Carrier-gas systems

Gas Cylinder or Generator. In most cases the supply of mobile phase is from commercial cylinders. These are connected to the carrier gas system of the chromatograph by means of a reducing valve. Hydrogen necessary for a flame-ionization detector may be supplied from a commercial tank or electrolytically generated. 

An alternative carrier-gas system uses a condensable gas, such as steam, as the carrier sweep fluid. One variant of this system is illustrated in Figure 9.7(d). Low-grade steam is often available at low cost, and, if the permeate is immiscible with the condensed carrier, water, it can be recovered by decantation. The condensed water will contain some dissolved organic and can be recycled to the evaporator and then to the permeate side of the module. This operating mode is limited to water-immiscible permeates and to feed streams for which contamination of the feed liquid by water vapor permeating from the sweep gas is not a problem. This idea has been discovered, rediscovered, and patented a number of times, but never used commercially [37,38], If the permeate is soluble in the condensable... 

Gas Chromatography. The basic components of a gas chromatograph are a carrier gas system, a column, a column oven, a sample injector, and a detector. Very pure helium is the near-universal carrier gas for environmental and many other analyses. Open tubular GC columns are constructed of fused silica with low-bleed stationary phases of varying polarity chemically bonded to the silica surface. Columns are typically 30-75 m in length and have inside diameters (ID) in the range of about 0.25-0.75 mm. The column oven is capable of precise temperature control and temperature programming at variable rates for variable times. 

Upon analysis of this transient period, either as the zero-pressure intercept on the lime axis for constant volume systems (Fig. 20.3-7a) or as the corrected zero-moment of the detector response for carrier-gas systems (Fig. 20.3-8), one can derive a kinetic parameter 8. referred ro as the "time lag".l5 26 77... 

The mobile-phase gas in GC is called the carrier gas and musl be chemically inert. Helium is the most common mobile-phase gas used, although argon, nitrogen, and hydrogen are also used. These gases arc available in pressurized tanks. Pressure regulators, gauges, and flow meters arc required to control the flow rate of the gas. In addition, the carrier gas system often contains a molecular sieve to remove impurities and water. 

O Table 53.1 illustrates the different approaches of determination of AS in the case of adsorption of volatile Re and Ir compounds with oxygen-containing carrier gas systems on TCC quartz surfaces. Undoubtedly, experiments are of primary importance in determining the entropy values. 

A low-cost alternative to the volumetric is the flow or carrier gas system. The disadvantage of this method is that the results are very uncertain and normally does not yield the isotherm. 

The capital cost of a THERMAL DeNO, system includes the costs of ammonia and carrier gas systems, injectors, instrumentation and controls, installation, engineering, licensing fees, and, for a retrofit, the cost of any nnodifications. Retrofit applications usually involve neither major modifications nor excessive downtime. The capital cost is application specific and depends on the initial NO, concentration, the size of the boiler, the NO, reduction required, the load following capability, and the ammonia carryover limitations. 

X3.5.5 When the reverse flow valve is turned there is a reversal of pressure conditions at the column ends that upsets the carrier gas flow. This flow should quickly return to the same flow rate and the base line level out. If it does not, the cause may be a leak in the carrier gas system, faulty flow regulator, or an unbalanced condition of the column or plumbing. 

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