Michael Modigell

Lab-scale bioreactor integrated with active membrane system for hydrogen production: experience and prospects

Abstract The development of new, low-energy consuming and clean technologies can include the utilization of organic wastes with the production of high-quality fuel gases (methane, hydrogen). This paper presents the results of organic wastes’ bioconversion into hydrogen and of the respective H 2 /CO 2 gas mixtures’ separation by using active membrane systems (membrane contactors) with moving liquid carriers. Rhodobacter capsulatus was used for lactate or low organic decomposition to H 2 -containing gas mixture and Thermohydrogenium kirishi was used for hydrogen production from glucose. Active membrane system was used for the separation of H 2 /CO 2 gas mixtures with the production of high-purity hydrogen. The possibility of integration of gas separating membrane systems with aerobic or anaerobic bioreactors are considered as well.

OXYCOAL-AC: Towards an integrated coal-fired power plant process with ion transport membrane-based oxygen supply

The cooperative project OXYCOAL-AC aims at the development of a zero-CO2-emission coal combustion process for power generation. The scope of the research comprises a multitude of aspects. This article focuses on membrane-based air separation modules and their design for oxycoal conditions, the specifics of coal combustion in a CO2/O2 atmosphere including related burner design as well as the cleaning of hot flue gas from oxycoal combustion.

Flow behaviour of semi-solid metal alloys

Abstract Semi-solid metal alloys, as used in industrial thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. It was analysed how the microstructure develops in dependence of the shear rate and cooling rate during the solidification and it was observed that the average particle size increased with increasing shear rate and decreasing cooling rate. In order to account for those phenomena, the rate of crystal growth and the relationship between average particle diameter and viscosity was modelled by applying the Sherwood two-film model for the mass transport. The dependence of the viscosity from the particle size were modelled with a modified Krieger–Dougherty model. Based on the rheological and microstructural observations an evaluation method was elaborated that allows for the construction of objective master curves that are independent of the particle growth during the experimentation. The isothermal experiments for the characterisation of the rheological behaviour consisted of step-change of shear-rate and yield-stress experiments. From the experimental data the steady-state flow curves could be determined as well as the time-dependent relaxation of the shear stress after a change of shear rate. The steady-state rheological behaviour was found to be shear thinning. Nevertheless, immediately after a shear-rate change an overshoot was observed that resulted from a short-time shear-thickening behaviour. The yield stress was found to strongly depend on the microstructure and the degree of agglomeration of the solid phase. With increasing rest time the yield stress was increasing strongly, because of the agglomeration of the solid particles. Based on the step-change of shear-rate experiments a single-phase flow has been developed that consists of a modified Herschel–Bulkley approach and accounts for the thixotropic as well as for the yield-stress behaviour of the alloys.

Photoproduction of hydrogen by Rhodobacter capsulatus from thermophilic fermentation effluent

Rhodobacter capsulatus was used for the phototrophic hydrogen production on effluent solution derived from the thermophilic fermentation of Miscanthus hydrolysate by Thermotoga neapolitana. Pretreatments such as centrifugation, dilution, buffer addition, pH adjustment and sterilization were suggested for the effluent before being fed to the photofermentation. Batch-wise experiments showed that R. capsulatus grows and produces hydrogen on the pretreated effluent solution. Moreover, it was found that the hydrogen yield increased from 0.3 to 1.0 L/Lculture by addition of iron to the effluent solution.

Dynamic modelling of a rotary kiln for calcination of titanium dioxide white pigment

Abstract A rigorous one-dimensional dynamic model of a rotary kiln for calcination of titanium dioxide white pigment is developed. The regenerative heat transfer in the kiln wall is described by a new mixed numerical/analytical approach. The model is validated by means of a dynamic test case representing a 15-day period of plant operation. The required process data are captured within a measurement campaign on a kiln run by TRONOX Pigments GmbH, Krefeld-Uerdingen, Germany. The predictive accuracy of the model is estimated by means of a sensitivity analysis considering uncertainties of model parameters and measured input values. The actual agreement between simulation and measurement results is significantly better than indicated by the sensitivity analysis.

A new tool for process modelling of metallurgical processes

Abstract A new modular process modelling tool has been developed to support the design and operation of metallurgical processes. A modelling concept was formulated and a flowsheeting software tool has been developed for the calculation of complex non-equilibrium phenomena. To test both the basic approach and software tool, the modelling and simulation of a LD converter process was undertaken. The validation of the simulation model shows good agreement of reported and calculated values for species concentration and temperature development in time. The aim of this approach is to achieve a high degree of accuracy in modelling and, at the same time, to correspond to the speed requirements of day to day design work. It is intended to extend the current research to obtain a tool not only for the design and simulation of established processes, but also for the computer-aided development of new process routes.

Integration study on a two-stage fermentation process for the production of biohydrogen

In order to make the hydrogen economy fully sustainable, renewable resources have to be employed for its production. Simulation models, developed with Aspen Plus to calculate mass and energy balances, will be used to integrate the process steps necessary to produce pure hydrogen from biomass in a 2-stage fermentation process. The main challenge is the reduction of water and heat demand connected to the low substrate concentration in the fermentation steps; the easiest solution is to partly recirculate outgoing process streams. Electrolyte equilibrium was considered during simulation of different recirculation options to evaluate important effects on the pH and on the system osmolality. The results show that certain recirculation options can reduce the heat and water demand significantly. (Less)

Rheological Characterization of a New Alloy for Thixoforming

A new aluminum alloy (AlSi5Mg0.5Cu0.3Ag) for semisolid die-casting applications was designed, starting from computational thermodynamics calculations by Computherm Database. The goal was to obtain a combination of good castability and proper concentration of hardening elements for strengthening precipitation treatment. The predicted thixotropic properties were verified by measuring the microstructural conventional parameters, such as globule size and shape factor, and the solidification range, by means of differential scanning calorimetry. To complete the characterization of this new alloy and to evaluate its applicability in industrial production, the shear rate and time-dependent flow behavior of the alloy in the semisolid state was studied in a Searle-type rheometer. A future aim of the present research is to try to use rheology testing as the tool to optimize the chemical composition, in order to design an alloy characterized by good mechanical performances and easy processability. Considering the strong influence of the solid fraction content on semisolid alloy viscosity, the rheology tests were interrupted after a certain time and the alloy was deeply freezed using vaporized liquid nitrogen, in order to fix the microstructure and verify the correctness of the thermodynamic simulation.

Pressure Loss and Separation Characteristics Calculation of a Uniflow Cyclone with a CFD Method

Calculations of pressure loss and separation efficiency of a uniflow cyclone were performed on the basis of CFD (computational fluid dynamics) simulations and compared with experimental data. It is shown that simplifications which are often made to reduce computational effort significantly limit the prediction quality. Turbulence modeling has the major influence on gas phase velocity and pressure distributions and thus also affects the calculation of solid particle trajectories. Errors in separation efficiency calculation are diminished by co-simulating the flow in the swirl generator in order to determine proper boundary conditions for cyclone flow. Although CFD for cyclones is momentarily not able to completely substitute experiments, it can reduce experimental costs for design and optimization.

Modeling of shear induced coarsening effects in semi-solid alloys

Abstract In long-term rheological shear experiments with semi-solid alloys, coarsening of the particles will falsify the interpretation of the experimental results. The coarsening is intensified by the shear induced convection and the mean size of the particles is changed significantly during the experiments. A simple model has been set up which takes the influence of the convection into account. The resulting growth law has been simplified for diffusion and convection dominated growth. The growth law was verified with shear experiments in a Searl-rheometer with A356 and tin-lead alloys. The experiments demonstrated that under convection the growth follows a linear time law and that the rate constant depends on the root of the shear rate. The correction of experimental results to gain the true viscosity function is demonstrated for a shear jump experiment with A356.