There are several recent reviews published in the literature on hydrothermal carbonization, liquefaction and supercritical water gasification of lignocellulosic biomass and algae. The potential of ...hydrochar, bio-oil or synthesis gas production and applications have also been reviewed individually. The comprehensive review on the hydrothermal treatment of wet wastes (such as municipal solid waste, food waste, sewage sludge, algae) covering carbonization, liquefaction and supercritical water gasification, however, is missing in the literature which formed the basis of the current review paper. The current paper critically reviews the literature around the full spectrum of hydrothermal treatment for wet wastes and establishes a good comparison of the different hydrothermal treatment options for managing wet waste streams. Also, the role of catalysts as well as synthesis of catalysts using hydrothermal treatment of biomass has been critically reviewed. For the first time, efforts have also been made to summarize findings on modelling works as well as techno-economic assessments in the area of hydrothermal treatments of wet wastes. The study concludes with key findings, knowledge gaps and future recommendations to improve the productivity of hydrothermal treatment of wet wastes, helping improve the commercial viability and environmental sustainability.
•The feasibility of handling wet waste via hydrothermal treatment was reviewed.•Formation of value-added products and reduction of waste volume was proven.•The mechanism and reaction pathways have not been developed enough.•Hydrothermal processing suffers from immature technology, demanding innovations.
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•Combined TEA and LCA of an integrated PtL-SAF system.•The MJSP is OPEX intensive due to high electricity consumption.•The WtWa GWP falls below the UK-SAF mandate threshold.•The WtWa ...water footprint of the PtL-SAF is greater than the one of fossil jet fuel.•SAF certificates could help to break-even with the conventional jet fuel.
The current research critically evaluates the technical, economic, and environmental performance of a Power-to-Liquid (PtL) system for the production of sustainable aviation fuel (SAF). This SAF production system comprises a direct air capture (DAC) unit, an off-shore wind farm, an alkaline electrolyser and a refinery plant (reverse water gas shift coupled with a Fischer-Tropsch reactor). The calculated carbon conversion efficiency, hydrogen conversion efficiency, and Power-to-liquids efficiency are 88%, 39.16% and 25.6%, respectively. The heat integration between the refinery and the DAC unit enhances the system's energy performance, while water integration between the DAC and refinery units and the electrolyser reduces the demand for fresh water. The economic assessment estimates a minimum jet fuel selling price (MJSP) of 5.16 £/kg. The process is OPEX intensive due to the electricity requirements, while the CAPEX is dominated by the DAC unit. A Well-to-Wake (WtWa) life cycle assessment (LCA) shows that the global warming potential (GWP) equals 21.43 gCO2eq/MJSAF, and is highly dependent on the upstream emissions of the off-shore wind electricity. Within a 95% confidence interval, a stochastic Monte Carlo LCA reveals that the GWP of the SAF falls below the UK aviation mandate treshold of 50% emissions reduction compared to fossil jet fuel. Moreover, the resulting WtWa water footprint is 0.480 l/MJSAF, with the refinery’s cooling water requirements and the electricity’s water footprint to pose as the main contributors. The study concludes with estimating the required monetary value of SAF certificates for different scenarios under the possible UK SAF mandate guidelines.
The aim of this work was to develop a model of an integrated biomass-to-liquid process consisting of hydrothermal liquefaction, evaporation, gasification and Fischer-Tropsch synthesis process using ...lignocellulosic forest residues as feedstock to produce hydrocarbons suitable for upgrading into drop-in biofuels. The energy, mass and carbon efficiencies achieved were 35%, 20% and 32%, respectively. The Fischer-Tropsch crude carbon chain length distribution peaked at carbon chain length 10 with a heavy right tail, a profile favorable for upgrading to jet fuel. The life cycle assessment showed high greenhouse gas performance in the Norrbotten coastal area and in Kalmar, both in Sweden. The reduction of life cycle greenhouse gas emissions, compared to the fossil fuel comparator and according to the European Union Renewable Energy Directive II, amounted to 85-95% for the Fischer-Tropsch crude produced in Norrbotten, and to 92-97% in Kalmar, depending on transportation distances and feedstock used.
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•Machine learning models developed for H2 production by dark fermentation.•GBM, SVR, RF and AdaBoost methods were robust models for the process.•All four models demonstrated close ...agreement with results (R2 ≥ 90%).•PVI was able to assess the relative importance of the inputs.•Acetate, butyrate, ethanol, Fe and Ni showed high importance in decreasing order.
Dark fermentation process for simultaneous wastewater treatment and H2 production is gaining attention. This study aimed to use machine learning (ML) procedures to model and analyze H2 production from wastewater during dark fermentation. Different ML procedures were assessed based on the mean squared error (MSE) and determination coefficient (R2) to select the most robust models for modeling the process. The research showed that gradient boosting machine (GBM), support vector machine (SVM), random forest (RF) and AdaBoost were the most appropriate models, which were optimized by grid search and deeply analyzed by permutation variable importance (PVI) to identify the relative importance of process variables. All four models demonstrated promising performances in predicting H2 production with high R2 values (0.893, 0.885, 0.902 and 0.889) and small MSE values (0.015, 0.015, 0.016 and 0.015). Moreover, RF-PVI demonstrated that acetate, butyrate, acetate/butyrate, ethanol, Fe and Ni were of high importance in decreasing order.
As the requirement for low cost, high volume production of composites increases, so does the requirement for modelling capability to help inform and optimise the composite manufacturing processes. In ...this paper a finite element approach is introduced to simulate the behaviour of a plain weave fabric during the double diaphragm forming process. Using a mutually constrained shell-membrane method to capture the characteristic behaviours of the textile, the approach is assessed in its ability to predict the severe deformations present within experimental trials. The model is validated against experimental results for different fibre orientations and for the simultaneous forming of multiple layers. The approach accurately predicts the severe wrinkles observed in the experiments and is used to help further understand the catalysts for defect formation in the double diaphragm forming process.
The mechanism of dehydration of a water-in-oil emulsion is complex and involves the growth of an emulsion of polydispersed water droplets in oil, under an electric field, and their gravitational ...settling and phase separation. In this work, a simple configuration is chosen to understand the mechanism of this complex process. A population balance-based model is developed to predict the performance of an electrocoalescer. The model explicitly accounts for the coalescence of water drops by the action of dipolar forces and gravity settling. A distributed parameter plug flow and a tank-in-series model are developed to account for the gravity settling. The dynamics of electrocoalescence are captured by analyzing the drop size distribution and mean diameter along with the height of the coalescer and time. A simplified model - considering that monodispersity prevails throughout the process is also developed, and the separation curves are compared with the polydispersed system. The effect of operational parameters, such as the strength of the electric field, water cut, viscosity of oil, the height of the coalescer, and polydispersity in the initial drop size distribution, is investigated. The main insight from this work is that there are essentially three stages of electrocoalescence, a slow initial incubation stage where droplets grow to around 1 mm in size without much settling, followed by a rapid settling of these droplets to set in the fast coalescence stage where most water is removed to result in a lean emulsion, followed by a slow simultaneous electrocoalescence and separation stage of this lean emulsion to result in a final separation. A scaled masterplot for the performance of an electrocoalescer, encompassing the effect of the process parameters is obtained. The model also suggests that electrocoalescence essentially leads to a polydisperse system and a population balance approach is critical to its analysis.
•Dehydration efficiency of W/O emulsion is predicted using population balance model.•Model accounts for droplet coalescence due to dipolar forces & gravity settling.•Effect of electric field, water cut, oil viscosity & other factors is investigated.•Scaled masterplot for performance, encompassing process parameters, is constructed.
Thermoplastic composites boast several advantages over thermoset composites including outstanding mechanical performance, thermoformability and recyclability. Coupled with automated fibre placement ...and out-of-autoclave in-situ consolidation, this has driven increased interest in thermoplastic composite materials. In-situ consolidation refers to heating and consolidating the thermoplastic towpregs as they are being laid. This leverages automation to reduce the process steps, costs, and turnaround. However, in-situ consolidated thermoplastic composites by automated fibre placement have not gained wider acceptance within the industry due to ongoing concerns regarding manufacturing induced defects such as voids, poor interlaminar bonding and dimensional stability. A powerful tool available to researchers and engineers to better understand the development of such defects is process modelling. Process modelling is the analytical or numerical simulation of the in-situ consolidation process which typically involves complex interactions between the mechanical, thermal, and physical phenomena. This review paper covers the modelling approaches and material models which researchers have employed to simulate and predict the in-situ consolidation process. Experimental work on optimising the process parameters is also briefly discussed. The current limitations and future directions of process modelling for in-situ consolidation are also discussed.
An FE model of the solution heat treatment, forming and in-die quenching (HFQ) process was developed. Good correlation with a deviation of less than 5% was achieved between the thickness distribution ...of the simulated and experimentally formed parts, verifying the model. Subsequently, the model was able to provide a more detailed understanding of the HFQ process, and was used to study the effects of forming temperature and speed on the thickness distribution of the HFQ formed part. It was found that a higher forming speed is beneficial for HFQ forming, as it led to less thinning and improved thickness homogeneity.
•A coupled thermo-mechanical FE model of the HFQ forming process is developed.•The simulation results are accurate within 5% of the experimental results.•A detailed understanding of deformation during the HFQ forming process is provided.•For HFQ, improved thickness homogeneity can be achieved with higher forming speeds.
•Lab synthesis of various adsorbents for adsorption-based PCC.•Bench and pilot-scale experimental studies of adsorption-based PCC.•Molecular simulation of adsorbents for post-combustion carbon ...capture.•Process modelling\simulation and techno-economic analysis of adsorption-based PCC.•Achievements, challenges and future prospect in adsorption-based PCC.
Adsorption-based post-combustion carbon capture is a promising emerging technology for capturing CO2 emissions from fossil-fueled power plants due to the ease of adsorbent regeneration in comparison with solvent-based technologies. To increase its competitiveness, research efforts have focused on the development of new adsorbent materials and processes. This paper presents a state-of-the-art review of such efforts, focusing on lab synthesis and characterization of adsorbent materials, (carbon capture) experimental studies, molecular simulation, process modelling\simulation and techno-economic analysis. Most experimental studies on adsorption-based post-combustion capture are at bench scale. Just a few experimental studies are at pilot scale. There are currently no commercial deployment of adsorption-based post-combustion capture technology. This review paper points out challenges encountered in these experimental investigations utilizing different adsorbent materials, limiting its commercial deployment. These gaps in experimental investigations need further research especially in the chemical modification of the adsorbent materials to increase the adsorption capacity. Molecular simulation of adsorbents and process modelling\simulation of carbon capture processes are cost-effective and time efficient approaches for the assessment of adsorbents’ CO2 capture performance. The review also highlighted the need for more research in the model development of adsorbent materials at molecular scale and the model development of adsorption-based post-combustion process adopting new reactor configurations to further reduce the cost of CO2 capture.
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