Cross-Reference to Related Application

This application is a continuation-in-part of Application Serial No. 711,943 filed September 4, 1996. Field of the Invention

The present invention generally relates to the treatment of exhaust vapors. More particularly, this invention relates to an apparatus and method for removing particulate matter and condensable gas from these vapors, as well as cooling the vapors. The apparatus comprises a scrubbing chamber and a heat exchange chamber. The present invention is especially suited for treatment of exhaust vapors from an open vat fryer.

Background of the Invention Gas scrubbing systems have long been used in industrial applications to purify exhaust vapors. In the scrubbing systems, hot exhaust gases are contacted with water, such that particulate matter is transferred to the water and condensable gases are condensed and collected. Many types of scrubbers are known including venturi, packed bed and spray. Spray scrubbers, a common form of which is a spray tower, often are used to treat exhaust gases, which contain particulate matter and condensable gases, from industrial operations. Using a spray scrubber, it is possible to capture particulates in the scrubbing liquid, to condense the condensable gaseous components of the exhaust gases and to cool the exhaust gases .

Spray towers may consist of one or more nozzles, which spray a liquid, such as water, into the interior of the scrubbing chamber. The sprayed liquid typically is dispersed in the chamber as droplets, an atomized mist or a fog using a nozzle having multiple holes through which the liquid is discharged. These

spray nozzles rely upon friction to create the droplets or mist. The spray typically is directed countercurrent to the gases passing through the chamber so as to maximize contact between the liquid droplets and the gases.

Such scrubbing systems have not had the ability to treat the exhaust gases thoroughly, especially exhaust gases containing condensable gases such as from a food processing plant having open vat fryers. When the liquid is introduced into the stream of exhaust gases, ribbon effects can occur, which will result in only a portion of the gases being treated. Furthermore, if the droplets of liquid are too large, the efficiency of the scrubber is reduced. Reducing the size of the holes in the nozzle to reduce droplet size, however, increases the potential for particulate matter to clog the holes, which also will reduce efficiency. Heretofore, attempts to increase the scrubber efficiency have focused on increasing the height of the tower and increasing the flow rate of scrubbing liquid being sprayed. Both of these modifications, however, can significantly increase the costs of operation.

There is a need for an improved treatment apparatus for treating hot exhaust gases containing condensable gases. Such an apparatus should provide improved mass and heat transfer within the scrubbing chamber so as to increase efficiency without requiring that the height of the tower or the flow rate of the liquid be increased substantially. Summary of the Invention

Generally, the present invention relates to an apparatus and method for treating hot exhaust vapors. More specifically, the invention relates to an apparatus for purifying and recovering heat from hot exhaust vapors, particularly exhaust vapors from a food

processing plant and more particularly from an open vat fryer.

The apparatus comprises a treatment unit having three separate internal chambers. A scrubbing chamber is positioned at the top of the unit, wherein a scrubbing liquid is contacted with the exhaust vapors. Below the scrubbing chamber, a heat exchange chamber is positioned to receive the scrubbing liquid after contact with the exhaust vapors. A heat exchanger contained within this chamber is utilized for the recovery of heat from the scrubbing liquid. Below the heat exchange chamber, a collection zone is positioned to collect the scrubbing liquid. Particulate matter and condensed gas having densities lighter than that of the scrubbing liquid are removed through an overflow outlet. An external pump recirculates the scrubbing liquid from the collection zone to the scrubbing chamber.

Alternately, two such units can be connected in series to provide additional treatment of the exhaust vapors. In such a double unit arrangement, the dimensions of the second unit need not be as large as those of the first, because a substantial portion of the vapors are treated, condensed and removed in the first unit and thus a lower volume remains for treatment in the second unit.

The method of the present invention includes contacting the exhaust vapors with a scrubbing liquid to remove particulate matter from the vapors, to condense condensable gases and to transfer the heat of the vapors to the scrubbing liquid. More specifically, the exhaust vapors are conducted from an external source to the scrubbing chamber. A nozzle disposed substantially centrally within the scrubbing chamber discharges scrubbing liquid upwardly into the chamber, forming an inverted, essentially conical wall of liquid. A fan

positioned downstream from the scrubbing chamber induces flow of exhaust vapors through the wall of liquid, resulting in a pressure drop through the scrubbing chamber sufficient for breaking up the wall of liquid into a web comprised of liquid droplets.

The exhaust vapors enter the scrubbing chamber below the web of scrubbing liquid and travel up through the web to exit the scrubbing chamber at the top through a vapor outlet . As the vapors pass through the web of scrubbing liquid, particulate matter is entrained in the scrubbing liquid, condensable gas is condensed and the vapors are cooled by the scrubbing liquid. The treated vapors can be vented to the atmosphere or to a second scrubber. After being discharged from the nozzle, the scrubbing liquid eventually falls down through the scrubbing chamber to collect at the bottom. The heated scrubbing liquid, having particulate matter entrained therein, and condensate pass from the scrubbing chamber into the heat exchange chamber. A heat exchanger is located within the heat exchange chamber. The scrubbing liquid and condensate flow through the heat exchanger, transferring heat to a coolant also flowing therein.

From the heat exchange chamber, the scrubbing liquid and condensate are collected in the collection zone. Materials having a density less than the scrubbing liquid float on the surface of the scrubbing liquid and are removed from the treatment unit through an overflow weir positioned at a predetermined level within the collection zone. The scrubbing liquid is pumped from a location at or near the bottom of the collection zone by a recirculating pump, through the liquid supply line and back to the nozzle and the scrubbing chamber.

In the double unit arrangement, the method of treating the exhaust vapors essentially is the same as in

a single unit arrangement, except that the treated vapors exiting the scrubbing chamber of the first treatment unit are vented to the scrubbing chamber of the second treatment unit for additional treatment before being vented to the atmosphere. Furthermore, the same supply of coolant can be utilized in both heat exchangers, where the coolant first passes through the second heat exchanger and then through the first heat exchanger. The waste streams containing particulate matter and condensed gas, which are removed through the overflow weirs of both units, can be disposed of separately or piped together for combined disposal .

It is an object of the invention to provide an apparatus and method for purifying hot exhaust vapors and recovering heat therefrom.

It is an object of the invention to provide an apparatus and method for treating heated exhaust vapors that minimizes the size of the scrubbing chamber yet provides at least the level of efficiency of known scrubbers.

It is another object of the invention to provide an apparatus and method which requires less energy when purifying and cooling hot exhaust vapors.

It is still another object of the invention to provide an essentially non-clogging nozzle which discharges liquid into a scrubbing chamber in an essentially conical shaped web for treating hot exhaust vapors.

Description of the Drawings The present invention will be described in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of an apparatus for treating exhaust vapors, where the apparatus embodies the features of the present invention;

FIG. 2 is an elevational view of the interior of the scrubbing chamber of the apparatus of FIG. 1 to illustrate placement of the nozzle in the open, spray position, but without showing any liquid flowing therethrough;

FIG. 3 is a cross-sectional view of the nozzle of FIG. 2 to illustrate the deflector plate, shaft and spring in the closed, off position;

FIG. 4 is a cross-sectional view of the nozzle of FIG. 3 to illustrate the deflector plate, shaft and spring in the open, spray position, but without showing any liquid flowing therethrough; and

FIG. 5. is a perspective view of an alternate embodiment of the invention where the apparatus of FIG. 1 is connected to a second apparatus to provide for further treatment of the vapors, with the vapor outlet of the first apparatus being vented to the vapor inlet of the second apparatus.

Detailed Description of the Invention As used herein, "scrubbing liquid" means the liquid initially charged to the treatment unit, as well as liquid condensed from the exhaust vapors and recirculated along with the initial charge through the treatment unit . As used herein, "condensable gas" includes any gas, principally water vapor, present in the exhaust vapors which is condensable at temperatures below the boiling point of water to provide "condensate".

As used herein, "organic matter" means organic liquid or particulates in the exhaust vapors which are scrubbed out in the scrubbing chamber. The organic matter is substantially insoluble in water and of lower density than water such that it forms a supernatant layer on the collected scrubbing liquid.

As used herein, "web of liquid" means scrubbing liquid which first is discharged into a chamber through an essentially continuous annular opening of a nozzle to form a curtain of liquid which subsequently is dispersed by the flow of gases therethrough in the chamber.

Referring to FIG. 1 there is illustrated a treatment unit 10 for treating exhaust vapors according to an embodiment of the present invention, and FIG. 2 is an elevational view of the scrubbing chamber of FIG. 1 for explaining the operation thereof. The apparatus generally comprises a treatment unit having three separate internal chambers, including a scrubbing chamber 12, a heat exchange chamber 14, a collection zone 16. The apparatus also generally includes a vapor inlet 18 and vapor outlet 20, a liquid supply line 22, and an overflow outlet 24. Located within the scrubbing chamber 12 is a nozzle 26 for discharging scrubbing liquid into the chamber 12.

Exhaust vapors from an external source (not shown) , such as an open vat fryer, may be conducted therefrom by induced or forced draft to the scrubbing chamber 12 along a source line 28 and through the vapor inlet 18. Treated vapors exit the scrubbing chamber 12 at the vapor outlet 20 and are released to the atmosphere. A fan 30 and damper 32 provide an induced or forced draft and control the flow of exhaust vapors from the external source and through the treatment unit 10. The composition of the exhaust vapors varies according to the particular external source of exhaust vapors to be treated. When exhaust vapors are vented from an open vat fryer for treatment, the exhaust vapors generally are comprised of superheated water vapor, starches, cooking oil, volatile organic compounds and particulate matter.

A liquid, such as water, is used to treat the exhaust vapors. Other liquids also can be used according to the composition of the exhaust vapors. Exhaust vapors are contacted with the scrubbing liquid to remove particulate matter and to condense any condensable gas present in the vapors. Particulate matter and condensed gas exit the scrubbing chamber 12 with the scrubbing liquid.

From the scrubbing chamber 12, the scrubbing liquid and organic matter pass through the heat exchange chamber 14, where heat is recovered, and then collect at the collection zone 16. In the collection zone, organic matter having a density less than the scrubbing liquid floats on the surface of the scrubbing liquid and is separated from the scrubbing liquid by removal at the overflow outlet 24. A recirculating pump 34 controls the recycle of scrubbing liquid through the liquid supply line 22 to the nozzle 26 from which the scrubbing liquid is discharged into the scrubbing chamber 12. More specifically, referring now to FIGS. 1 and

2, the treatment unit 10 is used to purify hot exhaust vapors, including a reduction of odor-causing organic vapors and of particulate matter in the exhaust vapors, as well as to recover heat from the exhaust vapors. The exhaust vapors, which are generated from an external source, such as a food processing plant, are vented along the source line 28 to an inlet duct 36 and in through the vapor inlet 18, which is located along the side of the treatment unit 10, at the location of the scrubbing chamber 12.

The external source may be any type of operation that produces exhaust vapors, suitably one which produces hot, humid exhaust vapors. The treatment unit 10 is especially suited for treating exhaust vapors from an open vat fryer, such as a potato fryer, where a

fatty substance, such as vegetable oil or shortening, is used to fry foods. Exhaust vapors from an open vat fryer generally are comprised of superheated water vapor, starches, cooking oil, volatile organic compounds and particulate matter. The moisture content of the exhaust vapors varies depending on the application. For example, the moisture content of exhaust vapors from a potato fryer generally is at least about 20%. The moisture content, however, varies even with the specific cut of potato being fried therein

The exhaust vapors enter the scrubbing chamber 12 at a height approximately equal to or below the middle of the scrubbing chamber 12 and below the scrubbing liquid discharged from the nozzle 26. The vapor inlet 18 is a rectangular opening at the side of the treatment unit 10 having dimensions of about 3 feet by about 1 foot and from which the inlet duct 36 extends to connect with the source line 28. From the vapor inlet 18, the vapors flow upward to the vapor outlet 20, which extends from the top of the scrubbing chamber 12. A fan 30 and damper 32 positioned external of the treatment unit 10 induce and control the flow of exhaust vapors from the source line 28 through the scrubbing chamber 12. Alternately, a variable speed fan alone can be used in place of the fan 30 and damper 32.

The fan draws the exhaust vapors through the system at a rate of about 700 standard cubic feet per minute (scfm) to about 1500 scfm, and the adjustable damper 32 regulates the flow. The fan also draws air through the system with the exhaust vapors, which affects the composition of the vapors. For example, as the volume of air drawn through the system increases, the moisture content of the vapors, as well as the concentration of organic matter, will decrease, because the total volume of exhaust vapors has increased by the

volume of air being drawn through the system. The operating pressure of the fan is about 2 inches of water. The nozzle 26, which is positioned centrally in the scrubbing chamber 12, discharges scrubbing liquid in an upwards direction into the scrubbing chamber 12. Referring now to FIG. 3, the nozzle 26 generally comprises a nozzle housing 100, which is connected to the end of the liquid supply line 22, a shaft 102 arranged vertically within the nozzle housing 100 and extending into the liquid supply line 22 and a deflector plate 104 connected to the upper end of the shaft 102 near the outlet end 106 of the nozzle housing 100.

The nozzle housing 100, which is open at the outlet end 106 and connected to the liquid supply line 22 at the opposite end, preferably is a cylindrical pipe.

Three tabs 108 spaced approximately 120° apart are welded to the inner surface 110 of the nozzle housing 100 and extend downward toward the center of the nozzle housing 100. The tabs 108 extend below the nozzle housing 100 and into the liquid supply line 22, where they are joined with a washer 112. Below the washer 112 is a spring 114 vertically aligned within the liquid supply line 22 and compressible between two spring retainers 116. One retainer 116 is positioned between the washer 112 and the top of the spring 114, and the other retainer 116 is positioned directly below the spring 114.

The shaft 102 fits within the spring 114. A lower portion 118 of the outside of the shaft 102 is threaded, and lug nuts 120 coupled to this portion 118 of the shaft 102 support the lower spring retainer 116. The lug nuts 120 can be loosened or tightened on the shaft 118 to adjust the compression of the spring 114. For example, loosening the lug nuts 120, so that they are positioned lower on the shaft 118, will decrease the compression on the spring 114, whereas tightening the lug

nuts 120 will position them higher on the shaft 118, thus increasing the compression of the spring 114.

The deflector plate 104 is secured to the end of the shaft 102 opposite the spring 114 and is movable between a closed, off position (FIG. 3) and an open, spray position (FIG. 4) . The deflector plate 104, which can be made of metal, plastic or any other rigid moisture-resistant material, preferably angles upward from the end of the shaft 102 and out towards an exposed edge 122 of the housing 100, essentially forming an inverted cone. The deflector plate 104 angles up from the horizontal plane at an angle of approximately 30°. In the closed position, the perimeter of the plate 104 contacts the exposed edge 122 of the nozzle housing 100, preferably extending slightly beyond the edge 122. The exposed edge 122 of the nozzle housing is tapered, angling down toward the center of the housing 100 at an angle substantially similar to that of the deflector plate 104 to better accommodate the angled deflector plate 104.

Referring now to FIG. 4, in the open position, the deflector plate 104 is lifted above the edge 122 of the nozzle housing 100, creating an essentially continuous annular opening 126 between the plate 104 and the edge 122. Scrubbing liquid from the liquid supply line 22 passes up through the nozzle housing 100 and out through this annular opening 126, forming an essentially continuous curtain of liquid around the perimeter of the deflector plate 104. The angled deflector plate 104 causes the scrubbing liquid to be discharged from the nozzle 26 at substantially the same angle, such that the liquid forms an inverted cone as it is discharged. The conical-shaped curtain of water has a lamellar surface. The scrubbing liquid is discharged from the nozzle 26 at

a flow rate of up to about 400 gallons per minute (gp ) , depending on the application.

When operating, the fan 30 creates a pressure drop in the chamber across the curtain of scrubbing liquid. This pressure drop is sufficient to disperse the curtain of liquid, changing it into a web of liquid comprised of atomized droplets. The web of liquid retains an essentially conical shape. The stream of exhaust vapors, which flows cocurrently with the scrubbing liquid through the scrubbing chamber 12, is interposed in the web of scrubbing liquid.

The deflector plate 104 and shaft 102 assembly are biased toward the closed position. Scrubbing liquid flowing from the liquid supply line 22 and up through the nozzle housing 100 exerts pressure on the underside 124 of the deflector plate 104, pushing it upwards into the open position. The pressure of the flow of scrubbing liquid determines the height to which the deflector plate 104 rises above the edge 122 of the nozzle housing 100, which in turn determines the cross-sectional area of the annular opening 126 through which the scrubbing liquid is discharged. For example, a lower flow rate of scrubbing liquid will create less pressure so that the deflector plate 104 only will rise a relatively short distance to create a smaller annular opening 126. A higher flow rate, however, will have more pressure and cause the plate 104 to rise a much greater distance and create a much larger opening 126.

Further, the spring 114 limits movement of the deflector plate 104 by limiting movement of the shaft 102. For example, if the spring 114 is relatively compressed between the spring retainers 116 when in the closed position, the shaft 102, and thus the deflector plate 104, will not be able to rise very high before the spring 114 is completely compressed thereby preventing

further movement of the shaft 102 and ^' deflector plate 104.

Referring now to FIG. 2, the vapor inlet 18 is positioned such that the exhaust vapors enter the scrubbing chamber 12 below the web of scrubbing liquid, forcing the exhaust vapors to pass up through the scrubbing liquid in order to exit the scrubbing chamber 12. The exhaust vapors are treated as they contact the scrubbing liquid. As the exhaust vapors are treated, organic matter becomes entrained in the scrubbing liquid and any condensable gas condenses. Further, the scrubbing liquid absorbs heat energy from the exhaust vapors.

An access opening 46 located opposite the vapor inlet 18 provides access into the scrubbing chamber 12 for maintenance and cleaning. The access opening 46 remains covered during operation of the apparatus 10.

A series of baffle screens 38 are positioned below the vapor outlet 20. Each baffle screen 38 is perforated, the perforations being sized to minimize the amount of excess moisture and residual organic matter that exit the scrubbing chamber 12 with the treated vapors. Any commercially available perforated sheet of metal, plastic or other suitable material, which has appropriately sized perforations can be used. The baffles 38 further prevent liquid discharged from the nozzle 26 from passing out through the vapor outlet 20.

Additionally, a plate 40 depending from the top of the scrubbing chamber 12 breaks up the flow of exhaust vapors through the scrubbing chamber 12. The plate 40 has a diameter less than the inner diameter of the scrubbing chamber 12. The plate 40 is provided with an opening 42 covered by another baffle screen 44 and having a second plate 41 positioned a predetermined distance above the opening 42. The treated vapors pass around the

plate 40 or through the opening 42 and around the second plate 41 before exiting the scrubbing chamber 12.

Referring also to FIG. 1 again, scrubbing liquid passes through the scrubbing chamber 12 to the heat exchange chamber 14 positioned below the scrubbing chamber 12. The heat exchange chamber 14 comprises a heat exchanger (not shown) for recovering heat energy from the scrubbing liquid and condensed gas. Preferably, a four or five pass shell-and-tube heat exchanger is used to maximize heat transfer. In one aspect of the invention, the heat exchanger is designed to prevent clogging by particulate or other matter as the scrubbing liquid passes therethrough.

A liquid, such as water, is used as a coolant to absorb the heat of the scrubbing liquid. The coolant enters the heat exchange chamber 14 through an inlet pipe 50, is circulated through the heat exchanger and exits through an outlet pipe 52. The coolant enters the heat exchange chamber 14 at a flow rate of from about 5 gpm to about 95 gpm, depending on the flow of scrubbing liquid from the scrubbing chamber 12 through the heat exchange chamber 14. The flow rate of the coolant is adjusted to maximize heat transfer from the scrubbing liquid. For example, with a flow rate of about 200 gpm to about 300 gpm of scrubbing liquid at a temperature between about 185° F. and 195° F. , the coolant flow rate should be at least about 35 gpm.

The coolant enters the heat exchange chamber 14 at a temperature lower than that of the scrubbing liquid and preferably at least about 100° F. lower. For example, when the temperature of the scrubbing liquid is about 185° F. , the temperature of the coolant should be no more than about 85° F. and more preferably about 50° F. As the scrubbing liquid and the coolant pass through the two sides of the heat exchanger, heat energy

from the scrubbing liquid is transferred to the coolant. The coolant exits the heat exchange chamber 14 at a temperature of about 170° F.

From the heat exchange chamber 14, the scrubbing liquid passes through the treatment unit 10 to the collection zone 16, which is located adjacent the heat exchange chamber 14 and preferably is below the heat exchange chamber 14. The scrubbing liquid accumulates in the collection zone 16. Organic matter floats on the surface of the collected scrubbing liquid, essentially forming a separate, supernatant layer.

An overflow weir 54 is positioned at a predetermined height in the collection zone 16. Preferably, the overflow weir 54 is an opened, v-shape weir. When the level of the supernatant layer rises to that predetermined height, organic matter is directed through the overflow weir 54 and exits the treatment unit 10 through the overflow outlet 24 for subsequent disposal. Preferably, the treatment unit 10 is operated with the level of liquid being sufficiently high so that the supernatant layer is near or at the overflow weir 54 and some amount of waste always flows out through the overflow outlet 24. Scrubbing liquid also may exit through the overflow outlet 24. The total amount of organic matter removed is dependent on the concentration of such matter in the exhaust vapors to be treated. In an important aspect of the invention up to at least about 90% of the organic matter present in the exhaust vapors is removed from the vapors and more preferably, at least about 95% is removed. Preferably, essentially all of the organic matter removed from the exhaust vapors exits the treatment unit 10 through the overflow outlet 24.

A recirculating pump 34 located external of the treatment unit 10 circulates the scrubbing liquid

accumulated in the collection zone 16 through the liquid supply line 22, which supplies liquid to the nozzle 26. The scrubbing liquid is removed from the collection zone 16 from a location at or near the bottom of the collection zone 16. The scrubbing liquid is recirculated at a rate of from about 1 gpm per 25 scfm of exhaust vapors introduced into the scrubbing chamber 12 to about 5 gpm per 25 scfm of exhaust vapors.

Although approximately 3 gpm of organic matter and scrubbing liquid exit the treatment unit 10 through the overflow outlet 24, it generally is not necessary to add scrubbing liquid to the system to recharge the supply of scrubbing liquid. When water is used as the scrubbing liquid, water present in the exhaust vapors condenses in the scrubbing chamber 12 to supply additional liquid to the system and maintain the volume of scrubbing liquid. For example, taking exhaust vapors containing about 40% water vapor, a flow rate of about 3000 actual cubic feet per minute of exhaust vapors entering the treatment unit 10 will result in approximately 3 gpm of condensate.

In another embodiment of the present invention, shown in FIG. 5, the treatment unit 10 shown in FIG. 1 can be used in conjunction with another unit 10' , where the two treatment units 10 and 10' are arranged in series to provide improved treatment of exhaust vapors. For ease of reading, features of the first treatment unit will be given the same reference numbers used above, and primed numbers will be used in describing the corresponding features of the second treatment unit. Generally, both treatment units 10 and 10' include a scrubbing chamber 12 and 12', a heat exchange chamber 14 and 14', and a collection zone 16 and 16' , as described above for the treatment unit of FIG. 1.

A treatment unit as shown in FIG. 1 and described above preferably is the first treatment unit 10

in the double unit arrangement . When connected in series to another treatment unit 10' , however, the vapor outlet 20 of the first treatment unit 10 is vented to the second treatment unit 10', rather than being vented to the atmosphere. Treated vapors from the first treatment unit 10 exit the vapor outlet 20 and flow to the vapor inlet 18' of the second treatment unit 10' , where the vapors are subjected to further treatment before exiting the second treatment unit 10' through the vapor outlet 20' . In order to improve the efficiency in the heat exchange chambers 14 and 14' , the same coolant can be directed through both heat exchange chambers 14 and 14 ' rather than having individual supplies of coolant for each heat exchange chamber 14 and 14' . For example, coolant first can be piped to the heat exchange chamber 14' of the second treatment unit 10' through a coolant inlet 50' . Coolant exiting the coolant outlet 52' can be directed to the coolant inlet 50 of the heat exchange chamber 14 of the first treatment unit 10. The coolant further absorbs heat from the scrubbing liquid therein before exiting at the coolant outlet 52. This arrangement maximizes the temperature gradients between the coolant and the heated scrubbing liquid in each of the treatment units 10 and 10' . More specifically, the temperature of the exhaust vapors entering the scrubbing chamber 12 of the first treatment unit 10 will be higher than the temperature of vapors entering the scrubbing chamber 12' of the second treatment unit 10' . Thus, the temperature of the scrubbing liquid passing through the first treatment unit 10 heat exchange chamber 14 will be higher than that passing through the second treatment unit 10' heat exchange chamber 14' .

The remaining features of the first treatment unit 10 in a double unit arrangement preferably are as

described above for the single treatment unit 10 shown in FIG. 1.

Because the vapors entering the second treatment unit 10' already have been substantially treated such that a substantial portion of particulate matter and condensed gas has been removed in the scrubbing chamber 12 of the first treatment unit 10, the dimensions of the second treatment unit 10' do not have to be as large as those of the first treatment unit 10. Thus, although the features of both the first and second treatment units 10 and 10' are essentially similar, the dimensions of the second treatment unit 10' can be scaled down relative to those of the first treatment unit 10 because the degree of treatment occurring in the second treatment unit 10' is less than in the first treatment unit 10.

Organic matter and scrubbing liquid removed from the treatment units 10 and 10' through the overflow outlets 24 and 24' can be combined for further use or disposal or can be handled separately.

In accordance with the method of the invention, hot exhaust vapors from an external source (not shown) are purified and the heat energy of the vapors is recovered as the exhaust vapors pass through a treatment unit 10. The exhaust vapors conducted through a source line 28 enter the treatment unit 10 through a vapor inlet 18 and are directed to a scrubbing chamber 12. A fan 30 positioned downstream from the scrubbing chamber 12 induces flow of the exhaust vapors through the treatment unit 10, and a damper 32 positioned before the fan 30 regulates the flow rate. Alternately, a variable speed fan can be used alone, rather than both the fan 30 and damper 32. Exhaust vapors enter the scrubbing chamber 12 at a flow rate of from about 700 scfm to about 1500 scfm and a temperature of from about 230° F. to about 270° F.

In the scrubbing chamber 12, scrubbing liquid is discharged from a nozzle 26. The scrubbing liquid is discharged upwards through an annular opening into the scrubbing chamber 12 and forms an inverted, substantially continuous conical-shaped curtain of liquid. The scrubbing liquid is discharged from the nozzle 26 at a flow rate of up to about 400 gpm, depending on the application.

When operating, the fan 30 creates a pressure drop in the chamber sufficient to disperse the curtain of liquid, changing it into a web of liquid comprised of atomized droplets. The web of liquid retains an essentially conical shape. The stream of exhaust vapors, which flows cocurrently with the scrubbing liquid through the scrubbing chamber 12, is interposed in the web of scrubbing liquid as the vapors pass through the scrubbing chamber 12 to exit at the vapor outlet 18.

The vapor inlet 18 is located below the outer surface of the inverted cone formed by the web of scrubbing liquid, such that as the exhaust vapors travel upwards to exit the scrubbing chamber 12, the flow of vapors is interposed in the web of liquid from the nozzle 26. As the exhaust vapors pass through the web of scrubbing liquid, organic matter is entrained in the scrubbing liquid and condensable gas is condensed.

Additionally, although the scrubbing liquid initially is discharged upwards into the scrubbing chamber 12, it eventually falls back down through the scrubbing chamber 12, further cooling the exhaust vapors and causing the vapors and any condensable gas to condense.

From the scrubbing chamber 12, the treated vapors exit through a vapor outlet 20 located at the top of the treatment unit 10 and are vented to the atmosphere. The vapors exit through the vapor outlet 20 at a temperature of from about 170° F. to about 185° F.

Baffle screens 38 located below the vapor outlet 20 minimize the amount of liquid that exits with the treated vapors. Additionally, a combination of plates, a larger plate having an opening 42 therein 40 and a smaller plate 41 above the opening 42, depending from the top of the scrubbing chamber 12 breaks up the flow of exhaust vapors through the scrubbing chamber 12. The treated vapors pass around the plate 40 or through the opening 42 and around the second plate 41 before exiting the scrubbing chamber 12.

Scrubbing liquid exits the scrubbing chamber.12 and enter the heat exchange chamber 14, where the liquid passes through a heat exchanger (not shown) . The scrubbing liquid enters the heat exchange chamber 14 at a temperature of from about 180° F. to about 195° F. The heat exchange chamber 14 comprises a heat exchanger (not shown) for recovering heat energy from the scrubbing liquid. Preferably, a four or five pass shell-and-tube heat exchanger is disposed within the heat exchange chamber 14 to maximize heat transfer. Further, the heat exchanger is designed to prevent clogging by particulate or other matter as the scrubbing liquid passes therethrough.

The heat energy of the scrubbing liquid is transferred to a coolant that flows separately through the heat exchange chamber 14. The coolant enters through a coolant inlet 50 at a temperature at least about 100° F. lower than that of the scrubbing liquid, or no more than about 80° F. to about 95° F. and more preferably about 50° F. The coolant is heated as it passes through the heat exchanger and exits at the coolant outlet 52 at a temperature of about 170° F.

After passing through and being cooled in the heat exchange chamber 14, the scrubbing liquid is collected in the collection zone 16. Any organic matter

having a density less than that of the scrubbing liquid floats on top of the scrubbing liquid in the collection zone 16. Whenever the level of the collected scrubbing liquid rises above a predetermined height, floating organic matter and some amount of scrubbing liquid will be directed from the collection zone 16 out through an overflow weir 54. Preferably, the treatment unit 10 operates such that the level of the collected liquid always is at least as high as the height of the overflow weir 54 to ensure that a substantial amount of organic matter is removed from the treatment unit 10.

Scrubbing liquid is pumped from a location at or near the bottom of the collection zone 16 by a recirculating pump 34 to a liquid supply line 22. Organic matter that either is water insoluble with a density greater than water or that is water soluble also may be pumped from the collection zone 16 along with the scrubbing liquid.

From the collection zone 16, the scrubbing liquid is pumped through the liquid supply line 22, which supplies scrubbing liquid to the nozzle 26 in the scrubbing chamber 12. Thus, the treatment unit 10 provides a means of re-using the scrubbing liquid. Further, when water is used as the scrubbing liquid, moisture in the exhaust vapors will condense during treatment and mix with the scrubbing liquid, thereby recharging the supply of scrubbing liquid in the treatment unit 10.

The treatment unit 10 is cleaned during operation with a cleaning solution. The cleaning solution, the composition of which is determined by the characteristics of the exhaust vapors being treated, is injected into the collection zone 16. The cleaning solution then is recirculated along with the scrubbing liquid, eventually passing through the entire treatment

unit 10. The concentration of cleaning solution in the scrubbing liquid decreases as the cleaning solution recirculates and exits through the overflow outlet 24.

In the double unit arrangement, exhaust vapors flow from an external source (not shown) through the vapor inlet 18 of the first treatment unit 10 to the scrubbing chamber 12. Instead of being vented through a gas outlet 20 to the atmosphere, however, the treated vapors are vented to a vapor inlet 18' of a second treatment unit 10' to a scrubbing chamber 12' . Treated vapors from the second scrubbing chamber 12' are vented to the atmosphere as they exit the treatment unit 10' through a vapor outlet 20' .

Both treatment units 10 and 10' have scrubbing chambers 12 and 12' substantially similar to that shown and described in FIG. 2 for the single treatment unit 10. Scrubbing liquid is discharged from the nozzle 26 (FIG. 2) into the first scrubbing chamber 12 at a rate of about 1 gpm to 5 gpm per 25 scfm of exhaust vapors and about 1 gpm to 5 gpm per 25 scfm into the second scrubbing chamber 12' for treating the incoming hot exhaust vapors. After being discharged from the nozzle 26, the scrubbing liquid and organic matter from the exhaust vapors follow essentially the same path through each of the treatment units 10 and 10' of the double unit arrangement as it follows through the single treatment unit 10 of FIG. 1 described above. Generally, the scrubbing liquid flows from the scrubbing chamber 12 and 12' to the heat exchange chamber 14 and 14' , where heat is transferred to a coolant also passing through the heat exchange chamber 14 and 14' , and then to the collection zone 16 and 16', where organic matter with a density less than water is removed through an overflow weir 54 and 54' . From the collection zone 16 and 16' , a recirculating pump 34 and 34' pumps the scrubbing liquid

through the liquid supply line 22 and 22' for reuse in the scrubbing chamber 12 and 12 ' .

The temperatures of the various streams in the second treatment unit 10' are somewhat lower than temperatures of the corresponding streams in the first treatment unit 10. For example, vapor exiting the vapor outlet 20 of the first treatment unit 10 enters through the vapor inlet 18' of the second treatment unit 10' at a temperature of from about 170° F. to about 185° F. Vapor exits through the vapor outlet 20' of the second treatment unit at a temperature of from about 60° F. to about 80° F. Scrubbing liquid passes to the heat exchange chamber 14' of the second unit 10' at a temperature of from about 95° F. to about 105° F. Coolant enters the heat exchange chamber 14 ' at a temperature of from about 50° F. to about 60° F. and exits at a temperature of from about 80° F. to about 95° F.

The following describes the dimensions of one example of a single treatment unit embodying the features of the present invention. The overall dimensions of the unit are about 9.5 feet (ft) to about 14.5 ft high. The outer diameter is about 3 ft to about 4 ft, and the inner diameter is about 2.5 ft to about 3.5 ft. The scrubbing chamber, which is located at the top of the unit, is about 4 ft to about 5 ft high and also includes a rounded top portion having a maximum height at the center of the unit of approximately 0.5 ft to 1.5 ft in height. The vapor inlet has dimensions of about 3 ft wide by about 1 ft high. The vapor outlet has an inner diameter of about 1.4 ft. The access opening has dimensions of about 1.3 ft. wide by about 1 ft high. The nozzle housing has a diameter of about 2 in. to about 4 in.

The heat exchange chamber is located below the scrubbing chamber and has a height of about 2.5 ft to about 3.5 ft. The collection zone is positioned beneath the heat exchange chamber and has a height of about 2 ft to about 3 ft in addition to a rounded bottom portion having a maximum height at the center of approximately 0.5 ft to 1.5 ft.

With a double unit arrangement, the first unit is sized similarly to the unit of a single unit arrangement, as just described. Sizing of the second unit will depend on the application, however, the dimensions of the second unit always are at least somewhat smaller than those of the first unit.

It will be understood that various changes in the detail, materials and arrangement of parts and assemblies which have been herein described and illustrated in order to explain the nature of the present invention may be made by those skilled in the art within the principle and scope of the present invention as expressed in the appended claims.