Concentrating evaporators – Processes
Reexamination Certificate
1999-11-09
2002-10-22
Manoharan, Virginia (Department: 1764)
Concentrating evaporators
Processes
C062S069000, C062S259400, C062S315000, C210S737000, C210S774000, C210S640000, C203S049000, C203S100000, C203S098000, C159S901000, C159SDIG002, C159S016100, C202S175000, C261S094000, C261S128000
Reexamination Certificate
active
06468389
ABSTRACT:
BACKGROUND—FIELD OF THE INVENTION
This invention relates to a self-cleaning, flexible film type of contacting surface media for use in evaporative processes that are prone to fouling, plugging or solids buildup.
BACKGROUND—DESCRIPTION OF PRIOR ART
Evaporative processes are fundamental in both nature and industry. Evaporative processes are used to provide cooling, chemical concentration and volume reduction. The reader is certainly familiar with the natural cooling processes of perspiration or spraying with water in the presence of a breeze. Industrial uses are demonstrated in cooling towers, atomizing environmental coolers, spray coolers, to name a few. Chemical concentration processes are exemplified in the manufacture of chemical concentrates, precipitates and salts. Food industries in which juices are concentrated and reduced in volume by means of evaporative processes are common. Sea water is evaporated and concentrated to precipitate sea salt for industrial, food, and pharmaceutical applications.
Evaporative processes operate by the conversion of a liquid into a vapor through the application of heat and sometimes pressure manipulation. Evaporation reduces the liquid volume and concentrates any entrained or dissolved solids. As the level of concentration increases, entrained solids form masses in the liquid and dissolved solids precipitate from the solution. In some instances the goal is to generate and collect the agglomerating, settling or precipitating solids. Evaporative precipitation processes attuned for the volumetric reduction, concentration and eventual precipitation and collection of the solutes from a solution are common. Such an example would be the harvesting of sea salt by means of evaporative ponds.
In many applications, however, the solids are not desired and can impart plugging and fouling problems to piping, heat exchangers and other evaporative process equipment. An example of such a situation is evaporative cooling processes wherein the buildup of precipitates can render evaporative cooling equipment useless.
Evaporation occurs with any liquid given the proper temperature and pressure environs. All liquids have an equilibrium pressure in the vapor surrounding the liquid that is established by the temperature of the liquid/vapor system An increase of the system temperature will generate vaporization with a consequential vapor pressure buildup. Similarly a reduction of system pressure will incite vaporization from the liquid which provides for regeneration of the pressure and, because of the heat required for such vaporization, the temperature of the system will fall. Equilibrium will be realized at a somewhat reestablished pressure and a lower temperature. The requisite pressure at a given temperature is the vapor pressure of the liquid, not the total pressure of the system. For a liquid such as water, the vaporization temperature at atmospheric pressure is 212° F. An open, heated container of water will vaporize at 212° F. The gases above the liquid water in such a container will be 100% water vapor at a vapor pressure of 1 atmosphere. If a vacuum pump were connected to the container and the pressure above the vaporizing water reduced, then the vaporization temperature would drop accordingly. Similarly, if the container were closed, the otherwise escaping water vapor will be contained and the pressure will build. As the pressure builds, the corresponding vaporization temperature also increases. In such a system, since the gas above the liquid water is entirely water vapor, the vapor and total pressure are equivalent. If a procedure is implemented to inject a gaseous contaminant, other than water vapor, into the vapor space in contact with the liquid water, then the vapor pressure and corresponding vaporization temperature would be reduced. The vapor pressure and volumetric dilution are essentially proportional. Liquid water, partially filling a closed container at a total pressure of one atmosphere, but in which the molal constituents of the gaseous phase above the liquid water is diluted to only one-half water vapor, will have a reduced vaporization temperature corresponding to a total pressure of only one-half atmosphere. This phenomenon is used to great advantage for the provision of low temperature evaporation and evaporative cooling.
Evaporative cooling applications employ airflow for dilution of water vapor in contact with liquid water. With sufficient air dilution, evaporative temperatures and consequentially liquid water temperatures can be brought very low. This process also can be employed to reduce the contacting air temperature. This low temperature water or the air cooled therein is consequentially used for cooling purposes. Evaporative cooling requires both adequate airflow, as well as sufficient water vapor to air contacting and consequential dilution, to be effective. The diluted water vapor must be in an equilibrium contact with the liquid water for the aspired low temperatures to be generated. The low temperature equilibrium occurs at the vapor to liquid interface. Thermal transfer between the liquid body and the vapor to liquid interface is necessary to provide cooling of the liquid body itself. Maximum cooling efficiency is therefore achieved by minimizing the distance of thermal transfer in the liquid body and by maximizing the surface area of the liquid body in contact with the airstream This is most efficiently accomplished by means of either breaking the liquid water into many small droplets and/or by providing a means for forming thin, high surface area liquid water films. Both these processes are used in evaporative technologies. Droplets are typically generated through nozzles and/or a myriad of splash inducing bars, referred to as splash bar fill, trays or panels, wherein water is introduced at a top of a series of these structures, is drawn gravitationally downward, impacting the bars and generating splash droplets. Film generating systems are also employed wherein water is introduced across a series of solid sheets, referred to as film fill or packing, forming thin, high surface area films as the water progresses downward. A version of this, wherein films are formed upon a wetted webbing system on which water dribbles through, is often used, particularly for airstream cooling and/or humidification purposes. In all cases, airflow is introduced through and in contact with the water droplets and films to provide the evaporative cooling effect. Water loss, resulting from evaporation, is compensated by recharge with additional clean water.
As stated earlier, evaporative processes are vulnerable to plugging and fouling in the presence of entrained and dissolved solids. Evaporative cooling equipment, especially the fill, is prone to fouling and scaling if poor quality water is employed. Fouling of the fill is usually counteracted by means of partial discharge and recharge with higher quality water. This process, in which the discharge is commonly referred to as the blow-down and the recharge as the makeup, generally includes some form of chemical treatment. The blow-down /makeup process provides a means for establishing and maintaining the water at a steady state level of sufficient quality to the minimize the fouling and scaling potential of the evaporating and concentrating water. In some circumstances, chemical treatment processes can be employed to further reduce the scaling, fouling and plugging potential of the water. These chemical treatment processes serve to reduce the required volume of blow-down and makeup.
The blow-down/makeup process works well but suffers from several drawbacks. The blow-down water is concentrated and thereby solids laden. The disposal of such water can be a financial as well as environmental liability. Blow-down removes water from the cooling cycle. This volume must be replaced. The makeup water volume must accommodate both the evaporative loss and the additional blow-down loss. This volume of make up water may be expensive, not available, or can exact an unacceptable burden on the water supply. Ge
Harris James Jeffrey
Harris James William
Crabtree Edwin H.
Mangolis Donald W.
Manoharan Virginia
Pizarro Ramon L.
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