device and method for measuring a chemical element in a sample of a gas

Abstract

The invention relates to a device (1) for measuring a chemical element in a sample of a gas. The device comprises a sensor (3) capable of measuring the concentration of the chemical element in a measurement space and a capsule (5) assembled to the sensor (3) to confine the measurement space. The capsule (5) and the sensor (3) are assembled to each other in a partially hermetic manner, so that the atmosphere contained in the measurement space can escape when the gas sample is injected. The invention also relates to a measuring method implementing this device. ( Figure 1 )

Description

Title of the invention: Device and method for measuring a chemical element in a sample of a gas FIELD OF THE INVENTION

[0001] The present invention relates to a device for measuring a chemical element in a sample of a gas. It also relates to a method for measuring this chemical element using this device. The invention finds its application in particular for determining the chemical composition of a synthesis gas, in particular for determining its concentration of methane and / or hydrogen. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Synthesis gas (or syngas) is the combustible gas produced from solid waste, also called biomass, by the fermentation of this biomass. This gas mainly comprises methane, hydrogen, and carbon dioxide. It forms a renewable energy source, particularly for rural areas or for developing areas in which biomass may be abundant.

[0003] Mastering the gasification processes for producing this synthesis gas requires precise characterization of the properties of the gas produced. In particular, we seek to determine its chemical composition, typically using a chromatograph, which is a relatively expensive and difficult to transport piece of equipment. This equipment is not suitable for use in production areas that may be isolated.

[0004] From the document “Low-cost, Arduino-based, portable device for measurement of methane composition in biogas”, by Shunchang Yang et al. published in the journal Renewable Energy,

[0005] Volume 138, 2019, Pages 224-229 a portable and inexpensive device for measuring the concentration of methane in a biogas. This device is formed of a hermetic chamber defining a measurement volume Vc in which is placed a methane sensor connected to an electronic acquisition system. The chamber is provided with an injection conduit through which a biogas sample having a determined volume Vi can be introduced in order to allow its analysis. The concentration X of methane in the sample can be estimated using the formula X = M(Vi+Vc) / Vi where M is the measurement provided by the sensor.

[0006] The method proposed by this document does, however, have limitations. First of all, the volume of the sealed chamber is difficult to determine precisely, in particular because of the measuring sensor located there. More notably, the non-homogeneous dilution that occurs when the sample is injected into the chamber leads to underestimating or overestimating the measured concentration of the chemical element. It should be noted in this regard that since the chamber is airtight, the injected volume of the sample is necessarily reduced in order to maintain a reasonable pressure in the chamber, the design of which must remain simple. SUBJECT OF THE INVENTION

[0007] The present invention aims to overcome all or part of the aforementioned drawbacks. More specifically, it aims to provide a device for measuring a chemical element in a gas sample, in particular a synthesis gas, which is simple in design, portable or transportable, but which nevertheless delivers a reliable measurement. BRIEF DESCRIPTION OF THE INVENTION

[0008] With a view to achieving one of these aims, the subject of the invention provides a device for measuring a chemical element in a sample of a gas, the device comprising:

[0009] - a sensor capable of measuring the concentration of the chemical element in a measurement space; - a capsule assembled to the sensor to confine the measurement space, the capsule comprising means for injecting the gas sample into the measurement space;

[0010] According to the invention, the capsule and the sensor are assembled to each other in a partially hermetic manner, so that the atmosphere contained in the measuring space can escape when the gas sample is injected.

[0011] According to the invention, the gas sample injected into the measuring device tends to expel the atmosphere from the measuring space to replace it. A reliable measurement can therefore be carried out; there is no need to homogenize the sample in the atmosphere before taking the measurement as may be necessary in the solutions of the state of the art.

[0012] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination:

[0013] - the injection means is formed of a conduit opening into the measuring space; - the sensor comprises a measuring head arranged inside the capsule;

[0014] - the capsule has an opening shaped to the measuring head so that only the measuring head is placed inside the capsule; - the measuring device comprises an acquisition box electrically connected to the sensor; - the measuring device also comprises a means for dosing the gas sample, this dosing means making it possible to introduce a volume gas controlled in device 1 using the injection means; - the controlled quantity is between 5 and 60 ml; - the sensor is capable of measuring the concentration of methane or hydrogen in the measurement space.

[0015] According to another aspect, the subject of the invention proposes a method for measuring a chemical element in a sample of a gas, the method implementing a measuring device as proposed previously and comprising the following steps:

[0016] - injecting the sample into the measurement space via the injection means; - record the measurement of the concentration of the chemical element provided by the sensor.

[0017] According to an advantageous and non-limiting characteristic of this aspect of the invention, the method also comprises the following additional steps:

[0018] - inject a standard sample into the measurement space and take a standard measurement of the concentration of the chemical element provided by the sensor; - calculate a calibration coefficient from the standard measurement; - apply the calibration coefficient to the measurement taken of the concentration of the chemical element in the sample: Brief description of the drawings

[0019] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0020] [Fig.l]

[0021] [Fig.2]

[0022] Figures 1 and 2 represent measuring devices according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] [Fig.l] represents a measuring device 1 according to the invention. A sensor 3 capable of measuring the concentration of a chemical element and arranged on a routing support 2. When the device 1 is used to determine the chemical composition of a synthesis gas, the sensor 3 can be configured to measure the concentration of methane or hydrogen.

[0024] As is well known per se, such sensors implement a sensitive material sometimes brought to temperature (for example SnO2) so the conductivity increases when it is exposed to the chemical element in question. This variation in conductivity is exploited by sensor electronics to provide a measurement of the concentration of the chemical element in the surrounding measurement space. As an example of such sensors, these may be the MQ4 sensors (for the measurement of the methane) or MQ8 (for H2 measurement) supplied by Hanwei Electronics Group Corporation, Zhengzhou, China.

[0025] In the example of [Fig.l], the sensitive element of the sensor is arranged in a measuring head 3b of the sensor 3, this head resting on a sensor body 3a in which the sensor electronics reside.

[0026] The routing circuit 2 makes it possible to connect the connection pins of the sensor 3 to an acquisition box 4 making it possible to interface the sensor 2 with a remote calculation device, not shown in the figure. The box 4 makes it possible in particular to supply the supply voltage to the sensor 3, and to record the concentration measurements provided by this sensor 3. It may be a low-cost box with a microcontroller, of the Arduino™ type for example.

[0027] Continuing the description of [Fig.l], the measuring device also comprises a capsule 5, forming a cover of the sensor 3, assembled thereto to confine its measuring space. In the example shown, the capsule 5 is formed of a semi-closed cylinder therefore having a main opening on the side of the cylinder facing the sensor 3. This opening is shaped to the head of the sensor 3a so that this head is arranged inside the capsule 5. The closed side of the cylindrical capsule is provided with a conduit opening into the internal space defined by the capsule 5 and forms a means for injecting the gas sample into the measuring space of the device 1. It is possible to provide this conduit with an optional valve so that it can be closed.

[0028] According to an important aspect of the present invention, the capsule 5 and the sensor 3 are assembled to each other in a partially hermetic manner. Also, when injecting the gas sample into the measuring space via the conduit 5a, the atmosphere contained in this space can be expelled and escape. This atmosphere can thus be replaced by the sample, for a retention time typically between 1 ms and 1 s, before carrying out the measurement during this retention time. The risk of non-homogeneity of the mixture in the measuring space is reduced because of the small volume of the available measuring space that the gas can occupy.

[0029] Preferably, and for this replacement of atmosphere to be effective, the sample is chosen so that it has a volume greater than the volume delimited by the capsule 5, this being typically between 5 and 60 ml. It will be possible to use a means for dosing the sample, for example a graduated syringe, to take a chosen quantity of the gas to be measured and form the sample before injecting it through the conduit.

[0030] [Fig.2] shows an advantageous arrangement of the measuring device 1. In this arrangement, the measuring device 1 as described with reference to [Fig.l], also includes a support 6 configured to arrange and hold the capsule 5 under the sensor 3. In this way, the gas injected vertically upwards tends to rise naturally towards the sensitive area of ​​the sensor 3.

[0031] A method for measuring a chemical element in a gas sample is now described using the device that has just been presented. As has been seen, the chemical element to be measured may be hydrogen or methane contained in any gas, such as, for example, a synthesis gas (or syngas).

[0032] During a first step, the sample is injected into the measurement space using the injection means. As already mentioned, a metering means, such as a graduated syringe, or any other device for withdrawing a determined volume of gas to form the sample may be used. The end of the syringe may be introduced into the injection conduit before actuating the syringe pump and forcing the injection of the sample into the measurement space confined by the capsule 5.

[0033] This capsule 5 being semi-hermetically assembled, and not sealed, to the sensor 3, the atmosphere residing in the confined measuring space is expelled and replaced by the sample. As previously stated, a sample volume greater than the confined volume of the measuring space will preferably be chosen to ensure that a large part, if not all of this atmosphere, is replaced by the sample to be analyzed.

[0034] At the end of this injection step, a measurement provided by the sensor 3 of the concentration of the chemical element is recorded.

[0035] The measurement may be influenced by parameters other than that of the concentration of the chemical element, for example by the degree of humidity or by the ambient temperature. Thus, advantageously, the measurement method comprises a calibration step. This step comprises a step of injecting a standard sample, that is to say a sample of a gas containing a concentration known in advance of the chemical element sought, followed by a step of reading a standard measurement. The ratio existing between the standard measurement recorded and the concentration known in advance of the chemical element in the sample makes it possible to establish a calibration coefficient. This coefficient can be applied to the measurements of the concentration of the chemical element read on the gas to be analyzed to obtain a faithful estimate of this concentration of chemical element.This procedure can naturally be repeated with a variety of standard samples, each sample having a different gas concentration known in advance, so as to establish, for example by averaging, a calibration coefficient with greater precision.

[0036] Of course, the invention is not limited to the method of implementation described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. A device (1) for measuring methane or hydrogen in a sample of a gas, the device comprising: - a sensor (3) comprising a sensitive element arranged in a measuring head (3b), the sensor being capable of measuring the concentration of methane or hydrogen in a measuring space; - a capsule (5) assembled to the measuring head (3b) of the sensor (3) to confine the measuring space, the capsule (5) comprising a means (5a) for injecting the gas sample into the measuring space; the capsule (5) and the sensor (3) being assembled to each other in a partially hermetic manner, so that the atmosphere contained in the measuring space can escape during the injection of the gas sample; the measuring device (1) also comprising a means for dosing the gas sample, this dosing means making it possible to introduce a controlled volume of gas.

2. Measuring device (1) according to the preceding claim in which the injection means (5a) is formed of a conduit opening into the measuring space.

3. Measuring device (1) according to one of the preceding claims, in which the capsule (5) has an opening shaped to the measuring head (3b) so that only the measuring head (3b) is arranged inside the capsule (5).

4. Measuring device (1) according to one of the preceding claims comprising an acquisition box (4) electrically connected to the sensor (3).

5. Measuring device (1) according to one of the preceding claims in which the controlled quantity is between 5 and 60 ml.

6. A method of measuring a chemical element in a sample of a gas, the method implementing a measuring device (1) according to one of the preceding claims and comprising the following steps: injecting the sample into the measuring space via the injection means (5a); - record the measurement of the concentration of the chemical element provided by the sensor (3).

7. Measuring method according to the preceding claim comprising the following additional steps: - inject a standard sample into the measurement space and take a standard measurement of the concentration of the chemical element provided by the sensor (3); - calculate a calibration coefficient from the standard measurement; - apply the calibration coefficient to the measurement taken of the concentration of the chemical element in the sample.

Images