Remediation of borosilicate Raschig rings

The legacy of the nuclear arms race has left numerous environmental remediation challenges. For example, a common practice from the 1950s to the 1970s for nuclear criticality control of fissile solutions in storage tanks was the use of borosilicate Raschig rings However, this practice subsided with the uncertainty in the long-term consistency of the boron concentration in the Raschig rings The result was numerous abandoned tanks that are relatively filled with contaminated borosilicate Raschig rings The focus of this study was on a radioactive waste stream from an uranium/thorium separation process that was conducted in the 1970s. The primary radioactive contaminants of this waste stream were thorium-228/229 and the associated decay products. Motivation for remediation of the Raschig rings is based on the associated costs of disposal of large volumes of radioactively contaminated Raschig rings. Additional inspiration behind this particular waste stream is the interest in thorium-229 as a bio-medical generator for alpha radioimmunotherapy In this study, successful remediation of radioactively contaminated borosilicate Raschig rings was achieved using a nitric acid solvent/ultrasonic agitation method followed by ion exchange separation and a combination surfactant/ultrasonic volume reduction method. Both methods resulted in a successful remediation with greater than 99% removal of the radioactive contaminants Furthermore, successful recovery of the thorium-229 was achieved through a combination of batch anion and cation ion exchange processes Consequently, this success has allowed clinical trials to begin on a new treatment for myelogenous leukemia using the decay products fi-om thorium-22

Gas-solid trickle flow hydrodynamics in a packed column

The pressure gradient and the static and the dynamic hold-up have been measured for a system consisting of a Fluid Cracking Catalyst (FCC) of 30–150 × 10−6 m diameter, trickling over a packed bed and with a gas streaming in countercurrent flow. The experiments were carried out at ambient conditions using a glass column of 25 × 10−3 m diameter. The packing material consisted of 8 × 8 × 3 mm ceramic Raschig rings, a mixture of 7 × 7 × 1 mm glass Raschig rings and 5 × 5 mm catalyst pellets and of stacked Kerapak ceramic mixing units of Sulzer, each unit 50 mm long and 25 mm in diameter. Four different gases have been tested. A correlation for the pressure gradient in the preloading region is derived based on the Ergun equation and taking into account the internal gas recirculation due to the solids trickles. The void fraction of the trickles is found to be independent of the physical properties of the gas phase. The behaviour of the GSTF-system in the preloading regime and the phenomena of loading and flooding are discussed. A correlation is given which relates the boundary between preloading and loading with the particle and gas properties and the solids flow rate

Hydrodynamic behaviour of a gas—solid counter-current packed column at trickle flow

Trickle flow of a more or less fluidized catalyst through a packed column is a promising new gas—solid counter-current operation. The hydrodynamic, behaviour of such a column, filled with dumped PALL rings, has been investigated, while some results have been obtained with RASCHIG rings and cylindrical screens as packing. The solid used was a microspherical catalyst carrier. Pressure drop, hold-up, loading and flooding were evaluated and compared with literature data for gas—liquid systems. The behaviour is analogous although the absolute magnitude is different.\ud \ud Pressure drop is low, up to 50% of the solid being carried by the packing. A correlation for the pressure drop, which is mainly caused by suspended particles, has been derived. At low gas velocities particle velocity is constant, whilst near flooding the slip velocity between gas and solid reaches a constant value. Using empirical values for particle velocity and slip velocity, hold-up, loading and flooding can be predicted. Scaling-up problems still need to be investigated. Results on mass transfer, axial dispersion of both phases and solid spread factors will be published later.\u

High pressure gas filter system Patent

Developing high pressure gas purification and filtration system for use in test operations of space vehicle

Radial heat transport in packed beds at elevated pressures

Values were measured for the effective radial heat conductivity λeff, r and the heat transfer coefficient at the wall αw in a packed bed. This was done for superficial velocities of 5 – 70 cm s−1 and at pressures from 1 – 10 bar. Values for λeff, r and αw were obtained by simultaneous fitting of measured axial and radial temperature profiles. The bed diameter was 5 cm; it was filled with 6.1 mm Raschig rings. Nitrogen gas was used in all cases. Values could be determined with reasonable accuracy. The agreement with correlations presented in the literature is good for λeff, r and less so for αw. The results obtained indicate that λeff, r and αw are a function of the product ‘velocity times pressure’ only. The correlations found can be represented by λeff, r/λg = 21 + 0.23Pe with an average relative error of 4% and Bi = 2.9Pe−0.40 with an average relative error of 5%. The experiments covered the range 25 < PE < 350. These correlations were obtained for one specific gas and one specific set-up.\u

Absorption of CO2 and H2S in Aqueous Alkanolamine Solutions using a Fixed-Bed Reactor with Cocurrent Downflow Operation in the Pulsing Flow Regime

Absorption rates of H2S and CO2 in several aqueous alkanolamines in a cocurrent downflow fixed-bed reactor operated in the pulse flow regime have been measured in order to obtain information on the potential selectivity and on the mass transfer parameters. From these experiments it can be concluded that this type of reactor seems to be very suitable for the selective removal of H2S from acid gases. It was not possible to derive correlations which are always valid for the calculation of the mass transfer parameters in laboratory-scale contactors. The results of the present study in combination with the data published in the literature were correlated with only one unknown parameter in which the influence of the physical properties of the system and the shape and material of the packing were combined. This parameter has to be determined empirically. Small amounts of acid gases in aqueous alkanolamine solutions have a pronounced effect on the properties, such as the foaming behaviour, of the liquid phase. The pressure drops measured in the cocurrently operated fixed-bed reactor were affected substantially by small amounts of acid gases present in the aqueous alkanolamine solutions and up to now this effect could not be explained satisfactorily. For the design of contactors for industrial purposes, detailed scale-up rules are required. In the present study this aspect is not investigated.

Wetting and separation efficiency of polypropylene packing modified by nanoparticles.

Masters Degree. University of KwaZulu-Natal. Durban.Packed columns are one of the main unit operations used in distillation, extraction, absorption and hydrotreating due to their ease of operation, versatility and adaptability to different chemical systems. The distribution of gas and liquid over the packing material is the basis of separation. Selection of the type of packing material is a crucial step in column design as the separation efficiency of the column is dependent on the ratio of wetted area to the total available surface of packing, known as the wetting efficiency. Glass and metal packing offer superior wetting efficiency when compared to random packing fabricated from plastic. Plastic packings offer better chemical resistance in selected systems, as well as being more lightweight and cost-effective. Literature indicates that the wetting behaviour of glass, metal and polymeric substrates may be modified by applying multilayer coatings of nanoparticles. These nanoparticles are often silica based. In this work, polypropylene random packing was modified by first being treated with the Piranha solution and then being coated by silica nanoparticles that were produced via the Stober Process. The first part of this project investigates the employment of a stimulus response technique in which an inert salt tracer is injected into an inlet liquid stream, pumped by a peristaltic pump, and allowed to flow over the packing material. The packing material being investigated in this study are glass, unmodified and modified polypropylene Raschig rings. The residence time distribution, reported as the mean residence time (MRT), and exit age distribution were determined for the three types of packing used in this study. By comparison to standard distribution curves obtained from the literature, the experimental exit age distribution curves were used to estimate the wetting efficiency of the different packing. The glass and unmodified packing had a MRT of 12 seconds while the modified packing was 19 seconds. The wetting efficiencies were 0.3, 0.4 and 0.8 respectively. The increase in MRT indicates that fluid elements resided in the column packed with modified polypropylene for a longer period while the increase in wetting efficiency shows clear improvement in wettability for the modified packing. For the second part of the study the absorption performance of the different packings was investigated. A system of water and carbon dioxide was selected to be used in the study as it is a very simple, non-toxic system and performance can be analysed using the titration method. For the 280 mm and 90 mm packed height with a 16 % carbon dioxide inlet concentration, modified packing showed improvements on absorption for all liquid flowrates for up to 10.24 % and 9.36% respectively when compared to the unmodified packing. The silica nanoparticle modification to the polypropylene packing was successful as overall, it performed better than the unmodified packing in absorption performanc