Time-Resolved X-Ray Tomography of a Fluidized Bed of Geldart A Particles

This paper discusses the influence of fines on the size of bubbles moving through a 23 cm ID fluidized bed of Geldart A particles imaged with an X-ray Tomographic Scanner. In earlier work [1], the bubble distribution in a fluidized bed of Geldart B particles was shown. The current study using Geldart A particles is more challenging to the reconstruction algorithm, since there are more bubbles, and they are smaller in size. We study the influence of adding fines (i.e. particles \u3c= 45 micron) to the system. When adding a mass fraction of fines of 24%, we find a decrease of the average bubble of 40% of the size for the original powder, in line with earlier results from pressure probes and optical probes [2]. We find that the entire distribution of the bubble sizes shifts to smaller values

Comparison of optical probes and X-ray tomography for bubble characterization in fluidized bed methanation reactors

The performance of many fluidized bed reactors strongly depends on the bubble behavior since they influence the mass transfer to the dense phase where the catalyst is present. An example is the methanation in a fluidized bed that allows for conversion of unsaturated hydrocarbons in the gasification gas without catalyst deactivation [1]. The BFB reactor is a very challenging step in the process chain to produce SNG out of biomass as feedstock since next to the bubble behavior a lot of other parameters like temperature, pressure, particle size, attrition of the catalyst, internals, bed height and reactor diameter etc. affect the overall performance. The focus of this research work lies on the determination of the bubble properties which are an important factor to model a bubbling fluidized methanation reactor in order to predict and optimize its performance and to support its scale-up [2]. Tomographic methods such as X-ray measurements are often used to characterize bubbles in a fluidized bed. Compared to intrusive measurement, e.g. optical probing, this method possesses the advantage of measuring bubbles throughout the entire cross section. However, X-ray measurements cannot be applied to all installation, especially not in large scale plants. For these purpose, we have developed optical probes that can be employed to investigate the fluidization state in a hot pilot scale reactor. A main drawback of the optical measurements lies in their locally limited detection of the hydrodynamic pattern since they are only able to measure at one point in the reactor. Therefore, conclusions on the bubble behavior of the whole cross section based on optical measurements are not easy to derive. To compare the influence of the measurement method on the measured bubble properties, in the scope of this study, an artificial optical signal is created out of the existing X-ray measurement data set for a cold flow model of the pilot scale methanation reactor. The obtained bubble properties of both methods (i.e. evaluation of the derived artificial optical probe signal and image reconstruction based on the original X-ray tomographic data) are compared with regard to the hold-up, bubble rise velocity and the bubble size (for the X-ray method) or chord length (for the optical evaluation method), respectively. The process to obtain an artificial optical signal is depicted in Figure 1. The comparison shows that for the evaluation of optical probe data, statistical effects have to be considered carefully. The detected mean chord length of the optical method does not represent the mean bubble size determined by the X-ray method. Moreover, also a difference in the bubble rise velocity was detected for some fluidization states. This knowledge may be the basis for the derivation of a statistically sound method to calculate different hydrodynamic properties in fluidized bed reactors based on optical probe measurements. Please click Additional Files below to see the full abstract

Impacts of a novel controlled-release TiO2-coated (nano-) formulation of carbendazim and its constituents on freshwater macroinvertebrate communities

Recently, the delivery of pesticides through novel controlled-release (nano-)formulations has been proposed intending to reduce (incidental) pesticide translocation to non-target sites. Concerns have however been raised with regards to the potentially enhanced toxicity of controlled-release (nano-)formulations to non-target organisms and ecosystems. We evaluated long-term (i.e. 1 and 3 month-) impacts of a novel controlled-release pesticide formulation (nano-TiO2-coated carbendazim) and its individual and combined constituents (i.e. nano-sized TiO2 and carbendazim) on naturally established freshwater macroinvertebrate communities. In doing so, we simultaneously assessed impacts of nano-sized TiO2 (nTiO2), currently one of the most used and emitted engineered nanomaterials world-wide. We determined ecological impacts on diversity (i.e. β-diversity), structure (i.e. rank abundance parameters), and functional composition (i.e. feeding guilds & trophic groups) of communities and underlying effects at lower organizational levels (i.e. population dynamics of individual taxa). Freshwater macroinvertebrate communities were negligibly impacted by nTiO2 at environmentally realistic concentrations. The controlled-release (nano-)formulation significantly delayed release of carbendazim to the water column. Nevertheless, conventional- (i.e. un-coated-) and nTiO2-coated carbendazim induced a similar set of adverse impacts at all investigated levels of ecological organization and time points. Our findings show fundamental restructuring of the taxonomic- and functional composition of macroinvertebrate communities as a result of low-level pesticide exposure, and thereby highlight the need for mitigating measures to reduce pesticide-induced stress on freshwater ecosystems.Horizon 2020(H2020)760813Environmental Biolog

Correction: Entrainment of nanosized clusters from a nanopowder fluidized bed

The article by Andrea Fabre et al. (Environ. Sci.: Nano, 2017, 4, 670–678) was published with an incorrect title (‘Modeling thesize distribution in a fluidized bed of nanopowder’). The correct article title is ‘Entrainment of nanosized clusters from a nanopowder fluidized bed’.FWN – Publicaties zonder aanstelling Universiteit Leide

Safe-and-sustainable-by-design framework based on a prospective life cycle assessment: lessons learned from a nano-titanium dioxide case study

Safe-and-sustainable-by-design (SSbD) is a concept that takes a systems approach by integrating safety, sustainability, and functionality throughout a product's the life cycle. This paper proposes a framework based on a prospective life cycle assessment for early safety and sustainability assessment. The framework's purpose is to identify environmental sustainability and toxicity hotspots early in the innovation process for future SSbD applicability. If this is impossible, key performance indicators are assessed. Environmental sustainability aspects, such as global warming potential (GWP) and cumulative energy demand (CED), and toxicity aspects, such as human toxicity potential and freshwater ecotoxicity potential, were assessed upon applying the framework on a case study. The case study regarded using nano-titanium dioxide (P25-TiO2) or a modified nano-coated version (Cu2O-coated/P25-TiO2) as photocatalysts to produce hydrogen from water using sunlight. Although there was a decrease in environmental impact (GWP and CED), the modified nano-coated version had a relatively higher level of human toxicity and freshwater eco-toxicity. For the presented case study, SSbD alternatives need to be considered that improve the photocatalytic activity but are not toxic to the environment. This case study illustrates the importance of performing an early safety and environmental sustainability assessment to avoid the development of toxic alternatives.Environmental Biolog

Apparatus and process for atomic or molecular layer deposition onto particles during pneumatic transport

The invention provides a process for depositing a coating onto particles being pneumatically transported in a tube. The process comprising the steps of providing a tube having an inlet opening and an outlet opening; feeding a carrier gas entraining particles into the tube at or near the inlet opening of the tube to create a particle flow through the tube; and injecting a first self-terminating reactant into the tube via at least one injection point downstream from the inlet opening of the tube for reaction with the particles in the particle flow. The process is suitable for atomic layer deposition and molecular layer deposition. An apparatus for carrying out the process is also disclosed.ChemE/Chemical EngineeringApplied Science