Title of Invention

A METHOD AND DEVICE FOR THE DETECTION OF CARBON MONOXIDE IN A HYDROGEN-RICH GAS STREAM

Abstract

The present invention relates to a method for the detection of CO in a hydrogen-rich gas stream, comprising feeding said gas stream past an electrochemical sensor, measurement of the current density through said electrochemical cell at a potel1tial for the sensor electrode applied such that no oxidation of CO will take place, whilst oxidation of hydrogen is possible, resulting in the electric current in said electric cell, and determination there from of the CO concentration, the hydrogen-rich gas stream being fed past the anode of said sensor and the cathode of said sensor being wetted with water by placing in a body of water, characterized in that the hydrogen- rich gas stream is fed only past said anode and said cathode is placed in direct contact with the water (liquid). The present invention also relates to a device for the detection of CO in a hydrogen-rich gas stream.

Full Text

METHOD FOR THE DETECTION OF CARBON MONOXIDE IS A HYDROGEN-RICH GAS STREAM The present invention relates to a method for the detection of CO in a hydrogen-rich gas stream, comprising feeding said gas stream past an electrochemical sensor, measurement of the current density through said electrochemical cell at a potential for the sensor electrode applied such that no oxidation of CO will take place, whilst oxidation of hydrogen is possible, resulting in the electric current in said electric cell, and determination there from of the CO concentration, the hydrogen-rich gas stream being fed past the anode of said sensor and the cathode of said sensor being wetted with water. Such a method is generally known in the art- By way of example, reference is made to US-A 4 820 386. The measurement of CO in a gas stream containing hydrogen is important when using fuel cells where CO is an undesired component, For large stationary installations, infrared measurements can be used, but such infrared measurements are too complex for small and in particular mobile installations. Therefore it has been proposed in the prior art to measure CO using a small electrochemical cell. In the case of air and other gas streams where CO can mainly be oxidised, carbon monoxide is detected by feeding carbon monoxide past an anode and oxidising it at the latter. The oxidation stream to be measured is a measure for tire CO concentration. With such a method a relatively high electrode voltage is applied in order to be able to oxidise CO. This voltage is dependent on the electrode material and the environment in question. A voltage of > 600 mV above the potential of the normal hydrogen electrode (NHE) is mentioned as a typical value. Examples thereof are described in US-A 5 650 054 end EP 1 154 267 A2. However, such a method is unsuitable in a hydrogen-rich environment such as is present in fuel cell installations whexe hydrogen-rich gas is a promising energy carrier. The hydrogen-rich gas is fed past the anode of a measurement cell. During this procedure carbon monoxide screens part of the anode catalyst and the yield of the cell for oxidation of hydrogen will decrease. METHOD FOR THE DETECTION OF CARBON MONOXIDE IN A HYDROGEN-RICH GAS STREAM The present invention relates to a method for the detection of CO in a hydrogen-rich gas stream, comprising feeding said gas stream past an electrochemical sensor, measurement of the current density through said electrochemical cell at a potential for the sensor electrode applied such that no oxidation of CO will take place, whilst oxidation of hydrogen is possible, resulting in the electric current in said electric cell, and determination there from of the CO concentration, the hydrogen rich gas stream being fed past the anode of acid sensor and the cathode of said sensor being wetted with water. Such a method is generally known in the art. 3y way of example, reference is made to US-A 4 820 386. The measurement of CO in a gas stream containing hydrogen is important when using fuel cells where CO is an undesired component, For large stationary installations, infrared measurements can be used, but such infrared measurements are too complex for small and in particular mobile installations. Therefore it has been proposed in the prior art to measure CO using a small electrochemical cell. In the case of air and other gas streams where CO can mainly be oxidised, carbon monoxide is detected by feeding carbon monoxide past an anode and oxidising it at the latter. The oxidation stream to be measured is a measure for the CO concentration- With such a method a relatively high electrode voltage is applied in order to be able to oxidise CO. This voltage is dependent on the electrode material and the environment in question. A voltage of > 600 mV above the potential of the normal hydrogen electrode(NHE) is mentioned as a typical value. Examples thereof are described in US-A 5 650 034 and EP 1 154 267 A2. However, such a method is unsuitable in a. hydrogen-rich environment such as is present in fuel cell installations where hydrogen-rich gas is a promising energy carrier. The hydrogen-rich gas is fed past the anode of a measurement cell. During this procedure carbon monoxide screens part of the anode catalyst and the yield of the cell for oxidation of hydrogen will decrease. According to a first embodiment it is possible to measure the equilibrium value of the current density that is established. However, this method is time-consuming. with carbon monoxide. After some time the CO is removed there from by increasing the potential on the anode and a new measurement cycle can start. With tills method, a relatively low potential is used at the sensor electrode to prevent oxidation of CO taking place, Of course, oxidation of hydrogen remains possible, With the method described above for the measurement of CO in. a hydrogen-rich environment the measurement gas is fed past both the anode and the cathode, In order to obtain an accurate measurement it is essential that the pressure of the gas is accurately controlled or is well known, The same applies in respect of the temperature of the cell. Another important factor is the relative humidity of the gas. This humidity is important because the membrane must have a constant proton-conducting capacity. If there is no proton-conducting capacity, the measurement result is inaccurate. It has been found that at a measurement cell temperature that is higher than the dew point of the gas insufficient moisture is present to achieve an accurate measurement measurement cell with a slow sensor response as a result. The aim of the present invention is to provide a method for the detection of carbon monoxide in a hydrogen-rich gas stream, This aim is achieved in the method described above in that the hydrogen -rich gas stream is fed only past said anode and said cathode is placed in a water bath. Claims 1. Method for the detection of CO in a hydrogen-rich gas stream, comprising feeding said gas stream past an electrochemical sensor, measurement of the current density through said electrochemical celt at a potential for the sensor electrode applied such that no oxidation of CO will take place, whilst oxidation of hydrogen is possible, resulting in the electric current in said electric cell, and determination there from of the CO concentration, the hydrogen-rich gas stream being fed past the anode of said sensor and the cathode of said sensor being wetted with water by placing in a water reservoir, characterized in that the hydrogen-rich gas stream is fed only past said anode and said cathode is placed in direct contact with the water (liquid). 2. Method according to claim 1, wherein said cathode is placed in the reservoir such that it forms the bottom of said reservoir, 3. Method according to claim 1, wherein determination of the CO concentration from the current intensity comprises calculation of the size of the decrease in current intensity, 4. Method according to one of the preceding claims, comprising brief application of a second, higher potential in order to oxidise the CO present on the anode. 5. Method according to one of the preceding claims, wherein the same catalyst material is used for said anode and cathode, 6. Method according to one of the preceding claims, wherein the inlet and the outlet of the sensor for the hydrogen-rich gas stream to be measured are connected to the anode only. 7. Device for the detection of CO in a hydrogen-rich gas stream, comprising an electrochemical cell (1,11) with anode (4,14), plastic membrane (5,15) and cathode (3,13), provided with an inlet (22) for gas and an outlet (23) for gas as well as control anode, wherein said cathode is provided with a water supply (2,12,16) characterized in that said gas inlet and gas outlet are connected to said anode only and in that said water supply provides direct contact of liquid water and said cathode. 6. Device according to claim 7, wherein said water supply comprises a reservoir the bottom of said reservoir being said cathode. 9. Device according to claim 6, Wherein said water supply comprises a water reservoir (2,12). 10. Device according to claim 7 or 8, wherein the cathode is provided with hydrogen gas discharge means (17), 11. Device according to one of claims 7-10, wherein the membrane is provided with a wetting zone (28) for the gas flowing past the anode and a measurement zone (29) for said gas located downstream of said wetting zone, 12. Device according to one of claims 7-10, wherein a path (21) for the gas to be measured is delimited between the anode and the adjoining component facing away from the membrane, 13. Installation, comprising a feed line for hydrogen-rich gas, wherein an auxiliary line in which the according to one of claims 7-l23 is incorporated branches from said line.

Documents:

1840-chenp-2005 abstract granted.pdf

1840-chenp-2005 claims granted.pdf

1840-chenp-2005 description (complete) granted.pdf

1840-chenp-2005 drawings granted.pdf

1840-chenp-2005-abstract.pdf

1840-chenp-2005-claims.pdf

1840-chenp-2005-correspondnece-others.pdf

1840-chenp-2005-correspondnece-po.pdf

1840-chenp-2005-description(complete).pdf

1840-chenp-2005-drawings.pdf

1840-chenp-2005-form 1.pdf

1840-chenp-2005-form 3.pdf

1840-chenp-2005-form 5.pdf

1840-chenp-2005-form18.pdf

1840-chenp-2005-pct.pdf