GB2483369A

GB2483369A - Steam Flow Meter with Thermoelectric Power Source

Info

Publication number: GB2483369A
Application number: GB1115190.9A
Authority: GB
Inventors: Ben Frisby; Neil Lee Squires; Rajan Deep Singh
Original assignee: Spirax Sarco Ltd
Current assignee: Spirax Sarco Ltd
Priority date: 2010-09-03
Filing date: 2011-09-02
Publication date: 2012-03-07
Also published as: GB201014666D0; GB201115190D0; GB2483293A

Abstract

There is disclosed a mass flow rate meter 12 for calculating the mass flow rate of steam flowing through a steam line 16. The meter comprises a velocity flow determining means for determining the flow velocity of the steam, a density determining means for determining the density of the steam; and a calculation unit for calculating the mass flow rate of the steam on the basis of the determined flow velocity and density. A wireless transmitter 22 may transmit the calculated mass flow rate to a receiver in a remote control room. The meter further comprises a thermoelectric power source 14 which is arranged to generate electricity from energy within the steam to power the mass flow rate meter.

Description

STEAM FLOW METER

The invention relates to a mass flow rate meter for calculating the mass flow rate of steam flowing through a steam line, and to a steam line having such an apparatus mounted thereon.

In order to control most industrial processes involving steam it is necessary to monitor the flow of the steam. This is achieved by using a flow meter. The output of the flow meter may be relayed to a computer display in a control room which can be a considerable distance from the flow meter itself. Typically, a power cable and a data cable are associated with each flow meter to supply power to the flow meter and to pass its output to the control room. In a typical industrial plant there can be significant lengths of cable taking power to flow meters and conveying data from the flow meters to the control room. This cable has to be able to withstand the ambient conditions and has to be carefully laid and marked which is a time-consuming and expensive process.

It may therefore be desirable to reduce the cabling associated with a flow meter for measuring the flow of steam through a steam line.

One of the previous approaches to this problem has been to fit the flow meter with batteries. Depending on the flow meter and the capacity of such batteries the flow meter can typically be relied upon for about a year. However, the batteries do have to be checked and replaced regularly and this can easily be overlooked, particularly if the flow meter is mounted in a location which is relatively difficult to access.

The invention is defined in the attached independent claim to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto.

According to an aspect of the invention there is provided a mass flow rate meter for calculating the mass flow rate of steam flowing through a steam line, comprising: a velocity flow determining means for determining the flow velocity of the steam; a density determining means for determining the density of the steam; a calculation unit for calculating the mass flow rate of the steam on the basis of the determined flow velocity and density; and a thermoelectric power source which is arranged to generate electricity from energy within the steam to power the mass flow rate meter.

The thermoelectric power source may be arranged to generate electricity from a temperature differential. The thermoelectric power source may comprise a thermoelectric generator, a first portion of which is subjected to thermal energy from the steam and a second portion of which is subjected to a lower temperature. The first portion of the thermoelectric generator may be arranged to be in thermal communication with the steam line. The second portion of the thermoelectric generator may be arranged to be in thermal communication with the ambient air.

The thermoelectric power source may further comprise a lower conductive member and an upper conductive member between which a thermoelectric generator is disposed. The first portion of the thermoelectric generator may be in contact with the lower conductive member and the second portion of thermoelectric generator may be in contact with the upper conductive member. The lower conductive member may be arranged to be mounted on the steam pipe. The lower conductive member may comprise a concave surface, the profile of which corresponds to the outer surface of the steam line. The thermoelectric power source may further comprise a non-conductive layer disposed between the lower and upper conductive members which may at least partially surround the thermoelectric generator. The non-conductive layer may be a ceramic.

The upper conductive member may be in thermal communication with a heat exchanger which is arranged to transfer heat from the upper conductive member to the ambient air. The heat exchanger may comprise a plurality of horizontally stacked plates. A heat pipe may thermally couple the upper conductive member to the heat exchanger.

The density determining means may comprise a temperature sensor which in use measures the temperature of the steam in the steam line; and means for determining the density of the steam on the basis of the measured temperature. The density determining means may comprise a pressure sensor which in use measures the pressure of the steam in the steam line; and means for determining the density of the steam on the basis of the measured pressure.

The mass flow rate meter may further comprise a temporary power store which is arranged to be charged by the thermoelectric power source and which can temporarily supply power to the mass flow rate meter. The temporary power store may be a re-chargeable battery or a super-capacitor.

The mass flow rate meter may further comprise a wireless transmitter for wirelessly transmitting data from the mass flow rate meter to a receiver. The mass flow rate meter may further comprise a data logger for logging detected and/or measured and/or calculated data. The mass flow rate meter may further comprise an on-board display for displaying detected and/or measured and/or calculated data.

The velocity flow determining means, density determining means and calculation unit may be part of a first discrete unit. The thermoelectric power source may be part of a second discrete unit which supplies electricity to the first discrete unit via a power cable.

The mass flow rate meter may be an integrated unit.

The calculation unit may be arranged to calculate process information. The process information may include one or more of the following: fuel cost, C02 output, water consumption.

The invention also relates to a steam system comprising a steam line having a mass flow rate meter in accordance with any statement herein mounted thereto.

According to another aspect of the invention there is provided an apparatus for measuring the flow of steam through a steam line which apparatus comprises a flow meter and a power source therefor, which power source, in use, generates electricity from energy within the steam.

The apparatus may include a re-chargeable battery, which can be charged by the power source. This may help to ensure that the monitoring device operates even if the supply of steam fails.

The power source may comprise a thermoelectric device which, in use, provides electrical energy when subject to a temperature differential between the steam and the ambient air.

One side of the thermoelectric device may be in thermal communication with a solid base which is mountable on a steam pipe. Another side of the thermoelectric device may be in contact with a heat sink via a heat pipe.

The apparatus may comprise a wireless transmitter which, in use, can transmit data from the flow meter to a receiver which may typically be located in a control room. The data may be wirelessly transmitted via relay stations if necessary.

The invention also relates to a steam line having an apparatus for measuring steam in accordance with any statement herein mounted thereon.

The flow meter and the power source may be separate and distinct units which in use are disposed adjacent to one another, for example the power source could be mounted on the steam pipe within 10cm to 30cm of the flow meter. However, it should be appreciated that the flow meter and the power source could be accommodated in the same physical housing.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a simplified front view, partly in section, of one embodiment of an apparatus for measuring the flow of steam mounted on a steam line; Figure 2 is a perspective view showing the rear of the apparatus shown in Figure 1; and Figure 3 shows the components within the circle Ill in Figure 1 on an enlarged scale.

Referring to Figures 1 and 2, there is shown a mass flow rate apparatus 10 for measuring the mass flow rate of steam through a steam line 16. In this particular embodiment the apparatus 10 comprises a velocity flow meter (or determining means) 12, a density meter (or determining means) and a thermoelectric power source 14.

The mass flow rate meter 10 also comprises control electronics (not shown) that are housed in a control box 20. The velocity meter 12, density meter and the associated control electronics are part of a first discrete unit and the thermoelectric power source 14 is part of a second discrete unit that supplies power to the first discrete unit via a power cable 26.

The velocity flow meter 12 is mounted in a steam line 16 so as to determine the velocity of the steam flowing within the line 16. The power source 14 is clamped to the steam line 16 immediately upstream of the flow meter 12. In the embodiment shown, the distance between the centre line of the flow meter 12 and the centre line of the power source 14 is about 10 cm.

In this particular embodiment the flow meter 12, which includes a hollow upstand 18 and a control box 20, comprises a strain gauge and cantilever connected by a spring to a shaft which is connected to a cone disposed within the steam line 16. As flow rate increases, the drag of the cone cause the cantilever, on which the strain gauge rests, to bend. The bending of the cantilever induces strain in the cantilever which is measured by the strain gauge. The measured strain is communicated to the control box 20 which is arranged to determine a flow velocity based on the measured strain.

The density meter comprises a temperature sensor that is arranged to measure the temperature of the steam within the steam line 16. If it is assumed that the steam is saturated steam, the density of the steam can be determined (or estimated) from the measured temperature. In alternative embodiments the pressure may be measured and the density of the steam can be determined from this.

A calculation unit housed within the control box 20 receives the flow velocity determined by the velocity flow meter 12 and the density determined by the density meter and calculates the mass flow rate of the steam. In addition to this, the calculation unit may calculate other process parameters such as the cost of the process, the carbon dioxide output or the water consumption.

A wireless transmitter 22 mounted on the control box 20 transmits the calculated mass flow rate to a receiver in a remote control room. The transmitter 22 may also transmit other parameters such as the temperature, density, flow velocity, process cost, carbon dioxide output or water consumption. In other embodiments the various parameters may be displayed by the control box 20 either in addition to, or instead of, being wirelessly transmitted.

A data logger is also housed within the control box 20 and logs the various measured and calculated parameters including flow velocity, temperature, density and mass flow rate. Therefore, if the wireless transmission link fails it is possible to recover the logged data from the data logger.

Power for the electronics in the control box 20 and the wireless transmitter 22 is provided by a temporary power source, such as a re-chargeable battery 24, which is connected to the power source 14 by a cable housed in an armoured sleeve 26. The temporary power source may be any device that can retain a charge. For example, in other embodiments capacitors or super-capacitors may be used. It should be appreciated that a temporary power source is not essential. For example, in other embodiments the control box 20 and wireless transmitter 22 may be directly powered by the power source 14.

The power source 14 is a thermoelectric power source and comprises a solid base (lower conductive member) 30, an array of thermoelectric devices (otherwise known as a thermoelectric generator) 28, and a heatsink. The solid base 30 is made from aluminium and has a concave lower surface, the profile of which corresponds to the outer profile of the steam line 16. In use, the concave surface of the solid base 30 engages and is held tightly against the outer surface of the steam line 16 by a U-bolt 32 arranged as shown. A thermally conductive paste 34 may be placed between the steam line 16 and the solid base 30 at the time of assembly to enhance heat transfer therebetween.

The power source 14 comprises an array 28 of thermoelectric generator devices. In this embodiment the thermoelectric generator devices are Seebeck-based devices which are capable of generating power from a temperature differential. One side of the array 28 is in contact with the solid base 30 and is therefore exposed to the heat from the steam in the steam line 16, and the other side of the array 28 is in contact with an upper conductive member 36 which is part of, or is thermally coupled to, a heatsink which is exposed to the temperature of the ambient air. The array 28 is substantially square and has a ceramic frame 29 around at least a part of its periphery.

As better shown in Figure 3 the array 28 and the ceramic frame 29 is disposed between the solid base 30 and the upper member 36 which is part of the heatsink, such that a first side of the array 28 is in intimate contact with the solid base 30 and a second opposing side of the array 28 is in intimate contact with the upper member 36.

The upper member 36 is secured to the solid member 30 by a multiplicity of set screws, each of which is made of a material of relatively low conductivity, in this case stainless steel and two of which are shown. The use of low-conductivity screws helps to maximise the thermal gradient between the solid base 30 and the upper member 36.

The ceramic frame 29 is also in contact with both the solid base 30 and the upper member 36. The ceramic frame 29 acts to space the solid base 30 and upper member 36 and prevents the solid base 30 and upper member 36 from being brought too close together which could potentially result in damaging of the thermoelectric array 28.

Further, the ceramic frame 29 has a relatively low-conductivity which prevents heat transfer through the frame 29 itself.

The upper member 36 is made of a thermally conductive material and forms the base of a heat sink. The heatsink further comprises a hollow upstand 38 which accommodates a heat pipe 40 which extends from the upper member 36 and which is provided with a heat exchanger 42 at its upper end. The heat exchanger 42 comprises a multiplicity of horizontally stacked and spaced discs which are secured to the periphery of the hollow upstand 38. In use, the heat pipe 40 transmits heat from the upper member 36 to the heat exchanger 42 which dissipates its heat to the ambient surroundings. This acts to cool the upper member 36 and therefore maximises the temperature drop across the thermoelectric device array 28. Maximising the temperature drop across the array 28 maximises the amount of power that the thermoelectric power source 14 generates.

In use, steam at 9 bar and 180°C was passed through steam line 16 in the direction of arrow 50. Heat from the steam passed through the solid base 30 and subjected the bottom of the array 28 of thermoelectric devices to a temperature of around 171°C.

The heat exchanger 42 dissipated heat so that the temperature at the top of the array 28 of thermoelectric devices was approximately 85°C thereby creating a temperature differential of about 86°C across the array 28 of thermo electric devices. The array 28 of thermoelectric devices 28 generated a current of approximately l5mA at 3.2 volts and continuously trickle-charged the re-chargeable battery 24.

For the purposes of our tests the array 28 of thermoelectric devices which we used was a 40 x 40mm thermoelectric generator model number GM-i 27-i 4-1 6-S purchased from European Thermodynamics Ltd. However, it should be appreciated that other thermoelectric devices could also be used, for example the high-temperature models from TE Technology Inc. Although it has been described that the flow meter 12 comprises a cantilever having a strain gauge mounted thereto, other types of flow meter could also be used. For example the flow meter 12 could be a turbine flow meter, a variable area flow meter, a spring loaded variable area flowmeter, a direct in-pipe variable area flow meter, a pilot tube or a vortex shedding flowmeter.

Claims

CLAIMS: 1. A mass flow rate meter for calculating the mass flow rate of steam flowing through a steam line, comprising: a velocity flow determining means for determining the flow velocity of the steam; a density determining means for determining the density of the steam; a calculation unit for calculating the mass flow rate of the steam on the basis of the determined flow velocity and density; and a thermoelectric power source which is arranged to generate electricity from energy within the steam to power the mass flow rate meter.
2. A mass flow rate meter according to claim 1, wherein the thermoelectric power source is arranged to generate electricity from a temperature differential.
3. A mass flow rate meter according to claim I or 2, wherein the thermoelectric power source comprises a thermoelectric generator, a first portion of which is subjected to thermal energy from the steam and a second portion of which is subjected to a lower temperature.
4. A mass flow rate meter according to claim 3, wherein the first portion of the thermoelectric generator is arranged to be in thermal communication with the steam line.
5. A mass flow rate meter according to claim 3 or 4, wherein the second portion of the thermoelectric generator is arranged to be in thermal communication with the ambient air.
6. A mass flow rate meter according to any of claims 3-4, wherein the thermoelectric power source further comprises a lower conductive member and an upper conductive member between which the thermoelectric generator is disposed, and wherein the lower conductive member is arranged to be mounted on the steam pipe.
7. A mass flow rate meter according to claim 6, wherein the lower conductive member comprises a concave surface, the profile of which corresponds to the outer surface of the steam line.
8. A mass flow rate meter according to claim 6 or 7, wherein the thermoelectric power source further comprises a non-conductive layer which is disposed between the lower and upper conductive members and which at least partially surrounds the thermoelectric generator.
9. A mass flow rate meter according to claim 8, wherein the non-conductive layer is a ceramic.
10. A mass flow rate meter according to any of claims 6-9, wherein the upper conductive member is in thermal communication with a heat exchanger which is arranged to transfer heat from the upper conductive member to the ambient air.
11. A mass flow rate meter according to claim 10, wherein the heat exchanger comprises a plurality of horizontally stacked plates.
12. A mass flow rate meter according to claim 10 or 11, wherein a heat pipe thermally couples the upper conductive member to the heat exchanger.
13. A mass flow rate meter according to any preceding claim, wherein the density determining means comprises: a temperature sensor which in use measures the temperature of the steam in the steam line; and means for determining the density of the steam on the basis of the measured temperature.
14. A mass flow rate meter according to any preceding claim, wherein the density determining means comprises: a pressure sensor which in use measures the pressure of the steam in the steam line; and means for determining the density of the steam on the basis of the measured pressure.
15. A mass flow rate meter according to any preceding claim, further comprising a temporary power store which is arranged to be charged by the thermoelectric power source and which can temporarily supply power to the mass flow rate meter.
16. A mass flow rate meter according to claim 15, wherein the temporary power store is a re-chargeable battery or a super-capacitor.
17. A mass flow rate meter according to any preceding claim, further comprising a wireless transmitter for wirelessly transmitting data from the mass flow rate meter to a receiver.
18. A mass flow rate meter according to any preceding claim, further comprising a data logger for logging detected and/or measured and/or calculated data.
19. A mass flow rate meter according to any preceding claim, further comprising an on-board display for displaying detected and/or measured and/or calculated data.
20. A mass flow rate meter according to any preceding claim, wherein the velocity flow determining means, density determining means and calculation unit are part of a first discrete unit, and wherein the thermoelectric power source is part of a second discrete unit which supplies electricity to the first discrete unit via a power cable.
21. A mass flow rate meter according to any of claims 1-19, wherein the mass flow rate meter is an integrated unit.
22. A mass flow rate meter according to any preceding claim, wherein the calculation unit is arranged to calculate process information.
23. A mass flow rate meter according to claim 22, wherein the process information includes one or more of the following: fuel cost, 002 output, water consumption.
24. A steam system comprising a steam line having a mass flow rate meter in accordance with any preceding claim mounted thereto.
25. A mass flow rate meter or a steam system substantially as described herein with reference to the accompanying drawings.