Emission-Limited Discharge

For emission-limited discharge, the charge emitted into the bulk of the photoreceptor during a transit time is small compared to the surface charge. Provided the field is uniform, the transit time is 

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Figure 2 shows results calculated from Eq. (28). The calculations assume g = 3.0, L = 20 im. VQ = 500 V. 7J0 = 1.0. and nQ = 10-6 cm2/ys at VQ. The results show the maximum intensities for which emission-limited discharge can be sustained for different values of Pe and Pm. The results show the importance of a field-dependent carrier supply and mobility on the discharge process. Only in the case where Pm = Pe is the discharge independent of the field dependencies of the photogeneration and transport processes. 

Results of emission-limited discharge measurements are frequently described as the xerographic gain, Gr The gain is defined as the ratio of the rate of decrease of the surface-charge density to the photon intensity, assuming the charge... 

Known models describing emission-limited discharge differ in mechanisms responsible for the charge transfer from the surface into the bulk. Most often these mechanisms include Schottky emission, tunneling, and thermal activation fiom discrete traps (Abkowitz et al. 1995 Kressman et al. 1999 Sessler 1999). Publications that allow for the continuous spectrum of surface traps are relatively few in number (Watson 1990 Watson et al. 1991), although the need for such an approach is obvious due to the highly disordered nature of the polymer surface. 

For the emission-limited discharge, the photogeneration quantum yield ( 1spd is given as ... 

Similarly, airborne emission limits have been estabHshed by the NRC for nonrestricted areas. Limits of surface contamination must be estabHshed to provide a safe workplace for users (19). The appHcation of the as-low-as-reasonably-achievable (ALARA) principle to the above draws on the creative talents of the user to regard the limits as nonapproachable barriers and not as tolerable maxima for discharge. 

The type of vapor treatment that is used will depend on factors such as the contaminant concentrations in the extracted vapors and the air emission discharge limitations for the site. Highly contaminated vapors at a site with stringent air emission limitations may require a multistep vapor treatment train, such as thermal oxidation, followed by carbon adsorption. Less contaminated vapors at a site with less stringent air emission limitation may require minimal or no vapor treatment. Fields et al.38 described the following rules of thumb for selecting vapor treatment ... 

Emission Standard A quantitative limit on the emission or discharge of a potentially toxic substance from a particular source. Tire simplest system is uniform emission standard where the same limit is placed on all emissions of a particular contaminant. 

Emission limits for discharging wastewater into running water are specific for each country. As an example, Table 11.10 show some key parameters sampled for German standards. 

Table 77.70 Limits of emissions for discharge to running water [22],...

Figure 2 The maximum intensities at which the photoinduced discharge can be sustained under emission-limited conditions.

Figure 6 The photoinduced discharge under emission-limited (dashed line) and space-charge-perturbed conditions (solid lines).

Another important consideration in drying PVC is the emission of VC. U.S. ERA emission limitations of <5 ppm on VC must be strictly maintained. This criterion on VC sometimes dictates the selection of the drying equipment for PVC. In other countries the discharge limit on VC emission may be less stringent. 

Previously a typical limit for the total dust concentration in the discharged gas has been 50 mg/Nm with a le content of 10 mg/Nm. However, other restrictions, such as a total mass emission limit for lead for the site, have required the meeting of a much lower lead concentration in the discharged gas. Typically a discharge of less than 5 mg Pb/Nm is required, and this has necessitated the use of high efficiency bag filters wherever possible. 

The Oslo and Paris Commission (OSPAR) has issued a Recommendation for emission and discharge limit values for E-PVC (2000/3) and a Decision for emission and discharge limit values for S-PVC (98/5). This commission has also issued a Recommendation on BAT for the manufacture of E-PVC (99/1). ... 

No EPA regulations or guidances specify the levels of destrnction, levels of air emissions, water discharge limits, or other environmental requirements for alternative treatment technologies used to treat nonstockpile materiel. Although some established environmental requirements may be applicable, EPA and the states usually develop environmental requirements on a case-by-case basis. 

Are the discharge results in compliance with the emission limits ... 

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

The Resource Conservation and Recovery Act (RCRA) controls the disposal of ha2ardous waste. SARA Tide III governs the toxic iaventory and emission reporting the Clean Water Act (CWA) sets the limits for metals that can be present ia water discharge and the Clear Air Act (CAA)... 

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