Mist Trap

Abstract

The present application relates to a mist trap for a wet scrubber abatement system. The mist trap includes a demisting chamber having a gas inlet for receiving mist-laden exhaust gas from the wet scrubber abatement system, a liquid capture surface where mist droplets can coalesce to form liquid, and a gas outlet where relatively dry gas can exit the chamber. The mist trap is configured such that at least a first portion of the trapped liquid exits the chamber via the gas inlet and returns to the wet scrubber abatement system. The present application also relates to a water collection baffle, an abatement system, and a method for mitigating particulate matter buildup in a primary flow path of an exhaust draw amplifier.

Description

[Technical field]

[0001] The present invention relates to a mist trap, and in particular to a mist trap for a gas abatement system. The present invention further provides a water-collecting baffle for the mist trap, an abatement system including the mist trap, and a method for mitigating particulate matter build-up in a primary flow channel of an exhaust draw amplification device. [Background technology]

[0002] The abatement device removes components of a process gas stream, such as compounds of a semiconductor or flat panel display manufacturing process, so that the removed gas stream can be more safely released into the environment.

[0003] The term wet scrubber refers to a variety of abatement devices that remove contaminants from furnace flue gas or other gas streams. In a wet scrubber, the contaminated gas stream is contacted with a scrubbing liquid, such as water, by spraying the liquid onto the contaminated gas stream, passing the contaminated gas stream through a pool of liquid, or by some other contacting method to remove the contaminants. Wet scrubbers can also remove solid particles by entrapping them in the liquid.

[0004] Before exiting the wet scrubber, liquid droplets in the scrubbed exhaust gas stream are separated by a subcomponent known as a mist eliminator, such as a mist filter or cyclone separator, and the pooled scrubbing liquor and entrained pollutants are treated before any eventual discharge or recycling within the plant.

[0005] Figure 1 is a simplified schematic diagram of a packed tower design wet scrubber (1). An exemplary mist filter (2) is disposed within the packed tower main chamber (3). The mist filter (2) is disposed between the packing (5) and the outlet (4) of the packed tower main chamber (3). Thus, substantially all mist can be removed from the exhaust gas stream (6) before it exits the main chamber (3) of the packed tower (1).

[0006] In some cases, exhaust draw amplifiers (EDADs) are employed downstream of the packed tower wet scrubber. As the name suggests, exhaust draw amplifiers increase the gas velocity at the exit of the wet scrubber and direct the exhaust along additional ducts for treatment and / or release to the atmosphere.

[0007] 2, a typical exhaust draw amplifier (10) includes a primary flow passage (11) through which exhaust gas flows, surrounded by a plenum (7) having ports (8, 9) that open into the gas stream. These ports (8, 9) can introduce jets of high velocity compressed dry air into the flow to increase the overall gas velocity. Summary of the Invention [Problem to be solved by the invention]

[0008] It has been reported in the field that exhaust draw amplifiers may exhibit insufficient Mean Time Between Cleaning (MTBC). In some cases, exhaust draw amplifiers may accumulate powder on the inner walls of their primary flow passages and / or jet ports. Typically, this powder is a by-product from reduction and is generally in the form of silica or silicon dioxide. As the powder accumulates, it can change the geometry of the device and reduce the effectiveness of the exhaust draw amplifier, especially when the gas flow velocity increases. In fact, it has been reported that powder may accumulate to such an extent that the system may trigger an alarm and / or automatic shutdown due to a worsening pressure condition.

[0009] The present invention addresses, at least in part, these and other problems in the prior art. [Means for solving the problem]

[0010] The present invention therefore provides in a first aspect a mist trap for a wet scrubber abatement system. The mist trap comprises a demisting chamber having a gas inlet for receiving mist-laden exhaust gas from the wet scrubber abatement system, a liquid capture surface in which mist droplets can coalesce to form liquid, and a gas outlet through which relatively dry gas can exit the chamber. The mist trap is configured such that at least a first portion of the captured liquid exits the chamber via the gas inlet and returns to the wet scrubber abatement system. Preferably the liquid exits the chamber via the gas inlet.

[0011] In investigating the above problem, it was discovered that relatively dry gas containing a small amount of powder may be discharged from the wet scrubber and passed through the exhaust draw amplifier. Without being bound to any particular theory, it is believed that the introduction of compressed gas into the exhaust draw amplifier may cause the powder to flash dry and deposit on the inner walls of the exhaust draw amplifier where the powder steadily accumulates and eventually causes blockages. The moisture content of the gas that has already passed through the mist filter is low, i.e. the transported powder is not wet enough to be washed away by any mist remaining in the exhaust gas. Furthermore, the gas does not have enough moisture to wet the surfaces of the EDAD and thereby prevent the deposition of evaporated powder on said surfaces.

[0012] By providing a separate mist trap, mist can be removed from the gas stream after it passes through the exhaust draw amplifier rather than before. The mist trap can capture some of this mist and redirect it as liquid back to the wet scrubber, allowing cleaning of the ducts / piping between the wet scrubber and the mist trap, including the interior surfaces of the exhaust draw amplifier (such as the primary flow path), reducing powder build-up there.

[0013] Thus, the mist trap can be in fluid communication with the exhaust draw amplifier and can be configured such that liquid exiting the chamber via the gas inlet is redirected back into the exhaust draw amplifier, thereby preventing further deposition of powder by the mist trap.

[0014] The demisting chamber can include at least one drainage outlet through which the second portion of the captured liquid exits the chamber. The demisting chamber can include two or more such drainage outlets. The at least one drainage outlet is preferably in fluid communication with a liquid storage tank, preferably a liquid storage tank used to supply liquid into an abatement system, such as in a packed tower of a wet scrubber.

[0015] The mist-laden air can be provided by a wet scrubber, specifically by an atomizer located in the packed-tower demisting chamber of the wet scrubber. Typically, a mist trap is used in combination with a wet scrubber in a gas reduction system that does not include a mist eliminator. The mist-laden air can flow out of the wet scrubber and pass through the exhaust draw amplifier. This has the advantage that the mist-laden gas can scrub the side walls of the exhaust draw amplifier as it passes through the exhaust draw amplifier from the packed tower to the mist trap. This scrubbing action can be in addition to the scrubbing action of the recovered liquid flowing in the reverse direction from the mist trap to the wet scrubber, preferably into a packed-bed abatement chamber.

[0016] Thus, in a further aspect, the present invention provides the use of an aqueous mist for cleaning powder deposits from an exhaust draw amplifier of a gas abatement system, in use, preferably wherein the aqueous mist is delivered from a packed column wet scrubber of the gas abatement system.

[0017] In a further aspect, the present invention provides an abatement system comprising an exhaust draw amplifier and a mist trap, the exhaust draw amplifier configured to direct mist-laden gas into the mist trap, and the mist trap configured to remove liquid from the mist-laden gas. The mist trap is further configured such that at least a portion of the liquid removed from the mist-laden gas is directed back to the exhaust draw amplifier, preferably through the exhaust draw amplifier into a wet scrubber demisting chamber. The mist-laden air is preferably provided by a wet scrubber. The wet scrubber preferably comprises a packed tower not including a mist eliminator.

[0018] In an embodiment, the abatement system may include a mist trap according to the previous aspect.

[0019] Typically, the mist trap is positioned vertically above the exhaust draw amplifier and / or packed bed demisting chamber such that liquid collected by the mist trap can flow back under the influence of gravity through the exhaust draw amplifier and / or into the packed bed demisting chamber.

[0020] In a further aspect, the invention provides a method for mitigating particulate buildup in a primary flow passage of an exhaust draw amplifier of a gas abatement system, the process including passing mist-laden air from the gas abatement process through a primary flow passage of the exhaust draw amplifier, removing liquid from the mist-laden gas exiting the exhaust draw amplifier, and passing the removed liquid back into the primary flow passage of the exhaust draw amplifier.

[0021] The method may be carried out using a mist trap according to the first aspect and / or an abatement system according to the previous aspect.

[0022] In all embodiments, the liquid capture surface may be provided by a baffle that at least partially, preferably completely, blocks the gas outlet of the mist trap from the gas inlet of the mist trap. The exhaust gas must preferably flow around the baffle on its path from the gas inlet to the gas outlet. The baffle may define one or more apertures that provide a flow path from the inlet to the outlet. Typically, in use, the one or more apertures defined by the baffle provide the only route from the gas inlet to the gas outlet.

[0023] In an embodiment, the baffle may have one or more skirts, and the one or more apertures defined by the baffle are preferably provided by the one or more skirts. Typically the or each skirt is castellated. If castellated, openings (grooves) may provide the apertures. However, it will be appreciated that the one or more apertures are not necessarily limited to any particular shape or form.

[0024] Accordingly, in a further aspect, the present invention provides a water collection baffle for a mist trap of a gas reduction system comprising a generally planar body and a skirt extending from the body adjacent an outer periphery of the body, the skirt defining one or more apertures configured to allow gas to flow around the baffle in use, and a side of the planar body along which the skirt extends configured to provide a liquid capture surface against which mist droplets may coalesce.

[0025] In all embodiments including a baffle, the size of the or each aperture may be adjustable.

[0026] In an embodiment, the baffle may include a first part, also including a skirt, nested within a second part, also including a skirt. Each said skirt may define one or more apertures in the baffle, and the first and second parts may be moveable relative to one another to vary the size of the one or more apertures. The first and second parts preferably have circular peripheries, for example they may be disk-like and / or annular. The skirt is preferably castellated. The first body is preferably rotatable relative to the second body, preferably to vary the size of the one or more apertures.

[0027] In an embodiment, the baffle may be configured such that, in use, the tip (eg, bottom end) of the skirt(s) is submerged in liquid collected by the baffle.

[0028] The baffle of this aspect may also be employed in any of the embodiments including the baffle of the previous aspect(s).

[0029] For the avoidance of doubt, all aspects and embodiments can be combined mutatis mutandis.

[0030] The invention will now be described with reference to the following figures, which are intended to be non-limiting. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 illustrates a prior art wet scrubber. [Diagram 2] FIG. 1 illustrates an exhaust draw amplification device (EDAD). [Diagram 3] FIG. 1 is a diagram showing the appearance of a mist trap according to the present invention. [Figure 4] FIG. 2 is a cross-sectional view of a mist trap according to the present invention. [Diagram 5] FIG. 2 illustrates a baffle assembly according to the present invention. [Figure 6] FIG. 1 shows an in situ diagram of a mist trap and EDAD in an abatement system including a packed tower wet scrubber. [Figure 7] FIG. 2 illustrates a method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention provides a mist trap (12) for a gas abatement system, with reference to Figure 3. The illustrated mist trap (12) includes a gas inlet (13) for receiving mist-laden exhaust gas from an abatement system, such as a packed tower of a wet scrubber.

[0033] The mist trap (12) further comprises a main chamber (14) defined by a housing (15) and a gas outlet (16) through which relatively dry gas can exit the main chamber (14). By the gas is relatively dry, it is meant that some, and preferably substantially all, of the mist has been removed from the gas by the mist trap. However, a relatively dry gas may, but does not necessarily, still have a relatively high relative humidity.

[0034] Typically, the housing (15) and / or mist trap (12) are generally of polymeric construction, preferably of airtight construction, and it is preferred that the entire exhaust gas flow passes through the mist trap (12).

[0035] The mist trap (12) further comprises one or more drains (17, 18) through which a portion of the collected liquid can flow out of the main chamber (14) of the mist trap (12). As better shown in FIG. 4, the mist trap (12) may comprise two or more such drains (17, 18). The liquid can flow out of the drains (17, 18) under the influence of gravity and / or pressure. Typically, the drains (17, 18) are located at the bottom of the mist trap (12). The drains (17, 18) are preferably located at the lowest part of the mist trap main chamber (14). As shown in FIG. 4, the base (19) of the mist trap (12) may be configured to direct the liquid towards the drains (17, 18) to aid in drainage. Additionally, in use, the opening (20) of the gas inlet (13) may be elevated relative to the drain holes (17, 18). In the illustrated example, the base (19) of the mist trap (12) is in the form of a truncated cone. The drainage holes (17, 18) are located in a trench (21) at the base of the cone (19). The top of the cone (19) contains the opening (20) for the gas inlet (13).

[0036] This arrangement has the advantage of allowing liquid to accumulate (pool) in chamber (14) before it begins to flow back down gas inlet (13) toward exhaust draw amplifier (10) and / or toward the piping back to the packed column chamber.

[0037] As best shown in FIG. 6, the drains (17, 18) are typically connected to a collection reservoir (22) or tank so that the liquid collected in the mist trap (12) can be reused in the abatement process. Typically, (polymeric) tubing (drain lines) (23, 24) is employed to connect the or each drain to the collection reservoir (22). A first end (25) of the drain line (23, 24) may be connected to the mist trap's drain and a second end (26) of the same drain line may be connected to the collection reservoir (22), preferably below the liquid level (e.g. water line) in the reservoir (22). The drain lines (23, 24) are preferably connected to the collection reservoir (22) below a lower level switch. Typically, liquid travels along the drain lines (23, 24) into the collection reservoir (22) under the influence of gravity and / or pressure. The higher the flow rate applied to the exhaust draw amplifier (10) in the system, the higher the pressure in the drain lines (23, 24) leading from the mist trap (10) to the tank (22). Advantageously, any powder entrained in the collected liquid can also be returned along the drain lines (23, 24) via the drains (17, 18) to the collection reservoir (22). The collection reservoir can be the liquid supply reservoir of the wet scrubber.

[0038] The mist trap (12) further includes a water collecting baffle (27). The baffle (27) includes a generally planar body (28), for example a disc-shaped body, and a skirt (29) extending from the body (28) adjacent, and preferably at, the outer periphery of the body (28). The skirt (29) preferably extends from the outermost edge of the body (28). As can be better seen in Figure 5, the skirt (29) defines a series of apertures (30). In use, exhaust gas flows through the apertures (30), around the baffle (27) and towards the gas outlet (16). Liquid preferably coalesces on the underside (31) of the baffle (27).

[0039] The skirt (29) is preferably configured such that, in use, it is at least partially submerged in the pool of liquid at the bottom (21, 19) of the chamber (14). The pool of liquid within the outer casing (15) presents additional resistance to the exhaust gas flow, thereby removing more mist from the exhaust gas.

[0040] A computational fluid dynamics investigation of the exemplary mist trap (12) demonstrated that low velocity and high pressure zones form within the trap, creating eddies in the exhaust gas flow. These velocity and flow disturbances separate the mist from the gas flow, allowing the mist to form larger droplets that are too heavy to be transported by the gas flow. These larger droplets combine, for example, on the underside of the baffle and pool at the bottom of the trap. This pool separates more mist by presenting additional resistance to the gas flow.

[0041] The size of the apertures (30) is preferably variable, i.e., the total cross-sectional area of ​​the flow path through the baffle (27) can be changed. The size of the apertures (30) can be changed manually, i.e., in response to user input, and / or automatically in response to the condition of the abatement system and / or mist trap. Increasing the size of the apertures can reduce the pressure drop in the mist trap, while decreasing the size of the apertures can increase the rate of mist merging and capture in the mist trap.

[0042] In an embodiment, a window (e.g., a transparent tube) can be provided in the duct (44) downstream of the mist trap (12). If droplets appear on the window, it indicates that not all of the mist is being trapped. Therefore, the size of the aperture (30) can be reduced until no droplets appear on the window. In another embodiment, an FTIR spectrometer can be used to analyze the exhaust gas to determine if a satisfactory level of demisting has been achieved.

[0043] Additionally or alternatively, if pressure increases within the abatement system, it may be desirable to open the aperture (30) to reduce the pressure drop through the mist trap (12).

[0044] In embodiments, such determinations and aperture size adjustments may be performed automatically, i.e., without user input. For example, the processor may continuously monitor the amount of mist leaving the demister and / or the system pressure, make a determination regarding the preferred size of the aperture(s), and instruct the controller to adjust the size of the aperture in response to the determination.

[0045] The baffle (27) may be configured such that, in use, the bottom edge (32) of the skirt (29) is submerged in liquid collected on the base (21, 19) of the main chamber. In an embodiment, the position of the baffle (27) relative to the base (19) of the main chamber (14) may be varied, thus varying the depth to which the bottom edge (32) of the skirt(s) (29) is submerged and / or varying the size of the aperture(s) (30). The movement of the baffle (27) relative to the base (19) of the chamber (14) may be controlled manually and / or automatically. In an embodiment, the positioning of the baffle (27) may form part of the automatic determination and adjustment of aperture size discussed above.

[0046] In the illustrated example, the baffle (27) has a two-piece construction. Specifically, the illustrated baffle (27) includes a first portion (33) including a skirt (35) nested within a second portion (34) including a skirt (29). The illustrated skirts (29, 35) are castellated to provide a series of skirt segments (29, 35). In the illustrated example, both skirts (29, 35) define an aperture (30) in the baffle (27). The first portion (33) and the second portion (34) are movable (e.g., rotatable) relative to one another to vary the size of the aperture (30). Specifically, the skirt segment (29) of the second portion (34) can slide over the skirt portion (35) of the first portion (33). Thus, the skirt segments (35, 29) may be present in a variety of side-by-side, overlapping, and radially aligned configurations, thereby varying the size of the apertures (30) in the baffle (27).

[0047] In the illustrated example, the body (36) of the first portion (33) is substantially disc-shaped and the body (37) of the second portion (34) is substantially annular, although the body (37) of the second portion (34) could also be disc-shaped. Advantageously, the illustrated arrangement provides an upper surface of the baffle (27) with a recess (39) within which powder particles can be trapped for subsequent removal.

[0048] As shown in FIG. 4, the baffle (27) is suspended from the roof (40) of the mist trap main chamber (14). In this example, a number of struts (41) connect the baffle (27) to the chamber roof (40). In the illustrated embodiment, an annular fixed plate (38) is employed to connect the struts (41) to the roof (40). The exhaust gas passes around the struts (41) before exiting the chamber (14) through the gas outlet (16). In the illustrated example, the first portion (33) is fixed to the roof (40) of the chamber (14). The second portion (34) is movable relative to the first portion (33) and the chamber wall (42). Powder particles impacting the struts (41) can collect on the upwardly facing surface (39) of the baffle (27).

[0049] In use, mist-laden air enters the chamber (14) through the opening (20) of the gas inlet (13). The mist-laden gas strikes the lower surface (31) of the baffle (27) and liquid from the mist coalesces on said lower surface (31) of the baffle (27). The liquid then runs down the baffle skirts (29, 35) and collects on the base (floor) (21, 19) of the chamber (14) and / or drips onto the base (19) of the main chamber and / or directly into the gas inlet (13). The mist droplets can also coalesce on other surfaces of the mist trap (12) and flow towards the base (19, 21) of the mist trap (12) as well. As liquid begins to accumulate on the bottom (19, 21) of the main chamber (14), some of it flows into one or more drains (17, 18).

[0050] Also, liquid exits the gas inlet (13) in a direction opposite to the exhaust gas flow direction, which is indicated by arrow A. The liquid flows along the inner surface of the duct, which in this embodiment is located upstream of the mist trap (12) containing the exhaust draw amplifier (10) (e.g., back towards the packed tower (43)). The liquid may entrain powder or other debris encountered on its path along the duct / pipe. The liquid may continue to flow until it again enters the packed tower (43) of the abatement system. Thus, the powder is washed out of the duct / pipe containing the exhaust draw amplifier (10), avoiding problematic powder build-up.

[0051] An exhaust draw amplifier (10) suitable for use in the present invention is shown in Figure 2. The exhaust draw amplifier includes a primary flow passage (11) through which exhaust gas flows, surrounded by a plenum (7) having ports (8, 9) that open into the exhaust gas stream. These ports (8, 9) can introduce jets of high velocity compressed dry air into the flow to increase the overall gas velocity.

[0052] In an embodiment, the primary flow passage (11) of the exhaust draw amplifier is axially aligned with the gas inlet (13) of the mist trap (12). The inlet flow passage (13) of the mist trap (12) and the primary flow passage (11) of the EDAD (10) are preferably arranged to provide a continuous inwardly facing surface.

[0053] As shown in Figure 6, in a preferred arrangement, the mist trap (12) is located directly adjacent to the exhaust draw amplifier (10) in the emission abatement system, and preferably directly above the exhaust draw amplifier (10). Liquid collected by the mist trap (12) preferably flows immediately into the exhaust draw amplifier (10), preferably under the influence of gravity.

[0054] In another arrangement, a mist filter can be placed between the exhaust draw amplifier and the mist trap and / or within the mist trap, which has been found to clean the exhaust draw amplifier while further enhancing drying of the exhaust gases.

[0055] In an embodiment, further liquid may be injected into the mist trap during use, preferably such that the liquid cascades over the baffle, preferably in the form of a weir, so that all the flue gas must pass through the liquid curtain. Additionally or alternatively, liquid may be sprayed as an aerosol onto the underside of the baffle, preferably by one or more spray nozzles, back into the incoming gas stream. The mist trap may be actively or passively cooled, preferably to a temperature substantially below the temperature of the gas entering the mist trap. The liquid introduced into the mist trap is preferably at a lower temperature than the flue gas entering the mist trap. Such an arrangement may have the advantage of cleaning the mist trap, further cooling the gas stream, reducing the relative humidity and removing more powder from the gas stream. In an arrangement including a mist filter, the liquid injected into the mist trap may also have the advantage of cleaning the mist filter.

[0056] The gas outlet (16) is typically connected to a pipeline along which the demisted (relatively dry) exhaust gas can continue for further treatment or, more typically, can be released into the atmosphere.

[0057] The mist in the present invention refers to a liquid-in-gas aerosol. Typically, the aerosol has a diameter of about 1000 μm or less, preferably about 2.5 μm to about 450 μm, preferably about 250 μm, measured, for example, using laser diffraction. Typically, the liquid is aqueous, such as water. Typically, the exhaust gas contains air. Typically, the mist is generated by a sprayer or the like in the packed tower (43) of the wet scrubber and is drawn into the mist trap along the piping. Typically, the temperature in the mist trap is at or below ambient conditions. This temperature is preferably about 5° C. to about 30° C., more preferably about 15° C. to about 25° C., in one example 20° C. This temperature is preferably such that no significant condensation occurs in the piping downstream of the mist trap. Typically, the water temperature in the packed tower chamber is about 10° C. to about 20° C., such as about 14° C. to about 17° C. Typically, the gas temperature is from about 10°C to about 20°C, such as from about 14°C to about 15°C.

[0058] Those skilled in the art will appreciate that the dimensions of the mist trap can vary depending on the size of the rest of the abatement system (particularly the exhaust draw amplifier), the amount of mist requiring removal, and site volume constraints, etc.

[0059] Generally, the mist trap has a diameter larger than the diameter of the gas inlet and / or gas outlet. Usually, the main chamber of the mist trap has an inner diameter of less than about 100 cm, preferably less than about 50 cm. Usually, the diameter of the main chamber is more than about 15 cm, preferably more than about 25 cm. Usually, the baffle has a diameter larger than the diameter of the gas outlet and / or gas inlet. The ratio of the diameter of the baffle to the diameter of the gas inlet and / or gas outlet is about 1:1 to about 5:1, preferably about 2:1 to about 3:1.

[0060] The present invention provides a method for mitigating particulate buildup in the primary flowpath of an exhaust draw amplifier of a gas abatement system, with reference to FIG.

[0061] The method includes the steps of passing mist-laden air from the gas abatement process through a primary flow path of an exhaust draw amplifier (45), removing liquid from the mist-laden gas exiting the exhaust draw amplifier (46), and passing at least a portion of the removed liquid back through the primary flow path of the exhaust draw amplifier (47). Optionally, after step (47), the liquid is subsequently transferred to a packed tower of a wet scrubber (48). The mist-laden air used in step (45) is preferably from the packed tower of the wet scrubber. Optionally, the method includes the step of directing a portion of the removed liquid to the wet scrubber without passing it through the exhaust draw amplifier.

[0062] It will be appreciated that the methods of the present invention may be carried out using the devices disclosed herein.

[0063] The present invention is further illustrated by the following examples, which are intended to be non-limiting. EXAMPLES

[0064] Test 1 A Y35 Atlas 1200 abatement unit with an EDAD was modified by removing the mist filter. This allowed mist from the atomizing spray generated in the packed tower to move downstream. A transparent inspection tube was introduced in the duct above the EDAD. During use, water droplets appeared on the transparent tube, confirming that mist was passing through the EDAD. A drain line from the exhaust duct was required to remove excess water. A significant reduction in EDAD occlusion and a significant increase in MTBC with EDAD occlusion were recorded during operation of the modified device compared to the unmodified device.

[0065] Test 2 A mist trap, such as those shown in Figures 3-5, was connected directly to the EDAD of a Y35 Atlas 1200 abatement device placed downstream of the EDAD. Again, the abatement device was modified by removing the mist filter. This allowed the mist from the atomizing spray generated in the packed tower to wash the powder away from the EDAD and travel to the mist trap. A polymer drain line was installed from the drain of the mist trap to a drain tank below the packed tower of the abatement device. A transparent inspection tube was connected to the outlet of the mist trap and to the downstream exhaust duct. When the mist trap baffle was set to full open, no droplets were observed on the clear polymer tube, indicating that the mist trap had removed all the mist. Liquid was observed flowing down the polymer drain line from the mist trap into the drain tank. While operating this modified device in combination with a mist trap, a significant reduction in EDAD occlusion and a significant increase in MTBC due to EDAD occlusion were recorded compared to the unmodified device. [Explanation of symbols]

[0066] 1. Packed Tower Wet Scrubber 2 Mist filter 3. Packed tower main chamber 4 Packing 5 Outlet of the packed tower main chamber 6 Exhaust gas flow 7 Plenum 8 Ports 9 Ports 10 Exhaust Draw Amplification Device (EDAD) 11 Primary flow path 12 Mist Trap 13 Gas inlet 14 Mist trap main chamber 15. Housing 16 Gas outlet 17 Drain 18 Drain 19 Base 20 Gas inlet opening 21 Groove 22 Recovery Reservoir 23 Drain Pipe 24 Drain pipe 25 First end of drain line 26 Second end of drain line 27 Mist trap baffle 28 Baffle body 29 Baffle Skirt 30 (single or double) baffle aperture 31 Underside of baffle 32 Bottom of skirt 33 First part of baffle 34 Second part of baffle 35 Skirt of the first part 36 Body of the first part 37 Body of the second part 38 Annular fixing plate 39 Baffle top recess 40 Main Chamber Roof 41 (singular and plural) support 42 Main chamber wall 43 Packed tower 44 Duct 45 The mist-laden air from the gas removal process is passed through the primary flow path of the exhaust draw amplifier. 46 Remove liquid from mist-laden gases emerging from exhaust draw amplifiers. 47 Passing at least a portion of the removed liquid back through the primary flow path of the exhaust draw amplifier. 48 The liquid is then transferred to a packed tower of the wet scrubber.

Claims

1. 1. A mist trap for a wet scrubber abatement system, the mist trap comprising a demisting chamber having a gas inlet for receiving mist-laden exhaust gas from the wet scrubber abatement system, a liquid capture surface through which mist droplets can coalesce to form liquid, and a gas outlet through which relatively dry gas can exit the chamber; the mist trap is configured to allow at least a first portion of the trapped liquid to exit the chamber via the gas inlet and return to the wet scrubber abatement system; A mist trap characterized by:

2. the liquid capture surface is provided by a baffle at least partially blocking the gas outlet from the gas inlet; 2. The mist trap of claim 1.

3. the baffle defines one or more apertures that provide a flow path from the gas inlet to the gas outlet.

3. A mist trap according to claim 2.

4. the baffle has one or more skirts, preferably the one or more apertures of the baffle are provided by the one or more skirts. A mist trap according to claim 2 or 3.

5. the demisting chamber includes at least one outlet through which a second portion of the trapped liquid may exit the chamber. A mist trap according to any one of claims 1 to 4.

6. 1. A mist trap water collection baffle for a gas abatement system, the baffle comprising a generally planar body and a skirt extending from the body adjacent an outer periphery of the body, the skirt defining one or more apertures configured to allow gas to flow around the baffle in use, the side of the planar body along which the skirt extends being configured to provide a liquid capture surface upon which mist droplets may coalesce. A water collecting baffle comprising:

7. the or each aperture is adjustable in size; A mist trap according to any one of claims 3 to 5, or a baffle according to claim 6.

8. the or each skirt is in the style of a rampart; A mist trap according to claim 4, 5 or 7, or a baffle according to claim 6 or 7.

9. the mist trap is in fluid communication with an exhaust draw amplifier and is configured such that liquid exiting the chamber through the gas inlet is redirected into the exhaust draw amplifier. A mist trap according to claim 1 to 5, 7 or 8.

10. 1. An abatement system comprising an exhaust draw amplifier and a mist trap, the exhaust draw amplifier configured to direct a mist-laden gas into the mist trap, the mist trap configured to remove liquid from the mist-laden gas, the mist trap further configured such that at least a portion of the liquid removed from the mist-laden gas is directed back into the exhaust draw amplifier.

13. A reduction system comprising:

11. The mist trap is as claimed in any one of claims 1 to 5, 7 or 8. The abatement system of claim 10.

12. The liquid passed through the exhaust draw amplifier returns to the packed bed demisting chamber. A mist trap according to claim 9 or an abatement system according to claim 10 or 11.

13. A mist trap baffle according to any one of claims 6 to 8, A mist trap according to claims 1 to 5 or 7 to 9, or an abatement system according to claims 10 to 12.

14. 1. A method for mitigating particulate buildup in a primary flowpath of an exhaust draw amplifier of a gas abatement system, comprising: a. passing mist-laden air from a gas abatement process through the primary flow passage of the exhaust draw amplifier; b. removing liquid from the mist-laden gas exiting the exhaust draw amplifier; c. passing at least a portion of the removed liquid back through the primary flow path of the exhaust draw amplifier; The method according to claim 1, further comprising:

15. Implemented using a mist trap according to any one of claims 1 to 5 or 7 to 9 or an abatement system according to claims 10 to 12, The method of claim 14.

16. Use of an aqueous mist to clean powder deposits from an exhaust draw amplifier of a gas abatement system in use, preferably said aqueous mist being delivered from a packed tower wet scrubber of said gas abatement system.

2. The use according to claim 1 ,

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