Browsing by Author "Jurado Pontes, Nelia"
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Item Open Access Design and commissioning of a multi-mode prototype for thermochemical conversion of human faeces(Elsevier, 2018-03-23) Jurado Pontes, Nelia; Somorin, Tosin; Kolios, Athanasios J.; Wagland, Stuart; Patchigolla, Kumar; Fidalgo, Beatriz; Parker, Alison; McAdam, Ewan; Williams, Leon; Tyrrel, SeanThis article describes the design and commissioning of a micro-combustor for energy recovery from human faeces, which can operate both in updraft and downdraft modes. Energy recovery from faecal matter via thermochemical conversion has recently been identified as a feasible solution for sanitation problems in low income countries and locations of high income countries where access to sewage infrastructures is difficult or not possible. This technology can be applied to waterless toilets with the additional outcome of generating heat and power that can be used to pre-treat the faeces before their combustion and to ensure that the entire system is self-sustaining. The work presented here is framed within the Nano Membrane Toilet (NMT) project that is being carried out at Cranfield University, as part of the Reinvent the Toilet Challenge of the Bill and Melinda Gates Foundation. For this study, preliminary trials using simulant faeces pellets were first carried out to find out the optimum values for the main operating variables at the scale required by the process, i.e. a fuel flowrate between 0.4 and 1.2 g/min of dry faeces. Parameters such as ignition temperature, residence time, and maximum temperature reached, were determined and used for the final design of the bench-scale combustor prototype. The prototype was successfully commissioned and the first experimental results, using real human faeces, are discussed in the paper.Item Open Access 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)(Elsevier, 2017-12-01) Darabkhani, Hamidreza Gohari; Jurado Pontes, Nelia; Prpich, George; Oakey, John E.; Wagland, Stuart T.; Anthony, Edward J.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.Item Open Access Effect of co-firing coal and biomass blends on the gaseous environments and ash deposition during pilot-scale oxy-combustion trials(Elsevier, 2017-02-20) Jurado Pontes, Nelia; Simms, Nigel J.; Anthony, Edward J.; Oakley, JohnThis paper presents the experimental results from co-firing blends of El Cerrejon (EC) coal and cereal co-product (CCP) using several ratios (100/0; 75/25; 50/50; 0/100 (w/w)) under air- and oxy-firing conditions, in a retrofitted 100 kWth pulverised fuel combustor. An on-line high-resolution multi-component Fourier Transform Infra-red (FTIR) analyser was used to measure CO2, O2, H2O, CO, NO, NO2, N2O, NH3, SO2, HCl, HF and CH4. A comprehensive evaluation of the major and minor species present in the flue gas was carried out to study the effects of the addition of biomass, the firing mode (air/oxy) and the type of recycle (wet/dry) on the gaseous environment in the combustor. It was found that similar CO2 levels can be reached when using pure coal or pure biomass, on a dry basis. For the minor species, the increase in the share of biomass had the effect of decreasing the SO2 levels reached in the flue gas and increasing the HCl content. No significant variation in the NOx levels was observed as a consequence of using high percentages of biomass. For ash deposit characterisation, two probes were used for which surface temperatures were controlled at 650° and 750 °C. Environmental scanning electron microscopy (ESEM) with energy dispersive X-ray (EDX) analysis, supported by X-ray diffraction (XRD), were used to study the deposits. The ESEM/EDX and XRD results showed similar sulphur levels in the deposits when varying the share of biomass even though EC coal contains 3.5 times more sulphur than CCP. This is thought to be a consequence of the reaction of sulphur with the alkalis, especially potassium, present at higher levels in the CCP, which produces higher levels of K2SO4 in the combustion gas. Chlorine was only found in the deposits generated using pure CCP under oxy-firing conditions. An evaluation of the different mineral species formed when varying the biomass share and the firing mode was also performed. Results obtained comparing the mineral species in deposits when using 100% CCP, switching from air to oxy-firing conditions, showed that in air-firing CCP deposits had higher levels of aluminium phosphate and arcanite (K2SO4). Also, under oxy-firing conditions, 100% CCP-derived deposits had a higher level of potassium magnesium chloride compared 100% EC.Item Open Access Experimental and modelling studies of coal/biomass oxy-fuel combustion in a pilot-scale PF combustor(Cranfield University, 2014-08) Jurado Pontes, Nelia; Oakey, John; Darabkhani, Hamidreza GohariThis thesis focuses on enhancing knowledge on co-firing oxy-combustion cycles to boost development of this valuable technology towards the aim of it becoming an integral part of the energy mix. For this goal, the present work has addressed the engineering issues with regards to operating a retrofitted multi-fuel combustor pilot plant, as well as the development of a rate-based simulation model designed using Aspen Plus®. This model can estimate the gas composition and adiabatic flame temperatures achieved in the oxy-combustion process using coal, biomass, and coal-biomass blends. The fuels used for this study have been Daw Mill coal, El Cerrejon coal and cereal co-product. A parametric study has been performed using the pilot-scale 100kWth oxy-combustor at Cranfield University and varying the percentage of recycle flue gas, the type of recycle flue gas (wet or dry), and the excess oxygen supplied to the burner under oxy-firing conditions. Experimental trials using co-firing with air were carried out as well in order to establish the reference cases. From these tests, experimental data on gas composition (including SO3 measurement), temperatures along the rig, heat flux in the radiative zone, ash deposits characterisation (using ESEM/EDX and XRD techniques), carbon in fly ash, and acid dew point in the recycle path (using an electrochemical noise probe), were obtained. It was clearly shown during the three experimental campaigns carried out, that a critical parameter was that of minimising the air ingress into the process as it was shown to change markedly the chemistry inside the oxy-combustor. Finally, part of the experimental data collected (related to gas composition and temperatures) has been used to validate the kinetic simulation model developed in Aspen Plus®. For this validation, a parametric study considering the factor that most affect the oxy-combustion process (the above mentioned excess amount of air ingress) was varied. The model was found to be in a very good agreement with the empirical results regarding the gas composition.Item Open Access An experimental investigation of the combustion performance of human faeces(Elsevier, 2016-07-27) Onabanjo, Tosin; Kolios, Athanasios; Patchigolla, Kumar; Wagland, Stuart Thomas; Fidalgo Fernandez, Beatriz; Jurado Pontes, Nelia; Hanak, Dawid P.; Manovic, Vasilije; Parker, Alison; McAdam, Ewan J.; Williams, Leon; Tyrrel, Sean F.; Cartmell, ElisePoor sanitation is one of the major hindrances to the global sustainable development goals. The Reinvent the Toilet Challenge of the Bill and Melinda Gates Foundation is set to develop affordable, next-generation sanitary systems that can ensure safe treatment and wide accessibility without compromise on sustainable use of natural resources and the environment. Energy recovery from human excreta is likely to be a cornerstone of future sustainable sanitary systems. Faeces combustion was investigated using a bench-scale downdraft combustor test rig, alongside with wood biomass and simulant faeces. Parameters such as air flow rate, fuel pellet size, bed height, and fuel ignition mode were varied to establish the combustion operating range of the test rig and the optimum conditions for converting the faecal biomass to energy. The experimental results show that the dry human faeces had a higher energy content (∼25 MJ/kg) than wood biomass. At equivalence ratio between 0.86 and 1.12, the combustion temperature and fuel burn rate ranged from 431 to 558 °C and 1.53 to 2.30 g/min respectively. Preliminary results for the simulant faeces show that a minimum combustion bed temperature of 600 ± 10 °C can handle faeces up to 60 wt.% moisture at optimum air-to-fuel ratio. Further investigation is required to establish the appropriate trade-off limits for drying and energy recovery, considering different stool types, moisture content and drying characteristics. This is important for the design and further development of a self-sustained energy conversion and recovery systems for the NMT and similar sanitary solutions.Item Open Access Kinetic simulation of a 100kWth oxy-combustor using Aspen Plus(C2ES, 2013-12) Jurado Pontes, Nelia; Gohari Darabkhani, Hamidreza; Anthony, Edward J.; Oakey, JohnOxy-fuel combustion is a clean coal technology based on firing fuel in an enriched oxygen atmosphere to obtain high CO2 concentrations in the exhaust gas. Experimental tests were performed at Cranfield University using a 100kWth retrofitted oxy-combustor. In parallel, a kinetic simulation model using Aspen Plus was designed and validated to serve as a computer tool to predict the behaviour of the oxy-combustion process for a wide range of fuels and conditions. The main input parameters varied in the simulation study were: fuel type (El Cerrejon coal, Daw Millcoal, Cereal Co-product biomass, and coal/biomass blends); percentage of recycled flue gas (55, 60,and 65%); type of recycled flue gas (wet or dry); percentage of excess oxygen (0 and 5%), and the amount of air ingress into the process (0, 2, 10, and 18% of the total flue gas fed to the oxycombustor).The last input condition, percentage of air ingress, is of greater importance as a result of the unit being a retrofitted oxy-combustor; for which air ingress is more probable and this represents a situation likely to be an issue for any boiler retrofitted for oxyfuel firing. Results from the simulations as well as the definition of the operating conditions that best represents the behaviour of the rig are presented.Item Open Access Oxy-combustion studies into the co –firing of coal and biomass blends: effects on heat transfer, gas and ash compositions(Elsevier, 2014-12-31) Jurado Pontes, Nelia; Darabkhani, Hamidreza Gohari; Anthony, Edward J.; Oakely, E. J.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 100 kWth 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.Item Open Access Selective-exhaust gas recirculation for CO2 capture using membrane technology(Elsevier, 2017-11-10) Russo, Giuseppe; Prpich, George; Anthony, Edward J.; Montagnaro, Fabio; Jurado Pontes, Nelia; Di Lorenzo, Giuseppina; Darabkhani, Hamidreza GohariMembranes 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.Item Open Access Simulation of oxy-combustion co-firing coal and biomass with ASU and steam turbine using Aspen Plus(International Centre for Sustainable Carbon, 2013-05) Jurado Pontes, Nelia; Gohari Darabkhani, Hamidreza; Oakey, John