Release of Gases

The rapid formation of a liquid can entrap a portion of the air which initially occupies the space between particles, and result in bubble formation. Rapid heating of such a melt can lead to expansion of these bubbles and foaming of the melt. It is possible for the foaming due to trapped air to cause the melt to rise above the upper rim of a crucible, if the crucible is initially filled to the top with batch. Since glass forming melts are usually very efficient at dissolving the bottom of furnaces, care should always be taken to ensure that this does not occur. 

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Practical separation techniques for hquid particles in gases are discussed. Since gas-borne particulates include both hquid and sohd particles, many devices used for dry-dust collection (discussed in Sec. 17 under Gas-Sohds Separation ) can be adapted to liquid-particle separation. Also, the basic subject of particle mechanics is covered in Sec. 6. Separation of liquid particulates is frequently desirable in chemical processes such as in countercurrent-stage contacting because hquid entrainment with the gas partially reduces true countercurrency. Separation before entering another process step may be needed to prevent corrosion, to prevent yield loss, or to prevent equipment damage or malfunc tion. Separation before the atmospheric release of gases may be necessaiy to prevent environmental problems and for regula-toiy compliance. 

FIG. 26-53 Effect of iuitial acceleratiou andhiioyaucy ou the release of gases. (Adapted from S. R. Hanna and F. J. TDtivas, Giiideliues for Use of Vapor Cloud Dispersion Models, 1987. Used hy permission of the American Institute of Chemical Engineers, Center for Chemical Fr ocess Safety. )... 

Incoming water is sprayed through a packed column, which provides for an enlarged surface area, and aids the release of gases from the thin film of water produced in the packing. Depending on the DA size and design, the applied vacuum is maintained either by vacuum pumps or by stream-jet eductors. 

Where complete containment is impractical, exhaust ventilation (preferably to a scrubber) can limit or eliminate exposure to toxic materials. The exhaust ventilation rate (velocity or volumetric rate) may be calculable for volatile liquids from spill size and vapor pressure (U.S. Environmental Protection Agency, Risk Management Program Guidance for Offsite Consequence Analysis, Appendix D, Equation D-l, 1999), but tests to determine concentrations in air usually would be needed for dusty processes and fugitive releases of gases. 

When the metals were studied, the release of gases and vapors was observed. For example, Paracelsus reported that when iron was dissolved in sulfuric acid air comes out like a wind. The differentiation of these kinds of air took more than two centuries. Research on the analysis of gases was extremely productive in developing the basic methods to handle and study gases and even paved the way to design techniques for elementary analysis of the constituents of organisms. Thus the study of gases became the second epoch of analytical chemistry it is called the pneumatic age. ... 

However, if a gaseous reagent or product is involved, the task of homogenisation becomes much more difficult, as the uptake and release of gases from solution are very slow processes. Generally, special designs of agitator are required. 

The energy which maintains the breaking wave is the release of gases and heat, behind the wave crest, so that there is continuous... 

A dry, 100-mL three-necked flask is equipped with a reflux condenser connected to a mineral oil bubbler for the release of gases, a 50-mL pressure-... 

A runaway reaction may have multiple consequences. The high temperature by itself may be critical, as the higher the final temperature, the worse the effects of the runaway. In case of a large temperature increase, some components of the reaction mixture may be vaporized, or some gaseous or volatile compounds may be produced. This, in turn, may lead to further consequences, a pressure increase in the system and/or release of gases or vapor, which may cause secondary damage due to toxicity or flammability. 

Smog Air pollution caused by the reaction of sunlight and chemical compounds such as nitrogen dioxide and hydrocarbons the compounds are usually produced by car exhaust and the release of gases from industries such as coal-fired power plants. 

Emission The release or discharge of a substance into the environment. Generally refers to the release of gases or particulates into the air. 

A growing body of evidence indicates that human activities are causing the earth to warm up. This so-called greenhouse effect is due principally to the release of gases such as methane and carbon dioxide into the atmosphere that act to hamper the radiation of heat into space. Now scientists have found a gas in the atmosphere that is the new champion of greenhouse gases. This gas is trifluo-romethyl sulfur pentafluoride (SF5CF3), which has the structure... 

Vacuum diatomaceous earth filters are a variation of this technology that offer the advantages of visibility during backwashing and of not requiring pressure vessels. Their primary disadvantage is that they run an increased risk of the release of gases in the filter cake that shorten filter runs. 

The crust, hydrosphere and atmosphere formed mainly by release of materials from within the upper mantle of the early Earth. Today, ocean crust forms at midocean ridges, accompanied by the release of gases and small amounts of water. Similar processes probably accounted for crustal production on the early Earth, forming a shell of rock less than 0.0001% of the volume of the whole planet (Fig. 1.2). The composition of this shell, which makes up the continents and ocean crust, has evolved over time, essentially distilling elements from the mantle by partial melting at about 100 km depth. The average chemical composition of the present crust (Fig. 1.3) shows that oxygen is the most abundant element, combined in various ways with silicon, aluminium (Al) and other elements to form silicate minerals. 

The amount of water also influences the BET surface area. The BET surface area of ZrOj is found to decrease with increasing the amount of water (see Table 2). This may be due to that water might retard the release of gases and the rapid expansion of the mixture. 

For a long time the search for petroleum was based on surface evidence of oil, the release of gases and the presence of bitumen-impregnated sand or limestone. This evidence is often misleading since it does not indicate the existence of petroleum at depth. These may be traces of former... 

Although Rebecca designs her pressure release valve to allow gas to escape when the pressure reaches 1000 kPa, she hopes it will never need to be used. To avoid the release of gases, she informs the rest of her team that they should be careful to design the process to keep the temperature well below 1295 °C. 

The importance of the Earth surface to atmospheric chemistry lies in the fact that it acts as an emitter and/or as a receiver of atmospheric trace substances. In this section we discuss concepts that have been found useful in describing these processes. The transport of gases across the ocean surface is reasonably well understood. The release of gases from soils, in contrast, cannot be modeled and must be explored by field studies. In the literature, much emphasis has been placed on the absorption of gases at the ground surface, a process referred to as dry deposition. 

Bar-Nun A, Herman G, Laufer D, Rappaport ML (1985) Trapping and release of gases by water ice and implications for icy bodies. Icaras 63 317-332... 

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