Gas stripping system

Double jacket, vacuum, VAGAS gas stripping system ... 

The Gas Stripping System. This system has been the most popular for denitrification stupes probably because it provides the most immediate and sensitive measurement of denitrification rates. It was first used by Gersberg et al. (13,14) to measure denitrification rates in rice paddy soils, sediments, and hypoltonion water, and later by Tiedje et al. (15) and Stout and More (16) to measure denitrification rates in soils. A schematic of the system used by our group is shown in Figure 1. 

Figure 1. Diagram of gas stripping system used to continuously monitor [ N]—NgO ana [ N]—produced from denitrification (i5. ...

Although the NOs" yields are 100-fold less with this system than with the 0(p,a) N reaction, these workers have been able to perform denitrification experiments with the gas stripping system. Their success with low-energy accelerators to produce should be encouraging to others interested in using this isotope, since these machines are more common. 

The gas stripping system has been the principal method for assay of denitrification rates by N, since one need only measure the rate of gas accumulation from a sample in which the native nitrate pool has been amended with tracer quantities of NOs". If the labeled nitrate is truly carrier-free, then the calculated labeled nitrate added is 10 - to lO -fold less than the indigenous nitrate pool and thus will not alter the natural denitrification rate. An example of data obtained by the stripping system is shown in Figure 3. These rates were calculated for the linear portion of these curves by multiplying the Adpm N gas time g soil by the specific activity of the nitrate (fig NO3"—present per total NOa" added), which is analogous to the equation shown below. 

FIGURE 11.6. Simulated adsorption and desorption curves for a two-bed cyclic isothermal purge gas stripping system showing progress towards the cyclic steady stale. Cycle numbers are indicated on the curves. Broken lines represent profiles at the end of the desorption cycle while solid lines represent profiles at the end of the adsorption cycle. (From Chao. 0... 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

Fixed-bed desulfuri2ation is impractical and uneconomical if the natural gas contains large amounts of sulfur. In this case, bulk sulfur removal and recovery (qv) in an acid gas absorption—stripping system, followed by fixed-bed residual cleanup is usually employed. 

Figure 14-6 illustrates the graphical method for a three-theoretical-plate system. Note that in gas absorption the operating line is above the equihbrium curve, whereas in distillation this does not happen. In gas stripping, the operating line will be below the equihbrium curve. 

Stripping Air stripping is applied for the removal of volatile substances from water. Henry s law is the key relationship for use in design of stripping systems. The minimum gas-to-liquid ratio required for stripping is given by ... 

BalHca and Ryu [158] correlated reductions in cell yield in Datura stramonium suspensions with the increased Reynolds stresses associated with higher aeration rates in a 1.2-1 ALR. A more recent study [159] of C. roseus suspensions cultivated in a 1.5-1 bubble column showed that the increased bubble sizes associated with both larger sparger pores and higher aeration rates caused a reduction in system performance. Here, also, it was postulated that the effects were due to increased Reynolds shear stresses in the flow field. However, it was not possible to rule out gas-stripping effects. 

A continuous circulation of groundwater is generated in the area surrounding the remediation well, as aquifer waters replace the annulus water. The circulation thus delivers new contaminants to the stripping zone. Volatile contaminants dissolved in the groundwater are transferred from the liquid to the gas phase and are extracted from the groundwater surface via a double-cased screen. Soil air from the unsaturated zone is also extracted and transported to the off-gas treatment system. 

The Thermatrix, Inc., PADRE process is a commercial, off-gas treatment technology that purifies airstreams contaminated with volatile organic compounds (VOCs). The PADRE vapor treatment process traps VOCs using filter beds that contain a proprietary resin. This regenerative adsorption method involves an on-line treatment bed for infiuent air, while another bed undergoes a desorption cycle. PADRE often works in conjunction with soil vapor extraction or air stripping systems. The PADRE process can be applied at site remediation projects, industrial wastewater facilities, and industrial air processing sites. 

Hereafter we will treat only perfectly mixed stirred-tank reactors, which are considered, and rightly so, as the reference reactors. We consider a rather general case of biotransformation processes involving aerated systems comprising both water and hydrophobic compounds. These last components are often volatile, as in the case of aroma. As a result, losses by gas stripping can be important. 

The HETP of a column, valid for either distillation or dilute-gas absorption and stripping systems in which constant molar overflow can be assumed, and in which no chemical reactions occur, is related to the height of one overall gas-phase mass-transfer unit, HQG, by the equation ... 

Another factor that affects membrane system design is the degree of separation required. The usual target of a gas separation system is to produce a residue stream essentially stripped of the permeable component and a small, highly concentrated permeate stream. These two requirements cannot be met simultaneously a tradeoff must be made between removal from the feed gas and enrichment in the permeate. The system attribute that characterizes this trade-off is called the stage-cut. The effect of stage-cut on system performance is illustrated in Figure 8.15. 

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