Lasse Rosendahl

Hydrothermal liquefaction of Spirulina and Nannochloropsis salina under subcritical and supercritical water conditions

Six hydrothermal liquefaction experiments on Nannochloropsis salina and Spirulina platensis at subcritical and supercritical water conditions (220–375 °C, 20–255 bar) were carried out to explore the feasibility of extracting lipids from wet algae, preserving nutrients in lipid-extracted algae solid residue, and recycling process water for algae cultivation. GC–MS, elemental analyzer, FT-IR, calorimeter and nutrient analysis were used to analyze bio-crude, lipid-extracted algae and water samples produced in the hydrothermal liquefaction process. The highest bio-crude yield of 46% was obtained on N. salina at 350 °C and 175 bar. For S. platensis algae sample, the optimal hydrothermal liquefaction condition appears to be at 310 °C and 115 bar, while the optimal condition for N. salina is at 350 °C and 175 bar. Preliminary data also indicate that a lipid-extracted algae solid residue sample obtained in the hydrothermal liquefaction process contains a high level of proteins.

Numerical Modeling of Thermoelectric Generators With Varing Material Properties in a Circuit Simulator

When a thermoelectric generator (TEG) and its external load circuitry are considered together as a system, the codesign and co-optimization of the electronics and the device are crucial in maximizing the system efficiency. In this paper, an accurate TEG model is proposed and implemented in a SPICE-compatible environment. This model of thermoelectric battery accounts for all temperature-dependent characteristics of the thermoelectric materials to include the nonlinear voltage, current, and electrothermal coupled effects. It is validated with simulation data from the recognized program ANSYS and experimental data from a real thermoelectric device, respectively. Within a common circuit simulator, the model can be easily connected to various electrical models of applied loads to predict and optimize the system performance.

Modelling the motion of cylindrical particles in a nonuniform flow

The models currently used in computational fluid dynamics codes to predict solid fuel combustion rely on a spherical shape assumption. Cylinders and disks represent a much better geometrical approximation to the shape of bio-fuels such as straws and woods chips. A sphere gives an extreme in terms of the volume-to-surface-area ratio, which impacts both motion and reaction of a particle. For a nonspherical particle, an additional lift force becomes important, and generally hydrodynamic forces introduce a torque on the particle as the centre of pressure does not coincide with the centre of mass. Therefore, rotation of a nonspherical particle needs to be considered. This paper derives a model for tracking nonspherical particles in a nonuniform flow field, which is validated by a preliminary experimental study: the calculated results agree well with measurements in both translation and rotation aspects. The model allows to take into account shape details of nonspherical particles so that both the motion and the chemical reaction of particles can be modelled more reasonably. The ultimate goal of such a study is to simulate flow and combustion in biomass-fired furnaces using nonspherical particle tracking model instead of traditional sphere assumption, and thus improve the design of biomass-fired boilers.

Further study of the gas temperature deviation in large-scale tangentially coal-fired boilers☆

Gas temperature deviation in upper furnace is an important but a less reported issue in large-scale tangentially fired boilers, since they endanger largely boilers operation. Simulations are conducted in this paper to study the deviation. Perfect agreement between the simulation results and key boiler design values and available site operation records indicates that the calculations are reliable. Based on the simulations, effect of some factors, including residual airflow swirling at furnace exit, super-heaters panels, coal particle trajectories and their combustion histories, on temperature deviations are studied in details. The most important cause and how it affects the temperature deviation are located. Two new methods, a nose on front-wall and re-arranged super-heater panels, are put forward unprecedentedly to alleviate the deviations.

Co-firing straw with coal in a swirl-stabilized dual-feed burner: modelling and experimental validation.

This paper presents a comprehensive computational fluid dynamics (CFD) modelling study of co-firing wheat straw with coal in a 150kW swirl-stabilized dual-feed burner flow reactor, in which the pulverized straw particles (mean diameter of 451microm) and coal particles (mean diameter of 110.4microm) are independently fed into the burner through two concentric injection tubes, i.e., the centre and annular tubes, respectively. Multiple simulations are performed, using three meshes, two global reaction mechanisms for homogeneous combustion, two turbulent combustion models, and two models for fuel particle conversion. It is found that for pulverized biomass particles of a few hundred microns in diameter the intra-particle heat and mass transfer is a secondary issue at most in their conversion, and the global four-step mechanism of Jones and Lindstedt may be better used in modelling volatiles combustion. The baseline CFD models show a good agreement with the measured maps of main species in the reactor. The straw particles, less affected by the swirling secondary air jet due to the large fuel/air jet momentum and large particle response time, travels in a nearly straight line and penetrate through the oxygen-lean core zone; whilst the coal particles are significantly affected by secondary air jet and swirled into the oxygen-rich outer radius with increased residence time (in average, 8.1s for coal particles vs. 5.2s for straw particles in the 3m high reactor). Therefore, a remarkable difference in the overall burnout of the two fuels is predicted: about 93% for coal char vs. 73% for straw char. As the conclusion, a reliable modelling methodology for pulverized biomass/coal co-firing and some useful co-firing design considerations are suggested.

Using a Multi-Parameter Particle Shape Description to Predict the Motion of Non-Spherical Particle Shapes in Swirling Flow

Abstract A new three-parameter particle shape description is introduced, to replace the standard single parameter (particle diameter) shape description used in the majority of CFD codes. The description is based on the superellipsoid, allowing for three variable parameters: the minor axis, the aspect ratio and the superelliptic exponent. The shape description has been incorporated into an extended modelling framework, which still allows for spheres whilst at the same time also allowing for more complex shapes, such as ellipsoids or cylinders, giving the model large flexibility. As the speed and accuracy of the new model are very similar to existing models of spheres, it represents significant benefits compared to standard models, particularly in engineering applications. The model has been tested on a tubular combustor test rig, and a number of significant parameters compared for various shapes and sizes under the same isothermal flow conditions. These indicate the importance of not taking into account non-sphericity when considering gas–particle systems.

Methods to improve prediction performance of ANN models

Abstract Artificial neural network (ANN) is a powerful tool and applied successfully in numerous fields. But there are still two limitations on its use. One is over-training, which occurs when the capacity of the ANN for training is too great because it is allowed too many training iterations. The other is that ANNs are not effective for extrapolation, which is sometimes very important because the existing data used to train an ANN do not necessarily cover the entire range. The two limitations degrade seriously the prediction performance of ANN models. In this paper, two practices are introduced to alleviate or overcome the negative effect of the limitations. Demonstrations based on these practices indicate that they are general and useful practices and can improve greatly the prediction performance of the resulting ANN models to make them really suitable for engineering applications.

Irreversible transfer processes of thermoelectric generators

We discuss a novel tool based on heat flow diagrams for analyzing irreversible processes associated with thermoelectric devices and discuss some ambiguous descriptions and errors in related investigations. We consider thermoelectric generators as a paradigm of a heat engine cycle and determine the heat flow distribution by treating the one-dimensional heat transfer differential equation. Representative heat flow diagrams are used to study the influence of internal and external irreversible processes of heat conduction and Joule heat generation.

Biomass Combustion Science, Technology and Engineering

Part 1 Introduction, supply chains and feedstock: Biomass combustion for power generation: An introduction Biomass supply chains Biomass feedstocks: Categorisation and preparation for combustion and gasification. Part 2 Biomass combustion and co-firing: Direct combustion of biomass Biomass co-firing Biomass gasification Fast pyrolysis of biomass for the production of liquids Intermediate pyrolysis of biomass. Part 3 Large-scale biomass combustion and biorefineries: Large-scale biomass combustion plants: an overview Industrial-scale biomass combustion plants: Engineering issues and operation Biorefineries: increased value from biomass conversion.

Conceptual design of an integrated hydrothermal liquefaction and biogas plant for sustainable bioenergy production.

Initial process studies carried out in Aspen Plus on an integrated thermochemical conversion process are presented herein. In the simulations, a hydrothermal liquefaction (HTL) plant is combined with a biogas plant (BP), such that the digestate from the BP is converted to a biocrude in the HTL process. This biorefinery concept offers a sophisticated and sustainable way of converting organic residuals into a range of high-value biofuel streams in addition to combined heat and power (CHP) production. The primary goal of this study is to provide an initial estimate of the feasibility of such a process. By adding a diesel-quality-fuel output to the process, the product value is increased significantly compared to a conventional BP. An input of 1000 kg h(-1) manure delivers approximately 30-38 kg h(-1) fuel and 38-61 kg h(-1) biogas. The biogas can be used to upgrade the biocrude, to supply the gas grid or for CHP. An estimated 62-84% of the biomass energy can be recovered in the biofuels.