Techno-economic and environmental assessment of BECCS in fuel generation for FT-fuel, bioSNG and OMEx

This study focuses on bioenergy with carbon capture and storage (BECCS) in fuel generation and assesses the potential of biofuel generation to decarbonise the fuel economy by reducing CO2emissions to the atmosphere. The research investigates the technical, economic, and environmental performances of three biofuel production routes, namely Fischer-Tropsch synthesis (FTS), bio-synthetic natural gas (bioSNG) and oxymethylene ethers (OMEx) synthesis using flowsheets developed in Aspen Plus. It constitutes the first attempt to holistically evaluate both the techno-economic performance and the environmental benefits of employing BECCS in fuel generation. For an input of 1020 dry tonnes per day of woody biomass, the FTS route yields 275 t d−1, the bioSNG route yields 238 t d−1and the OMExroute yields 635 t d−1of fuel and the energy efficiency is in the range of 44.9% to59.7% without CCS and 44.0% to 58.2% with CCS. In addition, negative emissions can be achieved for all routes with CCS in the range of 301 000 to 519 000 tCO2per year. For economic viability, the minimum selling price for FT-fuels, bioSNG, and OMExproduction with CCS have been calculated as £23.4 per GJ, £14.5 per GJ and £26.5 per GJ, respectively. However, competition with conventional fossil-derived fuels is not possible without the combination of existing financial incentives and a proposed carbon pricing. With carbon credit as the only financial incentive, carbon pricing in the range of £48 to £86 per tCO2needs to be applied to achieve feasibility. Also, more negative emissions need to be generated to decrease the value of this range and reasonably phase out dependence on fossil-derived fuels. Parametric studies identified as crucial parameters to be improved the fuel output, CAPEX, operating hours and feedstock cost

A techno-economic assessment of implementing power-to-gas systems based on biomethanation in an operating waste water treatment plant

The aim of the present study is to assess the techno-economic viability of integrating biomethanation into power to gas systems in a real waste water treatment plant (WWTP). The research is the first attempt to assess the viability of several scenarios based on the biomethanation technology that include both in- and ex-situ biomethanation as well as utilisation of on-site renewable electricity and grid electricity in a transient mode.Five scenarios were designed and evaluated and the calculated LCOE lies between 127.8 and 159.8 £/MWh. The consideration of existing policy mechanisms and revenues from by-products reduces the LCOEs to 31.4–68.1 £/MWh. The execution of a sensitivity analysis exposed that the electricity price and the electrolyser cost are the main cost contributors in all the scenarios. Future techno-economic advances along with imposing appropriate policy incentives can create the proper framework for two scenarios to generate profits. The study concludes that current and future power to gas application should focus on utilising on-site generated electricity

Biomethane production using an integrated anaerobic digestion, gasification and CO2 biomethanation process in a real waste water treatment plant: A techno-economic assessment

The biomethanation of CO2 from anaerobic digestion within the power to gas concept has recently emerged as a promising technology to upgrade biogas, to decarbonise the domestic and industrial heat sector, provide long term energy storage and deliver grid balancing services. In addition, the utilisation of the digestate, through a process such as gasification, offers a circular economy approach and has the potential to enhance the deployment of power to gas systems. To this direction, the study focuses on exploring the techno-economic feasibility of coupling biomethanation with digestate gasification for the wastewater industry. The study constitutes the first endeavour to assess the viability of such an integrated energy system. Four different scenarios have been designed and assessed. The energy efficiency of the concepts lies between 26.5% and 35.5% while the minimum selling price (MSP) of biomethane is in the range of 135–183 £/MWh. The implementation of appropriate policy mechanisms and the inclusion of by-products revenues reduces the MSPs by approximately 32%–42%. The conduction of a typical sensitivity analysis has identified the electricity price as the prime cost driver and this is followed by the cost of the electrolyser or the gasification plant depending on the scenario. Finally, a 2030 analysis, that incorporates projected techno-economic advances, has been carried out and revealed that under certain circumstances profits can be generated

Effect of Microporous Layer Ink Homogenisation on the Through-Plane Gas Permeability of PEFC Porous Media

The through-plane gas permeability and morphology of PEFC gas diffusion media (GDM) is investigated for different microporous layer (MPL) ink homogenisation techniques (bath sonication and magnetic stirring) for low- (Vulcan XC-72R) and high (Ketjenblack EC-300J)-surface-area carbon powders. The MPL composition is held constant at 80 wt.% carbon powder and 20 wt.% PTFE for a carbon loading of 1.0 mg cm−2. The MPL ink homogenisation time is held constant at two hours for both techniques and increased by one hour for bath sonication to compare with previous investigations. The results show that the through-plane gas permeability of the GDM is approximately doubled using magnetic stirring when compared with bath sonication for MPLs composed of Vulcan XC-72R, with a negligible change in surface morphology between the structures produced from either homogenisation technique. The variation in through-plane gas permeability is almost negligible for MPLs composed of Ketjenblack EC-300J compared with Vulcan XC-72R; however, MPL surface morphology changes considerably with bath sonication, producing smoother, less cracked surfaces compared to the large cracks produced via magnetic stirring for a large-surface-area carbon powder. An MPL ink sonication time of three hours results in a percentage reduction in through-plane gas permeability from the GDL substrate permeability by ~72% for Ketjenblack EC-300J compared to ~47% for two hours

Comprehensive process simulation of a biomass-based hydrogen production system through gasification within the BECCS concept in a commercial two-stage fixed bed gasifier

Hydrogen production through biomass gasification coupled with carbon capture has the potential to be a net negative emission process. Among the different designs of biomass gasifiers, the two-stage fixed bed gasifier has proved its ability to produce high quality syngas with minimum tar content at an industrial scale. However, it has not been investigated for hydrogen production. Hence, the current study is the first attempt to assess, through process modelling, the technical feasibility of hydrogen production in a 10 MWth two-stage gasification system using wood chips as feedstock. Mass and energy balances have been established in the Aspen Plus and MATLAB software. In contrast to most models in the literature, which were based on the equilibrium approach, the proposed system utilizes reliable kinetic models for the gasifier operation and the main downstream processes. An extensive validation of the gasifier kinetic model has been carried out and then a sensitivity analysis, which has revealed that the optimum steam-to-biomass ration (SBR) is 0.8 and 1.2 for the air-steam and the oxy-steam gasification systems, respectively. Further, the optimum steam-to-CO ratio (S/CO) for the water gas shift reactors (WGSRs) is 4, under which an overall 82.9% conversion of CO has been achieved. The results show that the 10 MWth two-stage gasifier can attain a specific hydrogen yield of 81.47 gH2/kg dry biomass. Based on the carbon footprint assessment, the process is net negative with an emission factor of −1.38 kgCO2-eq/kg biomass. Further, heat integration has also been conducted and it was found that the energy conversion efficiency of the whole system is 49.6%. This study is important since it provides a reliable data source for biomass-based hydrogen production through gasification in a commercial two-stage gasifier that can dictate operational strategies of pilot and demo plants

An improved kinetic modelling of woody biomass gasification in a downdraft reactor based on the pyrolysis gas evolution

Biomass gasification technology is evolving and more research through modelling alongside the experimental work needs to be performed. In the past, all the attention has been concentrated on the combustion and reduction stages to be the controlling reactions while the pyrolysis is modelled as an instantaneous process. In this study, a new enhanced model for the gasification process in the downdraft reactor is proposed with a more realistic representation of the pyrolysis stage as a temperature-dependent sequential release of gases. The evolution of the pyrolysis gas, followed by the combustion and reduction reactions, are kinetically controlled in the proposed model which is developed within the Aspen Plus software package. The simulation of the reactor temperature profile and the evolution of the pyrolysis gas is carried out in an integrated MATLAB and Aspen Plus model. The proposed model has been validated against experimental data obtained from the gasification of different woody biomass types and considering a range of scale reactor and power loads. The predicted results are in very good agreement with the experimental data, and therefore the model can be used with confidence to perform a sensitivity analysis to predict the performance of a gasifier at different load levels corresponding to the air flow rate range of 3–10 L/s. As the supplied air flow rate increases, the LHV decreases but the gas yield behaves conversely, and in turn the cold gas efficiency is maintained at a good level of energy conversion at ≥ 70%. Furthermore, the variation in the biomass moisture content, which is commonly in the range of 5–25 % has a significant effect on the gasification efficiency. Such that biomass that has a high moisture content substantially reduces the CO content and consequently the LHV of the produced gas. Hence, it is important to maintain the moisture content at the lowest level

Optimal sizing of a hybrid PV-WT-battery storage system: Effects of split-ST and combined ST + ORC back-ups in circuit charging and load following

This study explores the opportunities in deploying split Stirling and combined Stirling and organic Rankine cycle (ORC) in circuit charging and load following dispatch modes, respectively as the back-up of a hybrid renewable energy system. The optimal number of system components in each dispatch mode that simultaneously minimises the loss of power supply probability (LPSP), levelised cost of energy (LCOE) and dumped power have been found by implementing an evolutionary algorithm-based multi-objective optimisation approach. Then, a multi-criteria decision making tool is deployed to select the best configuration from the Pareto set. The optimal hybrid system configuration obtained have been compared to the traditional diesel generator back-up system base case, to demonstrate performance improvements with the deployment of the proposed back-ups. The results show deploying Stirling + ORC back-up in load following leads to 60.70% and 33.71% reductions in the LCOE and CO2 emissions, respectively compared to the base case but with slightly higher LPSP. While 61.4%, 33% and 24.47% reductions in the LCOE, CO2 emissions and LPSP have been observed with the deployment of split Stirling in circuit charging mode. Further results from the dynamic simulation highlight the energy cost, reliability, dumped power and battery performance of the optimal system respond to seasonal changes in the test location. Other observed results show the change in the market price and number of the photo-voltaic generator that generates 50% of the total power, strongly affect the performance of the optimal system. The proposed biomass powered Stirling based back-ups are promising alternatives to replace the traditional diesel generator back-ups in improving the green energy system's reliability

Multiphase, three-dimensional PEM fuel cell numerical model with a variable cross-sectional area flow channel

Purpose: This paper aims to investigate the impact of three different flow channel cross sections on the performance of the fuel cell. Design/methodology/approach: A comprehensive three-dimensional polymer electrolyte membrane fuel cell model has been developed, and a set of conservation equations has been solved. The flow is assumed to be steady, fully developed, laminar and isothermal. The investigated cross sections are the commonly used square cross section, the increasingly used trapezoidal cross section and a novel hybrid configuration where the cross section is square at the inlet and trapezoidal at the outlet. Findings: The results show that a slight gain is obtained when using the hybrid configuration and this is because of increased velocity, which improves the supply of the reactant gases to the catalyst layers (CLs) and removes heat and excess water more effectively compared to other configurations. Further, the reduction of the outlet height of the hybrid configuration leads to even better fuel cell performance and this is again because of increased velocity in the flow channel. Research limitations/implications: The data generated in this study will be highly valuable to engineers interested in studying the effect of fluid cross -sectional shape on fuel cell performance. Originality/value: This study proposes a novel flow field with a variable cross section. This design can supply a higher amount of reactant gases to the CLs, dissipates heat and remove excess water more effectively

IMECE2008-67512 INVESTIGATION INTO BIO-AVIATION REACTION MECHANISMS USING QUANTUM MECHANICAL METHODS

ABSTRACT Using high level model chemistries the C-C and C-H bond dissociation energies for methyl butanoate molecule (MB) were estimated using the Gaussian 03 program at the CBS-QB3 level of calculations. This consequently located the weaker bonds more likely to break. Thermal decomposition of MB over the temperatures 500 to 2000 K was theoretically studied and the rate constants for these channels were calculated. Crucial reactions in combustion, among which there are reactions of the fuel molecule with flame reactive radicals OH and CH 3 , were studied and the barrier heights for reactions including different hydrogen atoms transferring to the radicals were evaluated at the B3LYP/6-31+G(d,p) level of theory. The rate constants for these reactions are calculated over the temperatures 500 to 2000 K using the same level

Thermodynamic Analysis and Process System Comparison of the Exhaust Gas Recirculated, Steam Injected and Humidified Micro Gas Turbine

Stringent environmental emission regulations and continuing efforts to reduce carbon dioxide (CO2) from the energy sector, in the context of global warming, have promoted interest to improve the efficiency of power generation systems whilst reducing emissions. Further, this has led to the development of innovative gas turbine systems which either result in higher electrical efficiency or the reduction of CO2 emissions. Micro gas turbines are one of the secure, economical and environmentally viable options for power and heat generation. Here, a Turbec T100 micro gas turbine (MGT) is simulated using Aspen HYSYS® V8.4 and validated through experimental data. Due to the consistency and robustness of the steady state model developed, it is further extended to three different innovative cycles: (i) an exhaust gas recirculated (EGR) cycle, in which part of the exhaust gas is dried and re-circulated to the MGT inlet; (ii) a steam injected (STIG) cycle, and (iii) a humid air turbine (HAT) cycle. The steam and hot water are generated through the exhaust of the recuperator for the STIG and HAT cycle, respectively. Further, the steam is directly injected into the recuperator for power augmentation, while for the HAT cycle; the compressed air is saturated with water in the humid tower before entering the recuperator. This study evaluates the impact of the EGR ratio, steam to air ratio, and water to air ratio on the performance and efficiency of the system. The comparative potential for each innovative cycle is assessed by thermodynamic properties estimation of process parameters through the models developed to better understand the behavior of each cycle. The thermodynamic assessment indicates that CO2 enrichment occurs for the three innovative cycles. Further, the results indicate that the electrical efficiency increases for the STIG and HAT cycle while it decreases for the EGR cycle. In conclusion, the innovative cycles indicates the possibilities to improve the system performance and efficiency