Capture zone

Capture zones are zones in which source emissions will be captured by a source-capturing system, and where the capture efficiency is determined and shall be maintained over the working period. From the pollutant concentration point of view, the capture zone is uncontrolled (e.g., workers shall not enter a capture zone without additional protection). 

Figure 12.35b shows a model of the machine on the scale of 1 to 1. Many details and surfaces are made in the correct size and location to achieve a good reproduction of the actual capturing zone. The capture efficiency a is used for the evaluation of the system and it is defined as the ratio between the flow rate of the contaminant Sg directly captured from the process and the total flow rate of the contaminant S released from the process ... 

Fig.8a, b a Liposome immunocompetition assay (LIC) J l,liposome/PCB competition zone, b Liposome immunoaggregation assay (LIA) R2,liposome/antibody aggregation zone. Cl, C2 anti-biotin capture zones. Published with permission of ACS Copyright Office [209]... 

Typically, application of science involves prediction of function such as determining at what rate a well must be pumped to create a suitable capture zone. What period of time will be required to biodegrade a mass of contaminant within a plume How much activated carbon will be required to treat the discharged vapor What will be the cost of electricity to power the remediation system Engineers are more likely capable of designing a balanced remediation system that has flow rates matched to reaction times or water-air contact rates. Tank sizes, power consumption, and similar rate-time-related calculations also fall within the specialty of the engineer. 

Important to any aquifer restoration program is the radius of influence or capture zone to be anticipated during pumping. The radius of influence (rQ) for a vertical pumping well can be calculated using the following equation. 

Grubb, S., 1993, Analytical Model for Estimation of Steady-State Capture Zones of Pumping Wells in Confined and Unconfined Aquifers Ground Water, Vol. 31, No. 1, pp. 27-32. 

FIGURE 9.1 Capture zone at a brine spill site. 

Ahlfeld, D. P. and Sawyer, C. S., 1990, Well Location in Capture Zone Design Using Simulation and Optimization Techniques Ground Water, Vol. 28, No. 4, pp. 507-512. 

Javandel, I. and Tsang, C. F., 1986, Capture-Zone Type Curves A Tool for Aquifer Cleanup Ground Water, Vol. 24, No. 5, pp. 616-625. 

FIGURE 12.18 Corrected water table piezometer surface contour map showing regional hydrogeologic gradient toward the southwest. Note the impact of recovery systems within their area of influence or capture zones. (After Testa et al., 1989.)... 

The potential of washing the contaminant beyond the capture zone and the introduction of surfactants to the subsurface may cause problems. The technology should be used only where flushed contaminants and soil flushing fluid can be contained and recaptured. 

As a first assumption, we will assume that the New Brighton well was located in the center of the plume. Compute the capture zone and then the concentrations within this capture zone. The capture zone is given by... 

The solution to equation (E6.13.2) for this application is given in Figure E6.13.1 at various lateral distances from the peak concentration. The capture zone mean is 0.42 g/m or almost 100 times the recommended limit, which would raise concern in New Brighton. The leakage from the capture zone at x = 4,000 m for this scenario is computed to be 47 g, or sufficient mass to result in a concentration of 9 x 10 g/m for a similar capture zone. It is possible then that almost all of the plume was captured by the city of New Brighton, so the problem may not cover a wider area than the immediate downstream cities. This, at least, is one positive result of the low transverse dispersion of groundwater plumes. 

The advective control model presented in this chapter is an extension of the formulation presented by Mulligan and Ahlfeld (1999a) that uses both contaminant pathline and capture zone simulation to constrain plume capture designs. In this chapter, additional constraints and algorithmic procedures... 

Reverse tracking is also used in the advective control model, where the particles are used to delineate the capture zone of all extraction wells. Reverse tracking is performed by reversing the direction of all velocity vectors and integrating from the final location backward to the initial location... 

In the first stage of the solution process, the advective control model seeks a pumping scheme in which the capture zone fully encompasses all control points representing the contaminant plume. The capture zone is simulated by tracking particles from extraction wells backwards through the velocity field. To represent the plume capture constraints numerically, a distance measure is used in which the minimum distance between each plume control point and all particles (see Figure 1) is constrained. When the distance between a control point and particle pathline equals zero then the plume control point lies within the capture zone. To ensure capture of the entire plume, the constraint function must equal zero for all control points. The reverse tracking formulation is stated as... 

Figure I. In reverse tracking, pathlines represent the capture zone and the constraint function measures the minimum distance between a plume control point and all pathlines. Pathlines are shown as dashed curves and the gray area represents the contaminant plume to be contained.

Shafer, J. M. (1987). Reverse pathline calculation of time-related capture zones in nonuniform flow. Ground Water, 25(3), 283-289. 

The support plays an important effect in the adsorption kinetics of CO on supported clusters. Indeed CO physisorbed on the support is captured by surface diffusion on the periphery of the metal clusters where it becomes chemisorbed. The role of a precursor state played by CO adsorbed on the support is a rather general phenomenon. It has been observed first on Pd/mica [173] then on Pd/alumina [174,175], on Pd/MgO [176], on Pd/silica [177], and on Rh/alumina [178]. This effect has been theoretically modeled assuming the clusters are distributed on a regular lattice [179] and more recently on a random distribution of clusters [180]. The basic features of this phenomenon are the following. One can define around each cluster a capture zone of width Xg, where is the mean diffusion length of a CO molecule on the support. Each molecule physisorbed in the capture zone will be chemisorbed (via surface diffusion) on the metal cluster. When the temperature decreases, Xg increases, then the capture zone increases to the point where the capture zones overlap. Thus the adsorption rate increases when temperature decreases before the overlap of the capture zones that occurs earlier when the density of clusters increases. Another interesting feature is that the adsorption flux increases when cluster size decreases. It is worth mentioning that this effect (often called reverse spillover) can increase the adsorption rate by a factor of 10. We later see the consequences for catalytic reactions. 

The flow net is a helpful tool for depicting the area of an aquifer from which a well captures water. It is essential to be able to delineate this area to avoid pulling contaminated groundwater into a well used for drinking water production areas of known contamination must lie outside the well s capture zone. Alternatively, if a well is to be used for groundwater remediation (removal of contaminated groundwater), the capture zone must enclose the contaminated areas. Capture curves, which are the boundaries of capture zones, may be drawn readily by inspection if a flow net is available the capture zone includes all stream tubes that terminate in the well. The following are two examples of capture curves. 

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