Testing the validity of the spherical DEM model in simulating real granular screening processes

We investigate the flow of a granular material over a vibrated horizontal screen. We perform a direct quantitative comparison, across a range of operating conditions, between laboratory scale experiments and simulations using the discrete element method (DEM). We test the extent to which the commonly employed DEM approximation of particles being spherical affects the ability of the model to realistically reproduce the behaviour of industrial screening systems where the particles are generally non-spherical in shape.The simulation geometry and input particle size distribution are set up to exactly match the experimental system, which consists of a horizontal screen with a wire mesh cloth onto which quarry rock is fed at a series of input flow rates. The screen is vibrated, causing the granular bed to flow over the deck and vertically stratify with finer material passing through the screen, where it is collected in a series of bins located along the length of the screen. The size distribution of the material flowing through each section of the screen is found by analyzing the contents of each collection bin.The best agreement is found for very low flow rates, where the vast majority of the below aperture size material is rapidly captured just after it enters the screen in both the simulation and experiment. At higher flow rates, significant quantitative errors are found with the over-prediction of the flow rate through the screen for near grate sized particles. This is attributed to the higher rate of percolation through the bed and the easier capture by the screen surface of the spherical shaped material. The near aperture sized spherical particles also show a very strong tendency to peg the screen, becoming trapped in the screen openings and limiting further flow through those parts the screen. The use of spherical particles in the DEM simulation of vibrating screens is therefore found to be inadequate for modelling realistic flow and separation of particles that are not actually spherical.     

Neural Net Based Hybrid Modeling of the Methanol Synthesis Process

A Hybrid modeling approach, combining an analytical model with a radial basis function neural network is introduced in this paper. The modeling procedure is combined with genetic algorithm based feature selection designed to select informative variables from the set of available measurements. By only using informative inputs, the model's generalization ability can be enhanced. The approach proposed is applied to modeling of the liquid–phase methanol synthesis. It is shown that a hybrid modeling approach exploiting available a priori knowledge and experimental data can considerably outperform a purely analytical approach.     

Stereoselective hybrid catalysts: new opportunities

The combination of biotransformations and metal‐assisted catalysis within hybrid systems represents a promising strategy to extend the repertoire of reactions enabled in a biomolecular environment. Both covalent catalytic entities and supramolecular assemblies have been created recently to mediate transformations otherwise difficult to perform in ‘classical’ biocatalysis. In this context, various biopolymers can serve as ligand spheres simultaneously acting as chiral inducers. In particular, modular approaches embedding novel metal‐based catalytic centers via an affinity interaction are highly appealing, as this technology may serve as a versatile platform to incorporate diverse reactivities in a biological matrix in a stereoselective fashion. Copyright © 2007 Society of Chemical Industry     

Is cluster policy useful for the energy sector? Assessing self-declared hydrogen clusters in the Netherlands

Research on science-based industries has shown that it is important for organisations to be active in interorganisational networks. Cluster policy has been developed as a means to stimulate the development of these networks and thereby the success rate of these industries. Cluster policy is however not a common policy instrument in the energy sector. In this paper, we focus on three self-declared clusters active in hydrogen-related R&D in the Netherlands and address several characteristics of these clusters. We conclude that cluster policy is a useful addition to existing energy R&D policies but that monitoring whether self-declared clusters actually function as clusters and what their contribution is to the overall system is pivotal in reaping the benefits of cluster policy.     

Operational and safety analyses of a commercial PEMFC system

A commercial, transportable proton-exchange-membrane fuel-cell (PEMFC) system rated at 7 kW nominal power was the subject of an operational (reliability, availability, and maintainability) and process-safety analysis. The scope of the analysis included the system start-up to engine-run mode, the maintenance tasks, as well as the continuous power-production mode, carried out with a hazard and operability (HAZOP) study and a failure-scenarios' development. The failure and process-safety risks were categorized and the probabilities were assessed with a fault-tree analysis (FTA) using equipment-failure-rate data from the literature, if available. The results led to similar conclusions to those previously reported in similar studies, and the most important equipment/devices with respect to reliability and safety aspects were identified. While the most important uncertainty in the complete analysis comes from the generic equipment failure-rate data used, about three failures in the first year of operation are estimated together with an availability of about 98% (a point value figures, confidence interval analysis was also made). The process-safety analysis revealed four potential accident scenarios involving hydrogen releases, fires and explosions. Finally, detailed suggestions and recommendations for changes/improvements with respect to the reliability/availability, maintainability and safety aspects of the system analysed are presented.     

An experimental and kinetic modeling study of cyclopentadiene pyrolysis: First growth of polycyclic aromatic hydrocarbons

The importance of 1,3-cyclopentadiene (CPD) and cyclopentadienyl (CPDyl) moieties in the growth of polycyclic aromatic hydrocarbons (PAHs) was studied using new experimental data and ab initio calculations. The experimental investigation was performed in a tubular continuous flow pyrolysis reactor under both high (24molN₂/molCPD)$(24{\text{mol}}_{{\text{N}}_2}/{\text{mol}}_{\text{CPD}})$ and low (5molN₂/molCPD)$(5{\text{mol}}_{{\text{N}}_2}/{\text{mol}}_{\text{CPD}})$ nitrogen dilutions, covering a temperature range of 873–1123 K, at a fixed pressure of 1.7 bara. At the most severe conditions up to 84% of CPD is converted, and the amount of PAHs is more than 65 wt%. Major products observed during CPD pyrolysis were benzene, indene, methyl-indenes and naphthalene, in line with previous studies. On-line GC × GC-FID/(TOF-MS) also allowed to quantify minor species (methane, toluene, styrene, phenanthrene, anthracene, etc.), never reported before at this level of accuracy. The new experimental data have been used to further analyze the role of the successive interactions of CPD, indene, and naphthalene as well as the recombination and addition reactions of their resonantly stabilized radicals and refine their kinetics. The results of the modeling study are in good agreement with existing and new experimental observations.     

Evaluating the development of carbon capture and storage technologies in the United States

Carbon capture and storage (CCS) is seen as an important solution to solve the twin challenge of reducing GHG emissions, while utilizing fossil fuel reserves to meet future energy requirements. In this study an innovation systems perspective is applied to review the development of CCS technologies in the US between 2000 and 2009 and to come up with policy recommendations for technology managers that wish to accelerate the deployment of CCS. The analysis describes the successful built-up of an innovation system around CCS and pinpoints the key determinants for this achievement. However, the evaluation of the system's performance also indicates that America's leading role in the development of CCS should not be taken for granted. It shows that the large CCS R&D networks, as well as the extensive CCS knowledge base, which have been accumulated over the past decade, have not yet been valorized by entrepreneurs to explore the market for integrated CCS concepts linked to power generation. Therefore, it is argued that the build-up of the innovation system has entered a critical phase that is decisive for a further thriving development of CCS technologies in the US. This study provides a clear understanding of the current barriers to the technology's future deployment and outlines a policy strategy that (1) stimulates technological learning; (2) facilitates collaboration and coordination in CCS actor networks; (3) creates financial and market incentives for the technology; and (4) provides supportive regulation and sound communication on CCS.