Valve assembly control

Abstract

A method of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly mounted thereon is provided The valve assembly comprises a valve, the valve being mountable to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; and a controller. The method comprises the steps of: a human operator obtaining a first measurement of the amount of the first gaseous compound in the landfill gas; the human operator assessing a dilution rate of the landfill gas based on the first measurement; the human operator setting an initial valve position of the valve based on the assessment of the dilution rate; and, subsequently, the controller obtaining a second measurement of the amount of the first gaseous compound in the landfill gas using the first gas composition sensor; and the controller controlling the actuator based on the second measurement to set the valve position of the valve.

Description

[0001] Valve Assembly Control

[0002] Field of the Invention

[0003] The present invention relates to a method of controlling the flowrate of landfill gas out of a gas outlet (e.g. a wellhead or manifold). The present invention further relates to a valve assembly, and to a landfill.

[0004] Background

[0005] Deposited wastes in landfills generate landfill gas (LFG), which typically has a composition of approximately 60% methane and 40% carbon dioxide and traces of other gases. Air comprises approximately 79% nitrogen and 21 % oxygen. Landfilled wastes undergo biological degradation processes to produce LFG.

[0006] Landfills are not fully sealed systems; Methane escaping from landfills can be a significant contributor to global warming and a health and safety hazard. To control the escape of LFG from a landfill, a relatively gentle suction is placed on vertical wells via collection pipelines to extract gas at a similar rate to which LFG is generated by waste adjacent each well. Over extraction (an extraction flowrate greater than the rate at which LFG is generated in the region of the landfill that LFG is being drawn from) can cause air to be drawn into the landfill which dilutes the LFG, shocks the LFG generating microbes, slows down methane production and potentially creates sub-surface fires. Under extraction (an extraction flow less than the rate at which LFG is generated in the region of the landfill that LFG is being drawn from) may allow LFG to escape from the landfill and be emitted to the atmosphere, or migrate away from the site, causing pollution.

[0007] The amount of LFG available is influenced by short duration meteorological factors like atmospheric pressure changes and rainfall, as well as internal factors such as leachate extraction, that create a pressure differential between the atmosphere and the LFG extraction system, which can cause air to flow into the landfill (over extraction) or LFG emissions to escape out of the landfill (under extraction).

[0008] LFG generation and its liberation at each individual well or collection manifold varies continually so monitoring of wells is undertaken to ensure that the extraction rate (removal) of gas matches the LFG generation rate at each well location at any given time. Management of the LFG removal is performed (usually monthly) by manual monitoring of wells, then opening or closing of valves on the gas outlets of those wells, which increases or decreases the LFG flowrate. Ideally, more frequent monitoring and then management to react to environmental or internal events would be undertaken, but this is labour intensive and requires skilled staff, resulting in high operating costs. This means that extraction rates are rarely optimal between the infrequent manual adjustment events.

[0009] The present invention has been devised in light of the above considerations. Summary of the Invention

[0010] It is desired to provide a robust, standalone, cost-effective, intelligent, and automatic means for optimising the extraction of LFG from a gas outlet (e.g. a landfill well or manifold) for the generation of renewable electricity from methane. It is also desired to minimise LFG emissions from the landfill to atmosphere.

[0011] Accordingly, in a first aspect there is provided a method of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly mounted thereon, wherein: the valve assembly comprises: a valve, the valve being mountable to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; and a controller; and the method comprises the steps of: a human operator obtaining a first measurement of the amount of the first gaseous compound in the landfill gas; the human operator assessing a dilution rate of the landfill gas based on the first measurement; the human operator setting an initial valve position of the valve based on the assessment of the dilution rate; and, subsequently, the controller obtaining a second measurement of the amount of the first gaseous compound in the landfill gas using the first gas composition sensor; and the controller controlling the actuator based on the second measurement to set the valve position of the valve.

[0012] Such a method allows the flowrate of landfill gas out of a gas outlet to be controlled by first using the human operator’s assessment of the dilution rate of the landfill gas and a corresponding suitable first valve position, and subsequently the controller automatically controlling the valve position based on the landfill gas composition. Thus, advantageously, a simple, robust, standalone and cost-effective way of controlling the flowrate of landfill gas out of the gas outlet is provided.

[0013] The first gaseous compound may be, for example, oxygen, nitrogen, carbon dioxide, methane or hydrogen sulphide. The first gaseous compound being oxygen is advantageous in most directly and practically reflecting the dilution rate of the landfill gas compared to the other aforementioned gaseous compounds.

[0014] The gas outlet may be a wellhead or a manifold, for example, a wellhead on the well of a landfill site or a manifold connected to a well of a landfill site. The valve assembly being “mounted” on the gas outlet may be understood to mean that valve assembly, and all the components thereof, are supported on the gas outlet. For example, where the gas outlet is a gas pipe, the valve assembly may be suspended above the ground by being mounted on the gas pipe. The valve assembly and the components thereof may not be electronically connected to (by wired or wireless connection) any equipment external to the valve assembly (e.g. a controller not supported on the gas outlet). By way of example, the components of the valve assembly may be disposed in, and / or attached to (e.g. attached directly to) the exterior of, a valve assembly housing.

[0015] The dilution rate of the landfill gas may be understood as the flowrate or flux at which ambient air is flowing into the landfill. The dilution rate may be assessed by the human operator by comparison of the measured amount of the first gaseous compound against one or more of historical record of the amount of the first gaseous compound in the landfill gas from the gas outlet, amounts of the first gaseous compound at one or more other gas outlets of the landfill, a landfill gas specification, and / or the human operator’s understanding of the behaviour and / or sensitivity of the landfill.

[0016] The controller may be a computer-implemented controller. Advantageously, this allows the steps of the method conducted by the controller to be automated.

[0017] The controller may be electronically connected (e.g. via wired connection) to only the one or more gas composition sensors within the valve assembly (i.e. not to any gas composition sensors located outside the valve assembly). The controller may be electronically connected (e.g. via wired connection) to only the actuator within the valve assembly (i.e. not to any actuators located outside the valve assembly). In this way, there is no requirement for the valve assembly and / or the controller therein to communicate with other units outside the valve assembly within a larger system (e.g. the valve assembly is not part of a communication network that allows it and / or the controller to receive user inputs remotely via the network) and the valve assembly can be provided as a stand-alone, independent device. This allows the valve assembly to be simplified and thus made more robust (e.g. by reducing the number of possible points of failure).

[0018] The step of the controller controlling the actuator based on the second measurement may be conducted by the controller controlling the actuator based solely on the second measurement (i.e. without considering any other measurements). Advantageously, such a method, and the valve assembly required to execute such a method, is simple and robust.

[0019] As used herein, an ‘amount’ of the first gaseous compound in the landfill gas may be taken as a proportion (i.e. a percentage or fraction) of the first gaseous compound in the gas or a partial pressure of the first gaseous compound in the gas.

[0020] The human operator may obtain the first measurement using the first gas composition sensor. This is convenient in allowing the operator to make use of the first gas composition sensor that is already present, rather than further instrumentation. Alternatively, the human operator may obtain the first measurement using a portable monitoring instrument that is separate to the valve assembly. The portable monitoring instrument may determine the amount of one or more of oxygen, methane, carbon dioxide, nitrogen or hydrogen sulphide in the landfill gas.

[0021] The valve assembly may comprise a physical user interface configured to receive user inputs from the human operator. In this way, the human operator is able to input data into the valve assembly (e.g. for setting the controller) by direct physical interaction with the valve assembly; thus, there is no requirement for the valve assembly to communicate with other units within a larger system (e.g. the valve assembly is not part of a communication network that allows it to receive user inputs remotely via the network) and the valve assembly can be provided as a stand-alone, independent device. By way of example, the physical user interface may comprise one or more of: one or more buttons, a touchscreen, one or more dials, one or more switches, or one or more levers.

[0022] Where the valve assembly comprises a physical user interface, the step of setting the initial valve position of the valve may comprise the human operator inputting said initial valve position into the user interface as a user input. Accordingly, the initial valve position can be set by the human operator inputting data directly into the valve assembly by direct physical interaction with the valve assembly. Having received the initial valve position as a user input, the controller may actuate the valve position to the initial valve position using the actuator. Thus, the initial valve position is taken up by the valve following input of the initial valve position by the user, thereby providing the desired valve position to control the flowrate out of the gas outlet.

[0023] Where the valve assembly comprises a physical user interface and the first measurement is obtained by the human operator using the first gas composition sensor, the first measurement may be communicated to the human operator via the user interface (e.g. via a dial or gauge, or on a screen).

[0024] The first gas composition sensor may be a semiconductor gas sensor (e.g. a metal-oxide-semiconductor sensor), an electrochemical gas sensor (e.g. a galvanic gas sensor, a voltaic gas sensor, or an electrolytic gas sensor), an optical gas sensor (e.g. non-diffuse infrared gas sensor), or a pellistor bead gas sensor.

[0025] The first gas composition sensor may be configured as an in-line sensor. That is, the sensor may be positioned in the valve assembly such that is in series with the valve (i.e. positioned along a main flow path through the gas outlet). In this way, the method does not require a gas sampling step to determine the measurement of the amount of the first gaseous compound in the landfill gas (i.e. a sample gas does not need to be drawn out of the gas outlet for analysis), simplifying the method and reducing time delay between initiating obtaining a measurement and controlling the actuator, and the valve assembly does not require sampling equipment (e.g. a sample line and additional valves thereon, a sampling pump etc.), which allows the valve assembly to be simplified and thus made more robust (e.g. by reducing the number of possible points of failure). The first gas composition sensor is preferably disposed upstream of the valve along the gas outlet. In this way, a representative measurement of the gas from the landfill can be obtained using the first gas composition sensor The step of controlling the actuator based on the second measurement may comprise: comparing the second measurement and a pre-set first gaseous compound composition; and controlling the actuator to change the valve position by a pre-set increment when the second measurement differs from the pre-set first gaseous compound composition. Advantageously, this provides a simple control system to implement with the controller and only requires two input values (the pre-set first gaseous compound composition and the pre-set increment) to define the control system.

[0026] The pre-set first gaseous compound composition may be a point value relating to the amount of the first gaseous compound in the gas, e.g. a percentage of the first gaseous compound in the gas or a point value of the partial pressure of the first gaseous compound in the gas. Alternatively, the pre-set first gaseous compound composition may be a range of values relating to the amount of the first gaseous compound in the gas, e.g. a percentage range of the first gaseous compound in the gas or a range of partial pressures of the first gaseous compound in the gas. Where the pre-set first gaseous compound composition is a point value, the actuator may be configured to change the valve position by a pre-set increment (only) when the second measurement differs from the pre-set first gaseous compound composition by more than a first threshold, e.g. where the difference in magnitude between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold value, or where the percentage difference between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold percentage. Beneficially, this can avoid the control system ‘hunting’ for the pre-set first gaseous compound composition i.e. repeatedly actuating the valve to change the valve position by a small amount when the second measurement is very close to, but not exactly equal to, the point value of the pre-set first gaseous compound composition. Preventing this ‘hunting’ behaviour is advantageous in reducing the power consumption of the valve assembly by increasing the duration of time between the controller changing the valve position using the actuator.

[0027] The method may further comprise a step of the human operator inputting the pre-set first gaseous compound composition and / or the pre-set increment into the controller, for example, using the physical user interface (if present). In this way, the control exerted by the controller on the valve position in order to control the flowrate of landfill gas out of the gas outlet reflects the human operator’s understanding of the behaviour and characteristics of the landfill / well(s) that the gas outlet is receiving landfill gas from.

[0028] The valve assembly may comprise a single (i.e. only one) gas composition sensor (i.e. the first gas composition sensor may be the only gas composition sensor within the valve assembly). By way of example, the valve assembly may comprise an oxygen sensor as the single, first gas composition sensor and may not comprise any other gas composition sensors. The valve assembly being configured in this way allows the valve assembly to be simplified and thus made more robust (e.g. by reducing the number of possible points of failure). Moreover, the step of controlling the actuator is made simpler, as the controller only has to consider the measurement of a single gaseous compound. The first gaseous compound being oxygen is advantageous in most directly and practically reflecting the dilution rate of the landfill gas compared to the other aforementioned gaseous compounds. The dilution rate of the landfill gas can be understood as the flowrate or flux at which ambient air is flowing into the landfill. Oxygen makes up a large proportion of ambient air but is not produced in the landfill and should only be present in small quantities in the landfill gas.

[0029] The valve assembly may comprise a single (i.e. only one) valve and / or a single (i.e. only one) actuator configured to change the valve position of a valve. That is, the valve assembly may not comprise a plurality of valves and / or actuators. Accordingly, it can be understood that the valve assembly is a standalone unit for controlling the flow of landfill gas out of a single gas outlet to which the valve assembly is mounted, and does not form part of a larger, interconnected, system for interrelated control of the flow of landfill gas out of a plurality of gas outlet. The valve assembly being configured in this way allows the valve assembly to be simplified and thus made more robust (e.g. by reducing the number of possible points of failure). Moreover, the step of controlling the actuator is made simpler, as only the position of a single valve can be changed by the valve assembly.

[0030] Alternatively, the valve assembly may further comprise a second gas composition sensor, the second gas composition sensor being configured to measure the amount of a second gaseous compound in the landfill gas. Beneficially, this can facilitate the amount of a second gaseous compound in the landfill gas being monitored by the controller in addition to the amount of the first gaseous compound in the landfill gas being monitored by the controller. The second gaseous compound may be, for example, oxygen, nitrogen, methane or hydrogen sulphide. The second gaseous compound being hydrogen sulphide may be beneficial in monitoring the production and emission of hydrogen sulphide by the landfill, hydrogen sulphide production and emission being undesirable due to the harmful environmental and health impacts of exposure to high levels of hydrogen sulphide. The valve assembly may comprise one or more further gas compositions sensors, each second configured to measure the amount of a different gaseous compound in the landfill gas.

[0031] As used herein, an ‘amount’ of the second gaseous compound in the landfill gas may be taken as a proportion (i.e. a percentage or fraction) of the second gaseous compound in the gas or a partial pressure of the second gaseous compound in the gas.

[0032] The second gas composition sensor may be a semiconductor gas sensor (e.g. a metal-oxide- semiconductor sensor), an electrochemical gas sensor (e.g. a galvanic gas sensor, a voltaic gas sensor, or an electrolytic gas sensor), an optical gas sensor (e.g. non-diffuse infrared gas sensor), or a pellistor bead gas sensor.

[0033] The second gas composition sensor may be configured as an in-line sensor. That is, the sensor may be positioned in the valve assembly such that is in series with the valve (i.e. positioned along a main flow path through the gas outlet). In this way, the method does not require a gas sampling step to determine the measurement of the amount of the second gaseous compound in the landfill gas (i.e. a sample gas does not need to be drawn out of the gas outlet for analysis), simplifying the method and reducing time delay between initiating obtaining a measurement and controlling the actuator, and the valve assembly does not require sampling equipment (e.g. a sample line and additional valves thereon, a sampling pump etc.), which allows the valve assembly to be simplified and thus made more robust (e.g. by reducing the number of possible points of failure). The second gas composition sensor may be disposed upstream of, or downstream of, the valve along the gas outlet.

[0034] Where the valve assembly comprises the second gas composition sensor, the method may further comprise the steps of: the controller making a first determination as to whether the valve requires actuation based on the amount of the first gaseous compound in the landfill gas; and, subsequently, where the first determination is that the valve requires actuation to change the valve position, the controller controlling the actuator based on said first determination; and where the first determination is that the valve does not require actuation to change the valve position, the controller: obtaining a measurement of the amount of the second gaseous compound in the landfill gas using the second gas composition sensor; making a second determination as to whether the valve requires actuation based on the measurement of the amount of the second gaseous compound in the landfill gas; and controlling the actuator based on said second determination. Advantageously, by the method comprising these steps when the second gas composition sensor is present in the valve assembly, the method provides a simple control system that can utilise both gas composition sensors and also avoids conflict between the desired control based on the measurement by the first gas composition sensor and the desired control based on the measurement by the second gas composition sensor, since the second gas composition sensor measurement is only considered where the first gas composition sensor measurement indicates that the valve position does not need to change based on the amount of the first gaseous compound in the gas. Furthermore, the method comprising these steps provides a control system in which controlling the amount of the first gaseous compound in the landfill gas is prioritised over controlling the amount of the second gaseous compound in the landfill gas.

[0035] The step of controlling the actuator based on the second determination (i.e. the determination of whether the valve requires actuation based on the measurement of the amount of the second gaseous compound in the landfill gas) may comprise: comparing the measurement of the amount of the second gaseous compound in the landfill gas and a pre-set second gaseous compound composition; and controlling the actuator to change the valve position by a pre-set increment when the measurement of the amount of the second gaseous compound in the landfill gas differs from the pre-set second gaseous compound composition. Advantageously, this provides a simple control system to implement with the controller and only requires two input values (the pre-set second gaseous compound composition and the pre-set increment) to define the control system for the second gaseous compound. This (second) pre-set increment by which the valve position is changed based on the second determination may be the same as, or different to, the (first) pre-set increment by which the valve position is changed when the first gaseous compound composition differs from the pre-set first gaseous compound composition. Having this second pre-set increment differ from the first pre-set increment allows the controller to have different sensitivities to changes in the amounts of first and second gaseous compounds in the landfill gas.

[0036] The pre-set second gaseous compound composition may be a point value relating to the amount of the second gaseous compound in the gas, e.g. a percentage of the second gaseous compound in the gas or a point value of the partial pressure of the second gaseous compound in the gas. Alternatively, the preset second gaseous compound composition may be a range of values relating to the amount of the second gaseous compound in the gas, e.g. a percentage range of the second gaseous compound in the gas or a range of partial pressures of the second gaseous compound in the gas. Where the pre-set second gaseous compound composition is a point value, the actuator may be configured to change the valve position by a pre-set increment (only) when the measurement of the amount of the second gaseous compound in the landfill gas differs from the pre-set second gaseous compound composition by more than a second threshold, e.g. where the difference in magnitude between the pre-set second gaseous compound composition and the measurement of the amount of the second gaseous compound in the landfill gas is larger than a second threshold value, or where the percentage difference between the preset first gaseous compound composition and the measurement of the amount of the second gaseous compound in the landfill gas is larger than a second threshold percentage. Beneficially, this can avoid the control system ‘hunting’ for the pre-set second gaseous compound composition i.e. repeatedly actuating the valve to change the valve position by a small amount when the measurement of the amount of the second gaseous compound in the landfill gas is very close to, but not exactly equal to, the point value of the pre-set second gaseous compound composition. Preventing this ‘hunting’ behaviour is advantageous in reducing the power consumption of the valve assembly by increasing the duration of time between the controller changing the valve position using the actuator.

[0037] The method may further comprise a step of the human operator inputting the pre-set second gaseous compound composition and / or the (second) pre-set increment into the controller, for example, using the physical user interface (if present). In this way, the control exerted by the controller on the valve position in order to control the flowrate of landfill gas out of the gas outlet may reflect the human operator’s understanding of the behaviour and characteristics of the landfill / well(s) that the gas outlet is receiving landfill gas from.

[0038] The step of the controller obtaining the second measurement and the controller controlling the actuator based on the second measurement may be repeatedly conducted at a pre-set frequency.

[0039] Advantageously, this allows the controller to control the flowrate of landfill gas out of the gas outlet over an extended period of time over which the composition of the landfill gas is liable to change without further human intervention, thereby allowing the composition of the landfill gas out of the gas outlet to be maintained closer to the desired specification than if only less frequent manual monitoring and control were conducted. The pre-set frequency may be, for example, less than once an hour, less than once every two hours, less than once every 6 hours, less than once every 12 hours, less than once every 24 hours, less than once every 48 hours, less than once every week, less than once every fortnight, or less than once a month. The pre-set frequency may be, for example, greater than once an hour, greater than once every two hours, greater than once every 6 hours, greater than once every 12 hours, greater than once every 24 hours, greater than once every 48 hours, greater than once every week, greater than once every fortnight, or greater than once a month. It can be appreciated that the pre-set frequency at which these steps are conducted balances the tightness of the control provided by the method (i.e. how close the landfill gas stays to the desired composition e.g. the pre-set first gaseous compound composition) and the power consumption by the valve assembly, with a higher pre-set frequency resulting in tighter control but a higher power consumption (due to the increased processing by the controller and the greater frequency with which the actuator changes the valve position), and vice versa for a lower pre-set frequency. The method may further comprise a step of the human operator inputting the pre-set frequency into the user interface as a user input. In this way, the pre-set frequency reflects the human operator’s understanding of the variability of the landfill gas composition from the landfill / well(s) that the gas outlet is receiving gas from. By way of example, where the human operator understands that the composition of landfill gas from a given well does not vary by large amounts, then the human operator may input a lower pre-set frequency for the valve assembly receiving gas from that well in order to reduce the power consumption of the valve assembly with only a low risk of poor control of the landfill gas composition.

[0040] In a second aspect there is provided a valve assembly for controlling the flowrate of landfill gas out of a gas outlet, the valve assembly comprising: a valve, the valve being mountable to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; a controller configured to control the actuator based on the amount of the first gaseous compound in the landfill gas; and a physical user interface configured to receive one or more user inputs specifying the control of the actuator by the controller from a human operator.

[0041] Advantageously, such a valve assembly provides means for controlling the flowrate of landfill gas out of a gas outlet that is able to exert automatic control over the valve position based on the landfill gas composition (i.e. no human operator input is required after the control of the actuator by the valve has been initially specified), but that does not require the valve assembly to communicate with other units within a larger system (e.g. the valve assembly is not part of a communication network that allows it to receive user inputs remotely via that network). By facilitating the human operator inputting data specifying the control directly into the valve assembly by direct physical interaction with the valve assembly, the valve assembly can be provided as a stand-alone, independent device. By way of example, the physical user interface may comprise one or more of: one or more buttons, a touchscreen, one or more dials, one or more switches, or one or more levers.

[0042] Any one or more of the optional features set out with respect to the first aspect may be applied to the valve assembly according to the second aspect, except where such a combination is clearly impermissible or expressly avoided. Similarly, any one or more of the optional features set out with respect to the second aspect may be applied to the method according to the first aspect, except where such a combination is clearly impermissible or expressly avoided.

[0043] The valve assembly may not be connected to a network or other external control system.

[0044] Advantageously, this provides a valve assembly that is robust, standalone, and consumes less power than if it was connected to a network or other external control system. The valve assembly may comprise only the first gas composition sensor and no other sensors.

[0045] Advantageously, such a valve assembly is simple, robust and cost-effective, whilst still allowing the flowrate of landfill gas out of the gas outlet to be controlled.

[0046] The valve, gas composition sensor, actuator and controller of the valve assembly may all be physically connected, for example, they may be provided within a single unit. Advantageously, this provides a valve assembly that is easy to install on a gas outlet.

[0047] The valve may be a ball valve, a gate valve or a butterfly valve. The valve may have one or more intermediate positions between a maximum flow area (i.e. an open valve) and a minimum flow area (i.e. a closed valve), thereby allowing the flowrate through the valve to be regulated.

[0048] The user interface of the valve assembly may be configured to receive an initial valve position as a user input from the human operator. Accordingly, the initial valve position can be set by the human operator inputting data directly into the valve assembly by direct physical interaction with the valve assembly. Having received the initial valve position as a user input, the controller may actuate the valve position to the initial valve position using the actuator. Thus, the initial valve position is taken up by the valve following input of the initial valve position by the user, thereby providing the desired valve position to control the flowrate out of the gas outlet.

[0049] The valve assembly may be such that: the controller is configured to control the actuator based on a measurement of the amount of the first gaseous compound in the landfill gas using the first composition sensor by: comparing said measurement and a pre-set first gaseous compound composition; and controlling the actuator to change the valve position by a pre-set increment when the second measurement differs from the pre-set first gaseous compound composition; and the user interface is configured to receive the pre-set first gaseous compound composition and / or the pre-set increment as user inputs from the human operator. Advantageously, this provides a simple control system to implement with the controller and only requires two input values (the pre-set first gaseous compound composition and the pre-set increment) to define the control system. Moreover, by the user interface being configured to receive the pre-set first gaseous compound composition and / or the pre-set increment as user inputs from the human operator, the control exerted by the controller on the valve position in order to control the flowrate of landfill gas out of the gas outlet reflects the human operator’s understanding of the behaviour and characteristics of the landfill / well(s) that the gas outlet is receiving landfill gas from.

[0050] The pre-set first gaseous compound composition may be a point value relating to the amount of the first gaseous compound in the gas, e.g. a percentage of the first gaseous compound in the gas or a point value of the partial pressure of the first gaseous compound in the gas. Alternatively, the pre-set first gaseous compound composition may be a range of values relating to the amount of the first gaseous compound in the gas, e.g. a percentage range of the first gaseous compound in the gas or a range of partial pressures of the first gaseous compound in the gas. Where the pre-set first gaseous compound composition is a point value, the actuator may be configured to change the valve position by a pre-set increment (only) when the second measurement differs from the pre-set first gaseous compound composition by more than a first threshold, e.g. where the difference in magnitude between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold value, or where the percentage difference between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold percentage. Beneficially, this can avoid the control system ‘hunting’ for the pre-set first gaseous compound composition i.e. repeatedly actuating the valve to change the valve position by a small amount when the second measurement is very close to, but not exactly equal to, the point value of the pre-set first gaseous compound composition, because the controller will not control the actuator to change the valve position in such a scenario. Preventing this hunting’ behaviour is advantageous in reducing the power consumption of the valve assembly by increasing the duration of time between the controller changing the valve position using the actuator.

[0051] The controller may be configured to measure the amount of the first gaseous compound in the landfill gas using the first gas composition sensor at a pre-set frequency. The controller may be further configured to control the actuator based on this measurement of the amount of the first gaseous compound in the landfill gas following the measurement (i.e. at the same frequency). Advantageously, this allows the controller to control the flowrate of landfill gas out of the gas outlet over an extended period of time over which the composition of the landfill gas is liable to change without further human intervention, thereby allowing the composition of the landfill gas out of the gas outlet to be maintained closer to the desired specification than if only less frequent manual monitoring and control were conducted. The pre-set frequency may be, for example, less than once an hour, less than once every two hours, less than once every 6 hours, less than once every 12 hours, less than once every 24 hours, less than once every 48 hours, less than once every week, less than once every fortnight, or less than once a month. The pre-set frequency may be, for example, greater than once an hour, greater than once every two hours, greater than once every 6 hours, greater than once every 12 hours, greater than once every 24 hours, greater than once every 48 hours, greater than once every week, greater than once every fortnight, or greater than once a month. It can be appreciated that the pre-set frequency at which these steps are conducted balances the tightness of the control provided by the method (i.e. how close the landfill gas stays to the desired composition (e.g. the pre-set first gaseous compound composition) and the power consumption by the valve assembly, with a higher pre-set frequency resulting in tighter control but a higher power consumption (due to the increased processing by the controller and the greater frequency with which the actuator changes the valve position), and vice versa for a lower pre-set frequency.

[0052] The user interface may be configured to receive the pre-set frequency as a user input from the human operator. In this way, the pre-set frequency reflects the human operator’s understanding of the variability of the landfill gas composition from the landfill / well(s) that the gas outlet is receiving gas from. By way of example, where the human operator understands that the composition of landfill gas from a given well does not vary by large amounts, then the human operator may input a lower pre-set frequency for the valve assembly receiving gas from that well in order to reduce the power consumption of the valve assembly with only a low risk of poor control of the landfill gas composition.

[0053] The valve assembly may further comprise one or more of: an energy storage unit, a solar panel, and a wind turbine, and the energy storage unit, solar panel and / or wind turbine may be configured to provide power to the first gas composition sensor, the controller, the user interface and / or the actuator. Advantageously, this facilitates the valve assembly in being a robust and standalone means for controlling the flowrate of landfill gas out of a gas outlet, because such a valve assembly is not reliant on connection to an external power source (e g. mains electricity). It is particularly beneficial for the valve assembly to comprise an energy storage unit and one or more of a solar panel and a wind turbine, such that energy can be stored in the energy storage unit for use by the first gas composition sensor, the controller, the user interface, and / or the actuator when the solar panel and / or wind turbine are not generating power.

[0054] The valve assembly may further comprise a second gas composition sensor, the second gas composition sensor configured to measure the amount of a second gaseous compound in the landfill gas. The second gaseous compound may be different from the first gaseous compound. Beneficially, this can facilitate the amount of a second gaseous compound in the landfill gas being monitored by the controller in addition to the amount of the first gaseous compound in the landfill gas being monitored by the controller. The second gaseous compound may be, for example, oxygen, nitrogen, methane or hydrogen sulphide. The second gaseous compound being hydrogen sulphide may be beneficial in monitoring the production and emission of hydrogen sulphide by the landfill, hydrogen sulphide production and emission being undesirable due to the harmful environmental and health impacts of exposure to high levels of hydrogen sulphide. The valve assembly may comprise one of more further gas compositions sensors, each second configured to measure the amount of a different gaseous compound in the landfill gas. Where the valve assembly comprises one or more further gas composition sensors and an energy storage unit, solar panel and / or wind turbine, the power from the energy storage unit, solar panel and / or wind turbine may also be provided to the further gas composition sensor(s).

[0055] Where the valve assembly comprises two gas composition sensors, the controller may be configured to control the actuator based on the second measurement of the amount of the first gaseous compound in the landfill gas and a measurement of the amount of the second gaseous compound in the landfill gas. For example, the controller may be configured to make a first determination as to whether the valve requires actuation based on the amount of the first gaseous compound in the landfill gas and may be configured such that: where the first determination is that the valve requires actuation to change the valve position, the controller is configured to control the actuator based on said first determination; and, where the first determination is that the valve does not require actuation to change the valve position, the controller is configured to make a second determination as to whether the valve requires actuation based on the amount of the second gaseous compound in the landfill gas and to control the actuator based on said second determination. Advantageously, by the controller being configured in this manner when the second gas composition sensor is present in the valve assembly, the controller has a simple control system that can utilise both gas composition sensors and also avoids conflict between the desired control based on the measurement by the first gas composition sensor and the desired control based on the measurement by the second gas composition sensor, since the second gas composition sensor measurement is only considered where the first gas composition sensor measurement indicates that the valve position does not need to change based on the amount of the first gaseous compound in the gas. Furthermore, such a configuration provides a controller that is configured to prioritise controlling the amount of the first gaseous compound in the landfill gas over controlling the amount of the second gaseous compound in the landfill gas.

[0056] The valve assembly may comprise only the first and second gas composition sensors and no other sensors. Advantageously, such a valve assembly is simple, robust and cost-effective, whilst still allowing the flowrate of landfill gas out of the gas outlet to be controlled.

[0057] The controller may be configured to control the actuator based on the second measurement and a measurement of the amount of the second gaseous compound in the landfill gas by the controller controlling the actuator based solely on the second measurement and the measurement of the amount of the second gaseous compound in the landfill gas (i.e. without considering any other measurements). Advantageously, such a method, and the valve assembly required to execute such a method, is simple and robust.

[0058] The valve within the valve assembly may comprise a gas inlet side and a gas outlet side with a flow control element interposed therebetween, and the first gas composition sensor may be provided on the valve on the gas inlet side of the flow control element. Advantageously, this aids the first gas composition sensor in providing a representative measurement of the amount of the first gaseous compound the landfill gas when the valve is closed. Any further gas composition sensors within the valve assembly may be similarly positioned.

[0059] In a third aspect there is provided a landfill comprising a well; a gas outlet connected to the well; and a valve assembly according to the second aspect mounted on the gas outlet. Accordingly a landfill is provided that has a means for controlling the flowrate of landfill gas out of the gas outlet that is able to exert automatic control over the valve position based on the landfill gas composition (i.e. no human operator input is required after the control of the actuator by the valve has been initially specified), but that does not require the valve assembly to communicate with other units within a larger system (e.g. the valve assembly is not part of a communication network that allows it to receive user inputs remotely via the network). By facilitating the human operator inputting data specifying the control directly into the valve assembly by direct physical interaction with the valve assembly, the valve assembly can be provided as a stand-alone, independent device.

[0060] Any one or more of the optional features set out with respect to the first and second aspects may be applied to the landfill according to the third aspect, except where such a combination is clearly impermissible or expressly avoided.

[0061] The landfill may comprise a plurality of gas outlets and a plurality of valve assemblies according to the second aspect, each valve assembly mounted on a respective gas outlet; and each valve assembly may be configured to control the flowrate of landfill gas out of its respective gas outlet independently of the control exerted by other valve assemblies within the plurality of valve assemblies on their respective gas outlets. In this way, a landfill comprising means for controlling the flowrate of gas out of plural wells that does not require the valve assembly controlling each well to be in communication with the other valve assemblies is provided. This allows each valve assembly to be made a simple, stand-alone, independent device and also means each valve assembly consumes less power than if it was connected to a network or other external control system to put it in communication with the other valve assemblies.

[0062] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0063] Summary of the Figures

[0064] Methods of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly and said valve assemblies will now be discussed with reference to the accompanying figures, in which:

[0065] Figure 1 is a flowchart for a method, according to an embodiment of the invention, of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly;

[0066] Figure 2 is a flowchart providing a variation of the method in Figure 1 ;

[0067] Figure 3 is a flowchart for a step of controlling an actuator in a valve assembly;

[0068] Figure 4 is a schematic of a first valve assembly according to an embodiment of the invention;

[0069] Figure 5 is a schematic of a second valve assembly according to an embodiment of the invention; and

[0070] Figures 6A - 6C are engineering drawings of a valve assembly according to an embodiment of the invention.

[0071] Detailed Description of the Invention

[0072] Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0073] Figure 1 is a flowchart for a method of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly mounted thereon. The gas outlet in a landfill may be, for example, a wellhead or a gas manifold that is connected to a well of the landfill. The valve assembly used in the method in Figure 1 comprises at least: a valve, the valve being mounted to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; and a controller.

[0074] Firstly, Step S100 comprises a human operator obtaining a first measurement of the amount of the first gaseous compound in the landfill gas. This is typically conducted using a portable monitoring instrument that is separate to the valve assembly. The portable monitoring instrument may determine the amount of one or more of oxygen, methane, carbon dioxide, nitrogen or hydrogen sulphide in the landfill gas. However, alternatively the operator may use another sensor that is not part of the valve assembly.

[0075] Based on the first measurement at step S100, at step S200 the human operator then assesses a dilution rate of the landfill gas. The dilution rate of the landfill gas can be understood as the flowrate or flux at which ambient air is flowing into the landfill, and thus it is useful for the first gaseous compound to be oxygen, since this makes up a large proportion of ambient air, but is not produced in the landfill and should only be present in small quantities in the landfill gas. By way of example, it is typically desired for the proportion of oxygen in landfill gas to be less than 3%. However, it is also possible for the first gaseous compound to be a compound other than oxygen, for example methane, carbon dioxide or nitrogen. Based on comparison of the measured amount of the first gaseous compound against one or more of historical record of the amount of the first gaseous compound in the landfill gas from the gas outlet, amounts of the first gaseous compound at one or more other gas outlets of the landfill, a landfill gas specification, and / or the human operator’s understanding of the behaviour and / or sensitivity of the landfill, the human operator can assess the dilution rate (i.e. whether too much ambient air is being drawn into the landfill, or whether there is not too much ambient air being drawn in, and the landfill is being under extracted, leading to landfill gas leaks).

[0076] Subsequently, at step S300, the human operator sets an initial valve position (i.e. a flow area through the valve) based on their assessment of the dilution rate at step S200. This sets an initial flowrate of landfill gas out of the gas outlet before the controller within the valve assembly takes over control of the flowrate of landfill gas.

[0077] Subsequently to setting the initial valve position, step S400 of the method marks the commencement of automatic control of the valve position by the controller. At step S400, the controller obtains a measurement of the amount of the first gaseous compound in the landfill gas. This measurement makes use of the first gas composition sensor, which is in communication with the controller.

[0078] At step S500, the controller controls the actuator based on this second measurement of the amount of the first gaseous compound in the landfill gas. Depending on the amount of the first gaseous compound in the landfill gas according to the second measurement and the valve position at the time the second measurement is taken, the controller may control the actuator to maintain the valve position (i.e. the control exerted at step S500 may result in the actuator not changing the flow area through the valve), for example where the amount of the first gaseous compound in the landfill gas matches a specification within the controller. Alternatively, the controller may control the actuator to change the valve position (i.e. the control exerted at step S500 may result in the actuator changing the flow area through the valve), for example where the amount of the first gaseous compound in the landfill gas does not match a specification within the controller.

[0079] Figure 2 is a flowchart providing a variation of the method in Figure 1. In particular, Figure 2 contains additional detail on how steps S300 and S500 in Figure 1 may be implemented in a specific embodiment of the method in Figure 1 , and also includes additional steps S600, S700 and S800. Where steps in Figure 2 are the same as those in Figure 1 , i.e. steps S100, S200, and S400, a description of the steps is not repeated in relation to Figure 2, and reference may be made back to the preceding description of these steps in relation to Figure 1 .

[0080] Firstly, in Figure 2, step S300 comprises two sub-steps S310 and S320. The method in Figure 2 is for use with a valve assembly comprising a physical user interface (III) (e.g. one or more buttons, a touchscreen, or one or more dials) that the human operator can interact with to provide user inputs into the controller. Accordingly, in the method of Figure 2, the step of setting the initial valve position involves a first sub step S310 of the human operator inputting an initial valve position based on their assessment of the dilution rate into the Ul. Then, at step S320, the controller having received the initial valve position input from the Ul, the controller actuates the valve position to the initial valve position using the actuator. Thus, the initial valve position is taken up by the valve following input of the initial valve position by the user, providing the desired valve position to control the flowrate out of the gas outlet.

[0081] Secondly, in Figure 2, step S500 of the controller controlling the actuator based on the second measurement of the amount of the first gaseous compound in the landfill gas comprises three sub-steps S510 - S530. At sub-step S510, the second measurement is compared to a pre-set first gaseous compound composition. By way of example, the pre-set first gaseous compound composition may be a point value relating to the amount of the first gaseous compound in the gas, e.g. a percentage of the first gaseous compound in the gas that it is desired to maintain, or may be a range of values relating to the amount of the first gaseous compound in the gas e.g. a percentage range of the first gaseous compound in the gas that it is desired for the landfill gas to fall within. Where the first gaseous compound is, for example, oxygen, then it would be typical forthe pre-set first gaseous compound composition to be a specification that the percentage of the oxygen in the landfill gas should be less than or equal to 3% (i.e. a percentage range from 0% to 3%). However, it can be appreciated that an oxygen percentage higher than 3%, for example, 4% or 5% may be tolerated in some instances. As shown in Figure 2, the method may further comprise step S700 of inputting the pre-set first gaseous compound composition used in substep S510 into the controller. As with sub-step S310 of inputting the initial valve position, step S800 may be conducted by the human operator inputting the pre-set first gaseous compound composition into the controller via the user interface. By allowing the human operator to input the pre-set first gaseous compound composition, the control exerted by the controller on the valve position in order to control the flowrate of landfill gas out of the gas outlet reflects the human operator’s understanding of the behaviour and characteristics of the landfill / well(s) that the gas outlet is receiving landfill gas from.

[0082] At sub-step S520 in Figure 2, it is determined whether the second measurement differs from the pre-set first gaseous compound composition. Where the pre-set first gaseous compound composition is a range of values, then sub-step S520 involves determining whether the second measurement falls within that range. Where the pre-set first gaseous compound composition is a point value, then sub-step S520 may involve determining whether the second measurement differs from the pre-set first gaseous compound composition by more than a first threshold, e g. where the difference in magnitude between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold value, or where the percentage difference between the pre-set first gaseous compound composition and the second measurement is larger than a first threshold percentage. Making use of this first threshold where the pre-set first gaseous compound composition is a point value is useful in avoiding the control system hunting’ for the pre-set first gaseous compound composition by repeatedly actuating the valve by small amounts when the second measurement is very close to, but not exactly equal to, the point value of the pre-set first gaseous compound composition.

[0083] Where the determination at sub-step S520 is negative (i.e. where the second measurement differs from the pre-set first gaseous compound composition), then the method in Figure 2 progresses to step S530, where the controller controls the actuator to change the valve position by a pre-set increment. Continuing with the example discussed in relation to sub-step S510, if the determination at sub-step S520 is that the percentage of oxygen in the landfill gas from the second measurement is greater than 3%, then at substep S530 the controller will control the actuator to close the valve position by a pre-set amount, e.g. by 10% of the maximum flow area through the valve. It can be appreciated that step S530 may also involve changing the valve position such as to increase the flow area through the valve, e.g. where the second measurement is lower than the pre-set first gaseous compound composition.

[0084] As shown in Figure 2, the method may further comprise step S800 of inputting the pre-set increment used in sub-step S530 into the controller. As with sub-step S310 of inputting the initial valve position, step S800 may be conducted by the human operator inputting the pre-set first gaseous compound composition into the controller via the user interface. By allowing the human operator to input the pre-set increment, the control exerted by the controller on the valve position in order to control the flowrate of landfill gas out of the gas outlet reflects the human operator’s understanding of the behaviour and characteristics of the landfill / well(s) that the gas outlet is receiving landfill gas from.

[0085] Where the determination at sub-step S520 is positive (i.e. where the second measurement corresponds to the pre-set first gaseous compound composition), then the method in Figure 2 progresses to step S600, where there is a delay until the method then returns to step S400 to obtain another measurement of the amount of the first gaseous compound in the landfill gas. The method also progresses to step S600 following sub-step S530.

[0086] By returning back to step S400, the method provides a control scheme whereby the controller repeatedly measures the amount of the first gaseous compound in the landfill gas and controls the actuator based on the latest measurement (i.e. changes the valve position when necessary, or maintains the valve position).

[0087] However, the composition of the landfill gas is expected to change slowly in comparison to the time required to conduct steps S400 and S500 of the method. Accordingly, the delay at step S600 is implemented to control the frequency with which steps S400 and S500 are conducted. The method may be such that steps S500 and S600 are to be conducted at a pre-set frequency, typically between once every 6 hours and once a week, and accordingly, step S600 may delay the return to step S400 until the time period corresponding to that pre-set frequency (e.g. 6 hours to a week) has expired since steps S400 and S500 were last conducted. The pre-set frequency at which these steps are conducted balances the tightness of the control provided by the method (i.e. how close the landfill gas stays to the desired composition, e.g. the pre-set first gaseous compound composition) and the power consumption by the valve assembly, with a higher pre-set frequency resulting in tighter control but a higher power consumption (due to the increased processing by the controller and the greater frequency with which the actuator changes the valve position) and vice versa for a lower pre-set frequency. Similarly to steps S700 and S800, the method may also comprise the human operator inputting the pre-set frequency into the user interface of the valve assembly as a user input (not illustrated in Figure 2).

[0088] It can be appreciated that the modifications to steps S300 and S500 illustrated in Figure 2 can be made to the method in Figure 1 independently of each other. Similarly, step S600 in Figure 2 may be implemented into the method in Figure 1 independently of the modifications to steps S300 and S500.

[0089] Figure 3 is a flowchart for a method step S500A that is an alternative to step S500 of Figures 1 and 2. Step S500A is for use with a valve assembly further comprising a second gas composition sensor in addition to the first gas composition sensor, the second gas composition sensor being configured to measure the amount of a second gaseous compound in the landfill gas and being in communication with the controller. The second gaseous compound is different to the first gaseous compound, e.g. where the first gaseous compound is oxygen, the second gaseous compound may be hydrogen sulphide or methane. Having two gas composition sensors is useful where tighter control of the landfill gas composition is desired, however, a way of controlling the valve position based on two different measurements is then useful.

[0090] Accordingly, at a high level, step S500A involves making a first determination as to how to control the valve position based on the measurement of the amount of a first gaseous compound in the landfill gas and, where the first determination is that the valve position does not need altering, subsequently making a second determination as to how to control the valve position based on the measurement of the amount of a second gaseous compound in the landfill gas.

[0091] More specifically, step S500A firstly comprises sub-step S510A, where a first determination as to whether the valve requires actuation based on the second measurement obtained at step S400 (i.e. the amount of the first gaseous compound in the landfill gas). This determination may be made, for example, in the same manner as sub-steps S510 and S520 in Figure 2.

[0092] Subsequently, at sub-step S520A, it is checked whether the first determination is that the valve requires actuation to change the valve position. If the check at sub-step S520A is positive (i.e. the valve position should be changed based on the second measurement at step S400), then the method proceeds to sub-step S530A where the controller controls the actuator to change the valve position based on the first determination and then progresses to step S600 without measuring and / or considering the amount of the second gaseous compound in the landfill gas. Sub-step S530A may be conducted in the same manner as sub-step S530 in Figure 2.

[0093] However, if the check at sub-step S520A is negative (i.e. the valve position does not require changing based on the second measurement at step S400), then the method proceeds to sub-step S540A, where the controller obtains a measurement of the amount of the second gaseous compound in the landfill gas using the second gas composition sensor. Having obtained this measurement at sub-step S540A, the controller then makes a second determination at sub-step S550A as to whether the valve requires actuation based on the amount of the second gaseous compound in the landfill gas. This second determination may be made, for example, in the same manner as sub-steps S510 and S520 in Figure 2, but with respect to the second gaseous compound rather than the first gaseous compound.

[0094] Subsequently, at sub-step S560A, it is checked whether the second determination is that the valve requires actuation to change the valve position.

[0095] If the check at sub-step S560A is positive (i.e. the valve position should be changed based on the measurement of the amount of the second gaseous compound in the landfill gas at step S540A), then the method proceeds to sub-step S570A where the controller controls the actuator to change the valve position based on the second determination and knowing that the valve position does not require changing based on the amount of the first gaseous compound in the landfill gas. Sub-step S570A may be conducted in the same manner as sub-step S530 in Figure 2. The pre-set increment by which the valve position is changed by as part of sub-step S570A may be the same as, or different to, the pre-set increment by which the valve position is changed by in sub-step S530; having different pre-set increments can allow the controller to have different sensitivities to changes in the amounts of first and second gaseous compounds in the landfill gas. Subsequently to sub-step S570A, the method proceeds to step S600.

[0096] However, if the check at sub-step S560A is negative (i.e. the valve position does not require changing based on the measurement of the amount of the second gaseous compound in the landfill gas at substep S540A), then the method proceeds to step S600 without changing the valve position.

[0097] Accordingly, the method step S500A provides a method of controlling the flowrate of landfill gas from a gas outlet in which controlling the amount of the first gaseous compound in the landfill gas is prioritised over controlling the amount of the second gaseous compound in the landfill gas.

[0098] Figure 4 is a schematic of a first valve assembly 1 . The methods discussed in relation to Figures 1 and 2 above may make use of the first valve assembly 1 . The first valve assembly 1 comprises a valve 15 disposed on a gas outlet 100 (e.g. a wellhead or manifold) such that the flowrate of landfill gas out of the gas outlet 100 is controlled by the flow area through the valve 15. The valve 15 may be, for example, a ball valve, a gate valve, or a butterfly valve. The direction of flow of landfill gas in Figure 4 is indicated by the thick arrows along the gas outlet 100. The valve assembly 1 further comprises a first gas composition sensor 14, which in the case of the first valve assembly 1 in Figure 4, is disposed on a gas inlet side of the valve 15 along the gas outlet 100 (i.e. as an in-line gas sensor upstream of the valve 15). Accordingly, the first gas composition sensor 14 can measure the amount of the first gaseous compound in the landfill gas upstream of the valve 15. The first gas composition sensor 14 is the only gas composition sensor within the first valve assembly 1 illustrated in Figure 4.

[0099] Both the gas composition sensor 14 and valve 15 are connected to a control unit 10 of the valve assembly 1 , the control unit 10 comprising the controller 11 , the actuator 12 and a physical user interface 13 (e.g. one or more buttons, a touchscreen, one or more dials, one or more switches, or one or more levers). Specifically, the valve 15 is physically connected to the actuator 12, as the actuator 12 is configured to change a valve position of the valve to vary the flow area therethrough. The actuator 12 is in turn also connected to the controller 11 (e.g. a computer-implemented controller), which is configured to control the actuator 12 based on the amount of the first gaseous compound in the landfill gas. Accordingly, the controller 11 is also connected to the first gas composition sensor 14 such that it can receive a measurement of the amount of the first gaseous compound in the landfill gas. The controller 11 is further connected to the user interface 13, thereby allowing the user interface 13 to receive one or more user inputs specifying the control of the actuator 12 by the controller 11 from a human operator and to communicate such user inputs to the controller 11 .

[0100] Figure 5 is a schematic of a second valve assembly 2 that is a modification of the first valve assembly 1 in Figure 4. Where features in the second valve assembly 2 are equivalent to those in the first valve assembly 1 , they are given equivalent reference numbers (e.g. 15 and 25 for the valves in the first and second valve assemblies 1 , 2, respectively), and reference may be made back to the preceding description of these features in relation to Figure 4.

[0101] The second valve assembly 2 firstly differs from that in Figure 4 in that it comprises a second gas composition sensor 24b in addition to the first gas composition sensor 24a. The first and second gas composition sensors 24a-b are configured to measure the amounts of different gaseous compounds in the landfill gas, e.g. the first gas composition sensor 24a may measure the amount of oxygen in the landfill gas, and the second gas composition sensor 24b may measure the amount of hydrogen sulphide in the landfill gas. The first and second gas sensors 24a-b are both configured as in-line gas sensors positioned upstream of the valve 25. Both sensors 24a-b are disposed on the gas inlet side of the valve 25 and are connected to the controller 21 within the control unit 20 such that the controller 21 can receive measurements from the sensors 24a-b and control the actuator 22 accordingly. It can be appreciated that step S500A described in Figure 3 may be used with a valve assembly such as the second valve assembly 2 in Figure 5 in order for measurements from both sensors 24a-b to be used to inform control of the valve 25 using the actuator 22.

[0102] An additional difference between the second valve assembly 2 in Figure 5 and the first valve assembly 1 in Figure 4 is that the second valve assembly 2 further comprises a battery 26 and a solar panel 27. The battery 26 (an example of an energy storage unit) is connected to the control unit 20 and configured to supply electrical energy thereto in order to provide the controller 21 , actuator 22 and user interface 23 with the power required forthem to operate. The solar panel 27 is in turn connected to the battery 26 such that power from the solar panel 27 can be stored in the battery 26. Beneficially, the second valve assembly 2 being provided with a battery 26 allows the valve assembly 2 to be a robust and standalone means for controlling the flowrate of landfill gas out of the gas outlet 200, because it is not reliant on an external power source such as mains electricity in order to be able to function. Whilst it is possible for the valve assembly 2 to comprise a battery 26 and not also a solar panel 27 (or other means for generating power, such as a wind turbine), in which case the battery 26 will require intermittent maintenance by a user operator for charging and / or replacement, it is advantageous for a solar panel 27 or the like to be included in the valve assembly 2 so that the required frequency of maintenance of the valve assembly 2 by the user operator can be reduced.

[0103] It can be appreciated that two gas composition sensors 24a-b may be included in a valve assembly independently of that valve assembly also comprising a battery 26 and / or a solar panel 27.

[0104] Figures 6A - 6C provide engineering drawings of a valve assembly such as the first valve assembly 1 in Figure 4. Figure 6A is a view of the valve assembly 1 in plane perpendicular to a direction in which gas flows through the valve assembly 1 . Figure 6B is a side view of the valve assembly 1 in a plane parallel to the direction in which gas flows through the valve assembly 1 . Figure 6C is a cross-section through the valve assembly along the line A-A in Figure 6A.

[0105] It can be appreciated from Figures 6A - 6C that the valve 15, actuator 12 and controller 11 are all physically connected to each other, and are provided as part of a single unit, along with the gas composition sensor (not illustrated). Accordingly, the valve assembly 1 is easy to install on a gas outlet and is a standalone apparatus for controlling the flowrate of landfill gas through a gas outlet. The valve assembly 1 is mountable on a gas outlet such that the valve assembly 1 and all the components thereof are supported on the gas outlet, and are not electronically connected to any equipment external to the valve assembly 1 . The valve 15 in Figures 6A - 6C is provided with double male threaded end connections for attachment to the gas outlet; it can be appreciated that other connection means may be used in place of the male threaded end connections.

[0106] The control unit 10, which contains the controller 11 and actuator 12, is disposed adjacent to the valve 15 such that the actuator 12 can be provided in physical connection with a stem of the valve 15 that is used to vary the valve position (i.e. the flow area through the valve). The actuator 12 in Figures 6A - 6C takes the form of a rotary actuator comprising a gear driven by a motor within the control unit 10, the gear interfacing with teeth provided on the valve stem.

[0107] Although not illustrated in Figures 6A - 6C, the physical user interface of the valve assembly 1 may be provided on the outside of a housing of the control unit 10 such that it is easily accessible for the human operator to interact with. All of the components of the valve assembly 1 are either disposed in and / or attached to, the housing. Figure 6C illustrates how the controller 11 takes the form of a computer implemented controller, Figure 6C illustrating the controller 11 as a circuit board. Preferably, the computer implemented controller illustrated in Figure 6C is configured such that It is not able to be connected to a network or other external control system, in order to reduce the complexity and power consumption of the controller and provide more robust means for controlling the flowrate of landfill gas out of a gas outlet.

[0108] ***

[0109] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0110] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0111] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0112] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0113] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0114] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . A method of controlling the flowrate of landfill gas out of a gas outlet using a valve assembly mounted thereon, wherein: the valve assembly comprises: a valve, the valve being mountable to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; and a controller; and the method comprises the steps of: a human operator obtaining a first measurement of the amount of the first gaseous compound in the landfill gas; the human operator assessing a dilution rate of the landfill gas based on the first measurement; the human operator setting an initial valve position of the valve based on the assessment of the dilution rate; and, subsequently, the controller obtaining a second measurement of the amount of the first gaseous compound in the landfill gas using the first gas composition sensor; and the controller controlling the actuator based on the second measurement to set the valve position of the valve.

2. The method according to claim 1 , wherein the valve assembly comprises a physical user interface configured to receive user inputs from the human operator.

3. The method according to claim 2, wherein the step of setting the initial valve position of the valve comprises the human operator inputting said initial valve position into the user interface as a user input.

4. The method according to any preceding claim, wherein the step of controlling the actuator based on the second measurement comprises: comparing the second measurement and a pre-set first gaseous compound composition; and controlling the actuator to change the valve position by a pre-set increment when the second measurement differs from the pre-set first gaseous compound composition.

5. The method according to claim 2 or 3, or claim 4 as dependent on claim 2, wherein the method further comprises the step of the human operator inputting the pre-set first gaseous compound composition and / or the pre-set increment into the controller.

6. The method according to claims 2, 3 or 5 or claim 4 as dependent on claim 2, wherein:the step of the controller obtaining the second measurement and the controller controlling the actuator based on the second measurement are repeatedly conducted at a pre-set frequency; and optionally, the method further comprises a step of the human operator inputting the pre-set frequency into the user interface as a user input.

7. The method according to any preceding claim, wherein the first gas composition sensor is the only gas composition sensor within the valve assembly.

8. The method according to any preceding claim, wherein the first gas composition sensor is an in-line sensor.

9. A valve assembly for controlling the flowrate of landfill gas out of a gas outlet, the valve assembly comprising: a valve, the valve being mountable to the gas outlet such that the flowrate of landfill gas out of the gas outlet is controlled by the flow area through the valve; a first gas composition sensor configured to measure the amount of a first gaseous compound in the landfill gas; an actuator configured to change a valve position of the valve to vary the flow area therethrough; a controller configured to control the actuator based on the amount of the first gaseous compound in the landfill gas; and a physical user interface configured to receive one or more user inputs specifying the control of the actuator by the controller from a human operator.

10. The valve assembly according to claim 9, wherein the user interface is configured to receive an initial valve position as a user input from the human operator.

11. The valve assembly according to claim 9 or 10, wherein: the controller is configured to control the actuator based on a measurement of the amount of the first gaseous compound in the landfill gas using the first gas composition sensor by: comparing said measurement and a pre-set first gaseous compound composition; and controlling the actuator to change the valve position by a pre-set increment when the second measurement differs from the pre-set first gaseous compound composition; and the user interface is configured to receive the pre-set first gaseous compound composition and / or the pre-set increment as user inputs from the human operator.

12. The valve assembly according to any of claims 9 to 11 , wherein the controller is configured to measure the amount of the first gaseous compound in the landfill gas using the first gas composition sensor at a pre-set frequency.

13. The valve assembly according to claim 12, wherein the user interface is configured to receive the preset frequency as a user input from the human operator.

14. The valve assembly according to any one of claims 9 to 13, wherein: the valve assembly further comprises one or more of: an energy storage unit, a solar panel, and a wind turbine; and the energy storage unit, solar panel and / or wind turbine is configured to provide power to the first gas composition sensor, the controller, and / or the actuator.

15. The valve assembly according to any one of claims 9 to 14, wherein the first gas composition sensor is the only gas composition sensor within the valve assembly.

16. The valve assembly according to any one of claims 9 to 15, wherein the first gas composition sensor is an in-line sensor.

17. The valve assembly according to any preceding claim, further comprising a second gas composition sensor, the second gas composition sensor configured to measure the amount of a second gaseous compound in the landfill gas.

18. The valve assembly according to claim 17, wherein: the controller is configured to: make a first determination as to whether the valve requires actuation based on the amount of the first gaseous compound in the landfill gas; and the controller is configured such that: where the first determination is that the valve requires actuation to change the valve position, the controller is configured to control the actuator based on said first determination; and where the first determination is that the valve does not require actuation to change the valve position, the controller is configured to make a second determination as to whether the valve requires actuation based on the amount of the second gaseous compound in the landfill gas and to control the actuator based on said second determination.

19. A landfill comprising: a well; a gas outlet connected to the well; and a valve assembly according to any one of claims 9 to 18 mounted on the gas outlet.

20. The landfill according to claim 19, wherein: the landfill comprises a plurality of gas outlets and a plurality of valve assemblies according to any one of claims 9 to 18, each valve assembly mounted on a respective gas outlet; and each valve assembly is configured to control the flowrate of landfill gas out of its respective gas outlet independently of the control exerted by other valve assemblies within the plurality of valve assemblies on their respective gas outlets.

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