This invention generally relates to a packing element for use in mass transfer applications within a chemical processing apparatus. More particularly, embodiments of this invention are concerned with a plurality of packing elements that are randomly oriented in a vessel in which two fluids are made to contact each other to facilitate a desired mass transfer reaction. Mass transfer packing elements are used in chemical plants to facilitate processes such as decomposition, absorption, distillation and scrubbing of chemicals.
Examples of packing elements for use in mass transfer applications are disclosed in the following patents: U.S. Pat. No. 5,304,423; U.S. Pat. No. 5,747,143 and U.S. Pat. No. 6,007,915.
In particular embodiments, the present invention provides a packing element for mass transfer applications, a chemical processing apparatus and a process that use the packing elements.
In one embodiment, a packing element includes a peripheral wall defining at least three lobes and at least three channels radially disposed around a common axis and alternately spaced from one another. The lobes abut at least 60% of the circumference of the smallest circle that circumscribes the wall and the channels form openings that abut no more than 40% of the circumference.
Another embodiment relates to a chemical processing apparatus having a plurality of randomly oriented ceramic packing elements wherein the majority of elements each comprises a peripheral wall that defines at least three lobes and at least three channels that are radially disposed around a common axis and alternately spaced from one another. The lobes abut at least 60% of the circumference of the smallest circle that circumscribes the wall and the channels form openings that abut no more than 40% of the circumference.
Another embodiment relates to a mass transfer process comprising the step of simultaneously exposing at least two fluids to a plurality of randomly oriented ceramic packing elements wherein the majority of the elements each comprises a peripheral wall that defines at least three lobes and at least three channels radially disposed around a common axis and alternately spaced from one another. The lobes abut at least 60% of the circumference of the smallest circle that circumscribes the wall and the channels form openings that abut no more than 40% of the circumference.
As used herein, the phrase “chemical processing apparatus” is intended to describe equipment, such as tanks, burners, combustion chambers, piping, etc., that receives one or more raw materials and then chemically and/or physically converts it to one or more end products that are discharged from the apparatus. The conversion may involve desorption or absorption, a physical change (e.g., liquid to gas) to the raw material's state of matter and/or an increase or decrease in the temperature of the raw material. Chemical reactors are widely used in chemical manufacturing industries for a variety of purposes and are considered to be a subset of the phrase chemical processing apparatus.
The phrase “mass transfer”, when used herein, may be defined as the technology for moving one species in a mixture relative to another, and it consists basically of two types of operations: separation of components from each other or mixing them together. The mixture, which may be referred to herein as a fluid, may be a gas or a liquid. For such applications, the mixture to be treated is passed through a column containing randomly oriented packing elements which may be referred to herein as media. The packing elements are considered to be randomly oriented if they have been dumped into the reaction vessel without attempting to place or otherwise physically restrain the final orientation of the packing elements in the vessel. While some randomly oriented packing elements are designed to preferentially orient during the dumping process, thereby causing some of the elements to prefer a more horizontal or vertical orientation than would be achieved if the elements were completely randomly oriented, the elements are still considered to be randomly oriented if the individual elements are not deliberately restrained during the loading process. In contrast, monolith packing elements are carefully placed in a reaction vessel in order to align passageways in one packing element with passageways in another packing element. The labor costs and additional down time associated with loading the monolith packing elements, relative to the costs and time required to load an equivalent amount of randomly oriented packing elements, increases the cost of operating the mass transfer process and therefore may be undesirable.
Conventional wisdom indicates that the most efficient mass transfer elements are those that present the largest surface area per unit volume, also known as the packing element's geometric surface area, to the fluid to be contacted. There have been many attempts to design randomly oriented packing elements with the geometric surface area maximized. However, experience has shown that other characteristics of the packing elements may be desirable and may be considered when manufacturing packing elements for use in large scale commercial operations where initial cost, operating cost, and replacement cost of the packing elements as well as the reactor's operating efficiency may be factors. Other characteristics of the packing elements that may be considered include the cost of manufacturing the packing elements, the tendency for the packing elements to nest with one another, the density of the elements, and the pressure drop within the vessel caused by the packing elements. Pressure drop may be directly impacted by the individual packing element's open face surface area and intra-element porosity as well as the porosity between the packing elements. Balancing these requirements, which may be in competition with one another, may require considerable skill to achieve an advantageous design.
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One of the packing element's design features that impact the performance of the bed of packing elements in a processing apparatus may be its geometric surface area. As used herein, the geometric surface area is the total surface area of all the element's surfaces that can be contacted by a fluid when the element is housed in a processing apparatus. With reference to
As previously described, increasing the packing element's geometric surface area may be one of the design criteria that may be considered when designing a packing element to achieve the desired performance in a mass transfer application. To obtain the desired geometric surface area in one embodiment of packing elements according to this invention, the outermost portions of the lobed projections were made to coincide with portions of the perimeter of the smallest circle that encircles the packing element's entire peripheral wall and is represented in
With reference to the embodiment shown in
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Packing elements according to embodiments of the invention can be formed from any material that provides sufficient strength and does not deteriorate at an unacceptably high rate when exposed to the materials disposed in the chemical processing apparatus. For example, ceramic materials such as natural or synthetic clays, feldspars, zeolites, cordierites, aluminas, zirconia, silica or mixtures of these may be used. Clays are generically mixed oxides of alumina and silica and include materials such as kaolin, ball clay, fire clay, china clay, and the like. Example clays are high plasticity clays, such as ball clay and fire clay. The clay may have a methylene blue index, (“MBI”), of about 11 to 13 meq/100 gm. The term “feldspars” may be used herein to describe silicates of alumina with soda, potash and lime. Other components such as quartz, zircon sand, feldspathic clay, montmorillonite, nepheline syenite, and the like can also be present in minor amounts of the other ceramic-forming components.
Components to be fired together to produce the packing elements may be supplied in fine powder form and may be made into a shapeable mixture by the addition of a liquid, such as water, and optional processing aids, such as bonding agents, extrusion aids, lubricants, and the like to assist in the extrusion process. The mixture can be processed using several different techniques, such as extrusion or pressing, to achieve the desired shape. For example, an initial extrusion process may be followed by cutting the extrudate perpendicular to the direction of extrusion as the extrudate exits the extruder. To obtain packing elements having first and second ends that are curved as disclosed in
In one embodiment, the ceramic elements may be fabricated from a mixture of clays and feldspars and other minor ingredients to form a resultant body that may be comprised mainly of silicon oxide and aluminum oxide (an aluminosilicate). For example, the mixture used to form the elements may comprise at least about 90% of ceramic forming ingredients and the balance (typically up to about 10%) of processing aids. The ceramic forming ingredients may comprise 20-99% aluminum oxide and 0-80% silicon oxide. The processing aids may be largely volatilized during firing. It will be appreciated, however, that the packing elements can be composed of any material that is essentially inert to the material disposed in the processing apparatus and provides sufficient crush strength to prevent crushing of the packing elements when they are dumped into the apparatus. The components may be thoroughly mixed before adding water in an amount sufficient to enable the mixture to be shaped into the desired form and to retain that form during firing. Generally, the amount of water added may be from 12 to 30 ml for every 100 gm of the dry mixture of the components. The shapeable mixture can then be molded, or extruded to form the desired shape before the firing the shape in a kiln to a maximum temperature of from 1100° C. to 1400° C. The temperature in the kiln may be increased at a rate of between 50 to 90° C./hr. and the dwell time at the calcining temperature may be from 1 to 4 hrs before the kiln cools to ambient temperatures.
The above description is considered that of particular embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and are not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents.