Early detection of smoldering powder in a powder drying system including a co gas detection system

Abstract

The invention relates to a powder drying system comprising a CO gas detection system adapted to detect CO gas from smoldering powder in a component of the powder drying system, the CO gas detection system comprising: at least one inlet CO gas detector arranged on at least one gas inlet of the component of the powder drying system; at least one outlet CO gas detector arranged on at least one gas outlet of the component of the powder drying system; and an analysis unit adapted to receive at least one inlet CO gas content measurement and at least one outlet CO gas content measurement and to compare a sum of the at least one inlet CO gas content measurement with a sum of the at least one outlet CO gas content measurement while compensating for dilution, mixing, and time delay of the outlet CO gas content measurement.

Description

TECHNICAL FIELD

[0001] The present invention relates to a powder drying system having a system adapted for early detection of smoldering powder in a powder drying system component such as a spray dryer chamber, fluidized bed or bag filter by detecting carbon monoxide (CO) gas emitted during smoldering.

[0002] It should be noted that the term "measurement volume" as used herein is intended to mean the volume, area, line and / or point of the arrangement from which the CO gas detection system receives measurement information, or in other words the volume, area, line and / or point covered by the measurements made by the CO gas detection system.

[0003] It should be noted that the term "measurement range" as used herein is intended to mean the location in which the measurement volume is to be arranged, and can thus include not only the actual measurement volume, but also a zone or buffer zone immediately adjacent to the measurement volume.

[0004] It should be noted that the term "gas" as used herein is to be interpreted as encompassing any gas suitable as process gas in such a spray drying system. Some non-limiting examples of gases are process gases such as atmospheric air as well as suitable oxygen or nitrogen enhanced gases.

[0005] It should be noted that the term "powder drying system" is intended to encompass such systems forming and / or handling powdered or particulate material. The material can be provided as a feed of powdered or particulate material or as a liquid feed to be dried. The powder drying system is also intended to include cooling of the particulate material. In addition to the described spray dryer or alternatively, such a system can include one or more fluidized beds, cyclones, bag filters, pneumatic conveying systems, feed pretreatment etc. The powder drying system thus incorporates units for forming or handling powder in any suitable manner. Non-limiting examples include spray dryers, fluidized beds, flash dryers, ring dryers, spray dryers with integrated or external fluidized beds, cyclones etc. Typically, the powder drying system (e.g. at the top of a vertical dryer) has an inlet for liquid, paste or solid feed, where the liquid feed enters the dryer and encounters a stream of dry, hot air, so that droplets of the feed will fall into the dryer and liquid will be removed from the droplets, forming substantially dry particles. The liquid feed can be a slurry or suspension of particles, or a solution which is capable of forming particles upon removal of the solvent.

[0006] It should be noted that the term "powder drying system component" is intended to encompass any component of the powder drying system in which process gas is present at least during operation, such as but not limited to a drying chamber, a fluidized bed, a bag filter, a cyclone, a conduit (such as a cleaning device connection conduit).

[0007] It should be noted that the term "IR laser emitter" is intended to encompass any laser light source (such as a laser device or a diode) capable of emitting IR radiation in the IR band, said radiation being defined by electromagnetic radiation having a wavelength in the range of about 700 nm to about 1 mm.

[0008] It should be noted that the term "IR receiver" is intended to encompass any detector capable of detecting IR radiation. BACKGROUND

[0009] Smoldering powder (so-called nest), i.e. fine-grained combustion embers as well as aggregates, are a common ignition source in dust explosions and fires and pose a serious threat to powder drying systems such as spray dryers, which produce powders in food, pharmaceuticals, dairy, chemicals, agrochemicals, energy, biotechnology, healthcare, etc., thus producing e.g. milk powder, coffee whitener, infant formula, coffee powder, pharmaceuticals, chemicals, etc. During the spray drying process, deposition can occur typically when non-high-temperature droplets accumulate in smaller or larger deposits on the walls or floor of the dryer. Due to intrinsic chemical reactions, the product temperature of such deposits can increase, which can lead to smoldering of the powder or even to combustion when in an oxygen-filled atmosphere. During smoldering, CO gas is produced and oxidation and / or pyrolysis reactions occur. Smoldering product blocks can typically form in the spray chamber and / or air disperser / and / or atomizer, in the cyclone, or in the internal or external fluidized bed, or in the external bag filter.

[0010] If powder deposits are not removed from the drying system and reach a certain size, they can form blocks and fall within the system, even through the process flow and break up, thus causing so-called hotspots by the heat of the exothermic oxidation reaction. The hotspots can be exposed and at some point ignite the atmosphere filled with powder. Another scenario is that larger powder blocks are subjected to heat, e.g. at the bottom of a fluidized bed, and activate the smoldering reaction. This can also occur in low-oxygen atmospheres or similar. Subsequently, the smoldering blocks can pass through the process flow and eventually lead to a plant fire or dust explosion. Primary fire prevention is typically based on temperature monitoring and regular cleaning operations. Often, such primary prevention is not fast enough and thus insufficient due to process reaction delays; and additional measures are implemented in the form of early warning and smoldering detection systems for the protection of the drying system.

[0011] One prior art solution is produced and sold by FIKE under the name WarnEx. This system consists of a number of so-called Sampling and Detection Units (SDU) placed at each inlet and outlet of the powder drying system and a control unit that processes the signals received from the SDUs. The WarnEx system thus employs that a sample is extracted in the sampling part of the SDU and that the detection result is transmitted to the detection part of the SDU via a suitable cable.

[0012] DE 202014101777 U1 describes a spray dryer with a humidity detector having a measuring device that can also be used for detecting CO gas. However, no specific type of measuring device employed in the detection of CO gas by the humidity detector and the measuring method are mentioned.

[0013] Furthermore, DE 202014101777 U1 and other known CO gas detection systems for spray dryers employ that gas samples are extracted from the flow at least at one inlet and one outlet thereof and that these gas samples are transported via e.g. tubes to a common IR laser or a common NDIR detector system (non-laser) arranged at a distance from the chamber. Such CO gas detection systems are produced and sold by e.g. Hobré Instruments and ATEX.

[0014] However, the known CO gas detection systems have several drawbacks, including:

[0015] - the result reliability is reduced when measuring small amounts of gas in the gas samples,

[0016] - the samples can not be representative of the actual CO gas concentration in the outflowing or inflowing flow as it depends on the gas flow and dilution at the chosen extraction location,

[0017] - they require precise timing between the actual gas samples from the inlets / outlets in the system,

[0018] - frequent calibration is required to always ensure the required sensitivity, especially when the flow rate or volume size of the dryer is changed,

[0019] - the procurement, installation, operation, maintenance and inspection / calibration costs are high, and

[0020] - it is difficult to adapt to changes in the flow or volume size of the dryer, and

[0021] - an external control signal from another source is required.

[0022] Furthermore, prior art systems, such as the systems of ATEX and Hobre, as mentioned, employ a tube to transport the gas sample from the sampling point to the measuring point, i.e. the common external detector. Such a tube requires maintenance, can leak, is ergonomically difficult to handle at installation, and requires a large detector system cabinet and high power consumption. Furthermore, their system cabinet, which is floor standing, requires certain conditions for the installation area, such as that the temperature should be below 25°C, must be installed in a clean limited environment and the cabinet can be accessed from several sides, and a drain pipe is necessary for draining the concentrate from the system. Furthermore, the moisture in the sample must be removed before the measurement and compensation calculations for the detector system are required (for example for different geometries or flows in the tube), so that maintenance of the tube and connectors cannot be performed by the workshop staff but must be undertaken by a specialist (for example the detector supplier).

[0023] The response time of a CO gas detection system should be short and preferably real-time, and the sensitivity should be high in order to provide an effective early warning system.

[0024] However, the transport time of the air sample, plus the detector purge time, analysis time, calculation time and the inherent maintenance time in the common measuring chamber amount to a long response time of about 15-60 seconds for these prior art systems. It is desirable to reduce this response time, which can prove too long to constitute an early warning. With regard to sensitivity, some prior art systems cannot detect CO gas concentrations below about 1 ppm in general, and for the best prior art systems below about 0.4 ppm. However, in order to provide an effective early warning system, it is desirable to provide a sensitivity that can detect CO gas concentrations below 0.4 ppm in general and preferably below 0.1 ppm.

[0025] During initial commissioning of prior art CO gas detection systems for spray dryer systems, tests need to be performed in which hazardous CO gas is injected throughout the dryer system to test the gas residence time of the necessary calibration procedures for CO gas detection. It is important that the purchase and handling of CO gas is usually approved by local regulatory authorities. Some prior art systems require enhanced tests to be performed frequently on the system prior to opening operation of the spray dryer system as prescribed by the spray dryer system risk assessment or to ensure optimal system performance. One of the steps in this test is to use a specific certified test gas consisting of N2+CO (CO = 8.0 ppm) to confirm that the CO gas detection is measured correctly. This test gas is expensive and not universally available on the market. Another requirement is a leak test on the sample tubes of the prior art CO gas detection system. This test must be performed frequently to ensure that the CO gas detection system is actually measuring the process gas from inside the dryer system.

[0026] A further problem is that there is intruding false CO gas from external sources, in particular from weather fluctuations, changes in ambient air or from exhaust from cars, field burning of crops, human activities etc. which leads to environmental CO gas in the air entering the system to vary greatly depending on location and pollution in the plant, area, country and climate. Several tens of times more CO gas content can thus be present in the inlet air and mask or overpower the CO gas produced by any smoldering nests within the process. This problem of prior art systems is attempted to be solved by using a reference ambient air sample and / or by using a fixed reference CO gas value or a differential calculation (i.e. the sum of the CO gas content from all inlets minus the sum of the CO gas content from all outlets) to calculate the difference between the CO gas content of the samples at one or more inlets and the samples at one or more outlets. SUMMARY

[0027] Against this background, it is therefore an object of the present invention to provide a powder drying system suitable for early detection of smoldering nests by a carbon monoxide (CO) gas detection system, by which the above mentioned problems and drawbacks are mitigated.

[0028] In a first aspect of the present invention, these and further objects are achieved by a CO gas detection system adapted to detect CO gas from smoldering powder in a powder drying system component such as a spray dryer chamber, a fluidized bed or a bag filter, the CO gas detection system comprising at least one inlet CO gas detector arranged on at least one gas inlet of the powder drying system component to provide at least one inlet CO gas content measurement, at least one outlet CO gas detector arranged on at least one gas outlet of the powder drying system component to provide at least one outlet CO gas content measurement, and an analysis unit adapted to receive the at least one inlet CO gas content measurement from the at least one inlet CO gas detector, to receive the at least one outlet CO gas content measurement from the at least one outlet CO gas detector, and to compare a sum of the at least one inlet CO gas content measurement with a sum of the at least one outlet CO gas content measurement while compensating for dilution, mixing, and time delay of the outlet CO gas content measurements to provide a differential measurement value ΔC 出口 indicating the CO gas content from smoldering powder in the powder drying system component, wherein at least the at least one outlet CO gas detector comprises an IR laser emitter and is adapted to detect within a measurement volume and is arranged on the at least one gas outlet in such a way that said measurement volume extends directly within the gas flow in said at least one gas outlet.

[0029] Other components of the powder drying system to be investigated can be cyclones, ducts, etc. It is even possible to investigate the outside of the powder drying system, i.e. the space in which the powder drying system or its components are located.

[0030] The CO gas detection system according to the present invention thus employs the absorption of an IR laser beam at a specific wavelength emitted and detected by an IR detector as a measurement principle. For example, the absorption spectrum of CO shows a main peak at about 2.3 pm and about 4.7 pm. Therefore, the specific wavelength of the IR laser beam emitted and detected by the IR detector is typically about 2.2 to 2.4 pm. The absorption is proportional to the number of CO molecules in the gas, and therefore the concentration of the CO gas in the gas can be calculated from the absorption, the pressure and the temperature of the gas. Furthermore, since the absorption spectrum of methane (CH4) shows a main peak at about 2.2 pm, the CO gas detection system can also be used to detect CH4 gas.

[0031] By providing at least the at least one outlet CO gas detector as an IR laser detector adapted to perform the detection within a measurement volume and arranging it on the gas outlet in such a way that its measurement volume extends directly within the gas stream in the gas outlet, a direct measurement of the CO gas concentration at the measurement point is obtained in real time. Thus, only the measurement result needs to be transferred to the analysis unit, which can be done by simply transferring an electronic or optical signal in a wired or even better wireless electronic or optical communication line. In other words, using the system according to the present invention, sample collection, sample preparation and sample transport are not necessary. Thus, no expensive, time-consuming, and complex sampling equipment and a tube system for transporting the gas sample to the analysis unit are needed. This in turn provides a system comprising very few components and thus is cost-effective and easy to install and retrofit. Furthermore, the process flow in the spray dryer system components is not disturbed at all by the measurement process and thus the quality of the spray-dried product is not affected.

[0032] A further advantage is that the direct measurement of the CO gas concentration at the measurement point and the transfer of the result digitally, such as optically or electronically, to the analysis unit makes it possible to greatly reduce the response time of the system, i.e. the time delay between individual measurements, and in practice to reduce it to as little as about 1 second and even less. This applies to all sizes of spray dryer systems and is greatly reduced compared to prior art systems.

[0033] Furthermore, using the system according to the present invention, the commissioning of the CO gas detector only requires an initial calibration procedure once and this calibration can be performed by injecting methane gas into the entire system, which is more readily available than certified N2+CO gas. Thus, the need for a calibration by an expert other than the detector supplier and handling of dangerous CO gas cylinders for commissioning is eliminated. Thus, the system according to the present invention is also simple and cost-effective, safer and easier to commission in terms of maintenance. The verification of the measurement accuracy of the present invention only needs to be performed once a year. If the verification shows that the present invention needs to be adjusted / calibrated, a N2+CO (CO = 8.0 ppm) gas mixture or methane is used for the adjustment / calibration.

[0034] By providing the analysis unit adapted to compare the inlet CO gas content measurement value with the outlet CO gas content measurement value to compensate for dilution, mixing, and time delay of the outlet CO gas content measurement value in order to provide a differential measurement value AC 出口indicating the CO gas emitted from smoldering powder in the powder drying system components, so that false CO gas from external sources and dilution, mixing and time delays in the powder drying system can be taken into account in the analysis and thus is a true CO gas content measurement. Thereby a CO gas detection system is provided with which the reliability and sensitivity is greatly increased when measuring small gas volumes and the resulting CO gas measurement is very accurate and highly reliable.

[0035] Indeed, experiments on a powder drying system with a CO gas detector system according to the application have shown that the sensitivity of the system is sufficiently high to detect CO gas concentrations from smoldering residues of 1 ppm (parts per million) or lower. For example, it has been shown that for large powder drying systems, CO gas concentrations as low as 0.3 to 0.4 ppm can be detected, while a high sensitivity has been demonstrated corresponding to a detectability of CO gas concentrations as low as 0.04 ppm. For an early warning system, the sensitivity and accuracy of the measurement is of utmost importance. This is greatly reduced compared to prior art systems.

[0036] The reduced response time and the increased sensitivity in turn provide an effective early warning which enables measures to be taken at a very early point in time in the event that smoldering starts to occur.

[0037] In embodiments, the at least one inlet CO gas detector further comprises an IR laser emitter and is adapted to perform the detection within a measurement volume and is arranged on the at least one gas inlet in such a way that its measurement volume extends directly within the gas flow in said gas inlet.

[0038] Thereby, a CO gas detection system is provided in which similar advantages as those described above are also achieved when taking inlet CO gas measurements and the sensitivity of the system is increased.

[0039] In embodiments, at least the at least one outlet CO gas detector and / or at least the at least one inlet CO gas detector comprises an IR laser emitter and an IR receiver, and optionally a reflector, which are arranged in a position in which they are one of radially and / or longitudinally offset, diametrically opposite and diametrically opposed to each other, so that their measurement volume extends between said positions.

[0040] In a further, optional embodiment, the at least one inlet CO gas detector and / or outlet CO gas detector comprises an IR laser emitter and an IR receiver arranged at the same position and at least one reflector arranged at a position which is offset in a radial and / or longitudinal direction relative to the position of the IR laser emitter and / or IR receiver, opposite each other and diametrically opposite, such that the measurement volume of the at least one inlet and / or outlet CO gas detector system extends between said positions.

[0041] By means of any one of the two above-mentioned embodiments, a CO gas detection system is provided which is extremely simple in construction and very easy to install on an existing powder drying system, including retrofitting thereof. Such a CO gas detection system is also cost-effective both in terms of acquisition and in terms of maintenance. By using a reflector, the measurement volume can be increased and thus the sensitivity of the system can be improved.

[0042] In an embodiment, the measurement volume of the outlet CO gas detector and / or the measurement volume of the inlet CO gas detector extends over a length of at least 1 meter.

[0043] Thereby, a measurement volume is provided which is sufficiently large to obtain a CO gas content measurement which is both highly representative of the CO gas concentration in the inlet or outlet and which enables the required sensitivity to be achieved. It is noted that the optimal length depends on the type and action of the IR laser emitter and / or IR receiver used and can thus vary in accordance therewith.

[0044] In an embodiment, the measurement volume of the outlet CO gas detector and the measurement volume of the inlet CO gas detector can extend along any one of the following directions: a radial direction of the gas inlet or gas outlet, a longitudinal direction of the gas inlet or gas outlet perpendicular to the radial direction, and a direction inclined relative to the longitudinal direction and / or radial direction of the gas inlet or gas outlet.

[0045] Thereby, a CO gas detection system is obtained which is easy to install on a powder drying system, while at the same time ensuring that a sufficiently large measurement volume is provided in a particularly simple manner to obtain a CO gas content measurement which is both highly representative of the CO gas concentration in the inlet or outlet and which enables the required sensitivity to be achieved.

[0046] In an embodiment, the at least one outlet CO gas detector and / or the at least one inlet CO gas detector further comprises at least one purging device arranged and adapted to purge the CO gas detector prior to providing the CO gas content measurement.

[0047] By providing a purging device, powder residues originating from the spray drying process, which can accumulate over time on the outlet CO gas detector and / or the inlet CO gas detector of the CO gas detector system, especially on the IR receiver and optical components (e.g. lenses) placed in the conduit, can be removed or even completely avoided. This in turn provides for the elimination of noise and disturbances in the measurement originating from such powder accumulation, thereby even further improving the measurement quality.

[0048] Advantageously, the gas used by the purging device for purging the CO gas detector does not comprise CO gas. Thus, at least a small portion of the measurement range in front of the CO gas detector remains free of remaining CO in the system components in which the CO gas detector is to be placed, which can influence the accuracy of the measurement. Thereby, a strict definition of the starting point of the measurement volume containing a certain concentration of CO gas to be measured will be provided. On the other hand, if CO gas is present in the gas used by the purging device for purging the CO gas detector, this CO gas will also be detected by the CO gas detector and thus add an unnecessary contribution to the measurement.

[0049] In embodiments, at least the inlet CO gas detector and / or the outlet CO gas detector is cooled, preferably air cooled. Thereby, a drift of the measurement spectrum of the IR laser beam due to heating can be avoided. It is noted that in embodiments in which the outlet and / or inlet CO gas detector comprises a purging device, this purging device can be used at the same time for air cooling the CO gas detector.

[0050] In embodiments, the powder drying system further comprises a plurality of outlet CO gas detectors arranged on the same gas outlet and / or on the outlet of different powder drying system components, in order to provide a plurality of outlet CO gas content measurements, and / or a plurality of inlet CO gas detectors arranged on the same gas inlet and / or on the inlet of different powder drying system components, in order to provide a plurality of inlet CO gas content measurements.

[0051] Thereby, the CO gas concentration originating from smoldering powder at several locations can be detected at the same time. This in turn provides for a further improved early warning, while still keeping the system simple and cost efficient in terms of structure, installation and maintenance.

[0052] In embodiments, the analysis unit is adapted to compare the inlet CO gas content measurement and the outlet CO gas content measurement to obtain a differential measurement value AC 出口 (x), indicating the CO gas from smoldering powder in the powder drying system component at a given time x, by the following relation:

[0053] AC 出口(x) = C 出口，测量的 (x) - C 出口 (x)

[0054] wherein:

[0055]

[0056] and wherein:

[0057] C 出口，测量的 (x) is the CO gas concentration in ppm in the gas outlet at time x from the outlet CO gas content measurement measured by the outlet CO gas detector,

[0058] C 出口 (x) is the calculated CO gas concentration in ppm in the gas outlet at time x,

[0059] C 出口 (x - t s ) is the calculated CO gas concentration in ppm in the gas outlet at time x minus a sampling time t s , i.e. the most recent pre-calculated value of the CO gas concentration in ppm in the gas outlet,

[0060] C 入口 (x - t p ) is the CO gas concentration in ppm in the gas inlet at a number of seconds t p before time x from the inlet CO gas content measurement measured by the inlet CO gas detector,

[0061] V 喷雾干燥器 is the volume of the spray dryer in m 3 ,

[0062] flow 入口 is the air flow in m 3 / s in the main air inlet,

[0063] flow 出口 is the total gas flow in m 3 / s out of the spray dryer, calculated as the sum of the gas flow in each of the main gas outlet, the gas outlet of the static fluidized bed and the gas outlet of the VIBRO-FLUIDIZER TM , and

[0064] t s is the sampling time.

[0065] Thereby, not only false CO gas from external sources as well as dilution, mixing and time delay in the powder drying system can be taken into account, but also continuously from run to run or measurement to measurement by dynamic modeling of the powder drying system, instead of using fixed compensation values as in prior art systems. Furthermore, it has proven that the above described model is particularly accurate for all sizes of powder drying systems or plants and one advantage is that flow and volume variations can easily be incorporated into the model, e.g. directly from a PLC-system.

[0066] In an embodiment, the one or more inlet CO gas detectors and / or the outlet CO gas detector, including one or more purge devices, if provided, can be mounted on an inlet and / or outlet flange welded to the inlet and / or outlet conduit. Thereby, a simple, fast and durable mounting of the CO gas detectors is provided.

[0067] Thereby, the measurement range of the component can be cleaned before the CO gas content measurement is performed, which otherwise would adversely affect the CO gas content measurement, e.g. changing the length of the light beam path through the inlet or outlet. This in turn provides an increased measurement sensitivity.

[0068] According to the present application, the above and further objects are also achieved by a method for detecting smoldering powder in a powder drying system component, such as a spray dryer chamber, a fluidized bed or a bag filter, from a powder drying system comprising a carbon monoxide (CO) gas detection system, the method comprising the steps of providing an inlet CO gas content measurement value by an inlet CO gas detector arranged on a gas inlet of the powder drying system component, providing an outlet CO gas content measurement value by at least one outlet CO gas detector arranged on a gas outlet of the powder drying system component, receiving the inlet CO gas content measurement value from the inlet CO gas detector, receiving the outlet CO gas content measurement value from the at least one outlet CO gas detector, comparing the inlet CO gas content measurement value with the outlet CO gas content measurement value to compensate for dilution, mixing, and time delay of the outlet CO gas content measurement value in order to provide a differential measurement value ΔC 出口 , indicative of CO gas from smoldering powder in the powder drying system component, wherein the at least one outlet CO gas detector comprises an IR laser emitter and is adapted to perform detection within a measurement volume, and is arranged on the gas outlet in such a way that its measurement volume extends directly within the gas flow in the gas outlet before providing the outlet CO gas content measurement value.

[0069] Further features of the method according to the second aspect of the present application will become clear from the following detailed description and are listed in the independent method claim. BRIEF DESCRIPTION OF DRAWINGS

[0070] The application will be described in more detail below by non-limiting examples of preferred embodiments and with reference to the enclosed schematic drawings, in which:

[0071] Figure 1 A schematic view of the main components of a spray drying system in an embodiment of the first aspect of the application is shown, indicating different exemplary positions of the CO gas detection system according to the application;

[0072] Figure 2 A schematic view of a CO gas detection system in an embodiment of the application is shown, wherein the CO gas detection system is arranged on the outlet of a spray drying system;

[0073] Figure 3 A cross-section of a CO gas detection system according to Figure 2 is shown; and

[0074] Figure 4 The steps of a method according to an embodiment of the application are schematically illustrated. DETAILED DESCRIPTION

[0075] Figure 1 A schematic view of the main components of a powder drying system is shown, the powder drying system comprising a powder handling unit, which in the shown embodiment is exemplified in the form of a spray drying system 1. In a manner known per se, the spray drying system 1 comprises a spray dryer with a drying chamber 200, and a process gas supply device 300, typically comprising a gas disperser. A gas inlet 201 is provided for suction of gas to the process gas supply device 300 and further to the drying chamber 200. At the lower end of the drying chamber 200, an outlet 203 for dried material is provided, and in addition, for some types of powder drying systems, a further gas inlet 201’ can be present. The drying chamber 200 is further incorporated with atomizing means such as nozzles and / or rotating atomizing wheels.

[0076] In the shown spray drying system 1, a static fluidized bed 700 is provided with an air inlet 701, and a post-treatment unit in the form of a vibrating or static fluidized bed 500 is provided. At one end, the vibrating or static fluidized bed 500 comprises an inlet 503 at which dried material from the outlet 203 of the drying chamber 200 is received for further treatment of the material, which is then collected at an outlet 504 at the other end of the vibrating or static fluidized bed 500. The fluidized bed 500 further comprises gas inlets 501 and 501’ and a gas outlet 502. Further upstream or downstream devices can also be present.

[0077] Furthermore, the powder drying system comprises, in addition to the spray drying system 1, a filter unit 400 to which waste process gas, in which particles are entrained, is directed from the process gas. The filter unit 400 thus comprises a gas inlet 401 for waste process gas from one or more of the upstream operating units, a plurality of bag filters and a clean air outlet 601. The filter unit 400 can form part of a series of powder recovery units comprising further filter units and cyclones or bag filters or any combination thereof. Furthermore, Figure 1 The cleaning device 600 is shown in

[0078] The several transport lines interconnect the operating units in a manner known per se and will not be described in detail.

[0079] Reference will now be made in detail to Figures 2-3 the overall configuration of the CO gas detection system of the spray drying system according to the present application.

[0080] According to the present application, the spray drying system 1 further comprises a carbon monoxide (CO) gas detection system adapted to detect CO gas from smoldering powder in a spray drying system component such as the spray dryer chamber 200, the fluidized bed 500 or the bag filter unit 400.

[0081] Generally, the CO gas detection system comprises at least one CO gas detector arranged on the gas outlet, herein denoted as outlet CO gas detector, and at least one CO gas detector arranged on the gas inlet, herein denoted as inlet CO gas detector. In Figure 1 A number of exemplary and non-limiting possible positions of the outlet CO gas detector and the inlet CO gas detector are indicated in Figure 1 Since the at least one outlet CO gas detector and the at least one inlet CO gas detector have the same or similar structure, both are indicated by reference numeral 3 in Figures 2-3 Embodiments of the CO gas detector are shown, for example, arranged at the gas outlet 202, but it can also be arranged on the gas inlet.

[0082] Generally, the CO gas detection system comprises an outlet CO gas detector 3 arranged on the gas outlet (such as on the outer surface thereof) of a powder drying system component in order to provide an outlet CO gas content measurement. Reference is made to Figure 2 and 3, the CO gas detection system more specifically and by way of non-limiting example comprises an outlet CO gas detector 3 arranged at the gas outlet 202 of the drying chamber 200 of the spray drying system 1. More specifically, the outlet CO gas detector 3 is arranged on the outer surface 2021 of the gas outlet 202 of the drying chamber 200. Typically, the outlet CO gas detector 3 can alternatively or additionally be arranged on a second or further gas outlet of the same or a second spray drying system component (such as those described above and / or such as indicated in Figure 1 ).

[0083] The CO gas detection system can comprise at least one inlet CO gas detector arranged on (such as on the outer surface of) a gas inlet of a powder drying system component, so as to provide an inlet CO gas content measurement. The CO gas detection system more specifically and by way of non-limiting example comprises an inlet CO gas detector arranged at the gas inlet 201 of the drying chamber 200 of the spray drying system 1. More specifically, the inlet CO gas detector is arranged on the outer surface of the gas inlet 201 of the drying chamber 200. Typically, one or more inlet CO gas detectors can alternatively or additionally be arranged on one or more gas inlets of other spray drying system components (such as those described above and / or such as indicated in Figure 1 ).

[0084] For example, in some embodiments, the outlet CO gas detector 3 and / or the inlet CO gas detector can be mounted on a flange respectively welded to the gas outlet and / or the gas inlet, respectively.

[0085] The CO gas detection system further comprises an analysis unit 5. The analysis unit 5 is adapted to receive the inlet CO gas content measurement from the inlet CO gas detector, and to receive the outlet CO gas content measurement from the at least one outlet CO gas detector 3. The analysis unit 5 can thus comprise a receiver. The analysis unit 5 is further adapted to compare the inlet CO gas content measurement with the outlet CO gas content measurement to compensate for dilution, mixing, and time delay of the outlet CO gas content measurement, so as to provide a differential measurement 出口 indicative of the CO gas from the smoldering powder in the spray drying system component (i.e. in the embodiments shown in the spray drying chamber 200). The analysis unit 5 is thus electrically and / or optically connected to the inlet CO gas detector and the outlet CO gas detector 3( Figure 2 ) by a respective wired or wireless connection 13.

[0086] In case the comparison result shows an indication of CO gas from smoldering powder in a spray drying system component, the analysis unit 5 is further adapted to take appropriate action. Such appropriate action can include triggering an alarm, e.g. in the form of an acoustic or visual signal, and / or automatically shutting down the spray drying system and / or activating a fire protection device.

[0087] The analysis unit 5 can thus (and as shown in Figure 2 Fig. 1) form a component part or a stand-alone part of a safety system which further comprises an alarm unit, e.g. in the form of an acoustic or visual signal unit. The alarm unit can alternatively be built-in within the analysis unit 5. In any case, when the differential measurement value AC 出口 of CO gas from smoldering powder in a spray drying system component is higher than a predetermined threshold value (typically close to 0), the analysis unit is adapted to trigger the alarm unit and the alarm unit is adapted to sound an alarm. Furthermore, the alarm unit can also be triggered if the analysis shows that the CO gas detection system is malfunctioning, in particular to sound a signal dedicated to this purpose, which is a feature not possible in prior art systems. The analysis unit 5 is thus electrically and / or optically connected to the alarm unit by wired or wireless connection.

[0088] With reference to Figure 2 and 3 , the outlet CO gas detector 3 is an IR detector adapted to perform detection within a measurement volume 6. The outlet CO gas detector 3 is arranged at the outlet 202 in such a way that its measurement volume 6 extends directly within the (process) gas stream 20 in the outlet 202. More specifically, the outlet CO gas detector 3 comprises an IR laser emitter 7 and an IR receiver 8. The IR laser emitter 7 and the IR receiver 8 are arranged on opposite points of the outlet 202 (here on diametrically opposite points, but not necessarily always so), such that its measurement volume 6, i.e. the volume through which the IR laser beam 15 of the IR detector extends when in operation and measurement, extends through the interior 2022 of the outlet 202 over a length D between the opposite points of the outlet 202. The IR laser emitter 7 and the IR receiver 8 can also be electrically and / or optically connected by wired or wireless connection 12.

[0089] In alternative embodiments, the outlet CO gas detector 3 can also comprise one or more IR reflectors which can be arranged together with the IR laser emitter, e.g. in the same housing, or separately from the emitter, e.g. in a different housing from the IR laser emitter (such as in the housing of the IR receiver), or to redirect the laser light along one or more of the longitudinal direction, the radial direction and the cross-sectional direction of the gas outlet over one or more segments. The same applies to the inlet CO gas detector.

[0090] The outlet CO gas detector 3 can further comprise at least one purging device 9 arranged and adapted to purge the outlet CO gas detector 3 prior to providing an outlet CO measurement. The purging device 9 is connected to the outlet CO gas detector 3, in particular to the IR laser emitter 7 as well as to the outlet IR receiver 8, by means of an air pipe 14.

[0091] The inlet CO gas detector can also be substantially identical to the outlet CO gas detector 3. The inlet CO gas detector can preferably comprise an IR laser emitter and be adapted to detect within a measurement volume. The inlet CO gas detector is then arranged at the inlet 201 in such a way that its measurement volume extends directly within the (process) gas flow in the inlet 201. More in particular, the inlet CO gas detector system comprises an IR laser emitter and an IR receiver. The IR laser emitter and the IR receiver are arranged on opposite points of the inlet 201, possibly but not mandatorily diametrically opposite points, such that its measurement volume, i.e. the area in which the IR laser beam of the IR detector extends when in operation and measurement, extends through the interior of the inlet 201 over the length between the opposite points of the inlet 201. The IR laser emitter and the IR receiver can also be electrically and / or optically connected by means of a wired or wireless connection.

[0092] The inlet CO gas detector can further comprise at least one purging device arranged and adapted to purge the inlet CO gas detector prior to providing an inlet CO gas content measurement. The purging device is connected to the inlet CO gas detector, in particular to the IR laser emitter as well as to the inlet IR receiver, by means of an air pipe.

[0093] The measurement volume 6 of the outlet CO gas detector 3 as well as the measurement volume of the inlet CO gas detector can extend along any of the following directions: a radial direction R of the gas inlet or gas outlet as shown in Figure 3 Fig. 1, Figure 2 a longitudinal direction L of the gas inlet or gas outlet perpendicular to the radial direction R, Figure 2 and a direction oblique with respect to both the longitudinal direction L and the radial direction R of the gas inlet or gas outlet. The measurement volume 6 of the outlet CO gas detector 3 as well as the measurement volume of the inlet CO gas detector can extend over a length of more than 1 meter in order to provide a sufficiently large measurement volume to ensure the desired measurement sensitivity and accuracy.

[0094] The measurement principle employed by the present invention is thus the absorption of the IR laser beam at a specific wavelength emitted by the IR laser emitter 7. The absorption will be proportional to the number of CO molecules in the process gas. Thus, for example in the manner further described below, based on the analysis of the resulting absorption spectrum, the concentration of the CO gas can be calculated from the absorption together with the temperature and pressure of the process gas.

[0095] In a manner known per se to the person skilled in the art of IR-based CO gas content measurements, the outlet CO gas detector 3 can further comprise a first emitter 10 to measure the process gas temperature for providing process temperature compensation to the CO gas content measurement for compensating the effects of the elevated temperature caused by the IR laser beam on the measurement, or in particular the effects from the elevated process temperature compared to room temperature, which can otherwise cause a shift of the obtained absorption spectrum. The outlet CO gas detector 3 can further comprise a second emitter 11 to measure the process gas pressure for providing process pressure compensation to the calculation for compensating the effects of the elevated process pressure compared to atmospheric pressure on the measurement. Similarly, the inlet CO gas detector can further comprise a first emitter to provide process temperature compensation and / or a second emitter to provide process pressure compensation.

[0096] Furthermore, in some embodiments in which the CO gas detection system comprises a purge device 9, the purge device 9 can also be arranged and adapted to purge the measurement range 6' (6) within the gas outlet (gas inlet) before providing the outlet (inlet) CO gas content measurement value, and / or to purge the part of the measurement range within the gas inlet (gas outlet) before providing the inlet (outlet) CO gas content measurement value. Figure 3 ) before providing the outlet CO gas content measurement value, and / or to purge the part of the measurement range within the gas inlet (gas outlet) before providing the inlet (outlet) CO gas content measurement value.

[0097] Still further, in some embodiments, the outlet CO gas detector 3 and / or the inlet CO gas detector, such as comprising the IR laser emitter and / or the IR receiver, can be cooled, such as air-cooled or even water-cooled. For example, the purge unit can also act as an air cooling unit. Alternatively, a separate cooling device can be provided.

[0098] Reference will now be made to Figure 4 exemplary embodiments of the method according to the present application will be described.

[0099] Before step 1000, a spray drying system with a CO gas detection system according to the present application is provided by mounting said CO gas detection system on the spray drying system. In step 1000, an inlet CO gas content measurement is provided by said at least one inlet CO gas detector. In step 1200, an outlet CO gas content measurement is provided by said at least one outlet CO gas detector. In step 1300, the inlet CO gas content measurement from the inlet CO gas detector is received by the analysis unit 5. In step 1400, the outlet CO gas content measurement from the at least one outlet CO gas detector is received at the analysis unit 5. In step 1500, the inlet CO gas content measurement is compared with the outlet CO gas content measurement by the analysis unit 5 to compensate for dilution, mixing, and time delay of the outlet CO gas content measurement to provide a differential measurement AC 出口 , indicative of CO gas from smoldering powder in a component of the spray drying system. Finally, in step 1100, before step 1200 of providing the outlet CO gas content measurement, the at least one outlet CO gas detector is provided in the form of an outlet CO gas detector comprising an IR laser emitter and adapted for detection within a measurement volume and arranged on the gas outlet in such a way that its measurement volume extends directly within the gas stream 20 of the interior 2022 of the gas outlet 202.

[0100] The method can further comprise one or more of the following optional steps.

[0101] Before step 1000 of providing the inlet CO gas content measurement, step 900 of providing the inlet CO gas detector in the form of an inlet CO gas detector optionally comprising an IR laser emitter and adapted for detection within a measurement volume and arranging the inlet CO gas detector on the gas inlet in such a way that its measurement volume extends directly within the (process) gas stream inside the gas inlet 201.

[0102] In embodiments wherein at least the outlet CO gas detector comprises an IR laser emitter and an IR receiver, step of arranging the IR laser emitter and the IR receiver on the gas outlet 202, such as on the outer surface 2021 of the outlet 202, on opposing points, optionally diametrically opposing points, such that its measurement volume extends between the opposing points of the gas outlet 202.

[0103] In embodiments wherein the inlet CO gas detector comprises an IR laser emitter and an IR receiver, step of arranging the IR laser emitter and the IR receiver on the gas inlet 201, such as on the outer surface of the inlet 201, on opposing points, optionally diametrically opposing points, such that its measurement volume extends between the opposing points of the gas inlet 201.

[0104] Optional step of purging the outlet CO gas detector prior to the step 1200 of providing an outlet CO gas content measurement.

[0105] Optional step of purging the inlet CO gas detector prior to the step 1300 of providing an inlet CO gas content measurement.

[0106] Optional step of cooling the outlet CO gas detector, preferably with air, and / or step of cooling the inlet CO gas detector, preferably with air.

[0107] Optional step of providing a plurality of outlet CO gas detectors, arranging the plurality of outlet CO gas detectors on the same gas outlet and / or on the outlet of different spray drying system components, and step of providing a plurality of outlet CO gas content measurements.

[0108] Optional step of providing a plurality of inlet CO gas detectors, arranging the plurality of inlet CO gas detectors on the same gas inlet and / or on the inlet of different spray drying system components, and step of providing a plurality of inlet CO gas content measurements.

[0109] Optional step of providing process temperature compensation and / or process pressure compensation to the outlet CO gas detector and / or to the inlet CO gas detector prior to the step 1200 of providing an outlet CO gas content measurement and / or prior to the step 1000 of providing an inlet CO gas content measurement.

[0110] The following will describe a mathematical model hidden behind the comparison performed by the analysis unit 5 and constituting part of the method performed by the powder drying system according to the present application, and more specifically part of the comparison step of the method according to the present application.

[0111] The increase of the CO gas concentration C 入口 in the inlet air will over time lead to an increase of the CO gas concentration C 出口 in the outlet air. By mathematically modeling the spray drying system as an ideal mixing tank plus plug flow, t p (i.e. time delay), the CO gas concentration in the outlet air can be calculated based on the CO gas concentration in the inlet air. The calculated CO gas concentration C 出口 indicates natural occurring fluctuations of the CO gas concentration, which should not trigger the alarm system to respond to. Instead, the alarm system should only be triggered in response to an increase of the CO gas concentration originating from smoldering of the powder in the spray drying system. The increase of the CO gas concentration originating from smoldering, or the differential measurement value AC 出口 can be expressed as:

[0112] AC 出口 = C 出口，测量的 - C 出口 (1),

[0113] where C 出口，测量的 is the CO gas concentration in the outlet according to the outlet CO gas content measurement measured by the outlet CO gas detector.

[0114] To calculate C 出口 , the following model can be established. First, the amount of CO gas accumulated per time unit in the spray drying system can be expressed as:

[0115] C 入口 * flow rate 入口 - C 出口 * flow rate 出口 (2),

[0116] and V

[0117]

[0118] In the above equation, flow rate 入口 is the air flow rate in the main air inlet 201 in m 3 / s, flow rate 出口 is the total gas flow rate out of the spray drying system in m 3 / s, and V 喷雾干燥器 is the volume of the spray drying system in m 3 .

[0119] The air flow rate in the main air inlet 201 in m 3 / s, flow rate 入口 , is assumed to be constant over time, in the case of a static fluidized bed and a VIBRO-FLUIDIZER TM with a separate air inlet from the main air inlet, it is equal to the flow rate in the main air inlet, and if a common air inlet is used, it is equal to the sum of the flow rates in each of the main air inlet, the air inlet of the static fluidized bed, and the air inlet of the VIBRO-FLUIDIZER TM .

[0120] The total gas flow rate out of the spray drying system, flow rate 出口 , is calculated as the sum of the gas flow rates in each of the main gas outlet, the gas outlet of the static fluidized bed, and the gas outlet of the VIBRO-FLUIDIZER TM , in m 3 / s.

[0121] The volume of the spray dryer in m 3 , V喷雾干燥器 The value can be determined experimentally by introducing CO gas into the spray dryer. The theoretical value can be obtained as t p * flow rate 入口 where t p is the assumed time delay of the gas flow through the spray drying system, i.e. the time it takes for the gas flow to flow from the inlet CO gas detector through the spray dryer to the outlet CO gas detector.

[0122] Since ideal mixing is assumed in the spray dryer, the CO gas concentration in the outlet air is equal to the CO gas concentration in the spray drying system (dC 喷雾干燥器 / dt = dC 出口 / dt). Since the assumed time delay of the gas flow through the spray drying system t p , the inlet CO gas concentration measured by the inlet CO gas detector at a time t p before a given point in time x is used to calculate the outlet CO gas concentration of the spray drying system at time x:

[0123]

[0124] where C 入口 (x-t p ) is the concentration of CO gas in the inlet measured by the inlet CO gas detector in ppm at a time t p before the point in time x.

[0125] Using small sampling steps, t s , the following is obtained based on equation (4) above:

[0126]

[0127] Thus, by rearranging equation (5), the following relation is obtained for the calculated CO gas concentration in ppm in the outlet air at time x, C 出口

[0128]

[0129] where C 出口 (x-t s ) is the concentration of CO gas in ppm at time x minus t s -sampling time-, i.e. the most recent pre-calculated value of C 出口 .

[0130] Equation (6) can thus be used to compare the inlet CO gas content measurements with the outlet CO gas content measurements. The result can then be compared with the outlet CO gas content measurements C 出口，测量的 ​(x) (obtained at time x by the outlet CO gas detector) is inserted into equation (1) to calculate the differential measurement value AC 出口 (x), indicating an increase in the concentration of CO gas originating from smouldering at time x, is thus obtained:

[0131] AC 出口 (x) = C 出口，测量的 (x) - C 出口 (x) (7).

[0132] Based on the differential measurement value AC thus calculated, indicating an increase in the concentration of CO gas originating from smouldering 出口 For each calculation made, it can be determined whether an alarm should be triggered and / or other suitable actions should be taken.

[0133] It should be noted that the above description of preferred embodiments serves only as an example, and the person skilled in the art will appreciate that many variations can be made without departing from the scope of the claims.

[0134] For example, and optionally, since methane (CH4) has an absorption wavelength similar to that of CO, CH4gas in the gas inlet or gas outlet of the spray drying unit can also be detected using the method and / or apparatus according to the present application. The results of such CH4gas detection can also be used to take into account the influence of CH4gas production that interferes with the CO gas measurement, at least in the case of a reasonably large amount of CH4gas.

Claims

1. A powder drying system, comprising a CO gas detection system adapted to detect CO gas from smoldering powder in a component of the powder drying system, the CO gas detection system comprising: At least one inlet CO gas detector is arranged on at least one gas inlet of a component of the powder drying system to provide a measurement of at least one inlet CO gas content. At least one outlet CO gas detector is arranged on at least one gas outlet of a component of a powder drying system to provide at least one measurement of the outlet CO gas content, and The analysis unit is adapted to receive at least one inlet CO gas content measurement value from the at least one inlet CO gas detector, receive at least one outlet CO gas content measurement value from the at least one outlet CO gas detector, and compare the sum of the at least one inlet CO gas content measurement value with the sum of the at least one outlet CO gas content measurement value, while compensating for dilution, mixing, and time delay of the outlet CO gas content measurement value to provide a differential measurement value ΔC. 出口 This differential measurement indicates the CO gas content of smoldering powder from components of the powder drying system, wherein, At least one outlet CO gas detector includes an IR laser emitter and is adapted to perform detection within a measurement volume, and is arranged on the at least one gas outlet in such a manner that the measurement volume extends directly within the gas flow in the at least one gas outlet. The at least one inlet CO gas detector further includes an IR laser emitter and is adapted to perform detection within a measurement volume, and is positioned on the at least one gas inlet such that its measurement volume extends directly within the gas flow in the gas inlet. The analysis unit is adapted to compare the measured CO gas content at the inlet with the measured CO gas content at the outlet to obtain a differential measurement value ΔC. 出口 (x), this differential measurement indicates the CO gas content of smoldering powder from the powder drying system at a given time x, according to the following relationship: ， in: ， And among them: C 出口，测量的 (x) is the CO gas concentration in ppm at the gas outlet based on the CO gas content measured by the outlet CO gas detector at time x. C 出口 (x) is the calculated CO gas concentration in ppm at the gas outlet at time x. C 出口 (xt s () is time x minus sampling time t s The calculated CO gas concentration in ppm at the gas outlet, that is, the most recently calculated CO gas concentration in ppm at the gas outlet. C 入口 (xt p ) is a number of seconds t before time x. p The CO gas concentration in the gas inlet, expressed in ppm, is determined by the CO gas content measured by the inlet CO gas detector. V 喷雾干燥器 It is m 3 The volume of the spray dryer is calculated. flow 入口 It is m 3 / s is the airflow rate at the main air inlet. flow 出口 It is m 3 The total gas flow rate from the spray dryer, measured in units of / s, is calculated as the sum of the gas flow rates from each of the main gas outlet, the static fluidized bed gas outlet, and the vibrating fluidizer gas outlet. t s That is the sampling time.

2. The powder drying system according to claim 1, wherein, The powder drying system consists of a spray dryer chamber, a fluidized bed, or a bag filter.

3. The powder drying system according to any one of claims 1-2, wherein, At least one outlet CO gas detector and / or at least one inlet CO gas detector includes an IR laser emitter and an IR receiver, and a reflector, wherein the IR laser emitter and the IR receiver are arranged at positions offset from each other, opposite each other, and diametrically opposite each other in the radial and / or longitudinal directions, such that their measuring volume extends between said positions, and, The at least one inlet CO gas detector and / or outlet CO gas detector includes an IR laser emitter and an IR receiver and at least one reflector, wherein the IR laser emitter and the IR receiver are arranged in the same position, and the at least one reflector is arranged in a position offset from the position of the IR laser emitter and / or the IR receiver in one of the following directions: radial and / or longitudinal, opposite to each other, and diametrically opposite, such that the measurement volume of the at least one inlet and / or outlet CO gas detector system extends between said positions.

4. The powder drying system according to any one of claims 1-2, wherein, The measuring volume of the outlet CO gas detector and / or the measuring volume of the inlet CO gas detector extends over a length of at least 1 meter.

5. The powder drying system according to any one of claims 1-2, wherein, The at least one outlet CO gas detector and / or the at least one inlet CO gas detector further includes at least one purging device, which is arranged and adapted to purge the outlet CO gas detector before providing the outlet CO gas content measurement and / or purge the inlet CO gas detector before providing the inlet CO gas content measurement.

6. The powder drying system according to any one of claims 1-2, wherein, The measuring volume of the outlet CO gas detector and / or the measuring volume of the inlet CO gas detector can be extended in any of the following directions: -The radial direction of the gas inlet or outlet, - The longitudinal direction perpendicular to the radial direction of the gas inlet or outlet, and - The direction inclination relative to the longitudinal and / or radial direction of the gas inlet or outlet.

7. The powder drying system according to any one of claims 1-2, further comprising a plurality of outlet CO gas detectors arranged on the same gas outlet and / or on the outlets of different components of the powder drying system, to provide a plurality of outlet CO gas content measurements, and / or Multiple inlet CO gas detectors are arranged on the same gas inlet and / or the inlets of different components of the powder drying system to provide multiple inlet CO gas content measurements.

8. A method for detecting CO gas from smoldering powder in a powder drying system component of a powder drying system according to any one of claims 1-7 and including a carbon monoxide (CO) gas detection system, the method comprising the steps of: The inlet CO gas content is measured by an inlet CO gas detector located at the gas inlet of a component of the powder drying system. The outlet CO gas content is measured by at least one outlet CO gas detector arranged on the gas outlet of a component of the powder drying system. Receive the inlet CO gas content measurement value from the inlet CO gas detector. Receive the measured value of the outlet CO gas content from the at least one outlet CO gas detector. The inlet CO gas content measurement is compared with the outlet CO gas content measurement to compensate for dilution, mixing, and time delay of the outlet CO gas content measurement, in order to provide a differential measurement value ΔC. 出口 This differential measurement indicates the CO gas content of smoldering powder from components of the powder drying system, wherein, The at least one outlet CO gas detector includes an IR laser emitter and is adapted to perform detection within a measurement volume, and is arranged on the gas outlet in such a manner that its measurement volume extends directly within the gas flow in the gas outlet before providing the measurement value of the outlet CO gas content.

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