WO2015153273A1

WO2015153273A1 - Improved mist eliminator operation for quench effluent

Info

Publication number: WO2015153273A1
Application number: PCT/US2015/022695
Authority: WO
Inventors: Timothy Robert Mcdonel; Jay Robert COUCH; David Rudolph Wagner; Paul Trigg Wachtendorf
Original assignee: Ineos Europe AG
Current assignee: Ineos Europe AG
Priority date: 2014-03-31
Filing date: 2015-03-26
Publication date: 2015-10-08
Anticipated expiration: 2016-09-30
Also published as: CN104941380A; JP6579661B2; EA032744B1; EA201691954A1; TW201540359A; SA516371958B1; JP2017515655A; TWI666056B

Abstract

An apparatus comprises a quench vessel configured to provide a quenched gas stream, and a mist eliminator configured to receive the quenched gas stream. The mist eliminator comprises a mist eliminator surface, the mist eliminator surface configured to remove mist from quenched effluent gas. The mist eliminator includes a spray system that includes nozzles configured to spray on the mist eliminator surface. The spray system is effective for reducing formation of a foulant on the mist eliminator surface.

Description

IMPROVED MIST ELIMINATOR OPERATION FOR QUENCH EFFLUENT

FIELD OF THE INVENTION

[1] The disclosure is directed to an improved mist eliminator operation for quench effluent in the manufacture of acrylonitrile or methacrylonitrile.

BACKGROUND

[2] Various processes and systems for the manufacture of acrylonitrile and methacrylonitrile are known, see for example, U.S. Patent Nos. 3,936,360; 3,433,822; 3,399,120; and 3,535,849. Propylene, ammonia, and oxygen (as an air component) are fed to an acrylonitrile reactor, which contains catalyst and operates as a fluidized bed. A conventional practice is to operate the reactor with an excess amount of ammonia in the feed with respect to the amount of propylene fed to the reactor. Some of the extra ammonia is burned in the reactor due to the extreme conditions before it can combine with propylene to form acrylonitrile. The remaining extra ammonia, commonly referred to as "excess ammonia," exits the reactor in the effluent gas. This gas then typically goes through a cooler and then to a quenching vessel to remove the excess ammonia. See e.g., U.S. Patent Nos. 3,936,360; 4,166,008, 4,334,965, 4,341,535, 5,895,635, and 6,793,776.

[3] Conventional processes and systems for removing excess ammonia have several common factors and one common issue. Conventional processes and systems typically attempt to remove the excess ammonia in the form of ammonium sulfate, and recover that ammonia sulfate at a minimum processing cost. The ammonium sulfate is a reaction product from the common use of sulfuric acid to quench the effluent stream from the acrylonitrile reactor to remove the excess ammonia. This leads to a common issue with conventional processes and systems described in the art. In order to minimize the cost of the ammonium sulfate recovery, there is an inherent loss in the production efficiency of the acrylonitrile process. The recovery of acrylonitrile products in the effluent stream and the removal of excess ammonia in an efficient manner present technical challenges not recognized by or solved in conventional processes and systems described in the art. [4] Conventional processes and systems include a sprayed arrangement to distribute an aqueous stream comprising the acid in a manner designed to remove excess ammonia from the effluent gas stream. Conventional sprayed arrangements give rise to an issue of carryover of fine mist generated by the mixing of warm gasses and cooler liquids. Conventional processes and systems typically have a system of nozzles to distribute the liquid stream into a vessel designed to allow contacting of the vapor and liquid streams. This contacting typically generates a mist that contains various components. Some of these components comprise ammonia and salts of ammonia resulting from the acid used to remove the excess ammonia. If the mist containing the ammonia and ammonia salts is not removed from the gas stream, it will continue through the process to the stage where the acrylonitrile vapors are converted to a liquid stream. From this point forward, the ammonia present in the mist will cause degradation and polymerization of the acrylonitrile and result in lower operating efficiencies for the plant.

[5] There are conventional designs of mist eliminators. The conventional mist eliminators are typically designed to allow a place for the small droplets in the mist to coalesce into large enough droplets to overcome the vapor velocity in the given apparatus that is used to remove the mist. Once the mist is coalesced into droplets, then there is a potential location for acrylonitrile to be absorbed in the liquid and polymer to begin forming. Once this occurs, fouling results which in turn will eventually result in loss of efficiency of the mist eliminator or entrainment separator and/or increased pressure drop in the system such that operation of the plant can no longer be sustained. The plant must then be taken off line until the mist eliminator is cleaned of foulants or mist eliminator materials or structure that are new or clean of foulants are substituted for the mist eliminator materials or structure having the foulants. For conventional apparatus and methods, the operation of the plant may need to be shut down as frequently as about every 6-9 months in order to clean the mist eliminator of foulants or replace fouled surfaces of the mist eliminator. SUMMARY

[6] Accordingly, an aspect of this disclosure is to provide design criteria for the safe, effective and cost efficient removal of ammonia from the effluent gas of an acrylonitrile reactor. Specifically, this invention relates to the method and type of quench vessel used in the process to achieve the desired outcome.

[7] In an aspect, an apparatus is provided for quenching a gas. In an aspect, the apparatus comprises a quench vessel configured to provide a quenched gas stream, and a mist eliminator configured to receive the quenched gas stream. The mist eliminator comprises a mist eliminator surface, the mist eliminator surface configured to remove mist from quenched effluent gas. The mist eliminator comprises a water spray system that includes nozzles configured to spray water on the mist eliminator surface. The water spray system is effective for reducing formation of a foulant on the mist eliminator surface.

[8] The above and other aspects, features and advantages of the present disclosure will be apparent from the following detailed description of the illustrated embodiments thereof which are to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[9] A more complete understanding of the exemplary embodiments of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein:

[10] FIG. 1 is a schematic flow diagram of a side view of a water spray system in a quench vessel in accordance with at least one aspect of the disclosure;

[11] FIG. 2 is a schematic flow diagram of a side view of a mist eliminator in a vessel that is separate from a quench vessel in accordance with at least one aspect of the disclosure. [12] FIG. 3 illustrates a flow diagram of a method in accordance with aspects of the disclosure.

DETAILED DESCRIPTION

[13] In an aspect, an apparatus is provided for quenching of reactor effluent gas comprising acrylonitrile and ammonia. The apparatus includes a quench vessel having a first portion and a second portion. The first portion is located below the second portion. The first portion of the quench vessel comprises an inlet configured to receive a gas stream, the gas stream comprising acrylonitrile and ammonia. The second portion of the quench vessel comprises a quench liquid spray system that is configured to receive a quench liquid, wherein the quench liquid comprises an acid. The quench liquid spray system comprises nozzles configured to downwardly spray the quench liquid. The apparatus further comprises a mist eliminator, the mist eliminator located downstream of the second portion of the quench vessel. The mist eliminator comprises a water spray system. The water spray system is configured to spray water to a surface of the mist eliminator, wherein formation of droplets is reduced and corresponding fouling of the surface of the mist eliminator is reduced.

[14] In an aspect, by the use of a timed water spray to the underside or upstream side of the mist eliminator or entrainment separator, the collection of the droplets can be reduced in a manner such that the formation of fouling and polymer on a surface of the mist eliminator is reduced, and sustained operation of the quench vessel and the mist eliminator can be carried out for extended periods of time.

[15] An object of this disclosure is to provide design criteria for the safe, effective and cost efficient removal of ammonia from the effluent gas of an acrylonitrile reactor. Specifically, this invention relates to an apparatus and method for effective and sustained operation of a mist eliminator used downstream of the quenching or contacting vessel in an acrylonitrile production facility. It has been found that the following design features result in excellent performance of a mist eliminator or coalescer, including for example, a mist eliminator having chevron style sections in a horizontal configuration. [16] Regardless of the temperature of the quench operation, which can range from an outlet temperature of 90°F to 200°F, a mist eliminator may be used in a downstream or upper portion of a quench vessel to remove tiny mist droplets of quench liquid that contain small amounts of ammonia and ammonia salts from cooled or quenched effluent gas, the cooled effluent gas comprising acrylonitrile, acetonitrile, and hydrogen cyanide. The chosen mist eliminator or coalescer may be either integral to the quench vessel or free standing as a separate equipment item.

[17] Those skilled in the art will recognize that in accordance with the disclosure, any suitable type of demisting or coalescing material or structure may be used in the mist eliminator. For example, demisting or coalescing material or structure may be selected from the group consisting of steel wool pads, vanes, and chevron style arrangements. In an aspect, the mist eliminator comprises a chevron style arrangement or chevrons. In an aspect, the chevron style arrangement or chevrons comprise horizontal chevrons extending along a cross-section of the mist eliminator.

[18] In an aspect, full cone spray nozzles may be installed in a header arrangement with the full cone spray nozzles being evenly spaced from an adjacent full cone spray nozzle. In an aspect, the full cone spray nozzles may be located approximately one to two feet from an inlet surface of the mist eliminator. Each full cone spray nozzle may be sized to allow one to two gallons (about 3.5 liters to about 7.75 liters) per minute of water to spray from the nozzle based on available inlet water pressure. In an aspect, a source of clean water may be provided to prevent the addition of any solids that might add to the plugging or fouling tendencies of equipment in this service. Clean water refers to non-process water, such as for example water from a municipal water source.

[19] In an aspect, an automated controller may be configured to allow for full water pressure to the spray nozzles at evenly spaced intervals during operation. The time between intervals of full water pressure may be from about 1 to about 30 minutes. In an aspect, the time between intervals of full water pressure may be from about every 5 to 10 minutes. In an aspect, the duration of the sprays of water from the nozzles to the mist eliminator may range from about 5 to about 600 seconds. In a preferred embodiment, the duration of sprays of water from the nozzles to the mist eliminator may be about 30 to 60 seconds.

[20] Those skilled in the art will recognize that in accordance with the disclosure the spraying of clean water to the mist eliminator or demister will allow for flushing of any small accumulations of polymer and quench water that have collected in or on a surface of the mist eliminator during operation. By removing these foulants, sustained operation of the mist eliminator may be achieved for extended periods of time of up to at least five years. With this extended period of time of up to at least five years, shut down of the mist eliminator for foulant cleaning may be coordinated to occur at the same time of typical maintenance shutdown of the quench vessel. This extended period of time of up to at least five years for foulant cleaning is much longer than for conventional apparatus and methods that require plant shut down every 6-9 months for foulant cleaning of the mist eliminator.

[21] In one aspect, a major portion of a major portion of the quenched gas effluent stream contacts the mist eliminator surface. In this aspect, about 95% or more of the quenched gas effluent stream contacts the mist eliminator surface, in another aspect, about 96% or more, in another aspect, about 97% or more, in another aspect, about 98% or more, and in another aspect, about 99% or more.

[22] In another aspect, at least some of the water spray contacts substantially all of the mist eliminator surface. In this aspect, about 95% or more of the water spray contacts the mist eliminator surface, in another aspect, about 96% or more, in another aspect, about 97% or more, in another aspect, about 98% or more, and in another aspect, about 99% or more.

[23] Spray angles for the full cone spray nozzles may be between about 30 and 90 degrees, with a preferred angle of about 70 degrees to prevent excessive deflection of the water spray pattern entering the mist eliminator. [24] The apparatus and method of the present disclosure will now be described in further detail with reference to the figures.

[25] FIG. 1 is a schematic flow diagram of a side view of a water spray system in a quench vessel in accordance with at least one aspect of the disclosure. Quench vessel 10 may be configured to quench reactor effluent 12. Reactor effluent 12 may be obtained by the direct reaction of propane or propylene, ammonia and oxygen containing gas in a reaction zone (not shown) in the presence of a catalyst. Reactor effluent 12 is transported to quench vessel 10 via conduit 14, wherein the hot reactor effluent gases are cooled by contact with an aqueous stream or quench liquid 16 entering quench vessel 10 via lines 18, 20, 22, and 24. The cooled effluent gas comprising acrylonitrile (including co-products such as acetonitrile, hydrogen cyanide and impurities) may then be passed through an entrainment or mist eliminator 26, and then to an absorber column (not shown).

[26] As shown in FIG. 1 , quench vessel 10 comprises a first portion 28 and a second portion 30, wherein first portion 28 is located below the second portion 30. First portion 28 of the quench vessel 10 comprises an inlet 14 configured to receive a gas stream or reactor effluent 12, wherein the gas stream or reactor effluent 12 comprises acrylonitrile and ammonia. Second portion 30 of the quench vessel 10 comprises a multi-level spray system 34 that is configured to receive an aqueous stream or quench liquid 16, wherein the aqueous stream or quench liquid 16 comprises an acid 36. Acid 36 may be added via line 38 to quench liquid 16 at juncture 40. Acid 36 may be any suitable acid, e.g., sulfuric acid (such as 98% sulfuric acid). Quench liquid 16 comprises effluent exiting bottom 42 of quench vessel 10 and through line 44. Water may be added via line 46 to quench vessel 10 through inlet 48, or otherwise may be added to quench liquid 16 or elsewhere in the liquid recycle loop formed by streams 17, 44, and 65. Quench liquid 16 is circulated through line 44 and back to lines 18, 20, 22, and 24, using pump 50. A purge stream 67 may be withdrawn as part of the liquid effluent exiting through line 44, in order to maintain a relatively constant liquid level in the bottom of the quench vessel, offsetting the liquid added via lines 38 and 46. Purge stream 67 removes formed neutralization reaction products (e.g. , ammonium sulfate) and is also useful for preventing the accumulation of unwanted products in the liquid recycle loop, such as corrosion products and heavy organic materials. Effluent exiting bottom 42 of quench vessel 10 may be drawn from line 44 at siphon point 52.

[27] Multi-level spray system 34 comprises at least a first spray bar 54, corresponding to line 18, and a second spray bar 56 corresponding to line 20. As shown in FIG. 1, multi-level spray system 34 also comprises spray bar 58, corresponding to line 22, and spray bar 56, corresponding to line 24. Spray bars 54, 56, 58, and 60 extend substantially across a diameter 62 of quench vessel 10. As shown, spray bar 54 is located below spray bar 56, and substantially parallel to spray bar 56. Spray bar 58 is located above spray bar 56, and below spray bar 60. Spray bar 58 is substantially parallel to spray bar 60.

[28] Spray bars may 54, 56, 58, and 60 may each comprise a series of spray arms (not shown in FIG. 1). Spray arms may extend substantially across diameter or chords of quench vessel 10 that are perpendicular to diameter 62 of quench vessel 10. Each spray arm may comprise two or more extenders (not shown in FIG. 1). Each extender may extend substantially perpendicular to its respective spray arm. Each extender may comprise a spray nozzle at an end of its respective extender, wherein each spray nozzle faces downward. In an aspect, each nozzle of spray system 34 may be configured to downwardly spray a hollow cone spray of the quench liquid 16, wherein each hollow cone spray defines a center equidistant from the walls of the hollow cone spray. In an aspect, the nozzles of each spray bar may be spaced so that a portion of a first hollow cone spray of quench liquid from a first nozzle of the first spray bar overlaps with a portion of a second hollow cone spray of quench liquid from a second nozzle of the first spray bar to provide an overlap of the quench liquid, having an overlap center.

[29] Cooled effluent gas comprising acrylonitrile (including co-products such as acetonitrile, hydrogen cyanide and impurities) along with mist may then rise up from multi-level spray system 34 to mist eliminator 26. Mist eliminator 26 is configured to remove mist from the cooled effluent gas. Mist eliminator 26 is located downstream of the second portion 30 of the quench vessel 10. Mist eliminator 26 may comprise a water spray system 100. Water spray system 100 is configured to spray water to a surface 102 of mist eliminator 26, wherein collection of droplets is reduced and corresponding formation of fouling and formation of polymer on surfaces 102 of mist eliminator 26 reduced. As shown in FIG. 1, water spray system 100 comprises a water line 104 that feeds water to spray bar 106 through inlet 108.

[30] As used herein "mist" refers to a suspension of liquid droplets in a gas. In one aspect, droplet size may range from about 0.1 to about 1000 microns, in another aspect, about 0.1 to about 50 microns, in another aspect, about 0.1 to about 15 microns, in another aspect, about 1 to about 1000 microns, in another aspect, about 1 to about 500 microns, in another aspect, about 1 to about 100 microns, in another aspect, about 1 to about 50 microns, in another aspect, about 1 to about 15 microns, in another aspect, about 5 to about 1000 microns, in another aspect, about 5 to about 500 microns, in another aspect, about 5 to about 100 microns, in another aspect, about 5 to about 50 microns, in another aspect, about 5 to about 15 microns, in another aspect, about 10 to about 1000 microns, in another aspect, about 10 to about 500 microns, in another aspect, about 10 to about 100 microns, and in another aspect, about 10 to about 15 microns.

[31] Spray bar 106 may comprise a series of spray arms (not shown in FIG. 1). The spray arms of spray 106 may extend substantially across diameter or chords of quench vessel 10 that are perpendicular to diameter 62 of quench vessel 10. Each spray arm of spray bar 106 may comprise two or more extenders (not shown in FIG. 1). Each extender may extend substantially perpendicular to its respective spray arm. Each extender may comprise a spray nozzle at an end of its respective extender, wherein each spray nozzle faces upward. In an aspect, each nozzle of water spray system 100 may be configured to upwardly spray a full cone spray of water, wherein each full cone spray defines a center equidistant from the walls of the full cone spray. In an aspect, the nozzles of spray bar 106 may be spaced so that a portion of a first full cone spray of water from a first nozzle of spray bar 106 overlaps with a portion of a second full cone spray of water from a second nozzle of spray bar 106 to provide an overlap of the water having an overlap center.

[32] Upward spray of water 110 from the nozzles of spray bar 106 to surfaces 102 of mist eliminator 26 may be controlled and/or timed by an automated controller or timer 112. Controller 112 may control the opening and closing of valve 114 via communication line 116. As shown in FIG. 1, mist eliminator 26 may comprise a chevron arrangement or horizontal chevrons 118 having surfaces 102. Chevron arrangement or horizontal chevrons 118 extend along a cross-section of mist eliminator 26. Nozzles 120 of spray bar 106 are configured to provide an upward spray of water 110, preferably as full cone sprays, to surfaces 102, thereby preventing or reducing the formation of foulants and polymer on surfaces 102. While chevron arrangement 118 is shown in FIG. 1 , as previously noted, demisting or coalescing material or structure may be selected from the group consisting of steel wool pads, vanes, and chevron style arrangements.

[33] The quenched or cooled effluent gas comprising acrylonitrile (including co- products such as acetonitrile, hydrogen cyanide and impurities), after passing through mist eliminator 26, may exit quench vessel 10 as gas stream 13. Gas stream 13 may be passed through conduit 15 to an absorber column (not shown).

[34] In an aspect, controller 11 may be configured to process one or more signals corresponding to a measured parameter, e.g., the temperature measured by a temperature controller (not shown in FIG. 1). Controller 11 may be configured to determine whether the measured parameter is above or below a predetermined parameter range. Those skilled in the art will recognize that in accordance with the disclosure, the measured parameter may any suitable parameter useful in operation of the quench vessel, e.g., a temperature measured by the temperature controller at a predetermined location, or a liquid level measured by a level controller (not shown in FIG. 1) in boot 45 of the quench vessel 10, or a flow controller (not shown in FIG. 1). Controller 11 may be configured to adjust operation of one or more devices via communication lines or wireless communications (not shown in FIG. 1) if the measured parameter is below or above a predetermined parameter range. For example, controller 11 may be configured to adjust the amount of a stream conveyed to quench vessel 10, e.g., streams such as reactor effluent 12, water (conveyed through line 46 to quench vessel 10), and/or quench liquid 16 (including acid 36 conveyed through line 38). Those skilled in the art will recognize that in accordance with the disclosure, controller 11 may be configured to control operation of pump 50 and/or operation of other pumps and/or valves associated with the above streams in order to meet the predetermined range. Those skilled in the art will recognize that controller 11 may be configured to control operation of valve 114 or controller 112, which in turn may be configured to control operation of valve 114. Those skilled in the art will recognize that controller 11 may be configured to control operation other device(s) such as a pump (not shown) associated with the flow of water to spray bar 106 through inlet 108. Those skilled in the art will recognize that controller 11 or a similar controller may be located remote from a temperature controller, a level controller, or flow controller (not shown in FIG. 1), or may be located at and comprise a temperature controller, a level controller, or a flow controller.

[35] FIG. 2 is a schematic flow diagram of a side view of a mist eliminator 27 in a vessel 11 that is separate from quench vessel 10 in accordance with at least one aspect of the disclosure. Mist eliminator 27 may be the same as or substantially similar to mist eliminator 26 shown in FIG. 1. In FIG. 2, mist eliminator 27 comprises water spray system 101. Water spray system 101 may be the same as or substantially similar to water spray system 100 shown in FIG. 1. Quenched or cooled effluent gas exits quench vessel 10 as gas stream 19. Gas stream 19 may be passed through conduit 21 to vessel 11. After passing through mist eliminator 27 in vessel, the gas stream may exit vessel 11 as gas stream 23. Gas stream 23 may be passed through conduit 25 to an absorber column (not shown). Liquid dropping to the bottom of vessel 11 may be removed from vessel 11 as liquid 62.

[36] FIG. 3 illustrates a flow diagram of a method 300 in accordance with aspects of the disclosure. Method 300 may be carried out using apparatus previously described. Step 301 comprises contacting a quenched gas stream with a mist eliminator surface, the mist eliminator surface effective for removing mist from the quenched gas stream. Step 302 comprises spraying water on the mist eliminator surface in an amount and manner effective for reducing formation of foulant on the mist eliminator surface. Those skilled in the art will recognize that in accordance with the disclosure the method may include additional steps. For example, the method may further include receiving an effluent gas to a first portion of a quench vessel. The method may include spraying from a quench liquid spray system a quench liquid in a second portion of the quench vessel. The method may comprise contacting the sprayed quench liquid with the gas stream in the quench vessel to produce a quenched gas stream. The method may comprise removing mist from the quenched gas stream rising from the second portion of the quench vessel. The step of removing from the quenched gas stream may comprise contacting mist with a mist eliminator surface, wherein the mist eliminator surface is configured to remove mist from quenched effluent gas. The method may comprise spraying water to or on the mist eliminator surface, wherein formation of a foulant on the mist eliminator surface is reduced. Those skilled in the art will recognize that in accordance with the disclosure the effluent gas stream may comprise acrylonitrile and ammonia, and that the quench liquid may comprise an acid. The step of spraying water may comprise spraying water at a rate of about 1 to 2 gallons per minute (i.e., about 3.79 to 7.57 liters per minute) to the mist eliminator surface. The step of spraying of water may comprise spraying water to the mist eliminator surface at intervals of about every 5 to 10 minutes during operation of the quench vessel. The step of spraying water may comprise spraying water to the mist eliminator surface from about 5 to about 600 seconds. The spraying of water may comprise spraying water to the mist eliminator surface from about 30 to about 60 seconds.

While in the foregoing specification this disclosure has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the disclosure is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the disclosure. It should be understood that the features of the disclosure are susceptible to modification, alteration, changes or substitution without departing from the spirit and scope of the disclosure or from the scope of the claims. For example, the dimensions, number, size and shape of the various components may be altered to fit specific applications. Accordingly, the specific embodiments illustrated and described herein are for illustrative purposes only.

Claims

WE CLAIM:

1. An apparatus comprising:

a quench vessel configured to provide a quenched gas stream; and

a mist eliminator configured to receive the quenched gas stream;

the mist eliminator comprising a mist eliminator surface, the mist eliminator surface configured to remove mist from quenched effluent gas, the mist eliminator comprising a water spray system that includes nozzles configured to spray water on the mist eliminator surface, the water spray system effective for reducing formation of a foulant on the mist eliminator surface.

2. The apparatus of claim 1 , wherein at least one nozzle is configured to spray a full cone spray of water.

3. The apparatus of claim 1 or 2, wherein the at least one nozzle is configured to spray water upwardly to the surface of the mist eliminator surface.

4. The apparatus of claim 3, wherein the at least one nozzle is configured to spray water that overlaps in part with a spray of water from another nozzle.

5. The apparatus of claim 1, wherein the mist eliminator surface extends along a cross section of gas flow the quenched effluent gas.

6. The apparatus of claim 1 , wherein the mist eliminator surface is selected from the group consisting of steel wool pads, vanes, and chevrons.

7. The apparatus of claim 6, wherein the mist eliminator surface comprises a plurality of chevrons.

8. The apparatus of claim 7, wherein the plurality of chevrons are horizontal chevrons.

9. The apparatus of claim 1, wherein the nozzles comprise at least a first, second and third water spray nozzles in series, wherein the second water spray nozzle is spaced a first distance from the first water spray nozzle, and a second distance from the third water spray nozzle, the first distance the same as the second distance.

10. The apparatus of claim 1, wherein the nozzles are spaced from the mist eliminator surface by about 1 to 2 feet (about 30 cm to about 61 cm).

11. The apparatus of claim 10, wherein the nozzles are configured to allow about 1 to 2 gallons (about 3.5 liters to 7.75 liters) per minute to spray from each nozzle.

12. The apparatus of claim 1, wherein the water is clean water.

13. The apparatus of claim 1, comprising a controller, the controller configured to control flow of water to the water spray system.

14. The apparatus of claim 13, wherein the controller is configured to control flow of water to the water spray system so that the flow of water to the water spray system occurs at intervals of about every 5 to 10 minutes during operation of the quench vessel.

15. The apparatus of claim 1, wherein the controller is configured to control duration of flow of water from the nozzles to the mist eliminator surface from about 5 to about 600 seconds.

16. The apparatus of claim 15, wherein the controller is configured to control duration of flow of water from the nozzles to the mist eliminator surface from about 30 to about 60 seconds.

17. The apparatus of claim 2, wherein the full cone spray of water from the at least one nozzle has a spray angle of about 30 to 90 degrees.

18. The apparatus of claim 17, wherein the full cone spray of water from the at least one nozzle has a spray angle of about 70 degrees.

19. The apparatus of claim 1, wherein the mist eliminator is located in the quench vessel.

20. The apparatus of claim 1, wherein the mist eliminator is located in a vessel outside of the quench vessel.

21. The apparatus of claim 1, wherein the effluent gas stream comprises acrylonitrile and ammonia, and the quench liquid comprises an acid.

22. A process comprising the steps of:

contacting a quenched gas stream with a mist eliminator surface, the mist eliminator surface effective for removing mist from the quenched gas stream; and

spraying water on the mist eliminator surface in an amount and manner effective for reducing formation of foulant on the mist eliminator surface.

23. The process of claim 22, wherein the quenched gas stream comprises acrylonitrile and ammonia.

24. The process of claim 22, wherein the step of spraying water comprises spraying water at a rate of about 1 to 2 gallons per minute from at least one nozzle to the mist eliminator surface.

25. The process of claim 22, wherein the step of spraying comprises spraying water to the mist eliminator surface at intervals of about every 5 to 10 minutes during operation of the quench vessel.

26. The process of claim 22, wherein the step of spraying comprises spraying water to the mist eliminator surface from about 5 to about 600 seconds.

27. The process of claim 26, wherein the step of spraying comprises spraying water to the mist eliminator surface from about 30 to about 60 seconds.

28. The process of claim 22, wherein the step of spraying comprises spraying water and acid on the mist eliminator surface in an amount and manner effective for reducing formation of foulant on the mist eliminator surface.

29. A process for the continuous manufacture of acrylonitrile comprising contacting a quenched gas effluent stream comprising acrylonitrile and ammonia with a mist eliminator surface and spraying water on the mist eliminator surface.

30. The process of claim 29, wherein a major proportion of the quenched gas effluent stream contacts the mist eliminator surface.

31. The process of claim 30, wherein substantially all of the quenched gas effluent stream contacts the mist eliminator surface.

32. The process of claim 29, wherein at least some of the water spray contacts substantially all of the mist eliminator surface.

33. The process of claim 29, wherein the major proportion of the water flows co- currently with the quenched gas effluent stream.

34. The process of claim 29, wherein the major proportion of the water is sprayed onto the upstream surface of the mist eliminator surface.

35. The process of claim 29, wherein the major proportion of the water is sprayed through at least three spray nozzles.

36. The process of claim 29, wherein the major proportion of the water spray is intermittent.

37. The process of claim 29, wherein substantially all of the water spray is intermittent

38. The process of claim 29, wherein the major proportion of the water spray is applied to the mist eliminator surface for between 5 and 15% of the time during operation.

39. An apparatus comprising:

a quench vessel having a first portion and a second portion, the first portion located below the second portion;

the first portion of the quench vessel having an inlet configured to receive an effluent gas stream;

the second portion of the quench vessel comprising a quench liquid spray system, the quench liquid spray system configured to receive a quench liquid;

the quench liquid spray system comprising a first set of nozzles, the first set of nozzles configured to downwardly spray the quench liquid;

a mist eliminator, the mist eliminator located downstream of the second portion of the quench vessel, the mist eliminator comprising a mist eliminator surface, the mist eliminator surface configured to remove mist from quenched effluent gas, the mist eliminator comprising a spray system;

the spray system comprising a second set of nozzles, the second set of nozzles configured to spray to the mist eliminator surface.

40. The apparatus of claim 39, wherein at least one nozzle of the second set of nozzles is configured to spray a full cone spray of water.

41. The apparatus of claim 39, wherein the at least one nozzle of the second set of nozzles is configured to spray water upwardly to the surface of the mist eliminator surface.

42. The apparatus of claim 41 , wherein the at least one nozzle of the second set of nozzles is configured to spray water that overlaps in part with a spray of water from another nozzle of the second set of nozzles.

43. The apparatus of claim 39, wherein the mist eliminator surface extends along a cross section of gas flow of the quenched effluent gas.

44. The apparatus of claims 39, wherein the mist eliminator surface is selected from the group consisting of a steel wool pad, a vane, and a chevron.

45. The apparatus of claim 44, wherein the mist eliminator surface comprises a plurality of chevrons.

46. The apparatus of claim 45, wherein the plurality of chevrons are horizontal chevrons.

47. The apparatus of claim 39, wherein the second set of nozzles comprises at least a first, second and third water spray nozzles in series, wherein the second water spray nozzle is spaced a first distance from the first water spray nozzle, and a second distance from the third water spray nozzle, the first distance the same as the second distance.

48. The apparatus of claim 47, wherein the second set of nozzles are spaced from the mist eliminator surface by about 1 to 2 feet.

49. The apparatus of claim 48, wherein the second set of nozzles are configured to allow about 1 to 2 gallons per minute to spray from each nozzle.

50. The apparatus of claim 39, wherein the water is clean water.

51. The apparatus of claim 39, comprising a controller, the controller configured to control flow of water to the water spray system.

52. The apparatus of claim 51 , wherein the controller is configured to control flow of water to the water spray system so that the flow of water to the water spray system occurs at intervals of about every 5 to 10 minutes during operation of the quench vessel.

53. The apparatus of claim 39, wherein the controller is configured to control duration of flow of water from the second set of nozzles to the mist eliminator surface from about 5 to about 600 seconds.

54. The apparatus of claim 53, wherein the controller is configured to control duration of flow of water from the second set of nozzles to the mist eliminator surface from about 30 to about 60 seconds.

55. The apparatus of claim 39, wherein the full cone spray of water from the at least one nozzle of the second set of nozzles has a spray angle of about 30 to 90 degrees.

56. The apparatus of claim 55, wherein the full cone spray of water from the at least one nozzle of the second set of nozzles has a spray angle of about 70 degrees.

57. The apparatus of claim 39, wherein the mist eliminator is located in the quench vessel.

58. The apparatus of claim 39, wherein the mist eliminator is located in a vessel outside of the quench vessel.

59. The apparatus of claim 39, wherein the effluent gas stream comprises acrylonitrile and ammonia, and the quench liquid comprises an acid.