Contaminating gases

Air contaminants Gases sulphur oxides, halogen compounds Mists aerosols, salt, alkalies Particulates sand, dust, grease... 

Oxygen, nitrogen, carbon dioxide, ammonia, hydrogen sulfide, sulfur dioxide, and other contaminant gases are generally present to some degree in all steam and condensate systems. 

Although oxygen and carbon dioxide are the most important corrosive gases found in steam-condensate systems, small amounts of other contaminant gases are usually present. These may originate in various ways, for example ... 

If we consider the influence of gases on conductivity, we can understand how Rosenberg 1391 succeeded in separating of odorous substances by means of a device containing / -carotene. The detection contaminating gases in the atmosphere by organic semiconductors is also a possibility. 

The studies made on the Pd MIS structure have demonstrated that H2 sensors can be reliable devices, with high sensitivity and fast response. On the basis of the investigated structures and results, it has been established that the main mechanism responsible for the sensitivity is the change in contact potential. Once the a-Si H film is in some way protected from contaminating gases or liquids, MIS H2 sensor performances are mainly determined, controlled, and limited by the quality, poisoning, and stability of the Pd film or of any suitable catalytic material used. 

If the contaminating gases are condensible, the effective speed of evacuation can be increased by the use of cold traps. The effectiveness of a cold trap will depend on its effective area and on the shape of the connecting tubing while the temperature of the trap will determine which gases will be condensed. 

Preheat burners are usually designed to increase the temperature of the contaminated gases to the required catalyst discharge gas temperature without regard to the heating value of the contaminants (especially if considerable concentration variation occurs). 

In one application it has been shown that using OEC can increase the efficiency of SOx removal from exhaust gases from a combustion process. One way of removing SOx is to inject a transfer agent into the contaminated gases to collect S03 so that it can be released as H2S in a stripper. Additives are used to convert the S02 in the gases to S03. In a fluid catalytic cracker (FCC), OEC was used to reduce SOx.29... 

We consider a single bubble that undergoes a time-dependent change of volume in an incompressible, Newtonian fluid that is at rest at infinity. The bubble may either be a vapor bubble (that is, contains the vapor of the liquid) or it may contain a contaminant gas that is insoluble in the liquid (or at least dissolves only very slowly compared with the time scales associated with changes in the bubble volume) or a combination of vapor and contaminant gases. We assume, at the outset, that the bubble remains strictly spherical, and thus that the bubble surface moves only in the radial direction. It follows that the motion induced in the liquid must also be radial, so that... 

Contaminated gases are collected by a capture system and delivered to the preheater inlet, where they are heated by indirect contact with the hot incinerator exhaust. Gases are mixed thoroughly with the burner flame in the upstream portion of the unit, and then passed through the combustion zone, where combustion process is completed. An efficient thermal incinerator design must provide ... 

Fig. 6.11-5 Examples of media solutions for some of the more important contaminant gases (courtesy Purafil, Doraville, GA, USA)...

In the pressure range 10 7-10 9 mm, leak checking with He or H2 is as effective and simple as at higher pressures. Detection of any mercury vapor is particularly easy after bakeout. Cooling with liquid nitrogen reduces the mercury pressure permanently (p < 10 34 mm) with contaminant gases, the pressure drops only temporarily, and rises as soon as the cooled surface is saturated. Very small pinholes, which do not prevent the achievement of pressures less than 10-9 mm are, however, difficult to locate. Isolating parts of the system from the pumps to determine the pressure rise, and patience are the only remedies. 

Study sensor response to H2 in the presence of contaminant gases... 

Figure 3. Response of a Sensor to Low-Level Contaminant Gases in Air...

The first, third, fifth, and the last subsets of data were collected with 0.5% H2 in dry air with no contaminant gas, providing a reference background. The sensor exhibited enhanced response in the presence of CO and H2S. The sensor remains functional during and after repeated exposure to any of these contaminant gases. 

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