/pii/S0196890424005387?via%3Dihub#s0075:~:text=Appendix%20A.-,Supplementary%20material,-Data%20availability .The sugar refinery process as a food industry is at the pinnacle of the energy hierarchy. Depending on the source of carbon in this industry that could be either from biomass or fossil fuel hydrocarbons, this sector has the potential to become a carbon–neutral or negative industry depending on the type of fuel for power generation. This work will deliver a new proof of concept model for simultaneous sugar refining and carbon capture, thereby transforming sugar into the carbon negative commodity which relies on the utilisation of CO2 and fresh lime in the sugar refineries carbonisation tanks and in return byproduction of calcium carbonate that can be converted in the calciner of a calcium looping process. This study begins with the design and development of the calcium looping (CaL) process for the integration to the sugar refineries using various coupled and decoupled scenarios for the boiler units based on the type of the fuel, continues with an energy optimisation and techno-economic assessment of the proposed process, and finally culminates with the parametric study on the thermodynamic and economic performance of the sugar refinery retrofitted with the calcium looping. The process simulations revealed that the integrated CaL-sugar refinery can support the electricity exporter by installation of an onsite steam cycle which is able to generate electricity from surplus carbonation heat. The cost of CO2 avoided for integration of CaL to the reference sugar refinery for natural gas boilers and calciner will be 62 £/tCO2 which drops to 25 £/tCO2 if the carbon tax is considered in the analysis and negative carbon emissions are credited. This is equivalent to 61% costs reductions associated refining sugar combined together with carbon capture and storage (CCS)

Design, process simulation and construction of a 100 kW pilot-scale CO2 membrane rig: Improving in situ CO2 capture using selective exhaust gas recirculation (S-EGR)

Carbon capture and storage (CCS) from natural gas-fired systems is an emerging field and many of the concepts and underlying scientific principles are still being developed. Preliminary studies suggest this approach can boost the CO2 content in the feed gas up to 3 times compared to the ‘no recycle’ case (CO2 concentration increased to 18% vs. 6%), with a consequent reduction in flow to the post-combustion capture unit by a factor of three compared to conventional, non-S-EGR. For this project, Cranfield University developed a pilot-scale 100 kW CO2 membrane rig facility in order to investigate simultaneously EGR and S-EGR technologies, the latter being achieved by using a CO2 sweep air polymeric membrane. A bench-scale membrane rig has also been developed to investigate the permeability and selectivity of different polymeric membranes to CO2. Currently a small-scale polydimethylsiloxane (PDMS) membrane module is also being investigated to study its selectivity/permeability. The tests include exploring the performance improvement of the PDMS membrane using different operating conditions with a view to developing scale-up procedures for the membrane unit for the actual 100 kW pilot-scale rig. Process simulations were performed using Aspen Plus software to predict the behaviour of the pilot-scale rig using a model developed based on empirical parameters (i.e., mass transfer coefficient of CO2 through the membrane and permeance), measured in the bench-scale membrane test unit. The results show that CO2 concentrations of up to 14.9% (comparable to CO2 level in coal combustion) can be achieved with 60% EGR, with a 90% CO2 removal efficiency of the membrane units. However, the results generated with the membrane model in which specific permeance values to PDMS were applied, predicted concentrations of CO2 in flue gases up to 9.8% (v/v) for a selective recycle of 60%. The study shows that the S-EGR technique is an effective method that can provide similar conditions to that of a coal-fired power plant for the post-combustion capture system operating on natural gas-fired units, but also highlights the fact that more research is required to find more suitable materials for membranes that optimise the CO2 removal efficiencies from the flue gas

Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions

The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices [2-4]. A major hurdle for realistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors, remains their below room-temperature ferromagnetic transition temperature. Enhancing ferromagnetism in semiconductors requires understanding the mechanisms for interaction between magnetic dopants, such as Mn, and identifying the circumstances in which ferromagnetic interactions are maximized [5]. Here we report the use of a novel atom-by-atom substitution technique with the scanning tunnelling microscope (STM) to perform the first controlled atomic scale study of the interactions between isolated Mn acceptors mediated by the electronic states of GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn-Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples. Our experimental methods also provide a realistic approach to create precise arrangements of single spins as coupled quantum bits for memory or information processing purposes

Selective-exhaust gas recirculation for CO₂ capture using membrane technology

Membranes can potentially offer low-cost CO₂ capture from post-combustion flue gas. However, the low partial pressure of CO₂ in flue gases can inhibit their effectiveness unless methods are employed to increase their partial pressure. Selective-Exhaust Gas Recirculation (S-EGR) has recently received considerable attention. In this study, the performance of a dense polydimethylsiloxane (PDMS) membrane for the separation of CO₂/N₂ binary model mixtures for S-EGR application was investigated using a bench-scale experimental rig. Measurements at different pressures, at different feeding concentrations and with nitrogen as sweep gas revealed an average carbon dioxide permeability of 2943 ± 4.1%_{RSD} Barrer. The bench-scale membrane module showed high potential to separate binary mixtures of N₂ and CO₂ containing 5–20% CO₂. The permeability was slightly affected by feed pressures ranging from 1 to 2.4 bar. Furthermore, the separation selectivity for a CO₂/N₂ mixture of 10%/90% (by volume) reached a maximum of 10.55 at 1.8 bar. Based on the results from the bench-scale experiments, a pilot-scale PDMS membrane module was tested for the first time using a real flue gas mixture taken from the combustion of natural gas. Results from the pilot-scale experiments confirmed the potential of the PDMS membrane system to be used in an S-EGR configuration for capture of CO₂