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Title:
GAS METER WITH IMPROVED CALORIFIC MEASUREMENT
Document Type and Number:
WIPO Patent Application WO/2003/048692
Kind Code:
A1
Abstract:
A gas meter (10) is provided with a path (26) for a gas sample to be supplied to a reaction chamber (25). The gas chamber is subjected to flameless combustion by means of a combustion device (35) and a catalyst coated member (50). The temperature of the gaseous combustion products derived from a thermocouple (36) enables the calorific value of the gas to be calculated.

Inventors:
TORPY KEITH MARIO (AU)
Application Number:
PCT/AU2002/001633
Publication Date:
June 12, 2003
Filing Date:
December 03, 2002
Export Citation:
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Assignee:
EMAIL LTD (AU)
TORPY KEITH MARIO (AU)
International Classes:
G01N25/32; G01N33/22; (IPC1-7): G01F1/66; G01F15/00; G01N25/32; G01N33/22
Domestic Patent References:
WO1999053273A11999-10-21
Foreign References:
US5012432A1991-04-30
US5807749A1998-09-15
GB2312508A1997-10-29
Other References:
PATENT ABSTRACTS OF JAPAN
PATENT ABSTRACTS OF JAPAN
Attorney, Agent or Firm:
Halford, Graham William (New South Wales 2000, AU)
Download PDF:
Claims:
CLAIMS.
1. A gas meter for a combustible gas having: a) metering means generating an output representative of gas flow, b) means for supplying a sample of the gas to a reaction chamber, c) at least one catalyst member in said reaction chamber including a catalyst material capable of causing flameless combustion of the gas sample, d) means for introducing air to said chamber in a proportion relative to said gas sample as to provide substantially complete combustion thereof, e) means generating an output responsive to the temperature of the gaseous combustion products in the region of said catalyst member, and f) means utilising said outputs to calculate energy usage.
2. A gas meter according to claim 1 wherein said means for generating an output representative of temperature includes a temperature responsive device located sufficiently close to the zone of flameless combustion to be influenced by substantially all of said combustion products but by substantially no condensation products.
3. A gas meter according to claim 1 wherein said catalyst material consists of a coating of catalytic material on a gauze substrate in the path of said gas sample.
4. A gas meter according to claim 3 in which said output responsive to temperature is taken during continuous combustion of said gas in said chamber.
5. A gas meter according to claim 1 in which said output responsive to temperature is taken during combustion of a predetermined volume of said gas.
Description:
Gas Meter with Improved Calorific Measurement BACKGROUND OF INVENTION Conventional gas meters measure consumption based on gas volume flow through the meter. The meter reading is recorded on the consumer's account and multiplied by a conversion factor which is calculated to reflect the typical or average calorific value of the gas being supplied. This converts the volume measurement into a quantity of energy, which is the true commodity which the consumer is purchasing.

One of the disadvantages of traditional gas meters is that the amount of gas supplied is measured under operating conditions, while the average calorific value of the gas is often determined under standardised conditions. It is well known that natural gas, liquefied petroleum gas (LPG) and other energy gases are typically mixtures of hydrocarbons, having significant variations in calorific value depending on temperature, pressure, source, the ratios of the particular hydrocarbons. Further, the constituents of a gas may include water vapour and other non-combustible components. Moreover, the exact composition of the gas supplied may be unknown.

These variations may make the prior art energy calculations for individual consumers inaccurate.

The present applicant has proposed a gas meter incorporating calorific measurement by means of catalytic combustion (PCT/AU 99/00259). The meter includes a reaction chamber which draws a gas sample from the gas passing through the meter. The calorific value is determined using a resistor, coated with a catalyst material, that forms part of a Wheatstone bridge circuit. Oxidation of the gas-air mixture on the coated surface of the resistor causes a temperature and resistance change dependent on the calorific value of the gas. That change is detected by the Wheatstone bridge.

SUMMARY OF INVENTION

The present invention aims to provide a reaction chamber and gas sampling arrangement which is capable of a greater level of performance than the arrangement described above.

The invention broadly resides in a gas meter for a combustible gas having a) metering means generating an output representative of gas flow, b) means for supplying a sample of the gas to a reaction chamber, c) at least one catalyst member in said reaction chamber including a catalyst material capable of causing flameless combustion of the gas sample, d) means for introducing air to said chamber in a proportion relative to said gas sample as to provide substantially complete combustion thereof, e) means generating an output responsive to the temperature of the gaseous combustion products in the region of said catalyst member, and f) means utilising said outputs to calculate energy usage.

Preferably the means for generating an output representative of temperature includes a temperature responsive device located sufficiently close to the zone of flameless combustion to be influenced by substantially all of said combustion products but by substantially no condensation products.

Preferably also the catalyst material consists of a coating of catalytic material on a gauze substrate in the path of said gas sample.

Preferably also the output responsive to temperature is taken during continuous combustion of said gas in said chamber.

In an alternative embodiment the output responsive to temperature is taken during combustion of a predetermined volume of said gas.

The reaction chamber preferably includes an air intake adjacent a gas injector to said chamber, such that air is drawn by gas injection into the reaction chamber.

The meter preferably includes means for periodically or constantly withdrawing a gas sample, including a fixed volume chamber, an inlet valve, and an outlet valve, said inlet valve controlling the flow of the gas into said fixed volume chamber, said outlet valve controlling the flow of the gas into the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS Further preferred embodiments are now described with reference to the accompanying drawings, in which: Fig. 1 is a schematic of a preferred gas meter arrangement; Fig. 2 is a schematic of a volume chamber arrangement; Fig. 3 shows a reaction chamber; Fig. 3A is a detailed isometric view of a calorific member; Fig. 4 is a partly sectioned side elevation view of a combustion device; Fig. 5 is a section taken on the line 5-5 in Fig. 4; Fig. 6 is a graph showing the sensor signal versus time for continuous mode operation; and Fig. 7 is a graph showing the sensor signal versus time for batch mode operation.

DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows a gas meter/regulator unit 10 having a gas inlet 12 for connection to a high, variable pressure gas supply, typically at 40-600 kPa, and an outlet 13 for connection to the gas plumbing of the premises for which the meter/regulator unit is installed.

Within the unit 10, the gas flow path is divided into a high, variable pressure region between the inlet 12 and a regulator 14, and a low pressure region downstream of the regulator. The regulator 14 acts to reduce the high gas supply pressure to a lower, substantially constant pressure at which the gas is supplied to the premises, typically in the range of 0.5-3. 5 kPa. The regulator 14 may be mechanically operated, such as a

conventional spring-biased valve, but preferably is electronically controlled by a processor/controller 16.

Located upstream of the regulator 14 in the high pressure region of the gas path is an electronic metering apparatus 18, which may be of the type described in Australian Patent No. 682498 and employing acoustic transducers situated at upstream and downstream ends of a gas flow measurement tube. The transducers are controlled by the processor 16 to transmit and receive acoustic (e. g. ultrasonic) signals through the tube to determine the gas flow velocity through the tube and send outputs to the processor 16. The gas flow velocity is calculated from variations in the time taken for the signal to pass along the tube.

Pressure sensors (not shown) may measure the gas pressure in the high pressure region and generate an output to the processor 16. The pressure sensors may be situated either side of the metering means if it is anticipated that there will be significant pressure drop across the metering means.

The unit 10 further includes a volume chamber 20, through which, periodically or continuously as described below, passes from the gas flow path a gas sample for flameless catalytic combustion in a reaction chamber 25. The gas sample is withdrawn downstream of the regulator 14 so that the gas pressure is substantially constant. The operation of the volume chamber is controlled by the processor 16 as described below.

The processor 16 receives the outputs from the reaction chamber 25, the metering apparatus 18 and, optionally, from other sensors such as gas temperature and pressure sensors (not shown) and from this information calculates by means of a suitable algorithm the total energy value of the gas passing through the unit and into the premises. A cumulative energy reading is communicated to a display 17 on the unit.

The processor 16 may also be provided with an external communications link 22 allowing remote reading and control of the meter/regulator unit. For example, if an electronically controlled regulator is used, the unit may have facility for the gas supply

authority to send a signal causing the processor 16 to close the regulator valve 14, shutting off the gas supply to the premises.

As shown Figs. 2 and 3, the gas meter includes a gas sampling passage 26 communicating with the gas flow path through the meter and leading to a volume chamber 20 having an intake valve 27 and an outlet valve 28, through which gas is passed to the reaction chamber 25. The opening and closing of valves 27 and 28 is controlled by the processor 16 to control the flow of a gas sample to the reaction chamber 25 in either a continuous or a batch mode as described in more detail below.

The reaction chamber 25 includes a tube 24 surrounded by a thermally insulating housing 30, a gas and air intake 40 and a gas outlet baffle 33 vented to atmosphere.

The tube 24 is preferably of fused quartz glass or Vycor glass the low thermal mass of which facilitates the capturing of all reaction products in the temperature measurement described below.

Mounted in juxtaposition with the intake 40 is a gas injector 31. The action of the injector draws into air into the chamber for the combustion of the gas sample. The position of the injector 31 relative to the mouth of the tube 24 and the dimensions of the injector 31 and tube 24 are selected so that a substantially stoichiometric ratio of oxygen and combustible gases is provided, enabling complete combustion of the gas sample.

Positioned within the tube 24 near the intake 40 is a combustion device 32, shown in detail in Figs 4 and 5, including an igniter 34 and a catalytic combustion surface 35 for catalysing flameless combustion of the gas-air mixture. The igniter 34 in this embodiment consists of a coil of platinum resistance wire, wound on a quartz fibre rod 41 and mounted by passing its leads 42 and 43 through respective alumina sleeves 44 and 45 mounted by means of hardened alumina paste at 46 on a case 47, which may be externally threaded for engagement in a threaded hole in the wall of the chamber 25. The leads 42 and 43 are brought out of the case 47 to spade terminals 48.

Mounted immediately below the igniter coil 34 is a platinised mesh in the form of a half-round member 49, providing the catalytic combustion surface 35. While platinum is the preferred catalyst, other suitable catalyst materials include stannous oxide or other noble metals, optionally containing dopants such as palladium.

Downstream of the combustion device 32 a loosely coiled roll of platinised mesh 50 is placed in the tube 24. The mesh 50 ensures complete oxidation of the gas sample by presenting a large surface area to the gas flow, while its configuration, as shown in Fig. 3A, offers little obstruction to the flow.

A thermocouple 36 is mounted within the tube 24, spaced from the combustion device 32 and the mesh 50 so as to be responsive to the temperature of the gaseous reaction products of the flameless combustion, but not so far away from the combustion zone as to be affected by condensation products. The precise location of the device 32 will depend on the parameters of the chamber and will be determined by experiment.

To operate the reaction chamber, the heating filament is energised, which creates a localised heat zone on the catalytic element 35 of approximately 400-500°C. The gas sample undergoes oxidation catalysed by the heated platinum. As the catalytic element temperature is well below the approximately 800°C ignition temperature of the gas, the gas combustion is flameless. The oxidation reaction releases heat which goes to heating the gaseous combustion products, which in turn heat the thermocouple 36. By considered choice of parameters such as the gas flow rate and the catalytic member temperature, a sustainable exothermic oxidation reaction can be achieved.

Once a sustainable reaction is achieved, which occurs in less than one minute, power to the filament 34 can be stopped.

Once steady state conditions have been achieved as described below, we have found that there is a remarkably close correlation between the temperature of the combustion products measured in this arrangement with the gas calorific value.

As mentioned above, the apparatus thus described may be operated either by conducting the measurement on a continuous (and substantially constant) flow of gas or as a batch process.

In the continuous mode of operation, the inlet valve 27 remains open at all times and indeed may be dispensed with. With the igniter 34 energised, the gas sample is fed to the injector 31 by opening the valve 28, and the reactor operation commences as described above. Fig. 6 shows the form of the output voltage of the thermocouple 36 against time. The voltage is sampled at regular intervals (suitably once per minute) by the processor 16. It will be observed that after a period of time, which may be of the order of 30 minutes, the temperature conditions stabilise. The stable output value is the required measure of temperature. Once a stable value has been obtained, the measurements can be discontinued, and the sample gas flow turned off by closing the valve 28 until the next measurement is to be made. Alternatively, of course, the apparatus can run continuously.

While the volume chamber 20 is not essential in this continuous mode of operation, it is preferably employed, as it reduces the risk of regulator diaphragm flutter.

Where the apparatus is to be operated in what is referred to herein as a batch mode, in which measurement of calorific value is carried out on a gas sample of fixed volume, the measurement cycle begins with the opening of the inlet valve 27. When the volume chamber 20 is filled with gas, the outlet valve 28 is closed. The processor 16 monitors the pressure in the volume chamber to determine when the pressure reaches a pre-determined level (preferably the pressure in the supply line 26), and then the processor closes the inlet valve 27 to trap a fixed gas volume between valves 27 and 28, thus capturing a known volume of gas at a known temperature and pressure.

After closing intake valve 27, processor 16 energises the igniter 34 and opens outlet valve 28 to feed the gas sample from the volume chamber 20 to the reaction chamber 25. Flameless combustion of the gas sample proceeds as described above.

As the cycle progresses the pressure in the volume chamber 20 reduces. The processor 16 monitors the changes in pressure in the volume chamber to determine when the pressure reaches a pre-determined level (preferably atmospheric pressure), and then outlet valve 28 is closed. After closing the outlet valve, the processor may then open inlet valve 27.

In operation in this batch mode, the pressure of the gas in the volume chamber 20 progressively decreases, and the flow rate and concentration of the gas in the reaction chamber changes slowly with time. As a result the temperature indicated by the thermocouple 36 will also change with time. Fig. 7 shows the variation of the output of the thermocouple over the oxidation cycle of the fixed gas sample. During the ignition stage of the cycle, the ignition filament 34 is powered while the reaction is initiated, and the temperature of the thermocouple junction rises. The temperature plateaus when the reaction becomes self-sustaining. This is reflected in a substantially straight line signal as showed in Fig. 7. Finally the temperature drops as the gas sample is exhausted. The measured voltage is communicated to the processor 16 which calibrates the voltage with known gas calorific value measurements.

Preferably, the calorific value determination is based on integration of a whole or part of the voltage-time plot over the cycle. If integration over the whole cycle is used, the power provided to the ignition filament should be taken into account.

Preferably, however, the voltage-time measurement is integrated over a period which excludes the ignition phase, and preferably is integrated over some or all of the plateau phase.

Alternatively, the calorific value determination may be based on the measured voltage (temperature) at a set time lag after ignition.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.