Exhaust gas pollution reduction device and exhaust gas pollution reduction method

Abstract

A method for reducing contamination in exhaust gases and a system for treating the exhaust gases are provided. The method includes treating the exhaust gas stream with a treatment fluid. In one application, the treatment fluid is injected by spraying droplets into the exhaust gas stream. The system for treating the exhaust gases includes a reagent and a nozzle that sprays the reagent into the exhaust gas stream.

Description

[Technical field]

[0001] This disclosure relates to the reduction of particulate pollution in exhaust gases. [Background technology]

[0002] Industrial exhaust gases are highly diverse and typically contain volatile heavy metals such as mercury, which are usually volatilized from the feedstock or fuel and transported to the atmosphere. For example, cement kiln exhaust gases typically contain oxides of carbon, sulfur, nitrogen, alkalis, excess chlorides, and volatile heavy metals such as mercury. Mercury, in both its elemental and ionic forms, is generally emitted continuously through the exhaust stack at various concentrations depending on the operation of the kiln, the in-line feed mill, and the feedstock or fuel inputs.

[0003] These gases may also be reused for drying and heating in in-line raw material mills and exit the process as cement kiln exhaust gases. Heavy metals in the gases may then be released to the atmosphere after passing through a kiln baghouse, electrostatic precipitator, or other particulate collection device.

[0004] Typical mercury concentrations in cement kiln flue gases can vary widely, depending largely on the raw materials, process conditions, and fuels burned at each point in the clinker generating process. Previous attempts to capture and contain mercury in both elemental and oxide forms from cement kiln flue gases have generally yielded mixed results. These processes can be expensive. These processes include activated carbon injection, flue gas desulfurization scrubbers, and sorbent technologies. Additionally, the process fluids used in these processes can produce undesirable chemical by-products.

[0005] Treatment processes for power plants, such as those disclosed in Hurley US Pat. Nos. 7,407,602, 7,771,683, and 7,776,294, are similarly inapplicable or inappropriate for the cement kiln environment for a variety of reasons. Summary of the Invention

[0006] In an exemplary embodiment, a method for treating industrial exhaust gas is disclosed. The method includes providing a flue gas stream from an industrial process, providing a reagent, and mixing the reagent and the flue gas stream to generate a mixed stream and removing at least a portion of one heavy metal, such as mercury, from the mixed stream. The method may further include passing the mixed stream through a particulate collection system and recycling the collected particulates for use as a raw material.

[0007] When mixing the exhaust gas stream with the reagent, the method may include spraying the reagent into the exhaust gas stream. The method may include mixing the reagent with one or more solvents to create a reagent solution prior to mixing the exhaust gas stream with the reagent. Factors that influence the amount or ratio of reagent to solvent used include exhaust particulate loading, dispersion, exhaust gas velocity, the presence and amount of metals other than mercury, and any number of other environmental or process parameters. In many cases, it is desirable to use a small amount of reagent necessary to achieve a desired amount of heavy metal reduction.

[0008] The method may also include providing at least one of a surfactant, a dispersant, and a hyperdispersant, and mixing the reagent and solvent with at least one of the surfactant, dispersant, and hyperdispersant before mixing the exhaust gas stream with the reagent.

[0009] The reagent solution may further include one or more chelating agents. In an exemplary embodiment, the reagent solution may include a mixture of ethylenediaminetetraacetic acid ("EDTA") and aminotris(methylenephosphonic acid) ("ATMP") and / or their corresponding salts.

[0010] In some embodiments, the solvent may include a diol, such as propylene glycol. Thus, the solvent may include a water dilution of propylene glycol.

[0011] In an exemplary embodiment, a method for reducing pollution in an industrial environment is disclosed. In this embodiment, the method includes treating an exhaust gas stream with a treatment fluid. The treatment fluid may include one or more chelating agents (e.g., EDTA and ATMP), a solvent, such as propylene glycol, and at least one of a surfactant and a hyperdispersant.

[0012] Injecting the treatment fluid may include spraying droplets of the treatment fluid into the exhaust gas stream. The treatment fluid may be injected into the exhaust gas stream at a point when the exhaust gas stream has a temperature of about 350 degrees Fahrenheit. The treatment fluid may be injected into the exhaust gas stream following the first particulate collection system and prior to the second particulate collection system. The treatment fluid may be injected into a gas resonance chamber or into a conduit carrying the exhaust gas stream.

[0013] The treatment fluid may also contain water and at least one of a surfactant and a hyperdispersant. The system and method may be adapted so that the droplets have a size that allows them to have a minimum residence time of about 1 second to about 2 seconds in the exhaust stream. In some applications, this minimum residence time can be achieved when the droplets have an average size of about 20 microns or more, more particularly about 30 microns to about 40 microns. Similarly, longer residence times are both achievable and suitable for industrial applications with larger droplet sizes.

[0014] In an exemplary embodiment, a system for treating an exhaust gas is disclosed that includes a treatment fluid, at least one nozzle in communication with the exhaust gas flow and configured to spray droplets of the treatment fluid into the exhaust gas flow, and at least one container fluidly connected to the nozzle and configured to store the treatment fluid.

[0015] The nozzle may be configured to spray droplets having a size configured to allow the droplets to have a minimum residence time of about 1 second to about 4 seconds. The nozzle may be configured to spray droplets having an average size of about 20 microns or greater.

[0016] The treatment fluid may include a reagent containing one or more chelating agents, where the one or more chelating agents may include both EDTA and ATMP. The treatment fluid may include the reagent mixed with water and / or propylene glycol. The treatment fluid may also include at least one of a surfactant, a dispersant, and a hyperdispersant.

[0017] In exemplary embodiments, chelating agents in the treatment fluid may sequester particulate matter (e.g., heavy metals) within the exhaust gas stream. Additionally, in embodiments in which the treatment fluid includes propylene glycol, the viscosity of propylene glycol may provide a "sticking" effect that enhances the ability of the treatment fluid to capture particulate matter. The resulting particulates may be collected by a particulate collection system. In some embodiments, the particulates may be transferred to storage for controlled metering back to the cement grinder and / or used as filler in a concrete batching plant, an asphalt plant, or landfilled.

[0018] Utilization of the systems and methods disclosed herein in treatment fluid applications can provide an effective manner of capturing particulate contaminants (e.g., heavy metals such as mercury) in exhaust gas streams without producing undesirable by-products that may result from chemical reactions between the treatment fluid and the particulate matter. Additionally, the non-hazardous nature of the treatment fluid components can simplify on-site storage and / or inventory requirements.

[0019] These and other aspects of the disclosure will become more readily understood from the following description and the accompanying drawings.

[0020] Embodiments of the present disclosure are illustrated in the accompanying drawings, which are by way of example and not limitation, and in which like reference characters are intended to refer to like or corresponding parts and in which: [Brief description of the drawings]

[0021] [Figure 1]SUMMARY OF THE DISCLOSURE An embodiment of a system and method for treating exhaust gas to reduce pollution is presented where a treatment fluid is sprayed into a conduit containing particulate matter. [Diagram 2] An embodiment of a system and method for treating exhaust gas to reduce pollution is shown where a treatment fluid is sprayed into a gas resonating chamber, a cyclone, or an additional conduit containing particulate matter. [Diagram 3] An embodiment of a system and method for treating exhaust gas to reduce pollution is shown where a treatment fluid is sprayed into a gas resonating chamber, a cyclone, or an additional conduit between two particulate collection systems. [Figure 4] 1 illustrates an embodiment of a method for recycling raw materials. [Diagram 5] 1 illustrates an embodiment of an integrated injection system and method for treating exhaust gas to reduce pollution. [Figure 6] FIG. 6 shows an expanded view of a portion of the system of FIG. 5 including two injection points. [Figure 7] FIG. 7 shows a top cross-sectional view of the two injection points of FIG. [Figure 8] 8 illustrates an embodiment of a lance suitable for use in various embodiments of the present disclosure, including the systems of FIGS. 5-7. [Figure 9] FIG. 9 shows a schematic diagram of an embodiment of a spray pattern from a nozzle at one injection point of the system of FIGS. 5-8. [Figure 10] 10 illustrates an embodiment of a fluid connection at an injection point of the system of FIG. 9. [Figure 11] 9A-9C show schematic diagrams of embodiments of spray patterns through nozzles at different injection points of the systems of FIGS. 5-8. [Figure 12] 12 illustrates an embodiment of a fluid connection at an injection point of the system of FIG. 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Although detailed embodiments of systems, methods, and apparatus for reducing exhaust gas pollution are disclosed herein, it should be understood that the disclosed embodiments are merely exemplary of the systems, methods, and apparatuses that can be embodied in various forms. Thus, the specific functional details disclosed herein should not be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to employ various systems, methods, and apparatus for reducing exhaust gas pollution. For example, although reference may be made to reducing pollution in exhaust gases from cement kilns, it should be understood that the systems, methods, and apparatuses as described herein may be applicable to removing pollutants from by-products of other types of industrial processes.

[0023] Heavy metals such as mercury that are sought to be controlled by the systems, methods, and apparatus of the present disclosure may come primarily from raw materials that are chemically altered during the clinkering process, which releases raw materials into the cement kiln exhaust gas stream, including cement kiln dust, and into the atmosphere through the kiln baghouse, electrostatic precipitator (ESP), or other particulate collection system. These raw materials may include calcium, silica, iron, and alumina that come primarily from various forms of limestone, clay, shale, slag, sand, mill scale, iron-rich material (IRM), pumice, bauxite, recycled glass, ash, and similar materials.

[0024] In one exemplary embodiment, the flue gas may be a cement kiln flue gas that typically passes from a kiln through one or more stages, conduits, mills, cyclones, a particulate collection system such as a kiln baghouse, ESP, or other particulate collection system, and exits at the kiln stack. As shown in Figures 1-3, flue gas stream 22 containing particulate matter passes from a kiln (not shown) to a flue gas diverter gate 24. At the diverter gate 24, all or a portion of the flue gas stream 22 may pass through a conduit 26 for use in drying and heating in a raw material mill 28, or may pass through a bypass conduit 30. As shown in Figures 1-3, if all or a portion of the flue gas stream 22 is used in drying and heating in a raw material mill 28, the flue gas stream 22 passes from the raw material mill 28 and a conduit 32 to a raw material mill cyclone or cyclones 34 located above a kiln feed silo 36. After the exhaust gas stream 22 passes through the cyclone 34 , the exhaust gas stream 22 passes through a return conduit 38 that connects with the bypass conduit 30 .

[0025] The flue gas stream 22 in the bypass conduit 30 may then pass through one or more particulate collection systems 40, during which particulates may be collected. In some embodiments, the particulates may be used as modified cement kiln dust (mCKD) 42. After the particulate collection system 40, the flue gas stream 22 passes through a conduit 44 and exits through a kiln stack 46.

[0026] In an exemplary embodiment, the exhaust gas stream 22 is treated with a fluid, solution, or treatment fluid by injecting or spraying the treatment fluid into one or more conduits, chambers, or other process equipment carrying the exhaust gas stream 22. The treatment fluid can be supplied in a fully soluble form allowing for low-cost application and retrofit of existing facilities.

[0027] The treatment fluid may include a reagent including one or more chelating agents capable of sequestering particulate matter in the exhaust gas stream 22. Examples of such chelating agents include, but are not limited to, ethylenediaminetetraacetic acid ("EDTA") and aminotris(methylenephosphonic acid) ("ATMP"). In some embodiments, the reagent may include multiple chelating agents. For example, the reagent may include a combination of EDTA and ATMP to create a synergistic effect on capturing particulate pollutants.

[0028] The treatment fluid may include a solvent in addition to or instead of water to function as a "depositing component" to further capture particulate matter from the exhaust gas stream 22. In an exemplary embodiment, the solvent may be a diol, such as propylene glycol, which may be diluted with water in a ratio of 12 to 15 to 1. Thus, in an exemplary embodiment, the treatment fluid may include a combination of EDTA and ATMP in addition to propylene glycol to capture particulate contaminants by sequestration and van der Waals interactions without chemically altering the particulate matter or producing auxiliary chemical by-products.

[0029] The reagents and water (or solvent) may be mixed into the treatment fluid prior to injecting or spraying the treatment fluid into one or more conduits, chambers, or other process equipment carrying exhaust gas stream 22. For example, the reagents and water may be mixed well before (e.g., one hour or more, one day or more, one week or more, one month or more, etc.) or just before (e.g., one minute or more) injecting or spraying the treatment fluid into one or more conduits, chambers, or other process equipment.

[0030] Alternatively, the reagent and water may each be sprayed or injected separately into one or more conduits, chambers, or other process equipment carrying the flue gas stream 22 such that the reagent and water intersect, mix, interact, or combine in one or more conduits, chambers, or other process equipment to form a solution or composition in situ, forming droplets of the solution or composition with the reagent reacting with metals in the flue gas stream 22 for removal. In another variation, the treatment fluid may be introduced into the flue gas stream 22 by adding it to a conventional flue gas desulfurization solution that is sprayed into the conduit.

[0031] The process fluid may also include one or more surfactants, dispersants, and / or hyperdispersants to aid in the removal of metals from the exhaust gas stream 22. In some embodiments, the surfactant may be an amphoteric or zwitterionic surfactant. In one embodiment, the surfactant, dispersant, and / or hyperdispersant is comprised of one or more polyethylene oxide-polyethylene block copolymers and / or phosphate esters thereof. When included, the surfactant, dispersant, and / or hyperdispersant may be provided in an amount sufficient to aid in maintaining the reactants or reagents in the process fluid prior to reacting with the metals, e.g., about 1% or less. In the latter case, the surfactant, dispersant, and / or hyperdispersant is a polyethylene oxide-polyethylene block copolymer and a phosphate ester thereof.

[0032] In an exemplary embodiment, the reagents, water, and one or more surfactants, dispersants, and / or hyperdispersants may be mixed with the treatment fluid prior to injection or spraying the treatment fluid into one or more conduits, chambers, or other process equipment carrying exhaust gas stream 22. For example, the reagents, water, and one or more surfactants, dispersants, and / or hyperdispersants may be mixed well before (e.g., one hour or more, one day or more, one week or more, one month or more, etc.) or just before (e.g., one minute or more) injection or spraying of the treatment fluid into one or more conduits, chambers, or other process equipment.

[0033] In an exemplary embodiment, the treatment fluid is sprayed or injected into the flue gas stream 22. The treatment fluid may be sprayed or injected into the flue gas stream 22 through a gas resonating chamber or incorporated into appropriate piping before or after the kiln baghouse, electrostatic precipitator, or particulate collection system 40, and / or flue gas desulfurization scrubber. The gas resonating chamber or piping is configured to form an area that aids in contacting particulates and gas streams in the flue gas stream 22 with the treatment fluid. In some embodiments, the treatment fluid may physically capture metals and other particulate matter in the flue gas stream 22 by chelation and / or sequestration.

[0034] Once the flue gas stream 22 in the chamber or ductwork is acted upon by the treatment fluid, the particulate residue is typically captured downstream, in an existing kiln baghouse, electrostatic precipitator, secondary grinding baghouse, or other particulate collection system 40, depending on the particular configuration. In some embodiments, the captured particulates may be a dry material called modified cement kiln dust ("mCKD"). In the case of a cement kiln equipped with a flue desulfurization scrubber, the particulate residue may be captured in the scrubber as a component of the produced synthetic gypsum, resulting in modified synthetic gypsum ("mSyngyp"). The mCKD and / or mSyngyp may then be transferred to storage for controlled metering back to the cement grinder, and / or used as filler in a concrete batching plant, an asphalt plant, or landfilled as non-leachable mCKD and mSyngyp.

[0035] In an exemplary embodiment, the timing of spraying or injection of treatment fluid into the flue gas stream 22 may be timed to the operation of the raw material mill 28 and may be continuous or intermittent, as required by the plant. In certain applications, the system for injecting the fluid (also referred to herein as the injection system) operates when the exhaust is likely to exceed the applicable emission limits for the heavy metals to be captured. For example, in certain applications, the exhaust gas is likely to contain higher concentrations of heavy metals when the raw material mill 28 is not operating, at which point the injection system may operate appropriately. Other cement kiln operations may require the injection system to operate while the raw material mill 28 is also operating, depending on the cement manufacturing equipment and process in which the injection system is incorporated and the location of such injection system.

[0036] In an exemplary embodiment, an injection system for treating exhaust gas includes a tank or other suitable container for storing an atomizing or treatment fluid and a suitable fluid connection to the exhaust gas stream for transporting the fluid in operable proximity to the exhaust gas stream containing mercury and other metals to be captured. The injection system includes one or more nozzles, ports, or other suitable openings positioned such that the atomizing fluid is formed. Multiple nozzles at spaced locations and with different angular orientations create a suitable distribution pattern for contacting the exhaust gas stream.

[0037] A system and method for treating flue gas to reduce pollution according to an exemplary embodiment will be described with reference to FIG. 1. As illustrated in FIG. 1, the injection system includes one or more nozzles 48 integrated into piping used to transport the flue gas stream 22 from a kiln (not shown). In this exemplary embodiment, the nozzles 48 are integrated into an existing conduit. The nozzles 48 are appropriately positioned to communicate with the bypass conduit 30. The nozzles 48 are connected through one or more fluid connections 52, such as pipes and / or hoses, to a container 50 that stores a spray or treatment fluid. The treatment fluid may be stored in the container 50 and transported through the fluid connections 52 to the flue gas stream 22 in the bypass conduit 30. The treatment fluid can then be sprayed or injected into the flue gas stream 22.

[0038] In this embodiment, the nozzle 48 is positioned downstream of the raw material mill 28 and prior to the particulate collection system 40 in communication with the bypass conduit 30. Treatment by the injection system illustrated in FIG. 1 occurs prior to the exhaust gas stream 22 entering one or more particulate collection systems 40. In this manner, the injection system can be designed such that the inlet temperature of the conduit system is high enough to accommodate the temperature drop across the injection system during operation, while also meeting the operational requirements of the existing particulate collection system 40, baghouse, or ESP, such as an inlet temperature selected to avoid both high heat conditions (e.g., above 400° F. [204° C.]) and low dew point conditions (e.g., below 200° F. [93° ​​C.]) that may lead to corrosion. Of course, the temperature drop across the injection system during operation may depend on the inlet temperature, the amount of treatment fluid injected, and other variables of this type.

[0039] In an exemplary embodiment, the treatment fluid injected or sprayed through nozzles 48 has a droplet size large enough to allow the treatment fluid to block the cement kiln exhaust gas stream, either intermittently or continuously, for a minimum of about 1-2 seconds while the treatment fluid is injected and reaction occurs, although it will be appreciated that longer residence or block times may be used and preferred based on the particular application.

[0040] Treatment by the injection system illustrated in Figure 1 occurs before the exhaust gas stream 22 enters one or more particulate collection systems 40. Thus, in some embodiments, particulates are captured as a dry residual material, resulting in modified cement kiln dust (mCKD) 42. This mCKD 42 may not dissolve in terms of leachate in soil, cement, or concrete because the captured mercury and other metals are no longer permanently insoluble. The mCKD 42 may be used as one of the additional materials inserted into the finishing mill in the cement manufacturing process, which is described in more detail below with reference to Figure 4.

[0041] The injection system including nozzles 48 is integrated into or installed in an existing conduit (e.g., bypass conduit 30), although it will be appreciated that the injection system including nozzles 48 can be installed in one or more newly added, modified, or existing conduits at any number of different locations. For example, the injection system may be installed or positioned to contact the exhaust gas stream 22 upstream of the feed mill 28, downstream of the feed mill 28, in the bypass conduit 30, in the return conduit 38, downstream of the particulate collection system 40, upstream of the particulate collection system 40, or in one or more existing, modified, or incorporated additional conduits.

[0042] When an injection system similar to the integrated injection system illustrated in FIG. 1 is integrated or installed after or downstream of a particulate collection system 40, kiln baghouse or ESP, the injection system may be designed such that the inlet temperature of the injection zone is high enough to accommodate the temperature drop across the injection zone during operation while meeting the requirements of a secondary particulate collection system such as illustrated in FIG. 3. The integrated injection system may be configured to spray droplets having a droplet size large enough to allow the droplets to block the exhaust gas flow, either intermittently or continuously, for about 1-2 seconds or more while the process fluid is injected and reaction occurs. The resulting particulates may be conveyed directly into the secondary particulate collection system and included as a concentrated residue.

[0043] The piping incorporated into the injection system may be an existing or new installation as part of the injection system. Piping incorporated into the injection system, whether existing or new, may optionally be treated with a polymer or may require additional conduit arrangements, additional chambers, or other modifications to its geometry to ensure that the treatment fluid or chemical remains in an active form for a suitable time to treat the cement kiln exhaust gas stream as intended before entering the particulate collection system.

[0044] In other embodiments, additional piping, chambers (such as a gas resonating chamber), and / or modifications to existing piping may be used in creating a suitable treatment or injection system. Another system and method for treating exhaust gas to reduce pollution according to an exemplary embodiment is described with reference to FIG. 2. As shown in FIG. 2, the injection system includes additional piping and is installed or positioned upstream of the particulate collection system 40. The additional piping includes a first conduit 54, a resonating chamber or cyclone 56, and a second conduit 58. In this exemplary embodiment, the first conduit 54 is connected to the bypass conduit 30, the resonating chamber 56 is connected to the first conduit 54, and the second conduit 58 is connected to the resonating chamber 56 and the inlet of the particulate collection system 40. Thus, the exhaust gas flow 22 flows from the bypass conduit 30 through the first conduit 54, through the resonating chamber 56, and through the second conduit 58 to the particulate collection system 40.

[0045] In addition to additional piping, the injection system includes one or more nozzles 60 suitably positioned to communicate with the resonating chamber 56. In this exemplary embodiment, the nozzles 60 are connected through one or more fluid connections 64, such as pipes and / or hoses, to a container 62 that stores a spray or treatment fluid. The treatment fluid is typically stored in the container 62 and transferred through the fluid connection 64 to the exhaust gas stream 22 within the resonating chamber 56. The treatment fluid can then be sprayed or injected into the exhaust gas stream 22.

[0046] In this embodiment, the nozzle 60 is positioned in communication with the resonating chamber 56 downstream of the feed mill 28 and prior to the particulate collection system 40. Treatment by the injection system illustrated in FIG. 2 occurs before the exhaust gas stream 22 enters the particulate collection system(s) 40. Also, in this embodiment, the injection system can be designed such that the inlet temperature of the resonating chamber 56 is high enough to accommodate the temperature drop across the resonating chamber 56 during operation while also meeting the operational requirements of the existing particulate collection system 40, baghouse, or ESP, such as an inlet temperature selected to avoid both high heat conditions (e.g., above 400° F. [204° C.]) and low dew point conditions (e.g., below 200° F. [93° ​​C.]) that may lead to corrosion.

[0047] In an exemplary embodiment, the treatment fluid injected or sprayed through nozzle 60 has a droplet size large enough to allow the treatment fluid to block the cement kiln exhaust gas stream, either intermittently or continuously, for about 1-4 seconds or more while the reagents are injected and reactions occur. However, it will be appreciated that longer residence or block times may be used and preferred based on the particular application. As in the previous embodiment, the fines may be captured as a dry residual material, resulting in modified cement kiln dust (mCKD) 42. The mCKD 42 may be used as one of the additional materials inserted into the finishing mill in the cement manufacturing process, which is described in more detail below with reference to FIG. 4.

[0048] Another system and method for treating exhaust gas to reduce pollution according to an exemplary embodiment is described with reference to Fig. 3. As shown in Fig. 3, the injection system includes additional piping and is installed or positioned between the two particulate collection systems 40a and 40b. The additional piping includes a first conduit 66, a gas resonating chamber or cyclone 68, and a second conduit 70. In this exemplary embodiment, the first conduit 66 is connected to the outlet of the particulate collection system 40a, the resonating chamber 68 is connected to the first conduit 66, and the second conduit 70 is connected to the resonating chamber 68 and the inlet of the particulate collection system 40b. Thus, the exhaust gas flow 22 flows from the particulate collection system 40a through the first conduit 66, through the resonating chamber 68, and through the second conduit 70 to the particulate collection system 40b.

[0049] As in the previous embodiment, the injection system includes one or more nozzles 72 suitably positioned to communicate with the resonating chamber 68. In this exemplary embodiment, the nozzles 72 are connected to a container 74 that stores a spray or treatment fluid through one or more fluid connections 76, such as pipes and / or hoses. The treatment fluid is typically stored in the container 74 and transferred through the fluid connections 76 to the exhaust gas stream 22 within the resonating chamber 68. The treatment fluid can then be sprayed or injected into the exhaust gas stream 22.

[0050] In this embodiment, the nozzle 72 is positioned in communication with the resonating chamber 68 downstream of the particulate collection system 40a and prior to the particulate collection system 40b. Processing with the injection system illustrated in FIG. 3 occurs after the particulate collection system 40a and prior to the particulate collection system 40b. In this embodiment, as with the other embodiments, the injection system can be designed such that the inlet temperature of the resonating chamber 68 is high enough to accommodate the temperature drop across the resonating chamber 68 during operation while also meeting the operational requirements of the existing particulate collection system 40b, baghouse, or ESP, such as an inlet temperature selected to avoid both high heat conditions (e.g., above 400° F. [204° C.]) and low dew point conditions (e.g., below 200° F. [93° ​​C.]) that may lead to corrosion.

[0051] In this exemplary embodiment, as with the other embodiments, the treatment fluid injected or sprayed through nozzle 72 has a droplet size large enough to allow the treatment fluid to block the cement kiln exhaust gas flow, either intermittently or continuously, for a minimum of about 1-4 seconds while the reagents are injected and reactions occur, although it will be appreciated that longer residence or block times may also be used and preferred based on the particular application.

[0052] The resulting fines may be conveyed directly into the fines collection system 40b and included as concentrated residue 78. This residue 78 may no longer be a threat in terms of leachate in soil, cement, or concrete because the captured mercury and other metals are now permanently insoluble. The residue 78 may be highly concentrated with heavy metals and may require additional testing for disposal, or may be used as a process addition in the cement mill. Additionally, the fines captured by the fines collection system 40a (CKD 80) may be used alone or in combination with the residue 78 as one of the addition materials inserted into the finishing mill in the cement manufacturing process, as described in more detail below with reference to FIG. 4.

[0053] Although the system described above has been installed at a particular location, it will be appreciated that the system may be installed at any number of different locations. For example, the system may be installed or positioned to contact the flue gas stream upstream or downstream of a raw mill, upstream and / or downstream of one or more particulate collection systems, or between one or more existing conduits incorporated into the system. Thus, treatment may be accomplished through any of a variety of existing conduits, gas resonator chambers, dry scrubbers, or other suitable areas, either before or after one or more particulate collection systems, including cement kiln baghouses, electrostatic precipitators, or flue gas desulfurization scrubbers.

[0054] In the exemplary embodiments disclosed herein, the timing of spray injection may be timed to match the operation of the feed mill 28 or may be continuous depending on the needs or goals of the plant to reduce emissions or comply with any applicable regulations. Utilizing an injection system prior to an existing particulate collection system 40, as shown in Figures 1 and 2, can reduce capital and operational costs as opposed to wet scrubber, dry scrubber applications, or activated carbon injection.

[0055] Of course, in one or more of the embodiments disclosed herein, there is no requirement for a "Polishing Baghouse." The injection system may be installed along side the existing kiln baghouse and the collected material may simply be separated for the duration of the operation. A separate dust storage and metering system may be included to hold the material until it can be returned in a controlled manner into the finishing mill. The collected material may be successfully utilized as a process addition within the cement mill without risk of releasing the captured mercury. Once the residue is captured in the concrete, it is not re-released because it is substantially permanently bound in a stable, natural form, unlike what typically results from the use of activated carbon or sorbent technology. The captured mercury is contained in a stable, natural form. The captured mercury is not re-released into the air or leached into the soil unless it is physically processed again through a kiln or combustion system.

[0056] Any of the embodiments disclosed herein may include a dust storage and metering system for containment of the captured mCKD and reintroduction of the mCKD into the cement grinding process for use in further production steps, or recycling the mCKD back into the kiln process after removal of entrained heavy metals such as mercury. As an additional process, the mCKD can be transported directly to a storage silo for controlled metering back into the cement grinder, and / or used directly as fill material in a concrete batching plant, asphalt plant, or landfilled as non-leachable mCKD.

[0057] A method of recycling mCKD and other raw materials according to an exemplary embodiment is described with reference to Figure 4. Clinker 82 produced in the kiln may be cooled and transferred to a storage silo 84 for controlled metering back into one or more finishing mills 86. Additionally, gypsum 88 may be transferred to a storage silo 90 for controlled metering into the finishing mill 86. The gypsum 88 is used as a process addition to the finishing mill 86 and may, for example, replace about 5.0% of the total raw materials utilized. In an exemplary embodiment, the gypsum 88 is modified synthetic gypsum (mSyngyp) captured by a flue gas desulfurization scrubber.

[0058] As shown in Figure 4, a dust storage and metering system is included for containment of the captured mCKD 92 and reintroduction of the mCKD 92 into the cement grinding process. The mCKD 92 may be transported directly to a storage silo 94 for controlled metering into the finishing mill 86 as a process addition. The mCKD 92 may be used as a process addition to the finishing mill 86, replacing, for example, up to about 5.0% of the total raw materials utilized. Of course, the mCKD may comprise a greater or lesser percentage of the total material, as would be understood by one of ordinary skill in the art in view of the present disclosure.

[0059] The mCKD92 is ultimately bound into Portland cement for use as concrete, and the resulting material is stabilized and non-leaching. As shown in Figure 4, a dust storage and metering system is used to hold the mCKD92 until it can be transported back into the finishing mill 86 in a controlled manner. As mentioned above, because the mCKD92 may be substantially permanently bound in a stable, natural form, the recovered mCKD92 can be successfully utilized as a process addition in the present cement mill without risk of releasing the recovered mercury.

[0060] The installation of an mCKD dust storage and weighing system allows the plant to effectively manage mCKD materials 92 and test them prior to recycling, reuse, or disposal.

[0061] In another exemplary embodiment, a continuous emissions monitoring system capable of accurately measuring mercury and other heavy metals to monitor system performance may be implemented as part of the system.

[0062] An example of an integrated injection system according to an exemplary embodiment is described with reference to Figures 5-13. With reference to Figure 5, the integrated injection system is installed in a cement plant 96. The plant 96 produces a flue gas stream 98 from a kiln (not shown) which flows downstream from the kiln through a downcomer 102. A shedding box 104 at the base of the downcomer 102 is designed to allow any solidified material to fall out of the flue gas stream 98 and be separated from the gases and particulate matter continuing through the piping. A conduit 106 connected to the outlet of the shedding box 104 carries the flue gas stream 98 downstream to a particulate collection system 108. The flue gas stream 98 flows through the particulate collection system 108 into a conduit 110 which carries the flue gas stream 98 downstream to a stack 112 through which the flue gas stream 98 exits into the atmosphere.

[0063] 5 and 6, the integrated injection system includes a first injection point 114 installed in the downcomer 102 and a second injection point 116 installed in the conduit 106. The integrated injection system is located upstream of the fines collection system 108. Thus, and similar to the previous embodiment, fines are captured in the fines collection system 108 as a dry residual material, resulting in modified cement kiln dust (mCKD) 118. This mCKD 118 may no longer dissolve in terms of leachate in soil, cement, or concrete, since the captured mercury and other metals are now permanently insoluble. Also, as in the previous version, the mCKD 118 may be used as one of the additional materials inserted into the finishing mill of the cement manufacturing process as described above with reference to FIG. 4.

[0064] A schematic top view of the first and second injection points 114 and 116 according to an exemplary embodiment is described with reference to Figure 7. As shown in Figure 7, a first port 120 is installed in the downcomer pipe 102 at the first injection point 114 and a second port 122 is installed in the conduit 106 at the second injection point 116. As shown, the downcomer pipe 102 has a diameter of about 20 feet and there are nine first ports 120 around the circumference of the downcomer pipe 102. The conduit 106 has a diameter of about 11.5 feet and there are nine second ports 122 around the circumference of the conduit 106. However, it will be appreciated that the number of first ports 120 and the number of second ports 122 may be less than or greater than nine depending on the particular application and size of the conduit.

[0065] 7-11, the first port 120 and the second port 122 are 4 inches in diameter and are located at radially spaced locations around the circumference of the downcomer pipe 102 and the conduit 106, respectively. The ports are aligned parallel to one another. Depending on the particular application, it will be appreciated that the ports 120, 122 may be smaller or larger than 4 inches in diameter, the port 120 need not be the same size as the port 122, and the spacing and orientation may vary. The ports 120, 122 are designed to penetrate the side walls of the downcomer pipes 102, 106 for insertion of the lances 128a-r of the spray nozzles into the downcomer pipes 102, 106, as will be described below.

[0066] In this exemplary embodiment, a lance having one or more nozzles positioned thereon is inserted into a corresponding one of the ports 120, 122. Each of the ports 120, 122 is capable of holding a lance. However, it is understood that not all of the ports 120, 122 require a corresponding lance to be inserted therein during operation. The lance may have a length that allows it to extend across at least a portion of the conduit from the particular port in which it is received. It is understood that the lance may have different lengths and extend varying distances across the conduit. For example, the lance may extend substantially across the conduit from the corresponding port, or may be sized or otherwise configured to extend a portion of a path across the conduit from such port.

[0067] As seen in Figures 7, 9 and 11, the saddle-fitted cross-supports 132 and 136 of each lance (not shown) extend across and beneath the lance of the corresponding conduit and can engage or support such lance on either the underside or the top side. The cross-supports 132 and 136 extend at an angle (perpendicular in this version) to the corresponding lance and are seated through corresponding ports 124, 126.

[0068] An embodiment of one of the lances 128a-r according to an exemplary embodiment is further described with reference to FIG. 8. As shown in FIG. 8, a lance 128, such as one of the lances 128a-r described below, has one or more nozzles 130 disposed thereon. In this embodiment, the lance 128 is made of stainless steel. However, it will be appreciated that the lance 128 may be made of other materials, such as, but not limited to, iron, aluminum, polymers, and other materials of the kind. In this embodiment, the nozzles 130 are configured to disperse droplets of the process fluid. The droplet size must be large enough that the droplets can exist long enough to react with metals, such as ionic elemental mercury, in the exhaust gas stream. In this embodiment, the droplets may have an average size of about 20-40 microns, more particularly about 30-40 microns. A droplet size of about 30 to 40 microns is designed to allow the droplets to remain in the flue gas stream for a minimum of about 1 to 2 seconds when the temperature at the injection point averages about 350°F [177°C]. However, the droplet size can vary, for example, the droplets may have an average size of about 20 microns or more, depending on the flue gas temperature, process fluid concentration, water pressure, actual cubic feet per minute, particulate dust loading and mercury concentration, and other factors. For example, it will be appreciated that higher temperatures may be associated with larger droplet sizes, such as about 70 to 90 microns (although this is not an upper limit for suitable droplet sizes), and that at lower temperatures smaller droplet sizes may be used.

[0069] A schematic of a spray pattern through nozzles 130 in the downcomer 102 at the injection point 114 is shown and will be described with reference to Figure 9. As shown in Figure 9, nine evenly spaced lances 128a-i each have one or more nozzles 130 (shown in a circular pattern) and are inserted into nine of the first ports 120. In this embodiment, the lances 128a-i are supported by cross supports 132 that extend between the ports 124. The cross supports 132 may be fitted with saddles for the lances 128a-i to support the lances 128a-i as they extend across the conduit 102.

[0070] As shown in Figure 9, nozzle 130 (shown with a circular pattern) has a conical spray pattern with a round shaped impact area, however, it will be appreciated that nozzles having different shaped spray patterns and impact areas may be used.

[0071] In this embodiment, lances 128a and 128i each have one nozzle 130, lances 128b and 128h each have four nozzles 130, lances 128a, 128c, and 128g each have five nozzles 130, and lances 128d and 128f each have six nozzles 130. The spray pattern, shown as a circular pattern of nozzles 130, covers approximately 90% of the total cross-sectional area of ​​the downcomer pipe 102. However, it will be appreciated that a different nozzle arrangement or number, smaller, larger, or different spray patterns may be used, and the amount of coverage of the total cross-sectional area of ​​the downcomer pipe 102 may be varied to be a higher or lower percentage.

[0072] Similarly, a schematic of a spray pattern through a nozzle 130 in the conduit 106 at the injection point 116 is shown and described with reference to FIG. 11. As shown in FIG. 11, nine evenly spaced lances 128j-r, each having one or more nozzles 130 (shown in a circular pattern) are inserted into nine of the second ports 122. In this embodiment, the lances 128j-r are supported by cross supports 136 that extend between the ports 126. The cross supports 136 may be fitted with saddles for the lances 128j-r to support the lances 128j-r as they extend across the conduit 106.

[0073] As shown in Figure 11, nozzle 130 (shown with a circular pattern) has a conical spray pattern with a round shaped impact area, however, it will be appreciated that nozzles having different shaped spray patterns and impact areas may be used.

[0074] In this embodiment, lances 128j and 128r each have one nozzle 130, lances 128k-m and 1280-q each have four nozzles 130, and lance 128n has five nozzles 130. The spray pattern illustrated by the circular pattern of nozzles 130 covers approximately 90% of the total cross-sectional area of ​​the conduit 106. However, it will be appreciated that any number of nozzles having smaller or larger spray patterns may be used to cover a greater or lesser percentage of the total cross-sectional area of ​​the conduit 106.

[0075] As illustrated, with reference to Figures 8-10, the nozzle 130 is fluidly connected to one or more vessels storing the treatment fluid via one or more of the lances 128a-i through one or more fluid connections 134, such as pipes and / or hoses. The treatment fluid is stored in the vessels and transferred through the one or more lances 128a-i through the fluid connections 134 (e.g., via pumps) and out of the nozzle 130 in the downcomer 102. The treatment fluid then contacts the flue gas stream 98 in the downcomer 102. Similarly, as illustrated with reference to Figures 8, 11, and 12, the nozzles 130 of the lances 128j-r at the second injection point 116 in the conduit 106 are fluidly connected to a vessel containing the treatment fluid via one or more fluid connections 138, such as pipes and / or hoses.

[0076] The integrated injection system described above with reference to Figures 5-12 can be implemented in a cement plant 96 (Figure 5) to remove mercury from the flue gas stream 98. The temperature of the flue gas stream 98 varies with the operation of the in-line feed mill and / or kiln conditions. In this exemplary embodiment, the temperature at the inlet to the downcomer 102, upstream of the feed mill, varies from about 600-800°F [316-427°C]. The temperature at the inlet to the fines collection system 108 is typically in the range of about 240-300°F [116-149°C] to protect the fines collection system 108. When the feed mill is operating, the flue gas stream 98 loses heat as it passes through the feed mill to dry the feedstock while grinding is taking place. When the feed mill is not operating, it is typically necessary to reduce the temperature of the flue gas stream 98 by using high pressure water spray at the downcomer 102. This typically cools the exhaust gas stream 98 to approximately 325-395° F. [163-202° C.] at the inlet to the particulate collection system 108 to protect the particulate collection system 108 .

[0077] The particulate loading in the flue gas stream 98 can be as high as 20 tons per hour (tph) through the downcomer 102 and is independent of the operation of the raw mill. The gas volume in the flue gas stream 98 can vary by 4,000,000 standard cubic feet per hour (sal) [113,267 kL / hr] during operation due to temperature fluctuations and process conditions.

[0078] In an exemplary embodiment, the treatment fluid includes a reagent and a solvent. The reagent may be a chelating agent mixture including EDTA and ATMP. The solvent may include propylene glycol diluted in water. The reagent and solvent are injected when the feed mill is off and the temperature is reduced to approximately 350°F [177°C] at the outlet of conduit 106. As mentioned above, a first injection point 114 is installed in downcomer 102 prior to shedding box 104 and a second injection point is installed in conduit 106 after shedding box 104. The treatment fluid is injected through nozzle 130 at a rate of approximately 15 gallons [56.8 L] per minute, at a pressure of approximately 45 psi [306 kPa], and has an average droplet size of approximately 30 to 40 microns. The droplet size of about 30-40 microns is designed to allow the reagent to remain in the flue gas stream 98 long enough to contact and sequester particulates (e.g., heavy metals) in the flue gas stream 98 by chelation and / or physical interaction with the propylene glycol. In this embodiment, the 30-40 micron droplets remain in the flue gas stream 98, which has an average temperature of about 350°F [177°C], for a minimum of about 1-2 seconds before vaporizing. Additionally, the 30-40 micron droplets prevent the reagent from accumulating in the downstream preheater ID fan (not shown) present in the cement plant 96. Under these conditions, smaller droplets would not allow the droplets sufficient life to cause a reaction, while larger droplets would be carried to the preheater ID fan and could contribute to accumulation and vibration leading to fan failure.

[0079] Although the systems and methods disclosed herein are described with reference to specific embodiments, it is understood that industrial system configurations vary widely, and therefore the location and configuration of the treatment system relative to the exhaust gas stream may be correspondingly varied to suit a particular industrial system. It is also understood that any of the embodiments contemplated herein may or may not require one or more secondary particulate removal systems, depending on the particular application.

[0080] Depending on the operation, raw materials, and fuel of each individual kiln, the systems disclosed herein may operate only intermittently as necessary, or may operate substantially continuously to achieve the desired reduction goals, including injecting treatment fluid 100% of the time. In most cases, the highest periods of mercury emissions are associated with when the in-line vertical mill or raw material mill is off, or when there are temperature differences in the kiln baghouse, ESP, or other particulate collection system. Thus, treatment steps may be configured to run during such off-line periods, or may be triggered to run in response to any number of parameters, such as time, exceedance of certain emission thresholds, operating emission averages, measurements of gas components, and other such parameters. Each system may be adjusted for each cement kiln based on actual emission modeling, raw materials, costs, and any number of other operational, emission, or functional parameters.

[0081] In exemplary embodiments, conduits, chambers, or other treatment zones incorporated into the treatment system are configured to accommodate the temperature drop as the exhaust stream travels downstream. For example, as disclosed above, in certain embodiments, the treatment zones (conduits, chambers, cyclones, etc.) may be selected or configured such that the inlet temperature of the treatment zone is high enough to accommodate the temperature drop across the zone during operation while still meeting the operational requirements of the downstream baghouse, ESP, or other particulate collection system. Such inlet temperatures avoid both high heat and low dew point conditions that are conducive to corrosion.

[0082] The systems, methods, and processes disclosed herein are identified, adapted, and designed for the cement industry. In one aspect, the systems, methods, and processes disclosed herein can achieve lower capital costs, lower operating costs, and most importantly, reduced mercury emission levels.

[0083] Naturally, versions of this technology can also be applied to cement manufacturing plants equipped with wet scrubbers or already designed for the use of activated carbon injection. Retrofitting of existing facilities is explicitly mentioned as a possible configuration.

[0084] It should also be appreciated that using the systems and methods disclosed herein, mercury is captured regardless of where it is generated during the cement manufacturing process without the need for reheating. The systems and methods disclosed herein allow cement plants to use a greater variety of raw materials without fear of exceeding any applicable emission limits for mercury or other heavy metals captured as described in this disclosure. Depending on the amount of residual material produced, the portion that is not available as a process addition must be disposed of, but overall it is expected to be insignificant.

[0085] Although the above description generally relates to mercury capture, it will be appreciated that the systems, methods, processes, and techniques disclosed herein may be modified to capture hexavalent chromium and various other metals and exhaust hot spots.

[0086] The matter set forth in the foregoing description and accompanying drawings is offered by way of example only and not by way of limitation. Although the system, method, and apparatus for cement kiln exhaust gas pollution reduction has been described and illustrated with reference to specific embodiments, many variations and modifications will be apparent to those skilled in the art and can be made without departing from the spirit and scope of the disclosure. Thus, the disclosure is not limited to the precise details of the methodology or construction described above, as variations and modifications are intended to be included within the scope of the disclosure.

Claims

1. 1. A method for treating an exhaust gas stream from an industrial process, comprising: providing an exhaust gas stream; providing a treatment fluid including a reagent comprising one or more chelating agents, the one or more chelating agents comprising a mixture of ethylenediaminetetraacetic acid and aminotris(methylenephosphonic acid); providing at least one nozzle configured to communicate with the exhaust gas stream, the nozzle producing droplets of a treatment fluid sized to maintain a sufficient residence time for effective interaction with one or more heavy metals in the exhaust gas stream; providing a particulate collection system; injecting the treatment fluid through the nozzle into the exhaust gas stream to form a mixed stream prior to entering the particulate collection system, wherein the one or more chelating agents interact with one or more heavy metals in the exhaust gas stream via chelation or physical binding to form one or more particulates; separating the one or more particles comprising at least a portion of the one or more heavy metals from the mixed stream in the particle collection system by forming a particulate residue comprising the one or more heavy metals in a non-leachable form; A method comprising:

2. 1. A system for treating an exhaust gas stream from an industrial process, comprising: a treatment fluid comprising a reagent including one or more chelating agents, the one or more chelating agents comprising a mixture of ethylenediaminetetraacetic acid and aminotris(methylenephosphonic acid); at least one nozzle configured to be in communication with the exhaust gas flow; a particulate collection system; the at least one nozzle injects the treatment fluid into the exhaust gas stream to form a mixed stream prior to entering the particulate collection system, and the one or more chelating agents are configured to interact with one or more heavy metals in the exhaust gas stream via chelation or physical binding to form one or more particulates; the nozzle is configured to produce droplets of treatment fluid sized to maintain a sufficient residence time for effective interaction with one or more heavy metals in the exhaust gas stream; The particulate collection system is configured to separate the one or more particulates comprising at least a portion of the one or more heavy metals from the mixed stream by forming a particulate residue comprising the heavy metals in a non-leachable form.

3. 3. The system of claim 2, wherein the treatment fluid further comprises at least one selected from the group of surfactants, dispersants, and hyperdispersants to enhance dispersion of the chelating agent within the droplet phase and promote interaction of the one or more heavy metals with the gas phase.

4. The system of claim 2 , wherein the treatment fluid comprises a solvent including propylene glycol, the solvent maintaining stability of the droplets and increasing residence time of the treatment fluid in the exhaust gas stream.

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