Air injection

Another method to reduce silting is to periodically inject air into the cooling water. Air injection must normally be more frequent to achieve the same results as with backwashing. This method is also more expensive and adds to the venting problem. It has the advantage, however, that no process upsets occur as experienced occasionally when backwashing. Air injection, to be effective, must be performed on a routine schedule. A timing mechanism may be used to inject air for short time Intervals over a period of several days. 

Sometimes a combination of backwashing and air injection is used with good results. During backwashing, silt deposits may remain in the space between the back face of the tubesheet and the nozzle. Air can be injected through the lower tubesheet vent or drain connections to remove these deposits. 

Many factors affect the mechanical design of evaporator systems, particularly of the calandrias. The two most important are the temperatures and pressures to which the equipment will be subjected. Not only are the temperatures and pressure during normal operation important, but upset, startup, shutdown, dryout, cycling, pulsating pressure, and safety relief requirements are equally important. Other considerations include external loadings from supports or piping and vibrations transmitted from external sources. Wind loadings and earthquake loads must also be considered. Anticipated life expectancy and future service should be considered. 

An analysis of the process should be carefully conducted to determine the maximum fluid pressures and the degree of vacuum that can be anticipated. It is important to determine both minimum and maximum anticipated operating temperatures in order to obtain the design temperature. This combination of temperatures and pressures will determine the mechanical design of the equipment. 

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Like steam injection, in-situ combustion is a thermal process designed to reduce oil viscosity and hence improve flow performance. Combustion of the lighter fractions of the oil in the reservoir is sustained by continuous air injection. Though there have been some economic successes claimed using this method, it has not been widely employed. Under the right conditions, combustion can be initiated spontaneously by injecting air into an oil reservoir. However a number of projects have also experienced explosions in surface compressors and injection wells. 

If there are significant amounts of both volatile and nonvolatile contaminants, remediation may be achieved by a combination of Hquid and vapor extraction of the former, and bioremediation of the latter. This combination has been termed "bioslurping", where the act of pumping out the Hquid contaminant phase draws in air at other wells to stimulate aerobic degradation (20). Such bioremediation requites that there be enough nutrients to allow microbial growth, and fertilizer nutrients are frequendy added at the air injection wells. Bioslurping has had a number of weU-documented successes. 

The in situ combustion method of enhanced oil recovery through air injection (28,273,274) is a chemically complex process. There are three types of in situ combustion dry, reverse, and wet. In the first, air injection results in ignition of cmde oil and continued air injection moves the combustion front toward production wells. Temperatures can reach 300—650°C. Ahead of the combustion front is a 90—180°C steam 2one, the temperature of which depends on pressure in the oil reservoir. Zones of hot water, hydrocarbon gases, and finally oil propagate ahead of the steam 2one to the production well. 

Maintenance and propagation of the combustion front are problems. This has led to a near-weUbore technology in which the same well is used for air injection and oil production. The combustion front needs to be propagated for a relatively short distance (275). 

In most cases, FBCs employ some type of air injection system in the floor of the furnace both to impart turbulence into the burning fuel bed and supply combustion air. Secondary and tertiary air ports may be located above the burning fuel bed. 

Black Liquor Soap Recovery. Black Hquor soap consists of the sodium salts of the resin and fatty acids with small amounts of unsaponifiables. The soap is most easily separated from the black Hquor by skimming at an intermediate stage, when the black Hquor is evaporated to 25% soHds (7). At this soHds level, the soap rises in the skimmer at a rate of 0.76 m/h. At higher soHds concentrations, the tall oil soap is less soluble, but higher viscosity lowers the soap rise rate and increases the necessary residence times in the soap skimmer beyond 3—4 hours. The time required for soap recovery can be reduced by installing baffles, by the use of chemical flocculants (8,9), and by air injection into the suction side of the soap skimmer feed pump. Soap density is controUed by the rate of air injection. Optimum results (70% skimmer efficiency) are obtained at a soap density of 0.84 kg/L (7 lb/gal). This soap has a minimum residual black Hquor content of 15% (10—12). 

Injection of Humidified and Heated Compressed Air. Compressed air from a separate compressor is heated and humidified to about 60% relative humidity by the use of an HRSG and then injected into the compressor discharge. Figure 2-41 is a simplified schematic of a compressed air injection plant, which consists of the following major components ... 

A commercial combustion turbine with the provision to inject, at any point upstream of the combustor, the externally supplied humidified and preheated supplementary compressed air. Engineering and mechanical aspects of the air injection for the compressed air injection plant concepts are similar to the steam injection for the power augmentation, which has accumulated significant operating experience. 

Humidified Compressed Air Injeetion System are about the same. This is due to the faet that though the initial eost to install the Compressed Air System, for a turbine of about 100 MW, is about 3.7 million as compared to about 1.7 million for a steam injection system, the power generated by the Heated and Humidified Compressed Air Injection System is much higher. 

The rate of return on the steam injection system is higher than the Compressed Air Injection System. This is due to the fact that though the efficiency of the steam injection system and the compressed air injection system is about the same, however, the initial cost of the steam injected system being over 50% lower than the compressed air injection system accounts for the difference. 

Generator Power Output Capacity. The generator, as a general rule of thumb is oversized by about 20% above the turbine rated load. The changes have to be limited to that region by limiting the steam or Compressed Air Injection. 

With this particular design, primary cooling is achieved by film cooling with cold air injected through small holes over the airfoil surface (Figure 9-21). The temperature distribution is shown in Figure 9-22. 

Air, primary The actual quantity of air injected into a space before secondary air induction occurs. 

A service well is a well drilled or completed for the purpose of supporting production in an existing field. Wells of this class are drilled for the following specific purposes gas injection (natural gas, propane, hutane, or flue gas), water injection, steam injection, air injection, salt water disposal, water supply for injection, observation, injection for in-situ combustion. 

Serious research in catalytic reduction of automotive exhaust was begun in 1949 by Eugene Houdry, who developed mufflers for fork lift trucks used in confined spaces such as mines and warehouses (18). One of the supports used was the monolith—porcelain rods covered with films of alumina, on which platinum was deposited. California enacted laws in 1959 and 1960 on air quality and motor vehicle emission standards, which would be operative when at least two devices were developed that could meet the requirements. This gave the impetus for a greater effort in automotive catalysis research (19). Catalyst developments and fleet tests involved the partnership of catalyst manufacturers and muffler manufacturers. Three of these teams were certified by the California Motor Vehicle Pollution Control Board in 1964-65 American Cyanamid and Walker, W. R. Grace and Norris-Thermador, and Universal Oil Products and Arvin. At the same time, Detroit announced that engine modifications by lean carburation and secondary air injection enabled them to meet the California standard without the use of catalysts. This then delayed the use of catalysts in automobiles. 

It will be noted that for a Newtonian fluid (n = 1) equation 5.11 gives — 1 for all values of b. In other words, the pressure drop will be unaffected by air injection provided that the liquid flow remains laminar. In practice, because of losses not taken into account in the simplified model, the pressure drop for a Newtonian fluid always increases with air injection. 

Furthermore, it can be seen that for turbulent flow when n — 2, air injection would result in substantial increases in pressure drop. 

The pressure drop for a fluid exhibiting a yield stress, such as a Bingham plastic material, can be similarly reduced by air injection. 

In a practical situation, air injection can be beneficial in that, when a pipeline is shut down, it may be easier to start up again if the line is not completely full of a slurry. On the other hand, if the pipeline follows an undulating topography difficulties can arise if air collects at the high spots. 

Air injection may sometimes be an alternative to deflocculation. In general, defloccu-lated suspensions flow more readily but they tend to give much more highly consolidated sediments which can be difficult to resuspend on starting up following a shutdown. Furthermore, deflocculants are expensive and may adversely affect the suitability of the solids for subsequent use. 

The liquid feed line is known as the submergence limb and the line carrying the aerated mixture as the rising main. The ratio of the submergence (hs) to the total height of rising main above the air injection point (hr + hs) is known as the submergence ratio. + hr/hs)]-K... 

FIGURE 29.13 Influence of air injection on the silanization efficiency (mixer volume 45 L, fill factor 0.4, silanization temperature 145°C, time 150 s). 

Another measure to improve the removal of ethanol is air injection into the mixer during the silanization step. Air can be injected from the bottom part of the mixer using existing valves without any special outlet for the injected air. In these experiments air injection is switched on once the compound reached the silanization temperature (145°C) and the rotor speed is adjusted in order to maintain the silanization temperature. Figure 29.13 shows the properties of this compound compared to a compound that was silanized under the same conditions except with air injection switched off. Air injection lowers the Payne effect, Mooney viscosity, and water content in the compound, and ethanol removal is more effective. All other properties are comparable to the properties of a standard silica compound. 

Air injection This measure has a positive effect on the silanization efficiency without negatively influencing the properties of the material. The combination of air injection with working in an open mixer adds the positive effects of the two measures. 

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