A system for removing h2s and co2 from biogas

Abstract

The present disclosure generally relates to a processing system for methane gas mixtures from wellbore operations, anaerobic digesters, etc, and more particularly to the use of adsorbent material within a system to reduce the concentrations of H2S and CO2 in the gas mixture. The system has regeneration capabilities to allow the adsorbent material to be used repeatedly. The system consists of one or more vessels containing adsorbent materials. The vessels are connected to the gas supply and processed gas outlet using isolation valves. The vessels are connected to one or more blowers that can be used to blow air through the vessels to regenerate the adsorbent material. The gas from regeneration exits the vessel through a separate path than that for the processed gas. The regeneration inlet and outlet also have isolation valves. The isolation valves are operated so the vessel can be used to process or to be regenerated.

Description

[0001]A SYSTEM FOR REMOVING H2S AND CO2 FROM BIOGAS. TECHNICAL FIELD generally relates to a processing system for methane gas operations, anaerobic digesters, etc., and more particularly to the use of adsorbent material within a system to reduce the concentrations of H2S and CO2 in the gas mixture. The system has regeneration capabilities to allow the adsorbent material to be used repeatedly. BACKGROUND fuel are numerous and widely available and include well-heads and sources from oil and gas operations, and anaerobic digestion or other processing of food, animal, human, and other waste. One issue is that in many of these sources the methane is mixed with CO2, H2S, and other gases. CO2 is non-flammable and decreases the heating value of the gas by diluting the methane. H2S is highly corrosive and toxic. The presence of these gases complicates the capture, storage, transportation, and utilization of the fuel. By reducing the concentration of these unwanted gases, the value of the methane fuel is maximized, and the challenges of its utilization are reduced. Furthermore, methane fuel that is utilized is kept from venting to the environment. Methane is a potent greenhouse gas. Various methods have been introduced to process wellhead, biogas, and other methane sources having various efficiencies, optimal scales of operation, and cost structures including absorption, adsorption, scrubbing, biological filters, and so forth. Each method has its strengths and weaknesses depending on the overall process including final disposition of the fuel, scale of the operation, and resources available, but all are expensive at small treatment scales associated with most potential applications. The invention at hand is a system for processing biogas, wellhead gas, or other methane sources to remove unwanted constituents and maximize the utility and value of the gas. It is particularly suited for implementation where startup costs and operating costs need to be minimized. This it does by utilizing low-cost readily available equipment and materials, and the materials can be regenerated and reused. This method’s use of regeneration to reuse the adsorbent material compares favorably with an existing process that uses chemically coated adsorbent materials such as activated carbon that are available in the marketplace. The coating captures and retains H2S chemically but renders the adsorbent material good for single use only. After the coated material is saturated, it must be disposed of and replaced with fresh material, adding cost and complexity. In the present invention the adsorbent material is regenerated and reused. Summary The system consists of one or more processing vessels. Each vessel is filled with an adsorbent material of suitable performance also taking cost into account. Types of adsorbent material include activated carbon, zeolite, metal-organic framework (MAF). This material adsorbs CO2 and H2S from the methane ladened gas to be processed. One embodiment uses adsorbent material in powder form to maximize the adsorbent surface area per volume of material and uses Cenergy Solutions’ patented filter system. This filter system is incorporated inside the vessel ports and allows gas to flow out of the vessel without allowing adsorbent material to exit with the gas. The vessel has openings on opposite sides such that the flow of gas to be processed can be passed through the adsorbent material. When the adsorbent material becomes saturated or preempting this point in time to ensure full processing, the adsorbent material is regenerated by isolating the vessel from the methane gas to be processed, and then passing air through the adsorbent material to carry away the adsorbed CO2and H2S and restore its capacity to adsorb these gasses. The passing of air through the adsorbent material is done using a blower with the air entering one end of the vessel and leaving at the other end, having passed through the activated material. This may be done using the same penetrations used to pass the methane laden gas through the vessel or using additional penetrations. In either case, the flow passages for the methane laden gas and regenerating air flow are opened and closed as appropriate using valves. Check valves may be used in place of valves where there is sufficient pressure to open the check valves only under conditions in which they are desired to be opened, and otherwise remain closed. A vessel receives the gas to be processed after free water is removed by some existing and well-known process such as cooling the gas and condensing water out of the gas. The invented process however is robust to small amounts of water as it can retain some water and expel it during regeneration cycles. More than one vessel may be used such that one vessel may be regenerated while another is processing gas. This requires control valves and piping such that one vessel can be taken offline from processing and regenerated while another vessel is processing. As described previously, valves to allow or stop the gas flow or regeneration flow may be replaced with check valves so long as they are configured to open when appropriate and not allow leakage or reverse flow. For example, a valve placed to keep process gas from venting through the air blower may be replaced with a check valve so long as the process gas is at higher pressure than ambient air pressure such that the check valve remains closed methane laden gas cannot escape. However, when the air blower is turned on, the check valve should open and allow the air from the blower to regenerate the vessel when appropriate. Valves and the blower to push air through the vessel for regeneration may be manually controlled or automated. Automated valves may be operated by timers or may be controlled in a more complicated though more optimal manner as warranted by need and cost. For example, a control system may feature sensors that measure the concentration of CO2, or H2S. Such a sensor or sensors may detect when the level of the unwanted gas making its way out the treated gas outlet rises above some threshold, at which time a control system would command the valves to actuate to take that vessel offline from a treating perspective and commence to regenerate. A sensor or sensors may be positioned to measure gas levels at the regeneration outlet. When the level of a gas or gases at the regeneration outlet drop below some threshold, the control system would take the regeneration step to be completed. The regeneration procedure requires the raw gas inlet and processed gas outlet to be closed. The valves for the regeneration air inlet and regeneration outlet are to be opened and a blower or blowers are turned on to push air through the system to regenerate. For each vessel, the processing valve lineup is opposite the regeneration valve lineup and the blower is off. Those skilled in the art will be able to identify many variations for controlling one or more vessels for processing. Once regeneration is complete, the vessel is ready to process more gas for a period of time. However, after regeneration the vessel is filled with air from the regeneration process. If nothing is done, resumption of gas processing flow will initially expel air until the air is displaced and methane flows. One can configure the system to flow untreated gas into the system and have a valve open to let the air to be displaced by the gas and escape, at which point that outlet would be closed and the treated gas outlet would be opened. By using more than one tank and appropriately actuating the right valve sequence manually or automated, one can maintain a supply of treated gas only to the treated gas outlet. The control system may also be configured with a human-machine-interface (HMI) to display system status, logging capability to record performance, and communication capability to allow remote monitoring and operation, and troubleshooting. The regeneration outlet will contain CO2, H2S, and / or other gases removed by processing. These gases need to be vented in a safe manner or otherwise processed (particularly in converting H2S to a non-toxic form). We propose running the gas through an ammonia solution to remove H2S. Coupled with the oxygen in the air of that flow, the H2S may be reduced to a safe form. The gas from regeneration may also be flared. Each vessel is sized to give ample run time while minimizing upfront cost. The larger the vessel, the longer the system can process gas before needing to be regenerated. As presently implemented, there is no significant pressure swing, so the vessel material and design need to be sufficient to support itself with the activated carbon inside. BRIEF DESCRIPTION OF THE DRAWINGS Illustrative examples of the present disclosure are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein, and wherein FIG.1 is a schematic illustrating a single system for processing methane gas that is mixed with CO2, H2S, and other gases. FIG.2 is a schematic illustrating another embodiment of a single system for processing methane gas that is mixed with CO2, H2S, and other gases. FIG.3 is a schematic illustrating two systems configured such that one system may be regenerated while the other system is processing gas. DETAILED DESCRIPTION The present disclosure generally relates to a processing system for methane gas mixtures from wellbore operations, anaerobic digesters, etc., and more particularly to the use of adsorbent material within a system to reduce the concentrations of H2S and CO2 in the gas mixture. The system has regeneration capabilities to allow the adsorbent material to be used repeatedly. In the following detailed description of several illustrative examples, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, examples that may be practiced. These examples are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other examples may be utilized, and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the disclosed examples. To avoid detail not necessary to enable those skilled in the art to practice the examples described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the illustrative examples is defined only by the appended claims. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the examples of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. It should be noted that when "about" is at the beginning of a numerical list, "about" modifies each number of the numerical list. Further, in some numerical listings of ranges some lower limits listed may be greater than some upper limits listed. One skilled in the art will recognize that the selected subset will require the selection of an upper limit in excess of the selected lower limit. Unless otherwise specified, any use of any form of the terms "connect," "engage," "couple," "attach," or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. Further, any use of any form of the terms "connect," "engage," "couple," "attach," or any other term describing an interaction between elements includes items integrally formed together without the aid of extraneous fasteners or joining devices. In the following discussion and in the claims, the terms "including" and "comprising" are used in an open- ended fashion, and thus should be interpreted to mean "including, but not limited to." Unless otherwise indicated, as used throughout this document, "or" does not require mutual exclusivity. The embodiments described herein relate to the use of an adsorbent, vessel, and manifold system for processing methane rich gas mixtures that also contain CO2, H2S, and other gases. The purpose of the invention is to remove CO2 and H2S and increase the percentage of methane in the gas mixture. During processing, the gas to be processed is passed through adsorbent material contained within the vessel. The adsorbent material may be an activated carbon, a zeolite, a metal organic framework, or a combination thereof. As the gas flows through the adsorbent material, the CO2and H2S is preferentially adsorbed and the processed gas with reduced CO2and H2S concentrations flows from the vessel. At some point the adsorbent material will become saturated and its efficacy will be reduced. At or before this time, the adsorbent material is regenerated by blowing air through the vessel through the adsorbent material. This is done through an alternate flow path–the flow path for the gas to be processed is isolated or closed off, and the flow path for regeneration is opened such that the gasses are not mixed other than commingling that occurs inside the vessel. Vessel / piping / valve arrangements to perform these functions are represented in the figures below. FIG.1 is a depiction of a single processing system consisting of one vessel 1 for processing. Vessel 1 is filled with adsorbent material 2 and is configured with openings 4 and 6 on opposite ends of the vessel 1. Each of these openings 4 and 6 has attached fittings and piping 3 and 5 that serve as conduits between the openings 4 and 6 and isolation valves 11, 12, 13, and 14. These isolation valves 11, 12, 13, and 14 allow or disallow flow process flow of the natural gas mixture and regeneration air flow. For example, let opening 8 be the inlet for the natural gas mixture to be processed by the system and opening 7 be the outlet for the natural gas mixture. Furthermore, let opening 10 be the inlet for regeneration air flow and opening 9 be the outlet for regeneration flow. With process connections made as described, the system can process the methane gas mixture when valves 11 and 13 are open and valves 12 and 14 are closed. When the adsorbent material 2 requires regeneration, valves 11 and 13 are closed to isolate the process gas inlet and outlet, and valves 12 and 14 are opened to allow air to be blown through the adsorbent material 2. Those skilled in the art will know that the configuration of the connections 7, 8, 9, and 10 can be set up in various ways so long as the process flow and regeneration flow pass through the adsorbent material 2. Those skilled in the art will also see that one or more of the valves 11,12, 13, and 14 could be replaced with check valves if the pressures experienced during operation are such that a check valve would open if and only if it should be opened. For example, at the regeneration inlet 10 a blower supplying the air would increase the pressure upstream of where the valve 14 is, such that one could use a check valve instead. The check valve would automatically open when the blower is turned on. So long as the pressure inside the vessel 1 is greater than atmospheric pressure, the check valve would not open when it is supposed to be closed. FIG.2 is an embodiment similar to that of figure one, however the vessel 1 with adsorbent material 2 has four penetrations 3, 4, 5, and 6 each with its own piping and fittings connecting to the four valves 11, 12, 13, and 14. FIG.3 is an embodiment of how two vessels 1 and 2 each filled with adsorbent material 3 and 4 may be set up so that one system can process gas while the other may regenerate. This or a functionally equivalent configuration allows continuous gas processing. Let opening 20 be where the methane gas mixture enters the system. The piping 16 transports the gas to valves 10 and 12. When valve 10 is open, gas to be processed can enter vessel 1. When valve 12 is open, gas to be processed can enter vessel 2. Let opening 18 be where the processed methane gas is to exit the system. The piping 14 transports the gas from vessel 1 and / or vessel 2 when valve 6 or valve 8 are open, respectively. By opening valves 6 and 10, vessel 1 may process gas, and valves 5 and 9 should be closed. Likewise opening valves 8 and 12 allow vessel 2 to process gas, and valves 7 and 11 should be closed. As depicted, the fan 19, when on, supplies air to piping 15. When the fan 19 is on and valve 9 is open, air for regeneration is supplied to vessel 1. During regeneration of vessel 1, valve 5 should be open to let the regen gas enter piping 13 and exit the system at opening 17. Likewise, when the fan 19 is on and valve 11 is open, air for regeneration is supplied to vessel 2. During regeneration of vessel 2, valve 7 should be open to allow gas to enter piping 13 and exit the system at opening 17. Valves associated with regeneration and valves with processing for a given vessel should not be open at the same time, otherwise flow will be mis-directed. For example, if the valves are not in the correct state, regen gas may go where processed gas should go, or vice versa. It should be clearly understood that the embodiments referenced above are merely a general application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner by the figures presented. Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1.

1. A gas system comprising: a. a container configured to contain an adsorbent material, b. A quantity of adsorbent material stored inside said container; c. Flow passages such that the gas to be processed can be directed to flow substantially through the adsorbent material within the container. d. Flow passages such that a second gas, air, can be directed to flow substantially through the adsorbent material within the container.

2. The invention of claim 1 wherein valves are deployed at the first gas inlet and outlet such that the flow of the first gas can be allowed or stopped.

3. The invention of claim 2 wherein valves are deployed at the second gas inlet and outlet such that the flow of the second gas can be allowed or stopped.

4. The invention of claim 3 wherein the flow of the second gas is motivated to flow through the container and the adsorbent material by a fan or blower.

5. The invention of claim 4 where the valves are deployed such that a. The first gas to be processed flows though the container and adsorbent material therein from the first fluid inlet to the first fluid outlet while the valves controlling the flow of the second gas, air, are closed and the fan or blower is off, this is the processing mode. b. The second gas, air, flows through the container motivated by the fan or blower being on, from the second fluid inlet to the second fluid outlet while the valves controlling the flow of the first gas to be processed are closed, isolating the process gas from the regeneration air, this is the regeneration mode. c. All valves and the fan or blower are off. This is the offline mode.

6. The invention of claim 5 where check valves are used in place of one or more valves valve locations where check valves may be used in place of valves without loss of proper function.

Images