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  • 1.
    Andersson, H.M.
    et al.
    Luleå tekniska universitet.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Synnergren, Per
    Luleå tekniska universitet.
    Application of digital speckle photography to measure thickness variations in the vacuum infusion process2003In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 24, no 3, p. 448-455Article in journal (Refereed)
    Abstract [en]

    A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in-house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross-correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm. The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross-linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross-linking is reached.

  • 2. Andersson, Magnus
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Långström, R.
    Luleå tekniska universitet.
    Development of guidelines for the vacuum infusion process2000In: Proceedings of the 8th International Conference on Fibre Reinforced Composites, FRC 2000: Centre for Composite Materials Engineering, University of Newcastle, UK, 13 - 15 September 2000 / [ed] A. G. Gibson, Cambridge: Woodhead Publishing Materials , 2000, p. 113-120Conference paper (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion moulding for large surface area parts has increased the interest for an advanced modelling of the process. This paper presents a detailed experimental investigation of laminate thickness and out-of-plane flow front shape during impregnation of high permeability reinforcement on top of a non-crimp fabric reinforcement lay-up. The goal with the experiments is to increase the understanding of the process and to provide accurate data that can later be used for validation of numerical models. The laminate thickness was measured during impregnation with a stereoscopic digital speckle photography system and the flow front shape was determined by tracking of colour marks in the stacking. The laminate lay-ups studied are different combinations of non-crimp fabrics and flow layers while the resin used was a polyester developed specifically for vacuum infusion moulding. Results are presented both for the instantaneous thickness and the flow front shape for several different material combinations. It was found that the skewness of the flow front became more pronounced with increasing number of flow layers when the number of non-crimp fabric layers was kept constant. As a first step towards a complete numerical model of the impregnation process a simplified model for the compressibility and a proven model for permeability was implemented in a commercial CFD package that can handle moving boundaries and moving flow fronts. Only a qualitative comparison with experiments was done but the conclusion was that the overall behaviour of the model was encouraging. A validation of the numerical model based on the measurements in this paper is under development.

  • 3. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical model for vacuum infusion manufacturing of polymer composites2003In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 13, no 3, p. 383-394Article in journal (Refereed)
    Abstract [en]

    The focus is set on the development and evaluation of a numerical mgodel describing the impregnation stage of a method to manufacture fibre reinforced polymer composites, namely the vacuum infusion process. Examples of items made with this process are hulls to sailing yachts and containers for the transportation industry. The impregnation is characterised by a full 3D flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The numerical model has been implemented in a general and commercial computational fluid dynamic software through custom written subroutines that: couple the flow equations to the equations describing the stiffness of the fibre reinforcement; modify the momentum equations to account for the porous medium flow; remesh the computational domain in each time step to account for the deformation by pressure change. The verification of the code showed excellent agreement with analytical solutions and very good agreement with experiments. The numerical model can easily be extended to more complex geometry and to other constitutive equations for the permeability and the compressibility of the reinforcement.

  • 4. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Långström, R.
    Swedish Institute of Composites, Piteå.
    Flow-enhancing layers in the vacuum infusion process2002In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 23, no 5, p. 895-901Article in journal (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.

  • 5.
    Bergström, John
    et al.
    Luleå tekniska universitet.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    An Approximate CFD method for the interaction between stationary and rotating parts in hydraulic turbines1998In: Hydraulic Machinery and Cavitation: Proceedings of the XIX IAHR Symposium, Section on Hydraulic Machinery and Cavitation / [ed] H. Brekke, Singapore: World Scientific Publishing Co Pte Ltd , 1998Conference paper (Refereed)
  • 6.
    Bergström, John
    et al.
    Luleå tekniska universitet.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Estimation of numerical accuracy for the flow field in a draft tube1999In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 9, no 4, p. 472-486Article in journal (Refereed)
    Abstract [en]

    The potential for overall efficiency improvements of modern hydro power turbines is a few percent. A significant part of the losses occurs in the draft tube. To improve the efficiency by analysing the flow in the draft tube, it is therefore necessary to do this accurately, i.e. one must know how large the iterative and the grid errors are. This was done by comparing three different methods to estimate errors. Four grids (122,976 to 4,592 cells) and two numerical schemes (hybrid differencing and CCCT) were used in the comparison. To assess the iterative error, the convergence history and the final value of the residuals were used. The grid error estimates were based on Richardson extrapolation and least square curve fitting. Using these methods we could, apart from estimate the error, also calculate the apparent order of the numerical schemes. The effects of using double or single precision and changing the under relaxation factors were also investigated. To check the grid error the pressure recovery factor was used. The iterative error based on the pressure recovery factor was very small for all grids (of the order 10-4 percent for the CCCT scheme and 10-10percent for the hybrid scheme). The grid error was about 10 percent for the finest grid and the apparent order of the numerical schemes were 1.6 for CCCT (formally second order) and 1.4 for hybrid differencing (formally first order). The conclusion is that there are several methods available that can be used in practical simulations to estimate numerical errors and that in this particular case, the errors were too large. The methods for estimating the errors also allowed us to compute the necessary grid size for a target value of the grid error. For a target value of 1 percent, the necessary grid size for this case was computed to 2 million cells.

  • 7.
    Bergström, John
    et al.
    Luleå tekniska universitet.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Time-phase averaging for the approximate solution of the flow in a hydraulic turbine1999In: Proceedings of ASME/JSME FEDSM'99: ASME/JSME Fluids Engineering Division Summer Meeting, American Society of Mechanical Engineers , 1999Conference paper (Refereed)
    Abstract [en]

    The refurbishment of old hydropower installations and the continuos development of new installations has increased the interest for better design tools to improve their efficiency. Computational fluid dynamics has been used with great success to improve the design of the runner. However, extensive model testing has been necessary to improve the design of the surrounding waterways. Even after testing, some uncertainty has remained concerning the difference between the model scale and the full scale turbine system. The current trend is therefore to include as much as possible of the water conduits with a simultaneous solution of the flow in the turbine runner in an effort to reduce the need for model testing. However, if high numerical accuracy is required the number of mesh points for a complete model of the turbine system has to be at least 10^7. The mesh size together with the need for a time dependent mesh in the runner makes it unlikely that a full simulation with a rotating runner and advanced turbulence modeling will be possible within the next several years, even if the most optimistic estimate of future computer capacity are taken into account. It is therefore of great interest to find new approximations that will make a more refined analysis of the waterways external to the runner possible.In this paper we present a model for the runner that preserves any flow non-uniformity existing at the inlet of the runner in a realistic way through the runner. This has enabled a complete analysis of the interaction of the flow through the penstock, spiral casing and guide vanes with the flow in the draft tube. The mesh requirement and the computational time is considerably reduced compared to a full simulation with a sliding mesh model for the runner. The main drawback with the new model is believed to be that the blade wakes are averaged out of the problem.The model we propose is based on a time-phase averaging technique. The essence of the model is similar to the time averaging technique used by Adamczyk (Adamczyk, 1985), but with different averaging time and different mathematical notation that makes it possible to use the model in a general case, i.e. both for axial and radial machines. A phase function is central to the technique and is introduced for weighting in the averaging procedure. The phase function makes it possible to time average the flow inside a runner. It is constructed with generalised functions and a geometrical description of the suction and pressure side of a runner blade at a reference position. Exact equations for the time-phase averaged variables are derived by a formal time-phase averaging of the governing equations. Some of the terms are accounted for in an approximate way in the present simulation but it is possible to calculate better approximations with a simulation of an isolated runner in a rotating coordinate system. However, even with the crude approximations that we have used the simulation produces realistic results for the particle paths through the runner.

  • 8. Burman, Jörgen
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Influence from numerical noise in the objective function for flow design optimisation2001In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 11, no 1, p. 6-19Article in journal (Refereed)
    Abstract [en]

    The overall pressure drop in an axisymmetric contraction is minimised using two different grid sizes. The transition region was parameterised with only two design variables to make it possible to create surface plots of the objective function in the design space, which were based on 121 CFD calculations for each grid. The coarse grid showed to have significant numerical noise in the objective function while the finer grid had less numerical noise. The optimisation was performed with two methods, a Response Surface Model (RSM) and a gradient-based method (the Method of Feasible Directions) to study the influence from numerical noise. Both optimisation methods were able to find the global optimum with the two different grid sizes (the search path for the gradient-based method on the coarse grid was able to avoid the region in the design space containing local minima). However, the RSM needed fewer iterations in reaching the optimum. From a grid convergence study at two points in the design space the level of noise appeared to be sufficiently low, when the relative step size is 10-4 for the finite difference calculations, to not influence the convergence if the errors are below 5 per cent for this contraction geometry.

  • 9. Burman, Jörgen
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Mårtensson, H.
    Volvo Aero.
    Development of a blade geometry definition with implicit design variables2000In: AIAA Paper 00-671, American Institute of Aeronautics and Astronautics, AIAA , 2000Conference paper (Refereed)
    Abstract [en]

    This paper presents a method to create 3-dimensional blade geometries defined in terms of stacked profiles where each profile is described by four NURBS curves. The NURBS representations of the profiles are attractive since they can be exchanged with CAD/CAM systems and grid generators. The blade profiles are defined in terms of traditional design variables, e.g. maximum thickness and camber. A numerical optimisation loop is then used to adjust the basic parameters of the NURBS curves until the requested values of the traditional design variables are obtained. Normally the number of traditional design variables is less than the number of NURBS parametersI.t has therefore been necessaryt o define additional constraints that make the shape corresponding to a given set of traditional design variables unique.

  • 10. Burman, Jörgen
    et al.
    Papila, Nilay
    Shyy, Wei
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Assessment of response surface-based optimization techniques unsteady flow around bluff bodies2002In: A collection of technical papers: 9th AIAA/ISSMO Symposium on Multidisciplinary Analysis and Optimization : Atlanta, Georgia, 4 - 6 September 2002, Reston, Va.: American Institute of Aeronautics and Astronautics, AIAA , 2002Conference paper (Refereed)
    Abstract [en]

    The shape of a trapezoidal obstacle immersed in a 2D unsteady, viscous flow is optimized by response surface (RS) techniques based on combined criteria of minimum total drag and maximum mixing efficacy. Time-dependent Navier-Stokes computations are conducted to supply the database. In order to address the issues related to noise, an outlier analysis based on iteratively re-weighted least square (IRLS) method is applied. The results indicate that optimum designs having a low mean drag coefficient tend to be square-shaped, while designs having a large value of the mixing effectiveness are more trapezoidally-shaped. Both RS and IRLS models yield consistent designs, indicating that the present task is well handled by the techniques employed. In addition, the RS methodology is used to identify domains within the design space within which all designs are, for practical purpose, acceptable.

  • 11.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grönberg, Carola
    Energy Technology Centre, Piteå.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Risberg, Mikael
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Spatially resolved measurements of gas composition in a pressurised black liquor gasifier2009In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 28, no 3, p. 316-323Article in journal (Refereed)
    Abstract [en]

    Black liquor gasification is a new process for recovery of energy and chemicals in black liquor from the Kraft pulping process. The process can be combined with catalytic conversion of syngas into motor fuels. The potential for motor fuel production from black liquor in Sweden is to replace about 25% of the current consumption of gasoline and diesel. For Finland the figure is even higher while for Canada it is about 14% and for the USA about 2%.

  • 12.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Iisa, Kristiina
    National Renewable Energy Laboratory.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Computational fluid dynamics simulations of raw gas composition from a black liquor gasifier: comparison with experiments2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 9, p. 4122-4128Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained flow high temperature black liquor gasification can be used as a complement or a substitute to the Tomlinson boiler used in the chemical recovery process at kraft pulp mills. The technology has been proven on the development scale, but there are still no full scale plants. This work is intended to aid in the development by providing computational tools that can be used in scale up of the existing technology. In this work, an existing computational fluid dynamics (CFD) model describing the gasification reactor is refined. First, one-dimensional (1D) plug flow reactor calculations with a comprehensive reaction mechanism are performed to judge the validity of the global homogeneous reaction mechanism used in the CFD simulations in the temperature range considered. On the basis of the results from the comparison, an extinction temperature modification of the steam-methane reforming reaction was introduced in the CFD model. An extinction temperature of 1400 K was determined to give the best overall agreement between the two models. Next, the results from simulations of the flow in a 3 MW pilot gasifier with the updated CFD model are compared to experimental results in which pressure, oxygen to black liquor equivalence ratio, and residence time have been varied. The results show that the updated CFD model can predict the main gas components (H2, CO, CO2) within an absolute error of 2.5 mol %. CH4 can be predicted within an absolute error of 1 mol %, and most of the trends when process conditions are varied are captured by the model.

  • 13.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Iisa, Kristiina
    National Renewable Energy Laboratory, Golden, Colorado.
    High-speed imaging of biomass particles heated with a laser2013In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 103, p. 278-286Article in journal (Refereed)
    Abstract [en]

    In this work two types of lignocellulosic biomass particles, European spruce and American hardwood (particle sizes from 100 μm to 500 μm) were pyrolysed with a continuous wave 2 W Nd:YAG laser. Simultaneously a high-speed camera was used to capture the behavior of the biomass particle as it was heated for about 0.1 s. Cover glasses were used as a sample holder which allowed for light microscope studies after the heating. Since the cover glasses are not initially heated by the laser, vapors from the biomass particle are quenched on the glass within about 1 particle diameter from the initial particle. Image processing was used to track the contour of the biomass particle and the enclosed area of the contour was calculated for each frame.The main observations are: There is a significant difference between how much surface energy is needed to pyrolyses the spruce (about 75% more) compared to the hardwood. The oil-like substance which appeared on the glass during the experiment is solid at room temperature and shows different levels of transparency. A fraction of this substance is water soluble. A brownish coat is seen on the unreacted biomass. The biomass showed insignificant swelling as it was heated. The biomass particle appears to melt and boil at the front that is formed between the laser beam and the biomass particle. The part of the particle that is not subjected to the laser beam seems to be unaffected.

  • 14.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Furusjö, Erik
    Chemrec.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Black liquor gasification: CFD model predictions compared with measurements2010In: 2010 International Chemical Recovery Conference Proceedings, Norcross, GA: TAPPI Press, 2010, Vol. 2, p. 160-171Conference paper (Refereed)
  • 15.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Furusjö, Erik
    Chemrec.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Experiments and mathematical models of black liquor gasification: influence of minor gas components on temperature, gas composition, and fixed carbon conversion2010In: TAPPI Journal, ISSN 0734-1415, Vol. 9, no 9, p. 15-24Article in journal (Refereed)
    Abstract [en]

    In this work, predictions from a reacting Computational Fluid Dynamics (CFD) model of a gasification reactor are compared to experimentally obtained data from an industrial pressurized black liquor gasification plant. The data consists of gas samples taken from the hot part of the gasification reactor using a water cooled sampling probe. During the considered experimental campaign, the oxygen-to-black liquor equivalence ratio (λ) was varied in three increments, which resulted in a change in reactor temperature and gas composition. The presented numerical study consists of CFD and thermodynamic equilibrium calculations in the considered λ-range using boundary conditions obtained from the experimental campaign. Specifically, the influence of methane concentration on the gas composition is evaluated using both CFD and thermodynamic equilibrium. The results show that the main gas components (H2, CO, CO2) can be predicted within a relative error of 5% using CFD if the modeled release of H2S and CH4 are specified a priori. In addition, the calculations also show that the methane concentration has large influence on the reactor outlet temperature and final carbon conversion.

  • 16.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Comparison and validation of gas phase reaction schemes for black liquor gasification modeling2008In: Conference Proceedings 2008 AiChE annual meeting: Advances in gasification research, 2008Conference paper (Other academic)
    Abstract [en]

    Pressurized Entrained-flow High Temperature Black Liquor Gasification (PEHT-BLG) is a potential substitute or complement to the recovery boiler traditionally used for the recovery of chemicals and energy in black liquor in the Kraft pulping process. Black liquor consists of roughly 30 % moisture, 35 % inorganic pulping chemicals and 35 % combustible material (i.e. lignin). The PEHT-BLG technology can give an increase in total energy efficiency of the mill and provide new products with high added value, such as green motor fuels. The main parts of the recovery unit in the process are; a slagging refractory lined entrained-flow gasification reactor, with a gas assisted burner nozzle producing small black liquor droplets, used for direct gasification of the black liquor at about 1000 °C to produce a ‘raw' syngas and a liquid smelt containing mainly Na2CO3 and Na2S; a quench cooler beneath the reactor where the product gas and smelt are separated and the smelt is dissolved in water forming green liquor; a counter current condenser (CCC) that cools the syngas and condenses water vapor and any volatile and tar species that may be present. The heat recovered from the gas condensation is used to generate low/medium pressure steam that can be used in the pulp and paper process. Furthermore, the chemicals in the green liquor are recovered as cooking chemicals in the downstream processing. Due to lack of demonstration of long term operation of the technology, a development (pilot) plant for PEHT-BLG (named DP-1) with a capacity of 20 tones dry solids/24h is in operation by the technology vendor Chemrec AB at the Energy Technology Centre in Piteå, Sweden. An important tool for reduction of the technical risk associated with scale up of new technology is a comprehensive CFD model for the PEHT-BLG reactor. The current model includes drying, pyrolysis, char gasification and smelt formation of black liquor droplets as well as a simplified gas phase reaction mechanism. The current model has been validated against the outlet gas composition after the Counter Current Condenser (CCC). The model predicted a CO / CO2 ratio that was approximately 50% higher compared to the measurements. However, it is possible that the well known water-gas shift reaction is active in the quench and this could explain that the experimentally determined gas composition after the CCC differs from the computational results at the outlet from the hot zone. Recently, in-situ measurements have been performed in the DP-1 reactor and a further validation of the model has been made possible. The measurements have been performed by sampling gas with a water-cooled suction probe from the lower part of the hot zone, followed by offline gas analyses. The present paper investigates the difference between the current CFD-model and a modified version with an additional CO + O2 reaction added to the simplified gas phase reaction scheme. The simulation results are compared against measurements obtained by the gas sampling probe in the DP-1 reactor. The results suggest that by implementing the additional CO + O2 reaction local flame temperature was increased significantly. However, the effect on volume average and outlet gas temperature was minimal.The results also showed that the CO + O2 reaction had very little effect on outlet gas composition when the reaction was implemented in the PEHT-BLG-CFD model

  • 17. Carlsson, Per
    et al.
    Wiinikka, Henrik
    Energy Technology Centre, Piteå.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Grönberg, Carola
    Energy Technology Centre, Piteå.
    Pettersson, Esbjörn
    Energy Technology Centre, Piteå.
    Lidman, Marcus
    Energy Technology Centre, Piteå.
    Gebart, Rikard
    Energy Technology Centre, Piteå.
    Experimental investigation of an industrial scale black liquor gasifier: 1. Influence of reactor operation parameters on product gas composition2010In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 89, no 12, p. 4025-4034Article in journal (Refereed)
    Abstract [en]

    A novel technology to mitigate the climate changes and improve energy security is Pressurized Entrained flow High Temperature Black Liquor Gasification (PEHT-BLG) in combination with an efficient fuel synthesis using the resulting syngas. In order to optimise the technology for use in a pulp and paper mill based biorefinery, it is of great importance to understand how the operational parameters of the gasifier affect the product gas composition. The present paper is based on experiments where gas samples were withdrawn from the hot part of a 3 MW entrained flow pressurized black liquor gasifier of semi industrial scale using a high temperature gas sampling system. Specifically, the influence of process conditions on product gas composition (CO2, CO, H2, CH4, H2S, and COS) were examined by systematically varying the operational parameters: system pressure, oxygen to black liquor equivalence ratio, black liquor flow rate to pressure ratio and black liquor pre-heat temperature. Due to the harsh environment inside the gasification reactor, gas sampling is a challenging task. However, for the purpose of the current study, a specially designed high temperature gas sampling system was successfully developed and used. The results, obtained from two separate experimental campaigns, show that all of the investigated operational parameters have a significant influence on the product gas composition and present valuable information about to the process characteristics.

  • 18.
    Engström, T. Fredrik
    et al.
    Luleå tekniska universitet.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gyroscopic design of swirling flow diffusers1999In: Proceedings of ASME/JSME FEDSM'99: ASME/JSME Fluids Engineering Division Summer Meeting, American Society of Mechanical Engineers , 1999Conference paper (Refereed)
    Abstract [en]

    The flow in the draft tube of a hydro power plant is often swirling when the turbine is operating outside its best efficiency point. The swirl gives rise to gyroscopic effects when the flow is forced through the bend in the draft tube. The resulting complex flow field causes losses.The idea in this paper is to investigate the possibility of using a simple model to calculate a new geometry of the draft tube that avoids distortion of the vortex core. Simulations are carried out using the CFD code CFX. A Reynolds stress model, with wall functions, is used to model turbulence.A loss factor is calculated and it was found that the new design draft tube shows approximately the same loss as a non-modified draft tube. The explanation to the somewhat surprising result is that the flow through and after the bend is dominated by the centrifugal effects from streamline curvature. It is therefore concluded that the most important loss mechanism appears to be triggered by streamline curvature.

  • 19.
    Furusjö, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirtania, Kawnish
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Jafri, Yawer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Oller, Albert Bach
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundgren, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wetterlund, Elisabeth
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Landälv, Ingvar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Pettersson, Esbjörn
    SP ETC.
    Co-gasification of pyrolysis oil and black liquor - a new track for production of chemicals and transportation fuels from biomass2015Conference paper (Refereed)
    Abstract [en]

    Pressurized oxygen-blown entrained flow black liquor (BL) gasification, the Chemrec technology, has been demonstrated in a 3 MWth pilot plant in Piteå, Sweden for more than 25,000 h. The plant is owned and operated by Luleå University of Technology since 2013. It is well known that catalytic activity of alkali metals is important for the high reactivity of black liquor, which leads to a highly efficient BL gasification process. The globally available volume of BL is however limited and strongly connected to pulp production. By co-gasifying pyrolysis oil (PO) with BL it is possible to utilize the catalytic activity also for PO conversion to syngas. Adding PO leads to larger feedstock flexibility with the possibility of building larger biofuels plants based on BL gasification technology. This presentation summarizes new results from research activities aimed at developing and assessing the PO/BL co-gasification process. Results from laboratory experiments with PO/BL mixtures show that pyrolysis behavior and char gasification reactivity are similar to pure BL. This means that the decrease in the alkali metal concentration due to the addition of PO in the mixture does not decrease the reactivity. Pure PO is much less reactive. Mixing tests show that the fraction of PO that can be mixed into BL is limited by lignin precipitation as a consequence of PO acidity. Pilot scale PO/BL co-gasification experiments have been executed following design and construction of a new feeding system to allow co-feeding of PO with BL. The results confirm the conclusions from the lab scale study and prove that the co-gasification concept is practically applicable. Process performance of the pilot scale co-gasification process is similar to gasification of BL only with high carbon conversion and clean syngas generation. This indicates that the established BL gasification technology can be used for co-gasification of PO and BL without major modifications.

  • 20.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Analysis of heat transfer and fluid flow in the resin transfer moulding process1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis contains an analysis of fluid flow and heat transfer problems in the resin transfer moulding (RTM) process for manufacturing of polymer based fibre composites and it consists of five separate papers. The permeability of unidirectional fabrics, that are often used in advanced composites, is considered in Paper A and a theory for the permeability dependence on the micro geometry is developed. The theory is based on lubrication theory for narrow gaps which is motivated by the fact that most of the flow resistance comes from a small region where the fibres are closest to each other. Despite this limitation the results agree excellently with numerical results. 'Me best performance of the theory is expected at high fibre volume fractions (Vf) but the dependence on Vf is surprisingly good even at as low values as 0.3. Although the theory is formulated for an idealised geometry it can be used to predict the variation of the anisotropic permeability tensor with fibre volume fraction in real fabrics after fitting of three model parameters. Paper B is a study of the influence from different process parameters on the void content in the laminate. The void content is shown to be reduced strongly by an applied vacuum during mould filling. The main mechanism for void formation appears to be mechanical entrapment at the flow front. The voids are convected by the flow so that their concentration is highest close to the flow front. Microscopy investigation of the bubbles show that they are of two basic types, large spherical bubbles in the interstices between fibre bundles and smaller cylindrical bubbles inside the fibre bundles. The positive influence of vacuum compared to no vacuum can be explained as a combined effect of an increased mobility due to larger volume changes during mould filling and compression by the increased pressure during cure. In Paper C a comparison is made between the mould filling times for different injection strategies. The possible alternatives for a normal laminate are point injection, edge injection and peripheral injection. Theoretical results are derived that can be used to estimate the mould filling time with the different alternatives. In addition, fundamental theoretical results are derived from the governing equations showing the scaling of the mould filling time with the process parameters. This analysis also shows that the flow front motion during mould filling is only a function of the anisotropy of the reinforcement and the location of the gates. Paper D presents an analysis of the non-uniform flow at the flow front during impregnation of a stack of fabrics consisting of layers with different flow resistance. A detailed derivation of the theory and an analytical solution to the equations are presented in an addendum to Paper D. The theoretical model is compared with experimental results and is found to describe the experiment qualitatively well. The resulting permeability of a stack of different fabrics is derived from the basic equations and is found to be a weighted average of the permeability in the individual layers. This result is compared with experiments with different stacking sequences and it is found that the stacking sequence has no influence on the resulting permeability as expected from the theory. Experimental results in excellent agreement with Darcy's law are also presented for the case with radial flow and with unidirectional flow. Finally, Paper E is a theoretical study of the curing behaviour of thick laminates. A general solution independent of the cure kinetic model is derived. The solution is valid for low exothermal peak temperatures and it is characterised by two dimensionless numbers. The first parameter is the ratio between the time scales for the reaction and for heat conduction, the second parameter is the ratio between the processing temperature and the adiabatic temperature rise. The general solution is specialised to a second order autocatalytic cure model so that the results can be compared to numerical results. The agreement between the numerical and the analytical solution is excellent for small exothermal peak temperatures, as expected. The particular model used also serves as an example of the additional dimensionless parameters that are introduced by a specific kinetic model.

  • 21. Gebart, Rikard
    Critical parameters for heat transfer and chemical reactions in thermosetting materials1994In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 51, no 1, p. 153-168Article in journal (Refereed)
    Abstract [en]

    The equations of one-dimensional heat transfer with chemical reactions with isothermal initial conditions and constant wall temperature are solved approximately for all types of kinetic models. The general solution is valid for low exothermal peaks and it is characterized explicitly by two dimensionless parameters. The first parameter is the ratio between the time scale for heat conduction and that for the chemical reaction; the second parameter is the ratio between the processing temperature and the adiabatic temperature rise. The number of additional parameters depends on the particular choice of kinetic model. The maximum temperature in the solution always occur at the center line and its magnitude is proportional to the maximum rate of reaction. For a second-order autocatalytic kinetic model, closed form results can be obtained. The solution is in this case characterized by two additional dimensionless parameters. The analytical solution agrees excellently with numerical solutions for small exothermal temperature peaks (< 10% of the adiabatic temperature rise), but the qualitative agreement is very good also for cases with significant exothermal peaks. The general solution can be used also for the case when the kinetic model is unknown and only experimental DSC results are available.

  • 22. Gebart, Rikard
    Permeability of unidirectional reinforcements for RTM1992In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 26, no 6, p. 1100-1133Article in journal (Refereed)
    Abstract [en]

    The permeability of an idealized unidirectional reinforcement consisting of regularly ordered, parallel fibres is derived starting from first principles (Navier-Stokes equations) both for flow along and for flow perpendicular to the fibres. First, an approximate analytical solution for transverse flow is derived which differs from the Kozeny-Carman equation for the permeability of a porous medium in that the transverse flow stops when the maximum fibre volume fraction is reached. The solution for flow along the fibres has the same form as the Kozeny-Carman equation. A comparison shows excellent agreement between a numerical solution of the full flow equations and the approximate one at medium to high fibre volume fractions (Vf > 0.35). The theoretical predictions of permeability were tested in a specially designed mould. The results from the experiments with an unsaturated polyester resin (Jotun PO-2454) and the unidirectional reinforcement did in all cases show excellent agreement with results predicted by Darcy's law (the square of the flow front position increases linearly with time if the injection pressure is kept constant). The theoretical model could be fitted to the experimental data both for flow along the fibres and for cross flow based on data for flow along the fibres only. The fitting is obtained by adjusting one parameter in the model, the effective fibre radius, to a value about four times larger than the real fibre radius (15 μm). Scanning electron microscopy shows that the fibres are arranged in bundles looking like cylinders with ellipsoidal cross section which may be the explanation for the effective fibre radius in the fitted model equation being larger than the real fibre radius.

  • 23.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The importance of mechanics in black liquor gasification2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 61-Conference paper (Other academic)
  • 24.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gustavsson, HåkanLuleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.Karlsson, Rolf
    Proceedings of Turbine-99: workshop on draft tube flow2000Collection (editor) (Other academic)
    Abstract [en]

    The Turbine 99 workshop, held in Porjus, Sweden, 20-23 June 1999, was organized to determine the state-of-the-art of CFD simulations of draft tube flows. A total of 16 groups accepted the invitation to compute the draft tube flow. The following experimental data was available before the workshop: the axial and swirl velocity components at the inlet (with rms-values and one Reynolds' stress component) and the pressure distribution around the outlet cross section. Before the workshop, the groups submitted simulation results (using 12 different CFD codes) which were compiled by the organizers to an extensive set of data available at the workshop. The experimental data for the pressure recovery factor, pressure distributions along the draft tube walls and the detailed velocity field in one downstream cross section was presented during the workshop. In this report a summary of the main results and conclusions of the workshop is given, together with the written reports from the experiments and the simulations. In addition, the report contains all relevant background information for the workshop such as the draft tube geometry, provided data, requested information etc. and is thus the main document from the workshop. As the simulations provided more data than was available for comparison with the experiments, the simulation results will be available in a separate document provided by the organizers. One major conclusion of the workshop is that much attention must (still) be payed to the grid quality and the boundary conditions, factors that need to be strictly specified before a fully relevant comparison can be made between different flow models.

  • 25. Gebart, Rikard
    et al.
    Lidström, Peder
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Measurement of in-plane permeability of anisotropic fiber reinforcements1996In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 17, no 1, p. 43-51Article in journal (Refereed)
    Abstract [en]

    Three of the most common methods (two with parallel flow and one with radial flow) for determination of the in-plane permeability tensor are studied both theoretically and experimentally. An error analysis shows that the difference between the methods is negligible if the error levels are equal. However, the radial flow method is found to be susceptible to large errors from mold deflection in an experimental comparison between the methods. Additional experiments with the radial flow method in a stiffer mold show that the method gives the same values for the permeability tensor as the other two methods. A new method with multiple cavities in parallel is proposed that combines the simplicity of the radial flow method with the stiff mold of the parallel flow method. Only mass and time need to be measured in one experiment and it eliminates the need to measure fluid viscosity, temperature, and injection pressure. The method depends on the availability of a reference material with known permeability.

  • 26.
    Gebart, Rikard
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Lundström, Staffan
    Influence on the permeability of unidirectional reinforcement from fibre geometry1991In: The polymer processing society: european regional meeting , final program and abstracts, Palermo-Italy September 15-18/1991, 1991Conference paper (Other academic)
  • 27.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sandlund, Erik
    In-plane permeability measurements on fiber reinforcements by the multi-cavity parallel flow technique1999In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 20, no 1, p. 146-154Article in journal (Refereed)
    Abstract [en]

    This report discusses the advantages and drawbacks of the multi-cavity parallel flow technique for permeability measurements. An experimental series with repeated measurements on material from the same roll shows that the repeatability of the technique is very good considering the manufacturing variability of the fabric. The measured standard deviation in the repeatability study is about 10%. It is, however, shown that the permeability can vary considerably- between reinforcements of similar geometry. Furthermore, computer simulations were used to estimate the errors when highly anisotropic materials are oriented at an angle to the material principal direction in the parallel flow technique. The conclusion based on the simulations is that the length to width ratio of the cavity should be larger than the anisotropy of the reinforcement for an acceptable error.

  • 28.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vahlund, C. Fredrik
    Luleå tekniska universitet.
    Analysis of an image processing method for fiber orientation in polymer composites2001In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 22, no 3, p. 327-336Article in journal (Refereed)
    Abstract [en]

    The errors in fiber orientation distribution measurements of compression molding materials have been investigated, for generated as well as for real distributions. Because of the size of the sample, only a finite number of fibers are visible in a picture leading to a statistical error in the measurement. A method is proposed to express this error as function of the number of visible fibers and the number of subintervals the distribution is divided into. Studies of the error In a Fraunhofer/FT based fiber orientation distribution analysis have been performed, including effects of increasing number of fibers (fiber-fiber intersections) in generated pictures and investigation of the errors in real fiber images. All steps in a fiber orientation distribution analysis of SMC/GMT kind of material are described, including suitable equipment, image enhancement methods and investigation of the errors present in analysis of a real image as well as comparisons to hand-measured data.

  • 29.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vahlund, C.F.
    Squeeze flow rheology in large tools1999In: Fifth International Conference on Flow Processes in Composite Materials: Proceedings, University of Plymouth Press, 1999, p. 365-372Conference paper (Refereed)
  • 30.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marklund, M.
    Energy Technology Centre, Piteå.
    Carlsson, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grönberg, C.
    Weiland, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Johansson, A-C
    Öhrman, Olov
    Recent advances in the understanding of pressurized black liquor gasification2011In: Cellulose Chemistry and Technology, ISSN 0576-9787, Vol. 45, no 7-8, p. 521-526Article in journal (Refereed)
  • 31.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Energy Technology Centre, Piteå.
    Pettersson, Esbjörn
    Energy Technology Centre, Piteå.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Carlsson, Per
    Energy Technology Centre, Piteå.
    Turning a pulp mill into a biorefinery: A possible outcome from the 2nd black liquor gasification program2008In: NWBC 2008: 2008 Nordic Wood Biorefinery conference : 11-14 March, 2008 : City Conference Centre, Stockholm, Sweden, Stockholm: STFI-Packforsk AB , 2008, p. 56-61Conference paper (Refereed)
  • 32.
    Grip, Carl-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Sandström, Erik
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Karlsson, Jonny
    Industrial ecology in northern areas: practical experience and development2010Conference paper (Refereed)
    Abstract [en]

    The possibilities to develop the industrial ecology in the northern regions of Europe are influenced by some common characteristics, e.g.: The regions are rich in natural re-sources and energy- and material intensive base industries. These industries cover sev-eral branches, e.g., Mining, Iron and Steel, Metal production, Pulp and Paper. Low popu-lation density and relatively long distances to the main customers are difficulties espe-cially for transport and use of rest products. District heating with waste heat from the in-dustries is an important part of the energy system that reduces the emission of green-house gases and improves the overall energy efficiency. The problems and possibilities connected to the industrial ecology are described for two examples, the energy system in Luleå and the Solander science park in Piteå

  • 33. Göktepe, Burak
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Fernandes, Edgar
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Leitão, Noel
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Leitão, Ivo
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Merícia, Janaína Gomes de
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Simultaneous pressure and heat release measurements in a 150kW wood powder burner2010Conference paper (Other academic)
  • 34. Göktepe, Burak
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Leitao, Noel
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Fernandesc, Edgar
    Instituto Superior Técnico, Dpartment of Mechanical Engineering/Center IN.
    Visualization of the reactive swirling flows in a 150 KW wood powder burner2010Conference paper (Other academic)
  • 35.
    Göktepe, Burak
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hazim, Ammar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cold flow experiments in an entrained flow gasification reactor with a swirl-stabilized pulverized biofuel burner2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 85, p. 267-277Article in journal (Refereed)
    Abstract [en]

    Short particle residence time in entrained flow gasifiers demands the use of pulverized fuel particles to promote mass and heat transfer, resulting high fuel conversion rate. The pulverized biomass particles have a wide range of aspect ratios which can exhibit different dispersion behavior than that of spherical particles in hot product gas flows. This results in spatial and temporal variations in temperature distribution, the composition and the concentration of syngas and soot yield. One way to control the particle dispersion is to impart a swirling motion to the carrier gas phase. This paper investigates the dispersion behavior of biomass fuel particles in swirling flows. A two-phase particle image velocimetry technique was applied to simultaneously measure particle and gas phase velocities in turbulent isothermal flows. Post-processed PIV images showed that a poly-dispersed behavior of biomass particles with a range of particle size of 112-160 μm imposed a significant impact on the air flow pattern, causing air flow decelerated in a region of high particle concentration. Moreover, the velocity field, obtained from individually tracked biomass particles showed that the swirling motion of the carrier air flow gives arise a rapid spreading of the particles

  • 36.
    Göktepe, Burak
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Does distance among biomass particles affect soot formation in an entrained flow gasification process?2016In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 141, no 1, p. 99-105Article in journal (Refereed)
    Abstract [en]

    Soot creates technical challenges in entrained flow biomass gasification processes, e.g. clogging of flow passages, fouling on system components and reduced efficiency of gasification. This paper demonstrates a novel soot reduction method in a laboratory-scale entrained flow reactor by forced dispersion of biomass particles. Gasification of small biomass particles was done in a flat flame burner where a steady stream of biomass was sent. The flat flame burner was operated with a premixed sub-stoichiometric methane–air flame to simulate the conditions in an entrained flow gasifier. The dispersion of biomass particles was enhanced by varying the flow velocity ratio between particle carrier gas and the premixed flame. Primary soot particles evolved with the distance from the burner exit and the soot volume fraction was found to have a peak at a certain location. Enhanced particle separation diminished the peaks in the soot volume fraction by 35–56% depending on the particle feeding rates. The soot volume fraction was found to decrease towards an asymptotic value with increasing inter-particle distance.

  • 37.
    Göktepe, Burak
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hazim, Ammar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Soot reduction in an entrained flow gasifier of biomass by active dispersion of fuel particles2017In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 201, p. 111-117Article in journal (Refereed)
    Abstract [en]

    Soot is an undesired by-product of entrained flow biomass gasification since it has a detrimental effect on operation of the gasifier, e.g. clogging of flow passages and system components and reduction of efficiency. This study investigated how active flow manipulation by adding synthetic jet (i.e. oscillating flow through orifice) in feeding line affects dispersion of fuel particles and soot formation. Pine sawdust was gasified at the conditions similar to pulverized burner flame, where a flat flame of methane-air sub-stoichiometric mixture supported ignition of fuel particles. A synthetic jet flow was supplied by an actuator assembly and was directed perpendicular to a vertical tube leading to the center of the flat flame burner through which pine sawdust with a size range of 63–112 μm were fed into a reactor. Quartz filter sampling and the laser extinction methods were employed to measure total soot yield and soot volume fraction, respectively. The synthetic jet actuator modulated the dispersion of the pine sawdust and broke up particle aggregates in both hot and cold gas flows through generation of large scale vortex structures in the flow. The soot yield significantly reduced from 1.52 wt.% to 0.3 wt.% when synthetic jet actuator was applied. The results indicated that the current method suppressed inception of young soot particles. The method has high potential because soot can be reduced without changing major operation parameters.

  • 38.
    Hammami, A.
    et al.
    U. A. E. University, Al-Ain.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Analysis of the vacuum infusion molding process2000In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 21, no 1, p. 28-40Article in journal (Refereed)
    Abstract [en]

    The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1-D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part.

  • 39.
    Hammami, A.
    et al.
    Swedish Institute of Composites, Piteå.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Model for vacuum infusion moulding process1998In: Plastics, rubber and composites processing and applications, ISSN 0959-8111, E-ISSN 1876-4681, Vol. 27, no 4, p. 185-189Article in journal (Refereed)
    Abstract [en]

    The vacuum infusion moulding process is becoming increasingly popular for large surface area components. The reasons for this interest are the obvious environmental advantages of the process and also the economic benefits that can be obtained. The modelling of the process remains poorly developed and hence optimisation of the process is difficult. Existing models for resin transfer moulding can not be applied since the flexible vacuum bag and the varying pressure inside the mould cavity creates a varying cavity thickness during impregnation. A useful simulation model must incorporate this phenomenon. In the present work a one-dimensional model for the vacuum infusion moulding process has been described. This model was derived assuming that an elastic equilibrium holds in the mould cavity during mould filling. The constitutive model describing the compressive behaviour of the reinforcement is a simple power law model while the permeability is modelled with the Kozeny-Carman equation. Both models are fitted to experimental data from independent experiments. Agreement between the simulation model results and experiments with vacuum infusion of a flat plate is very good. However, it is concluded that additional work is required both on the numerical model and on constitutive modelling of the compression behaviour of the fabric

  • 40.
    Hazim, Ammar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Göktepe, Burak
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Active fuel particles dispersion by synthetic jet in an entrained flow gasifier of biomass: Cold flow2016In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 302, p. 275-282Article in journal (Refereed)
    Abstract [en]

    Pulverized fuel (PF) burners play a key role for the performance of PF fired gasification and combustion plants, by minimizing pollutant emission, fuel consumption and hence fuel costs. However, fuel diversity in power generation plants imposes limitations on the performance of existing PF burners, especially when burning solid fuel particles with poor flowability like biomass sawdust. In the present study, a vertically downward laminar flow was laden with biomass particles at different particle mass loading ratios, ranging from 0.47 to 2.67. The particle laden flow was forced by a synthetic jet actuator over a range of forcing amplitudes, 0.35–1.1 kPa. Pulverized pine particles with a sieve size range of 63–112 μm were used as biomass feedstock. Two-phase particle image velocimetry was applied to measure the velocity of the particles and air flow at the same time. The results showed that the synthetic jet had a large influence on the flow fields of both air and powdered pine particles, via a convective effect induced by vortex rings that propagate in the flow direction. The particle velocity, particle dispersion and hence inter-particle distance increased with increasing forcing amplitude. Moreover, particles accumulated within a specific region of the flow, based on their size. The effect on particle dispersion was more pronounced in the forced flows with low mass loading ratios

  • 41.
    Häggström, Caroline
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öhrman, Olov
    Rownaghi, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Catalytic methanol synthesis via black liquor gasification2012In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 94, no 1, p. 10-15Article in journal (Refereed)
    Abstract [en]

    Biofuel production from gasified black liquor is an interesting route to decrease green house gas emissions. The only pressurised black liquor gasifier currently in pilot operation is located in Sweden. In this work, synthesis gas was taken online directly from this gasifier, purified from hydrocarbons and sulphur compounds and for the first time catalytically converted to methanol in a bench scale equipment. Methanol was successfully synthesised during 45 h in total and the space time yield of methanol produced at 25 bar pressure was 0.16–0.19 g methanol/(g catalyst h). The spent catalyst exposed to gas from the gasifier was slightly enriched in calcium and sodium at the inlet of the reactor and in boron and nickel at the outlet of the reactor. Calcium, sodium and boron likely stem from black liquor whereas nickel probably originates from the stainless steel in the equipment. A slight deactivation, reduced surface area and mesoporosity of the catalyst exposed to gas from the gasifier were observed but it was not possible to reveal the origin of the deactivation. In addition to water, the produced methanol contained traces of hydrocarbons up to C4, ethanol and dimethyl ether.

  • 42.
    Jafari, Pantea Hadi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    On the Influence from Turbulence Modeling on Particle Suspension Flow in Cyclone Gasifiers2014Conference paper (Refereed)
    Abstract [en]

    Air-blown cyclone gasification is an entrained flow gasification process in which biomass powder fuel is burnt in a gasifier that operates similarly to a cyclone separator. Cyclone separators are widely used in industry to separate a dispersed solid phase (e.g. particles) from a continuous flow of gas based on density differences. Due to its simple design, the cyclone is a reliable apparatus with low cost for manufacture and maintenance.The performance of an isothermal cyclone separator can be predicted satisfactorily with the model developed by Muschelknautz et al. However, the flow in a non-isothermal cyclone gasifier has additional complexities, e.g. the production of gas from the fuel particles, that are outside the scope of the Muschelknautz model. In order to incorporate these effects more advanced modeling based on Computational Fluid Dynamics is needed. One problem with the CFD approach in combination with turbulent heat transfer and chemical reactions is that the complexity of the global model makes it difficult to assess the accuracy of the sub-models. Recently published models are based on relatively simple eddy-viscosity turbulence models. The agreement between these models and experiments has been encouraging but one cannot rule out the possibility that the apparently good performance of the model is a lucky coincidence due to cancellation of errors in the different sub models.The present paper is focusing on the fluid dynamics modeling of the flow in a cyclone gasifier in order to develop a better foundation for continued modeling. Since simulation of dispersed phase behavior is based on a precise modeling of the continuous phase flow field, it is valuable to assess different numerical approaches to find the most promising one for simulating the turbulent gas phase flow. Due to the complexity of turbulent swirling flow in a cyclone gasifier, a careful selection of turbulence models is needed to fulfill accurate numerical calculations of flow parameters. Two families of turbulence models are supposed to be tested: the two-equation eddy viscosity models including k-epsilon and k-omega, and the Reynolds stress model. For the k-epsilon model, steady-state and transient simulations are implemented. The gas cyclone of Obermair et al. with relevant operating conditions was chosen as a benchmark. The simulation results are compared to the Laser Doppler Anemometry (LDA) velocity measurements of the gas cyclone. The simulations are implemented in the commercial CFD (computational fluid dynamics) code ANSYS CFX 14.5; which uses an element-based finite volume approach. The method involves discretization of the spatial domain using a three-dimensional mesh to build up finite volumes over which relevant quantities like mass, momentum, and energy are conserved. In all, the capability of the mentioned approaches for representing the flow field in general and the precessing vortex core and its related fluctuations in particular will be discussed.

  • 43.
    Jafri, Yawer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirtania, Kawnish
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Performance of a Pilot-Scale Entrained-Flow Black Liquor Gasifier2016In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 4, p. 3175-3185Article in journal (Refereed)
    Abstract [en]

    Pilot-scale entrained flow gasification experiments were carried out at the 3 MWth LTU Green Fuels black liquor gasification (BLG) plant, using ∼140 tons of Kraft black liquor (BL) with a dry solids content of ∼72.5%. Comprehensive mass and energy balances were performed to quantify process performance under varying pressure, load, and oxygen/fuel ratio. Carbon conversion efficiency of the BLG process was 98.3%–99.2% and did not vary systematically in response to process changes. The unconverted carbon is almost exclusively present as dissolved organic carbon in the green liquor (GL) stream. GL is an aqueous solution of sodium carbonate and sodium sulfide used to recover the inorganic pulping chemicals present in BL for reuse in the pulp mill. A small fraction of syngas CO is converted to formate ions dissolved in GL through reaction with hydroxide ions. Unconverted carbon present in GL solids is insignificant. Syngas produced is subsequently upgraded to methanol and dimethyl ether (DME) in an integrated fuel synthesis facility. Concentration of H2 in syngas is not significantly affected by operating point changes in the domain investigated, while CO and CO2 concentrations are. Syngas hydrocarbon concentration values are typically in the single-digit parts per million (ppm) with the exception of C6H6, which was present at 16–127 ppm. CH4 is present at 0.5%–1.2%, with lower concentrations at higher temperatures, and shows good correlation with C6H6. A quantity of 24%–27% of BL sulfur ended up in the syngas as 1.5%–1.7% H2S and 64–72 ppm COS. Cold gas efficiencies (CGEs) on a lower heating value (LHV) basis, when including syngas CH4, were 52%–55% and decreased at higher temperature. CGEs on an LHV basis, when considering only H2 and CO with a sulfur-free BL heating value relevant for catalytic syngas upgrading, were 58%–60% and showed the opposite temperature dependence. Good mass and energy balance closures show the figures presented to be reliable. The results obtained from this study demonstrate process stability at varying operating conditions and can be further used for techno-economic analysis and design purposes.

  • 44.
    Jafri, Yawer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kirtania, Kawnish
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Granberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    A study of black liquor and pyrolysis oil co-gasification in pilot scale2018In: Biomass Conversion and Biorefinery, ISSN 2190-6815, E-ISSN 2190-6823, Vol. 8, no 1, p. 113-124Article in journal (Refereed)
    Abstract [en]

    The effect of the blend ratio and reactor temperature on the gasification characteristics of pyrolysis oil (PO) and black liquor (BL) blends with up to 20 wt% PO was studied in a pilot-scale entrained-flow gasifier. In addition to unblended BL, three blends with PO/BL ratios of 10/90, 15/85, and 20/80 wt% were gasified at a constant load of 2.75 MWth. The 15/85 PO/BL blend was used to investigate the effect of temperature in the range 1000–1100 °C. The decrease in fuel inorganic content with increasing PO fraction resulted in more dilute green liquor (GL), and a greater portion of the feedstock carbon ended up in syngas as CO. As a consequence, the cold gas efficiency increased by about 5%-units. Carbon conversion was in the range 98.8–99.5% and did not vary systematically with either fuel composition or temperature. Although the measured reactor temperatures increased slightly with increasing PO fraction, both unblended BL and the 15% PO blend exhibited largely similar behavior in response to temperature variations. The results from this study show that blending BL with the more energy-rich PO can increase the cold gas efficiency and improve the process carbon distribution without adversely affecting either carbon conversion or the general process performance.

  • 45.
    Krispinsson, J.
    et al.
    Luleå tekniska universitet.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Jekabsons, Normunds
    Luleå tekniska universitet.
    Specimen preparation and image analysis of fibre orientation in compression moulded parts1996In: Realising their commercial potential: ECCM-7, Seventh European Conference on Composite Materials, 14 - 16 May 1996, London / [ed] Michael G. Bader, Cambridge: Woodhead Publishing Materials , 1996, p. 253-261Conference paper (Refereed)
  • 46.
    Landälv, Ingvar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marke, Birgitta
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, TVM Green Fuels Operation.
    Granberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, TVM Green Fuels Operation.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Löwnertz, Patrik
    Chemrec AB, Stockholm.
    Öhrman, Olov
    Energy Technology Centre, Piteå.
    Sørensen, Esben Lauge
    Haldor Topsøe A/S, R&D Department.
    Salomonsson, Per
    Volvo Group Trucks Technology, Gothenburg.
    Two years experience of the BioDME project: A complete wood to wheel concept2014In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 33, no 3, p. 744-750Article in journal (Refereed)
    Abstract [en]

    Dimethyl ether (DME), is an excellent diesel fuel that can be produced through gasification from multiple feedstocks. One particularly interesting renewable feedstock is the energy rich by-product from the pulping process called black liquor (BL). The concept of utilizing BL as gasifier feed, converting it via syngas to DME and then compensating the withdrawal of BL energy from the pulp mill by supplying biomass to a conventional combined heat and power plant, is estimated to be one of the most efficient conversion concepts of biomass to a renewable fuel on a well-to-wheel basis. This concept has been demonstrated by the four-year BioDME project, including field tests of DME-fueled heavy-duty trucks that are operated commercially. Up till the summer of 2013 more than 500 tons of BioDME has been produced and distributed to 10 HD trucks, which in total has run more than 1 million km in commercial service

  • 47. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    An evaluation of the mould filling simulation code TIMS1992Report (Other academic)
  • 48. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Effect of perturbation of fibre architecture on permeability inside fibre flows1995In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 29, no 4, p. 424-443Article in journal (Refereed)
    Abstract [en]

    The influence on the permeability inside fibre tows from fibre packing arrangement and non-uniform fibre diameter is investigated. The analysis mainly consider flow transverse to the fibres and is based on the fibre geometry. Perturbations from perfect quadratic and hexagonal arrangements of fibres at constant fibre volume fraction are considered. The importance of microgeometry on permeability is pointed out and it is indicated how to deal with this problem. The analysis shows that the fibre transverse permeability is strongly dependent on the fibre size distribution. When an arrangement of equally sized fibres is continuously changed from quadratic to hexagonal it is furthermore found that the transverse permeability is highest just before the packing gets hexagonal. The analysis is also applied to a simple FORTRAN code to simulate removal of fibers from a quadratic arrangement. The simulations shows that the transverse permeability decreases with increased number of removed fibres under constant fibre volume fraction.

  • 49. Lundström, Staffan
    et al.
    Gebart, Rikard
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Influence from process parameters on void formation in resin transfer molding1994In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 15, no 1, p. 25-33Article in journal (Refereed)
    Abstract [en]

    The influence of different process variables on the void content in resin transfer modling (RTM) has been investigated experimentally. The moldings were made in a flat mold filled by a parallel flow from one edge of the laminate to the other. The viods were found concentrated in a narrow region close to the ventilation side of the laminate. The void volume fraction in this region was almost constant and dropped over a short distance to basically no voids in the rest of the laminate. Micrographs from cross sections in different directions revealed that the voids were of two different types, long cylinderical bubbles inside the fiber bundles. An efficient way of reducing the void content was to use vacuum assistance during mold filling. This technique was benefical both for the magnitude of the void content and for the extent of the void region. The void content with the highest level of vacuum assistance (≈ 1 kPa absolute pressure), was practically negligible. Strong indications for void generation by mechanical entrapment at the flow front was found. The lowering of the void content with vacuum assistance can be interpreted as aresult of compression of voids when the vacuum is released and a higher mobility of voids created at a lower pressure.

  • 50.
    Lundström, Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Void formation in RTM with and without vacuum assistance2002In: Proceedings of the PPS European Regional Meeting, 2002Conference paper (Refereed)
12 1 - 50 of 76
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