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AbstractThe OxyCAP-UK (Oxyfuel Combustion - Academic Programme for the UK) programme was a £2M collaboration involving researchers from seven UK universities, supported by E.On and the Engineering and Physical Sciences Research Council. The programme, which ran from November 2009 to July 2014, has successfully completed a broad range of activities related to development of oxyfuel power plants. This paper provides an overview of key findings arising from the programme. It covers development of UK research pilot test facilities for oxyfuel applications; 2-D and 3-D flame imaging systems for monitoring, analysis and diagnostics; fuel characterisation of biomass and coal for oxyfuel combustion applications; ash transformation/deposition in oxyfuel combustion systems; materials and corrosion in oxyfuel combustion systems; and development of advanced simulation based on CFD modelling.

Abstract Oxyfuel combustion, where the fuel is combusted in a mixture of pure oxygen and recycled flue gases instead of air, is one of the leading options for carbon capture from coal-fired power plants. Accurate simulation of the operation of such plants is critical for successful development of the technology. A major challenge of such a simulation is how to account for the fundamental differences in gaseous physical and thermal properties; in particular the radiative and convective heat transfer coefficients. In this paper a combined CFD-process approach is developed whereby a detailed CFD model is utilised to represent the complex gas-phase combustion and radiative heat transfer to the furnace walls and the radiant section of the boiler. This is then combined with a full plant process simulation which includes modifications to the heat transfer components to account for differing gas compositions. The novel integrated calculations have been completed for air-firing and for oxyfuel under a range of conditions and a comparison reveals that there is a possible ‘working range’ of oxygen concentrations/recycle ratios under which the distribution of heat transfer in the system is similar to air firing and hence the steam conditions can be controlled to set-point temperatures and flows.

Process analyzers for in-situ monitoring give advantages over the traditional analytical methods such as their fast response, multi-chemical information from a single measurement unit, minimal errors in sample handing and ability to use for process control. This study discusses the suitability of Raman spectroscopy as a process analytical tool for in-situ monitoring of CO2 capture using aqueous monoethanolamine (MEA) solution by presenting its performance during a 3-day test campaign at PACT pilot plant in Sheffield, UK. Two Raman immersion probes were installed on lean and rich streams for real time measurements. A multivariate regression model was used to determine the CO2 loading. The plant performance is described in detail by comparing the CO2 loading in each solvent stream at different process conditions. The study shows that the predicted CO2 loading recorded an acceptable agreement with the offline measurements. The findings from this study suggest that Raman Spectroscopy has the capability to follow changes in process variables and can be employed for real time monitoring and control of the CO2 capture process. In addition, these predictions can be used to optimize process parameters; to generate data to use as inputs for thermodynamic models, plant design and scale-up scenarios.

AbstractAn integrated model of a micro-turbine coupled to a CO2 capture plant has been developed with Aspen Plus, and validated with experimental data obtained from a Turbec T100 microturbine at the PACT facilities in the UKCCS Research Centre, Beighton, UK. Monoethanolamine (MEA) was used as solvent and experimental measurements from the CO2 capture plant have been used to validate the steady-state model developed with Aspen Plus®. The optimum liquid/gas ratio and the lean CO2 loading for 90% CO2 capture has been quantified for flue gases with CO2 concentrations ranging from 3 to 8 mol%.

Using the GAUSSIAN 03 (Frisch et al., 2004, GAUSSIAN 03, Revision C.02, Gaussian, Inc., Wallingford, CT) program, the electronic structure of the C-14 and C-7 methyl esters, C14H28O2 (methyl tridecanoate) and C7H14O2 (methyl hexanoate), was estimated. For the electronic calculations, the density functional theory at the B3LYP/6-311G(d,p) level and the complete basis set (CBS-QB3) were applied. Bond dissociation energies for C-14 and C-7 esters were evaluated and compared with those of methyl butanoate, C5H10O2. Using the KHIMERA program (2007, KHIMERA04, Version 1.1, Motorola Inc; Novoselov et al., 2002, “CHIMERA: A Software Tool for Reaction Rate Calculations and Kinetics and Thermodynamics Analysis,” J. Comput. Chem., 23, pp. 1375–1389), contributions from energies, harmonic vibrational frequencies, and moments of inertia were utilized to construct modified Arrhenius rate expressions for bimolecular reactions. C7H14O2 was selected as a surrogate for the C14 fuel in order to study the bimolecular reactions with flame radicals. In the present work, reactions of carbon numbers 4 and 5 of C7H14O2, where carbon number 1 is the one single bonded to oxygen atom, with flame reactive radicals such as CH3, HO2, and H were studied where the rates for the reactions of other carbon sites can be obtained from studying methyl butanoate’s reactions. The rate expressions were estimated using transition state theory as implemented in KHIMERA over the temperature of 500–2000 K.

This study investigates the comparative impact of inherently different biomass and coal ashes on the laboratory and pilot scale degradation of 30 wt% aqueous monoethanolamine (MEA), relevant to post-combustion CO2 capture. Thermal and oxidative degradation experiments were carried out at 135 °C and 40 °C respectively with CO2 loading (0.5 molCO2/molMEA), with and without the presence of ash. Nuclear magnetic resonance (NMR) data is provided for the major MEA degradation compounds such as N-(2-hydroxyethyl)formamide (HEF) and N-(2-hydroxyethyl)imidazole (HEI) along with the characterisation of a new MEA oxidative degradation product, N-(2-hydroxyethyl)imidazole-N-oxide (HEINO) which had been previously misassigned. Degradation products were quantified using 1H NMR and gas chromatography mass spectrometry (GC–MS) to assess the impact of potassium and various ashes from combustion (olive, white wood and two types of coal ash) on the rates of amine degradation. Woody biomass fly ashes were found to reduce the presence of the oxidative degradation products. Both types of coal fly ash and the olive biomass ash were found to enhance the formation the newly identified degradation product, HEINO. Solvent samples taken from a pilot scale facility support these laboratory findings.

Recent national and international emission legislations to reduce emissions of carbon dioxide are forcing power generation industries using coal to look at various alternatives, such as biomass and especially by co-firing techniques. Biomass is transported to the burners either mixed with the primary fuel, in general, coal, or used in dedicated pipelines. In both cases, transportation of biomass is difficult due to its composition, size, shape and physical behaviour in comparison to the transportation of coal. This study considers experimental measurements for biomass particle transportation in a pipeline with a transverse elbow and compares the results with those using computation fluid dynamic (CFD) techniques. Various materials: flour, willow, wood, bark and a mixture of flour and willow, have been considered in the present investigation. The experimental work was performed using the dynamic changes in the electrostatic charges of biomass particles in conjunction with correlation signal processing techniques. The CFD simulations were performed by considering the effects of gravity, non-spherical drag (based on estimated shape factor), detailed information of the particle distribution, particle wall collisions and particle–particle interactions. Good quantitative and qualitative agreement was obtained between the CFD simulations and the experimental data. It is concluded that particle–particle interactions are of less importance if the mass loading ratio of particles to air is less than 0.03.