System and method for monitoring an exhaust gas treatment system

Description

[0001] The invention relates to a system and a method for monitoring the functionality of an exhaust gas purification system connected to an emission source, in particular to a ship's engine.

[0002] According to the MARPOL Convention (International Convention for the Prevention of Marine Pollution from Ships) and other local regulations, ships today must demonstrate compliance with required emission limits. This can be achieved through the use of exhaust gas cleaning systems, such as scrubbers, where emissions are recorded using emission measuring devices. Alternatively, high-quality and therefore more expensive fuel can be used during ship operation, and its use can be documented.

[0003] If the exhaust gas cleaning system and / or the emission measuring devices are unavailable or not operational, manual documentation and subsequent evaluation by a specialist is often necessary. However, if an exhaust gas cleaning system and / or emission measuring devices fail, documenting them to third parties, i.e. to a flag state during a ship's voyage, is either very time-consuming and involves increased costs, or in extreme cases, is not feasible. Furthermore, repair of exhaust gas cleaning systems and / or emission measuring devices by a suitable specialist during a voyage is rarely or not possible at all. A period without proof of the correct functionality of the exhaust gas cleaning systems generally increases the cost risk for the corresponding ship transport, as, for example, fines may be incurred or a particularly clean fuel must be used.

[0004] To reduce difficulties caused by the lack of evidence of emissions from exhaust gas purification systems, redundant emission measurement devices can be used. However, these require correspondingly higher acquisition and operating costs.

[0005] Proof of the correct functioning of a ship's exhaust gas cleaning system often depends on the readings from a single sensor, for example, an exhaust gas sensor at the outlet of a scrubber. If such an exhaust gas sensor fails or delivers erroneous readings, the operation of the exhaust gas cleaning system is considered faulty. The exhaust gas sensor is then usually repaired as soon as possible in a port near the ship's current position.

[0006] However, it is possible that the exhaust gas purification system could continue to operate correctly even if the exhaust gas sensor fails, and its emissions levels could remain below specified limits. If such operation with low emissions levels could be demonstrated, for example, despite a failure or incorrect readings from the exhaust gas sensor, the exhaust gas purification system, and thus the entire ship, could operate more smoothly.

[0007] From KR 2021 0155464 A a system and a method with the features according to the respective preambles of the independent claims are known.

[0008] An object of the invention is to provide a method and a system which ensure the correct operation of an exhaust gas purification system even in the event of a malfunction of one of its sensors.

[0009] This object is achieved by a system and a method having the features of the independent claims. Advantageous developments of the invention are specified in the subclaims, the description, and the drawings.

[0010] The system is intended for monitoring an exhaust gas purification system that is functionally connected to an emission source, which is in particular a ship's engine. The system comprises an emission sensor that detects an emission signal indicating emissions from the emission source upon exiting the exhaust gas purification system, several additional sensors that output respective measurement signals related to the exhaust gas purification system, and an electronic processing unit. The processing unit is configured to determine a process state of the exhaust gas purification system based on the measurement signals from the additional sensors in order to evaluate the emission signal and the process state, respectively, with regard to an anomaly.Furthermore, the processing unit is designed to determine and output a compliant emission state of the exhaust gas purification system when there is no anomaly in the emission signal, and when there is an anomaly in the emission signal, while at the same time no anomaly in the process state has been determined or the anomaly in the emission signal satisfies an exception condition.

[0011] The exhaust gas purification system is installed, for example, in or on a ship and can therefore include a so-called scrubber for cleaning exhaust gases from a ship's engine. A first type of such a scrubber, also known as a wet scrubber, uses wash water, usually taken from the sea or another body of water, and passed through the scrubber to clean the exhaust gases. Alternatively, dry scrubbers can be used for exhaust gas purification on ships, in which lime granules are used instead of the wash water. In addition, so-called Denox scrubbers are also used for exhaust gas purification on ships. The term "Denox" refers to the removal of nitrogen oxides (NO x ) from the exhaust gases of the ship's engine. The removal of nitrogen oxides in a Denox scrubber can be achieved in a similar way to the removal of exhaust gases from motor vehicles that use a catalytic converter.

[0012] A scrubber can usually remove several different substances from a ship's engine exhaust. For example, while the wet and dry scrubbers mentioned above are primarily designed to remove sulfur, they are also suitable for soot and nitrogen oxides. Conversely, depending on the design, a Denox scrubber can remove other substances from the exhaust in addition to nitrogen oxides, such as sulfur and soot.

[0013] The emissions sensor detects the emissions in the exhaust gas after cleaning by the exhaust gas cleaning system. In addition, there are other sensors that are related to the exhaust gas cleaning system and thus to the emission status. For example, in a wet scrubber, these additional sensors measure the pH value of the wash water and / or process parameters of the scrubber and the ship's engine. In dry and DeNox scrubbers, process parameters of the respective scrubber can be measured in a similar way using additional sensors that are provided in addition to the emissions sensor. These additional sensors can measure the condition of a particular medium used to clean the exhaust gas in the respective scrubber type.

[0014] The emissions from the emission source, for example, the ship's engine, can be defined by a mass and / or volume concentration, a quantity, or a mass of one or more gases, which are measured after purification by the exhaust gas purification system. The emissions are represented, for example, by the SO2 concentration and / or the CO2 concentration in the exhaust gas in ppm or vol%.

[0015] If the exhaust gas purification system is installed on a ship, it includes a device for treating the water that is passed through the scrubber so that the water can then be returned to the sea or other body of water. In this case, some of the additional sensors can be installed on or in the water treatment device, for example, to measure its temperature or water flow rate. Furthermore, the additional sensors can also include a sensor that indicates the condition of the water after treatment and before being returned to the sea or other body of water.

[0016] Furthermore, the additional sensors may include sensors that are indirectly related to the exhaust gas purification system and are installed, for example, on or in components of a ship that determine the amount of exhaust gas absorbed by the exhaust gas purification system. Such additional sensors may, for example, be a sensor for engine power and / or other parameters of the ship's engine, as well as sensors that measure the ship's speed and acceleration.

[0017] The measurement signals from the additional sensors each define a process parameter that corresponds to the measured variable represented by the respective measurement signal. The totality of these process parameters describes the process state of the exhaust gas purification system, i.e., similar to components of a vector that represents the process state. The anomaly of the emission signal and the process state is determined by comparing the emission signal and the measurement signals from the additional sensors with the respective validity criteria. If the emission signal or one of the measurement signals from the additional sensors does not meet the respective validity criterion, an anomaly in the emission signal or the process state may exist. For example, an anomaly in the emission signal may exist if it lies above a legally specified limit.Furthermore, the emissions signal anomaly may involve determining that the emissions sensor has failed or is outputting a meaningless or questionable value. In this case, the process status is assessed to determine whether the emission control system is functioning correctly and the emissions status is compliant despite the emissions sensor anomaly.

[0018] The electronic processing unit thus detects an anomaly in the emissions signal if the emissions signal fails to meet the predetermined validity criterion or a combination of predetermined validity criteria. This can occur if the emissions sensor fails or systematic measurement errors occur, such as drift or jumps. Furthermore, the emissions signal lies above the predetermined validity range if, for example, a scrubber in a ship's exhaust gas purification system is malfunctioning and the amount of emissions emitted exceeds a specified limit.

[0019] Furthermore, the electronic processing unit determines whether a sufficient number of valid process parameters can be determined based on the measurement signals from the other sensors, thus describing the process state. If this is the case, the electronic processing unit determines whether the process parameters meet the predetermined validity criteria.

[0020] In the simplest case, the determination and output of the compliant emissions status can simply involve stating that the current emission quantity from the exhaust gas purification system is below a legally prescribed limit. Alternatively or additionally, however, a determined emission quantity, such as sulfur, can be specified quantitatively. In the context of the emissions status, the term "compliant" refers to the fact that the determined emission quantity meets legal requirements and, for example, is below the limit specified in a flag state.

[0021] An advantage of the system and the method described below is that the emission status of the emission control system can be determined and output even if there is an anomaly in the emission signal, for example, a failure of the emission sensor or a faulty emission signal. This maximizes the period during which correct functioning of the emission control system can be demonstrated.

[0022] This allows the exhaust gas purification system to continue operating even if there is an anomaly in the emissions signal or the emissions sensor, and this can be compensated for using the measurement signals from the other sensors to determine the compliant emissions status. This allows the system or the application of the method to avoid unwanted operational interruptions, for example, during a ship's voyage, as long as the process status allows the determination of the compliant emissions status, for example, based on the measurement signals from the other sensors.

[0023] This leads to improved information regarding the correct functioning of the exhaust gas cleaning system. Additional costs associated with malfunctions of the exhaust gas cleaning system can be reduced, for example, because the frequency of manual documentation of the emission status is reduced and redundant emission devices are no longer required. Overall, the reliability of the method for verifying the emission status of the exhaust gas cleaning system is improved. Furthermore, the use of expensive fuel for operating ships is no longer necessary. Since the process status of the exhaust gas cleaning system is determined based on the measurement signals from several additional sensors, malfunctions of the exhaust gas cleaning system can be detected early and reported, for example, via a warning system.

[0024] According to one embodiment, the exception condition may include the emission signal deviating from a normal state for less than a predetermined period of time, which is defined by a validity criterion for the emission signal detected by the emission sensor. By limiting the time limit for the exception condition, the amount of unwanted emissions can be reduced. Although these emissions are often tolerated by legislators for such an exception condition, they still pose a burden to the environment.

[0025] The determination of the respective validity criterion, i.e., for the emission signal and for the aforementioned signals from the other sensors that define the process state, can be made directly or indirectly based on one or more validity criteria for the measurement signals from the emission sensor and the other sensors. The validity criteria can, for example, include a lower and an upper limit for the respective measurement signal.

[0026] If an anomaly in the process state is detected and the emission signal anomaly does not meet the exception condition, the electronic processing unit can issue a specific error message. The output of the specific error message enables early detection of malfunctions in the exhaust gas purification system.

[0027] According to a further embodiment, the electronic processing unit calculates a substitute signal for the emission signal based on the measurement signals from the additional sensors if an anomaly in the emission signal is present while no anomaly in the process state is detected. Furthermore, the electronic processing unit can determine the compliant emission state based on the substitute signal if an anomaly in the emission signal is present while no anomaly in the process state is detected. Otherwise, i.e., if no anomaly in the emission signal is detected, the emission state is determined based on the emission signal.

[0028] Using the substitute signal, the compliant emission status of the exhaust gas purification system can be determined even if there is an anomaly in the emission signal, for example, in the event of an emission sensor failure. In the event of such an emission sensor failure or another anomaly in the emission signal or emission sensor, the substitute signal can be used to demonstrate correct functioning of the exhaust gas purification system with emissions below permissible limits. Therefore, if the exhaust gas purification system is installed on a ship, a ship's voyage can be continued without interruption to a planned destination port even in the event of an emission sensor failure. This, in turn, can avoid the costs associated with unplanned port stays.

[0029] The replacement signal can be determined based on the measurement signals from the additional sensors using a prediction method, for example, a machine learning algorithm that can be implemented using a regression model, e.g., a neural network. The learning phase of such a neural network can, for example, be carried out during correct operation of the emission sensor, in which a compliant emission state exists. When using such a neural network, a calculation model can also be used that links the process state of the exhaust gas purification system and the replacement signal for the emission signal with the measurement signals from the additional sensors. Furthermore, such a calculation model can be adaptively adjusted during operation of the emission control system.

[0030] In addition, comparative data can be determined for the emissions signal and at least some process parameters that describe the process state using calculation models, for example, also through a prediction method using a regression model. This can improve the reliability of the output emissions status and the exhaust gas purification system as a whole, because the comparative data enables early detection of malfunctions.

[0031] According to another embodiment, the electronic processing unit can determine the number of valid process parameters that can be determined based on the measurement signals from the additional sensors and thus describe the process state. An anomaly in the process state can only be determined by the electronic processing unit if the number of valid process parameters is greater than a predetermined value. Otherwise, the electronic processing unit outputs a specific error message. The number of valid process parameters can be determined, for example, by evaluating the individual signals for each of the additional sensors, for example, by comparing them with respective validity criteria. Thus, in this embodiment, a minimum number of valid process parameters is required to demonstrate a process state without anomalies.The minimum number of valid process parameters can also be a prerequisite for determining the substitute signal for the emissions signal described above. The requirement that a sufficient number of valid process parameters must be determined, in turn, increases the reliability of determining the acceptable emissions level of the exhaust gas purification system.

[0032] Furthermore, the electronic processing unit can suppress the determination and output of the emission status if it determines a non-assessable operating status of the exhaust gas purification system based on at least one of the measurement signals from the additional sensors. In this case, a specific error message can be output for the non-assessable operating status. The non-assessable operating status can, for example, include a status with the scrubber of a ship's exhaust gas purification system switched off and / or with the ship's engine switched off. Furthermore, the non-assessable operating status can include an operating transition, for example a restart of a previously switched off scrubber. By detecting the non-assessable operating status based on the measurement signal from one of the additional sensors, it is possible to prevent an incorrect emission status from being output for the emission source.

[0033] According to another embodiment, the system comprises a further emission sensor that detects a further emission signal, which, like the aforementioned original emission signal, is evaluated with regard to the anomaly by means of the electronic processing unit. In this embodiment, the signals of at least two emission sensors are therefore taken into account, wherein the evaluation with regard to the anomaly of the respective emission signal can be carried out iteratively. By taking the further emission signal into account, the reliability of the acceptable emission state of the exhaust gas purification system, which is output by the method, is further increased. The compliant emission state of the exhaust gas purification system is determined and output in this embodiment when there is no anomaly in the emission signals or (iethen) if an anomaly of at least one of the emission signals is present, while at the same time no anomaly of the process state is detected or the anomaly of the emission signals satisfies a respective exception condition.

[0034] The electronic processing unit may further be configured to carry out the above-described prediction method for a substitute signal of the emission signal and / or for comparison data, for example using a machine learning algorithm that may be implemented by means of a regression model.

[0035] Furthermore, the invention relates to a method for monitoring an exhaust gas purification system that is functionally connected to an emission source, which is in particular a ship's engine. According to the method, an emission signal is first detected by an emission sensor, which indicates emissions from the emission source as they exit the exhaust gas purification system. In addition, measurement signals related to the exhaust gas purification system are detected by several additional sensors. Based on the measurement signals from the additional sensors, a process status of the exhaust gas purification system is determined.

[0036] The emission signal and the process state are then each evaluated for an anomaly. A compliant emission state of the exhaust gas purification system is determined and output either when there is no anomaly in the emission signal, or when there is an anomaly in the emission signal, but at the same time either no anomaly in the process state is detected or the anomaly in the emission signal satisfies an exception condition.

[0037] The system described above therefore comprises the emission sensor, the plurality of additional sensors, and the electronic processing unit, which together carry out the steps of the method. The above statements regarding the system according to the invention therefore also apply to the method according to the invention, particularly with regard to the disclosure, the advantages, and the preferred embodiments.

[0038] The invention is described below by way of example using an advantageous embodiment with reference to the accompanying figures. They show, schematically: Fig. 1 shows an exhaust gas cleaning system of a ship and Fig. 2 shows a flow diagram of a method for monitoring the emission status of the exhaust gas cleaning system of Fig. 1 .

[0039] Fig. 1 shows a schematic representation of an exhaust gas purification system 10 of a ship. The exhaust gas purification system 10 comprises a system according to the invention, which is used to carry out a method 100 (cf. Fig. 2 ) is provided for monitoring the emission status of the exhaust gas purification system 10.

[0040] The exhaust gas purification system 10 has a scrubber 11 that receives untreated exhaust gas 13 emitted by a ship's engine (not shown). The untreated exhaust gas 13 is cleaned in the scrubber 11 and then discharged into the atmosphere as cleaned exhaust gas 15 from the scrubber 11. To clean the untreated exhaust gas 13, seawater 16 is fed into the scrubber 11. With the help of the seawater 16, certain components of the untreated exhaust gas 13, such as sulfur, are washed out of the untreated exhaust gas 13.

[0041] The exhaust gas purification system 10 further comprises an emissions sensor, which is designed as an exhaust gas sensor 17 and monitors the composition of the purified exhaust gas 15. This particularly relates to the sulfur content of the purified exhaust gas 15. Furthermore, the exhaust gas purification system 10 comprises an electronic processing unit 19, a water treatment device 21, and further sensors 23, 24. Sensors 23 are in direct contact with the exhaust gas purification system 10, while sensors 24 are provided for detecting measurement signals that directly or indirectly influence the exhaust gas purification system 10.

[0042] Specifically, the sensors 24 are designed to measure the engine power and other parameters of the ship's engine (not shown). Additionally, the sensors 24 include sensors that indicate the ship's speed and acceleration, as well as other operating variables. The speed of the ship's engine and the ship's acceleration, for example, are indirect indicators of the amount of untreated exhaust gas 13 captured by the scrubber 11.

[0043] The water treatment device 21 receives the wash water that is previously passed through the scrubber 11. The water treatment device 21 is connected to a sludge tank 25 that receives substances that are filtered out by the water treatment device 21 from the wash water that the water treatment device 21 receives from the scrubber 11. Further details of such a water treatment device 21 used in an exhaust gas purification system 10 for ships are known in the art and will not be described further below.

[0044] The emission or exhaust gas sensor 17 and the additional sensors 23, 24 are communicatively coupled to the electronic processing unit 19. The electronic processing unit 19 thus receives an emission signal from the emission or exhaust gas sensor 17 and measurement signals from the additional sensors 23, 24. The sensors 23, which are in direct contact with the exhaust gas purification system 10, measure operating parameters of the scrubber 11, such as its temperature and / or internal pressure, and operating parameters of the water treatment device 21, such as its temperature, water flow rate, etc.

[0045] In addition, further sensors 23 are provided to detect the condition of the wash water after it exits the water treatment device 21 and is ultimately returned to the seawater 16. The condition of the wash water can be detected, for example, by its turbidity and / or its acidity or pH value, so that a corresponding measurement signal can be derived based on this condition.

[0046] The exhaust gas purification system 10 optionally has a return line 27 for purified wash water, which is returned from the water treatment device 21 to the scrubber 11. In this case, the exhaust gas purification system 10 has a closed circuit for the wash water ("closed-loop scrubber"). Alternatively, the exhaust gas purification system 10 does not have the return line 27 for the wash water ("open-loop scrubber").

[0047] As an alternative to the scrubber 11, which uses seawater 16 or wash water, the exhaust gas purification system 10 can comprise a dry scrubber or a Denox scrubber. The dry scrubber uses lime granules instead of the wash water, while the term "Denox" refers to the removal of nitrogen oxides (NO x ) from the exhaust gas 13 of the ship's engine. The removal of nitrogen oxides in such a Denox scrubber can be achieved in a similar way to the removal of exhaust gases from motor vehicles that use a catalytic converter.

[0048] With the help of the scrubber 11, several different substances can usually be removed from the exhaust gas 13 of the ship's engine. For example, the scrubber 11 of Fig. 1, which uses seawater 16, and dry scrubbers are primarily intended for removing sulfur, but they are also suitable for removing soot and nitrogen oxides. Conversely, depending on the design, a Denox scrubber can remove other substances from the exhaust gas in addition to nitrogen oxides, such as sulfur and soot.

[0049] In the case of dry and denox scrubbers, the additional sensors 23 can also be connected directly to the respective scrubber in order to detect operating parameters of the scrubber, such as its temperature and / or internal pressure and / or a state of a respective medium for cleaning the exhaust gas 13.

[0050] During operation, ships must be able to demonstrate compliance with the required emission limits. This is particularly problematic or even impossible with existing exhaust gas cleaning systems if a failure or anomaly of an emission sensor, such as the exhaust gas sensor 17 of Fig. 1In such a case, manual documentation of emissions and subsequent evaluation by a specialist are often required. However, this is often associated with increased costs or is not feasible, so a ship's voyage must be interrupted and the ship must dock at the nearest port to make appropriate repairs to the exhaust gas purification system.

[0051] To overcome such difficulties, the system according to the invention and the method according to the invention are provided, which, in addition to the emission signal of the exhaust gas sensor 17, use the signals of the further sensors 23, 24 to describe an overall process state of the exhaust gas purification system 10 and to be able to demonstrate that the exhaust gas purification system 10 operates correctly even in the event of a failure or an anomaly of the exhaust gas sensor 17 and emits emissions in the form of the purified exhaust gas 15 which complies with the required limit values.

[0052] Fig. 2shows schematically a method 100 for operating the Fig. 1 illustrated exhaust gas purification system 10. In step 110, an emission signal from the emission or exhaust gas sensor 17 is detected, while in step 120, measurement signals from the additional sensors 23, 24 are detected. The emission signal indicates the concentration of emissions exiting the exhaust gas purification system 10, i.e., the emission content of the purified exhaust gas 15, while the measurement signals from the additional sensors 23, 24 are directly or indirectly related to the exhaust gas purification system 10, as explained above. The emissions are indicated, for example, as SO 2 concentration and / or CO 2 concentration in the exhaust gas in ppm or vol.%.

[0053] In step 130, the emission signal and the signals from the additional sensors are evaluated. Specifically, signals from sensors 17, 23, 24 are compared with respective validity criteria. Furthermore, the measurement signals from the additional sensors represent process parameters, or they enable the determination of additional process parameters of the exhaust gas purification system 10 in order to describe an overall process state of the exhaust gas purification system 10. For example, information about the power of the ship's engine and the acceleration of the ship can be used to estimate the quantity of untreated exhaust gas 13 that is absorbed by the scrubber 11 using a model. Furthermore, in step 130, it is determined whether an anomaly in the emission signal and / or the process state exists in order to be able to execute the subsequent steps 140 to 180, in which decisions about the operation of the exhaust gas purification system 10 are made.Steps 140 to 180 ultimately lead either to an output of a compliant emission status at 200, which indicates the correct functionality of the emission control system 10 within legally prescribed limits, or to a specific error message at 210.

[0054] At 140, the process parameters based on the measurement signals from the additional sensors 23, 24 are used to determine whether a non-assessable operating state of the exhaust gas purification system 10 exists. Such a non-assessable operating state includes, for example, that the scrubber 11 is currently switched off or is in an operating transition with a restart. If a non-assessable operating state exists, a corresponding error message is output at 210.

[0055] However, if an operating condition exists at 140 that can be evaluated, step 150 determines whether the emission signal from exhaust gas sensor 17 satisfies a predetermined validity criterion. In other words, step 150 checks whether an anomaly in the emission or exhaust gas sensor 17 itself exists. Such an anomaly exists if the emission or exhaust gas sensor 17 has failed or if unexpected drifts or jumps occur in the emission signal.

[0056] If it is determined at 150 that the emissions signal is available and valid, i.e., that there is no emission sensor failure and plausible values ​​for the emissions signal are present, it is determined at 160 whether the emissions signal is above a predefined threshold or limit, which is, for example, prescribed by law. If the quantity of emissions detected by the exhaust gas sensor 17 is below the threshold, it is output at 200 that a compliant emissions state currently exists. If the emissions signal is above the predefined threshold, it is determined at 170 whether a temporary permitted limit has been exceeded.

[0057] A short-term limit violation is permissible, for example, for the emissions signal if the vessel accelerates for a certain period of time, which is associated with increased power of the vessel's engine and thus with an increased quantity of untreated exhaust gas 13. The existence of a short-term, permissible limit violation can therefore be determined, for example, by means of an acceleration sensor belonging to the sensors 24 (see Fig. 1 ). However, the maximum duration of a permitted limit violation is not yet specified in detail by legislators. However, it is expected that such a maximum duration will be in the range of minutes and significantly shorter than an hour. If a short-term permitted limit violation is determined at 170, a compliant emission status is determined at 200.

[0058] However, if either a missing or invalid emission signal is detected at 150, or if it is determined at 170 that there is no brief permissible limit violation, a check is carried out at 180 based on the process parameters or the measurement signals from the additional sensors 23, 24 to determine whether the process is permissible or is working correctly. First, it is determined whether a sufficient number of valid process parameters are available to be able to assess the emission status. In detail, each of the additional sensors 23, 24 is checked for an anomaly, whereby it is determined whether the respective additional sensor 23, 24 has failed, and if this is not the case, whether the measurement signal from the respective additional sensor 23, 24 is plausible. If a sufficient number of valid process parameters can be determined based on the measurement signals from the additional sensors 23, 24, a determination is then made as to whether the measurement signals from the sensors 23, 24 orwhich, based on these determined process parameters, each satisfy predetermined validity criteria that correspond to a compliant emission state. If this is also the case, it is assumed at 170 that the process is operating correctly. A correctly operating process includes, for example, that the pH value of the wash water exiting the water treatment system 21 lies between predetermined limits.

[0059] An emission quantity exiting the exhaust gas purification system 10, including, for example, the sulfur content in the purified exhaust gas 15, can also be estimated based on the process parameters using a model. This estimated emission quantity thus represents a substitute value for the emission signal that is unavailable or unusable due to an anomaly in the emission or exhaust gas sensor 17. If the estimated emission quantity is below the legal limit described above, a compliant emission status is subsequently output at 200. However, if it is determined at 170 that the cleaning process of the scrubber 11 is not working correctly, a specific error message is output at 210.

[0060] As explained above, the specific error message at 210 indicates that either an unassessable operating condition exists or that the cleaning process in scrubber 11 is not working correctly. The specific error message at 210 further includes either an indication of the possible cause of the unassessable operating condition or an indication of which measurement signal from sensors 17, 23, 24 does not meet a corresponding validity criterion. This allows a malfunction of one of sensors 17, 23, 24 to be detected and remedied at an early stage.

[0061] Overall, the evaluation of the emission signal and the signals from the additional sensors 23, 24 at 130 enables the determination in steps 140 to 180 of whether there is an anomaly in the emission signal or emission sensor 17 and / or an anomaly in a process state of the exhaust gas purification system 10 based on the measurement signals from the additional sensors 23, 24. This makes it possible to determine an acceptable emission state of the exhaust gas purification system 10 even if there is an anomaly or failure of the emission or exhaust gas sensor 17. Consequently, the correct operation of the exhaust gas purification system 10 can be verified and documented even in such a case. Thus, the period during which correct functioning of the exhaust gas purification system can be verified can be maximized.

[0062] If the exhaust gas purification system 10 continues to operate correctly despite an anomaly in the emission or exhaust gas sensor 17 and its emission values ​​are below specified limits, the operation of the exhaust gas purification system 10 and thus of the entire ship can be continued without interruption by executing method 100 upon determination of the compliant emission status (see step 200). This allows unwanted interruptions in operation, for example, during a ship's voyage, to be avoided as long as the process status allows the determination of the acceptable emission status based on the measurement signals from the additional sensors 23, 34. List of reference symbols

[0063] 10 Exhaust gas cleaning system 11 Scrubber 13 Untreated exhaust gas 15 Cleaned exhaust gas 16 Seawater 17 Exhaust gas sensor 19 Electronic processing unit 21 Water treatment device 23 Additional exhaust gas cleaning system sensors 24 Additional ship sensors 25 Sludge tank 27 Wash water recirculation 100 Processes 110-210 Process steps

Claims

1. A system for monitoring an exhaust gas purification system (10) which is functionally connected to an emission source, in particular to a ship's engine, wherein the system comprises: an emission sensor (17) which acquires an emission signal, a plurality of further sensors (23, 24) which output respective measurement signals related to the exhaust gas purification system (10), and an electronic processing unit (19) which is configured to determine a process state of the exhaust gas purification system (10) based on the measurement signals of the further sensors (23, 24), characterized in that the emission signal acquired by the emission sensor (17) indicates emissions of the emission source on the exiting from the exhaust gas purification system (10), and the electronic processing unit (19) is further configured to assess the emission signal and the process state in each case with respect to an anomaly in that: the electronic processing unit (19) determines whether the emission signal of the emission sensor (17) fulfills a predetermined validity criterion or a combination of predetermined validity criteria, and the electronic processing unit (19) then, if a sufficient number of valid process parameters can be determined based on the measurement signals of the further sensors (23, 24), further determines whether the process parameters determined based on the respective measurement signals of the sensors (23, 24) each fulfill predetermined validity criteria, and to determine and to output a compliant emission state, which indicates a correct functionality of the exhaust gas purification system (10), when no anomaly of the emission signal is present and when an anomaly of the emission signal is present while at the same time no anomaly of the process state is present or the anomaly of the emission signal satisfies an exception condition.

2. A system according to claim 1, wherein the exception condition comprises that the emission signal deviates for less than a predetermined time period from a normal state which is defined by one or more of the predetermined validity criterions for the emission signal acquired by the emission sensor (17).

3. A system according to claim 1 or 2, wherein the electronic processing unit (19) outputs a specific error message when an anomaly of the process state is present and when the anomaly of the emission signal does not satisfy the exception condition.

4. A system according to any one of the preceding claims, wherein the electronic processing unit (19) calculates a substitute signal for the emission signal based on the measurement signals of the further sensors (23, 24) when an anomaly of the emission signal is present and no anomaly of the process state is present.

5. A system according to claim 4, wherein the electronic processing unit (19) determines the compliant emission state based on the emission signal when no anomaly of the emission signal is present and determines the compliant emission state based on the substitute signal when an anomaly of the emission signal is present and no anomaly of the process state is present.

6. A system according to any one of the preceding claims, wherein the electronic processing unit (19) determines the number of valid process parameters which can be determined based on the measurement signals of the further sensors (23, 24) and only assesses the process state with respect to an anomaly when the number of valid process parameters is greater than a predetermined value, and otherwise outputs a specific error message.

7. A system according to any one of the preceding claims, wherein the electronic processing unit (19) suppresses the determination and the output of the emission state when the electronic processing unit (19) determines a non-assessable operating state of the exhaust gas purification system (10) based on at least one of the measurement signals of the further sensors (23, 24), and outputs a specific error message for the non-assessable operating state.

8. A system according to any one of the preceding claims, that further comprises a further emission sensor (17) which acquires a further emission signal, and wherein the electronic processing unit (19) is further configured: to assess the further emission signal with respect to an anomaly and to then determine and to output a compliant emission state of the exhaust gas purification system (10) when no anomaly of the emission signals is present and when an anomaly of at least one of the emission signals is present while at the same time no anomaly of the process state is determined or the anomaly of the emission signals satisfies a respective exception condition.

9. A method for monitoring an exhaust gas purification system (10) which is functionally connected to an emission source, in particular to a ship's engine, wherein the method comprises that: an emission signal is acquired by means of an emission sensor (17), measurement signals which are each related to the exhaust gas purification system (10) are acquired by a plurality of further sensors (23, 24), a process state of the exhaust gas purification system (10) is determined based on the measurement signals of the further sensors (23, 24), characterized in that the emission signal indicates emissions of the emission source on the exiting from the exhaust gas purification system (10), the emission signal and the process state are assessed with respect to an anomaly in each case in that: it is determined whether the emission signal of the emission sensor (17) fulfills a predetermined validity criterion, and then, if a sufficient number of valid process parameters can be determined based on the measurement signals of the further sensors (23, 24), it is further determined whether the process parameters determined based on the respective measurement signals of the sensors (23, 24) each fulfill predetermined validity criteria, and a compliant emission state which indicates a correct functionality of the exhaust gas purification system (10) is then determined and output when no anomaly of the emission signal is present and when an anomaly of the emission signal is present while at the same time no anomaly of the process state is determined or the anomaly of the emission signal satisfies an exception condition.