Continuous release

Once the scenario has been identified, a source model is used to determine the quantitative effect of an accident. This includes either the release rate of material, if it is a continuous release, or the total amount of material released, if it is an instantaneous release. Eor instance, if the scenario is the mpture of a 10-cm pipe, the source model would describe the rate of flow of material from the broken pipe. 

The dispersion model is typically used to determine the downwind concentrations of released materials and the total area affected. Two models are available the plume and the puff. The plume describes continuous releases the puff describes instantaneous releases. 

While either rupture disks or relief valves are allowed on storage tanks by Code, rupture disks by themselves should not be used on tanks for the storage of highly hazardous toxic materials since they do not close after opening and may lead to continuing release of toxic material to the atmosphere. 

Assume a continuous release of pressurized, hquefied cyclohexane with a vapor emission rate of 130 g moLs, 3.18 mVs at 25°C (86,644 Ib/h). (See Discharge Rates from Punctured Lines and Vessels in this sec tion for release rates of vapor.) The LFL of cyclohexane is 1.3 percent by vol., and so the maximum distance to the LFL for a wind speed of 1 iti/s (2.2 mi/h) is 260 m (853 ft), from Fig. 26-31. Thus, from Eq. (26-48), Vj 529 m 1817 kg. The volume of fuel from the LFL up to 100 percent at the moment of ignition for a continuous emission is not equal to the total quantity of vapor released that Vr volume stays the same even if the emission lasts for an extended period with the same values of meteorological variables, e.g., wind speed. For instance, in this case 9825 kg (21,661 lb) will havebeen emitted during a 15-min period, which is considerablv more than the 1817 kg (4005 lb) of cyclohexane in the vapor cloud above LFL. (A different approach is required for an instantaneous release, i.e., when a vapor cloud is explosively dispersed.) The equivalent weight of TNT may be estimated by... 

Characteristic source dimension for continuous releases of dense gases, defined by Eq. (26-72), length... 

Initial plume volume flux for dense gas dispersion, voliime/time Continuous release rate of material, mass/time Instantaneous release of material, mass Release duration, time T Absolute temperature, K... 

Sutton Micrometeorology, McGraw-Hill, 1953, p, 286) developed a solution to the above difficulty by defining dispersion coefficients, O, Gy, and O, defined as the standard deviation of the concentrations in the downwind, crosswind, and vertical x, y, z) directions, respectively, The dispersion coefficients are a function of atmospheric conditions and the distance downwind from the release. The atmospheric conditions are classified into six stability classes (A through F) for continuous releases and three stability classes (unstable, neutral, and stable) for instantaneous releases. The stability classes depend on wind speed and the amount of sunlight, as shown in Table 26-28,... 

The plume model describes continuous release of material. The solution depends on the rate of release, the atmospheric conditions, the height of the release above ground, and the distance from the release. In this case, the wind is moving at a constant speed u in the x direction. The equation for the average concentration for this case is (Crowl and Louvar, 1990, p. 142) ... 

Example 1 Continuous Release What continuous release of chlorine is required to result in a concentration of 0.5 ppni at 300 m directly downwind on the ground Also, estimate the total area affected. Assume that the release occurs at ground level and that the atmospheric conditions are worst case. 

One of the effects of wind speed is to dilute continuously released pollutants at the point of emission. Whether a source is at the surface or elevated, this dilution takes place in the direction of plume transport. Figure 19-2 shows this effect of wind speed for an elevated source with an emission of 6 mass units per second. For a wind speed of 6 m s", there is 1 unit between the vertical parallel planes 1 m apart. When the wind is slowed to 2 m s there are 3 units between those same vertical parallel planes 1 m apart. Note that this dilution by the wind takes place at the point of emission. Because of this, wind speeds used in estimating plume dispersion are generally estimated at stack top. 

For continuous release of gas or vapour the steady-state dilution ventilation required to reduce the atmospheric pollutant to a level below its hygiene standard is given by... 

Instantaneous and continuous releases including spills, leaks, fires, explosions, and BLEVEs. 

Continuous releases of concentrated HjS streams must be segregated in a separate flare system to limit the extent of fouling and plugging problems. Releases of HjS such as diversion of sour gas product to flares during shutdown or upset of a downstream sulfur recovery unit are considered to be continuous, but safety valve releases are not included in this category. However, if a special HjS flare system is provided for continuous releases, the concentrated HjS safety valve releases should be tied into it rather than into the regular flare system. Due to the nature of HjS one should plan on frequent inspection and flushing of HjS flares to remove scale and corrosion products. 

The diffusion of individual plume elements, according to Gifford (1959) can be deiernnned from the general Gaussian diffusion model. The model is usually in two basic forms, a puff release - appropriate for an accident, and a continuous release for "routine" release or an accident of long duration. 

AFTOX is a Gaussian dispersion model that is used by the Air Force to calculate tu accidental releases. Limited to non-dense gases, it calculates the evaporation rate from liquid spills. It treats instantaneous or continuous releases from any elevatic ... 

Technica, 1988 Wheatley, 1988 Ziomas, 1989). Plume dispersion consists of two phases the gravityslumping and passive dispersion period. Continuous releases with any time-profile and puff releases as of short duration continuous releases are treated using the release category and th r... 

Wheatley, C.J., et al., 1988, Comparison and Test of Model for Atmospheric Dispersion of Continuous Releases of Chlorine, SRD Report R438, UKAEA, July. ... 

Investigations revealed that the initial fire was due to a small, continuous release from the transfer lines. The leakage was ignited by hot surfaces of the truck s engine. The fireball was found to have a maximum diameter of approximately 40 m (130 ft). It rose to 25 m (80 ft) above ground level. 

In a later paper, Brasie (1976) gives more concrete recommendations for determining the quantity of fuel released. A leak potential can be based on the flashing potential of the full amount of liquid (gas) stored or in process. For a continuous release, a cloud size can be determined by estimating the leak rate. For a combined liquid-vapor flow through holes of very short nozzles, the leak rate (mass flow per leak orifice area) is approximately related to the operating overpressure according to ... 

As mentioned earlier, toxic releases may consist of continuous releases or instantaneous emissions. Continuous releases usually involve low levels of to.xic emissions, wiiich are regularly monitored and/or controlled. Such releases include conlinuous slack emissions and open or aerated chemical processes in wliich certain volatile compounds are allowed to be stripped off into the atmosphere tliroiigh aeration or agitation. Mathematical models for these releases to tlie enviroiuncnt are covered in detail in Part III. 

Aromatic biguanides such as proguanil (181) have been found useful as antimalarial agents. Investigation of the metabolism of this class of drugs revealed that the active compound was in fact the triazine produced by oxidative cyclization onto the terminal alkyl group. The very rapid excretion of the active entity means that it cannot be used as such in therapy. Consequently, treatment usually consists in administration of either the metabolic precursor or, alternately, the triazine as some very insoluble salt to provide slow but continual release of drug. 

Another example is the determination of bentazone in aqueous samples. Bentazone is a common medium-polar pesticide, and is an acidic compound which co-elutes with humic and/or fulvic acids. In this application, two additional boundary conditions are important. Eirst, the pH of the M-1 mobile phase should be as low as possible for processing large sample volumes, with a pH of 2.3 being about the best that one can achieve when working with alkyl-modified silicas. Secondly, modifier gradients should be avoided in order to prevent interferences caused by the continuous release of humic and/or fulvic acids from the column during the gradient (46). 

Surprisingly the water consumption of a starter battery, provided it contains anti-monial alloys, is affected by the separator. Some cellulosic separators as well as specially developed polyethylene separators (e.g., DARAMIC V [76]) are able to decrease the water consumption significantly. The electrochemical processes involved are rather complex and a detailed description is beyond the scope of this chapter. Briefly, the basic principle behind the reduction of water loss by separators is their continuous release of specific organic molecules, e.g., aromatic aldehydes, which... 

For the preparation of nanoparticles based on two aqueous phases at room temperature one phase contains chitosan and poly(ethylene oxide) and the other contains sodium tripolyphosphate. The particle size (200-1000 nm) and zeta potential (between -i- 20 mV and -l- 60 mV) could be modulated by varying the ratio chitosan/PEO-PPO. These nanoparticles have great proteinloading capacity and provide continuous release of the entrapped protein (particularly insulin) for up to one week [100,101]. 

The presence of nanopartides suspended within the starch matrix would ensure continuous release of ions into the nutrient media. Copper ions released by the nanopartides may attach to the negatively charged bacterial cell wall and rupture it, thereby leading to protein denaturation and cell death [31]. The attachment of both ions and nanopartides to the cell wall caused accumulation of envelope protein precursors, which resulted in dissipation of... 

It is easy to speculate that in an active neuron with a rapid firing pattern, the continued release of a peptide may eventually lead to depletion of the peptide occurring. This has been shown in the peripheral nervous system. If this also happens in the CNS it would provide a mechanism whereby the release and resultant receptor effects of a transmitter no longer match the firing pattern and demands of the neuron and so could contribute to long-term adaptations of neurons by a reduction in the time over which a peptide is effective. 

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