Supercritical carbon dioxide injectors

Two practical yet important operating processes that experience witness severe Joule-Thomson effect have been thoroughly assessed -one for hydrate prevention for starting up a supercritical carbon dioxide injector, and the other for packing up a carbon dioxide pipeline to get ready for injecting carbon dioxide to injection wells ... 

Several critical key findings have been identified out of the assessment of hydrate potential associated with starting up a supercritical carbon dioxide injector. Recommendations on operational envelopes have been developed for preventing the formation of hydrate during the well start-up process. 

Annular Pressure Assessment for Supercritical Carbon Dioxide Injectors Designed for Carbon Capture AND Sequestration... 

Figure 6.4—Schematic of a supercriticalfluid chromatograph. Carbon dioxide reaches a supercritical state between the pump and the injector. A pressure regulator (restrictor) is located after the column and either before or after the detector, depending on its type. It allows the mobile phase to be kept under supercritical conditions until its exit from the column.

In addition, solute focusing is possible by maintaining a low initial temperature (e.g. 40 °C) for a long period of time (8-12 min ) to allow the mixture of decompressed carbon dioxide, helium gas and the solutes to focus on the GC column. The optimization of the GC inlet temperature can also lead to increased solute focusing. After supercritical fluid analysis, the SF fluid effluent is decompressed through a heated capillary restrictor from a packed column (4.6 mm i.d.) directly into a hot GC split vaporization injector. 

When on-column injection is used the end of the transfer capillary is inserted into the column inlet or retention gap where decompression of the supercritical fluid occurs. Carbon dioxide gas exits through the column and the seal made between the restrictor and septum (unless a closed injector is used). The analytes are focused by cold trapping in the stationary phase. The transfer line must be physically removed from the injector at the completion of the extraction to establish the normal carrier gas flow for the separation. Analyte transfer to the column is virtually quantitative but blockage of the restrictor is more conunon and involatile material accumulates in the injection zone eventually degrading chromatographic performance. The on-column interface is probably a better choice for trace analysis of relatively clean extracts with modest fluid flow rates than the split interface. When optimized both the on-column and split interfaces provide essentially identical peak shapes to those obtained using conventional solution injection. 

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