Thermal oxidizer systems and components and uses thereof

Abstract

Systems for thermally oxidizing contaminants in air streams comprise mixing vessels; one or more regenerative thermal oxidizers (RTOs), each comprising a combustion chamber for thermally oxidizing contaminants to yield an exhaust gas stream; exhaust gas lines for conveying portions of exhaust gas streams to mixing vessels to raise the dry bulb temperature of air streams to reduce condensation; vents for venting remaining portions of exhaust gas streams; diverters for dividing exhaust gas streams; and controllers to determine the amounts to divide exhaust gas streams to raise the dry bulb temperature. Monolithic poppet valve assemblies comprising two or more poppet valves, which can be incorporated into the systems, among other applications. Methods for reducing condensation, e.g., using the systems.

Description

THERMAL OXIDIZER SYSTEMSAND COMPONENTS AND USES THEREOFBACKGROUND

[0001] Air streams in industrial processes, such as ventilation air exiting a mine shaft, often contain one or more contaminants, e.g., hydrocarbons, volatile organic compounds (VOCs), combustible inorganic compounds, or greenhouse gases (GHGs). Environmental regulations require that such contaminants be eliminated prior to venting the air streams to the atmosphere. Elimination can be performed by thermal oxidation in regenerative thermal oxidizers (RTOs), among other techniques.

[0002] Regardless how the contaminants are eliminated, doing so requires on-site operation of large and complex equipment. Such equipment has relatively high capital and operating expenses.

[0003] In the particular example of the mining industry, mine shaft ventilation air is typically at a dry bulb temperature of 50°F-70°F (10°C-21°C) and near or at 100% relative humidity. Under cold and / or windy weather conditions, such as prevail at high latitudes, during winter, or the like, ambient temperature on-site may be below the dew point of the ventilation air. As a result, water vapor in the ventilation air may condense in ductwork between the mine shaft and the equipment for elimination of contaminants, or in that equipment. Condensed water can impede air flow and / or corrode ductwork or equipment, which can inhibit operations and / or necessitate further expense for repair.

[0004] Attempts have been made to address this problem by heat tracing (the use of electrical heating elements) and / or insulating ductwork, in a bid to maintain the ventilation air at a temperature above the dew point. Heat tracing and insulation add to capital expenses. Also, heat tracing is energy intensive and thus adds greatly to operating expenses.

[0005] Other attempts to address this problem include the use of corrosion-resistant alloys and / or internal coatings, such as are known for submerged applications. These alloys and coatings add greatly to capital expenses. In addition, condensation still occurs, which maygenerate hundreds of gallons or thousands of liters of water inside the ductwork every hour. This condensation must be handled to assure adequate air flow to components of the system (flow assurance), thereby further adding to capital and operating expenses.

[0006] Also, liquid-from-air separation is known, but comes with relatively high capital expense. Further, liquid-from-air separation restricts air flow, creating a pressure drop which raises operating expenses.

[0007] There is a need in the art for relatively inexpensive systems for maintaining flow assurance in systems processing air streams, e.g., mine shaft ventilation air.

[0008] Also, in systems involving flow of large volumes of air or other gases from a source to a destination (such as, but not limited to, a heat recovery chamber in an RTO system), flow to the destination can be regulated by a poppet valve. Multi-destination systems (e. , multichamber RTO systems) often include discrete poppet chambers, one per destination (e.g., one per heat recovery chamber), with the poppet chambers supported by independent assemblies and connected in series with individual ductwork components.

[0009] This common design presents a number of challenges, from relatively large needs for labor and raw materials in manufacturing to more difficult installation, given that each independent assembly and individual ductwork component of adjacent poppet chambers requires individual fit, and thus can give rise to leak points which reduce system flow assurance, increase maintenance and operations efforts, and increase risk of system downtime.

[0010] There is a need in the art for poppet assemblies that reduce one or more of these challenges.SUMMARY

[0011] The present disclosure addresses these needs.

[0012] In certain aspects, the present disclosure provides systems that have improved flow assurance through ductwork from an air stream source (e.g., a mine shaft) to destinations, such as regenerative thermal oxidizers (RTOs). RTOs eliminate contaminants by reactionsthat are generally exothermic, meaning thermal oxidation in the combustion chambers of RTOs generates more heat than is required to maintain the combustion chambers at operating temperature. Flow assurance can be improved by raising the dry bulb temperature of air streams using portions of hot exhaust gases to reduce condensation in systems.

[0013] Rather than emit all hot exhaust gas to the atmosphere, some systems according to the present aspects of the disclosure are configured such that a portion of the exhaust gas generated by one or more RTOs is delivered to a mixing vessel. In the mixing vessel, the portion of the exhaust gas from the RTO or RTOs is mixed with an air stream, such as a ventilation air stream from a mine shaft, to raise the dry bulb temperature of the ventilation air above the dew point, thereby preventing condensation within ductwork or other components of the system.

[0014] Appropriate temperature sensors, e.g., thermocouples, can be included at various locations in the systems to monitor temperatures of various air streams, such as ventilation air before and after mixing with the portion of the exhaust gas.

[0015] The present aspects of the disclosure provide RTOs comprising an exhaust gas line in fluid communication with the mixing vessel, a diverter to divide a portion of the exhaust gas for delivery to the mixing vessel, and a controller. These RTOs are referred to herein as “type 1” RTOs. Type 1 RTOs can be used in conjunction with RTOs lacking a diverter, referred to herein as “type 2 RTOs.” Type 2 RTOs comprise a combustion chamber and a vent for emission of all their exhaust gases to the atmosphere. In some embodiments, an RTO, whether type 1 or type 2, comprises a combustion chamber and two, three, or more heat recovery chambers. The dimensions and / or volume of combustion chambers and heat recovery chambers can vary depending on the expected types and amounts of contaminants and / or the expected flow rate of process air, among other parameters.

[0016] The systems of the present aspects of the disclosure comprise one or more type 1 RTOs, optionally with one or more type 2 RTOs. Typical RTO systems comprise anywhere from four to twelve RTOs. Generally, the exhaust gas from one to three RTOs is sufficient to raise the dry bulb temperature of the ventilation air above the dew point. Hence, manysystems according to the present aspects of the disclosure comprise a combination of the two types of RTOs. Such combinations typically provide adequate dew point control from the type 1 RTOs while saving capital expenses by using less complex type 2 RTOs.

[0017] Although RTOs typically generate sufficient exhaust gas to raise the dry bulb temperature of the ventilation air above the dew point, systems according to the present aspects of the disclosure can further comprise a supplemental fuel injector (SFI), by which fuel gas is injected into the air stream.

[0018] In some embodiments, airflow to components of systems according to the present aspects of the disclosure, e.g., to heat recovery chambers of type 1 RTOs and / or type 2 RTOs, is regulated by poppet valves. Optionally, multiple (e.g., two or three) poppet valves can be deployed in a monolithic poppet valve assembly.

[0019] In other aspects, the present disclosure relates to monolithic poppet valve assemblies, comprising two or more (e.g., two or three) poppet valves, a process gas ductwork in fluid communication with the poppet valves, and an exhaust gas ductwork in fluid communication with the poppet valves. Optionally, the poppet valves are operably linked to actuators. The actuators can be configured to move the poppet valves, e.g., horizontally. Monolithic poppet valve assemblies may be simpler to incorporate into systems than individual, per-poppet valve assemblies, and may impart improved leak resistance in systems, such as RTO systems, among others.

[0020] Systems according to the present disclosure which improve flow assurance by raising the dry bulb temperature of air streams using portions of hot exhaust gases are described in herein.

[0021] Monolithic poppet valve assemblies are described herein.

[0022] Systems according to the present disclosure which improve flow assurance by raising the dry bulb temperature of air streams using portions of hot exhaust gases and which incorporate one or more monolithic poppet valve assemblies described herein, are described herein.

[0023] The present disclosure also relates to methods for reducing condensation in an air stream comprising one or more contaminants and water vapor.

[0024] Methods according to the present disclosure for reducing condensation, e.g., using the systems of the present disclosure, are described herein.BRIEF DESCRIPTION OF THE FIGURES

[0025] FIG. 1 schematically depicts an exemplary system comprising two type 1 RTOs and four type 2 RTOs. For brevity, only one type 1 RTO and one type 2 RTO are depicted in detail. Also for brevity, each depicted RTO is shown as comprising one heat recovery chamber and one combustion chamber.

[0026] FIG. 2 schematically depicts an exemplary system comprising two RTOs of any type, one of which is serviced by poppet valves each housed in individual assemblies, and one of which is serviced by poppet valves housed in a monolithic poppet valve assembly. For brevity, each depicted RTO is considered as comprising two heat recovery chambers and one combustion chamber.

[0027] FIG. 3 schematically depicts an exemplary system comprising two type 1 RTOs and four type 2 RTOs, poppet valves housed in individual assemblies, and poppet valves housed in a monolithic poppet valve assembly. For brevity, only one type 1 RTO, one type 2 RTO, one poppet valve housed in an individual assembly, and two poppet valves housed in a monolithic poppet valve assembly are depicted in detail.

[0028] FIG. 4 is a perspective conceptual view of a system comprising two type 1 RTOs and ten type 2 RTOs. The RTOs of both types are depicted as comprising two heat recovery chambers and one combustion chamber.

[0029] FIG. 5 is a perspective conceptual view of a monolithic poppet valve assembly comprising two poppet valves. A monolithic poppet valve assembly of the disclosure can contain any number of poppet valves (e.g., two, three, four, five or more poppet valves). The monolithic poppet valve assembly illustrated in FIG. 5 can be used in conjunction with a thermal oxidizer system comprising one or more RTOs, in which one RTO can be disposedsuch that each of its heat recovery chambers is above and has airflow regulated by one poppet valve.DETAILED DESCRIPTION1.1. Definitions

[0030] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. Throughout this specification and embodiments, the words “have” and “comprise,” or variations such as “has,” “having,” “comprises,” or “comprising,” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. All publications and other references mentioned herein are incorporated by reference in their entirety. Although a number of documents are cited herein, this citation does not constitute an admission that any of these documents forms part of the common general knowledge in the art.

[0031] Contaminant: As used herein, “contaminant” refers to any compound of any of the following classes when present in an air stream: hydrocarbons, volatile organic compounds (VOCs), combustible inorganic compounds, or greenhouse gases (GHGs) other than carbon dioxide. A contaminant may be a member of two or more of the foregoing classes. For example, methane is a hydrocarbon, a VOC, and a GHG.

[0032] Horizontal: a direction is horizontal if it is perpendicular to the line of action of gravitational force on Earth.

[0033] Monolithic: As used herein, a structure comprising two or more poppet valves is “monolithic” if ductwork serving the inlets and ductwork serving the outlets is not welded, riveted, soldered, or otherwise interconnected transverse to the line of flow between any two adjacent poppet valves.

[0034] Type 1: As used herein, the phrase “type 1” is used as an adjective to describe a component or product of a type 1 RTO.

[0035] Type 2; As used herein, the phrase “type 2” is used as an adjective to describe a component or product of a type 2 RTO.1.2. Thermal Oxidizer Systems

[0036] Regenerative thermal oxidizer (RTO) systems for the reduction of contaminants in an air stream comprise one or more RTOs in fluid communication with a source of the air stream. Generally, each RTO comprises a combustion chamber. In a combustion chamber, one or more contaminants in the air stream are thermally oxidized to yield an exhaust gas stream. Thermal oxidation in combustion chambers converts hydrocarbon and VOC contaminants, such as methane, into carbon dioxide and water, and possibly minor fractions of other oxides depending on which elements other than carbon and hydrogen might be present in contaminant compounds. Combustion chambers typically comprise ceramic interiors, which can survive temperatures in the range of 1400°F-1600°F (760°C-871°C) and can retain heat for greater overall efficiency of thermal oxidation. However, other materials can be used, as will be known to persons of ordinary skill in the art having the benefit of the present disclosure.

[0037] RTOs also typically comprise at least two (e.g., two, three, four, or more) heat recovery chambers. Each heat recovery chamber is thermally regenerated by heat from the combustion chamber. Heat recovered from thermal regeneration of heat recovery chambers can be used to heat air entering combustion chambers to improve overall efficiency of thermal oxidation in RTOs.

[0038] Typically, air streams enter heat recovery chambers, where they are heated to temperatures at which, upon entry into combustion chambers, any contaminants are thermally oxidized. For contaminants that are hydrocarbons and / or volatile organic compounds (VOCs), such as methane, thermal oxidation generates exhaust gas comprising carbon dioxide and water vapor, which have much lower greenhouse potential than methane and are acceptable for atmospheric release. Generally, exhaust gases comprise nitrogen,oxygen, and other components of air. The exhaust gas can be removed from the RTO and vented to atmosphere by vents in fluid communication with combustion chambers and atmosphere, by which exhaust gas is vented to the atmosphere after heat is recovered therefrom.

[0039] If exhaust gases comprise levels of various thermal oxidation products that are not acceptable for release (e.g., some sulfur oxides or nitrogen oxides), the exhaust gases can be treated to reduce such levels to be acceptable for venting to atmosphere.

[0040] In FIG. 1, type 2 RTO 132 schematically depicts components of a general RTO described above. For readability, only one heat recovery chamber 140 is shown in type 2 RTO 132; it will be understood that type 2 RTOs typically comprise at least two (e.g. two, three, four, or more) heat recovery chambers. Two or more heat recovery chambers are typically included to permit bidirectional flow, thus better maintaining heat balance within ceramic media.

[0041] Thermal oxidation is generally exothermic. Accordingly, if the contaminant concentration is high enough, heat recovery chambers can heat air streams to a temperature hot enough for thermal oxidation without application of heat from an external source. Such operation can be termed “autothermal.” However, at low contaminant concentration, autothermal temperatures cannot be maintained. For example, when the contaminants are VOCs, a concentration of less than 0.0009 lb / ft3(0.0144 kg / m3) may be insufficient for combustion chambers to be maintained at autothermal temperatures.

[0042] Accordingly, RTO systems can also include supplemental fuel injectors (SFIs), which are in fluid communication with a fuel gas source and are configured to inject fuel gas into the air stream Operation of SFIs may be desirable when the contaminant types and / or concentrations are too low to generate enough heat to maintain combustion chambers at autothermal temperatures. SFIs may operate under direction of SFI controllers which receive input pertaining to contaminant types and / or concentrations in air streams, and / or temperatures of exhaust gases of RTO combustion chambers.

[0043] The fuel gas can be hydrogen, alcohols such as ethanol or butanol, hydrocarbons or mixtures comprising hydrocarbons such as methane, propane, butane, gasoline, or kerosene, or combinations thereof. Methane has relatively high energy content per volume, has well- established infrastructures for deployment at operating sites, and may be available as mine gas or be already provided for on-site utility generation.

[0044] The system of FIG. 1 is depicted with an SFI 198, which regulates the flow of fuel from fuel gas source 196 to a mixing vessel 110, and thence to RTOs such as type 2 RTO 132.

[0045] Exemplary thermal oxidizer systems include those described in Section 1.3.

[0046] Airflow within RTO systems, and particularly into and out of heat recovery chambers, can be regulated by poppet valves housed in assemblies disposed in proximity to inlets to heat recovery chambers. Similarly to the pistons of an internal combustion engine cylinder, poppet valves in RTO systems can move between a position in which air streams comprising contaminants can enter heat recovery chambers of RTOs, and a position in which exhaust gas streams can exit combustion chambers via heat recovery chambers for venting. Poppet valves can be disposed in a horizontal orientation, operably linked to actuators and control systems such that the amount of the air stream passed to the heat recovery chamber and the amount of the exhaust gas received from the combustion chamber are regulated. Generally, in the operating layout of RTO systems, one heat recovery chamber can be paired with one poppet valve, and the poppet valves can be deployed in series such that portions of air streams that are not directed by a first poppet valve to a first heat recovery chamber are passed to a second poppet valves paired with a second heat recovery chamber, and so on to the final poppet valve / heat recovery chamber pair in the system.

[0047] Poppet valves and associated ductwork can be manufactured in individual assemblies, such that a single poppet valve and associated ductwork can be shipped as an individual unit to an operating location, where the individual assemblies can be installed to align ductwork from an air stream source to subsequent poppet valves in series, and to align poppet valves with heat recovery chambers. A framework serving one poppet valve and its immediatelyassociated ductwork can be termed an “individual poppet valve assembly.” An exemplary individual poppet valve assembly is schematically depicted in FIG. 2 as individual poppet valve assembly 210. In addition or alternatively, thermal oxidizer systems can incorporate one or more monolithic poppet valve assemblies, as described in Section 1.4.1.4.

[0048] The various components of thermal oxidizer systems, both in general and in specific systems described in Section 1.3, can be fabricated from any appropriate materials. Exemplary materials include carbon steel, ferrous alloys, and non-ferrous alloys, among others. A particular material for a given component can be selected based on the gases and streams the component is expected to handle and / or the anticipated service life of the component and / or the system as a whole, among other considerations.

[0049] In systems described in Section 1.3, components can be fabricated from corrosionresistant alloys and / or materials with internal coatings known for submersible applications. However, there is no advantage to doing so. Such alloys and coatings add capital expense that is not expected to pay for itself by reduction of operating expenses of systems of the present disclosure.1.3. Systems comprising Type 1 RTOs and optional Type 2 RTOs

[0050] In some embodiments, the present disclosure relates to systems for thermally oxidizing one or more contaminants in an air stream comprising water vapor. The systems described herein can be used with any air stream comprising contaminants and water vapor. For example, the air stream can be a mine ventilation air stream. Alternatively or additionally, the air stream can comprise methane as a contaminant to be thermally oxidized by the system.

[0051] Systems comprise a mixing vessel in fluid communication with a source of the air stream and one or more regenerative thermal oxidizers (RTOs) and one or more type 1 RTOs. Optionally, the systems comprise one or more type 2 RTOs. The systems may further comprise one or more additional components.

[0052] Mixing vessels are described in Section 1.3.1. Type 1 RTOs are described in Section 1 .3.2. Type 2 RTOs are described in Section 1.3.3. Other components are described inSection 1.5. An exemplary, non-limiting system 100 comprising a mixing vessel, type 1 RTOs, type 2 RTOs, and other components is depicted in FIG. 1. Another exemplary, nonlimiting system 400 is shown in conceptual perspective view in FIG. 4. Exemplary systems 100 and 400 will be referred to in Sections 1.3.1-1.3.3.1.3.1. Mixing vessels

[0053] Systems of the present disclosure comprise mixing vessels. The mixing vessels are in fluid communication with a source of the air stream and one or more regenerative thermal oxidizers (RTOs).

[0054] In mixing vessels, air streams from sources (typically 50°F-70°F (10°C-21°C) and near or at 100% relative humidity) are mixed with exhaust gases from type 1 RTOs (typically 1400°F-1600°F (760°C-871°C)). Mixing thus raises the dry bulb temperature of the air stream to a selected temperature that will depend on the temperatures of the air streams, the exhaust gases, and the relative proportions of each. The selected temperature can be chosen by the system operator such that, even if ambient conditions are cold and / or windy, the air stream will remain above its dew point, and water will not condense in the system.

[0055] In the exemplary system 100 shown in FIG. 1, a mixing vessel 110 is in fluid communication with a mine shaft 102, from which issues a ventilation air stream comprising one or more contaminants and water vapor. In FIG. 1, flow of air and other gases is represented by thick solid lines. The air stream flows from mixing vessel 110 to heat recovery chambers 140 of both type 1 RTOs (e.g, type 1 RTO 122) and type 2 RTOs (e.g, type 2 RTO 132). Mixing vessel 110 is also in fluid communication with type 1 RTOs 122 and 124, particularly exhaust gas lines thereof (e.g, type 1 exhaust gas line 170 of type 1 RTO 122).1.3.2. Type 1 RTOs

[0056] Systems of the present disclosure can comprise one or more type 1 RTOs. Like other RTOs, type 1 RTOs comprise combustion chambers, heat recovery chambers, and vents, as described in Section 1.2.

[0057] In addition to the aforementioned components, type 1 RTOs also comprise components that enable diversion of at least first portions of exhaust gas streams to type 1 exhaust gas lines and thence to mixing vessels, thus raising the dry bulb temperature of air streams in mixing vessels as described above.

[0058] Type 1 RTOs comprise diverters in fluid communication with combustion chambers, vents, and type 1 exhaust gas lines to be described below. Diverters divide type 1 exhaust gas streams generated by combustion chambers into first portions and second portions. Second portions of type 1 exhaust gas streams are vented, as described above. First portions of type 1 exhaust gas streams are issued to type 1 exhaust gas lines as will be described below.

[0059] Diverters can divide type 1 exhaust gas streams by fixed hardware or by dynamic adjustment, e.g., by flow control dampers with modulating positioners or splitter valves. Flow control dampers or other dynamic adjustment devices can be manually or automatically controlled. In dynamic adjustment, the proportions between first and second portions of type 1 exhaust gas streams can be determined by controllers, as will be described below. The proportions can be communicated from controllers to users for manual control, or can be implemented by controllers when dynamic adjustment devices are configured for automatic control.

[0060] Type 1 RTOs comprise controllers configured to determine the amounts of the first portion and the second portion to raise the dry bulb temperature to the temperature at which water vapor in the air stream does not condense. Controllers can be instantiated as hardware, software, firmware, or any combination thereof. Controllers typically comprise one or more inputs, through which information pertaining to system operating conditions can be received by the controller; a processor; and one or more outputs, by which the operation of the diverter can be regulated.

[0061] Input(s) to controllers can comprise information pertaining to the temperature(s) of air streams at one or more locations in the systems. Other information that can be received by controllers includes, but is not limited to, information pertaining to relative humidity,contaminant types and / or quantities, and / or air flow rate in air streams at one or more locations in the systems.

[0062] Information can be input to the controllers by manual entry, using human / computer interface devices such as keyboards, number pads, touchscreens, knobs, dials, or virtual and / or augmented reality input devices, among others. Alternatively or in addition, information can be input to the controllers by automated devices.

[0063] In some embodiments, systems can comprise first thermocouples to determine the temperature of air streams entering mixing vessels and / or second thermocouples to determine the temperature of air streams exiting mixing vessels.

[0064] Type 1 RTOs also comprise type 1 exhaust gas lines in fluid communication with combustion chambers (via diverters) and mixing vessels, by which at least first portions of type 1 exhaust gas streams are conveyed to mixing vessels to be mixed with air streams to raise the dry bulb temperature of the air streams to temperatures at which water vapor in the air streams does not condense in systems. Second portions of the type 1 exhaust gas streams are vented to atmosphere.

[0065] An exemplary type 1 RTO is shown in FIG. 1 as Type 1 RTO 122. The type 1 RTO 122 receives a ventilation air stream from mixing vessel 110 via heat recovery chamber 140. For readability, only one heat recovery chamber 140 is shown; it will be understood that type 1 RTOs typically comprise at least two (e.g., two, three, four, or more) heat recovery chambers.

[0066] The heat recovery chamber 140 heats the ventilation air stream using heat recovered from earlier combustion. The heated ventilation air stream enters the combustion chamber 150, where contaminants are thermally oxidized, e.g., to carbon dioxide and water vapor. Heat is recovered from the combustion chamber 150 by the heat recovery chamber 140.Although heat is recovered therefrom, type 1 exhaust gas typically remains hotter than the ventilation air stream issuing from mine shaft 102.

[0067] Type 1 exhaust gas exits the combustion chamber 150 and is received by diverter 175. The diverter 175 divides the type 1 exhaust gas, such as by the action of a flow controldamper with a modulating positioner (not shown), into a first portion and a second portion. The division by the diverter 175 is directed by output of the controller 160. The controller 160 determines the proportions of the first and second portions based on temperature information received from a first thermocouple (TC) 192 (which monitors the temperature of the ventilation air stream between the mine shaft 102 and the mixing vessel 110) and a second TC 194 (which monitors the temperature of the ventilation air stream between the mixing vessel 110 and the type 1 RTO 122).

[0068] The controller 160 can direct division by the diverter 175 dynamically. For example, if the temperature at the second TC 194 falls from an earlier time point to a later time point, while the temperature at the first TC 192 remains essentially constant, this may indicate a drop in ambient temperature, an increase in ambient wind, or a decrease in contaminant content (with concomitant decrease in heat generated by exothermic thermal oxidation reactions, resulting in a decrease in the temperature of the type 1 exhaust gas conveyed to the mixing vessel 110 by type 1 exhaust gas line 170), among other possibilities. In view of such a drop in the temperature at the second TC 194, the controller 160 can increase the proportion of the type 1 exhaust gas directed to the first portion by diverter 175 and reduce the proportion of the type 1 exhaust gas to be vented to atmosphere via vent 180.

[0069] After division by the diverter 175, the first portion of the type 1 exhaust gas passes via type 1 exhaust gas line 170 to mixing vessel 110. In the mixing vessel 110, the first portion of the type 1 exhaust gas mixes with the ventilation air stream issuing from the mine shaft 102. A sufficient proportion of type 1 exhaust gas mixed with the ventilation air stream can raise the dry bulb temperature of the ventilation air stream to a temperature at which water vapor in the air stream does not condense in the system.

[0070] Depending on prevailing conditions at operating locations, the expected contaminant types and concentrations in air streams generated at the operating locations, the expected airflow of the air streams, and other parameters, one type 1 RTO may be sufficient to divert first portions of type 1 exhaust gases in amounts sufficient to raise the dry bulb temperature of the air stream to a temperature at which water vapor in the air stream does not condense in the system. Two type 1 RTOs may be desirable for redundancy during operation, e.g., onetype 1 RTO can be taken offline for maintenance while another type 1 RTO remains active. However, systems comprising type 1 RTOs are not limited to one or two type 1 RTOs.

[0071] In some embodiments, systems comprise one type 1 RTO

[0072] In some embodiments, systems comprise two type 1 RTOs.

[0073] In some embodiments, systems comprise three type 1 RTOs.1.3.3. Type 2 RTOs

[0074] Optionally, systems of the present disclosure comprise one or more type 2 RTOs.Type 2 RTOs resemble type 1 RTOs in each having a combustion chamber, in which the one or more contaminants are thermally oxidized to yield an exhaust gas stream (in type 2 RTOs, a type 2 exhaust gas stream); at least two (e.g, two, three, four, five or more) heat recovery chambers, which are thermally regenerated by heat from the combustion chamber; and vents in fluid communication with the combustion chamber and an atmosphere, by which the type 2 exhaust gas stream is vented to the atmosphere after heat is recovered therefrom.

[0075] In some embodiments, type 2 RTOs lack exhaust gas lines in fluid communication with combustion chambers and mixing vessels, diverters in fluid communication with combustion chambers and exhaust gas lines, and controllers configured to determine amounts of exhaust gas streams to enter exhaust gas lines.

[0076] An exemplary type 2 RTO is shown in FIG. 1 as Type 2 RTO 132. The type 2 RTO 132 receives a ventilation air stream from mixing vessel 110 via heat recovery chamber 140. The heat recovery chamber 140 heats the ventilation air stream using heat recovered from earlier combustion. The heated ventilation air stream enters the combustion chamber 150, where contaminants are thermally oxidized, e.g, to carbon dioxide and water vapor. Heat is recovered from the combustion chamber 150 by the heat recovery chamber 140.

[0077] Type 2 exhaust gas exits the combustion chamber 150 and is vented to atmosphere via vent 180.

[0078] Depending on expected contaminant types and concentrations in air streams generated at operating locations, the expected airflow of the air streams, and otherparameters, a minimum number of RTOs may be required to remove contaminants to a desired extent from air streams. This particular minimum number can be greater than the number of type 1 RTOs to be included in the system. Thus, systems can comprise a number of type 2 RTOs such that the number of type 1 RTOs plus the number of type 2 RTOs equals or exceeds the required minimum number. (A sum greater than the required minimum number may be desirable to handle increases in contaminant concentrations and / or air stream airflow over levels originally expected; to provide redundancy in case of mechanical difficulty and / or routine maintenance, etc.).

[0079] Because type 2 RTOs have fewer components than type 1 RTOs, type 2 RTOs will typically be less expensive than type 1 RTOs. Accordingly, in some embodiments, systems comprise only one, two, or three type 1 RTOs and the balance will be type 2 RTOs.

[0080] In some embodiments, systems comprise three type 2 RTOs.

[0081] In some embodiments, systems comprise four type 2 RTOs.

[0082] In some embodiments, systems comprise five type 2 RTOs.

[0083] In some embodiments, systems comprise six type 2 RTOs.

[0084] In some embodiments, systems comprise seven type 2 RTOs.

[0085] In some embodiments, systems comprise eight type 2 RTOs.

[0086] In some embodiments, systems comprise nine type 2 RTOs.

[0087] In some embodiments, systems comprise ten type 2 RTOs.

[0088] Systems can comprise any number of total RTOs of either or both type 1 and type 2, in view of expected contaminant types and / or concentrations in air streams, air stream flow rates, climates in which systems are deployed, and other parameters. For example, in hot climates, in which the ambient temperature is not expected to drop below the dew points of air streams, systems can comprise only type 2 RTOs and zero type 1 RTOs.

[0089] Common deployments may comprise from four to twelve RTOs; however, this is exemplary and not limiting. In some embodiments, systems comprise one RTO. In someembodiments, systems comprise two RTOs. In some embodiments, systems comprise three RTOs. In some embodiments, systems comprise four RTOs. In some embodiments, systems comprise five RTOs. In some embodiments, systems comprise six RTOs. In some embodiments, systems comprise seven RTOs. In some embodiments, systems comprise eight RTOs. In some embodiments, systems comprise nine RTOs. In some embodiments, systems comprise ten RTOs. In some embodiments, systems comprise eleven RTOs. In some embodiments, systems comprise twelve RTOs. In some embodiments, systems comprise thirteen RTOs. In some embodiments, systems comprise fourteen RTOs. In some embodiments, systems comprise fifteen RTOs. In some embodiments, systems comprise sixteen RTOs.

[0090] In some embodiments, one or more RTOs each comprise one combustion chamber and two heat recovery chambers. In some embodiments, one or more RTOs each comprise one combustion chamber and three heat recovery chambers. In some embodiments, one or more RTOs each comprise one combustion chamber and four heat recovery chambers. In some embodiments, one or more RTOs each comprise one combustion chamber and five heat recovery chambers. These embodiments are not mutually exclusive; e.g., a system can comprise RTOs with two heat recovery chambers and RTOs with three heat recovery chambers; RTOs with two heat recovery chambers and RTOs with four heat recovery chambers; RTOs with two heat recovery chambers and RTOs with five heat recovery chambers; RTOs with two heat recovery chambers, RTOs with three heat recovery chambers, and RTOs with four and / or five heat recovery chambers; RTOs with three heat recovery chambers and RTOs with four heat recovery chambers; RTOs with three heat recovery chambers and RTOs with five heat recovery chambers; RTOs with three heat recovery chambers, RTOs with four heat recovery chambers, and RTOs with five heat recovery chambers; and so forth.

[0091] The exemplary system schematically represented in FIG. 1 comprises two type 1 RTOs 122 and 124, and four type 2 RTOs 132, 134, 136, and 138.

[0092] FIG. 4 provides a conceptual perspective view of an exemplary system 400 comprising type 1 RTOs and type 2 RTOs. Each RTO comprises two heat recovery chambersand one combustion chamber. For readability of the figure, only heat recovery chambers 140a(l) and 140a(2) and combustion chamber 150a of type 2 RTO 130a are identified by reference numerals.

[0093] From a mine shaft 102, ventilation air flows to mixing chamber 110, where it is mixed with portions of type 1 exhaust gases from either or both of type 1 RTOs 120a and 120b. The portions of type 1 exhaust gases are passed from the type 1 RTOs 120a, 120b by type 1 exhaust gas lines 170a and 170b. The system 400 also comprises ten type 2 RTOs, 130a-l 30j .

[0094] Airflow into any combustion chamber of any RTO of either type can be regulated by a poppet valve disposed in an individual poppet valve assembly, such as those described in Section 1.2 and / or in a monolithic poppet valve assembly, such as those described in Section 1.4.1.4. Monolithic Poppet Valve Assemblies

[0095] The present disclosure provides monolithic poppet valve assemblies, comprising two or more poppet valves housed in a monolithic poppet valve assembly. Poppet valves and their operation were described in Section 1.2 in the context of thermal oxidizer systems, but poppet valves can be used in any application in which air flow from a source to a destination and exhaust flow from the destination are to be regulated.

[0096] In some embodiments, poppet valves and associated ductwork can be manufactured in monolithic poppet valve assemblies, such that two, three, or more poppet valves and the associated ductwork of each can be fabricated and shipped as a monolithic multi-valve assembly. Monolithic multi-poppet valve assemblies or chambers can be single weldment structures comprising a single support structure, a common floor plate, common side panels, and a common top plate for the multiple poppet valves. By “single weldment” is meant that all welds or other interconnections between structures, plates, and / or panels is made at essentially the same time and place (e.g., in a single factory by the same or essentially similar sets of equipment on one day or a few consecutive days). Single structures and / or common plates and / or panels can reduce the need for additional weldments and individual ductworkcomponents, as various pathways (e.g., process air inlets, cleaned air outlets, and / or air flow between heat recovery chambers) can be included within the monolithic poppet valve assembly.

[0097] Because they can be fabricated in a single weldment, monolithic poppet valve assemblies can reduce direct manufacturing effort by reducing the total number of discrete fabricated components and reducing handling of raw materials during fabrication. Monolithic poppet valve assemblies also can be more efficient from a weight perspective, by consuming less raw material than a corresponding number of individual assemblies and reducing the amount of assembly hardware.

[0098] Monolithic poppet valve assemblies also can enable assembly and test of a complete RTO flow control system at the factory prior to deployment to an operating site, thus reducing the risk that performance-related deficiencies are identified for the first time in the field after installation.

[0099] Also, monolithic poppet valve assemblies can be more reliable, with fewer potential leak points by virtue of having fewer connections and fewer individual ductwork components than individual assemblies. This increases flow assurance and efficiency of systems comprising monolithic poppet valve assemblies (e.g., RTO systems), thus potentially reducing maintenance and operations effort, and system downtime.

[0100] Monolithic poppet valve assemblies comprise ductwork between the two, three, or more poppets that can be fabricated in the factory, using emplaced equipment that does not need to be portable and has a well-regulated power supply, and in which the skill level of the manufacturing personnel can be better known to the manufacturer. One or more of these factors can lead to a higher quality of ductwork fabrication, e.g., a lower incidence of leaks during operation, for installed systems comprising monolithic multi-poppet valve assemblies compared to individual poppet valve assemblies. In the latter, ductwork is typically welded together on site using potentially less effective locally available equipment, potentially lower-skilled locally available personnel, and / or in the presence of uncontrollable environmental conditions (e.g., extreme heat, extreme cold, high wind, rain, otherprecipitation, drought, etc.), among other factors that will be known to persons of ordinary skill in the art.

[0101] Further, monolithic poppet valve assemblies can be safer and easier to install at a field location. Installation of a monolithic poppet valve assembly can be accomplished by a single lift by construction equipment, rather than multiple lifts of individual poppet valve assemblies.

[0102] Additionally, monolithic poppet valve assemblies can require significantly less handling and logistics effort during transportation and installation. For example, a monolithic poppet valve assembly that is less than 53 feet (16.15 m) long, 8.5 feet (2.59 m) wide, and 9 feet (2.74 m) tall can be legally transported by flatbed truck in the United States and Canada. Monolithic poppet valve assemblies of comparable dimensions are expected to be legally transportable by flatbed truck in the United Kingdom, the European Union, Australia, and other jurisdictions. In many use cases, it is expected that the maximum transportable dimensions will encompass monolithic poppet valve assemblies with two or three poppet valves and associated ductwork.

[0103] In some embodiments, two poppet valves are housed in a monolithic poppet valve assembly.

[0104] FIG. 5 shows a conceptual perspective view of an exemplary monolithic poppet valve assembly 500. The monolithic poppet valve assembly 500 comprises two poppet valves 221 and 223. Each is under the control of an actuator 231 or 233, respectively. The actuators 221 and 223 independently move the poppet valves 221 and 223 in a horizontal direction to allow an air stream (e.g., an air stream comprising contaminants) to flow from process air duct 240 up and into a destination (e.g., a heat recovery chamber of an RTO) deployed above the poppet valve and allow a processed air stream (e.g., decontaminated air) to be exhausted (e.g, from a combustion chamber via a heat recovery chamber of an RTO) via exhaust air duct 250.

[0105] In some embodiments, three poppet valves are housed in a monolithic poppet valve assembly.

[0106] Systems (e.g., RTO systems) can comprise more than one monolithic poppet valve assembly.

[0107] In some embodiments, all poppet valves of a system (e.g., an RTO system) are housed in monolithic poppet valve assemblies.

[0108] Systems e.g., RTO systems) can comprise a mix of individual poppet valve assemblies and monolithic poppet valve assemblies in any proportion.

[0109] The monolithic poppet valve assemblies can be incorporated into systems for regulating air streams. The systems can comprise a monolithic poppet valve assembly comprising two or more poppet valves, with each poppet valve in fluid communication with a source of the air stream and a destination of the air stream, and regulating flow of the air stream into the destination.

[0110] The systems comprising monolithic poppet valve assemblies can be RTO systems in which air flow into the heat recovery chambers of RTOs is regulated by poppet valves. The RTO systems can be used for the thermal oxidation of one or more contaminants, such as methane. Although particular examples of monolithic poppet valve assemblies are described in deployments in RTO systems, monolithic poppet valve assemblies are not so limited.[OHl] An exemplary, non-limiting system 200 comprising two or more poppet valves disposed in a single monolithic poppet valve assembly in an RTO deployment is depicted in FIG. 2.

[0112] Whether any given heat recovery chamber of an RTO receive an air stream via a poppet valve deployed in an individual assembly or a monolithic poppet valve assembly is independent of whether the RTO is a type 1 RTO or a type 2 RTO. For example, monolithic poppet valve assemblies can be used in systems comprising only type 2 RTOs, only type 1 RTOs, or a mix of type 1 RTOs and type 2 RTOs. In systems comprising both types of RTOs, poppet valves in monolithic poppet valve assemblies can be used to provide air to type 1 RTOs, type 2 RTOs, or both; and / or poppet valves in individual poppet valve assemblies can be used to provide air to type 1 RTOs, type 2 RTOs, or both.

[0113] FIG. 2 schematically represents a system 200 comprising four RTOs 232, 234, 236, and 238. Each RTO can be a type 1 RTO or a type 2 RTO. Individual poppet valve assemblies 210 and 212 (e.g., assemblies comprising only one poppet valve 211 or 213, respectively) contain poppet valves which regulate air flow into heat recovery chambers 242 and 244 of RTO 232. A monolithic poppet valve assembly 220 (e.g., an assembly comprising two or more poppet valves, e.g., two poppet valves 221 and 223) contains poppet valves which regulate air flow into heat recovery chambers 246 and 248 of RTO 234.

[0114] Although FIG. 2 depicts RTOs 232 and 234 as each comprising two heat recovery chambers, in other embodiments (not shown), RTOs can comprise more than two (e.g., three, four, five or more) heat recovery chambers.

[0115] Exemplary airflow regulation systems described in the foregoing embodiments can be described with reference to the exemplary RTO system 400 of FIG. 4. The system 400 comprises twelve RTOs, each with two heat recovery chambers, e.g., heat recovery chambers 140a(l) and 140a(2) of RTO 130a. The heat recovery chambers 140a(l) and 140a(2) recover heat from exhaust gases generated in combustion chamber 150a. Regulation of airflow into heat recovery chambers of system 400 by poppet valves would entail 24 poppet valves. The system 400 could comprise 24 individual poppet valve assemblies; twelve two-valve monolithic poppet valve assemblies 500; or any combination thereof.

[0116] In airflow regulation systems in which three poppet valves regulate airflow into a particular structure, the systems can comprise one, any two, or all three of three-valve monolithic poppet valve assemblies; two-valve monolithic poppet valve assemblies 500 installed with individual poppet valve assemblies for a given structure; and / or three individual poppet valve assemblies installed together for a given structure.1.5. Other components

[0117] Systems comprising RTOs can further comprise supplemental fuel injectors (SFIs) in fluid communication with a fuel gas source and the mixing vessel, by which fuel gas is injected into the air stream. Injected fuel gas will then combust in combustion chambers of both types of RTOs.

[0118] Systems described in Section 1.3 can comprise any one, any two, or all three of first thermocouples, second thermocouples, and SFIs.

[0119] Systems can comprise alternative or additional components known to persons of ordinary skill in the art of RTOs.1.6. Systems Comprising Type 1 RTOs and Monolithic Poppet Valve Assemblies

[0120] In some embodiments, the present disclosure relates to RTO systems comprising type1 RTOs (and optionally also comprising type 2 RTOs) and in which air flow into heat recovery chambers of RTOs is regulated by poppet valves, with two or more poppet valves being disposed in a single monolithic poppet valve assembly. Mixing chambers, type 1 RTOs, and type 2 RTOs can be as described in Section 1.3. Monolithic poppet valve assemblies can be as described in Section 1.4. Other components, such as thermocouples and SFIs, can be as described in Section 1.5.

[0121] FIG. 3 schematically depicts an exemplary system 300 comprising type 1 RTOs and a monolithic poppet valve assembly. Reference numerals in FIG. 3 that are identical to reference numerals in FIG. 1 or FIG. 2 refer to like components and for the sake of brevity will not be described here. The system 300 is shown as comprising an individual poppet valve assembly 210 regulating air flow into type 1 RTO 124, and a monolithic poppet valve assembly 220 regulating air flow into heat recovery chambers 246 and 248 of a type 2 RTO 133. This depiction is purely exemplary. Systems described in this section can comprise monolithic poppet valve assemblies regulating air flow into type 1 RTOs; ; or monolithic poppet valve assemblies comprising three poppet valves (e. ., for regulation of air flow into RTOs comprising three heat recovery chambers), among other variants that will be apparent to persons of ordinary skill in the art. Further, systems described in this section can lack type2 RTOs, individual poppet valve assemblies, or both.

[0122] For brevity, FIG. 3 does not depict any poppet valve or assembly thereof regulating air flow into type 1 RTO 122 or type 2 RTO 132. This is purely for the sake of readability; itwill be understood that air flow into RTOs 122 and 132 can be regulated by poppet valves that are not shown.1.7. Methods for reducing condensation

[0123] In some embodiments, the present disclosure also relates to methods for reducing condensation in air streams comprising one or more contaminants and water vapor in fluid communication with one or more regenerative thermal oxidizers (RTOs) for thermal oxidation of the contaminants. The methods comprise mixing at least portions of exhaust gas streams from one or more of the RTOs with the air streams to raise the dry bulb temperatures of the air streams to temperatures at which water vapor in the air streams does not condense.

[0124] In some embodiments, methods further comprise determining temperatures of air streams prior to mixing and temperatures of air streams after mixing, and selecting the amount of the portions of the exhaust gas streams to raise the dry bulb temperatures to the temperatures at which water vapor in the air streams does not condense.

[0125] Additionally or alternatively, methods can further comprise determining whether air streams have insufficient contaminant contents to maintain the one or more RTOs in an autothermal condition and / or whether exhaust gas streams have insufficient heat contents to both mix at least the portions thereof with the air streams to raise the dry bulb temperatures to the temperatures at which water vapor in the air streams does not condense, and maintain the one or more RTOs in an autothermal condition; and injecting fuel gases into the air streams prior to mixing.

[0126] In any methods, the one or more contaminants can comprise methane and / or the air streams can be mine ventilation air streams.

[0127] Methods for reducing condensation can be performed, e.g., using systems of the present disclosure, or using other systems.

Claims

AMENDED CLAIMS received by the International Bureau on 01 October 2025 (01.10.2025)What is claimed is:

1. A system for thermally oxidizing one or more contaminants in an air stream comprising water vapor, the system comprising: a mixing vessel in fluid communication with a source of the air stream and a type 1 regenerative thermal oxidizer (RTO), wherein the type 1 RTO comprises: a combustion chamber, in which the one or more contaminants are thermally oxidized to yield a type 1 exhaust gas stream; a type 1 exhaust gas line in fluid communication with the combustion chamber and the mixing vessel, wherein the type 1 exhaust gas line is configured to convey at least a first portion of the type 1 exhaust gas stream to the mixing vessel to be mixed with the air stream to raise a dry bulb temperature of the air stream to a temperature at which water vapor in the air stream does not condense in the system; two or more heat recovery chambers configured to be thermally regenerated by heat from the combustion chamber; a vent in fluid communication with the combustion chamber and an atmosphere, wherein the vent is configured to vent at least a second portion of the type 1 exhaust gas stream to the atmosphere after recovering heat therefrom; a diverter in fluid communication with the combustion chamber, the vent, and the type 1 exhaust gas line, by which the type 1 exhaust gas stream is divided into the first portion and the second portion; and a controller configured to determine amounts of the first portion and the second portion to raise the dry bulb temperature to the temperature at which water vapor in the air stream does not condense.

2. The system of claim 1 , further comprising a first thermocouple configured to determine a first temperature of the air stream entering the mixing vessel and a secondthermocouple configured to determine a second temperature of the air stream exiting the mixing vessel.

3. The system of claim 1 , further comprising a supplemental fuel injector (SFI) in fluid communication with a fuel gas source and the mixing vessel, wherein the SFI is configured to inject fuel gas into the air stream.

4. The system of claim 1 , wherein the mixing vessel is in fluid communication with one or more additional type 1 regenerative thermal oxidizers (RTOs).

5. The system of claim 1 , wherein the mixing vessel is in fluid communication with one or more type 2 RTOs, each type 2 RTO comprising: an additional combustion chamber configured to thermally oxidize the one or more contaminants to yield a type 2 exhaust gas stream; and two or more additional heat recovery chambers configured to be thermally regenerated by heat from the additional combustion chamber; and an additional vent in fluid communication with the additional combustion chamber and the atmosphere, wherein the additional vent is configured to vent the type 2 exhaust gas stream to the atmosphere after recovering heat therefrom.

6. The system of claim 5, wherein each type 2 RTO lacks an exhaust gas line in fluid communication with the additional combustion chamber and the mixing vessel, a diverter in fluid communication with the additional combustion chamber, and a controller configured to determine an amount of an exhaust gas stream.

7. The system of claim 5, wherein the one or more type 2 RTOs comprise two or more type 2 RTOs.

8. The system of claim 1 , wherein the one or more contaminants comprise methane.

9. The system of claim 1 , comprising a poppet valve in fluid communication with the mixing vessel and one of the two or more heat recovery chambers, wherein thepoppet valve is configured to regulate flow of the air stream into the one of the two or more heat recovery chambers.

10. A monolithic poppet valve assembly, comprising: two or more poppet valves; a process gas ductwork in fluid communication with the two or more poppet valves; and an exhaust gas ductwork in fluid communication with the two or more poppet valves.

11. The monolithic poppet valve assembly of claim 10, further comprising two or more actuators, each actuator of the two or more actuators operably linked to a respective one of the two or more poppet valves.

12. The monolithic poppet valve assembly of claim 11 , wherein the two or more actuators are configured to move the two or more poppet valves horizontally.

13. The monolithic poppet valve assembly of claim 10, wherein the two or more poppet valves are housed in the monolithic poppet valve assembly.

14. A system for thermally oxidizing one or more contaminants in an air stream comprising water vapor, the system comprising: a mixing vessel in fluid communication with a source of the air stream and one or more regenerative thermal oxidizers (RTOs); wherein the one or more RTOs comprise one or more type 1 RTOs, each type 1 RTO comprising: a first combustion chamber, in which the one or more contaminants are thermally oxidized to yield a type 1 exhaust gas stream; a type 1 exhaust gas line in fluid communication with the first combustion chamber and the mixing vessel, wherein the type 1 exhaust gas line is configured to convey at least a first portion of the type 1 exhaust gas stream to the mixing vessel to be mixed with the air stream to raise the dry bulbtemperature of the air stream to a temperature at which water vapor in the air stream does not condense in the system; two or more heat recovery chambers configured to be thermally regenerated by heat from the first combustion chamber; a vent in fluid communication with the first combustion chamber and an atmosphere, wherein the vent is configured to vent at least a second portion of the type 1 exhaust gas stream to the atmosphere after recovering heat therefrom; a diverter in fluid communication with the first combustion chamber, the vent, and the type 1 exhaust gas line, by which the type 1 exhaust gas stream is divided into the first portion and the second portion; and a controller configured to determine the amounts of the first portion and the second portion to raise the dry bulb temperature to the temperature at which water vapor in the air stream does not condense; wherein the one or more RTOs comprise one or more type 2 RTOs, each type 2 RTO comprising: a second combustion chamber configured to thermally oxidize the one or more contaminants to yield a type 2 exhaust gas stream; and two or more additional heat recovery chambers configured to be thermally regenerated by heat from the second combustion chamber; and an additional vent in fluid communication with the second combustion chamber and an atmosphere, wherein the additional vent is configured to vent the type 2 exhaust gas stream to the atmosphere after recovering heat therefrom; and a monolithic poppet valve assembly, comprising two or more poppet valves, a process gas ductwork in fluid communication with the mixing vessel and the two or more poppet valves, and an exhaust gas ductwork in fluid communication with the two or more poppet valves and thetype 1 exhaust gas line of a type 1 RTO and / or the additional vent of a type 1 RTO and / or a type 2 RTO.

15. The system of claim 14, further comprising a first thermocouple configured to determine a first temperature of the air stream entering the mixing vessel and a second thermocouple configured to determine a second temperature of the air stream exiting the mixing vessel.

16. The system of claim 14, further comprising a supplemental fuel injector (SFI) in fluid communication with a fuel gas source and the mixing vessel, wherein the SFI is configured to inject fuel gas into the air stream.

17. The system of claim 14, which comprises two or more type 1 RTO.

18. The system of claim 14, wherein each type 2 RTO lacks an exhaust gas line in fluid communication with the second combustion chamber and the mixing vessel, a diverter in fluid communication with the second combustion chamber, and a controller configured to determine an amount of an exhaust gas stream.

19. The system of claim 14, wherein the one or more contaminants comprise methane.

20. The system of claim 14, wherein two or more type 1 RTOs each comprise three or more heat recovery chambers.

21. The system of claim 14, wherein two or more type 2 RTOs each comprise three or more heat recovery chambers.

22. The system of claim 14, wherein the monolithic poppet valve assembly further comprises two or more actuators, each actuator operably linked to a respective one of the two or more poppet valves.

23. The system of claim 22, wherein the two or more actuators are configured to move the two or more poppet valves horizontally.

24. The system of claim 14, wherein two or more poppet valves are housed in the monolithic poppet valve assembly.

25. The system of claim 14, comprising a plurality of monolithic poppet valve assemblies.

26. The system of claim 14, wherein all of the two or more poppet valves are housed in monolithic poppet valve assemblies.

27. A system for reducing one or more contaminants in an air stream comprising water vapor, comprising: means for fluid communication of the air stream from a source to one or more means for contaminant reduction; one or more type 1 means for contaminant reduction, each comprising: means for conveying a first portion of a type 1 exhaust gas of the type 1 means for contaminant reduction to the means for fluid communication to be mixed with the air stream to raise a dry bulb temperature of the air stream to a temperature at which water vapor in the air stream does not condense in the system; means for venting a second portion of the type 1 exhaust gas to an atmosphere; means for dividing the type 1 exhaust gas into the first portion and the second portion; and means for supplemental fuel injection into the air stream.

28. The system of claim 27, further comprising one or more type 2 means for contaminant reduction, each comprising means for venting a type 2 exhaust gas to the atmosphere.

29. The system of claim 27, further comprising first means for temperature determination of the air stream entering the means for fluid communication and secondmeans for temperature determination of the air stream exiting the means for fluid communication.

30. (Canceled).

31. The system of claim 27, wherein each type 2 means for contaminant reduction lacks means for conveying a first portion of an exhaust gas to the means for fluid communication and lacks means for dividing an exhaust gas.

32. The system of claim 27, wherein the one or more contaminants comprise methane.

33. A method for reducing condensation in an air stream comprising one or more contaminants and water vapor in fluid communication with one or more regenerative thermal oxidizers (RTOs) for thermal oxidation of the contaminants, the method comprising: mixing at least a portion of an exhaust gas stream from one or more of the one or more RTOs with the air stream to raise a dry bulb temperature of the air stream to a temperature at which water vapor in the air stream does not condense.

34. The method of claim 33, further comprising: determining a first temperature of the air stream prior to mixing and a second temperature of the air stream after mixing, and selecting, based on the first temperature and the second temperature, an amount of the portion of the exhaust gas stream to raise a dry bulb temperature to the temperature at which water vapor in the air stream does not condense.

35. The method of claim 33, further comprising: determining whether the air stream has an insufficient contaminant content to maintain the one or more RTOs in an autothermal condition and / or whether the exhaust gas stream has an insufficient heat content to both mix at least the portion thereof with the air stream to raise a dry bulbtemperature to the temperature at which water vapor in the air stream does not condense, and maintain the one or more RTOs in the autothermal condition; and injecting a fuel gas into the air stream prior to mixing.

36. The method of claim 33, wherein the one or more contaminants comprise methane.

37. The method of claim 33, wherein the air stream comprises one or more contaminants and water vapor is a mine ventilation air stream.

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