Process and apparatus for determining ratio of fluid components such as methanol and water for reforming feed

• US 20030016030A1
• Filed: 05/15/2001
• Published: 01/23/2003
• Est. Priority Date: 05/15/2001
• Status: Active Grant

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Braatz, Paul O., Kirby, Kevin W., Schwartz, Robert N.
• Granted Patent: US 6,690,180 B2
• Time in Patent Office: Days
• US Class Current: 324/670
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: H01M 8/04089 of gaseous reactants
• CPC Class Codes: H01M 8/04194 Concentration measuring cells
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A method and sensor for determining the ratio of two components in a fluid mixture comprising a test cell in open communication with the fluid mixture and a reference cell containing a desired fluid mixture not in contact with the fluid mixture being tested, said reference and test cells having the same cell geometry. By use of a capacitance divider system, one determines the relative capacitances of said cells correlated with the dielectric constants of the respective fluid mixtures and ascertains the ratio of one component to the other component in the fluid mixture on the basis of the linear and monotonic correlation between the dielectric constant of the mixture at a given temperature and the ratio of one component to the other component. Preferably a mixture of methanol and water is tested such as for use as a feed to a reformer used in supplying hydrogen to a fuel cell. A fixed capacitor equivalent to the reference cell at a given temperature is usually substituted for the latter.

Claims

1. A process for testing a fluid mixture containing methanol and water in a given ratio so as to determine said ratio, which comprises:

establishing a test cell between opposed electrodes contacting said fluid mixture, said fluid mixture being tested at a given temperature and said test cell being in open flow communication with said fluid mixture being tested;

imposing an alternating voltage of a given frequency across said electrodes;

measuring the dielectric response of the fluid mixture in said test cell at said temperature and frequency, and

determining the ratio of methanol to water in said mixture on the basis of the dielectric response thus measured.

2. A process according to claim 1, in which the fluid mixture is a liquid mixture.

3. A process according to claim 1, in which the fluid mixture is a gas mixture.

4. A process according to claim 1, wherein the dielectric response of the test cell is measured in terms of the dielectric constant of the fluid mixture in said cell, the dielectric response of the fluid mixture being tested varying in an essentially linear and monotonic relation to the ratio of methanol to water in said mixture at a given temperature of said fluid.

5. A process according to claim 2, wherein the electrodes of the test cell are substantially totally immersed in the liquid mixture.

6. A process according to claim 1, which further comprises:

providing a reference cell established by opposed electrodes having operational characteristics equivalent to those of the electrodes of the test cell and containing therebetween a fluid mixture having a known ratio of methanol to water;

maintaining said fluid mixture of said reference cell at the same temperature as the fluid mixture being tested, said electrodes of the reference cell being subject to an alternating voltage of the same frequency as imposed on the electrodes of the test cell;

measuring the dielectric response of the reference cell; and

comparing said dielectric response measured in said reference cell to that measured in the test cell so as to determine the ratio of the methanol to water in the fluid mixture in the test cell.

7. A process according to claim 6, in which the fluid mixture of the reference cell has a ratio of methanol to water corresponding to a desired value.

8. The process according to claim 6, wherein one of the opposed electrodes of the test cell and one of the opposed electrodes of the reference cell are respectively connected to opposite poles of a source of the alternating voltage and the other electrodes of the opposed electrodes of each of said cells are connected so that the electrodes of said cells are in series, the impedance of the test cell being determined in relation to that of the reference cell at a given voltage and frequency of the voltage source so as to compare the respective dielectric responses of said cells.

9. A process according to claim 8, wherein the voltage drop across the electrodes of the test cell is determined in relation to the voltage drop across the electrodes of the reference cell so as to determine the respective impedances of said cells, the capacitive components of said impedances being correlated with the dielectric constants of the fluid mixture being tested and that of the reference cell.

10. A process according to claim 1, which comprises providing a reference element of given impedance, said impedance being equivalent to that of a reference cell having equivalent operating characteristics to those of the test cell, said reference cell having a fluid mixture of methanol and water of a known ratio and of known temperature and being operated at the same frequency as that of the test cell, and which further comprises:

measuring the temperature of the fluid mixture being tested,

measuring the impedance of the fluid mixture in the test cell,

comparing the impedance of the test cell to that of the reference element so as to determine the capacitance of the test cell, and

determining the ratio of methanol to water in the fluid mixture of the test cell on the basis of the capacitance and temperature of the mixture in the test cell.

11. A process according to claim 10, in which the fluid mixture is a liquid mixture.

12. A process according to claim 3, which comprises providing a reference element of given impedance, said impedance being equivalent to that of a reference cell having equivalent operating characteristics to those of the test cell, said reference cell having a gas mixture of methanol and water of a known ratio and of a known temperature and pressure and being operated at the same frequency as that of the test cell, and which further comprises:

measuring the temperature and pressure of the gas mixture being tested,

measuring the impedance of the gas mixture in the test cell, comparing the impedance of the test cell to that of the reference element so as to determine the capacitance of the test cell, and

determining the ratio of methanol to water in the test cell on the basis of the capacitance, temperature and pressure of the gas mixture in the test cell.

13. A process according to claim 1, in which the fluid mixture being tested is being supplied to a reformer reactor for producing hydrogen.

14. A process according to claim 1, in which the dielectric response of the fluid mixture is measured substantially continuously.

16. A sensor according to claim 15, in which the electrical circuit act as a capacitance divider circuit to determine the capacitances of the respective cells.

17. A sensor according to claim 15, in which the test cell is contained in an enclosure containing the mixture of two fluid components being tested.

18. A sensor according to claim 15, in which the opposed electrodes of the test cell are contained in an enclosure having a mixture of two liquids being tested.

19. A sensor according to claim 18, in which the opposed electrodes of the test cell are positioned so as to be totally immersed in the mixture of liquids in the container and the opposed electrodes of the reference cell are positioned to be totally immersed in the liquid mixture in the reference cell.

20. A sensor according to claim 15, which comprises:

compartment walls defining a compartment for the test cell, said compartment walls including an opening communicating with the interior of an enclosure containing the fluid being tested,

said walls further defining an adjacent compartment for the reference cell, said compartment not having an opening communicating with the interior of the enclosure containing the fluid being tested, there being a common wall separating said compartments,

said compartments, being in effective heat exchange relationship with the fluid being tested so as to maintain the fluids within the test cell and within the reference cell at substantially the same temperature.

21. A sensor according to claim 20, wherein the common wall is provided by a common electrode for both compartments, each of said pairs of opposed electrodes of the test cell and reference cell, respectively, including the common electrode, and the other electrode of each of at least the pair of opposed electrodes defining the reference cell having an exposed outer surface in contact with the fluid in the enclosure, whereby said exposed surface provides heat exchange with the fluid mixture being tested.

22. A sensor according to claim 15, in which the opposed electrodes are parallel plates.

23. A sensor according to claim 15, in which the opposed electrodes are coaxial cylinders.

25. A sensor according to claim 24, in which the test cell is contained in an enclosure containing a mixture of two fluid components being tested.

26. A sensor according to claim 24, in which the opposed electrodes of the test cell are contained in an enclosure having a mixture of two liquids being tested and are positioned as to be totally immersed in said liquid mixture.

27. A sensor according to claim 24, in which the opposed electrodes are parallel plates.

28. A sensor according to claim 24, in which the opposed electrodes are coaxial cylinders.

29. A sensor according to claim 28, in which the cylindrical electrodes are radially spaced from each other by respective electrically insulating means adjacent the opposite ends of said cylindrical electrodes to form an annular space for the flow of the fluid being tested, said insulating means including passageways to permit the flow of said fluid.

30. The sensor according to claim 25, in which the enclosure contains a mixture of two gaseous components being tested, and which includes a pressure measuring device for measuring the pressure of the gaseous mixture in the test cell, the ratio of the two gas components in the test cell being determined on the basis of the impedance of a gas mixture in the test cell and the impedance of the reference element and the temperature and pressure of said gas mixture as measured by the temperature measuring device and pressure measuring device, respectively, the impedance of the reference cell element being the same as that of a reference cell of equivalent operating characteristics as those of the test cell, said reference cell having a gas mixture of the same two components in a known ratio and at a specific temperature and pressure.

15. A sensor for determining the ratio of two components in a test fluid mixture, mixtures with different ratios of said components having respectively different dielectric constants at a given frequency of an imposed alternating voltage and at a given temperature of said test fluid mixture when said test fluid mixture is subjected to said alternating voltage, said sensor comprising:

a first pair of opposed electrodes establishing therebetween a test cell, the opposed electrodes of said test cell being in contact with said test fluid mixture being tested, said test cell having a test cell impedance;

a reference cell established by a second pair of opposed electrodes having equivalent operating characteristics to those of the first pair of opposed electrodes, said reference cell containing a reference fluid mixture of the two components in a known ratio and being isolated from said test fluid mixture, said reference cell having a reference cell impedance;

an electrical circuit wherein one of the opposed electrodes of the first pair of electrodes is connected to one pole of a source of alternating voltage and one of the electrodes of the second pair of electrodes is connected to the other pole of the source of alternating voltage, and wherein the other of the opposed electrodes of the first and second pair of electrodes are connected together for serial flow between said pairs of electrodes of the test cell and reference cell, respectively; and

a voltage measuring device connected to said circuit for measuring the voltage drop across the test cell so as to determine the voltage drop across the test cell in relation to the voltage drop across the reference cell;

said relative voltage drops being used to determine said test cell impedance relative to said reference cell impedance and thus to determine the dielectric constant of the test fluid mixture relative to that of the reference fluid mixture at a given temperature of said test and reference fluid mixtures and at a given voltage of the imposed alternating voltage, whereby the ratio of said components of the test fluid mixture to the ratio of the components of the reference fluid mixture is correlated with the respective dielectric constants of said test and reference fluid mixtures.

24. A sensor for determining the ratio of two components in a test fluid mixture, mixtures with different ratios of said components having given dielectric constants at a given frequency of an imposed alternating voltage and at a given temperature of said test fluid mixture when said test fluid is subjected to said alternating voltage, which comprises:

a pair of opposed electrodes establishing therebetween a test cell, the opposed electrodes of said test cell being in contact with said test fluid, said test cell having a test cell impedance;

a reference element including a capacitor having two terminals, said reference element having a known impedance, said impedance being the same as that of a reference cell of equivalent operating characteristics to those of the test cell, said reference cell having a reference fluid mixture of the same two components in a known ratio and at a specific temperature;

an electrical circuit wherein one of the opposed electrodes of the test cell is connected to one pole of a source of alternating voltage of a given frequency and one of the terminals of the capacitor is connected to the other pole of the source of alternating voltage, and the other of the opposed electrodes and the other terminal of the capacitor are connected together for serial flow between the test cell and the capacitor;

a temperature measuring device for measuring the temperature of the mixture in the test cell; and

a voltage measuring device connected to said circuit for measuring the voltage drop across the test cell so as to determine the voltage drop across the test cell in relation to the voltage drop across the capacitor;

said relative voltage drops being used to determine said test cell impedance relative to said capacitor impedance and thus to determine the dielectric constant of the test fluid mixture relative to that of the reference fluid mixture at a given temperature of said test fluid mixture as determined by the temperature measuring device, and at a given voltage of the imposed alternating voltage, whereby the ratio of said components of the test fluid mixture to the ratio of the components of the reference fluid mixture is correlated with the respective dielectric constants of said test and reference fluid mixtures.