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5th generation district heating and cooling networks operating at near ground temperature offer a low-cost, zero-carbon energy solution. Detailed understanding and accurate estimation of ground behaviour for its heat storage and recharge potential are of paramount importance for the success of such networks. In this paper, an advanced modelling tool, based on a coupled Thermal-Hydraulic (TH) modelling framework, is presented to calculate and predict temperature and soil-moisture behaviour of a shallow ground under complex atmospheric, temperature and hydraulic boundary conditions. Atmospheric data e.g., solar radiation, rainfall, humidity, air temperature, wind velocity is considered together with subsurface soil data to investigate thermal and hydraulic responses of the ground, and its individual soil layers. Furthermore, a transient method for estimating shallow ground source heat (SGSH) resources is proposed based on the simulated temperature and saturation distributions of the ground. The model is applied to predict the long-term ground temperature and saturation level of a test site located in Warwickshire County, UK. The total heat content per unit area and the annual/seasonal/monthly net heat content per unit area of the site are predicted for a five-year period. The total heat content of the sandy clay layer varied between 2.32 and 11.6 MJ/m2, silty clay from 34.0 to 50.5 MJ/m2, and mudstone from 50.7 to 55.0 MJ/m2. A parametric sensitivity study is also conducted to investigate the effects of soil types and hydraulic drainage conditions on the ground heat supply potential, and it revealed that the spatial and temporal distributions of ground heat is significantly affected by the underlying soils. This study highlights the influences of atmospheric conditions and coupled ground processes, and the parameters that should be considered for designing a 5th generation low-temperature heat network.

This paper presents a coupled thermo-mechanical model to investigate the ground response during underground coal gasification (UCG). The model incorporated the temporal and spatial development of temperature, the gradual growth of the cavity, and temperature-dependent material properties. Model verification was made against two benchmarks to acquire the confidence for the predictive purpose. The first exercise demonstrated the correctness of the model implemented in COMPASS. The second exercise showed that using the ash-filled cavity to represent null or empty zones is a good option in the numerical modeling and provided highly comparable results to other models. Based on the Hanna UCG trial, different cases were simulated to investigate the effects of the cavity size in the coal seam and the thermal expansion coefficient of the caprock and base rock on key features that take place during the process of UCG. A maximum temperature in the range of 1200–1500 ℃ was induced by the gasification of coal, and a cavity with a maximum length of 13.5 m was formed after 30 days of simulation. Meanwhile, small vertical displacement in the range of -5–12 mm took place near the cavity because of the thermal expansion of the geologic materials and the reduction of the overall weight with the creation of the cavity. In addition, it was found the thermal expansion coefficients can influence the thermo-mechanical response of geologic materials, but the effects were insignificant when its order of magnitude was smaller than 10-6 K-1.

This paper presents a coupled thermal-hydraulic-chemical numerical model to study the temperature development and solid–gas conversion during underground coal gasification (UCG). Theoretical formulations are based on the porous medium approach, involving the gas flow, solid mass loss, and heat flow, and the chemical reactions driving the phase change and transformation of gaseous species are considered by the kinetics model. A modified empirical relationship is proposed for the increase of porosity due to combustion and gasification, and the corresponding variation of permeability is expressed by a semi-empirical relationship. A numerical solution is obtained via the coupling of the transport model and the kinetics model for the sink/source terms due to chemical reactions. Verification tests have been conducted and compared with alternative numerical solutions to build confidence in the accuracy of the implementation of the model. Evaluation of the model against literature benchmarks including temperature development and syngas composition variation indicates that the coupled model can predict the UCG process.

Along with horizontal drilling techniques, multi-stage hydraulic fracturing has improved shale gas production significantly in past decades. In order to understand the mechanism of hydraulic fracturing and improve treatment designs, it is critical to conduct modelling to predict stimulated fractures. In this paper, related physical processes in hydraulic fracturing are firstly discussed and their effects on hydraulic fracturing processes are analysed. Then historical and state of the art numerical models for hydraulic fracturing are reviewed, to highlight the pros and cons of different numerical methods. Next, commercially available software for hydraulic fracturing design are discussed and key features are summarised. Finally, we draw conclusions from the previous discussions in relation to physics, method and applications and provide recommendations for further research.

Modelling horizontal ground loops for a horizontal ground source heat pump (HGSHP) system is complex and computationally expensive. The computation precision is highly reliant on the prescription of an undisturbed ground temperature in the unsaturated ground as well as realistic and accurate atmospheric processes at the ground surface boundary. Conventionally, modelling of such a system would include direct application of the atmospheric processes at the soil-atmosphere boundary and solve it in a single-stage approach. However, low efficiency is found for large spatial domain and long-term transient problems as the boundary processes need to be solved and expressed in terms of primary model variables at each simulation time-step. This paper proposes an equivalent two-stage modelling approach, for the first time, based on an advanced coupled thermal-hydraulic (TH) model to improve computation efficiency while maintaining adequate accuracy. In this approach, firstly, the model is solved for an intact ground that is imposed by complex atmospheric processes, e.g., rainfall, solar radiation, humidity, evaporation, etc. at the soil-atmosphere boundary, and the spatial and temporal variations of the primary model variables are recorded. Afterwards, the recorded data are incorporated in the simulator, as model inputs, for the same ground including a HGSHP system. Predicted results from both 2D and 3D simulations show that the ground temperatures calculated by the proposed two-stage approach are in good agreement with that of the traditional single-stage approach. However, the two-stage approach is computationally robust. For the presented 2D and 3D simulations, it required only 32% and 37% of the time of the single-stage approach, respectively, while maintaining great accuracy. This demonstrates the utility of the proposed two-stage approach for modelling complex scenarios of realistic HGSHP systems installed in a large spatial domain and for long-term operation.

This paper deals with the characterisation of inorganic constitutions generated at various operating conditions in the context of underground coal gasification (UCG). The ex situ small-scale experiments were conducted with coal specimens of different rank, from the South Wales Coalfield, Wales, UK, and Upper Silesian Coal Basin, Poland. The experiments were conducted at various gaseous oxidant ratios (water: oxygen = 1:1 and 2:1), pressures (20 bar and 36 bar) and temperatures (650°C, 750°C and 850°C). Increasing the amount of water in the oxidants proportionately decreased the cationic elements but increased the concentrations of anionic species. The temperature played minor impact, while the high-pressure experiments at temperature optimum to produce methane-rich syngas (750°C) showed significant reduction in cationic element generation. However, both coal specimens produced high amount of anionic species (F, Cl, SO4 and NO3). The “Hard” bituminous coal from Poland produced less gasification residues and condensates than the South Wales anthracitic coal due to its higher reactivity. The inorganic composition found in the solid residue was used in the theoretical calculation to predict the dissolved product concentrations when the solid residue interacts with deep coal seam water in the event of UCG cavity flooding. It was evident from the solubility products of the Cr, Ni and Zn that changes in the groundwater geochemistry occur; hence, their transportation in the subsurface must be studied further. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-15780-8.

Purpose A novel modelling approach is proposed to study ozone distribution and destruction in indoor spaces. The level of ozone gas concentration in the air, confined within an indoor space during an ozone-based disinfection process, is analysed. The purpose of this work is to investigate how ozone is distributed in time within an enclosed space. Design/methodology/approach A computational methodology for predicting the space- and time-dependent ozone concentration within the room across the consecutive steps of the disinfection process (generation, dwelling and destruction modes) is proposed. The emission and removal of ozone from the air volume are possible by means of a generator located in the middle of the room. This model also accounts for ozone reactions and decay kinetics, and gravity effect on the air. Finding This work is validated against experimental measurements at different locations in the room during the disinfection cycle. The numerical results are in good agreement with the experimental data. This comparison proves that the presented methodology is able to provide accurate predictions of the time evolution of ozone concentration at different locations of the enclosed space. Originality/value This study introduces a novel computational methodology describing solute transport by turbulent flow for predicting the level of ozone concentration within a closed room during a COVID-19 disinfection process. A parametric study is carried out to evaluate the impact of system settings on the time variation of ozone concentration within the space considered.

Many SCR catalysts without V species are developed and used for the NO abatement. The content of Ca in the real flue gas will result in the deactivation of catalysts. In this work, the effect of Ca(OH)2 on the denitration performance of the Fe–Ce/TiO2 catalyst for SCR reaction was explored. The BET, XRD, XPS, NH3-TPD, Py-IR, UV–Vis DRS, H2-TPR, and SEM–EDS mapping techniques were used to characterize the evolution of active species and the surface properties over the studied catalysts. The gained results demonstrate that the Ca(OH)2 results in serious deactivation of Fe–Ce/TiO2 catalyst for NH3-SCR reaction and the degree of deactivation is closely related to the loading of Ca(OH)2. Such serious deactivation caused by Ca(OH)2 is attributed to the smaller surface area, the declined redox ability and surface acidity, the lower content of Ce3+ and Fe3+, as well as the less surface adsorbed oxygen species. Moreover, the addition of Ca(OH)2 leads to poor dispersion of Ce and Fe species over the catalyst surface, which may also be responsible for the fall of the catalytic performance of the catalyst.

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.

The Fe–Ce/Ti catalysts with different molar ratios of Fe and Ce were synthesized by the precipitation method and impregnation method and used for the SCR reaction. BET, XRD, NH3-TPD, XPS, H2-TPR, UV–Vis, TEM, SEM–EDS mapping techniques were performed to explore the physicochemical properties of catalysts synthesized by different methods. As a result, the catalysts synthesized by precipitation method yields higher catalytic activity than that of the catalysts prepared by the impregnation method. The precipitated catalysts possess larger specific surface areas, higher ratios of Ce3+/Ce4+ and Fe3+/Fe2+ and more surface chemisorbed oxygen, as well as the enhanced surface acid sites and redox ability. Besides these, it holds a high dispersion of active species and more uniform smaller nanoparticles. All mentioned above will result in a higher catalytic performance of catalysts.

Mn–Ce/TiO2 catalysts were co-pretreated with SO2 and Ca and applied for the selective catalytic reduction (SCR) of NO with ammonia. The effect of co-pretreatment of SO2 and Ca on the physicochemical properties of catalysts was investigated by BET, XRD, XPS, NH3-TPD, H2-TPR, and UV–Vis techniques. The results show the co-pretreatment of SO2 and Ca greatly influences the physicochemical properties of catalysts such as texture characteristics, surface acidity and redox ability, amounts of active species and surface OH group, and therefore affects the catalytic activity of catalysts. The Mn–Ce–Ti(S–OH) catalyst co-pretreated with SO2 and Ca(OH)2 exhibits better catalytic activity than Mn–Ce–Ti(S–Cl) catalyst co-pretreated with SO2 and CaCl2. The Mn–Ce–Ti(S–OH) catalyst possesses larger specific surface area, higher concentrations of surface active species and surface chemisorbed oxygen, better surface acidity and redox ability, which may contribute to the accelerated catalytic activity.

This work presents a hybrid discrete fracture-dual porosity model of compressible fluid flow, adsorption and geomechanics during CO2 sequestration in coal seams. An application of the model considers the influence of hydraulic fractures on CO2 transport and the stress field of the coal. The low initial permeability of coal is compounded by the injectivity loss associated with adsorption-induced coal swelling, which is recognised as the major challenge limiting CO2 sequestration in coal seams. In this model, the natural fracture network and coal matrix are described by a dual porosity model, and a discrete fracture model with lower-dimensional interface elements explicitly represents any hydraulic fractures. The two models are coupled using the principle of superposition for fluid continuity with a local enrichment approximation for displacement discontinuity occurring at the surface of hydraulic fractures. The Galerkin finite element method is used to solve the coupled governing equations, with the model being verified against analytical solutions and validated against experimental data. The simulation results show that the presence of a hydraulic fracture influences the distribution of gas pressure and improves the gas flow rate, as expected. The stress field of a coal seam is disturbed by CO2 injection, especially the vertical stress, and the presence of a hydraulic fracture leads to a reduction in stress with permeability recovery starting earlier.

The different forms of Ca (CaCl2 and Ca(OH)2) poisoned manganese and cerium oxides supported on TiO2 catalysts were prepared by impregnation method and used for selective catalytic reduction (SCR) of NO with NH3. The Ca poisoning effects were investigated by many characterization methods including N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, H2-temperature programmed reduction and NH3-temperature programmed desorption techniques. The results showed that the addition of Ca led to greatly decrease of catalytic activity of catalysts and the catalytic activity was ranked in the order: CaCl2 poisoned catalyst

Mn-Ce-Ti catalysts were prepared by different precursors (including manganese nitrate, manganese acetate, and manganese chloride) and used for selective catalytic reduction (SCR) of NO with ammonia. The relationships among the structure, physicochemical properties, and catalytic activity were explored by N2 adsorption/desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), scanning electron microprobe (SEM) and energy dispersive spectroscopy (EDS) techniques. The results show that the different Mn precursors play important roles in the catalytic activity. The Mn-Ce-Ti(N) catalyst synthesized by manganese nitrate precursor exhibits the best catalytic activity, while the Mn-Ce-Ti(C) and Mn-Ce-Ti(Cl) catalyst prepared by manganese acetate and manganese chloride, respectively, exhibit relatively low catalytic activity. The manganese nitrate precursor could promote the specific surface area and redox ability, enhance the amounts of Bronsted and Lewis acid sites, and enrich the surface active species such as Mn4+, Ce3+ and surface chemisorbed oxygen of the catalyst, all of which will contribute to the SCR performance. Moreover, the Mn-Ce-Ti(N) catalyst possesses highly dispersed and uniform surface active species, which will result in the optimal physicochemical properties and superior catalytic performance.

This paper presents the baseline geochemistry and hydrogeology of a site in the South Wales Coalfield. Three deep exploration boreholes were drilled up to 650 m for that purpose and investigated together with the surrounding surface environment. The present study reports (i) General geological description, mineralogy and chemical composition (ii) Geochemistry of the coal seam water, surface waters and water from a shallow water table (iii) Periodic monitoring of temperature, water level and (iv) Adsorbed methane on rock samples and free gas concentrations acquired from three exploration boreholes. Rock specimens from the deep (425 m to 656 m) contained a minor amount of clay minerals such as clinochlore and kaolinite. Along with the major sandstone constitutions such as quartz and feldspar, rutile was also found in minor quantities. The trace elements such as arsenic, barium and thorium were found in various depths. The water temperature was stable around 13.5 °C (at 240 m) in Borehole 1, 15.6 °C (at 255 m) in Borehole 2 and 18.1 °C (at 453 m) in Borehole 3 throughout the monitoring period. The thermal profiling indicated the temperature gradient of 1.5 °C/100 m with maximum water temperatures at 22 to 24 °C which shows the thermal energy potential of the site. The low water temperature gradient in deep strata below 580 m, where the coal seams were encountered, indicated fluid movement in the deep coal seam aquifers. The gas analysis results showed the availability of the methane in the coal seams, and the water chemistry from the boreholes also exhibited the similar characteristics of the methane-producing wells around the world. The water chemistry of the shallow aquifers at the site was different from the water chemistry of the aquifers near the coal seam. The water quality measurements demonstrated the surface water quality was not affected by the drilling operations. Overall, this paper provides insights into the geochemistry and hydrogeology of the South Wales Coalfield that represents the environmental baseline data for any future industrial exploration or development activities.

The experimental analysis aimed at investigating the high-pressure (sub- and super-critical) CO2 sorption behaviour on two high-rank coals of different sizes is presented in this paper. Coals from the same seam (9ft seam), but from depths of 150 m (BD coal) and 550 m (AB coal) and different locations of the South Wales (UK) coalfield, known to be strongly affected by tectonically developed fracture systems, are employed for that purpose. Hence, the sorption behaviour of powdered (0.25-0.85 mm, 2.36-4.0 mm) and core samples obtained from locations associated with the deformation related changes is analysed in this paper to assess the CO2 storage potential of such coals. The results show that the coals exhibit maximum adsorption capacities up to 1.93 mol/kg (BD coal) and 1.82 mol/kg (AB coal). No dependence of the CO2 maximum sorption capacity with respect to the sample size for the BD coal is observed, while for the AB coal the maximum sorption capacity is reduced by more than half between the powdered and core samples. The CO2 sorption rates on BD coal decrease by a factor of more than 9 from 0.25-0.85 mm to 2.36-4.0 mm and then remain relatively constant with further increase in sample size. The opposite is observed for the AB coal where sorption rates decrease with increasing sample size, i.e. reducing by a factor of more than 100 between the 0.25-0.85 mm and core samples. The differences in behaviour are interpreted through the structure each coal exhibits associated with the burial depths and sampling locations as well as through the minor variations in ash contents. This study demonstrates that anthracite coals, having experienced sufficient deformation resulting in changes in fracture frequency, can adsorb significant amounts of CO2 offering great prospect to be considered as a CO2 sequestration option.

Background: Little is known on investigating how healthcare teams in dementia wards act for promoting personhood in persons with Alzheimer’s disease (PWA). Objective: The current research aimed to identify the social networks of dementia health carers promoting the personhood of PWA in acute or long-term dementia wards in public and private psychiatric hospitals. Methods: We used a mixed-method research approach. Ethnographic observations and two-mode Social Network Analysis (SNA) captured the role and social networks of healthcare professionals promoting PWA personhood, using SocNetv version 2.4. The social network graphs illustrated how professionals participated in PWA care by computing the degree of centrality (%DC) for each professional; higher values indicated more statistical significance of a professional role compared to others in the provision of personhood care. The categories of personhood were biological, individual, and sociologic. Nurses, doctors, ward managers, hospital managers, clinical psychologists, occupational therapists, care coordinators, physiotherapists, healthcare assistants, and family members were observed if they were promoting PWA personhood. Method: We used a mixed-method research approach. Ethnographic observations and two-mode Social Network Analysis (SNA) captured the role and social networks of healthcare professionals promoting PWA personhood, using SocNetv version 2.4. The social network graphs illustrated how professionals participated in PWA care by computing the degree of centrality (%DC) for each professional; higher values indicated more statistical significance of a professional role compared to others in the provision of personhood care. The categories of personhood were biological, individual, and sociologic. Nurses, doctors, ward managers, hospital managers, clinical psychologists, occupational therapists, care coordinators, physiotherapists, healthcare assistants, and family members were observed if they were promoting PWA personhood. Results: The highest %DC in SNA in biological personhood was held by the ward nurses (36%), followed by the ward doctors (20%) and ward managers (20%). All professional roles were involved in 16% of cases in the promotion of individual personhood, while the hospital managers had the highest %DC (33%) followed by the ward managers and nurses (27%) in the sociologic personhood. Conclusion: All professional roles were deemed to promote PWA personhood in dementia wards, although some limitation exists according to the context of the assessment.

This paper presents the inclusion of explicit dual poroelastic mechanical behaviour as part of an existing dual porosity numerical model of multiphase, multicomponent chemical-gas transport. The dual poroelastic framework employed considers the pore structure changes occurring as a result of high pressure carbon dioxide injection into coal, particularly the adsorption-induced coal swelling that has been found to limit injectivity in field trials of carbon sequestration in coalbeds around the world. To address this issue, the surface stress of the fluid-solid interface is introduced into the constitutive relation for dual porosity effective stress in order to investigate the coal deformation and porosity changes related to adsorption behaviour. A new porosity model is presented, in which the impacts of gas flow and coal deformation are incorporated, and an interaction coefficient is proposed to explain the effect of fracture-matrix interactions on the porosity evolution. The model is verified and validated in this work against relevant analytical solutions and experimental results, and applied to study the gas flow behaviour and structural changes of coal. The results show that carbon dioxide injection not only causes coal swelling but also has the potential to change the internal pore structure of coal. The variation of fracture porosity is not monotonic as a competing result of effective stress and internal fracture-matrix interactions. However, the matrix porosity is found to increase during carbon dioxide injection, which seems to be a key contributor to the swelling phenomenon.

Peter Wells will be remembered internationally for his many outstanding contributions in the field of medical ultrasound. He pioneered the development of non-invasive imaging techniques in the development of ultrasonics as a diagnostic and surgical tool. He was the originator and developer of instruments for ultrasonic surgery and ultrasonic power measurement, as well as the two-dimensional, articulated-arm ultrasonic general purpose scanner and the water-immersion ultrasonic breast scanner. He demonstrated ultrasonic-pulsed Doppler range-gating, and was the discoverer of the ultrasonic Doppler signal characteristic of malignant tumour neovascularization. He investigated ultrasonic bioeffects and formulated ultrasonic safety guidelines and conditions for prudent use of ultrasonic diagnosis. His outstanding and sustained achievements in the medical applications of ultrasound extend continuously from the 1960s until a few days before his death at the age of 80. Anyone who has ever benefited from an ultrasound procedure owes a debt of gratitude to Peter Wells.

Fe–Ce–Al catalysts were synthesized by the co-precipitation method (labeled as Fe–Ce–Al–P), co-impregnation method (Fe–Ce–Al–I), and direct mixing method (Fe–Ce–Al–M), respectively, and used for effective removal of NO. The synthesized catalysts were characterized by many methods including N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desorption (NH3-TPD), H2-temperature programmed reduction (H2-TPR), high-resolution transmission electron microscopy (HR-TEM), and energy dispersive spectroscopy (EDS) mapping. The results show that the synthesis methods greatly influence the catalytic performance of catalysts. The Fe–Ce–Al–P catalyst prepared by the co-precipitation method yields the highest catalytic performance, while the Fe–Ce–Al–I and Fe–Ce–Al–M catalysts exhibit relatively low catalytic activity. The co-precipitation method can promote the accumulation and dispersion of more surface active species on the catalyst surface, and provide smaller particle size of active species and generate more uniform particle size distribution, while these characteristics can't be obtained by the co-impregnation method and direct mixing method. Moreover, the co-precipitation method could produce the highest surface area and enhanced redox ability and surface acidity of the catalyst, which resulted from the high dispersion and uniform distribution of surface active species. These may be the key factors to the superior catalytic performance of the Fe–Ce–Al–P catalyst.

Predicting the transport and fate of organic and inorganic contaminants in co-contaminated soils is challenging, since various complex, inter-related processes are involved. In the presence of soil microbes that metabolise organic compounds (e.g., phenol), the chemical and the physical properties of the soil may alter and consequently affect the transport of inorganic trace metals e.g., Cu, Cd, Ni, Pb. However, the impact of their spatial distributions on the co-transport processes are still poorly understood and rarely available in literature. Here, we distribute the microbial colonies spatially in uniform and various non-uniform configurations and observe that the transport of weakly-sorbed Cd and Ni is greatly influenced by the distance of the colonies from the contaminant source rather than the size of the colonies. Whereas, for strongly-sorbed Pb and Cu, both the distance and the size are important. The spread of phenol in the model domain was substantially restricted by distributing the colonies more towards the transverse direction than in the longitudinal direction of the groundwater flow. In the context of co-contaminated soil remediation, this study demonstrates that optimum and efficient spatial distribution patterns can be obtained to restrict the spread of both organic and inorganic contaminants, with subsequent reduced environmental impacts.

Coupled thermo‐hydro‐mechanical‐chemical modelling has attracted attention in past decades due to many contemporary geotechnical engineering applications (e.g., waste disposal, carbon capture and storage). However, molecular‐scale interactions within geomaterials (e.g., swelling and dissolution/precipitation) have a significant influence on the mechanical behaviour, yet are rarely incorporated into existing Thermal‐Hydro‐Mechanical‐Chemical (THMC) frameworks. This paper presents a new coupled hydro‐mechanical‐chemical constitutive model to bridge molecular‐scale interactions with macro‐physical deformation by combining the swelling and dissolution/precipitation through an extension of the new mixture‐coupling theory. Entropy analysis of the geomaterial system provides dissipation energy, and Helmholtz free energy gives the relationship between solids and fluids. Numerical simulation is used to compare with the selected recognized models, which demonstrates that the swelling and dissolution/precipitation processes may have a significant influence on the mechanical deformation of the geomaterials.

Tortuosity is widely used as a critical parameter to predict transport properties of porous media, such as rocks and soils. But unlike other standard microstructural properties, the concept of tortuosity is vague with multiple definitions and various evaluation methods introduced in different contexts. Hydraulic, electrical, diffusional, and thermal tortuosities are defined to describe different transport processes in porous media, while geometrical tortuosity is introduced to characterize the morphological property of porous microstructures. In particular, the rapid development of microscopy imaging techniques has made digital microstructures of porous media increasingly accessible, from which geometrical and physical tortuosities can be evaluated using various image analysis and numerical simulation methods. These tortuosities are defined differently and can differ greatly in value, but in many works of literature, they are used interchangeably. To address this situation, we systematically examine geometrical, hydraulic, electrical, diffusional, and thermal tortuosities from the viewpoints of the definition and evaluation method. For the same porous medium, visible discrepancies are found in the evaluated geometrical and physical tortuosities, depending on the specific definition and the evaluation method adopted. This observation makes it questionable to directly use the geometrical tortuosity as a substitute for physical tortuosities, a common practice in the literature. Thus, the correlations between geometrical and physical tortuosities are further analyzed, which also takes into account the influence of both image size and resolution. From the correlation analysis, phenomenological relations between geometrical and physical tortuosities are established, so that the latter can be accurately predicted by using the former which is much cheaper to evaluate from digital microstructures.

Heterogeneous materials such as rocks and composites are comprised of multiple material phases of different sizes and shapes that are randomly distributed through the medium. The random microstructure is typically described by using various statistical descriptors, which include volume fraction, two-point correlation function, and tortuosity, to name a few. Capturing different morphological features, a large number of statistical descriptors are proposed in different research fields, such as material science, geoscience and computational engineering. It is well known that these statistical descriptors are not independent from each other, but until recently it remains unclear what descriptors are more similar or more different. In particular, it is extremely difficult to look for quantified relations between various descriptors, since they are often defined in very different formats. The lack of quantified understanding of descriptors’ relations can cause uncertainties or even systematic errors in heterogeneous materials studies. To address this issue, we propose a novel and generic correlation analysis strategy and establish, for the first time, the quantified relations between various statistical descriptors for heterogeneous materials. Based on data science techniques, our approach consists of three operational steps: data regularization , dimension reduction and correlation analysis. A total of 41 statistical descriptors are collected and analysed in this study, which is readily extensible to include other new descriptors. The generic and quantified correlation results are compared with other established descriptor relations that are obtained from analytical analysis or physical intuition, and good agreements are observed in all cases. The quantified relations between various descriptors are summarized in a single correlation graph, which provides useful guiding information for the characterization, reconstruction and property prediction of heterogeneous materials.

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH3-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts. And these catalysts were characterized by BET, XRD, Raman, UV-vis DRS, XPS, H2-TPR, and NH3-TPD techniques. The obtained results demonstrate that Ca doping could lead to an obvious decrease in the catalytic activity of catalysts. The reasons for this may be due to the smaller specific surface area and pore volume, the decreased ratio of Fe3+/Fe2+ and Ce3+/Ce4+, as well as the reduced redox ability and surface acidity.

This study presents a coupled dual porosity thermal-hydraulic-mechanical (THM) model of non-isothermal gas flow during CO2 sequestration in coal seams. Thermal behaviour is part of the disturbed physical and chemical condition of a coal seam caused by CO2 injection, and must be understood for accurate prediction of CO2 flow and storage. A new porosity-permeability model is included for consideration of the fracture-matrix compartment interaction. The new model is verified against an analytical solution and validated against experimental measurements, before being used to analyse coupled THM effects during CO2 sequestration in coal. A simulation of CO2 injection at a fixed rate shows the development of a cooling region within the coal seam due to the Joule-Thomson effect, with the temperature in the vicinity of the well declining sharply before recovering slowly. The temperature disturbance further from the well is more gradual by comparison. Under the simulation conditions studied, CO2 injection increases coal matrix porosity and decreases the porosity and permeability of the natural fracture network, especially in the vicinity of the injection well, due to adsorption-induced coal swelling. Compared with the effects of gas pressure and temperature, the matrix-fracture compartment interaction plays an important role in changes of porosity and permeability. Considering the temperature disturbance caused by CO2 injection under the set of representative conditions studied, the coupled model can provide an insight into the associated effects on CO2 flow and storage during its sequestration in coal seams. The first author gratefully acknowledges the financial support provided by the Welsh European Funding Office (WEFO), through the FLEXIS project. The financial support from the China Scholarship Council for the PhD studentship of the second author is also gratefully acknowledged.

This paper presents an analysis of contaminants generated from large-scale, laboratory-based, underground coal gasification (UCG) experiments using a high-rank coal from the South Wales Coalfield. The experiments were performed at atmospheric and elevated pressures (30 bar) by varying the oxidants’ composition. The experiments were designed to predict the amount of produced water and contaminants generated at each stage of the operating conditions. The mass balance of water supplied and produced in the experiments was accounted for. Chemical analyses of produced water, char and ash contents were performed to quantifytheinorganicandorganicchemicalparameters. Mostof the contaminant concentrationsinthe produced water from the 30-bar pressure experiment were lower than the concentrations generated from the atmospheric pressure experiment. The measured concentrations of theinorganicchemicalspeciesandtheinorganicparameters of the coal seam water from the South Wales Coalfieldwereusedintheoreticalcalculationstopredict\udthe dominant equilibrium species concentrations in a hypothetical scenario of effluent contaminated groundwater.Thebiodegradationoforganiccontaminantssuch as phenol, benzene and sorbed fractions of inorganic contaminants from the produced water on iron oxide in theashresiduewaspredictedusingexistingbiotransformation kinetics and surface complexation models, respectively. The biodegradation of phenol and benzene would be a slow process even at optimum conditions and the iron oxide left in the cavity can act as a sorbent for a few inorganic species. The evidence from the present study suggests future work towards (i) developing an appropriate water treatment process during gas cleaning, (ii) operational procedure (pressure and proportions of oxidant) and (iii) developing UCG-specific experimental prediction of contaminant transportation and transformation kinetics.\udKeywords High-rankcoal.Undergroundcoal gasification.Highpressure.Producedwater.Inorganic organiccontaminants.Ash

This paper presents the development of a discrete fracture model of fully coupled compressible fluid flow, adsorption and geomechanics to investigate the dynamic behaviour of fractures in coal. The model is applied in the study of geological carbon dioxide sequestration and differs from the dual porosity model developed in our previous work, with fractures now represented explicitly using lower‐dimensional interface elements. The model consists of the fracture‐matrix fluid transport model, the matrix deformation model and the stress‐strain model for fracture deformation. A sequential implicit numerical method based on Galerkin finite element is employed to numerically solve the coupled governing equations, and verification is completed using published solutions as benchmarks. To explore the dynamic behaviour of fractures for understanding the process of carbon sequestration in coal, the model is used to investigate the effects of gas injection pressure and composition, adsorption and matrix permeability on the dynamic behaviour of fractures. The numerical results indicate that injecting nonadsorbing gas causes a monotonic increase in fracture aperture; however, the evolution of fracture aperture due to gas adsorption is complex due to the swelling‐induced transition from local swelling to macro swelling. The change of fracture aperture is mainly controlled by the normal stress acting on the fracture surface. The fracture aperture initially increases for smaller matrix permeability and then declines after reaching a maximum value. When the local swelling becomes global, fracture aperture starts to rebound. However, when the matrix permeability is larger, the fracture aperture decreases before recovering to a higher value and remaining constant. Gas mixtures containing more carbon dioxide lead to larger closure of fracture aperture compared with those containing more nitrogen.

In the present work, fresh and Ca poisoned Fe-Ce/Ti catalysts were prepared and used for the NH

This paper presents the results of an extensive experimental analysis of underground coal gasification (UCG) using large bulk samples in an ex-situ reactor under atmospheric and high-pressure (30 bar) conditions. The high-rank coal obtained from the South Wales (UK) coalfield is employed for that purpose. The aim of this investigation is to define the gas production rates, gas composition, gas calorific value, process energy efficiency and temperature changes within the UCG reactor during the gasification process based on the pre-defined reactants and flow rates. Two UCG trials, each lasting 105 h, consisted of six stages where the influences of oxygen, water, air and oxygen enriched air (OEA) under different flow conditions on the gasification process were investigated. Based on the results of two multi-day experiments, it is demonstrated that the gasification under high pressure conditions produces syngas with higher average calorific value (8.49 MJ/Nm3) in comparison to syngas produced at atmospheric pressure conditions (6.92 MJ/Nm3). Hence, the overall energy efficiency of the high-pressure experiment is higher compared to the atmospheric pressure test, i.e. 57.67% compared to 51.72%. This is related to the fact that the high-pressure gasification produces more methane (11.97 vol%) than the atmospheric pressure gasification (2.30 vol%). Under elevated pressure, the temperatures recorded in the roof strata are about 100 °C higher compared to the UCG process under atmospheric pressure conditions. This work provides new insights into the gasification of carbon-rich coals subject to different gasification regimes and pressures.

In this work, the potential of carrying out inverse problems with linear and non-linear behaviour is investigated using deep learning methods. In inverse problems, the boundary conditions are determined using sparse measurement of a variable such as velocity or temperature. Although this is mathematically tractable for simple problems, it can be extremely challenging for complex problems. To overcome the non-linear and complex effects, a brute force approach was used on a trial and error basis to find an approximate solution. With the advent of machine learning algorithms it may now be possible to model inverse problems faster and more accurately. In order to demonstrate that machine learning can be used in solving inverse problems, we propose a fusion between computational mechanics and machine learning. The forward problems are solved first to create a database. This database is then used to train the machine learning algorithms. The trained algorithm is then used to determine the boundary conditions of a problem from assumed measurements. The proposed method is tested for the linear/non-linear heat conduction, convection–conduction, and natural convection problems in which the boundary conditions are determined by providing three, four, and five temperature measurements. This study demonstrates that the proposed fusion of computational mechanics and machine learning is an effective way of tackling complex inverse problems.

This paper presents the validation of a recently developed dual porosity numerical model and provides insights into coal core flooding experiments with N2 and CO2. Experimental data for anthracite coal from the South Wales Coalfield, UK, allows the coal-gas constitutive behaviour to be defined, leading to the validation of the model using gas flooding data for a mm long and mm diameter core. N2 and CO2 injection scenarios are considered with the coal initially saturated with CH4. It is demonstrated that the model can simulate the physical and chemical phenomena involved in multicomponent gas flow and storage in coal. Further analysis shows that N2 breakthrough in the effluent gas is controlled by dual porosity flow without significant influence of adsorption-desorption, whereas for CO2 this influence is greater. Coal swelling caused by CO2 is identified as the predominant factor, with the preferential displacement of adsorbed CH4 being limited by the time scale of flow across the core relative to the CH4 desorption kinetics. These insights are useful for future experiments concerning the influence of core size. The importance of using sorption data from intact coal rather than powdered coal is highlighted by comparing the numerical predictions and experimental measurements.

The feasibility of recovering heat energy from mine water contained within an abandoned coal mine in South Wales is assessed for a proposed district heating scheme. The study area is the village of Caerau, in the Upper Llynfi Valley, Bridgend County Borough, South Wales, UK, comprising around 750 residential houses, a primary school and 17 commercial properties. This paper describes: an archival geological and mining desk study focussed on Caerau colliery, consideration of regional mine linkages, GIS techniques used to create a 3D initial conceptual geological mine model of Caerau workings, permitting and licencing requirements, community engagement activities undertaken and the findings of a single exploratory borehole. The borehole intersected a void space in flooded mine workings around the horizon of the Six Foot seam at a depth of 224 m below ground level, as predicted by the conceptual mine model. The rest water level within the borehole lies at 92m below ground level and the measured in situ temperature of the mine water at the base of the borehole was 20.3 °C. An unexpectedly high and sustained geothermal gradient of approximately 53 °C/km was calculated from repeated measured temperature profiles.

This work presents the state-of-the-art review of investigations related to the adsorption process, adsorption models, experimental adsorption results, and influencing factors, considering the main contaminants produced by underground coal gasification (UCG) technology as adsorbates and the various rocks and soils surrounding the UCG cavity as adsorbents. Based on the literature reviewed, it is found that claystone, coal, coal char, shale, and clay materials present a good prospect for effective phenol adsorption; coal, coal char, shale, and clay materials can also remove benzene and some heavy metals from aqueous solutions. However, their performance varies under the effect of the influencing factors, such as the initial concentration of adsorbates in solution, the pH of the solution, the temperature and contact time controlled in the adsorption process, and the adsorbent dosage. A preliminary assessment of the potential of rocks and soils to act as natural buffers in UCG application is provided. The impact of UCG process on the adsorption of contaminants on the surrounding strata together with the major challenges and future perspectives are highlighted and outlined, to identify knowledge deficiencies regarding the retardation of UCG contaminants using the natural buffers. The prospect of surrounding strata as natural buffers can benefit the site selection, design, and commercialization of UCG.

Modelling of coupled thermal (T), hydro (H), mechanical (M) and chemical (C) processes in geomaterials has attracted attention in the past decades due to many significant contemporary engineering applications such as nuclear waste disposal, carbon capture and storage etc. However, in very-low permeability membrane geomaterials, the couplings between chemical osmosis and thermal osmosis and their consequent influence on temperature, water transport and mechanical deformation remain as a long-lasting challenge due to the gap between geomechanics and geochemistry. This paper extends Mixture Coupling Theory by bridging the chemical-thermal field based on non-equilibrium thermodynamics, and develops a new constitutive THMC fully-coupled model incorporating the interactions between chemical and thermal osmosis. Classic Darcy's law has been fundamentally extended with osmosis as the major driving force of the diffusion process. A simple numerical simulation used for the demonstration purpose has illustrated that the couplings between chemical and thermal osmosis will significantly change the water flow directions, consequently influencing the saturation variation and mechanical deformation.

Underground coal gasification (UCG) has a great potential to be accompanied by the technology of (enhanced) coal bed methane ((E)CBM) and carbon capture and storage (CCS), enhancing coal energy efficiency and mitigating climate change. This study aims to assess the environmental impact of three field-scale UCG hypothetical sites targeting deep-buried seams during the UCG operational stage in the combined CBM-UCG application. For this purpose, a risk assessment methodology is developed with consideration of the geomechanical and hydrogeological impact of UCG operations on the overlying strata by analogy to longwall mining operations. A series of numerical simulations are conducted to investigate the effect of variations in the saturation conditions around the UCG reactor, the change of rock permeability, and the UCG reactor operation duration on the propagation of heat, moisture and gaseous chemicals. The results demonstrate that CBM-UCG activities in the three sites are not likely to cause negative impacts on the environment during the UCG process when the behaviour of the reactor and the change of the surrounding strata are in control as expected. This work can provide insights in terms of environmental decision making, regulation and management to prevent reduction in gasification efficiency, to conduct the post-UCG (E)CBM process and to mitigate the UCG gas leakage and contamination of surrounding aquifers, highlighting where additional information is required in CBM-UCG activities.

Clayey material that possesses semipermeable membrane property may experience osmotic consolidation in presence of an osmotic gradient. In this paper, a fully coupled H-M-C model has been presented to study solute transport under the combined influence of mechanical and osmotic consolidations and vice versa. The model has been tested against the results of relevant importance and good agreements have been achieved. The model has been applied to investigate long-term solute transport behavior and consequent deformations/settlements in a natural clay liner. The results suggest, at early stages, solute transport is dominated by mechanical consolidation; however, physicochemical interaction associated with osmotic processes and osmotic consolidation dominates in the long term. Osmotic settlement shows decreasing trend past the maximum deformation of the clay liner indicating reduction of osmotic gradient across the semipermeable membrane. It is also evident that overall soil consolidation and transport of solute are affected by the concentration of the solute at the source or the injection boundary.

© 2018, Canadian Science Publishing. All rights reserved. This paper presents the development of a dual porosity numerical model of multiphase, multicomponent chemical-gas transport using a coupled thermal, hydraulic, chemical, and mechanical formulation. Appropriate relationships are used to describe the transport properties of nonideal, reactive gas mixtures at high pressure, enabling the study of geoenergy applications such as geological carbon sequestration. Theoretical descriptions of the key transport processes are based on a dual porosity approach considering the fracture network and porous matrix as distinct continua over the domain. Flow between the pore regions is handled using mass exchange terms and the model includes equilibrium and kinetically controlled chemical reactions. A numerical solution is obtained with a finite element and finite difference approach and verification of the model is pursued to build confidence in the accuracy of the implementation of the dual porosity governing equations. In the course of these tests, the time-splitting approach used to couple the transport, mass exchange, and chemical reaction modules is shown to have been successfully applied. It is claimed that the modelling platform developed provides an advanced tool for the study of high-pressure gas transport, storage, and displacement for geoenergy applications involving multiphase, multicomponent chemical-gas transport in dual porosity media, such as geological carbon sequestration. Welsh European Funding Office

Soil atmospheric interactions play an important role within the thermal energy balance and seasonal temperature variations of the ground. This paper presents a formulation for the surface boundary conditions related to interactions between soil and atmosphere. The boundary condition formulated considers heat flow at the soil–atmosphere interface through mechanisms of shortwave radiation, long-wave radiation, sensible radiation and latent heat radiation. The effects of surface moisture flux on energy balance at the interface are explicitly included in the formulation. The developed boundary condition has been implemented in a numerical model for coupled thermal, hydraulic and mechanical behaviour of unsaturated soils. The evaporation component of the model is tested, and the results are compared with data from an experimental study at the surface of an area of agricultural land reported in the literature. The results of modelling have been found to compare favourably with the reported data set. The formulation developed for the soil atmospheric boundary condition allows climatic variables, including solar radiation, ambient air temperature, relative humidity, wind speed, rainfall and evaporation, to be incorporated in the long-term analysis of energy balance. This also enables a further detailed inspection of the climate’s role in ground thermal behaviour of ground source heat systems.