AGENTS IN A WET AIR SCRUBBER

[0001] This application claims priority to U.S. Provisional Application Ser. No.

61/455,706 filed October 25, 2010, the disclosure of which is incorporated herein by reference.

BACKGROUND

[0002] Rendering facilities can produce emissions in the form of volatile organic compounds ("VOCs") as a result of their operations. Pollutants such as organic sulfides and disulfides (e.g., dimethyl disulfide), thiols (e.g., methane thiol), aldehydes (e.g., hexanal, 2- methylbutanal, and 3-methylbutanal), alcohols, ketones, amines, aliphatic hydrocarbons (e.g., octane), aromatic compounds (e.g., quinoline and pyrazines) and organic acids are commonly produced. These VOCs are generally considered an odor nuisance when rendering facilities are in close proximity to residential areas, and so emission control measures are generally directed toward odor reduction and/or elimination. Air scrubbers may be employed at rendering facilities as one method of emission control and odor elimination.

SUMMARY

[0003] In an aspect the disclosure provides a method of operating a wet air scrubber, the method comprising: adding an amount of a dosing composition comprising a tracer and a treatment agent to the wet air scrubber; obtaining a fluid sample from the wet air scrubber; determining a concentration of the tracer in the fluid sample; comparing the concentration of the tracer in the fluid sample to a target tracer concentration; and adjusting the amount of the dosing composition in the wet air scrubber when there is a difference between the

concentration of the tracer in the fluid sample and the target tracer concentration; wherein the target tracer concentration corresponds to a target concentration of the treatment agent. In some embodiments the tracer may comprise a triazole. In some embodiments, the triazole may comprise at least one of a benzotriazole, a polytriazole, a tolyltriazole, and combinations thereof.

[0004] In a further aspect the disclosure provides a method of operating a wet air scrubber, the method comprising: adding an amount of a dosing composition comprising a triazole tracer and a treatment agent to the wet air scrubber, wherein the treatment agent comprises at least one of an odor control agent, an oxidizing agent, a strong base, an acid, a surfactant, a dispersant, a wetting agent, an enzyme, a pH control agent, a defoamer, and combinations thereof, and wherein the concentration of the tracer in the dosing composition is about 0.1 % to about 10% (w/w%); obtaining a fluid sample from the wet air scrubber, wherein obtaining occurs about 1 minute to about 12 hours after adding the dosing composition to the wet air scrubber; filtering the fluid sample wherein filtering comprises a filter having a pore diameter of about 0.5 μηι or less; using colorimetric analysis to determine the concentration of the tracer in the fluid sample, wherein colorimetric analysis comprises a colorimetric reagent within the fluid sample; comparing the concentration of the tracer in the fluid sample to a target tracer concentration; and adjusting the amount of the dosing composition in the wet air scrubber when there is a difference between the concentration of the tracer in the fluid sample and the target tracer concentration; wherein the target tracer concentration corresponds to a target concentration of the treatment agent.

[0005] In another aspect the disclosure provides a method of reducing the amount of one or more pollutants emitted from a wet air scrubber, the method comprising: adding an amount of a dosing composition comprising a tracer and a treatment agent to the wet air scrubber; obtaining a fluid sample from the wet air scrubber; determining a concentration of the tracer in the fluid sample; comparing the concentration of the tracer in the fluid sample to a target tracer concentration; and adjusting the amount of the dosing composition in the wet air scrubber when there is a difference between the concentration of the tracer in the fluid sample and the target tracer concentration, wherein the adjusting of the amount of the dosing composition is effective to reduce the amount of the one or more pollutants emitted from the wet air scmbber; wherein the target tracer concentration corresponds to a target concentration of the treatment agent.

[0006] The disclosure provides additional aspects and embodiments that will be apparent in light of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] Fig. 1 shows an embodiment of a wet air scrubber. DETAILED DESCRIPTION

[0008] The disclosure provides methods of determining the concentration of a treatment agent in a wet air scrubber using a tracer compound. Among other advantages, the disclosed methods provide for the straightforward and convenient operation of a wet air scrubber and maintaining an effective target concentration of a treatment agent in the wet air scrubber.

[0009] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0010] It also is specifically understood that any numerical value recited herein includes all values from the lower value to the upper value, i.e., all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application. For example, if a concentration range or a beneficial effect range is stated as 1% to 50%, it is intended that values such as 2% to 40%, 10% to 30%, or 1% to 3%, etc. are expressly enumerated in this specification. These are only examples of what is specifically intended.

[0011 ] The organic load in a wet air scrubber can vary with time. For example, in a rendering facility, the organic load may vary over time due to factors such as, for example, fluctuations in raw material composition (e.g. relative fat and protein content, percent moisture content, the presence of hair or feathers) and raw material availability in the rendering plant. As the raw material and/or raw material availability changes in the rendering plant from hour to hour, day to day, or season to season, the concentration and composition of gases entering the wet air scrubber may also change. As such, it may be desirable to monitor the concentration of a treatment agent in the wet air scrubber water to insure optimal emission control and odor elimination.

[0012] Because it is typically challenging or impractical to measure the concentration of treatment agents in a wet air scrubber directly, it is desirable to instead measure the presence, amount, or concentration of a tracer chemical, the concentration of which is known in relation to the treatment agent(s), and the analysis of which is simple, inexpensive, and accurate. Wet Air Scrubbers

[0013] In an aspect, the disclosure provides a method of dosing a wet air scrubber, the method comprising adding a dosing composition comprising a tracer and a dosing agent to the wet air scrubber and monitoring the concentration of the tracer over the course of air scrubber operation. Thus, the methods disclosed herein are useful in the operation of a wet air scrubber. Wet air scrubbers can be deployed for any suitable use. Typically, wet air scrubbers remove pollutants such as VOCs from a gas stream by moving the gas stream through an aqueous cleaning solution including one or more treatment agents. After passing through the aqueous cleaning solution, the gas stream emerges without the pollutants or with reduced amount of pollutants than were present in the gas stream before treatment in the wet scrubber. In order for VOCs to be efficiently removed from the gas stream, it may be important to monitor the concentration of treatment agent(s) in an aqueous cleaning solution used in the wet scrubber.

[0014] FIG. 1 is a schematic view of one embodiment of a high-intensity wet air scrubber suitable for use in removing VOCs from a gas stream. Direction of air flow (dashed arrow) and water flow (solid arrow) within the scrubber media are indicated for this non-limiting embodiment. The wet air scrubber can include any scrubber routinely used or otherwise known in the art such as, for example, a packed tower scrubber, a spray tower scrubber, an orifice scrubber, a venturi scrubber, a fiber-bed scrubber, an impingement-plate scrubber, a spray nozzle scrubber, a fluidized-bed scrubber, a packed-bed scrubber, multiple-stage scrubbers, baffle spray scrubber, a counter-flow scrubber, a crossflow scrubber, and combinations thereof. Wet air scrubbers also include those that are custom designed by, for example, an independent designer, or competent staff at a rendering facility. Wet air scrubbers are commercially available, for example, from Verantis, AC Corporation, Sep Control Inc., and Millpoint Industries Inc.

[0015] The methods described herein may be used with wet air scrubbers at any suitable location, such as at factories or plants including, but not limited to, rendering plants, municipal wastewater plants, food processing plants, flavor and fragrance plants, breweries, and grain operations, such as, for example, corn processing. The methods may also provide air scrubbers with more effective pollution control. Dosing Compositions

[0016] In some embodiments, the method comprises a dosing composition that can include a tracer and a treatment agent. In some embodiments, the tracer may be substantially inert in the environment of a functioning wet chemical scrubber. The tracer suitably comprises a reagent having a moiety that is readily detectable by any appropriate method such as, for example, a spectrometric (e.g., mass spectrometry) or spectrophotometric (e.g., UV/Vis, fluorescence, phosphorescence, infrared) method. In some embodiments, the tracer can suitably include a triazole such as, for example, a benzotriazole, a polytriazole, a tolyltriazole, and/or combination thereof. In some embodiments, the tracer may comprise a 4-methyl-1H-1,2,3-benzotriazole, a 4-methyl-2H- 1,2,3 -benzotriazole, a 5-methyl-1H- benzotriazole, a hydroxybenzotriazole, a carboxy benzotriazole, a dialkylamino alkyltriazole, a bis-[4H-5-hydroxy-1,2,4-triazol-3-yl] methane, or combinations thereof.

[0017] In some embodiments, the treatment agents can include those known in the art, for example, oxidizing agents (e.g., sodium hypochlorite, chlorine dioxide, hydrogen peroxide), strong bases (e.g., sodium hydroxide and potassium hydroxide), acid (e.g., sodium acid sulfate, citric acid, hydrochloric acid), surfactants (e.g., nonionic, cationic, anionic, amphoteric, detersive, polymeric), dispersants, wetting agents, enzymes, pH control agents, defoamers, and combinations thereof. In some embodiments, treatment agents can comprise odor control agents formulated for wet air scrubber use, such as, for example, RENEW BALANCE™ (Diversey, Sturtevant, Wisconsin), RENEW™ A (Diversey, Sturtevant, Wisconsin), RENEW™ B (Diversey, Sturtevant, Wisconsin), and ODOR-OUT™ (ReNew Systems, Bay City, Michigan), which are commercially available. Additional treatment agents that may be useful according to the present application are described in International Patent Application No. PCT/US 10/47344, which is incorporated herein by reference in its entirety.

[0018] In some embodiments, the concentration (weight percent) of the tracer in the dosing composition may be about 0.1 % to about 10% by weight, about 0.5 % to about 5% by weight, about 1% to about 4% by weight, and about 1.5% to about 3% by weight. In some embodiments, the concentration of tracer in the dosing composition may be at least about 0.1% by weight, at least about 0.5% by weight, at least about 1% by weight, at least about 1.5% by weight, at least about 2% by weight, at least about 3% by weight, at least about 4% by weight, or at least about 5% by weight. In some embodiments, the concentration of tracer may be less than about 10% by weight, less that about 8% by weight, and less than about 6% by weight.

[0019] In some embodiments, the target concentration in parts per million of the treatment agent in the water of the wet air scrubber (e.g., μΐ. chemical dosing mixture/L water in wet air scrubber) may be about 10 ppm to about 500 ppm, about 50 ppm to about 400 ppm, about 100 ppm to about 350 ppm, and about 150 ppm to about 300 ppm. In some

embodiments, the target concentration in parts per million by volume of the treatment agent in the water of the wet air scrubber can be at least about 10 ppm, at least about 50 ppm, at least about 100 ppm, at least about 150 ppm, at least about 200 ppm, at least about 300 ppm, at least about 350 ppm, at least about 400 ppm, or at least about 450 ppm. In some embodiments, the target concentration in parts per million by volume of the treatment agent in the water of the wet air scrubber can be less than about 500 ppm, less than about 400 ppm, less than about 350 ppm, or less than about 300 ppm.

Fluid Sampling and Detection of Tracer Concentration

[0020] After the dosing composition has been added (or after the amount is adjusted) to the wet air scrubber, the concentration of tracer in the wet air scrubber may be determined by obtaining a fluid sample from the wet air scrubber, followed by detection of tracer concentration of the fluid sample. In some embodiments, obtaining of the fluid sample can occur after a period of time that is effective to allow for distribution of the composition throughout at least a portion of the scrubber. Some embodiments comprise obtaining a plurality of fluid samples over a period of time (e.g., at regular time points during wet air scrubber operation) so as to allow for the detection of variance of tracer concentration during wet air scrubber operation. In some embodiments, the time is about 10 seconds to about 12 hours, about 1 minute to about 12 hours, about 2 minutes to about 6 hours, about 3 minutes to about 3 hours, about 4 minutes to about 2 hours, or about 5 minutes to about 1 hour after adding the dosing composition to the wet air scrubber. In some embodiments, obtaining of the fluid sample can occur less than about 12 hours, less than about 6 hours, less than about 3 hours, less than about 2 hours, less than about 1 hour, less than about 45 minutes, less than about 30 mmutes, less than about 15 minutes, less than about 10 minutes, less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, or less than about 1 minute after adding the dosing composition to the wet air scrubber. In some embodiments, obtaining of the fluid sample can occur at least about 10 seconds, at least about 20 seconds, at least about 30 seconds, at least about 40 seconds, at least about 50 seconds, at least about 1 minute, at least about 2 minutes, at least about 3 minutes, at least about 4 minutes, at least about 5 minutes, at least about 10 minutes, at least about 15 minutes, at least about 30 minutes, at least about 1 hour, at least about 2 hours, at least about 3 hours, at least about 4 hours, at least about 5 hours, at least about 6 hours, at least about 7 hours, at least about 8 hours, at least about 9 hours, at least about 10 hours, or at least about 11 hours after adding the dosing composition to the wet air scrubber.

[0021] Detection of tracer concentration can be achieved by any suitable method known to those skilled in the art. In some embodiments, detection of tracer concentration is achieved by colorimetric analysis (e.g., UV/Vis). Colorimetric analysis of the fluid sample can be carried out by methods know in the art using Beer's Law:

where A is absorbance, ε is molar absorptivity, / is path length, and c is the concentration of an absorbing species in the material.

[0022] In some embodiments, colorimetric analysis can be carried out using a triazole testing method, such as, for example, Hach Company Method 8079 (Hach Company, Loveland, Colorado) using a DR/890 colorimeter (Hach Company, Loveland, Colorado) and colorimetric reagent such as, for example, a triazole reagent powder pillow (product # 21412- 99; Hach Company, Loveland, Colorado). In some embodiments, the target tracer concentration in the wet air scrubber in parts per million by volume of the water in the wet air scrubber may be about 0.1 ppm to about 10 ppm, about 0.2 ppm to about 8 ppm, about 0.3 ppm to about 6 ppm, about 0.4 ppm to about 5 ppm., about 0.5 ppm to about 4 ppm, about 1 ppm to about 3.5 ppm, and about 1.5 ppm to about 3 ppm. In some embodiments, the target tracer concentration in parts per million by volume of the tracer in the water of the wet air scrubber can be at least about 0.1 ppm, at least about 0.5 ppm, at least about 1 ppm, at least about 1.5 ppm, at least about 2 ppm, at least about 3 ppm, at least about 3.5 ppm, at least about 4 ppm, at least about 5 ppm, at least about 6 ppm, at least about 7 ppm, at least about 8 ppm, at least about 9 ppm, and at least about 10 ppm. In some embodiments, the target tracer concentration in the wet air scrubber in parts per million by volume of the water in the wet air scrubber may be less than about 10 ppm, less than about 9 ppm, less than about 8 ppm, less than about 7 ppm, less than about 6 ppm, less than about 5 ppm, less than about 4 ppm, less than about 3.5 ppm, less than about 3 ppm, less than about 2 ppm, less than about 1.5 ppm, less than about 1 ppm, less than about 0.5 ppm, or less than about 0.1 ppm.

[0023] In some embodiments, the fluid sample can be filtered before colorimetric analysis. In some embodiments, filtering of the sample can include using a filter having a pore diameter of about 0.5 μm or less. In some embodiments, the filter can have a pore diameter of about 0.45 μm to about 0.22 urn. In some embodiments, the filter can be a MILLEX ^® filter (Millipore, Billerica, Massachusetts).

Dosing Composition Amount and Rate of Addition Adjustment

[0024] If there is a detectable difference between the concentration of the treatment agent as determined by detecting the tracer concentration and the target concentration of the treatment agent in the wet air scrubber which corresponds to the target tracer concentration, the amount of the dosing composition in the wet air scrubber can be adjusted. Adjusting the amount of the dosing composition in the wet air scrubber can involve altering the frequency, duration, and/or rate of dosing composition addition from the dosing pump. In some embodiments, adjusting the amount of the dosing composition in the wet air scrubber can include adding dosing composition to the wet air scrubber. In some embodiments, adjusting the amount of the dosing composition in the wet air scrubber may further comprise adjusting a rate of addition of the dosing composition. In some embodiments, adjusting the rate of addition can include increasing the rate of addition. In some embodiments, adjusting the rate of addition can include decreasing the rate of addition. Suitably, the amount of the dosing composition is adjusted when the difference between the concentration of the tracer measured in the wet air scrubber and the target tracer concentration is at least 1% or more of the target tracer concentration (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 125%, 150%, 175%, 200%, 300%, 400%, or 500% or more).

[0025] The examples that follow exemplify certain illustrative aspects and embodiments of the disclosure and are not limiting to the scope of the disclosure or the appended claims. EXAMPLES

Example 1: Determining the concentration of ReNew A in a wet air scrubber

[0026] A water sample is drawn from the wet air scrubber. If the scrubber water is highly turbid, an aliquot can be filtered through a 0.45μηι filter sufficient to fill a Hach test cuvette to the 25 mL mark. A second, matched cuvette is filled with a sample of the scrubber water. The second sample will serve as the blank to "zero" the spectrophotometer. The contents of a Hach triazole foil pillow (product # 2141299; Hach Company, Loveland, Colorado), which upon exposure to UV light will catalyze the triazole to form a colored complex via photolysis, are added to both cuvettes. A UV pen (product # 2082800; Hach Company, Loveland, Colorado) is inserted into the test cuvette and the UV pen is turned to the "On" position for about 5 minutes to perform photolysis within the test sample. At the end of 5 minutes, the UV pen is turned off and the spectrophotometer is zeroed with the blank cuvette, which has not undergone photolysis by application of UV light. Thereafter, the test cuvette is placed in the spectrophotometer and the absorbance is obtained or, if the spectrophotometer has been programmed to read in ppm, the concentration of the test sample is obtained. If a Hach DR/890 spectrophotometer is used, Program 3 is used to time the duration of UV light exposure and to convert absorbance to ppm of tolyltriazole. The method described above supports that detecting methods can be used to determine a desired target tracer

concentration, a correlation between the tracer concentration and the treatment agent, or the concentration of the tracer in the wet air scrubber during operation.