Patent Application
20230113433
Hydrogen sulfide (H2S) is a colorless, flammable gas that can be toxic if inhaled. The sulfur-like odor is easily recognized at lower concentration, but higher concentrations result in olfactory insensitivity. The United States Occupational Safety and Health Administration establishes worker exposure limits on the permissible amount of hydrogen sulfide, often measured in parts per million, ppm. The peak limit is 50 ppm (for up to 10 minutes) and the limit for an 8-hour shift is 10 ppm. Hydrogen sulfide is typically produced from microbial breakdown of organic matter and may be found in biogas extracted from landfills. Hydrogen sulfide may also be found in anerobic digesters which process manure from farms. The liquid sludge in the digesters is treated to remove pollutant from the mixed phase material, and the resulting biogas may be sold as fuel, while the treated manure solids are used in the fields. While biogas may be an environmentally sound approach for generation of methane, hydrogen sulfide must be removed from the biogas prior to its sale and use.
The present embodiments include an adsorbent composition to capture hydrogen sulfide from a contaminated medium. For contaminated biogas, hydrogen sulfide may be extracted to produce clean fuel and to prevent the escape of hydrogen sulfide into the atmosphere where it acts as a greenhouse gas. The adsorbent composition disclosed herein is cost effective at removing pollutants including hydrogen sulfide from gas, liquid, or sludge, on the same pollutant removed per gram of adsorbent basis. Additionally, the capture of pollutants is chemical so that the spent adsorbent composition does not require further treatments for disposal.
In some embodiments, an adsorbent composition for capturing pollutants includes a porous composition that includes a plurality of ferric oxyhydroxide particles and an additional component in the porous composition. The additional component includes one of copper chloride (CuCl2), zinc chloride (ZnCl2), polyvinylpolypyrrolidone, silicon carbide, silicon dioxide, activated carbon or other carbonaceous material, and a combination thereof.
In some embodiments, an apparatus for capturing pollutants in a gaseous stream includes a housing with an inlet and an outlet, and the adsorbent composition disposed in the housing, such that the gaseous stream is in contact with the adsorbent composition as the gaseous stream flows from the inlet to the outlet.
In some embodiments, an apparatus for capturing pollutants in contaminated liquid includes a chamber with an inlet that receives the contaminated liquid into the chamber, an agitator located inside the chamber, operable to agitate the contaminated liquid, and the adsorbent composition disposed in the chamber, such that the contaminated liquid is in contact with the adsorbent composition.
In some embodiments, a process of capturing hydrogen sulfide in a contaminated feed stream includes providing the contaminated feed stream that includes hydrogen sulfide to an inlet of an adsorption apparatus containing a porous composition comprising ferric oxyhydroxide particles. The process also includes providing optimal contact between the porous composition and the contaminated feed stream to produce treated feed stream. The process also includes allowing the treated feed stream to exit through an outlet of the adsorption apparatus.
In some embodiments, a process of capturing hydrogen sulfide in contaminated liquid includes treating the contaminated liquid that includes hydrogen sulfide using the adsorbent composition comprising ferric oxyhydroxide particles added to the liquid and allowing adsorption to take place between hydrogen sulfide in the liquid and the adsorbent composition. The treated liquid is then extracted from the mixture.
In some embodiments, a process of capturing hydrogen sulfide in sludge contained in an anaerobic digester includes treating the sludge that includes hydrogen sulfide using the adsorbent composition comprising ferric oxyhydroxide particles added to the sludge in the digester with agitation and allowing adsorption to take place between hydrogen sulfide in the sludge and the adsorbent composition. The treated sludge may then be spread into fields, and the generated biogas may be captured for fuel.
The present embodiments include an adsorbent to capture contaminants including hydrogen sulfide (H2S) from various forms of contaminated media. The adsorbent, when in contact with contaminated media, captures contaminants including at least one of H2S, ammonia, and volatile compounds. The absorbent composition is in a solid form, such as a porous composition, that includes ferric oxyhydroxide with at least one additional component. Goethite or a-ferric oxyhydroxide (α-FeOOH) may be used as ferric oxyhydroxide. The additional component may include one or more from a group that includes copper chloride (CuCl2), zinc chloride (ZnCl2), polyvinylpolypyrrolidone, silicon carbide, silicon dioxide, activated carbon or other carbonaceous material, and combination thereof. The selection of an additional component is based on the usage. For example, when used in a gaseous stream, the additional component is selected to optimize the flow rate of the gaseous stream. The adsorbent composition may also include iron sulfide. In a usage scenario, the adsorbent may be used as a flow-through medium in contact with the contaminated media.
In certain embodiments, a nominal diameter of ferric oxyhydroxide particles in the adsorbent composition are between 0.1 mm and 5 mm. In certain embodiments, ferric oxyhydroxide particles in the composition have surface area between 20 and 1000 m2/g. Ferric oxyhydroxide particles may make up between 50% and 75% of the total volume of the composition. Additional components may fill between 25% and 50% of the total volume of the composition.
Capturing the contaminants from a medium, such as biogas, may prevent the escape of pollutants including H2S into the atmosphere where the pollutants act as a greenhouse gas. The adsorbent disclosed herein is cost effective at removing the pollutant from gas, liquid, or sludge, on the same pollutant removed per gram of adsorbent basis. Advantageously, the capture of pollutants is chemical so that the spent adsorbent does not require a further treatment for disposal.
The adsorbent may be contained in a replaceable cartridge, such that a spent adsorbent may be replaced easily. The cartridge may be of any shape to accommodate the existing infrastructure. The adsorbent may be placed in a flow-through medium, such as in a gaseous stream or mixed in when, for example, used to remove pollutant in liquid. The present disclosure includes two example usage of the adsorbent to capture pollutants. The first example captures H2S from a gaseous stream, and the second example captures H2S from a sludge in anaerobic digester. As the adsorbent is a versatile porous composition that may be used in a replaceable cartridge or without an enclosure, the usage is not limited to the examples presented.
In the first example, gaseous streams that contain impurities such as H2S are passed through the adsorbent composite. The contact time between the adsorbent and the gaseous stream is controlled by the flow rate of the gaseous stream and the back pressure resulting from the (controllable) volume of adsorbent that may be in a cartridge. The contact time is adjusted to be sufficient to remove pollutants to an acceptable range. In the case of hydrogen sulfide, the contact time removes all but trace amounts from a stream that typically contains 0.01% to 1% of the target. The gaseous stream to be treated may arise from any source, but of particular interest is landfill biogas. Since the adsorbent removes other unwanted chemicals including ammonia and volatile organic compounds, the resulting biogas may be suitable for use as “clean” fuel.
In certain embodiments, flow control valve 222 controls the flow of untreated gas stream 232 to optimize the contact time between the gas stream and composition 216. Flow controlled untreated gas stream 234 flows into the adsorption cartridge 210 through the inlet 212. Flow controlled untreated gas stream 234 makes contact with the adsorbent composition 216 in cartridge 210. Pollutants including hydrogen sulfide in the gas stream are captured by composition 216 by adsorption process. Treated gas stream 236 with pollutants removed exits the cartridge through outlet 214. Monitoring unit 224 monitors at least the flow rate and the composition of treated gas stream 236. The monitored parameters may be used for controlling the flow control valve 222 to optimize the flow rate.
Typically, untreated biogas stream may contain between 1 and 100 ppm of hydrogen sulfide. In certain embodiments, when the flow rate of the gas stream through the gas treatment system 200 is configured such that gas pressure of 1 to 10 pounds per square inch gauge and the flow rate of 1 to 3 standard cubic feet per hour are maintained, gas treatment system 200 removes between 5 and 290 mmol of hydrogen sulfide per gram of adsorbent composition 216. Other pollutants that may be removed or significantly reduced include ammonia and volatile organic compounds, such that treated gas stream 236 may be used or sold as clean fuel.
In certain embodiments, gas treatment system 200 further includes additional piping, fittings, and valves for easy replacement of a spent cartridge. A spent cartridge 210 may be replaced, and the spent adsorbent composition 216 without further treatment may be safely discarded.
In another example usage of the adsorbent composition, H2S is also found in anaerobic digesters that process manure from farms. In anaerobic digesters, liquid sludge is treated to remove pollutants from the mixed phase material, and in the process, biogas may be generated. After the digester, while the treated manure solids may be used in the fields, the biogas may further be treated for removal of any remaining pollutants including H2S.
In an example use scenario of the anaerobic digester 300, sludge 302 that includes pollutants is entered into the digester 300 via the inlet 312. Inside the digester 300, the sludge 302 is mixed with adsorbent composition 316, where the composition 316 acts as a fining agent to bind with pollutants including H2S. To help with the mixing process, the mixture may be stirred or vibrated by agitator 318. The agitator 318 may be a mechanical stirrer or an agitator jet that move the mixture by gas flow. The sludge may have a few thousand ppm of H2S, and the added amount of the adsorbent composition 316 increases to compensate for the expected concentration. The treated sludge is removed from the digester via the outlet 314. The spent adsorbent composition 316 may be replaced, or if the composition is enclosed in a cartridge, the cartridge may be replaced after each usage.
The step 410 includes providing a contaminated feed stream that includes hydrogen sulfide to an inlet of an adsorption apparatus containing a porous composition comprising ferric oxyhydroxide particles. The contaminated feed stream may be an untreated gaseous stream containing, in part, pollutants including hydrogen sulfide. In some embodiments, the feed stream is a part of biogas treatment system for a landfill. For example, gas treatment system 200 utilizing one or more adsorption cartridge may be a part of a biogas treatment system. Untreated biogas stream, which may contain pollutants including hydrogen sulfide in concentration of 1 to 100 ppm, enters the gas treatment system 200 through the inlet 212 of the adsorption cartridge 210 to be treated for pollutants.
In another example of step 410, the anaerobic digester 300 is fed a contaminated feed stream that is mostly sludge 302 via the inlet 312. The anaerobic digester 300 includes inside the adsorbent composition 316 comprising ferric oxyhydroxide particles. As the sludge 302 is expected to have a higher concentration of H2S in the range of a few thousand ppm as compared to biogas in the example above, the amount of added adsorbent composition 316 is increased proportionally.
The step 420 includes providing optimal contact between the porous composition and the contaminated feed stream. The step 420 may include a step 422 for inline gaseous stream treatment or a step 424 for liquid or sludge treatment. The steps 422 and 424 may also be used in combination as well. The step 422 includes controlling a flow of the feed stream, such that a uniform contact time between the feed stream and the porous composition is maintained. In an example of step 422, the flow control valve 222 of
The step 424 includes agitating the mixture of the contaminated feed stream and the porous composition. In an example of step 424, the sludge 302 in mixture with the adsorbent composition 316 is agitated using the agitator 318. The agitation may include stirring or vibrating the mixture. An agitation jet may also be used to provide forced gas to provide agitation to the mixture. The agitation results in optimizing the contact time between the sludge 302 and the adsorbent composition 316.
The step 420 in both examples provides sufficient contact time, controlled by the flow control valve 222 in step 422 and by the agitation of the sludge mixture in step 424, to allow for optimal adsorption process to take place. In an embodiment, adsorption process allows, in each example, for each gram of adsorbent compositions 216 and 316 to remove 5 to 290 mmol of hydrogen sulfide from a contaminated medium (e.g., the gas stream or sludge) that contains 1 to 1000 ppm of hydrogen sulfide.
The step 430 includes allowing the feed stream to exit through the outlet of the adsorption apparatus. The exiting treated stream contains significantly less or no amount of pollutants including ammonia, volatile organic compounds, and hydrogen sulfide. The treated gas stream may be used or sold as “clean” fuel.
The steps in the process 400 may be repeated to achieve a desired level of pollutants. Additionally, the process 400 in some implementations may include additional steps, fewer steps, different steps, or differently arranged steps than those depicted in
Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.
This application claims the benefit of priority from U.S. Provisional Application No. 63/253,987 filed Oct. 8, 2021, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63253987 | Oct 2021 | US |
