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  • 101. Zhang, Xiaojing
    et al.
    Yan, Jinying
    Li, Hailong
    Chekani, Shabnam
    KTH.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Investigation of thermal integration between biogas production and upgrading2015In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 102, p. 131-139Article in journal (Refereed)
    Abstract [en]

    Thermal integration of anaerobic digestion (AD) biogas production with amine-based chemical absorption biogas upgrading has been studied to improve the overall efficiency of the intergraded system. The thermal characteristics have been investigated for industrial AD raw biogas production and amine-based chemical absorption biogas upgrading. The investigation provides a basic understanding for the possibilities of energy saving through thermal integration. The thermal integration is carried out through well-defined cases based on the thermal characteristics of the biogas production and the biogas upgrading. The following factors are taken into account in the case study: thermal conditions of sub-systems, material and energy balances, cost issues and main benefits. The potential of heat recovery has been evaluated to utilise the waste heat from amine-based upgrading process for the use in the AD biogas production. The results show that the thermal integration has positive effects on improving the overall energy efficiency of the integrated biogas plant. Cost analysis shows that the thermal integration is economically feasible.

  • 102. Zhao, Z.
    et al.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Solute transport in a single fracture with time-dependent aperture due to chemically medicated changes2014In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 66, p. 69-75Article in journal (Refereed)
    Abstract [en]

    In addition to mechanical loading, the transport properties of rock fractures are also affected by chemically mediated changes, such as pressure solution, stress corrosion and free-face dissolution, among others. Based on a time-dependent model of fracture closure under constant normal stresses, the transport behavior of contaminants in a slowly closing fracture is studied using a finite difference scheme. The results show that the contaminant penetrating along the fracture plane gradually becomes slow or almost negligible during the process of fracture closure induced by chemical processes, whereas the matrix diffusion of contaminants is active all the time. This finding indicates that diffusion into the rock matrix perpendicular to the advective flow direction always plays an important role in determining the fate of contaminant in rock fractures. The smaller the fluid flow due to fracture closure and the larger impact the matrix diffusion can further delay the solute transport.

  • 103.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lannu
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Stress effects on nuclide transport in fractured rocks: A numerical study2010In: ROCK MECHANICS IN CIVIL AND ENVIRONMENTAL ENGINEERING, 2010, p. 783-786Conference paper (Refereed)
    Abstract [en]

    The main objective of this study was to investigate the influence of stresses on radioactive nuclide transport in fractured rocks, based on Discrete Element Method (DEM) and a particle tracking approach. Matrix diffusion was also considered in the transport simulation. The results show that stresses not only influence the particle residence time in fracture network, but also change the particle transport paths significantly.

  • 104.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Evaluation of hydrodynamic dispersion parameters in fractured rocks2010In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 2, p. 243-254Article in journal (Refereed)
    Abstract [en]

    A numerical procedure to determine the equivalent hydrodynamic dispersion coefficients and Péclet number (Pe) of a fractured rock is presented using random walk particle tracking method. The geometrical effects of fracture system on hydrodynamic dispersion are studied. The results obtained from the proposed method agree well with those of empirical models, which are the scale-dependent hydrodynamic dispersion coefficients in an asymptotic or exponential form. A variance case is added to investigate the influence of longitudinal hydrodynamic dispersion in individual fractures on the macro-hydrodynamic dispersion at the fracture network scale, and its influence is demonstrated with a verification example. In addition, we investigate the influences of directional flow and stress conditions on the behavior of hydrodynamic dispersion in fracture networks. The results show that the magnitudes of the hydrodynamic dispersion coefficients are relatively smaller when the flow direction is parallel to the dip directions of fracture sets. Compressive stresses significantly reduce hydrodynamic dispersion. However, the remaining questions are: (1) whether the deformed fracture network under high stress conditions may make the scale-dependent hydrodynamic dispersion coefficients have asymptotic or exponential forms, and (2) what the conditions for existence of a welldefined equivalent hydrodynamic dispersion tensor are. They need to be further investigated.

  • 105.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Particle mechanics model for the effects of shear on solute retardation coefficient in rock fractures2012In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 52, p. 92-102Article in journal (Refereed)
    Abstract [en]

    Damage on rock fracture surfaces during shear process changes the mechanical and hydrological properties of the fractures, therefore, affects the solute migration in fractured rocks. Laboratory experiments on this issue are rarely reported in literature due to technical difficulties in measuring the asperity damage and gouge generation. To conceptually investigate the effects of rock fracture surface damage on solute sorption during shear, this paper presents, for the first time, a retardation coefficient model considering the wear impacts and a generic numerical evaluation procedure. The particle mechanics model was employed to investigate the effects of gouge generation (abrasive wear) and microcrack development in the damaged zones, on the solute retardation coefficient in rock fractures. The results from demonstration examples show that the shear process significantly increases the retardation coefficients, by offering more sorption surfaces in the factures due to gouge generation (wear), microcracking and crushing of gouge particles. Conceptually three damage zones are classified to characterize the various wear impacts on the solute transport in single fractures. Outstanding issues of the present model and suggestions for future study are also presented.

  • 106.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    A new numerical method of considering local longitudinal dispersion in single fractures2014In: International journal for numerical and analytical methods in geomechanics (Print), ISSN 0363-9061, E-ISSN 1096-9853, Vol. 38, no 1, p. 20-36Article in journal (Refereed)
    Abstract [en]

    The solutions of advection-dispersion equation in single fractures were carefully reviewed, and their relationships were addressed. The classic solution, which represents the resident or flux concentration within the semi-infinite fractures under constant concentration or flux boundary conditions, respectively, describes the effluent concentration for a finite fracture. In addition, it also predicts the cumulative distribution of solute particle residence time passing through a single fracture under pulse injection condition, based on which a particle tracking approach was developed to simulate the local advection-dispersion in single fractures. We applied the proposed method to investigate the influence of local dispersion in single fractures on the macrodispersion in different fracture systems with relatively high fracture density. The results show that the effects of local dispersion on macrodispersion are dependent on the heterogeneity of fracture system, but generally the local dispersion plays limited roles on marodispersion at least in dense fracture network. This trend was in agreement with the macrodispersion in heterogeneous porous media.

  • 107.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Analytical solution of coupled stress-flow-transport processes in a single rock fracture2011In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 37, no 9, p. 1437-1449Article in journal (Refereed)
    Abstract [en]

    A closed-form solution is presented for modeling the coupled stress-flow-transport processes along a single fracture embedded in a porous rock matrix. Necessary assumptions were made to simplify the subject into a two-dimensional (2D) problem, considering the changes of fracture aperture and matrix porosity under various stress conditions. The cubic law was assumed to be valid for the fluid flow in the fracture, with an impermeable rock matrix. For transport mechanisms, advective transport along the fracture, longitudinal hydrodynamic dispersion in the flow direction, and the matrix diffusion were considered in three different transport models under constant concentration or constant flux (Danck- werts’) inlet boundary conditions. This analytical solution can be used as a constitutive model, or as an example for validation of similar constitutive models, for modeling the coupled hydro-mechanical- chemical (HMC) processes in fracture networks of crystalline rocks. The influences of stress/deformation processes on different transport mechanisms in a single fracture under different inlet boundary conditions were studied for the first time. The results show that changes of fracture, as controlled by a combination of normal closure and shear dilatancy, have a significant influence on the solute concentration distribution both along the fracture and in the rock matrix, as well as on the solute residence/breakthrough time, especially when shear-induced dilatancy occurs. Under compressions, the decreasing matrix porosity slightly increases the solute concentration along the fracture and in the rock matrix.

  • 108.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Numerical modeling of stress effects on solute transport in fractured rocks2011In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 38, no 2, p. 113-126Article in journal (Refereed)
    Abstract [en]

    The effects of stress/deformation on fluid flow and contaminant transport in fractured rocks is one of the major concerns for performance and safety assessments of many subsurface engineering problems, especially radioactive waste disposal and oil/gas reservoir fields. However, very little progress has been made to study this issue due to difficulties in both experiments and numerical modeling. The objective of this study is to systematically investigate the influence of stress on solute transport in fractured rocks for the first time, considering different stress and hydraulic pressure conditions. A hybrid approach combining discrete element method (DEM) for stress-flow simulations and a particle tracking algorithm is developed. The impact of matrix diffusion (diffusion of molecular size solutes in and out of the rock matrix, and sorption onto the surface of micropores in rock matrix) is also included. The numerical results show that stress not only significantly changes the solute residence time through the fracture networks, but also changes the solute travel paths. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small, which is often encountered in practice.

123 101 - 108 of 108
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