Gas separation: apparatus – Solid sorbent apparatus – With control means responsive to sensed condition
Reexamination Certificate
2000-10-30
2003-03-04
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
With control means responsive to sensed condition
C096S125000, C096S130000, C096S142000, C096S150000, C096S154000
Reexamination Certificate
active
06527836
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to adsorbent type fractionators and separator systems and the like, and specifically relates to an improved rotating drum adsorber process and system for fractionating fluids including a novel control method for attaining maximum performance and optimum product quality, and more particularly, when applied to the removal of water vapor from a gas or air, in which the lowest product dew point is achieved.
Multi-chamber adsorbent fractionators are commonly used for air drying. Some examples of this type of adsorbent fractionators are disclosed in U.S. Pat. Nos. 5,256,174, 4,468,239, 4,552,570, 4,247,311 and 3,258,899. Multi-chamber adsorbent fractionators generally include two or more chambers, each filled with an adsorbent medium, such as silica gel, activated alumina, molecular sieve, activated titanium dioxide or activated carbon. One or more chambers are placed on-stream to process the feed gas while the others are isolated off-stream to affect adsorbent regeneration. In one type of adsorbent fractionator, regeneration is accomplished by passing a heated purge gas through the adsorbent containing chamber until the contaminant, previously adsorbed, is desorbed and driven out of the chamber. Such devices entail significant size and weight to accommodate large quantities of adsorbent and complex valving systems to control the operation of the variant adsorbent chambers. Furthermore, extensive logic control systems are required to automatically operate the flow directing valves with system intelligence. An important application of adsorbent fractionators is to provide safe moisture levels in compressed air systems. Moisture in a compressed air system can cause erosion, corrosion and biological effects which can result in product spoilage, equipment malfunction and system failure. For example, in a compressed air line, water is fluidized to an aerosol mist by the turbulent air flow and the droplets are then propelled downstream at high velocities until they impact on the first obstruction in their path, such as a piping elbow, a valve disc, an orifice plate, or an air motor blade. The resulting repeated impulses produce honeycomb-like pits which provide havens for salt ions and acids and which further corrode the surface by chemical action. The weakened surface is then prone to stress corrosion by mechanical vibration and flexing. Erosion can be controlled by eliminating liquid aerosols and particles in air and removing water vapor, which can condense and form liquid droplets, from compressed air systems. Thus, in installations where compressed air lines are exposed to low temperatures and are prone to condensation, it is important that the air be dried to a dew point below the lowest possible temperature.
In addition to erosion, moisture in compressed air systems can cause corrosion and destructive biological effects. Oxygen corrosion in compressed air systems can be prevented by the removal of moisture and oil. The water vapor content must be reduced to very low levels to protect uncoated surfaces such as piping, valves, nozzles, and air motors. Acidic oil vapors should also be removed if significant quantities are present. Water and oil vapors can be removed by adsorption processes. Liquid aerosols may be removed from the air stream by such means as coalescing filters. Wet corrosion in compressed air systems is particularly aggressive because of the absorption of corrosive agents from the air. It occurs primarily in low velocity stagnant regions of the system, such as in valve body cavities and low undrained horizontal piping runs where water droplets are allowed to collect. Pits and crevices also provide ideal locations for corrosion to occur. While pure liquid water is not itself corrosive, very corrosive solutions are formed when water is combined with salt particles or acidic gases. In addition, water molecules adhering to metal surfaces attract oxygen molecules, thereby continuing the corrosion process. Although oxidation is extremely slow on clean metal surfaces at below 50% relative humidity, the presence of an oxide film greatly increases the concentration of water and oxygen and therefore, the corrosion rate until the relative humidity is brought below 2%. This is equivalent to a dew point of −30° F. at 50° F. temperature. Thus, corrosion can be controlled by drying the air to its the lowest possible dew point.
Further, moisture in compressed air systems is harmful because moist air permits the growth of bacteria, fungus and mold and these organisms produce acidic waste, fostering corrosion of compressed air systems. For example, moisture in compressed air can cause product contamination by both direct and indirect means. Often the effects are not immediately noticeable, but they can be detrimental to product quality. Both water droplets and water vapor can be absorbed by the product in direct contact processes, such as, by way of example, in chemical mixing, and paint spraying applications. The absorption of water can adversely affect the chemical and physical properties of the product. Moreover, moisture may indirectly contribute to the generation of particles through erosion and corrosion and to the growth of microorganisms which also contaminate products. Microorganisms may also accumulate in instrumentation tubing and air motor bearings, resulting in malfunction, excessive wear rates, and seizure. Studies show that reducing the relative humidity to below 10% will halt growth of microorganisms, thereby eliminating their harmful effects. Thus, it is advantageous for controlling harmful biological effects, to dry the air to a dew point which reduces the relative humidity to below 10%.
Dry compressed air is used in a wide range of applications including food processing, chemical and pharmaceutical operations and the manufacture of electronic componentry. In the food industry, dry air is used to dehydrate grains, dairy products, vegetables and cereals. In the electronics industry, dry compressed air is used to remove demineralized water and cleaning solvents from silicon devices and circuit boards. In such applications, −40° F. to −100° F. dew point air is used and therefore, it is advantageous to utilize a drying process in which the air is dried to its lowest possible dew point. For example, compressed air used in analytical instrumentation also must be extremely pure and contain minimal levels of water vapor. Infrared analyzers and gas chromatographs used to analyze air for environmental chamber and physiological respiration testing typically require stable quality air and dew point levels below −60° F. Such high purity air, called “zero air,” is also beneficial in prolonging the life of instrument solenoid valves and other sensitive components, in preventing contamination of the test samples and in preventing undesirable side reactions during analyses.
The degree of dryness required must be determined by an analysis of each individual compressed air system and the air drying system should be designed to reduce the water vapor content to the lowest dew point level.
Removal of moisture from an air feed stream depends upon several factors including the rate of flow of the stream, the rate of moisture adsorption and moisture content of the adsorbent, as well as the temperature and pressure of the air within the bed.
Therefore, there is a need for an efficient, reliable adsorption process and system for increasing the purity of an air feed stream and achieving the lowest effluent dew point, and a method for designing and controlling such an adsorption process and system.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved rotating drum adsorber process and system for fractionating fluids is provided for increasing the efficiency, reliability and longevity of a fractionation system, improving the regeneration of an adsorbent medium, achieving a higher degree of fractionation, increasing the purity of the outlet fluid and, when removing moisture, achievi
Acosta Agustin
George Byron P.
Thelen John E.
Thomas Robert G.
Tsargorodsky Mkhail
Baker & Hostetler LLP
Flair Corporation
Spitzer Robert H.
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