Patent Publication Number: US-8110028-B2

Title: Regenerable purification system for removal of siloxanes and volatile organic carbons

Description:
RELATED APPLICATION 
     This is a divisional patent application based on a prior utility patent application Ser. No. 11/233,479, filed Sep. 21, 2005 now U.S. Pat. No. 7,410,524. This application is based on a prior copending provisional application, Ser. No. 60/611,276, filed on Sep. 21, 2004, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §119(e). This application is further a continuation-in-part application of patent application Ser. No. 11/079,459, filed Mar. 8, 2005 now U.S. Pat. No. 7,393,381, which is based on a prior copending provisional application Ser. No. 60/550,343, filed on Mar. 8, 2004, the benefits of the filing dates of which are 10 hereby claimed under 35 U.S.C. §119(e) and 120. This application is also a continuation-in-part application of patent application Ser. No. 10/871,920, filed Jun. 18, 2004 now U.S. Pat. No. 7,264,648, which is based on a prior copending provisional application, No. 60/479,592, filed on Jun. 19, 2003, the benefits of the filing dates of which are hereby claimed under 35 U.S.C. §119(e) and 120. 
    
    
     BACKGROUND OF RELATED APPLICATION 
     As energy prices continue to rise, alternative energy sources become increasingly important. In particular, the use of waste methane (from renewable sources, such as municipal digesters and landfills) as a fuel is becoming increasingly widespread. Recent incentives offered by State and Federal Governments have led to the installation of more and more digester and landfill biogas power generation projects. As many developers of such projects have found, biogas is similar to crude oil in that it must be “refined” in order to use biogas as a reliable fuel. Biogas frequently contains high levels of moisture, high levels of hydrogen sulfide, and moderately high levels of halogenated contaminants. Most often, biogas also contains significant levels of organosilicons (siloxanes in particular), which are common additives to personal care products such as shaving cream, lipstick, hand cream, deodorants and hair styling products. Combustion of organosilicons forms silicon dioxide and other silicas or silicates. Silicon dioxide is the main ingredient in sand, and such silicates can damage power generation equipment. Because of the damage inflicted by silicates, it is desirable to remove organosilicons (a source of such silicates) from biogas, to prevent such damage and prolong the life and reliability of power generation equipment. Organosilicon levels above 50 parts per billion by volume (ppbv) in 5 biogas used as a fuel can cause severe damage to power generation equipment such as micro-turbines and turbines. Organosilicon levels above 100 ppbv in biogas used as a fuel can cause premature wear and damage to internal combustion engines used as generators. 
     While removal of organosilicons from biogas used as a fuel is clearly desirable, unfortunately such removal has proved to be quite challenging accomplish economically. Moreover, removal of all the organosilicons in a particular biogas is difficult, due to the wide variety of different organosilicons present in many biogas streams. Different varieties of organosilicons exhibit different molecular weights and different volatilities, complicating any removal strategy. Conventional removal methods employing activated carbon, silica gel and cold chilling lack either the ability to completely remove all of the various types of organosilicons present in a biogas stream, or are too costly. It would therefore be desirable to provide an economical technique for removing different varieties of organosilicons from biogas streams. 
     Non-regenerable systems, most often utilizing activated carbon or silica gel in “fixed” or stationary media beds, can only partially remove organosilicons from biogas, and even then such systems are operational only for relatively brief periods of time before requiring the media to be replaced. Activated carbon and silica gel are both negatively affected by moisture in the gas, significantly reducing their capability to remove organosilicons and almost completely eliminating their ability to remove halogenated chemical species. Moreover, highly contaminated biogases, such as those with volatile organic carbon (VOC) burdens above 400 parts per million by volume (ppmv) can cause a rapid heating of both activated carbon and silica gel media, thereby creating a dangerous condition that can lead to ignition of the organic materials picked up by the media. Non-regenerable biogas treatment systems also generate spent media, a waste product that requires replacement and disposal, generating additional expenses. Regenerable systems employing activated carbon or silica gel, with a classical stationary “deep bed” approach (i.e., including a bed of media several feet in depth), are unwieldy to operate due to heating and cooling cycle times associated with the regeneration of the media. They are also costly to operate, due to their relatively high energy consumption. In addition, such systems generally exhibit a relatively poor removal efficiency for organosilicons and halogenated organics. Regeneration of the adsorbent media also produces a waste stream, generally a foul smelling liquid organic/water waste stream that must be disposed of at an additional cost. Disposal 5 of such wastes further carries inherent risks of future liability if the ultimate disposal site requires cleanup. Moreover, both regenerable and non-regenerable systems employing activated carbon or silica gel in deep bed vessels require a significant amount of space, which may not be readily available. It would therefore be desirable to provide a regenerable system having a relatively small footprint, and which is capable of removing a large number of different organosilicons and VOCs, thereby minimizing any waste stream. 
     Another biogas treatment technique is cold chilling, which is based on the principle of lowering the temperature of the biogas to a temperature below the condensation point of the organosilicons and halogenated chemical species contained in the biogas. Such systems generally require a refrigeration unit capable of operating to as low as −20 degrees F, to effectively chill the biogas to −9 degrees F. Although these systems can remove many organosilicons and halogenated VOCs, they are ineffective on contaminants exhibiting very low boiling points and high vapor pressures. Because these systems operate below the freezing point of water, ice forms in the heat exchangers and the heat exchangers must periodically be thawed out. For this reason, duplicate systems must be installed to provide for continuous operation. Energy consumption, expressed as a “parasitic load,” is the highest with this type of biogas treatment equipment. Such systems produce a large volume of water waste and volatile chemical condensate wastes that must be disposed of at an additional cost. Furthermore, cold chilling systems also require a relatively significant amount of space for installation, which is not always readily available at potential development sites. 
     More recently, fluidized media bed systems have been introduced for control of VOC emissions and solvent recovery from air. Such systems generally utilize a relatively small sized particle of adsorbent material manufactured from pyrolized petroleum coke or synthetic resins. While effective for solvent recovery and to remove VOCs from air, such systems are not particularly effective at removing organosilicons and halogenated organics from biogas. In general, systems configured to remove contaminants from air include components than cannot readily withstand the harsh chemical conditions associated with the processing of biogas. As a result, rapid corrosion and failure of key components occurs. Furthermore, the moisture present in biogas can cause the relatively small adsorbent particles in such systems to conglomerate, degrading the fluidity of the media bed, which leads to system failure. In addition, an outside fuel source must be utilized to destroy the organics once they 5 are removed from the air stream, or energy must be used to condense the removed organics so they may be re-used or disposed of as a liquid waste stream. 
     Because such air purification technology is designed for relatively low pressure or ambient (i.e., atmospheric) pressure streams, the equipment cannot withstand the higher biogas pressures required by many types of power generation equipment. Even at relatively low pressures, distortion of rectangular process equipment components occurs, resulting in gas leaks. Biogas leaks pose several problems. Since biogas is a fuel and has a commercial value, gas leaks in treatment equipment can be expensive, as well as being dangerous. Biogas is also highly odiferous, containing condensable organics referred to as “skunk oil.” Thus, it is desirable to prevent gas leakage. 
     A significant drawback of existing fluidized media bed technology is a lack of adequate automation. Most projects involving the combustion of biogas for power generation require biogas systems to be operational with less than a 5% downtime. It would therefore be desirable to develop automated systems capable of operating with minimal downtime. 
     A drawback of the biogas treatment systems discussed above is that they generally are not able to attain the high purity level required by most biogas combustion equipment. Thus, it would be desirable to provide for a nominally complete removal of organosilicons and halogenated volatile chemicals. 
     SUMMARY 
     A novel approach for removing organosilicons and halogenated chemical species from biogas using a single treatment system. Removal of organosilicons will reduce damage to power generation equipment caused by silica and silicates. Removal of halogenated chemical species will reduce damage to expensive emission catalysts. The basis for this treatment technology is a fluidized media bed reactor, configured to concentrate offending organics, coupled with another reactor vessel configured to strip the offending organics off the media with a hot inert gas. The removed organics are further concentrated into an inert gas stream that is conveyed to a small flare for greater than 99% destruction. The energy required to strip the organics from the spent media, and to energize the flare, is generated by the combustion of a small quantity of the purified biogas. Empirical studies indicate a biogas purified using such techniques contains less than 50 ppbv organosilicons and halogenated organics. And the cleaned biogas is suitable for use as a fuel in many types of power transported in industrial and commercial pipelines. 
     The primary use of the technique disclosed herein is to purify gaseous fuels, and in particular, biogas (municipal anaerobic digester gas and landfill gas). 
     A key feature of the technique and system disclosed herein is their ability to remove organosilicons and halogenated chemicals from biogas, to protect power generation and emission abatement equipment. 
     A second key feature of the technique and system disclosed herein is their ability to process a large volume of biogas in a system of relatively small size. 
     A third key feature of the technique and system disclosed herein is their ability to prevent flammable and odorous gas leakage, and to facilitate recovery and disposition of same. 
     A fourth key feature of the technique and system disclosed herein is their ability to sense and control an adsorbent media recycle rate, where media is transferred from a concentrator vessel to a regeneration vessel and back again, by the use of single rotary gas-tight valves, or dual gas-lock valves. 
     A fifth key feature of the technique and system disclosed herein is their ability to sense and control oxygen content in a concentrated, stripped VOC gas stream, to minimize a possibility of the formation of explosive conditions. 
     A sixth key feature of the technique and system disclosed herein is a logic-based control system for automating the process and system. 
     A seventh key feature of the technique and system disclosed herein is the employment of a fiber optic sensing system for measurement and control of adsorbent media levels at critical locations in the processing equipment. 
     An eighth key feature of the technique and system disclosed herein is the utilization of the biogas itself to provide the energy to strip and concentrate the biogas contaminants into a separate waste stream. 
     A ninth key feature of technique and system disclosed herein is the utilization of the biogas itself to provide energy for the destruction of the stripped biogas contaminants in a small enclosed ground flare. 
     A tenth key feature of the technique and system disclosed herein is the production of ultra-pure biogas for use in applications requiring high purity (i.e., a very low contaminant level) biogas, such as turbine-driven generators, pipelines, and fuel cells. 
     An eleventh key feature of the technique and system disclosed herein is enabling operational downtimes of less than about 5% to be achieved. 
     A twelfth key feature of the technique and system disclosed herein is the utilization of heat produced by the process to pre-condition the gas to be treated. 
     A thirteenth key feature of the technique and system disclosed herein is a low energy consumption rate, as measured by a parasitic biogas utilization rate of less than about 0.5% by volume. 
     A fourteenth key feature of the technique and system disclosed herein is enabling biogas to be processed at elevated pressures without gas leaks. 
     An exemplary process for removing organosilicon and halogenated contaminants from a gas stream to achieve a clean fuel gas disclosed herein includes the steps of passing the gas stream through a filter vessel including a filter media configured to remove organosilicon and halogenated contaminants from the gas stream, thereby producing a clean fuel gas and spent filter media, removing a portion of the spent filter media from the filter vessel, using a portion of the clean fuel gas to generate a hot inert gas, using the hot inert gas to remove contaminants from the spent filter media, thereby regenerating the filter media, returning the regenerated filter media to the filter vessel, and using a portion of the clean fuel gas to treat the contaminants removed from the spent filter media. 
     An exemplary system for removing organosilicon and halogenated contaminants from a gas stream to achieve a clean fuel gas disclosed herein includes a filter vessel including a filter media configured to remove organosilicon and halogenated contaminants from the gas stream, thereby producing a clean fuel gas and spent filter media, a regeneration vessel configured to remove contaminants from spent filter media, a filter media transfer subsystem configured to transfer spent filter media from the filter vessel to the regeneration vessel, and to transfer regenerated filter media from the regeneration vessel to the filter vessel, a hot inert gas generator configured to use a portion of the clean fuel gas to generate a hot inert gas, the hot inert gas generator being coupled in fluid communication with the filter vessel to receive the clean fuel gas, and with the regeneration vessel, to direct hot inert gas into the regeneration vessel to regenerate the spent filter media, and a flare subsystem configured to use a portion of the clean fuel gas to treat contaminants removed from the spent filter media by the hot inert gas, the flare subsystem being coupled in fluid communication with the filter vessel to receive the clean fuel gas, and with the regeneration vessel to receive the hot inert gas loaded with contaminants, removed from the regenerated filter media. 
     This Summary has been provided to introduce a few concepts in a simplified form that are further described in detail below in the Description. However, this Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DRAWINGS 
       Various aspects and attendant advantages of one or more exemplary embodiments and modifications thereto will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a flowchart which illustrates the overall sequence of steps utilized in an exemplary method to remove organosilicon and halogenated contaminants from a gas stream to achieve a clean fuel gas suitable for use in electrical power generation equipment. 
         FIG. 2  is a block diagram of an exemplary system for removing organosilicon and halogenated contaminants from a gas stream to achieve a clean fuel gas suitable for use in electrical power generation equipment. 
         FIG. 3  is a block diagram schematically illustrating a modification to the system of  FIG. 2  which enables leak proof operation to be achieved even with relatively high gas stream pressures. 
         FIG. 4  is a detailed process diagram illustrating an exemplary low pressure system based on the exemplary system of  FIG. 2 , including a fluidized media concentrator, a fluidized media regenerator, a pneumatic media transfer component including two gas lock rotary valves, an inert gas generator, a heat exchanger, an enclosed ground flare, and a control system for automation. 
         FIG. 5A  schematically illustrates logical inputs for automation of the ground flare from start up to shut down. 
         FIG. 5B  schematically illustrates logical inputs for automation of the inert gas generator from start-up to shut down. 
         FIG. 5C  schematically illustrates logical inputs for process automation from start-up to shut down. 
         FIG. 6  schematically illustrates an exemplary panel cover with inputs from the various process components. 
     
    
    
     DESCRIPTION 
     Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended that the embodiments and Figures disclosed herein are to be considered illustrative rather than restrictive. 
     Overview of the Disclosure Provided Herein 
     As discussed above, biogas and digester gas frequently include organosilicons and halogenated chemical species. When such gas is combusted, the organosilicons are converted to very abrasive silicates, which can cause extensive damage to electrical power generation equipment. The halogenated chemical species can poison expensive emissions catalysts. Disclosed herein are methods and systems for removing organosilicons and halogenated chemical species using a single system exhibiting a relatively small footprint and a minimal parasitic load. 
       FIG. 1  is a flowchart  110  including exemplary method steps for removing organosilicons and halogenated chemical species from a fuel gas stream (such as biogas or digester gas). In a step  112 , the dirty fuel gas is filtered to remove organosilicons and halogenated chemical species, thereby generating a clean fuel gas and spent filter media. Details of preferred filter media are provided below. In a step  114 , a portion of spent filter media is automatically transferred to a regeneration vessel. In a preferred implementation, pneumatic subsystems are used to move filter media back and forth between a filter vessel and the regeneration vessel. In a step  116 , a portion of the clean fuel gas is combusted to generate a hot inert gas (i.e., exhaust gas containing low levels of oxygen). In a step  118 , the hot inert gas is used to remove contaminants from the spent filter media. In a step  120 , a portion of the clean fuel gas is used treat the hot inert gas laden with contaminants removed from the spent filter media. In a step  122 , a portion of the regenerated filter media is returned to the filter vessel, such that additional quantities of dirty fuel gas can be treated. Significantly, this technique uses cleaned fuel gas for generating the hot inert gas and destroying the removed contaminants, achieving a method for removing organosilicons and halogenated chemical species from a fuel gas stream that has a minimal parasitic load. A controller  124  is preferably configured to automate the process. 
       FIG. 2  is a block diagram of an exemplary system  130  configured to remove organosilicons and halogenated chemical species from a fuel gas stream (such as biogas or digester gas). A biogas stream  132  (or digester gas, or some other fuel stream contaminated with organosilicons and halogenated chemical species) is 5 directed into a filter vessel  134 , which includes filter media configured to remove organosilicons and halogenated chemical species, thereby generating a clean fuel gas  136  and spent filter media. A portion of clean fuel gas  136  is preferably conveyed to power generating equipment  138 , although it should be understood that the clean fuel gas can be stored for later use, or conveyed to other types of processing equipment needing a filtered fuel gas. System  130  includes a filter media transfer subsystem  140 , configured to move filter media between filter vessel  134  and a regeneration vessel  144 . Spent filter media moves from filter vessel  134  to regeneration vessel  144  to be regenerated, while regenerated filter media is transferred from regeneration vessel  144  to filter vessel  134  for reuse. A hot inert gas generator  142  uses some of clean gas  136  to generate a hot inert gas. As will be described in greater detail below, hot inert gas generator  142  is configured to generate an exhaust gas that is sufficiently depleted of oxygen so as to reduce any chance of causing a fire or explosion in regeneration vessel  144 . The hot inert gas from hot inert gas generator  142  is passed through the spent filter media in regeneration vessel  144 , thereby stopping the contaminants from the spent filter media and regenerating the filter media. The hot inert gas laden with contaminants is then directed to a ground flare  146 , which uses some of the clean fuel gas to combust the hot inert gas and contaminants according to accepted environmental practices (greater than 99% destruction). Significantly, the energy required to strip the organic from the spent media, and to energize the flare, is generated by the combustion of a small quantity of the purified biogas. Empirical studies indicate a biogas purified using such techniques contains less than 50 ppbv organosilicons and halogenated organics, and the cleaned biogas is suitable for use as a fuel in many types of power generation equipment, including methane fuel cells. The cleaned biogas can be safely transported in industrial and commercial pipelines. A controller  148  is logically coupled to filter media transfer equipment  140 , hot inert gas generator  142 , in ground flare  146 , to facilitate automated operation of the system. Incoming dirty fuel gas streams can have widely varying pressures. 
       FIG. 3  schematically illustrates a modification of system  130  to enable the system to safely accommodate relatively high pressure dirty fuel gas streams. A pressure lock volume  154  is disposed between a filter vessel  134   a  and a regeneration vessel  144   a  (filter media transfer equipment have been eliminated from this figure to simplify the drawing, although it should be understood that such filter media transfer equipment are included). A valve  150  is configured to selectively place pressure lock 5 volume  154  in fluid communication with filter vessel  134   a . A valve  152  is configured to selectively place pressure lock volume  154  in fluid communication with regeneration vessel  144   a . Valves  150  and  152  are capable of leak proof operation even under relatively high pressures. With valve  152  closed, valve  150  is opened to transfer a portion of spent media from filter vessel  134   a  into pressure lock volume  154 . Valve  150  is then closed, and valve  152  is opened to transfer the spent filter media from pressure lock volume  154  into regeneration vessel  144   a . Pressure lock volume  154  isolates filter vessel  134   a  from regeneration vessel  144   a , such that only filter vessel  134   a  needs to be configured to operate under high pressures. A similar pressure lock volume is used to transfer regenerated filter media from regeneration vessel  144   a  back into filter vessel  134   a  for reuse. 
     Preferred Filter Media 
     The techniques and system described herein can utilize several different types of filter media. Conventional filter media include carbon based adsorbents and silica gel based adsorbents. Because the filter media will be transferred back and forth between the filter vessel and the regeneration vessel, preferred filter media will have a size and shape facilitating transfer of the filter media back and forth between the filter vessel and the regeneration vessel. Furthermore, preferable filter media will be abrasion resistant, to minimize the amount of dust or fines generated during the transfer process. Particularly preferred filter media include, but are not limited to, spherical pyrolized carbonaceous adsorbents, such as those available from the Kureha Chemical Company, spherical synthetic adsorbent resinous materials, and spherical synthetic silica and mineral based adsorbents (available from Applied Filter Technology, Inc., Snohomish Wash.). Such media are generally spherical, have diameters ranging from about 0.2 mm to about 3.5 mm, and are abrasion resistant. Additional media types that may be used include polymorphous graphite pellets (also available from Applied Filter Technology), activated carbon in pellet or granular form, silica gels, zeolites, and other adsorbent media of small particle size, nominally from about 0.5 mm to about 3 mm. These additional media types are preferably characterized by high hardness and resistance to abrasion. Such media are described in greater detail in the following copending and commonly assigned U.S. patent Applications: Ser. No. 11/079,459, entitled Removing Siloxanes from a Gas Stream Using a Mineral Based Adsorption Media, filed Mar. 8, 2005, and Ser. No. 10/871,920, entitled Removing Siloxanes from a Gas Using a Segmented 5 Filtration System Customized to the Gas Composition, filed Jun. 18, 2004, the specification and disclosure of which are hereby specifically incorporated by reference. 
     Detailed Description of an Exemplary Low-Pressure System 
       FIG. 4  illustrates the overall process components and interconnectivity for system and method disclosed herein. Referring to  FIG. 4 , there are five distinct main process operations encompassed in the present disclosure. The first of these is a process whereby the biogas contaminants are concentrated onto a regenerable media in a concentrator  4 . A second process involves a pneumatic conveyance of the media from concentrator  4  to a regenerator  16 , and back to concentrator  4 . A third process involves stripping the concentrated contaminants from the spent media in regenerator  16 . A fourth process is the production of a hot inert regenerant gas by an Inert Gas Generator  31 , for use by regenerator  16 . A fifth process is the destruction of the spent regenerant gas stream in a small enclosed ground flare  38 . In an exemplary system three Programmable Logic Controllers (PLCs) control the entire process. Ground flare  38  is controlled by a separate PLC  83 , and inert gas generator  31  (IGG  31 ) is controlled by a separate PLC  84 , each of which are interlinked to a main PLC  85 , which controls all of the system components. 
     The Concentration of Biogas Contaminants 
     Contaminated biogas from the gas source enters the Biogas Purification System through a suitably sized pipe  1 , and is conveyed first to a heat exchanger  2 , which elevates the temperature of the gas approximately 20° F. to reduce its ability to condense water vapor. This heat exchanger receives heated air from a heat jacket  46  incorporated into inert gas generator  31 , by means of a blower  48  via pipe  49  (an uncontrolled flow) and pipe  3  (a controlled flow). After the hot air is used in the heat exchanger, it is passed to the atmosphere through a vent pipe  51 . The contaminated biogas exits heat exchanger  2  and proceeds to a bottom side inlet  50  of concentrator vessel  4  (a generally cylindrical stainless steel cone bottom vessel with a dish top, able to withstand pressures above atmospheric). After entering concentrator vessel  4 , the contaminated biogas flows upward around a baffle  8  (to divert it away from a spent media flow, described in detail below), then through a series of horizontally mounted perforated trays numbering from four to eight or more ( FIG. 4  illustrates a configuration utilizing four perforated trays, although the number of trays shown is intended to be exemplary, rather than limiting). Perforated trays  7 A- 7 D  5  each support a layer of adsorbent media  6 A-D, nominally one to two inches in depth (such dimensions are intended to be exemplary, rather than limiting). The upward flow of the contaminated biogas through perforated trays  7 A- 7 D and adsorbent media layers  6 A- 6 D is at a prescribed velocity, which causes media layers  6 A- 6 D to acquire a semi-fluidized state. This state of semi-fluidization causes the media  6 A to flow horizontally toward one side of its corresponding perforated tray  7 A, where there is an opening  5 A. Once the fluidized media reaches opening  5 A at the side of perforated tray  7 A, the media is no longer fluidized, and the media falls through opening  5 A to tray  7 B, where it is re-fluidized (as indicated by media layer  6 B). Media layer  6 B similarly flows to an opening  5 B in tray  7 B. Again, once the fluidized media in tray  7 B reaches opening  5 B, the media is no longer fluidized and falls through the opening to the tray below. This process repeats through trays  7 C and  7 D (with media passing through an opening  5 C in tray  7 C to reach tray  7 D), until the filter media falls through an opening SD in tray  7 D, and flows by gravity into an internal reservoir  9 , where it is collected and stored. 
     The flow of adsorbent media with respect to the biogas flow is countercurrent. As the biogas flows upward through the perforated trays  7 A- 7 D (containing the adsorbent media), more and more contaminants are removed, and the biogas becomes cleaner and cleaner. As the filter media moves media downward through perforated trays  7 A- 7 D, the filter media becomes more and more contaminated (i.e., filter media  25  layer  6 D is more contaminated than filter media layer  6 A). As the adsorbent media picks up more and more of the contaminants from the biogas, its density increases. The treated biogas exits the concentrator vessel through an opening  30 A the top center of concentrator vessel  4  and is conveyed to power generation or combustion equipment through a pipe  30 B having the same diameter as inlet pipe  1 . 
     Adsorbent Media Transport 
     From spent media internal reservoir  9  in the bottom of concentrator vessel  4  the spent adsorbent media flows by gravity through a “Y” pipe junction  10  to the inlet of a spent media motor-driven rotary valve  11 , which prevents gas leakage from concentrator vessel  4 , and which controls the flow rate of the media. Note that rotary valves generally leak at pressure greater than about 1.5 PSI, thus the system of  FIG. 4  is intended to be used with relatively the pressures. Different valve configurations, generally discussed above with respect to  FIG. 3 , can be implemented for higher pressures. The spent media then continues to flow by gravity through a media conduit leg of “Y” pipe junction  10  to the inlet of a spent media  5  transport venturi  12 , which receives air from an pneumatic blower  78 . The internal configuration of venturi  12  and the motive air from pneumatic blower  78  substantially fluidizes the spent media, forcing the spent media to travel vertically upward through a spent media transfer pipe  13 , to a small spent media receiving vessel  14 , at which point the spent media is no longer fluidized. From small spent media receiving vessel  14  the spent media flows downward by gravity through a pipe  15 A into a top side inlet  15 B of a regenerator vessel  16 A. 
     The regenerated media (the process of regenerating the media is described in greater detail below) is returned to concentrator vessel  4  in the following manner. From a regenerated media reservoir  20 B in the bottom of the regenerator vessel  16 A, the regenerated media flows by gravity through a “Y” pipe junction  21  to the inlet of a regenerated media venturi  22 , which receives air from pneumatic blower  78 . The internal configuration of venturi  22  and the motive air from pneumatic blower  78  substantially fluidizes the regenerated media, forcing it to travel vertically upward through a regenerated media transfer pipe  23  to a small regenerated media receiving vessel  24 , where the regenerated media is no longer fluidized. A length of regenerated media transfer pipe  23  and an air flow volume from pneumatic blower  78  are configured to provide cooling to the regenerated media, so that when it arrives at regenerated media receiving vessel  14 , the regenerated media is substantially at ambient temperature. From small spent media receiving vessel  14 , the regenerated media flows downward by gravity through a pipe  26 A into a top side inlet  26 B of concentrator vessel  4 . 
     The prevention of gas leaks and odors escaping from the purification system via spent media receiving vessel  14  is accomplished by recycling part of spent media pneumatic transport air through a spent media transport air return pipe  29  and a spent media transport air return pipe “T” junction  80 . At spent media transport air return pipe “T” junction  80 , part of the spent media pneumatic transport air is conveyed to an inlet of an IGG combustion air blower  33 , through spent media air return pipe  29  to an IGG combustion air blower intake pipe  72 . Part of the spent media pneumatic transport air is conveyed to the inlet of spent media transport venturi  12 , which provides for a closed loop to prevent leakage of odors and transport air to the atmosphere. 
     The regenerated media transport air is vented into a “T” pipe  27  A, where part of it is returned through a pipe  27 B to the inlet of pneumatic blower  78 . The 5 remainder of the regenerated media transport air is conveyed through a pipe  27 C to heat jacket  46  of IGG  31 . This air is used to cool IGG  31 , and after the air absorbs heat from IGG  31 , the heated air is conveyed through a pipe  47  to an inlet of a hot air blower  48  for transport through a pipe  49  and a hot air flow control valve  81  to heat exchanger  2 , discussed above. After heat has been transferred from the heated air to the incoming biogas, the air is discharged from heat exchanger  2  to the atmosphere through vent pipe  51 . 
     Spent Adsorbent Media Regeneration 
     After entering regenerator vessel  16 A, the spent media falls onto an uppermost perforated tray  18 A, then through a series of horizontally mounted perforated trays  18 A- 18 D, numbering from four to eight or more (it should be recognized that the number of trays shown is intended to be exemplary, rather than limiting). Perforated trays  18 A- 18 D each support a layer of spent adsorbent media (i.e., layers  17 A- 17 D), nominally one to two inches in depth (such dimensions are intended to be exemplary). An upward flow of hot inert gas through perforated trays  18 A- 18 D and spent adsorbent media layers  17 A- 17 D is at a prescribed velocity, which causes spent media layers  17 A- 17 D to acquire a semi-fluidized state. This state of semi-fluidization causes spent media in layer  17 A to flow horizontally toward one side of perforated tray  18 A, where an opening  19 A is disposed. Once the media in layer  17 A reaches opening  19 A, the spent media is no longer fluidized and falls through opening  19 A to the next perforated tray (i.e., perforated tray  18 B), where it is re-fluidized in layer  17 B. The spent adsorbent media in layer  17 B then commences its flow in a direction countercurrent to the flow of media in layer  17 A on perforated tray  18 A. The spent adsorbent media in layer  17 B moves toward an opening  19 B at the side of perforated tray  18 B. When the spent adsorbent media reaches opening  19 B, it is no longer fluidized and falls through the opening to perforated tray  18 C, where it is similarly re-fluidized. This process repeats, and spent absorbent media in layer  17 C moves to an opening  19 C in perforated tray  18 C, where the spent adsorbent media falls through opening  19 C to reach perforated tray  18 D. Similarly, spent absorbent media in layer  17 D moves towards an opening  19 D in perforated tray  18 D. The spent absorbent media falls through opening  19 D and flows by gravity into internal reservoir  20 B, where it is collected and stored. The media collected and stored in the internal reservoir is now regenerated. 
     The flow of spent adsorbent media with respect to the hot inert regenerant gas flow is countercurrent. The hot inert regenerant gas enters the regenerator vessel  5  through a hot inert gas inlet  43  and flows upward around a baffle  20 A, to divert it away from the (now regenerated) media flow from opening  19 D in bottom perforated tray  18 D. As the hot inert regenerant gas flows upward through perforated trays  18 A- 18 D, containing spent absorbent media in layers  17 A- 17 D, the hot inert regenerant gas becomes more and more saturated with the contaminants, while the spent adsorbent media layers  17 A- 17 D becomes more and more purged of the contaminants, as the spent absorbent media progresses from uppermost perforated tray  18 A, downward past bottom perforated tray  18 D, and into spent media reservoir  20 B at the bottom of regenerator vessel  16 A. As the adsorbent media in layers  17 A- 17 D is increasingly purged of contaminants in its journey through regenerator vessel  16 A, its density decreases. The spent hot inert regenerant gas (now referred to as “concentrated waste gas”) exits the regenerator vessel through an opening  16 B in the top center of the regenerator vessel  16 A, and is conveyed into a concentrated waste gas outlet pipe  36 . From concentrated waste gas outlet pipe  36  the concentrated waste gas is conveyed through a pipe  37  to a small enclosed ground flare  38  for destruction. 
     Production of a Hot Regenerant Gas 
     Regenerator vessel  16 A receives hot inert gas from IGG  31 , which provides the energy to strip the contaminants from the spent adsorbent media. In order to generate the hot inert gas, IGG  31  receives purified biogas through a pipe  72 , which is mixed with air from Inert Gas Generator Combustion Air Blower  33 , and combusts this biogas/air mixture in an internal burner  31 A. Internal Burner  31 A is specially designed to effectively burn biogas that is nominally 35% methane to 75% methane. The hot, inert gas is drawn from IGG  31  by a Hot Inert Gas Fan  34 , which boosts a pressure of the hot inert gas before it enters regenerator vessel  16 A. PLC  84  is configured to maintain a temperature of nominally between about 400° F. and about 550° F., and a volumetric flow commensurate with the internal dimensions of regenerator vessel  16 A. 
     Significantly, the hot inert gas is not simply hot air, but rather a mixture of hot carbon dioxide, nitrogen, and water vapor. Preferably PLC  84  is configured to control the oxygen level of the hot inert gas generated to nominally range from about 0.5% by volume to less then about 4% by volume. If the oxygen in the hot inert gas is not properly controlled, a large volumetric flow of hot inert gas would be required to prevent potentially explosive conditions from being generated. Controlling the oxygen content in the hot inert gas reduces an amount of purified  5  biogas consumed by IGG  31 , as well as an amount of purified biogas consumed by ground flare  38 , enhancing the overall economics of the system. 
     Destruction of the Stripped Contaminants Using an Enclosed Ground Flare 
     The hot inert gas strips the contaminants from the spent adsorbent media in regenerator vessel  16 A. As noted above, the hot inert gas containing the stripped contaminants is referred to as the concentrated waste gas stream after it exits regenerator vessel  16 A through top center opening  16 B and enters concentrated waste gas stream outlet pipe  36 . From outlet pipe  36  the concentrated waste gas stream is conveyed to a side inlet on enclosed ground flare  38  through pipe  37  and into an enclosed ground flare burner  38 A, which is ignited by an enclosed ground flare burner pilot  38 A. A spark ignition is used to ignite enclosed ground flare burner pilot  38 A, which burns an admixture of air and propane. The propane gas for enclosed ground flare burner pilot  38 A is supplied from a compressed propane cylinder  39  through a motorized and automated enclosed ground flare pilot gas supply valve  74 B and the enclosed ground flare burner pilot propane pipe. 
     Simultaneously, purified biogas enters enclosed ground flare  38  through enclosed ground flare purified biogas inlet  41 A, which is fed by the enclosed ground flare burner purified biogas pipe  41 . Upstream of enclosed ground flare burner purified biogas inlet  41  A, and located on enclosed ground flare burner purified biogas pipe  41  is a flame arrestor  44 , which is preceded by a motorized automated flow control valve  69 , which is in turn preceded by a motorized automated “Open/Close” purified biogas flow valve  70 . Simultaneously with the importation of the concentrated waste gas stream and the purified biogas stream is the conveyance of combustion air into enclosed ground flare  38  by an enclosed ground flare combustion air blower  42 . Enclosed ground flare burner  38 A mixes and combusts the concentrated waste gas stream, the purified biogas, and the combustion air to effectively destroy more than 99% of the contaminants in the concentrated waste gas stream. The resulting combustion gases are vented from enclosed ground flare  38  to the atmosphere through an exhaust stack  45 . The energy required for the destruction of the contaminants is partially supplied by the concentrated waste gas stream itself and partially supplied by the purified biogas stream. This combination of two fuel sources from within the system itself yields an extremely low energy cost for destruction of the contaminants (i.e., a low parasitic load). 
     Instrumentation and Controls 
     An integral part of the Biogas Purification System described above is full 5 automation by the use of three separate but interlinked PLCs. These include PLC  83  for controlling enclosed ground flare  38 , PLC  84  for controlling IGG  31 , and PLC  85 , which interlinks the other PLCs and provides other required automation (such as control of the rotary valves responsible for transferring spent filter media to the regeneration vessel, and transferring regenerated filter media to the filter/concentrator vessel). 
     The PLCs control the startup and shutdown of the Biogas Purification System, the operation of IGG  31 , the operation of enclosed ground flare  38 , the operation of all fan and blower motors, and the operation of all motorized valves. While manual valves are utilized in the system (i.e., a concentrator media drain valve  76  and a regenerator media drain valve  75 ), the manual valves are used only if media is required to be removed from the system during a shutdown, and do not control the operation of any of the critical functions. PLCs therefore control all gas flows, gas temperatures, gas pressures, and gas oxygen levels within the entire system. 
       FIG. 5A  schematically illustrates inputs logically coupled to PLC  83 , which controls enclosed ground flare  38 . PLC  83  operates enclosed ground flare combustion air blower  42  using a signal from a sensor  67 . PLC  83  operates purified biogas flow valve  69  using a signal from a sensor  68 . PLC  83  operates purified biogas flow control valve  70  using a signal from a sensor  71 . PLC  83  operates enclosed ground flare pilot gas supply valve  74 B using a signal from a sensor  74 A. PLC  83  also monitors the temperature of the exhaust gas exiting the enclosed ground flare through a sensor  73 . The input from sensor  73  causes PLC  83  to modulate the gas flow at purified biogas flow control valve  70 , and causes PLC  83  to modulate the combustion air flow from enclosed ground flare combustion air blower  42 . Such modulation controls the temperature to range from about 1600° F. to about 1900° F., to assure a greater than 99% destruction of the contaminants in the concentrated waste gas stream is achieved. PLC  83  also monitors enclosed ground flare burner  38 A for a flame through a sensor  66 . In the absence of a flame, PLC  83  will shut down the enclosed ground flare by closing enclosed ground flare pilot gas supply valve  74 B, turning off enclosed ground flare combustion air blower  42 , and closing purified biogas control valve  69  (preferably in that order) for safety. PLC  83  will also send a signal to main biogas purification PLC  85  to divert the concentrated the concentrated waste gas stream to a bypass pipe (not shown) so that it is no longer conveyed to the enclosed ground flare. 
       FIG. 5B  schematically illustrates inputs logically coupled to PLC  84 , which controls IGG 31 . PLC  84  for IGG 31  operates all functions of the IGG through an on-board processor that conforms to NFPA standards. This on-board processor controls the purified biogas and combustion air flows to the pilot burner and main burner and compensates for fluctuating methane concentrations in purified inert gas generator combustion air blower  33 . PLC  84  accomplishes these tasks using signals from various sensors, and sending control inputs to various components, including, a hot inert gas generator outlet temperature sensor  35 , a hot inert gas fan on/off switch  63 , an ultraviolet (UV) sensor  64  for the inert gas generator burner, inert gas generator combustion air blower  65 , a valve  60  for supplying purified biogas to IGG  31 , and a motor  59  configured to actuate valve  60 . 
       FIG. 5C  schematically illustrates inputs logically coupled to Main Biogas Purification System PLC  85 , which monitors the temperature of the incoming biogas through a sensor  52 A, and the heated biogas temperature at a sensor  52 B, and controls the temperature of the incoming biogas exiting heat exchanger  2 . This is accomplished by modulating a hot air supply valve  81  using a signal from a sensor  82 . Hot air blower  48  is turned on or off using a signal from a sensor  77 , which is linked to Main Biogas Purification System PLC  85 . A rate of regenerated media flowing into concentrator vessel  4  at inlet  20 B is modulated by a rotary gas lock valve  25 , which communicates with Main Biogas Purification System PLC  85  via a sensor  53 . The rate of spent media flowing from concentrator vessel  4  is modulated by a rotary gas lock valve  11 , which communicates with Main Biogas Purification System PLC  85  via a sensor  54 . Both rotary gas lock valves are modulated by a signal that originates from high and low spent media level sensors  61  and  62 . Pneumatic blower  78  is controlled (i.e. turned on or off) using a signal from Main Purification System PLC  85  via a sensor  55 . A regenerator temperature sensor  56 , a regenerator oxygen level sensor  57 , and a concentrated waste gas pressure sensor  58  are interlinked between Main Purification System PLC  85 , IGG PLC  84 , and enclosed ground flare PLC  83 . Preferably each input linked to PLC  83  and  84  is also linked directly to PLC  85 . 
     Although the present invention has been described in connection with the preferred form of practicing it and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made to the present invention within the scope of the claims that follow. Accordingly, it is not intended 5 that the scope of the invention in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow. 
     In compliance with the statute, the invention described herein has been described in language more or less specific as to structural features. It should be understood however, that the invention is not limited to the specific features shown, since the means and construction shown is comprised only of the preferred embodiments for putting the invention into effect. The invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the amended claims, appropriately interpreted in accordance with the doctrine of equivalents.