MXPA99005864A - Method and means for purifying air with a regenerable carbon cloth sorbent - Google Patents

Abstract

A method and apparatus for removing contaminates from an air stream in which an adsorbent activated carbon cloth (10) is positioned in said air stream. The method and apparatus provide for impressing an electric current through the cloth adsorbent (10) to desorb any contaminates adsorbed thereon.

Description

METHOD AND RESOURCE FOR PURIFYING THE AIR WITH A REGENERATING SORBENT OF CARBON FABRIC The present invention relates to a method for removing unwanted contaminants from an air stream, by the use of an activated carbon cloth medium and, in particular, to an adsorbent cloth that can be regenerated by the direct application of a electric current. The invention is particularly well adapted to increase the purity of air within enclosed spaces, such as rooms, buildings or vehicles.

BACKGROUND OF THE INVENTION In recent years, there has been a growing interest in air quality, especially in health-related aspects, such as the "Sick Building Syndrome", and in relation to odors inside buildings and other structures. . These interests have become more acute with the advent of energy-related trends for the reduction of air exchange regimes within buildings, which increase the odorous, stale air, and potentially harmful components in the air of the building . This, in turn, has led to an increased interest in systems and devices to reduce the amount of these unwanted contaminants in the air that is breathed. Unwanted materials, which are to be removed from the air, are generally found in two fundamental forms: in the form of particles and gas or vapor. For the removal of particulate materials, a number of processes are currently available and practiced, which include barrier filtration, electrostatic precipitation, etc. For gas and vapor components, which are often organic compounds, technologies that involve the adsorption of activated carbon are typically recommended. Physical adsorption on activated carbon is the most efficient means of removing a mixture of a wide variety of air pollutants, at levels in parts per million by volume (ppmv) or lower concentrations. There are several resources to apply activated carbon, each with its associated advantages and disadvantages. Frequently, granular activated carbon (GAC) or activated carbon in pellets, is placed in trays, or loose or retained by a retention screen, and placed within the air stream of a building HVAC system. Alternatively, the carbon can be placed inside a device that manages the air, with a dimension to treat the air of a single room. The carbon particle size is relatively large, several millimeters in diameter, to increase the size of the voids between the particles and thus reduce the pressure drop at a given linear air velocity. However, the large particle size also increases the length of the diffusion path that a contaminating molecule must travel and, therefore, the time for adsorption. Consequently, the residence time of the contaminated air in contact with the GAC must be increased proportionally. Problems with such systems include high pressure drops and the need for periodic carbon replacement as capacity is expended. Such replacements can be laborious and potentially hazardous, when they are removed by harmful or dangerous material systems. An alternative to GAC is powdered activated carbon (PAC). The PAC has particle sizes 50 to 100 times smaller and thus shorter diffusion trajectories for adsorption. As a result, the residence time that the gas must be in contact with the coal bed is reduced proportionally. This allows depths of very thin beds, with thicknesses of millimeters. However, the PAC is very difficult to contain, and the pressure drop across the bed can be extremely high.

Some of these management sequels have been addressed by enclosing carbon (GAC or PAC) otherwise loose within some kind of matrix. A) Yes, the carbon can be bonded to itself or to a supporting structure to form a self-supporting block, panel or plate (WO 94/03270, PCT / US93 / 06274). It can also be adhered to fibers in a woven or non-woven web structure. The coal can then be handled as a number of units of carbon media, rather than as a loose material. Pressure drops through the media are served by supplying hollow spaces inside the matrix. The spacing of the carbon particles decreases the pressure drops to acceptable levels, but the efficiency of the medium filter is reduced because a substantial portion of the air passes through the filter without contact with a carbon particle. However, this solution does not address the problem of the finite carbon adsorption capacity for contaminants. As a result, the need for replacement remains. In fact, the process of bonding coal often causes a reduction in capacity, since some of the carbon surface is occluded by the adhesive. Methods are also known by which the capacity of the activated carbon, or an activated carbon medium, can be substantially regenerated. This reduces the frequency with which maintenance is required. Alternatively, regeneration allows the use of smaller amounts of coal, which reduces the cost of capital and space requirements, without an associated reduction in effectiveness. The process of regeneration is often achieved by heating the carbon bed by some means. It is known in the art that the capacity of an activated carbon for the materials removed by the physical adsorption mechanism is decreased at elevated temperatures. Thus, when the temperature of a quantity of activated carbon increases, which has been greatly loaded to saturation with a given contaminant, the contaminant will be desorbed from the pore structure of the coal and can be swept and separated with an adequate purge stream. . Thus, when the coal cools, a significant portion of the original capacity is restored. The actual temperature of the internal structure of the coal at any point in time, dictates the adsorption capacity of the contaminants and thus the amount of desorption, and the capacity recovered by the next adsorption cycle. Commonly, the heat needed to heat the coal is supplied externally. Thus, the temperature of the external heat source must always be greater than or equal to the structure of the activated carbon. The coal bed is commonly heated by the application of hot air, such as by heating a scavenging gas, or with steam. It can also be heated by placing heating elements in contact with the carbon particles or carbon media (WPI 77-02666 Y / 02). It is known in the art that activated carbon, due to its localized structure similar to graphite, is capable of conducting electricity. It is also known that the strength properties are such that useful heat can be generated in this manner. Thus, some attempts have been made to use this property to generate the heat necessary to achieve the regeneration of the activated carbon beds (DE 4104513). Unfortunately, this method has generally been tried with granular or pelletized carbon beds, or media derived therefrom, and has had only limited success. Problems encountered typically include non-uniform heating patterns, hot zones and short circuits. In addition to the well-known traditional physical forms of activated carbon (ie, granular, pelletized, spherical or powdered), it is also known that activated carbon can be prepared in the form of an activated carbon fabric (ACC) or a activated carbon felt (ACF). These adsorption media consist of activated carbon in the form of woven or knitted activated carbon fibers (ACC) or in a loose mat (ACF). The fibers have a diameter similar to the PAC and, therefore, provide diffusion trajectories and adsorption regimes similar to the PAC. The advantage of ACF and ACC is that they are easy to apply in very thin beds of millimeter dimensions, such as the PAC attached to supports, with suitably low pressure drops, but with efficiencies as high as the deepest GAC beds. Because the ACC fibers can be of a very small diameter and because the pressure drop through a number of layers of fabrics can be small, the ACC has dynamic properties that are well suited to the problem of purification from air. The forms of the ACC and the ACF, however, suffer from some limitations according to their adsorption capacity of the other forms of activated carbon. Thus, the time between replacements may be unacceptably short. Some attempts to regenerate the ACC and ACF means by heating with air or by placing the means in contact with an electric heater (JP 2046852, JP 2046848). Therefore, it is an object of the present invention to provide a means and method for increasing the purity of an air stream without the corresponding disadvantages inherent in the methods of the prior art. It is a further object of the invention to provide a method for removing contaminants in air streams using a woven or knitted ACC, which can be regenerated very effectively and uniformly, by directly heating with an electric current. It is also an object of the invention to provide a method and apparatus for continuously adsorbing organic materials and other contaminants from an air stream and then regenerating the capacity of the ACC.

SUMMARY OF THE INVENTION The present invention provides an improved method for removing objectionable contaminant gases or vapors from an air stream. In general, the present invention provides a method for contacting an air stream having materials to be adsorbed with an activated carbon fabric, movably placed through the stream, to provide substantially continuous adsorption and desorption. of the materials adsorbed by electrically heating the fabric. The contaminants to be removed include any of a number of odorous or potentially harmful gases, such as toluene, xylene, propane, butane, benzene, hexane, hydrocarbons, mercaptans, aldehydes, ketones, amines, sulfides, and the like. The method is particularly useful in removing contaminants from air currents within various construction structures, such as commercial, residential or industrial buildings, due to their high efficiency and compact space requirements. It is also applicable and useful for treating air currents in vehicles. One embodiment of the present invention also provides a means for removing contaminants from the air by contacting the contaminated air stream with an activated carbon fabric (ACC), comprising activated carbon fibers. The fibers may be woven or knitted or otherwise assembled in any of a number of ways to supply the fabric. In general, the fabric is moved through the air stream at a rate determined by the flow of air, the level of contaminants and the capacity of the ACC. The ACC removes contaminants by means of physical adsorption on activated carbon fibers. When the fabric is loaded with contaminants to an adequate portion of its capacity, the ACC regenerates by removing the adsorbed contaminants by passing an electrical current through it. This fabric is essentially returned to its initial state not loaded. The electric current causes the temperature of the fibers to rise, causing desorption of the adsorbed contaminant. Thus, carbon fibers function as an adsorbent surface and a source of heat. Because no heat transfer is required from a second heating body, the method is inherently more thermally efficient than prior art methods. It is also more efficient because the heat for desorption is generated within the sorbent medium itself, where the thermodynamics of the absorption or desorption processes are dictated. During the period when the current is passed through the carbon cloth, the method of the present invention supplies a suitable purge stream of air or the inert gas used to transport the desorbed contaminants away from the fabric to an appropriate location , for ventilation or other means of disposal. Other advantages of the invention will become apparent from the careful reading of the following description of the presently preferred embodiments, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a currently preferred means for practicing the methods of the present invention. Figure 2 is a schematic representation of a currently preferred embodiment of the invention, in which the absorbent medium of such is shown in a continuous loop.

PRIORLY PREFERRED MODALITIES With reference to Figure 1, a currently preferred embodiment of the invention is shown, in which the absorbent means 10 includes an activated carbon fabric 11, placed through a hole in an air stream containing the contaminants. that are going to be removed. In the preferred embodiment, the fabric 11 is wound around the rollers 14 and 16. In this embodiment, the electrodes 14 and 18 are placed adjacent to one of the opposite rollers, 14 and 16, respectively. Motors, not shown, or other means, are operatively connected to the rollers 14 and 16 to movably place the fabric 11 through the air flow by winding it in one or more rollers. In this way, the air stream can be exposed to fresh sections of the fabric, as desired, or in a continuous or discontinuous mode. In continuous mode, the fabric moves continuously through the air stream at a selected rate, according to the flow and charges on the fabric. In the discontinuous mode, the fabric is placed through the air stream and remains there until saturation approaches, at this time, an und absorbed section of the fabric is placed to adsorb the contaminants.

As the cloth 11 is collected on the take-up roll (in this case 14), in the regeneration chamber 21, the width of the cloth is passed over the rolls 14 and 18, which become electrically conductive and serve as a first pair. of electrodes. When the fabric is judged it no longer has the adequate capacity to remove the contaminants of interest, it is regenerated by desorbing the contaminants from it. In accordance with the method of the present invention, desorption is achieved by reversing the path of the fabric and applying an appropriate electrical current to the fabric, as it passes between two electrodes. As the fabric temperature increases, as a result of electrical resistance, contaminants are desorbed. The desorbed contaminants are swept out of the regeneration chamber by a small stream of air, which is discharged through the vent 22, which may be to the atmosphere or to a waste site. Additionally, it should be understood by those skilled in the art that rollers 16 and 19 can also act as electrodes, so chamber 26 acts as a regeneration chamber, whereby continuous adsorption and regeneration is allowed. In any mode, it is important that the fabric makes adequate contact with the electrodes to provide electrical contact.

Another embodiment of the method of the present invention involves a continuous web 11, which passes over the opening 15 of the air duct, as illustrated in Figure 2. In this embodiment, the contaminated air stream makes contact with the web 11. of carbon cloth twice, either of the first or the guide fabric section lia or the second or trailing cloth layer 11b have been recently regenerated and thus can better remove contaminants that remain after passing through the first cloth layer. When the guide fabric layer is not adsorbed, it may work to reduce the higher concentrations of contaminants, before entering the regeneration zone. The regeneration by means of the electric current is achieved as before, ie by passing the fabric over two conductive surfaces, for example the rollers 14 and 18 or the potential grid 24 to which an electric potential is applied. If desired, a regeneration apparatus can be placed on both sides of the duct, so that the cloth web is regenerated before both passes through the air duct. In this embodiment, additional rollers, 28 and 29, in the regeneration chamber 21, are shown and the additional roller 31 is placed in the chamber 26. The additional rollers are used to guide the fabric, but can also act as additional electrodes for preheat the fabric before regeneration. The method of the present invention has been found to be useful for removing various impurities from air streams,. and to return the adsorbent material to almost its native condition. The present invention is further illustrated in the following examples, of which other advantages will be apparent.

Example l Three layers of activated carbon cloth of type FMI-250 Charcoal Cloth International, Ltd.) were held in place through rectangular openings, measuring 3.9 x 3.9 cm, in a plastic sample holder. Layers of copper sheets were placed on two opposite sides of the fixture, between the layers of fabric, but not within the opening of the fixture. The strips extended beyond the edge of the accessory to allow wires to be attached to these strips. Cycle 1: (Adsorption). A stream of air, containing 80 ppmv of n-butane and 50% relative humidity, was then passed through the fabric at a linear velocity of 10 cm / sec. The concentration of the butane in the effluent desorption water vapor was monitored. The temperature of the effluent air at a point about 1 cm above the fabric was 68 ° during the desorption period. Desorption continued until the measured butane concentration was <10 ppmv. At this time, the electric current was turned off and the fabric allowed to cool in the purge stream. 18.1 mg of butane was removed from the cloth sample. Cycle 2: (rption) The fabric sample was exposed again to the air stream containing 80 ppmv of butane, as in Cycle 1, until the effluent reached 63 ppmv. 19.5 mg of butane was removed from the air stream. (Desorption) The electric current and the dry air purge of cycle 1 (desorption) were restored as before, and were maintained until the butane concentration in the desorption effluent was < 10 ppmv. The fabric was allowed to cool under the purge. 19.5 mg of butane were desorbed. Cycle 3: The rption and desorption stages of cycle 2 were repeated, except that the rption charge was continued at an effluent concentration of 75 ppm. 22.2 mg of butane were removed in the rption step and 22.2 mg of butane were desorbed in the desorption step.

Example 2 The apparatus and procedures of Example 1 were repeated, except that toluene at 80 ppmv was used as the contaminant instead of butane. The adsorption was carried out until the effluent reached 14 ppmv. The desorption was carried out using a current of 10V and 2A, until the desorption effluent reached 10 ppmv. The amounts of toluene adsorbed and desorbed are listed in Table 1.

Table 1 Cycle No. Toluene Adsorbed Toluene Desorbed (rag) _ (mg) 1 255 153 2 168 145 3 171 154 While presently preferred embodiments of the invention have been shown and described in particular, they may be carried out in another manner, within the scope of the appended claims.

Claims (16)

1. A method for removing unwanted contaminants from an air stream, this method comprises the steps of contacting the contaminated air with an adsorbent medium, comprising an activated carbon cloth, to adsorb air pollutants and then passing a current Through this activated carbon fabric, this electric current is sufficient to cause the temperature of the fabric to rise above that of the air, and cause desorption of the unwanted component and direct these desorbed contaminants to a secondary stream, separated from the air.

2. A method, as set forth in claim 1, which includes the step of moving, discontinuously or continuously, the fabric in contact with the air, to provide at least areas of contact with the air for the adsorbent contaminants.

3. A method, as set forth in claim 1 or 2, which includes the step of supplying the fabric, which has been subjected to desorption, for contact by air.

4. A method, as set forth in claim 2, which includes the step of moving the fabric that has made contact, out of the air stream,. as a portion of the fabric reaches a substantial portion of the adsorption capacity, and apply electric current to that portion that has moved out of the stream.

5. Apparatus for the removal of pollutants from an air stream, this apparatus includes: a. a housing, which has an air passage for conducting the air stream; and b. an activated carbon fabric, placed through the passage, this fabric has at least a first and second ends; c. at least one first and second electrodes, in contact with the first and second ends, respectively; and d. an element for applying an electric current between the electrodes.

6. Apparatus, as stated in the claim 5, in which the activated carbon fabric is of a length greater than the passage and includes: e. a first and second fabric positioning element, this positioning element is located through the passage with respect to each other and the first and second ends of the fabric are joined to the respective positioning elements.

7. Apparatus, as set forth in claim 6, wherein the positioning element comprises rollers.

8. Apparatus, as stated in the claim 7, in which the first and second rollers comprise the first and second electrodes.

9. Apparatus, as set forth in claim 7, including two additional rollers, one of the rollers is placed adjacent to the first roller and the other of the rollers is placed adjacent to the second roller.

10. Apparatus, as set forth in claim 9, wherein one of the first adjacent additional roller or the second adjacent additional roller comprises the first and second electrodes.

11. Apparatus, as set forth in claim 9, wherein each of the first adjacent additional roller and the second adjacent additional roller comprise a first and second electrodes.

12. Apparatus, as stated in the claim 9 or 10, which includes a desorption chamber for mounting the first and second electrodes, to capture desorbed contaminants and a waste element to remove the desorbent captured from it.

13. Apparatus, as set forth in claims 6, 7, 8, 9 or 10, in which the first and second rollers include controllable elements for rotating the associated roller.

14. Apparatus, as set forth in claims 5, 6, 7, 8, 9, or 10, in which the first and second electrodes are connected, in controllable form, to a source of electrical energy.

15. Apparatus, as stated in the claim 12, which includes a desorption chamber.

16. Apparatus, as stated in the claim 13, which includes a desorption chamber.