Contaminated gas

The minienvironment approach to contamination control has been increasing in use. A minienvironment is a localized environment created by an enclosure that isolates the product wafer from contamination and people (48). Another approach is using integrated processing, where consecutive processes are linked in a controlled environment (32). Both requite in situ sensors (qv) to measure internal chamber temperatures, background contamination, gas flow rates, pressure changes, and particularly wafer temperature (4). 

Water used as the coolant in an indirect-contact condenser (i.e., shell-and-tube heat exchanger), not in contact with contaminated gas stream, and is reusable after cooling... 

The use of canopy hoods or remote capture of fume is usually considered only after the rejection of source or local hood capture concepts. The common reasons for rejecting source or local hood capture are usually operating interference problems or layout constraints. In almost all cases, a canopy hood system represents an expensive fume collection approach from both capital and opetating cost considerations. Remote capture depends on buoyant ait curtents to carry the contaminated gas to a canopy hood. The rising fume on its way to the hood is often subjected to cross-drafts within the ptocess buildings or deflected away from the hood by objects such as cranes. For many of these canopy systems, the capture efficiency of fume may be as low as 30-50%. 

Scrubbing The process of cleaning contaminated gas by passing it through a water spray or cascade. 

Soiling index The degree of soiling of a filter paper fitted in a sampling device tluough which a contaminated gas has been passed. 

Wet scrubbers have found widespread use in cleaning contaminated gas streams because of their ability to effeetively remove both particulate and gaseous pollutants. Specifically, wet scrubbing describes the technique of bringing a contaminated gas stream into intimate contact with a liquid. The types most widely used for particulate control are spray towers, packed-bed units, ionizing wet scrubbers, and venturi scrubbers. 

Viewed in this context, the Three-Mile Island (TMI) accident was the coup de grace for an already foundering industry. In spite of the fact that the hydrogen gas bubble that accumulated in Reactor 2 did not explode, although some contaminated gas escaped and that the commissions who investigated the accident faulted human error rather than equipment failure, TMI caused (as the New York Times... 

Where FW contains bicarbonate or carbonate alkalinity (as calcium, magnesium, or sodium salts), these salts undergo thermal decomposition in the boiler, and the steam-volatile contaminant gas carbon dioxide is introduced into the steam distribution system, as shown ... 

Minimum Duct Velocity. Once the types and locations of hoods, enclosures and booths have been established and the exhaust rates determined, it is necessary to design the ductwork to transfer the contaminated gas to the collection or cleaning device. An essential parameter required for this purpose is the minimum duct or conveying velocity, Vfmm, which is required to ... 

The idea behind this hypothesis is that an early generation of AGBs might have evolved and polluted the interstellar medium with nuclearly processed material, so that the new generations of stars were born from an already contaminated gas (D Antona et al. 1983 Cottrell Da Costa 1981). 

Using the modelling approach above, the predicted response of a CO2 correlation spectroscopy system will now be shown. This requires knowledge of the transmission spectrum of CO2 gas, so that predictions from the model can be made, for the expected modulation index, SNR (signal to noise ratio) and cross-sensitivity to a contaminant gas. 

The capture of C02 from process streams has been performed already for some decades in various industries. Examples of the capture of C02 from industrial applications are the production of hydrogen-containing synthesis gas for the production of ammonia or synthetic fuels or the purification of natural gas (from contaminated gas fields). Since in these processes, C02 is usually considered an undesired by-product, it is then released into the atmosphere. 

APHA. 1985b. Organic contaminants Gas chromatographic/mass spectrophotometric method-method 516. In Standard methods for the examination of water and wastewater. 16th ed. American Public Health Association, Washington, DC, 612-619. 

Semiconductors Process gases, plasma gases, substrate analysis for contaminants Gas composition analysis Raw materials screening Trace analysis Quality control... 

Occelli, M. L. and Stencel, J. M., "Surface-metals Interactions in Fluid Cracking Catalysts During the Upgrading of Nickel Contaminated Gas Oils," 9th Int. Congr. Catalysis, Calgary, Canada (1988), accepted. 

The contaminant absorption and recovery (CAR) technology treats volatile organic compounds (VOCs) in gas streams from such processes as soil vapor extraction, air sparging, and air stripping. The contaminated gas stream passes through an absorption solvent, which is a nonvolatile... 

For reasons that will be explained in a subsequent chapter, the team found that the application of a technology known as bioflitration was considered the best remediation method. The contaminated gas is pumped through a column packed with a material that performs two functions (1) it provides for efficient contact between the air passing through it and water, and (2) it serves as a scaffold for the development of a bacterial colony. Figure 1.7 shows a typical biofiltration arrangement. The team must develop a system that has a very low pressure drop so that the process can be constructed from plastic tanks and low-pressure pumps to save money. In a further effort to save money, the process should have a small footprint. 

Cyclone a device for extracting dust from industrial waste gases. It is in the form of an inverted cone into which the contaminated gas enters tangential from the top the gas is propelled down a helical pathway, and the dust particles are deposited by means of centrifugal force onto the wall of the scrubber. 

For those processes producing contaminated gas streams that have no recovery value, incineration may be the most acceptable route when the gas streams are combustible. There are presently two methods in common use direct flame and catalytic oxidation. The former usually has lower capital-cost requirements, but higher operating costs, particularly if an auxiliary fuel is required. Either method provides a clean, odorless effluent if the exit-gas temperature is sufficiently high. 

The adsorption column is a vertical cylinder with an inside diameter of 6 ft (1.8 m) and a height of 15 ft (4.57 m). It operates on the following cycle 4 h in the adsorption mode, 2 h for heating and desorbing, 1 h for cooling, 1 h for standby. An identical column treats the contaminated gas while the first one is not in the adsorption mode. The system is required to recover 99.5 percent of the TCE by weight. 

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