Gas-expansion separators

The first report on using a gas expansion separator for separation of volatile hydrides from the liquid reaction mixture in a n system with AAS detection was made by Astrom... 

Gas-diffusion separations may be further divided into single and dual-phase separation systems. Single-phase systems are used for spectrophotometry, electrochemistry and chemiluminescence etc., with which liquid phase is used in both donor and acceptor channels. Dual-phase systems use a suitable gas as the acceptor stream, while the donor stream is liquid such systems are used with mass spectrometric (cf. Sec. 5.4.6) or electron capture detection [7J, but may also be used as a substitute for gas expansion separation in vapK>ur generation atomic spectrometric determinations (cf. Sec. 5.5.1 FI hydride generation manifolds with dual phase gas diffusion separators)... 

Gas-expansion Separators for Vapour Generation Atomic Spectrometric Systems... 

Recently, Marshall and van Staden [45] described a gas expansion separator used for FI hydride generation AAS which is separated into two compartments by a cotton gauze membrane. The reaction mixture is allowed to flow on the membrane from the top compartment, where a flow of argon gas is directed parallel to the membrane to sweep the hydrogen and hydrides into a quartz atomizer, while the liquid phase is pumped out from the base of the lower compartment (cf. Sec. 5.5.1). 

Basic FI Hydride Generation Manifolds with Gas-expansion Separators... 

The basic FI manifold configuration for hydride generation atomic spectrometry has varied little since the early publications, and a typical manifold using the gas-expansion separator in Fig. 5.4 b is shown in Fig. 5.9. The injected samples are usually preacidified to contain IM HCI and transponed by an IM HCl carrier stream to merge with the borohydride reductant flow at a confluence point. The reaction mixture passes through a length of reaction coil and merges with an inert carrier gas flow which carries the liquid-gas mixture into the gas expansion separator. The separation of the gas from the reaction mixture is achieved as described in Sec. 5.2.4. and the hydride is transported into the heated T-shaped quartz atomizer for atomization. 

The following points in the design of a FI hydride generation AAS system, based mainly on our own experiences using gas expansion separators, is worth mentioning... 

The importance of the withdrawal rate of solution waste fliom the gas-expansion separator was stressed in Sec. 5.42. Forced withdrawal using a pump is strongly recommended in preference over free outflow of reaction waste for ensuring optimum precision and long term trouble-free operation. This aspect should not be overlooked, at least in the design of a FI hydride generation system using gas-expansion separators. When gas-diffiision separators are used, the requirements may be different. 

Despite the favourable results obtained by Yamamoto et al., results on using similar tubular separators reported by Wang and Fang [44] and Welz and Schuben-Jacobs [18] show inferior performance in sensitivities and reliability compared to gas-expansion separators, and the latter was preferred. The contradictory reports in the evaluation of gas-diffusion and gas-expansion separators are probably due to the difference in performance... 

Barnes and Wang [48,49] studied the performance of both sandwich and tubular-type dual-phase membrane gas-di sion separators in the determination of As(V) by hydride generation ICP-OES, and obtained better detection limits with a sandwich design, while both were found to be superior to using a gas-expansion separator. Their results seem to suggest that dual-phase membrane separators are better suited at least for combination to ICP-OES systems in comparison to gas expansion separators, but further research efforts may be necessary to reach decisive conclusions. 

Earlier ehapters explained tliat air separation expanders are mrbines that expand gases in two steps, using primary and seeondary gas expansion deviees. Inlet guide vanes (or inlet nozzles) are the primary expansion deviee. Their funetion is to eonvert almost half of... 

Expansion turbines are related in many design features to the centrifugal compressor. The key exception being that the turbine receives a high pressure gas for expansion and power recovery to a lower pressure and is usually accompanied by the recovery of the energy from the expansion. For example, applications can be (1) air separation plants (2) natural gas expansion and liquefaction (for gas let-down in pipeline transmission to replace throttle valves where no... 

Figure 5.9 The Joule-Thompson cycle (Linde cycle). The gas is first compressed and then cooled in a heat exchanger, before it passes through a throttle valve where it undergoes an isenthalpic Joule-Thomson expansion, producing some liquid. The cooled gas is separated from the liquid and returned to the compressor via the heat exchanger.

The field development imposes dramatic changes in fluid processing at the GCs. As a result, the amount of GC process equipment will more than double, correspondingly, the number of modules will be doubled as shown on the plot plan. Figure 9. The control system requires expansion proportionate to the amount of new equipment. Although this new equipment will be in new modules, it cannot be treated independently because it is closely coupled and highly interactive with the rest of the process. The low pressure separation project will add new first stage gas/oil separators which... 

The methyl-acetylene and propadiene in the C3 cut are hydrogenated to propylene in a liquid-phase reactor. Polymer-grade propylene is separated from propane in a C3- splitter. The residual propane is either recycled for further cracking, or exported. C4s and hght gasoline are separated in a debutanizer. Gas expansion (heat recovery) and external cascade using ethylene and propylene systems supply refrigeration. 

About 30% of the urea solution that leaves the reactor is expanded and enters a gas/liquid separator in a recirculation stage operating at a reduced pressure. After expansion, the urea solution is heated by MP steam. By heating the urea solution, the unconverted carbamate is dissociated into NH3 and CO. ... 

Separation by gas expansion, often assisted by a suitable carrier gas, in a chamber where the liquid phase is directed to waste, and the gas released from an upper outlet. 

Fig. 4 Gas-expansion gas-liquid separators. a modified Vijan-type U-tube separator b. Perkin-Elmer W-configuration separator and c, modified W-configuralion separator with PTFE tube scrubber. G-L, gas-liquid mixture D, to detection system W. to waste pump B. glass beads T, microporous PTFE lube with blocked end O, outer tube with gas outlet.

In order to define the gas volumes more precisely, and overcome the problems associated with the mercury in contact with the gas and the limited temperatme range because gas and mercury were at the same temperatme, expansion methods were later devised where the gas was allowed to expand from one vessel into another, previously evacuated, vessel (and in some cases into a series of other vessels). The volumes had previously been accurately determined by weighing with water or mercury. The gas was separated from the manometer, which can be at room temperature, by a differential pressure gauge. 

Brinkman, J. R. (1989, August). Separating shock waves and gas expansion breakage mechanisms. In Proceedings of the 2nd international symposium on rockfragmentation by blasting. Keystone, CO. 

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