WO2011076355A1 - Gas supply device having a mass flow rate sensor - Google Patents

Abstract

The invention relates to a gas supply device, which serves to supply gas from a gas reservoir assembly (7) to a gas consumer assembly (8). For said purpose a gas pipe assembly (1) is provided between the gas reservoir assembly (7) and the gas consumer assembly (8). A mass flow rate meter (2) for measuring the amount of gas in the gas flowing in the gas pipe assembly (1) on the basis of the mass flow (m) of the gas is arranged in the gas pipe assembly. The measured values of the mass flow rate meter (2) can be passed to a control means (11), which in turn actuates a valve assembly (12) in order to keep the mass flow rate at a predetermined value.

Description

 Gas supply device with mass flow sensor

The invention relates to a gas supply device and a method for supplying gas from a gas supply device to a gas consumption device.

The supply of gas is z. B. necessary as part of a liq ssiggasdosierung for heaters or reformer fuel cell systems that are used for on-board power supply in recreational vehicles, commercial vehicles and boats.

Leisure vehicles, commercial vehicles and boats generally have a liquefied gas supply at an overpressure level of 30 mbar (50 mbar in exceptional cases), to which gas appliances such as cookers, heaters, hot water preparation systems, air conditioners, refrigerators and systems for on-board power supply are connected. The latter may be engine-generator systems or reformer fuel cell systems. Fuel storage for all gas consumers takes place either via tanks installed in the vehicle or boat or, more commonly, via commercially available 5 or 11 kg bottles. The gas consumption devices are connected via pipelines to the liquid gas supply. The liquefied gas is usually supplied to the gas consuming devices in the gaseous state. In this context, propane, butane or mixtures thereof are referred to as liquefied gas.

Liquefied petroleum gas is generally offered in different compositions, which may vary regionally as well as seasonally. In addition, when the gas is withdrawn from the gaseous phase of a tank, there occurs an effect that the gas composition changes during the purge operation due to different vapor pressures. Thus, the compounds with higher vapor pressures and, in the course of emptying, more and more molecules of compounds with low vapor pressure tend to be taken out first. In practice, this means that the extracted gas initially contains more propane and the equilibrium shifts more and more towards butane. In extreme cases, a gas appliance must therefore be able to work with 100% propane and 100% butane.

Various devices and methods for liquefied gas metering in gas appliances are known from the prior art: When dosing via a nozzle or orifice plate, the liquid gas is passed through a nozzle at a constant admission pressure (typically 30 mbar in the liquid gas leisure area). This is known for example in liquid gas burners in heating devices of recreational vehicles. Due to the different gas properties such as density and viscosity, however, depending on the gases supplied (propane, butane or mixtures thereof) results in a difference in the carbon amount of up to about 14%. Similar deviations exist with regard to the calorific values of the gases.

In another type of liquid metering, the volume flow is measured, which may result in a defined volume flow of propane and butane, a difference in the amount of carbon or in the calorific value of up to about 36%. This results mainly from the different densities of the gases.

Thus, the amount of carbon and the calorific value vary considerably depending on the quality and composition of the supplied liquefied gas.

A disadvantage of the devices and methods mentioned here is that the different material properties of the liquefied gas, i. of the propane-butane mixture, only insufficiently taken into account. For heaters with LPG burners, this means that the heating power can vary depending on the composition of the LPG.

For liquefied gas fueled reformer fuel cell systems is due to the changing Flüssiggaszu compositions with different reformate gas qualities, ie. with different amounts of hydrogen and residual gas compositions (CO, C0 ₂ or water vapor) to be expected. In various types of reforming such. As the steam reforming or autothermal reforming is the molar ratio of water (steam) to carbon (carbon) - the so-called S / C ratio - a characteristic value. If this value is to be kept substantially constant with changing gas composition and given water flow, a defined carbon flow must be ensured. This is not possible with a conventional liquid gas metering according to the prior art.

The invention is therefore based on the object to provide a Flüssiggasdosiervorrichtung or a gas supply device and a corresponding method, whereby a safe and continu ously operation of a gas consuming device with as constant as possible performance even with changing It is possible to achieve variable gas compositions without having to measure the gas composition.

The object is achieved by a gas supply device according to claim 1 and by a corresponding method according to claim 1 2. Advantageous embodiments of the invention are stated in the dependent claims.

The basic idea of the invention is based on the use of the principle of the thermal mass flow measurement for the liquid gas metering, whereby the abovementioned disadvantages or inaccuracies in the prior art can be largely eliminated.

Accordingly, a gas supply device for supplying gas from a gas storage device to a gas consuming device comprises a gas line device extending between the gas storage device and the gas consuming device, and a thermal mass flow measuring device provided in the gas line device for measuring the gas quantity of the gas flowing in the gas line device due to its mass flow.

The principle of thermal mass flow measurement is based on passing a gas stream over a cooled or heated area. As a result, the medium is heated or cooled. Depending on the technical design is closed by the formation of a temperature profile, the heating or cooling power used or due to temperature changes to the mass flow of the medium, since the heat transfer into the gas is dependent on the mass flow. In addition, the measurement depends on the specific heat capacity of the medium to be measured.

The mass flow measuring device may comprise: a heating or cooling element, a first temperature sensor arranged upstream of the heating or cooling element, a second temperature sensor arranged downstream of the heating or cooling element, and an evaluation device for evaluating a first temperature measured by the first temperature sensor and a second temperature measured by the second temperature sensor and for driving the heating or cooling element. Depending on the configuration, two different measuring methods are possible with the aid of the evaluation device. Accordingly, in a first measurement method, the heating or cooling element can be controlled such that a constant temperature difference between the first temperature sensor and the second temperature sensor is adjusted, wherein the mass flow is determined on the basis of the requisite heating or cooling power. In the second, alternative measuring method, the heating or cooling element can be set to a predetermined heating or cooling power, the mass flow being ascertained on the basis of a subsequently measured temperature difference between the first temperature sensor and the second temperature sensor.

Thus, two alternative technical versions of thermal mass flow meters are given. In the first alternative, the heating element can be regulated to a constant temperature difference between the two temperature sensors, wherein from the heating power is then closed to the mass flow. In the second alternative, the occurring temperature differences between the temperature measuring points are evaluated at a defined heat output and thus deduced the mass flow.

In the gas line device can be provided a controllable valve means for adjusting the mass flow in the gas line device, wherein a controller is provided for driving the valve device in response to a measurement signal from the mass flow measuring device.

The controller may be designed such that it maintains the mass flow of the gas flowing in the gas line device to a predetermined value by actuating the valve device.

This makes it possible to use the measuring method with an actuator, for. B. to combine a proportional valve or a control valve to form a control loop. The measurement and control function can be z. B. integrated in a thermal mass flow controller or combined with this.

The method is basically suitable for all types of Gasverbrau chseinrichtung, which are operated with gaseous hydrocarbons u er different gas compositions. Also, the gas consuming device and the gas supply device described can be used not only in recreational vehicles, boats and commercial vehicles, but also in all other appli ngsbereichen (stationary, mobile), in which a gaseous hydrocarbon to be dosed.

The mass flow measuring device (also referred to as sensor in the following) is tuned by the manufacturer to a specific gas. Should the sensor be for a If another gas is used, a conversion factor must be calculated which converts the flow of one gas into that of the other gas.

The conversion of propane to butane results in a conversion factor of 0.9946. This means that with a thermal mass flow sensor the mass flows of propane and butane can be measured with the same sensor with a deviation of 0. 54%. With the same measurement signal, 0, 54% less butane flows than propane. These values are based on the specific heat capacities at 298 K and 1013 hPa. Because the heat capacities of propane and butane are relatively strongly dependent on the temperature, slight changes occur with changing gas temperatures.

The measuring principle described can be used in manifold gas appliances. Thus, it is possible to carry out a mass flow measurement based on the carbon mole flow in a reformer fuel cell system. In the case of a heating device, the mass flow measurement can be based on the heating or calorific value.

Accordingly, due to the measured amount of gas with the aid of the mass flow measuring device, it is possible to regulate the carbon mole flow of the gas flowing in the gas line device, wherein the controller can be designed in such a way that it substantially controls the carbon mole flow of the gas by activating the valve device keeps constant at a predetermined value.

As already mentioned above, this mass flow measurement based on the carbon mole flow can be used advantageously in a reformer fuel cell system. There, depending on the reforming process (steam reforming or autothermal reforming), the molar ratio of water (steam) to carbon (carbon) - the so-called S / C ratio - is decisive for the composition and quality of the hydrogen-containing reformer produced - matgases or even for the proper functioning and long-term stability of the reformer system itself. The regulation of the S / C ratio for such systems is therefore crucial - especially when in practice the composition of the reformer fuel cell system supplied liquefied gas may have continuously changing propane and butane fractions.

If the value of the S / C ratio is to be kept substantially constant with changing gas composition and given water supply, then a defined carbon flow can be provided. The molar flow of carbon at the same mass flow of butane is about 1, 1% higher than propane. Taking into account the deviation from the mass flow measurement of propane and butane - with the same measuring signal of the mass flow measuring device 0, 54% less butane is metered (see explanation above) - the maximum total deviation of the carbon mole flow is 0.55%. This deviation is thus significantly below the deviations mentioned above.

A liquid gas metering based on the principle of thermal mass flow measurement represents a suitable method for a corresponding reformer system in order to measure the amount of liquid gas with respect to the S / C ratio or in combination with a control device, eg. B. a proportional valve, to regulate. In this case, the mass flow measuring device can be used for measuring the mass flow of the liquefied gas.

In an alternative embodiment, which - as already stated above - is particularly suitable for a heating device - is based on the measured Gasmen ge a heating or calorific value of the gas flowing in the gas conduit means determinable. The control can be designed such that it keeps the heating and / or calorific value of the gas essentially constant at a predetermined value by driving the valve device.

This related to the heating or calorific value mass flow measurement can be advantageously used in a heater. According to the prior art, the metering of liquefied petroleum gas in heating devices takes place via a diaphragm or nozzle, which may result in deviations of up to approximately 14% in the calorific value, depending on the dosage of propane and butane. The result is fluctuating Heizleistu lengths of the heater, depending on the composition of the supplied propane-butane gas mixture it.

For the calorific values of propane and butane, in each case based on the mass, there is a deviation of 1.3%. Taking into account the above-mentioned deviation of the mass flow measurement of 0.54%, this leads to a total deviation of the calorific value of a maximum of approximately 1.85%, if in extreme cases 100% Bu tan or 1 00% propane are supplied. This deviation is considerably lower than the deviation of 36% in the prior art.

The principle of liquid gas metering on the basis of thermal mass flow measurement therefore has a considerably higher accuracy than that of conventional conventional dosing via orifices or Düs sen. Even in extreme cases the use of pure propane or pure butane results in only a relatively small deviation. In combination with an actuator, z. B. a control or proportional valve, in this way a very accurate control of the heating or calorific value of Gasverbrau chseinrichtungen be guaranteed.

The system is also capable of compensating for variations due to pressure differences in pressure control. It has already been stated above that LPG metering is often carried out at a target value of 30 mbar. In practice, however, it is readily usual for the pressure values to be between 25 and 35 mbar. These pressure fluctuations cause fluctuations in the mass flow, which can be detected during the mass flow measurement and can be compensated by control technology in order to achieve a constant heating power.

A display device may be provided for displaying a mass flow value measured by the mass flow measuring device. This allows the operator, in addition to the controller or alternatively to the controller, to intervene in a regulating manner via a corresponding valve if the mass flow value is outside a predetermined tolerance range.

The gas line device may have a main gas line and a secondary gas line provided parallel thereto, wherein the mass flow measuring device may optionally be arranged both in the secondary gas line and in the main gas line. Corresponding correction values are then used to deduce the total gas quantity.

The mass flow measuring device may be provided separately from the gas consuming device. It is also possible to provide the measuring device to the Gasvorratseinrichtu ng or integrate into the gas appliance. The integration into the gas consuming device may be useful if the measuring method is combined with the valve device to form a control loop.

These and further features of the invention are explained in more detail below by means of examples with the aid of the accompanying figures. Show it:

1 shows the basic structure of a thermal mass flow measuring device; Fig. 2 shows the schematic structure of a gas consumption system with the erfindu ngsgemäßen Gaszufü supply device.

Fig. 1 shows in schematic form a Gasleitu ng 1, in which a mass flow m of a gas, for. B. a liquefied gas is being led. In the gas line 1, a thermal mass flow meter 2 is used.

The mass flow meter 2 has a heating or cooling element 3, a first temperature sensor 4 provided upstream thereof and a second temperature sensor 5 provided downstream thereof.

In addition, an evaluation device 6 is provided in the mass flow meter 2. In addition, it is still possible to provide additional measuring points for temperature measurement, if this increases the accuracy of measurement.

The heating or cooling element 3 (depending on the application, the mass flow can be heated or cooled) can be operated such that a constant temperature difference between the two temperature sensors 4, 5 sets. Accordingly, the evaluation device 6 controls the heating or cooling element 3 in order to maintain this constant temperature difference. From the necessary heating or cooling capacity can then be closed in a known manner to the mass flow.

Another possibility is to evaluate the temperature differences between the two tempera ture sensors 4, 5 at a defined heating and cooling power maintained by the evaluation device 6, and in this way to draw conclusions about the mass flow.

The mass flow can thus be determined as the gas mass per unit time.

Fig. 2 shows in schematic form a gas supply or consumption system.

In this case, the gas line 1 connects a serving as Gasvorratseinrichtu ng liquid gas supply 7 with a gas consumer 8 (gas consumption device). Downstream of the liquefied gas reservoir 7, a pressure regulator 9 is provided with which the voltage applied to the liquefied gas reservoir 7, usually relatively high pressure to a suitable operating pressure, for. B. 30 mbar is regulated. Downstream of the pressure regulator 9 is a check valve 10, z. B. a solenoid valve disposed, which can be controlled via a controller 1 1. The Steueru ng 1 1 is thus able to open the gas supply to the gas consumer 8 via the check valve 1 0 and close.

Once again downstream of the check valve 10, the above-explained thermal mass flow meter 2 is arranged, to which a valve device 1 2 controllable via the controller 11 closes downstream. The valve device 12 may be a solenoid valve, a control valve (for example a proportional valve) or a different type of actuator.

Downstream of the valve device 12 is finally the gas consumer 8, z. B. a heater, a Kühlvorrichtg (air conditioning, refrigerator) or a reformer fuel cell system arranged. The gas consumer 8 may in particular be burners (catalytic, conventional), reforming reactors, reaction chambers of fuel cells or combustion chambers of engines.

As already explained in detail above, it is possible with the aid of the mass flow meter 2 to determine the carbon quantity in the gas guided via the gas line 1 and to transmit corresponding information to the control unit 1 1. The controller 1 1 then controls the valve device 1 2 such that a desired mass flow is achieved. This desired mass flow is z. B. due to a desired heat output (for heating) or based on a desired S / C ratio for the reformer fuel cell system.

The components check valve 10, control 1 1, mass flow meter 2, valve device 12 and 8 gas consumers can be integrated in the form of a gas consumption system 13. The gas consumption system 13 then contains in addition to the gas consumer 8 itself also the other components that are required to control the mass flow.

Claims

claims 1 . Gas supply device for supplying gas from a Gasvorratsein direction (7) to a Gasverbrauchseinrichtu ng (8), with  a gas line device (1) extending between the gas supply device (7) and the gas consumption device (8);  a mass flow measuring device (2) provided in the gas-conducting device (1) for measuring the gas quantity of the gas flowing in the gas-conducting device (1) on the basis of its mass flow. 2. Gas supply device according to claim 1, characterized in that  the mass flow measuring device (2) has:  + a heating or cooling element (3);  + a first temperature sensor (4) arranged upstream of the heating or cooling element (3);  + a second temperature sensor (5) arranged downstream of the heating or cooling element (3); and  + an evaluation device (6) for evaluating a first temperature measured by the first temperature sensor (4) and a second temperature measured by the second temperature sensor (5) and for driving the heating or cooling element (3); and that  you're looking at the evaluation device (6) either  + the heating or cooling element (3) can be controlled in such a way that a constant temperature difference between the first temperature sensor (4) and the second temperature sensor (5) is set, the mass flow being determined on the basis of the required heating or cooling power; or  + the heating or cooling element (3) is adjustable to a predetermined heating or cooling capacity, wherein due to a subsequently measured temperature difference between the first temperature sensor (4) and the second temperature sensor (5), the mass flow is determined. 3. Gas supply device according to claim 1 or 2, characterized in that in the gas conduit means (1) a controllable valve means (1 2) for adjusting the mass flow in the Gasleitu ngseinrichtu ng (1) is provided; and that a controller (11) is provided for controlling the valve device (12) in response to a measurement signal from the mass flow measuring device (2). 4. Gas supply device according to one of claims 1 to 3, characterized in that the controller (11) is designed such that it maintains the mass flow of the gas in the gas conduit means (1) flowing gas at a predetermined value by driving the valve means (12) , 5. Gas supply device according to one of claims 1 to 4, characterized in that  a carbon mole flow of the gas flowing in the gas line device (1) can be determined on the basis of the measured amount of gas;  in that the controller (11) is designed in such a way that it keeps the carbon mole stream of the gas essentially constant at a predetermined value by actuating the valve device (12). 6. Gas supply device according to one of claims 1 to 5, characterized in that  a heating and / or calorific value of the gas flowing in the gas line device (1) can be determined on the basis of the measured gas quantity;  in that the controller (11) is designed in such a way that it keeps the heating and / or calorific value of the gas essentially constant at a predetermined value by actuating the valve device (12). 7. Gas supply device according to one of claims 1 to 6, characterized by a display device for displaying a mass flow value measured by the mass flow measuring device (2). 8. Gas supply device according to one of claims 1 to 7, characterized in that the gas consuming device (8) comprises a reformer fuel cell system, a heater, a cooling device or a gas engine. 9. Gas supply device according to one of claims 1 to 8, characterized in that the mass flow measuring device (2) and the gas consumption device (8) in a gas consumption system (13) are integrated. 10. Gas supply device according to one of claims 1 to 9, characterized in that  the gas consuming device (8) comprises a reformer fuel cell system;  in a gas supply line (1) of a reformer of the reformer fuel cell system, the mass flow meter (2) and the valve means (12) are arranged;  via the gas supply line (1) a carbon-containing gas can be fed;  downstream of the mass flow measuring device (2) and the valve device (12), water vapor can be fed into the gas supply line (1) and thus to the carbon-containing gas.  a controller (11) is provided, which is designed such that by controlling the valve device (12) a water vapor / carbon ratio (S / C ratio) in the over the gas supply line (1) guided total gas flow at a predetermined Value holds. 11. Gas supply device according to one of claims 1 to 10, characterized in that  the gas is a liquefied gas; and that  the LPG contains propane, butane or a mixture thereof. 12. A method for supplying gas from a gas storage device (7) to a gas consumption device (8), comprising the steps of:  Supplying the gas via a gas line device extending between the gas supply device (7) of the gas consumption device (8);  Measuring the amount of gas flowing in the gas line device (1) gas due to its mass flow by means of a thermal mass flow measuring method. 13. The method according to claim 12, characterized in that  Activating a valve device (12) provided in the gas line device (1) in order to keep the mass flow in the gas line device (1) at a predetermined value.