AU2001100600A4 - Powered gas meter - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT POWERED GAS METERS BACKGROUND OF THE INVENTION This invention relates to electrically powered gas meters.

The requirements of a gas meter include that it be relatively cheap to manufacture and have high reliability in its remote operating location while providing accurate metering. These requirements have proven limiting in providing an electronic gas meter due to the power needs of such a meter.

An electronic gas meter is preferred to a conventional gas meter because it can provide more accurate metering and provide additional features, such as pre-payment or cut-off valves, communication devices etc, that are not possible with non-powered metering devices. However the limitations in the power source have prevented electronic meters from being seriously implemented. A battery or other charge storage device with the required longevity has been prohibitively expensive. Cheaper batteries can be used but do not provide the required lifetime.

SUMMARY OF THE INVENTION In a first aspect, the invention provides a gas meter including electrically powered means for measuring the flow of gas through said meter, said measuring means being powered by the conversion to electrical energy of chemical energy from a portion of said gas.

m In a second aspect, thc invention resides in a method of powering an electrically powered gas meter, including the steps of taking a portion of the gas flow through the meter, converting the chemical energy of said gas portion to electrical energy and using said electrical energy to power said meter.

In one preferred form, the measuring means is connected to a charge storage device provided with electrical energy from said chemical to electrical energy conversion.

Preferably, the meter includes a reaction chamber adapted for flameless combustion of said gas portion, the reaction chamber preferably including air intake means for mixing said gas portion with air, combustion means for producing combustion of said gas-air mixture, and exhaust means for combustion products formed by said combustion. Preferably also the combustion means includes an ignition means including an ignition filament, and combustion means including a catalytic combustion surface formed on a catalytic combustion clement surrounding said filament.

The invention further resides in electricity generation modules that may be fitted onto existing electrically powered gas meters as an energy source for such meters.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred features and embodiments of the invention will be described by way of example only with reference to the accompanying figures in which:- Fig. 1 is a schematic diagram of an electronic meter/regulator unit having an energy generation module; Fig. 2 is a schematic of a first embodiment of an energy generation module; Fig. 3 is a schematic of a thermoelectric device adapted for use in a second embodiment; and Fig. 4 is a schematic of a second embodiment of an energy generation module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 an electronic gas meter and regulator unit incorporating an energy generation module is shown generally at 10 and includes a gas supply line 11 to an electronic gas meter 12 and regulator 13 and an outlet 14 from the unit 13 that continues downstream towards a premises.

The gas supply line 11 includes a secondary gas path 15 passing through an energy generation module 16 and further vented to air. A control valve 17, for example a piezoelectric valve, controls the flow of gas through the bypass line The gas meter/regulator unit may include any known electronic gas meter such as the ultrasonic gas meter of the ultrasonic transmitter/receiver type, for example as described in our co-pending application no. PCT/AU99/00258, the contents of which are incorporated herein by reference. In addition, the regulator may also be electrically powered as described in the co-pending application mentioned above. The meter/regulator unit 12, 13 is connected to a charge storage device 18, which is continually recharged by the energy generation module 16.

A first embodiment of an energy generation module will now be described with reference to Fig. 2. The energy generation module is shown generally at 16 and includes a heat source 21 and a thermoelectric device 22. With reference to Fig. 3, the thermoelectric device 22 is provided with a plurality of semiconductor couples 30 (Pand N-type semiconductors) connected electrically in series and thermally in parallel, sandwiched between the first 31 and the second electrodes 32. A circuit is completed by connecting the electrodes through the charge storage device 18.

The heat source 21 (Fig. 2) includes a heating filament 23 disposed in contact with a catalytic bed 25 such as a platinum coated mesh or platinum impregnated alumina matrix. A solid thermal conductor 24 is placed in contact with thermoelectric device 22.

The catalytic bed is disposed in the gas bypass line 15. To operate the heat source 21 the heating filament is energised which creates a localised heat zone on the catalytic bed 25 of approximately 400-500 0 C. At the same time, gas is introduced into the bed surrounds where it undergoes oxidation catalysed by the heated platinum. As the bed temperature is well below the approximately 800 0 C ignition temperature of the gas, the gas combustion is flameless. The oxidation reaction releases heat which goes to heating the entire bed 25. By considered choice of parameters such as the gas flow rate and the bed 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 23 can be stopped.

The heat produced from the flameless combustion of the gas heats the thermal conductor 24 to approximately 200 0 C. This heat is transferred to the first electrode of the thermoelectric device. The semiconductor elements in the thermoelectric device 22 typically have a maximum operating temperature of approximately 230 0 C before standard thermionic electron excitation destroys the semiconductor effect. The temperature drop across thermal conductor 24 will keep the surface temperature of the thermoelectric of the thermoelectric device to within acceptable parameters.

The energy generation module 16 described with reference to Fig. 2, can operate on relatively small gas amounts. The catalytic bed is approximately 12 by 12 mm.

Operating at 400-500'C with gas flow at approximately 30-50 cc/min a temperature differential of 70 0 C can be generated across the thermoelectric device, which can generate an electric current of 72 mA at 1.0 V. This voltage can be increased to approximately 3.3V by DC transformer (not shown) to recharge the battery 18.

The above described embodiment has been described with specific reference to platinum catalysts though other oxidative catalysts can be employed, for example other noble metals.

The energy generation modules described above can produce sufficient energy to power the gas meter and regulator from very small amounts of gas that represent a negligible loss to the gas supplier.

The charge storage device that stores the electrical energy produced and powers the gas meter and regulator, may be a rechargeable battery or a low-leakage capacitor.

An advantage of the preferred embodiment described herein is that the construction of the energy generation module also allows the calorific value of the gas sample to be measured. This is significant for gas meters that output an energy consumption value as opposed to a volume consumption value. Such meters are described in our copending application No. PCT/AU99/00259, the contents of which are incorporated herein by reference.

To ascertain the calorific value of the gas sample, the heating filament comprises a catalysed coil, for example a platinum coil. Prior to running the energy generation unit, the filament is at ambient temperature which can be determined by measuring the resistance of the filament. The filament is then heated by an electrical current as the control valve 17 is opened to provide a gas sample. Oxidation of the gas sample by the heated filament and the catalysed bed 25 uniformly heats the bed 25 to the point where a sustainable oxidation reaction is achieved, at which point charging of the filament is no longer necessary and the power to the filament is stopped. The temperature of the filament during this steady state reaction is dependant on the rate of the oxidation reaction which is in turn dependant on the calorific value of the gas.

The steady state temperature is determined by taking a second measurement of the resistance of the filament. The difference between the two measured resistances or temperatures can be converted to a calorific value using a look-up table or a mathematical algorithm that can take into account other relevant factors such as pressure etc. The calorific valve can then be used in a calculation of energy consumption.

m The amount of electrical energy that can be generated by the thermoelectric device is dependent on the amount of heat generated by oxidation of the gas sample and the capacity of the heat sink.

Referring to Fig. 4, 40 is an energy generation module consisting of heating filament 41 and a cylindrical catalyst element 42 such as platinum coated mesh or platinum impregnated alumina matrix, within an aluminium tube 43. A gas jet 45 supplies the gas portion to the reactor, and entrains an air stream 46.

An aluminium or other thermally conductive block 44 transmits heat from the reactor wall 43 to one side of the thermoelectric device 22.

The thermoelectric device 22 produces a current whenever a temperature differential exists across the semiconductors.

To provide the required temperature gradient the other side of the thermoelectric device is placed against a portion of the gas meter/regulator unit that is of large thermal mass in order to achieve as great a temperature differential across the semiconductor elements as possible.

The energy generation module is preferably operated by a CPU that controls the timing of operations such as opening and closing of the control valve 17 (Fig. and any necessary priming of the gas reactions required to commence electricity production, for example energising the filament of the thermoelectric device. The CPU also performs the necessary calculations for determining the calorific value of the gas sample and may also incorporate other functions of the gas meter such as calculation of energy consumption.

The timer may be set to operate the energy module for one or more sessions each day, each session being of approximately 30-60 minutes duration, but this can be varied depending on the power requirements of the specific meter and regulator employed.

Preferably, the sessions are timed to occur at times of minimum gas usage by the consumer, which may be predicted on the basis of typical usage patterns or triggered by sensing a long period of minimal gas use. A one hour energy generation session per day, at 50cc of gas per minute, is expected to be sufficient to keep the electronic gas meter fully powered. Alternatively the energy module may operate continuously, though this will consume more gas, or it may operate only when certain flow conditions through the meter and regulator are achieved.

The combustion products of the energy generation modules may be vented to atmosphere.

The energy generation unit may be made integral with the meter/regulator unit.

Preferably, the energy generation unit is also made as a module that can be retro-fitted onto an existing powered gas meter either as a substitute or supplement to the existing power supply.

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.

It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates.

It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates.

Claims (4)

1. A gas meter including electrically powered means for measuring the flow of gas through said meter, said measuring means being powered by the conversion to electrical energy of chemical energy from a portion of said gas.

2. A gas meter according to claim 1 including a reaction chamber adapted for flameless combustion of said gas portion.

3. A gas meter according to claim 2 further including a gas control valve for controlling drawing of said gas portion from the gas flowing through the meter and supply of said portion to said reaction chamber.

4. A gas meter according to claim 2 including a thermoelectric device and thermally conductive means transferring heat generated by said flameless combustion to said thermoelectric device adapted for converting thermal energy to electrical energy. A method of powering an electrically powered gas meter, including the steps of taking a portion of the gas flow through the meter, converting the chemical energy of said gas portion to electrical energy and using said electrical energy to power said meter.