Device and system for reducing an oxygen gas concentration in a main gas flow and associated method

Abstract

Devices and systems for reducing an oxygen gas concentration in a main gas flow, comprising a. a main gas flow channel having a main gas flow inlet for the main gas flow and a main gas flow outlet for a deoxygenated main gas flow; b. a reactant gas flow channel comprising a reactant gas inlet at a first end and being connected to the main gas flow channel at a second end, such as to allow injection of a reactant gas into the main gas flow channel, the reactant gas flow channel comprising a mass flow controlling device downstream of the reactant gas inlet; c. a reactor means arranged in the main gas flow channel downstream of the connection location and upstream of the main gas flow outlet; and d. a control unit adapted for controlling the mass flow controlling device to control an injection of flow of the reactant gas into the main gas flow in the main gas flow channel, based on inlet process conditions of the main gas flow and / or outlet process conditions of the deoxygenated main gas flow; and associated methods.

Description

[0001] Device and system for reducing an oxygen gas concentration in a main gas flow and associated method.

[0002] Technical field

[0003] The present disclosure relates to a device and system for reducing an oxygen gas content in a main gas flow such as in a predominantly nitrogen or carbon dioxide gas flow, especially to devices or systems comprising a control unit for controlling an injection flow of a reactant gas into said main gas flow, and to related methods.

[0004] Background art

[0005] Deoxygenation devices remove oxygen gas from a main gas stream. They do so by forcing the oxygen gas to react with a reactant gas through a reactor means such as a catalytic bed, which reduces the barrier of reaction between oxygen gas and the reactant gas. Two types of solutions are possible for the reactant gas:

[0006] 1 . The reactant gas is the same as the main gas.

[0007] 2. The reactant gas is different from the main gas.

[0008] In solutions of the second type, the reactant gas must be injected in the main gas stream prior to entering the reactor means. The amount of reactant gas injected is typically calculated based on the rated conditions and the stoichiometric relation between oxygen gas and the reactant gas, i.e. the reaction is assumed to be perfect and all the oxygen gas is expected to react away. However, this may cause either an over-usage of the reactant gas if the application does not require the deoxygenation to be complete, or an insufficient deoxygenation since a slight over-stoichiometric dosage of reactant gas is required to remove all the oxygen gas, again, if required by the application. This renders the overall deoxygenation process respectively inefficient, or unsatisfactory.

[0009] Furthermore, the reactant gas source is often not considered in the operation of the deoxygenation device. Depending on the type of source, this may result in an on / off control strategy, which can significantly impact the performance and lifetime of the reactant gas source / generator.

[0010] There exists a need in the industry for improved solutions of the second type.

[0011] Summary of the disclosure

[0012] It is an objective of the present disclosure to provide a device according to claim 1 and a system according to claim 11 , and to provide an associated method for controlling the device or system according to claim 20. In a first aspect of the present disclosure, a device is disclosed for reducing an oxygen gas concentration in a main gas or main gas flow, the system comprising a. a main gas flow channel having a main gas flow inlet for the main gas flow and a main gas flow outlet for a deoxygenated main gas flow; b. a reactant gas flow channel comprising a reactant gas inlet for a reactant gas flow at a first end and being connected, for instance fluidly connected, to the main gas flow channel at a second end, at a connection location, such as to allow injection of a reactant gas into the main gas flow channel, the reactant gas flow channel comprising a mass flow controlling device downstream of the reactant gas inlet ; c. a reactor means arranged in the main gas flow channel downstream of the connection location and upstream of the main gas flow outlet; d. a control unit adapted for controlling the mass flow controlling device in order to control an injection flow of the reactant gas into the main gas flow in the main gas flow channel to a required reactant gas flow, based on inlet process conditions of the main gas flow and / or outlet process conditions of the deoxygenated main gas flow.

[0013] It is an advantage that the reactant gas can be used more efficiently, and over-usage can be avoided. Furthermore, the performance and lifetime of an associated reactant gas generator is expected to be improved.

[0014] A mass flow controlling device can for instance comprise at least one valve.

[0015] A reactor means can for instance comprise a reactor chamber or vessel, for instance comprising a catalytic bed.

[0016] According to preferred embodiments, the control unit is adapted for calculating the required reactant gas flow to be injected in the main gas flow based on the main gas flow at the main gas flow inlet, an oxygen gas concentration at the main gas flow inlet, and a required ratio of reactant gas concentration over oxygen gas concentration.

[0017] For instance, the required ratio of reactant gas concentration over oxygen gas concentration can be constant.

[0018] Alternatively, the required ratio of reactant gas concentration over oxygen gas concentration can be dependent on an oxygen gas concentration target of the deoxygenated main gas flow.

[0019] According to preferred embodiments, the required ratio of reactant gas concentration over oxygen gas concentration is dependent on a flow rate load of the device (or system according to the second aspect). The flow rate load of the device (or system) can for instance be expressed as a fraction, e.g. a percentage, of a maximal flow rate or nominal design flow rate of the device (or system).

[0020] According to preferred embodiments, the control unit is adapted for calculating the required reactant gas flow to be injected in the main gas flow based on an actual oxygen gas concentration of the deoxygenated main gas flow. According to preferred embodiments, the control unit is adapted for calculating the required reactant gas flow to be injected in the main gas flow based on an actual reactant gas concentration of the deoxygenated main gas flow.

[0021] According to preferred embodiments, the control unit is adapted for calculating the required reactant gas flow to be injected in the main gas flow based on an actual oxygen gas concentration and on an actual reactant gas concentration of the deoxygenated main gas flow.

[0022] According to preferred embodiments, controlling the mass flow controlling device by the control unit comprises at least periodically or continuously providing first flow setpoint values for the required reactant gas flow to be injected to the mass flow controlling device.

[0023] According to preferred embodiments, the control unit is further adapted for controlling a flow rate of the reactant gas entering the reactant gas flow channel from the reactant gas inlet.

[0024] In a second aspect of the present disclosure, a system for reducing an oxygen gas concentration in a main gas flow is disclosed, comprising a device according to any of the embodiments of the first aspect, and further comprising a reactant gas generator connected, preferably fluidly connected, to the reactant gas inlet, and optionally a reactant gas buffer arranged downstream of the reactant gas generator and upstream of the reactant gas inlet, wherein the control unit is further adapted for controlling a flow rate of the reactant gas generator.

[0025] The reactant gas generator can for instance be a hydrogen gas or carbon dioxide generator, for instance a hydrogen gas electrolyser.

[0026] According to preferred embodiments, controlling the flow rate of the reactant gas generator comprises at least periodically or continuously providing second flow setpoint values for the reactant gas flow to be generated to the reactant gas generator, preferably by the control unit.

[0027] For the purpose of the present disclosure, a control unit can be a single central control unit, or can comprise two or more distributed, separate control units. Throughout the description, an abstraction is made thereof. For instance, the control unit adapted for controlling a flow rate of the reactant gas generator and the control unit adapted for controlling the mass flow controlling device in order to control an injection flow of the reactant gas into the main gas flow in the main gas flow channel can be the same control unit or different control units. Preferably these control units are the same, single central control unit.

[0028] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function, for instance a polynomial function, for instance a linear function, of at least one first flow setpoint or on a set of the first flow setpoints.

[0029] The second flow setpoint values can be based on or derived from at least one first flow setpoint or a set of the first flow setpoints. The second flow setpoint values can correspond to a multiplication of a corresponding first setpoint value with a, for instance time-dependent, scalar value. According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function of a reactant gas pressure measured in the reactant gas flow channel upstream of the mass flow controlling device or in the reactant gas generator.

[0030] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function of a predicted availability of, preferably low carbon emitting, electricity overtime.

[0031] According to preferred embodiments, wherein the second flow setpoint values are a, preferably timedependent, function of a predicted cost of energy over time.

[0032] According to preferred embodiments, the respective functions comprise a polynomial, preferably linear dependency of the reactant gas pressure measured in the reactant gas flow channel upstream of the mass flow controlling device or in the reactant gas generator and / or of the predicted availability of electricity over time and / or of a predicted cost of energy overtime, respectively.

[0033] According to preferred embodiments, the main gas or main gas flow mainly comprises nitrogen gas or carbon dioxide. Preferably, it comprises an initial amount of oxygen gas that needs to be reduced or removed from the main gas flow.

[0034] According to preferred embodiments, the reactant gas flow mainly comprises hydrogen gas or carbon monoxide.

[0035] In a third aspect of the present disclosure, a method is disclosed for controlling a system or device according to any of the embodiments of the first or second aspect, comprising controlling the mass flow controlling device in order to control an injection flow of the reactant gas into the main gas flow in the main gas flow channel to a required reactant gas flow, based on inlet process conditions of the main gas flow and / or outlet process conditions of the deoxygenated main gas flow.

[0036] According to preferred embodiments, the method comprises calculating the required reactant gas flow to be injected in the main gas flow based on the main gas flow at the main gas flow inlet, the oxygen gas concentration at the main gas flow inlet, and a required ratio of reactant gas concentration over oxygen gas concentration.

[0037] According to certain embodiments, the required ratio of reactant gas concentration over oxygen gas concentration is constant.

[0038] According to preferred embodiments, the required ratio of reactant gas concentration over oxygen gas concentration is dependent on an oxygen gas concentration target of the deoxygenated main gas flow.

[0039] According to preferred embodiments, the required ratio of reactant gas concentration over oxygen gas concentration is dependent on a flow rate load of the device.

[0040] According to preferred embodiments, the method comprises calculating the required reactant gas flow to be injected in the main gas flow based on an actual oxygen gas concentration of the deoxygenated main gas flow. According to preferred embodiments, the method comprises calculating the required reactant gas flow to be injected in the main gas flow based on an actual reactant gas concentration of the deoxygenated main gas flow.

[0041] According to preferred embodiments, the method comprises calculating the required reactant gas flow to be injected in the main gas flow based on an actual oxygen gas concentration and on an actual reactant gas concentration of the deoxygenated main gas flow.

[0042] According to preferred embodiments, the method comprises at least periodically or continuously providing first flow setpoint values for the required reactant gas flow to be injected to the mass flow controlling device.

[0043] According to preferred embodiments, the method further comprises controlling a flow rate of the reactant gas entering the reactant gas flow channel from the reactant gas inlet.

[0044] According to preferred embodiments, the method is adapted for the system or the device comprising the reactant gas generator, further comprising controlling a flow rate of the reactant gas generator.

[0045] Preferably, controlling a flow rate of the reactant gas generator comprises at least periodically or continuously providing second flow setpoint values for the reactant gas flow to be generated to the reactant gas generator.

[0046] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function, for instance a polynomial function, of at least one first flow setpoint or on a set of the first flow setpoints.

[0047] The second flow setpoint values can be based on or derived from at least one first flow setpoint or a set of the first flow setpoints. The second flow setpoint values can correspond to a multiplication of a corresponding first setpoint value with a, for instance time-dependent, scalar value.

[0048] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function of a reactant gas pressure measured in the reactant gas flow channel upstream of the mass flow controlling device or in the reactant gas generator.

[0049] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function of a predicted availability of, preferably low carbon emitting, electricity overtime.

[0050] According to preferred embodiments, the second flow setpoint values are a, preferably timedependent, function of a predicted cost of energy over time.

[0051] According to preferred embodiments, the respective functions comprise a polynomial, preferably linear dependency of the reactant gas pressure measured in the reactant gas flow channel upstream of the mass flow controlling device or in the reactant gas generator and / or of the predicted availability of electricity over time and / or of a predicted cost of energy overtime, respectively.

[0052] Features and advantages disclosed for one of the above aspects of the present disclosure are hereby also implicitly disclosed for the other aspects, mutatis mutandis, as the skilled person will recognize. Especially, aspects described for the device and system aspect, are also applicable and considered disclosed for the method aspect, and vice versa.

[0053] Brief description of the drawings

[0054] The disclosure will be further elucidated by means of the following description and the appended figures.

[0055] • Fig. 1 is a schematic overview of a system according to a preferred embodiment of the present disclosure.

[0056] • Fig. 2 is a schematic overview of a feedforward control of the reactant gas flow according to preferred embodiments of the present disclosure.

[0057] • Fig. 3 illustrates a relation between the required ratio of reactant gas concentration over oxygen gas concentration and the oxygen gas concentration target according to preferred embodiments of the present disclosure.

[0058] • Fig. 4 illustrates a relation between the required ratio of reactant gas concentration over oxygen gas concentration and the flow load of the device, where the maximum flow load of the device represents a 100% load, according to preferred embodiments of the present disclosure.

[0059] • Fig. 5 illustrates a feedback control of the reactant gas flow based on an oxygen gas concentration of the deoxygenated main gas flow according to preferred embodiments of the present disclosure.

[0060] • Fig. 6 is a schematic overview of a feedforward and feedback control of the reactant gas flow based on the oxygen gas concentration of the deoxygenated main gas flow, according to preferred embodiments of the present disclosure.

[0061] • Fig. 7 is a schematic overview of a feedback control of the reactant gas flow based on the reactant gas concentration of the deoxygenated main gas flow, according to preferred embodiments of the present disclosure.

[0062] • Fig. 8 is a schematic overview of a feedforward and feedback control of the reactant gas flow based on the reactant gas concentration of the deoxygenated main gas flow, according to preferred embodiments of the present disclosure.

[0063] • Fig. 9 is a schematic overview of a feedback control of the reactant gas flow based on the oxygen gas concentration of the deoxygenated main gas flow and the reactant gas concentration of the deoxygenated main gas flow, according to preferred embodiments of the present disclosure.

[0064] • Fig. 10 is a schematic overview of a feedforward and feedback control of the reactant gas flow using the oxygen gas concentration of the deoxygenated main gas flow and the reactant gas concentration of the deoxygenated main gas flow, according to preferred embodiments of the present disclosure. • Fig. 11 illustrates a constant relation between cpand the reactant gas pressure, according to preferred embodiments of the present disclosure.

[0065] • Fig. 12 illustrates a pressure band relation between cpand the reactant gas pressure, according to preferred embodiments of the present disclosure.

[0066] • Fig. 13 illustrates a refined operating pressure band relation between cpand the reactant gas pressure, according to preferred embodiments of the present disclosure.

[0067] • Fig. 14 illustrates a sigmoid operating pressure band relation between cpand the reactant gas pressure, according to preferred embodiments of the present disclosure.

[0068] Detailed description of preferred embodiments

[0069] The present disclosure will be described with respect to particular embodiments and with reference to certain drawings, but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.

[0070] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order.

[0071] The various embodiments, although referred to as "preferred" are to be construed as examples in which the disclosure may be implemented rather than as limiting the scope of the disclosure.

[0072] A preferred embodiment of device 1 and system 9 for reducing an oxygen gas concentration in a main gas or main gas flow (or main gas stream) 1000 is disclosed in Fig. 1 . The device 1 comprises a main gas flow channel 10 having a main gas flow inlet 101 for a main gas flow 1000 and a main gas flow outlet 102 for a deoxygenated main gas flow 1000*. It has to be understood that a deoxygenated main gas flow 1000* should be considered as a main gas flow having a lower oxygen content than the initial main gas flow 1000, that may still comprise a certain, but at least reduced amount of oxygen, an amount which is depending on the actual context and intended use of the deoxygenated main gas flow 1000* downstream of the device 1 or system 9.

[0073] The device 1 comprises a reactant gas flow channel 20 for a reactant gas flow 2000 comprising a reactant gas inlet 201 at a first end and being connected, preferably fluidly connected, to the main gas flow channel at a second end 202 (reactant gas outlet), at a connection location C, such as to allow injection of a reactant gas into the main gas flow channel 10. The reactant gas flow channel 20 comprises a mass flow controlling device 21 downstream of the reactant gas inlet 201 for controlling the reactant gas flow. The device 1 comprises a reactor means 3 arranged in the main gas flow channel 10 downstream of the connection location C and upstream of the main gas flow outlet 102.

[0074] The device 1 and system 9 further comprise a control unit 4 adapted for controlling the mass flow controlling device 21 in order to control an injection flow of the reactant agent / gas into the main gas flow 1000 in the main gas flow channel 10 to a required reactant gas flow, based on inlet process conditions of the main gas flow 1000 and / or outlet process conditions of the deoxygenated main gas flow 1000*.

[0075] Preferably, the system 9 further comprises a reactant gas generator 222 connected, preferably fluidly connected to the reactant gas inlet 201 , and the control unit 4 is further adapted for controlling a flow rate of the reactant gas generator 222. The system 9 can further comprise a reactor gas buffer 22 upstream of the reactant gas inlet 201 (and e.g. upstream of the mass flow controlling device 21) and downstream of the reactant gas generator 222. Note that the reactant gas buffer 22 can be either a dedicated buffer vessel or just the internal volume of the piping connecting the reactant gas generator 222 with the device 1 , for instance to the reactant gas inlet 201 thereof.

[0076] The device 1 and system 9 preferably comprise measurement means such as sensors arranged at various locations.

[0077] For instance, a pressure sensor S1 can be provided and arranged for measuring a pressure of the reactant gas in the reactant gas generator 222 or downstream thereof, for instance also upstream of said reactant gas inlet 201 , or upstream of said reactant gas buffer 22.

[0078] For instance, an oxygen sensor S2 can be provided and arranged for measuring an oxygen gas content of the main gas flow 1000, and / or a pressure sensor S3 can be provided and arranged for measuring a pressure of the main gas flow 1000, or a flow measurement means such as a flow meter or sensor S4 can be provided and arranged for measuring a gas flow rate of the main gas flow 1000, at a location downstream of the main gas flow inlet 101 and upstream of the connection location C.

[0079] For instance, an oxygen sensor S5 and / or a reactant sensor S6 can be provided and arranged for measuring an oxygen gas concentration and / or a reactant gas concentration in the deoxygenized main gas flow 1000* downstream of the reactor means 3 and upstream of the main gas flow outlet 102.

[0080] Any of the above sensors are adapted for communicating measurement values to the control means or unit 4, and the control unit 4 is configured and adapted for receiving measurement values from the sensors which are present of the respective sensors S1 to S6.

[0081] Whether one or more of the above-described sensors S1 to S6 is required to be present in the device 1 or system 9 depends on the need for respective measurements in the methods performed by the control unit 4, as the skilled person will recognize and explained further on in the description.

[0082] It is an advantage of embodiments of the present disclosure that the reactant gas can be used more efficiently, and over-usage can be avoided. Furthermore, the performance and lifetime of an associated reactant gas generator 222 is expected to be improved. A goal of embodiments of the present disclosure is to calculate the required amount of reactant gas for deoxygenation of a main gas flow 1000, based on multiple process conditions, to continuously match the deoxygenation requirements, to reduce the reactant gas consumption, and to operate the reactant gas source efficiently based on the calculated value.

[0083] This provides for instance the following advantages:

[0084] 1 . Ensure that the device 1 meets the outlet requirements continuously;

[0085] 2. The reactant gas consumption is minimised;

[0086] 3. The reactant gas generator 222 is operated efficiently.

[0087] In a preferred embodiment, the reactant gas is hydrogen gas or carbon monoxide. In the former case, the required amount of reactant gas may be transmitted to a reactant gas generator 222 embodied as a hydrogen gas generator, in a preferred embodiment being an electrolyser.

[0088] The operation and control of gases for deoxygenation relies on a central controller 4, which transmits a Flow setpoint to a mass flow controlling device 21 that injects the according amount of reactant gas flow in the main gas flow 1000. This Flow setpoint is calculated based on inlet and / or outlet process conditions, sensed with appropriate devices, as elaborated in subsequent paragraphs.

[0089] In addition, the central controller 4 preferably transmits a Generator setpoint equivalent with the reactant gas flow that must be produced by the reactant gas generator 222. This setpoint is in direct relation with the Flow setpoint, and dependent on, among other aspects, the reactant gas process conditions. The operation is described in more detail in following paragraphs.

[0090] A. Control of the reactant gas flow in the deoxygenation device

[0091] The control of the Flow setpoint, i.e. the reactant gas flow target transmitted to the mass flow controlling device 21 , and possibly used in the calculation of the Generator setpoint if a reactant gas generator 222 is available, is based on inlet process conditions of the main gas flow 1000 and / or outlet process conditions of the deoxygenated main gas flow 1000*. The following control schemes are proposed.

[0092] 1. Control of the flow setpoint based on feedforward control.

[0093] In the feedforward control scheme, the required amount of reactant gas is continuously calculated based on the inlet process conditions of the main gas flow 1000, more particularly the main gas flow 1000 at the main gas flow inlet 101 , an oxygen gas concentration at the main gas flow inlet 101 , and a required ratio of reactant gas concentration over oxygen gas concentration. This is depicted in the block diagram of Fig. 2 where the calculated value for the reactant gas flow labelled as “Reactant gas flow target” represents the Flow setpoint, and is subsequently transmitted to the mass flow controlling device 21 . Remark that for the oxygen gas concentration at the main gas flow inlet 101 , a maximal limit is added using a maximum inlet O2 concentration parameter. Similarly, the reactant gas flow target is limited by a minimum reactant gas flow parameter. Both conditions are not mandatory in the entire control system.

[0094] The required ratio of reactant gas concentration over oxygen gas concentration enables to modulate the reactant gas flow target based on the following approaches. o In a first feedforward control scheme, the required ratio of reactant gas concentration over oxygen gas concentration is kept at a fixed value, which may be the stoichiometric coefficient in the reaction between the reactant gas and oxygen gas. o In another control scheme, the required ratio of reactant gas concentration over oxygen gas concentration is dependent on an oxygen gas concentration target of the deoxygenated main gas flow 1000*.

[0095] Fig. 3 depicts a trend where the lower the oxygen gas concentration target of the deoxygenated main gas flow 1000*, the higher the required ratio of the deoxygenated main gas flow 1000*. o Another variation forthe modulation of the required ratio of reactant gas concentration over oxygen gas concentration is a dependence on a flow rate load of the device 1. It is known that the technological limitation of the flow sensing devices causes measurement deviations in a lower flow region. These deviations can be compensated via the required ratio of reactant gas concentration over oxygen gas concentration.

[0096] Figure 4 depicts, as an example, a trend where the lowerthe flow rate load of the device 1 , the higher the required ratio of reactant gas concentration over oxygen gas concentration. o In still another feedforward control scheme, both oxygen gas concentration target and the flow rate load of the device 1 can be combined for a compound modulation of the required ratio of reactant gas concentration over oxygen gas concentration. Control of the flow setpoint based on feedback control using an actual oxygen gas concentration of the deoxygenated main gas flow.

[0097] In this feedback control scheme, an actual oxygen gas concentration of the deoxygenated main gas flow is used in the control of the reactant gas flow. This implies that the controller unit 4 is able to provide a feedback control in the form of PID control, or a variant thereof (P, PI, ...).

[0098] The control scheme is depicted in the block diagram of Fig. 5 where the calculated value for the reactant gas flow labelled as “Reactant gas flow target” represents the Flow setpoint, and is subsequently transmitted to the mass flow controlling device 21 . A baseline value, the variable y, is used to minimize the reactant gas consumption since this value will systematically be corrected by an error on the oxygen gas concentration of the deoxygenated main gas flow, y may be dependent on a nominal flow rate of the device 1 or may for example be equal to a minimum reactant gas flow.

[0099] The error on the oxygen gas concentration of the deoxygenated main gas flow is multiplied by a total outlet gas flow, which is a sum of the main gas flow at the main gas flow inlet and an injected reactant gas flow. This multiplication shall only be representative of the total outlet gas flow. For certain applications, the reactant gas flow can be ignored because it is significantly smaller than the main gas flow.

[0100] Such a feedback scheme places the reactant gas flow directly in relation with a desired output of the device 1 . In addition, the feedback scheme ensures that the device 1 meets its outlet requirements continuously by correcting for inaccuracies of sensing and actuating devices used in the control scheme. Control of the flow setpoint based on feedforward and feedback control using an actual oxygen gas concentration of the deoxygenated main gas flow.

[0101] In the control scheme depicted in Fig. 6, feedforward and feedback control schemes are combined by using a feedforward signal as a baseline, and correcting for the error on the oxygen gas concentration of the deoxygenated main gas flow.

[0102] Remark that the required ratio of reactant gas concentration over oxygen gas concentration may be modulated using all the alternatives proposed in the control of the flow setpoint based on feedforward control.

[0103] Such a feedback scheme allows faster start-up and quicker response to load changes since the baseline is directly related to the main gas flow. Furthermore, the feedback scheme places the reactant gas flow again directly in relation with a desired output of the device 1 , which allows to correct for inaccuracies of sensing and actuating devices used in the control scheme. Control of the flow setpoint based on feedback control using an actual reactant gas concentration of the deoxygenated main gas flow.

[0104] In this feedback control scheme, depicted in Fig. 7, an actual reactant gas concentration of the deoxygenated main gas flow is used in the control of the reactant gas flow.

[0105] A baseline value, the variable y, is used to minimize the reactant gas consumption since this value will systematically be corrected by the error on the oxygen gas concentration of the deoxygenated main gas flow, y may be dependent on the nominal flow rate of the device 1 or may for example be equal to the minimum reactant gas flow. The outlet reactant gas concentration target shall nevertheless be high enough to ensure a full deoxygenation.

[0106] This control scheme is of particular interest in case the reactant gas appears to be detrimental for a process using the deoxygenated main gas flow.

[0107] 5. Control of the flow setpoint based on feedforward and feedback control using the actual reactant gas concentration of the deoxygenated main gas flow.

[0108] In the following control scheme, depicted in Fig. 8, feedforward and feedback control schemes are combined by using a feedforward signal as a baseline, and correcting for the error on the reactant gas concentration of the deoxygenated main gas flow.

[0109] Remark that the required ratio of reactant gas concentration over oxygen gas concentration may be modulated using all the alternatives proposed in the control of the flow setpoint based on feedforward control.

[0110] Such a feedback scheme allows faster start-up and quicker response to load changes since the reactant gas flow is directly in relation with a desired output of the device 1 .

[0111] This control scheme is of particular interest in case the reactant gas appears to be detrimental for the process using the deoxygenated main gas flow.

[0112] 6. Control of the flow setpoint based on feedback control using the actual oxygen gas concentration and the actual reactant gas concentration of the deoxygenated main gas flow.

[0113] In this feedback control scheme, depicted in Fig. 9, the actual oxygen gas concentration as well as the actual reactant gas concentration of the deoxygenated main gas flow are used in the control of the reactant gas flow.

[0114] The baseline flow value y is hereby corrected by a less stringent outlet requirement of the device 1 .

[0115] 7. Control of the flow setpoint based on feedforward and feedback control using the actual oxygen gas concentration and the actual reactant gas concentration of the deoxygenated main gas flow. In this further embodiment, depicted in Fig. 10, the feedforward scheme is combined with the feedback control scheme using both the actual oxygen gas concentration and the actual reactant gas concentration of the deoxygenated main gas flow.

[0116] This control scheme is of particular interest in case the reactant gas appears to be detrimental for the process using the deoxygenated main gas flow.

[0117] B. Control of the operation of the reactant gas generator

[0118] The operation of the reactant gas generator can be determined by the Generator setpoint, which is transmitted every Time horizon to the reactant gas generator according to following equation:

[0119] Generator setpoint^t) — g(Flow setpoint(t') . Time horizon) * cp(t) * ce(t) * cc(t)

[0120] As such, the Generator setpoint is a time-dependent quantity calculated by multiplying a function g, that provides a baseline flow target for the reactant gas generator dependent on the Flow setpoint and the Time horizon, with a pressure coefficient cp, an emission coefficient ce, and a cost coefficient cc.

[0121] It should be noted that one or two of cP(t), ce(t) or cc(t) can be equal to 1 ; in other words, the Generator Setpoint equation can be dependent on only one or two parameters selected from the group of cP(t), Ce(t) and cc(t)

[0122] • The Generator setpoint shall reflect a desired flow rate to be generated by the reactant gas generator 222. If a value for a desired quantity expected by the reactant gas generator 222 differs from a flow rate, an additional calculation shall translate the calculated flow rate to the desired quantity. This desired quantity may be a percentage of the nominal flow rate of the reactant gas generator, a current equivalent to the flow rate, etc.

[0123] • The function g is dependent on the Flow setpoint (t) and the Time horizon. The Flow setpoint(t') is calculated continuously by the control unit 4 employing one of the schemes proposed in previous section. The Time horizon is a time value that represents the period that will be reviewed in the past.

[0124] As such, the function g performs an algebraic manipulation on the time-dependent Flow setpoint over the Time horizon. Several manipulations are proposed, for instance: o g(Flow setpoint(t'), Time horizon) — maximum(Flow setpoint(t —

[0125] Time horizon, .... Flow setpoint(t)), that is the maximum consumption over the last time horizon. o g(Flow setpoint(t'), Time horizon) — average(Flow setpoint(t —

[0126] Time horizon, .... Flow setpoint(_t')'), that is the average consumption over the last time horizon. o g(Flow setpoint(t), Time horizon) = Flow setpoint' t') * t, that is the consumption based on the instantaneous time-derivative of the consumption. o g(Flow setpoint(t), Time horizon) = Flow setpoint (t), that is the instantaneous consumption, assessed every Time horizon.

[0127] • The pressure coefficient cpis calculated based on the reactant gas process conditions, more particularly the reactant gas pressure downstream of the reactant gas generator at an instant t, e.g. in the reactant gas buffer. Several options are proposed forthe calculation of cp.

[0128] Note that pressure limits of the reactant gas generator 222 may stop its operation in its own pressure operating range, independently from the Generator setpoint, and thus cp. In that case, these pressure limits become the decisive pressures and every modulation of cpin pressures beyond these pressure limits will be ineffective. o A first example of operation strategy maintains cpconstant at a value a. The Generator setpoint is hence scaled by cp. This is illustrated in the graph of Fig. 11. o A second example of operation strategy, illustrated by the graph of Fig. 12, introduces an active modulation of cpbased on pressure parameters defined in the control unit 4. More precisely a pressure band is introduced, defined by the start pressure pstartand stop pressure pstopin the control unit 4. pstartmay be equal to a fixed value but shall be higher than a pressure of the main gas flow at the main gas flow inlet to ensure proper injection of the reactant gas in the main gas flow. Thus, pstartmay be defined as where 8 represents a pressure value that can be freely chosen. Pstop may be equal to the maximum pressure at which the reactant gas generator 222 can produce reactant gas.

[0129] When the reactant gas pressure downstream of the reactant gas generator 222, in the reactant gas buffer 22, is equal to the start pressure, cp- a.

[0130] When the reactant gas pressure in the reactant gas buffer 22 reaches the stop pressure, cp- 0 and the reactant gas generator222 stops producing reactant gas until the reactant gas is consumed by the device 1 . o A third example of operation strategy introduces the use of an operating pressure popat which the pressure of the reactant gas in the reactant gas buffer 22 is preferentially kept. popmay be equal to a pressure center pointPstop Pstart. The pressure band is now separated in intervals of similar length around pop. Four intervals are provided in the example graph depicted in Fig. 13. This implies that cpbecomes strongly dependent on the pressure of the reactant gas. The maximal value of cpis set to a variable value p that may be chosen. The amount of steps and width (pressure range) of the steps may be chosen as well and quantified by additional parameters of cp. o Another option is a refinement of the previous pressure dependent expression of cp. In this case, the pressure coefficient is expressed as a sigmoid-type function, illustrated in Fig. 14.

[0131] A benefit of this expression of cpis that the pressure is more strongly corrected towards an operating pressure at the edges of the pressure band. This may be more effective in case of a fluctuating reactant gas demand.

[0132] • The emission coefficient cerepresents the CO2 emissions at an instant t associated with the available electricity for the operation of the reactant gas generator 222. This results in an emission coefficient greater than one if low-carbon electricity is available, and vice versa.

[0133] Assessing the availability of low-carbon electricity can be done based on e.g. renewable forecasts. This step can for instance be performed in the control unit 4, which can for instance be connected to a database or information source, for instance on the internet.

[0134] • The cost coefficient ccat an instant t is in direct relation with the cost of a kWh of energy. This results in a cost coefficient greater than one if low-cost electricity is available, and vice versa.

[0135] Assessing the electricity cost can be done based on actual cost or based on expected energy cost and expected consumption. This step can for instance be performed in the control unit 4, which can for instance be connected to a database or information source, for instance on the internet.

[0136] One or multiple of the following goals are hereby fulfilled.

[0137] 1 . Reduce a number of start-stops of the reactant gas generator 222 by keeping the pressure of the reactant gas in the reactant gas buffer in the operation pressure band between pstartand Pstop > which increases the lifetime of the reactant gas generator 222. This is achieved by changing the Generator setpoint based on the reactant gas consumption of the device 1 , i.e. the Flow setpoint, and correcting for pressure through cp;

[0138] 2. Reduce an operating cost and / or CO2 emissions by producing the reactant gas based on respectively the availability of low-cost and low-carbon electricity; 3. More stable pressure of reactant gas causing more accurate injection and guaranteeing a lower design pressure of components due to the selectable operating pressure.

[0139] Note that in the case of a pressure-regulated reactant gas generator 222, cpand the function g may loose their value as all regulation is achieved through pressure values of the reactant gas generator 222, ratherthan reactant gas flow targets. The emission coefficient ceand the cost coefficient ccremain valid in that case.

Claims

Claims1 . A device (1) for reducing an oxygen gas concentration in a main gas flow (1000), the device comprising a. a main gas flow channel (10) having a main gas flow inlet (101) for the main gas flow (1000) and a main gas flow outlet (102) for a deoxygenated main gas flow (1000*); b. a reactant gas flow channel (20) comprising a reactant gas inlet (201) for a reactant gas flow (2000) at a first end and being connected to said main gas flow channel (10) at a second end (202), at a connection location (C), such as to allow injection of a reactant gas into said main gas flow channel (10), said reactant gas flow channel (20) comprising a mass flow controlling device (21) downstream of said reactant gas inlet (201); c. a reactor means (3) arranged in said main gas flow channel (10) downstream of said connection location (C) and upstream of said main gas flow outlet (102); d. a control unit (4) adapted for controlling said mass flow controlling device (21) in order to control an injection flow of said reactant gas into said main gas flow (1000) in said main gas flow channel (10) to a required reactant gas flow, based on inlet process conditions of the main gas flow (1000) and / or outlet process conditions of said deoxygenated main gas flow (1000*).

2. The device according to claim 1 , wherein said control unit (4) is adapted for calculating the required reactant gas flow to be injected in said main gas flow (1000) based on said main gas flow (1000) at said main gas flow inlet (101), an oxygen gas concentration at said main gas flow inlet (101), and a required ratio of reactant gas concentration over oxygen gas concentration.

3. The device according to claim 2, wherein said required ratio of reactant gas concentration over oxygen gas concentration is constant.

4. The device according to claim 2, wherein said required ratio of reactant gas concentration over oxygen gas concentration is dependent on an oxygen gas concentration target of said deoxygenated main gas flow (1000*).

5. The device according to claim 2 or 4, wherein said required ratio of reactant gas concentration over oxygen gas concentration is dependent on a flow rate load of said device (1).

6. The device according to any of the previous claims, wherein said control unit (4) is adapted for calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual oxygen gas concentration of said deoxygenated main gas flow (1000*).

7. The device according to any of the previous claims 1 to 5, wherein said control unit (4) is adapted for calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual reactant gas concentration of said deoxygenated main gas flow (1000*).

8. The device according to any of the previous claims 1 to 5, wherein said control unit (4) is adapted for calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual gas oxygen concentration and on an actual reactant gas concentration of said deoxygenated main gas flow (1000*).

9. The device according to any of the previous claims, wherein controlling said mass flow controlling device (21) by said control unit (4) comprises at least periodically or continuously providing first flow setpoint values for said required reactant gas flow to be injected to said mass flow controlling device (21).

10. The device according to any of the previous claims, wherein said control unit (4) is further adapted for controlling a flow rate of the reactant gas entering said reactant gas flow channel (20) from said reactant gas inlet (201).11 . A system (9) for reducing an oxygen gas concentration in a main gas flow (1000) comprising a device (1) according to any of the previous claims, further comprising a reactant gas generator (222) connected, preferably fluidly connected, to said reactant gas inlet (201) and optionally a reactant gas buffer (22) arranged downstream of said reactant gas generator (222) and upstream of said reactant gas inlet (201), wherein said control unit (4) is further adapted for controlling a flow rate of said reactant gas generator (222).

12. The system according to claim 11 , wherein controlling the flow rate of said reactant gas generator (222) comprises at least periodically or continuously providing second flow setpoint values for said reactant gas flow (2000) to be generated to said reactant gas generator (222).

13. The system according to claim 12, wherein the system (9) comprises a device (1) according to claim 9, wherein said second flow setpoint values are a, preferably time-dependent, function of at least one first flow setpoint or on a set of said first flow setpoints.

14. The system according to claim 12 or 13, wherein said second flow setpoint values are a, preferably time-dependent, function of a reactant gas pressure measured in said reactant gas flow channel (20) upstream of said mass flow controlling device (21) or in said reactant gas generator (222).

15. The system according to any of claims 12 to 14, wherein said second flow setpoint values are a, preferably time-dependent, function of a predicted availability of, preferably low carbon emitting, electricity over time.

16. The system according to any of claims 12 to 15, wherein said second flow setpoint values are a, preferably time-dependent, function of a predicted cost of energy over time.

17. The system according to any of claims 14 to 16, wherein said respective functions comprise a polynomial, for instance linear, dependency of said reactant gas pressure measured in said reactant gas flow channel (20) upstream of said mass flow controlling device (21) or in said reactant gas generator (222) and / or of the predicted availability of electricity overtime and / or of a predicted cost of energy overtime, respectively.

18. The system according to any of the previous claims 11 to 17, wherein the main gas flow (1000) mainly comprises nitrogen gas or carbon dioxide.

19. The system according to any of the previous claims 11 to 18, wherein said reactant gas flow (2000) mainly comprises hydrogen gas or carbon monoxide.

20. A method for controlling a device (1) or system (9) according to any of the previous claims, comprising controlling said mass flow controlling device (21) in orderto control an injection flow of said reactant gas into said main gas flow (1000) in said main gas flow channel (10) to a required reactant gas flow, based on inlet process conditions of the main gas flow (1000) and / or outlet process conditions of said deoxygenated main gas flow (1000*).

21. The method according to claim 20, comprising calculating the required reactant gas flow to be injected in said main gas flow (1000) based on said main gas flow (1000) at said main gas flow inlet (101), the oxygen gas concentration at said main gas flow inlet (101), and a required ratio of reactant gas concentration over oxygen gas concentration.

22. The method according to claim 21 , wherein said required ratio of reactant gas concentration over oxygen gas concentration is constant.

23. The method according to claim 21 , wherein said required ratio of reactant gas concentration over oxygen gas concentration is dependent on an oxygen gas concentration target of said deoxygenated main gas flow (1000*).

24. The method according to claim 21 or 23, wherein said required ratio of reactant gas concentration over oxygen gas concentration is dependent on a flow rate load of said device (1).

25. The method according to any of claims 20 to 24, comprising calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual oxygen gas concentration of said deoxygenated main gas flow (1000*).

26. The method according to any of the previous claims 20 to 24, comprising calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual reactant gas concentration of said deoxygenated main gas flow (1000*).

27. The method according to any of the previous claims 20 to 24, comprising calculating the required reactant gas flow to be injected in said main gas flow (1000) based on an actual oxygen gas concentration and on an actual reactant gas concentration of said deoxygenated main gas flow (1000*).

28. The method according to any of the previous claims 20 to 24, comprising at least periodically or continuously providing first flow setpoint values for said required reactant gas flow to be injected to said mass flow controlling device (21).

29. The method according to any of the previous claims 20 to 28, further comprising controlling a flow rate of the reactant gas entering said reactant gas flow channel (20) from said reactant gas inlet (201).

30. The method according to claim 29, for controlling the system (9) or the device (1) comprising a reactant gas generator (222), further comprising controlling a flow rate of said reactant gas generator (222).

31. The method according to claim 30, wherein controlling a flow rate of said reactant gas generator (222) comprises at least periodically or continuously providing second flow setpoint values for said reactant gas flow (2000) to be generated to said reactant gas generator (222).

32. The method according to claims 28 and 31 , wherein said second flow setpoint values are a, preferably time-dependent, function of at least one first flow setpoint or on a set of said first flow setpoints.

33. The method according to claim 31 or 32, wherein said second flow setpoint values are a, preferably time-dependent, function of a reactant gas pressure measured in said reactant gas flow channel (20) upstream of said mass flow controlling device (21) or in said reactant gas generator (222).

34. The method according to any of claims 31 to 33, wherein said second flow setpoint values are a, preferably time-dependent, function of a predicted availability of, preferably low carbon emitting, electricity over time.

35. The method according to any of claims 31 to 34, wherein said second flow setpoint values are a, preferably time-dependent, function of a predicted cost of energy over time.

36. The method according to any of claims 33 to 35, wherein said respective functions comprise a polynomial, preferably linear dependency of said reactant gas pressure measured in said reactant gas flow channel upstream of said mass flow controlling device (21) or in said reactant gas generator (222) and / or of the predicted availability of electricity overtime and / or of a predicted cost of energy overtime, respectively.

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