Front-flush

WAVE is based on the legacy DW PS software called ROSA (which was described in the first edition of this book) but there are several key differences as described in Table 10.2. Some of the key differences reflect the multi-technology nature of WAVE. For instance, users can simulate the use of RO permeate or concentrate for backwash, front flush or CIP (Clean-In-Place) purposes using WAVE. 

The reaction front reaches the end of the aquifer in the simulation after somewhat less than three pore volumes have been displaced. At this point, the contaminant begins to pass out of the domain. Remediation of the aquifer, however, proceeds slowly, as shown in Figure 32.2. Even after 30 pore volumes have been flushed, some lead remains sorbed to weak sites in the aquifer sediments, and the Pb++ concentration in the groundwater remains above the limits sets as drinking water... 

An optical flame sensor installed at the beginning of the pipeline is the most suitable device for such an isolation system, since the propagating flame from the explosion has to be detected and extinguished. Pressure detectors alone are, in principle, not suited to the case on hand because there is no distinct separation between the pressure and flame fronts for explosion in pipelines. Optical ir sensors that have a relatively low sensitivity to daylight are normally chosen and have proved themselves amply in industrial practice. Therefore, daylight into the pipe in the vicinity of the sensor must be avoided. It is necessary to flush the optical lens with gas (e.g., nitrogen, air) to keep it dust-free. 

Modern pump designs also include a means for flushing the piston with solvent behind the pump seal (not shown in Figure 13.4). The solvent for this is drawn in from a separate reservoir and pumped back into this same reservoir. The purpose is to continuously rinse the piston free of mobile phase residue such that abrasive solute crystals resulting from a mobile phase that has dried out on the piston will not deposit there. These solutes, such as the salts dissolved in the buffered mobile phases used in ion exchange chromatography, may otherwise crystallize on the piston and then damage the piston or the pump seal when the piston moves back and forth. Mobile phases that contain such solutes must be flushed from the system after use so that there is also no crystallization on the front side of the seal. 

Figure 1.11 Reduction of A. vinosum hydrogenase in an FTIR cuvette by illumination in the presence of deazaflavin. An Ar-flushed solution of enzyme in the ready state, supplemented with deazaflavin and EDTA, was illuminated with white light for periods of about 4 min. After each illumination a spectrum was recorded. Reduction proceeds from the front to the back. Using the overview in Fig. 7.6, one can easily identify the several states of the enzyme by looking at the v(CO) frequency. Adapted from (Pierik et al. 1998a).

Horizontal treaters. Multiwell installations normally require horizontal treaters. Fig 2 shows a typical design. Flow enters the front section of the tteatei where gas is flushed. Liq uid falls to the vicinity of the oil-water interface where it is water washed and freewater separated Oil and emulsion rise past the lire tubes and are. skimmed into the oil surge i Irani -her. "Fhe oil-water interface in the inlet section is controlled by an interface level controller that operates a dump valve for the freewater... 

Figure 5. Digital images of surfactant fronts for a) Box A flushed with 4% Tween at a Darcy velocity of 4.7 cm/hr (0.4 pore volumes) and b) Box B flushed with 4% Tween 80 + 5% EtOH at a Darcy velocity of 4.8 cm/hr (0.5 pore volumes).

To evaluate the effects of cosolvent on surfactant delivery and PCE recovery, Box B was flushed with 4% Tween 80 + 5% EtOH at a Darcy velocity of 4.8 cm/hr. The surfactant/cosolvent mixture, which had a density of 0.994 g/cm3, was also representative of a neutral buoyancy flood solution (Shook et al, 1998). It is important to recognize that "neutral buoyancy" refers to density of flushing fluid after solubilization of the DNAPL. Thus, the initial density of the surfactant formulation must be less than that of the resident aqueous phase. Figure 5b shows the location and shape of the 4% Tween 80 + 5% EtOH front after flushing Box B with 0.5 pore volumes of solution. The lower density of the 4% Tween 80 + 5% EtOH solution (0.994 g/cm3) relative to the density of resident pore water (0.998 g/cm3) caused the injected solution to flow preferentially along the top of Box B (Figure 5b). This effect can become severe at low flow rates (Taylor, 1999). The... 

Test Site. The second phase of this investigation was conducted in the hangar deck structure. The walls and floor of the compartment are of brick, the roof is of steel. The front is designed with ten equidistantly spaced 3-foot-square portholes, arbitrarily numbered from 1 to 10, from left to right, when facing the structure. Tests were conducted on painted 1/8 inch thick steel panels which were fitted over the ports flush with the inner wall, painted surface toward the outside. The initial series of tests was conducted on panels with a dry film thickness of 3 to 5 mils (representative of two top coats) the second series of tests was determined on panels with a dry film thickness of over 5 mils (representative of four top coats). 

Install the front piston over the threaded rod and position it flush against the edge of the outer casing.There are no threads in the front piston,so a temporary clamp is set up with a 3/8 nut and a large flat washer. 

Ten of the twelve washers are now slipped over the 9/32 Inch tube. The front washer (end cap) should be flush with the front end of tha tubing. The rear washer is placed one inch from the rear of the tube. The remaining eight washers are spaced equally between the front and rear. Solder all ten washers in lace. 

A 1 piece and a V piece of brass pipe are used to make the endcap assembly. Split the 1 piece and trim as before until It will slip into the V piece, flush with one end. Solder in place. A IV washer is slipped into this end and is soldered in place. The endcap should now slide into the front end of the 8 tube and come to rest against both It, and the front of the 4 tube. Tape the endcap in place for step 0. 

---