GB2490601A

GB2490601A - Portable flue gas analysing unit with water-removing tube located in handle

Info

Publication number: GB2490601A
Application number: GB201207896A
Authority: GB
Inventors: Paul Basham; Mark Osborne
Original assignee: Crowcon Detection Instruments Ltd
Current assignee: Crowcon Detection Instruments Ltd
Priority date: 2011-05-05
Filing date: 2012-05-04
Publication date: 2012-11-07
Anticipated expiration: 2032-05-04
Also published as: GB2490601B; GB201207896D0; GB201107492D0

Abstract

A portable flue gas analysing unit comprises a gas detector for measuring the presence of a target gas; a body defining a housing, wherein part of the housing defines a handle 18; and moisture removing apparatus for removing moisture from the target gas. The moisture removing apparatus comprises a conduit or tube 16 having a first end 17 operable to be in fluid communication with a gas source to be tested and a second end 26 operable to be in fluid communication with the detector. The conduit comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (Nafion (RTM)), or its chemical analogue and is incorporated at least in part in the handle. The moisture removing tubing acts as a porous membrane that absorbs water vapour and releases it to the surrounding atmosphere. The housing may have one or more ventilation holes 20 and the device preferably operates at high temperatures of the order of 100ÂºC. The analysing unit may further comprise a probe 12, which may be detachable, for sampling the gas to be detected.

Description

Water removal in gas sensing equipment

Technical field

The present invention relates to apparatus for removing moisture from a gas stream for use in portable gas analysers. In particular the invention relates to the removal of moisture from flue gases.

Background to the invention

It is desirable to be able to detect the presence of certain gases from a heating source, such as a boiler, to ensure that the buming occurs at a maximum efficiency. Such analysis can be performed using wet chemical analyser or digital detection instrumentation such as flue gas analysers. Such analysers are commercially available.

A flue gas analyser samples the gas in the boiler to search for the presence of gases such as carbon monoxide (CO), carbon dioxide (C02) and oxygen (02) which indicate poor or inefficient combustion. Typically the gases in a boiler have a humidity of %. Water is known to be problematic to gas sensors, commonly giving rise to erroneous resuhs and shortening sensor lifetimes. For example humid gas streams interfere with infrared CO2 sensors absorbing radiation or condensing on optical components with the resuhant absorption and scatter of light. The water in a gas sensor may also degrade the sensor, shortening the life of the sensor and requiring replacement. Therefore it is desirable to remove water from the gas before it reaches the sensors.

Commercially available instrumentation is typically used with a condensing water trap to cool down the gas and remove water from the gas stream. When the gas reaches the condenser it has a temperature of the order 150°C and needs to be cooled considerably in order for the water to condense out of the gas. Such condensers are able to remove the moisture from the gas stream whilst leaving behind the gases which are being measured, such as CO, CO2 and 02.

The water traps used are bulky and cumbersome. The cooling pipes and condenser may be around 1 metre in the length, and need to be carried by the technicians during the day. Therefore the technician is required to carry large pieces of equipment. A heating technician will often analyse the gas in several boilers during the course of a working day and will have to transport the large flue gas analyser as part of their equipment to several locations.

In addition some customers or technicians forget to empty the water trap the ingress of water often leads to instrument reliability problems caused by sensor deterioration.

Furthermore, a gas engineer who may typically use such a sensor in several properties will need to empty the water trap after each use. The water in the trap may be mildly acidic due to the gases and may need to be dispensed of carefully. Again the equipment required to trap water is typically bulky to transport.

Additionally with the water traps in order to remove moisture the gas must be cooled considerably. Once the moisture has been removed the cooled gas is passed onto the sensor and measured. In general, gas sensors work less efficiently at lower temperatures and take longer to take measurements.

To mitigate at least some of the above problems associated with the prior art, there is provided a portable moisture removing apparatus for removing moisture from the target gas, the moisture removing apparatus comprising: a conduit having a first end operable to be in fluid communication with a gas source to be tested and a second end operable to be in fluid communication with the detector; wherein the conduit comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (Nafion) or its chemical analogue.

There is also provided a gas analysing unit comprising: a gas detector for measuring the presence of a target gas; moisture removing apparatus for removing moisture from the target gas, the moisture removing apparatus comprising: a conduit having a first end operable to be in fluid communication with a gas source to be tested and a second end operable to be in fluid communication with the detector; wherein the conduit comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (Nation) or its chemical analogue.

Preferably wherein the chemical analogue is one of Nafion-imidazole and sulfonated poly ether ether ketone ketone. Preferably wherein the target gas detected by the gas detector is of order of 100°C, preferably 50°C. Preferably wherein the conduit has a length sufficient to reduce the moisture in a gas to less than 20% and preferably less than 5%. Preferably wherein the unit has a body which defines a housing, optionally wherein the gas detector is at least partially retained in the housing and/or wherein part of the housing defines a handle for the gas analysing unit, and/or wherein the housing has one or more ventilation holes, and/or wherein the conduit is at least partially retained in the housing. Preferably wherein the length of the conduit is greater than the length of the part of the housing in which the conduit is retained.

Preferably wherein the conduit serpentines through the housing and/or wherein the conduit comprises one or more u-bends. Preferably wherein the conduit is approximately 10cm in length. Preferably further comprising a probe for sampling the gas to be detected, and/or wherein the probe is connectable to the conduit, preferably via airtight connectors, and/or wherein the probe is detachable from the unit.

Preferably wherein the conduit is porous. Preferably wherein the conduit is configured to absorb the moisture from the gas and release the moisture to the surrounding atmosphere.

There is also provided a method of detecting gas with a flue gas detector the method comprising the steps of: sampling a flue gas to be measured; passing the sampled gas through a conduit comprising a sulfonatcd tetrafluoroethylene based fluoropolymer-copolymer (Nafion), or its chemical analogue, to remove moisture from the sampled gas; detecting the presence of one or more gases in the dried gas with the detector.

Preferably wherein the chemical analogue is one of Nafion-imidazole and sulfonated poly ether ether ketone ketone, and/or wherein the target gas detected by the gas detector is of order of 100°C, preferably 50°C.

Advantageously in order to remove moisture from the gas stream the gas stream does not need to be cooled. This allows the gas sensors to measure hot gases from a boiler, resuhing in faster response times and a more efficient function. The present invention does not require a water trap, or condenser and is smaller and therefore easier to transport. The invention therefore provides a portable apparatus which is typically smaller than known systems for drying gases. A further advantage of the present invention is that because Nafion's water absorption properties increase at higher temperatures, and because the gas stream being sampled remains hot (i.e. it does not need to be cooled to remove the water) the amount of Nafion required is small and further reducing the size of the water removing unit.

Brief description of the figures

Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawing in which: Figure 1 is a schematic representation of an embodiment of the invention in use; Figure 2 is an example of the water removing tubing in an embodiment of the invention; Figure 3 is an example of the handle of a gas analyser used in the embodiment shown in Figure 2;

Detailed description of an embodiment

According to an aspect of the invention there is provided an apparatus to clean up and modify a gas stream before measurement by removing moisture from the stream.

Figure 1 shows a schematic representation of a gas monitoring device measuring the gas from a boiler using the water removing tubing or conduit according to an aspect of the invention.

There is shown a boiler 10; probe 12 having a boiler end 15 and a unit end 17; a gas analysing unit 13 comprising a flue gas analyser 14; water removing tubing 16 or conduit and handle 18. The gas analysing unit 13 is a portable unit.

In an example, the unit 13 has a rugged thermoplastic casing in which the flue gas analyser 14 is contained. The handle 18 is attached to the casing allowing the unit 13 to be carried. To minimise the size of the unit, the water removing tubing 16 is integrated within the handle 18 of the unit 13. Therefore, the invention defines a portable gas analysing unit 13.

In use, a technician inserts the boiler end 15 of the probe 12 into the boiler 10 in order to analyse the gas via the flue gas analyser 14. Hot humid gas, typically with a temperature of 180°C and a humidity of'-95% travels from the 10 along the length of the probe 12 to the unit end 17 of the probe where it connects to the gas analysing unit 13. The tubing 16 is therefore in fluid communication with the gas to be detected, via the probe 12. The probe 12 is made from stainless steel and comprises the boiler end 15 which is inserted into the boiler and the unit end 17 which is connected to the water removing tubing 16 which is preferably located in the handle 18 of the analyser 14.

The gas passes though the probe 12 and tubing 16 and onto the sensors in the analyser (not shown) which detect the presence, or absence, of the specific gases. Therefore the tubing is also in fluid communication with the sensors/detectors.

Therefore, the gas analysing unit 13 which is attachable to the probe 12 provides an integrated unit 13 which is able to remove moisture from the gas stream and analyse the gas. The gas analysing unit 13 is, in the preferred embodiment, a portable unit which a user, such as a gas technician can carry about as part of their equipment.

The flue gas analyser 14 part of the gas analysing unit 13 and probe 12, are commercially available analysers and probes such as the Sprint V flue gas analyser sold by Crowcon Detection Instruments. In further embodiments other gas analysers are used.

The water removing tubing 16, or conduit, is made from a sulfonated tetrafluoroethylene based fluoropolymer-copolymer material which is sold under the trade name Nafion RTM. Nafion® is a copolymer of tetrafluoroethylene (Teflon®) and perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonic acid manufactured by DuPont.

Like Teflon, Nafion is highly resistant to chemical attack, but the presence of its exposed sulphonic acid groups confers unusual properties in that Nafion absorbs up to 22% by weight of water. Advantageously, Nafion absorbs moisture from the gas at high temperatures. Therefore, unlike conventional water removing traps the gas does not need to be cooled in order to remove moisture from the stream.

The tubing 16 is made from a porous Nafion membrane. As the gas passes through the tubing 16 the water/moisture is absorbed by the Nafion and removed from the gas stream. As the tubing 16 is porous the absorbed water passes through the pores of the tubing 16 and is released into the atmosphere. As the gas has not been cooled, and therefore typically has a temperature of50°C, the moisture is released in the gaseous phase and dissipates in the surrounding atmosphere.

Therefore, the tubing removes the need for a bulky and cumbersome water trap as the water is naturally dispersed into the surrounding atmosphere. This further has the advantage of eliminating the need of the user to remove the extracted water from the trap as the dissipation of the moisture into the atmosphere occurs naturally.

A further advantage is that the Nafion also acts to remove water soluble pollutants from the gas stream such as NO2, N20 and 502 which are typically not desirable to be measured by flue gas sensors 14. The gases arc absorbed by the Nafion tubing 16 and are then safely emitted into the surrounding atmosphere.

It has been advantageously recognised due to the hot nature of the gas in the gas probe 12 and the tubing 16 the Nafion is able to extract the moisture more efficiently than for cooler gases. A beneficial consequence is that this allows for a reduction in the length of the tubing 16 and results in a compact water removal apparatus.

In the prior art, vapour extraction systems which require extended lengths of tubing to remove water vapour are known. These systems typically require that the length of tubing is of the order of 300mm or longer in length. Such systems are therefore bulky and difficult to carry as they require sections which are typically over 300mm in length. Tests have shown that a section of Nafion tubing 16 of approximately 10cm in length is sufficient to reduce the humidity of the gas extracted from a typical domestic boiler from -95% to -â%. This level of gas humidity is found not to adversely affect the function of gas sensors. Such a reduced length of Nafion tubing can be more easily integrated into a portable unit. Therefore a Photo-ionisation detector (PID) in the analyser, whose longevity is typically compromised by high humidity levels, will have an extended lifetime when compared to PIDs which are exposed to higher levels of humidity.

The relatively short length of Nafion tubing 16 rcsuhs in a system that is cheaper to produce and manufacture. As the removal of water in the present invention occurs from a single relatively short piece of tubing 16 rather than the more complex cooling systems which typically have a condenser and water trap, the complexity and therefore cost of manufacture and maintenance of the instrument is low.

Furthermore as the size of the tubing 16 is small, and as the water trap and condenser are no longer required, tile water removing apparatus can be integrated within a portable unit 13 resulting in a system which is smaller and less cumbersome than the systems typically used.

The tubing 16 connects to the sensors of the analyser 14, such as a PID, in a known manner and the gas is analysed in the conventional manner for commercially available systems. As the gas has not been cooled, the sensors/detectors in the analyser 14 detect gases of the order of 150°C and have a shorter response time. Therefore, the performance of the gas detector is not affected by the removal of the moisture from the gas stream.

Advantageously, whilst the Nafion tubing 16 removes water soluble NO2, N20 and SO2, which are typically not measured by flue gas analysers, the tubing 16 does not remove CU, CO2 or 02 which are the gases typically measured by flue gas analysers in order to measure the burning efficiency of a boiler. Furthermore, as Nafion is highly resistant to chemical attacks, the presence of potentially corrosive gases in the gas stream does not adversely affect the tubing 16 and therefore the tubing 16 has a long-life.

In a preferred example to minimise the amount of volume space required for the tubing 16, in order to increase the portability of the unit 13, the tubing 16 is integrated within the handle 18 of the sensor in a serpentine or folded manner.

Figure 2 shows an example of the water removing tubing 16 which is enclosed in the handle 18 of a flue gas sensor 14. The handle 18 defines a housing and comprises a number of ventilation holes 20. The tubing 16 is connected to the probe 12 at the unit end 17 via an airtight connector 24 and connected to the sensor conduit 22, at the sensor end 26 which leads to the flue gas analyser's 14 sensor (not shown) at the sensor end. The connection between the tubing 16 and sensor conduit 22 also via an aright connector 24. The tubing 16 serpentines through the handle 18 via u-bends 28.

There is shown the tubing 16 which in the example shown is fully enclosed with the handle 18 of the gas analysing unit 13. The probe 12 is attached to the tubing 16 at the unit end 17 via an airtight connector 24. The airtight connector 24 is a simple straight connector type connector. The probe 12 passes moist gas from the boiler 10 to the tubing 16. As the gas passes through the tubing 16 moisture is removed and dry gas exits at the sensor end 26 a flows to the sensor(not shown) via the sensor conduit 22.

The temperature of the gas that exits the tubing is typically 25 C. As the gas may be hot, in order to prevent the user/technician from touching the hot gas the tubing 16 is enclosed in the handle 18.

In order to incorporate the desired length of tubing 16 (in the preferred embodiment -10cm) in the handle 18 the tubing 16 serpentines through the handle 18. The tubing 16 is configured to fit in a housing (in the present embodiment the handle) that is shorter in length than the tubing. To fit in the confined space, the tubing 16 incorporates one or more u-bends 28. Other shapes of bends or configurations of tubing 16 may be used depending on the relative size of the housing of the tubing 16.

Therefore, the handle 18 can be smaller in length than the tubing 16.

The handle 18 is made from a thermoplastic material, and preferably contains a plurality of ventilation holes 20. The holes 20 extend along the length of the handle 18 and allow water absorbed from the gas, which has passed through the porous membrane of the tubing 16, to be released into the surrounding atmosphere. As the gases released, typically water vapour and N20, are harmless they can be released into the atmosphere and there is no need to collect the gases and dispose of them in a controlled manner.

The combination of the handle 18 which incorporates the folded or serpentine tubing 18, and the handle preferably having the ventilation holes 20 is incorporated into the gas analysing unit 13. The apparatus required to remove moisture from the gas to be tested is small and compact. Furthermore, by incorporating the tubing 16 into the handle 18, the tubing 16 can be easily accessed allowing for easy maintenance of the part. A further advantage is that when the handle comprises the ventilation holes 20 the gases can be released directly into the atmosphere thus avoiding the need for a water trap or the like.

Figure 3 shows an example of the handle 18 shown in Figure 2. The ventilation holes preferably extend the length of the handle in order to efficiently remove the extracted moisture from the tubing 16. The configuration and number of holes 20 may be varied according to design preference.

The above described system therefore defines an integrated gas analysing unit 13 wherein the flue gas analyser 14 with handle 18 and water removing tubing 16 form an integrated unit. The probe 12 can also form part of the unit 13 or it can be selectively attached and removed from the gas analysing unit 13. This integrated unit 13 is therefore portable and easy to transport. Advantageously, as the probe 12 is detachable from the gas analysing unit the size of the unit is reduced, whilst maintaining the ability to remove moisture from the sampled gas streams. As stated above by integrating the water removing tubing 16 into the handle 18 the space requirement for the water removing apparatus is minimised. Furthermore, by having the tubing placed in the handle 18 in a serpentine, or non-straight manner the space requirements are further reduced. It is the advantageous realisation that approximately 10cm of tubing 16 is sufficient to remove 95% of the moisture from the gas that further adds to the space saving.

Whilst the above embodiment has been described in relation to a flue gas analyser the water removing tubing 16 can be used for other gas sensors where moist gas is analysed.

Furthermore, whilst a tubing or conduit of sulfonated tetrafluoroethylene based fluoropolymer-copolymers has been described chemical analogues of sulfonated tetrafluoroethylene based fluoropolymer-copolymers which have similar water removing properties may also be used. A chemical analogue is understood to be a chemical compound which has similar chemical properties and has a similar chemical structure to the original compound. A skilled person would be aware of and could identify chemical analogues ofNafion which are suitable in the present invention. For example, some suitable chemical analogues are Nafion-imidazole and sulfonated poly ether ether ketone ketone (SPEEKK). These are found to be suitable to clean and modify gas streams in gas sensing instruments.

In another embodiment the tubing 16 is placed within the housing of the gas analysing unit 13 (i.e. it is not placed within the handle 18). The tubing 16 extracts the moisture as described above, and preferably in order to remove the extracted moisture from the gas stream the housing of the unit 13 comprises one or more ventilation holes 20.

In further embodiments the Nafion is used to coat other component parts of the analyser 14. Components such as the sensor and interior housing of the sensor are coated with Nafion to ensure that ambient moisture, as well as moisture from the gas stream, which may have ingressed the analyser is removed.

Optionally, the entire length of the probe 12 is made from Nafion to remove moisture from the sampled gas. However as tests have shown that a length of'-10cm of Nafion tubing is sufficient to reduce the moisture content of a gas to -5%, and due to the increased costs in production such an embodiment in many situations is less preferred.

Claims

Claims 1. A portable flue gas analysing unit comprising: a gas detector for measuring the presence of a target gas, a body defining a housing, wherein part of the housing defines a handle for the portable flue gas analysing unit.moisture removing apparatus for removing moisture from the target gas, the moisture removing apparatus comprising: a conduit having a first end operable to be in fluid communication with a gas source to be tested and a second end operable to be in fluid communication with the detector; wherein the conduit comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer (Nafion) or its chemical analogue, and wherein the conduit is incorporated at least in part in the handle.
2. A gas analysing unit according to claim 1 wherein the chemical analogue is one ofNafion-imidazole or sulfonated poly ether ether ketone ketone
3. A gas analysing unit according to any preceding claim wherein the target gas detected by the gas detector is of order of 100°C, preferably 50°C.
4. A gas analysing unit according to any preceding claim wherein the conduit has a length sufficient to reduce the moisture in a gas to less than 20% and preferably less than 5%.
5. A gas analysing unit according to any preceding claim wherein the gas detector is at least partially retained in the housing.
6. A gas analysing unit according to claim 5 wherein the housing has one or more ventilation holes
7. A gas analysing unit according to any of claims 5 or 6 wherein the conduit is at least partially retained in the housing.
8. A gas analysing unit according to claim 7 wherein the length of the conduit is greater than the length of the part of the housing in which the conduit is retained.
9. A gas analysing unit according to claim 8 wherein the conduit serpentines through the housing.
10. A gas analysing unit according to claim 8 01 9 wherein the conduit comprises one or more u-bends.
11. A gas analysing unit according to any preceding claim wherein the conduit is approximately 10cm in length.
12. A gas analysing unit according to any preceding claim further comprising a probe for sampling the gas to be detected.
13. A gas analysing unit of claim 12 wherein the probe is connectable to the conduit, preferably via airtight connectors.
14. A gas analysing unit of claim 12 or 13 wherein the probe is detachable from the unit.
15. A gas analysing unit according to any preceding claim wherein the conduit is porous.
16. A gas analysing unit according to any preceding claim wherein the conduit is configured to absorb the moisture from the gas and release the moisture to the surrounding atmosphere.