Multi-level modelling of the hydrodynamics in gas phase polymerisation reactors

The gas-solid fluidised bed process is the most versatile process for the production of polyolefins, because it allows the production of polyolefins with a broad distribution of both the product density and molecular weight. In spite of the excellent heat transfer characteristics of a fluidised bed, the production capacity is still limited by the rate of heat removal and temperature control in the polyolefin production process is a major point of attention. The rate of heat removal is largely determined by the large scale convection patterns prevailing in the gas phase olefin polymerisation reactor, induced by the in situ formed and growing gas bubbles. Moreover, the bubbles play an intricate role in the particle mixing and segregation behaviour of the fluidised bed. To improve the design, operation and scale-up of these gas-fluidised bed processes, a better understanding\ud and a quantitative description of these phenomena is required. Therefore, the main objective of this project was the development of fundamental hydrodynamic models to describe and study the hydrodynamic behaviour of the gas-solid fluidised bed reactor

Validation of the granular temperature prediction of the kinetic theory of granular flow by particle image velocimetry and discrete particle model

In order to give a detailed description of the hydrodynamics in large industrial scale fluidized beds, continuum models are required. Continuum models often use the kinetic theory of granular flow (KTGF) to provide closure equations for the internal momentum transport in the particulate phase. In this work the outcome of the continuum model is compared with both an experimental technique and detailed simulations, i.e. particle image velocimetry (PIV) and the discrete particle model (DPM).\ud PIV is used for the measurement of an instantaneous velocity field of the flow in the front plane of a fluid bed. The classical PIV analysis is extended to enable the measurement of the local velocity fluctuations in the interrogation area, i.e. the granular temperature. In the DPM, each particle is tracked individually. In this model detailed collision models can be incorporated, rendering the DPM a valuable research tool to validate the underlying assumptions in the KTGF concerning the particle-particle interactions and the particle velocity distribution functions.\ud The aforementioned experimental and numerical techniques are used to measure the granular temperature distribution around a single bubble rising in a gas-fluidized bed. It was found that the results of PIV and the DPM are very similar. Although the initial bubble shape and size are well predicted by the continuum model, it fails once the bubble has detached from the bottom plate. Further research in the area of KTGF closures is needed to improve the predictions of the TFM

Normalizing dietary exposure across age by scaling to body size

RIVM/SIR PORS no. 12063It is usually assumed that the higher dietary exposure to substances (in mg/kg bw) in young individuals compared to adults is the resultant of a relatively high consumption needed for growth. When this relatively high exposure of young individuals temporarily exceeds the human limit value, the assessment of possible health risks is not straightforward. The aim of this study was to find a way of scaling exposure in order to reduce the effect of age on the dietary intake. Several (allometric) scaling approaches were applied to explore their impact on age-related intake patterns. It was demonstrated that allometric scaling reduces the effect of body weight. Nevertheless, the results indicate that the higher exposure in young individuals is not only the resultant of a relatively high consumption needed for growth, but still contains influences of body weight. Therefore the conclusion was drawn that a different scaling of dietary exposure is not expedient. It is advised that, when a human limit value is exceeded for a relatively short period, the characteristics (e.g. accumulating properties) of the compound and the design of the toxicological studies informing the human limit value are examined closely to assess the health risk.VW

Comparison of continuum models using the kinetic theory of granular flow with discrete particle models and experiments: extent of particle mixing induced by bubbles

The bubble formation and extent of particle mixing induced by a single bubble injected in a mono-disperse uidised bed at incipient \ud uidisation conditions has been studied with a Two-Fluid continuum Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) and com-\ud pared with experiments and simulation results obtained from a Discrete Particle Model (DPM). The eect of dierent gas-particle drag models and frictional viscosity models on the bubble behaviour and extent of particle mixing has been assessed. To describe the extent of particle\ud mixing well, a frictional viscosity model needs to be included, however, the currently available frictional viscosity models need further improvement

Modelling of large-scale dense gas–solid bubbling fluidised beds using a novel discrete bubble model

In order to model the complex hydrodynamic phenomena prevailing in industrial scale gas–solid bubbling fluidised bed reactors and especially the macro-scale emulsion phase circulation patterns induced by bubble–bubble interactions and bubble coalescence, a discrete bubble model (DBM) has been developed. In the DBM, the (larger) bubbles are modelled as discrete elements and are tracked individually during their rise through the emulsion phase, which is considered as a continuum. The DBM, originally developed for the description of gas–liquid flows, has been adapted to cope with bubbles with a diameter larger than the size of an Eulerian cell, which is required in view of the large bubble size distribution at higher gas flow rates. Moreover, a new drag model for a single bubble rising in a fluidised bed derived from empirical correlations has been implemented, as well as a simple model to account for bubble coalescence and break-up. The strong advantage of the DBM compared to other models previously reported in the literature for the description of large-scale fluidised beds is that it fully accounts for the two-way coupling between the bubbles and the emulsion phase, which enables direct computation of the emulsion phase velocity profiles. Comparison of the results of simulations ignoring bubble coalescence and simulations taking bubble coalescence properly into account demonstrated the significant effect of bubble coalescence on the large-scale circulation patterns prevailing in bubbling fluidised beds. The simulation results for the lateral profiles of the visible bubble flow rate have been compared qualitatively with experimental results reported by Werther [1974. Influence of the bed diameter on the hydrodynamics of gas fluidized beds. A.I.Ch.E. Symposium Series 70(141), 53–62]. The effect of the superficial gas velocity on the velocity and porosity profiles has been studied. In general, it can be concluded that the DBM is able to capture the salient features of the hydrodynamics of bubbling fluidised beds. However, further research is required to improve the closure equations for the bubble behaviour, bubble–bubble interactions and bubble coalescence and break-up to enable a complete quantitative description

"Kip, ik heb je!" Het vangen van vleeskuikens - een economische verkenning van verschillende potentieel dierenwelzijnsverbeterende alternatieven

Dieronvriendelijke omstandigheden in de veehouderij komen grotendeels voort uit kostenbesparende maatregelen. In het overgrote deel van de gevallen resulteert een verbetering van het dierenwelzijn in hogere productiekosten.Het doel van deze studie is het bestuderen van een situatie van verminderd dierenwelzijn bij het vangen van vleeskuikens en het maken van een kostenberekening voor de verschillende alternatieven. Hiervoor werden in totaal vijf scenario's (inclusief basisscenario) bestudeerd. Aan elk van de alternatieve scenario’s zijn extra kosten ten opzichte van het basisscenario verbonden.Hier tegenover staan geen extra opbrengsten als gevolg van het diervriendelijk vangen van kuikens. Mogelijk dat door voorlichting draagvlak gecreëerd kan worden voor de extra kosten van een uitbetalingssysteem naar kwalitei

Sensory profiles of breast meat from broilers reared in an organic niche production system and conventional standard broilers

BACKGROUND: Breast meat from broilers produced in very different production systems may vary considerable in sensory profile, which may affect consumer interests. In this study the aim was to evaluate differences in the sensory profiles of breast meat from five broiler products: two conventional standard products (A and B) and three organic niche genotypes (I657, L40 and K8) reared in an apple orchard. RESULTS: Thirteen out of 22 sensory attributes differed significantly between the products. The aroma attributes ‘chicken’, ‘bouillon’ and ‘fat’ scored highest and the ‘iron/liver’ aroma lowest for the niche products. The meat was more ‘tender’, ‘short’ and ‘crumbly’ and less ‘hard’ and ‘stringy’ in the standard products than in one or more of the niche products. Product ‘I 657’ was less ‘juicy’ than the rest. Products ‘I 657’ and ‘L 40’ were more ‘cohesive’ and tasted more ‘sourish’ and less of ‘sweet/maize’ than the standard products. The ‘overall liking’ score was significantly higher for the ‘K 8’ product than for the ‘Standard A’ and ‘L 40’ products. The ‘overall liking’ score was significantly correlated with the scores for aroma and taste of ‘chicken’, ‘umami/bouillon’, ‘iron/liver’ and ‘fat’ aroma. CONCLUSION: The sensory profiles differed particularly between conventional standard broilers and organic niche broilers, although differences were also found between breeds. The present study indicates that aroma and taste attributes were more important for the assessors than meat ‘tenderness’ for the overall liking of broiler meat. �c 2011 Society of Chemical Industry