DK202000116U3 - EXHAUST GAS CLEANING SYSTEM - Google Patents

Abstract

An exhaust gas purification system (1) is provided for purifying exhaust gas (EG) on board a ship. The exhaust gas cleaning system (1) comprises a scrubber (7) arranged to wash the exhaust gas (EG) with a scrubber fluid (SF) which is circulated through the scrubber (7) and a first heat exchanger (3) arranged in connection with the scrubber (7) for cooling the scrubber fluid (SF) circulating through the scrubber (7). Furthermore, the exhaust gas cleaning system (1) comprises a circulation tank (5) arranged in connection with the scrubber (7) for delivering the scrubber fluid (SF) to the scrubber (7) and for receiving the scrubber fluid (SF) from the scrubber (7), and a cleaning unit (11) arranged in connection with the circulation tank (5) for receiving the scrubbing fluid (SF) from the circulation tank (5) and for dividing it into a first and a second fraction (SF1, SF2), where the second fraction (SF2 ) is more polluted than the first fraction (SF1). The exhaust gas cleaning system (1) is characterized in that it further comprises a heating device (9) arranged in connection with the circulation tank (5) and the cleaning unit (11) for heating the scrubber fluid (SF) after it has left the circulation tank (5). , and before it is received by the cleaning unit (11).

Description

DK 202000116 U3

EXHAUST GAS CLEANING SYSTEM Technical field The invention relates to an exhaust gas cleaning system for cleaning exhaust gas on board a ship, e.g. from a maritime engine, burner or boiler. > Background of production Large ships are typically powered by engines running on sulfur-containing fuel. During the combustion of such fuel, exhaust gases containing sulfur oxides (SOx) are formed. The exhaust gas typically also contains particulate matter such as soot, oil and heavy metals as well as nitrogen oxides (NOx). To reduce the impact of the exhaust gas on the environment, the exhaust gas should be purified before being released into the atmosphere. The exhaust gas can e.g. passed through a scrubber to be washed with a scrubber fluid, whereby pollutants in the exhaust gas are trapped in the scrubber fluid. The scrubber can be a scrubber with a so-called open veil, and the scrubber fluid can be seawater, where the natural alkalinity of the seawater is used to leach the sulfur oxides from the exhaust gas. Seawater is then passed from the sea through the scrubber to absorb SOx and particulate matter from the exhaust gas before being discharged directly back into the sea. Alternatively, the scrubber may be a so-called closed loop scrubber which - uses circulating fresh water or seawater in combination with an alkaline agent such as sodium hydroxide (NaOH) or sodium carbonate (Na> COs) as scrubbing fluid to leach sulfur oxides and particulate matter from the exhaust gas. In such a scrubber, the amounts of aqueous sulfite, sulfate salts and particulate matter in the circulating fresh water or seawater will be gradually increased. Thus, in order to control the quality of the circulating fresh water or seawater, a small amount thereof can be periodically or continuously replaced with clean fresh water or seawater and either stored on the ship or discharged overboard after purification from the particulate matter. When the hot exhaust gas comes in contact with the scrubber fluid inside the scrubber, it cools and large amounts of water contained in the scrubber fluid evaporate. This evaporated water leaves the scrubber together with the exhaust gas and can create an unwanted visible cloud when it comes in contact with ambient air conditions. According to a known solution to this problem, the exhaust gas containing the evaporated water is heated before being released from the ship.

DK 202000116 U3 2 so that the cloud becomes less visible. However, the equipment used for this purpose is large and expensive. It also consumes a lot of energy, which from an environmental point of view is negative. Summary The object of the present invention is to provide an exhaust gas purification system for purifying exhaust gas on board a ship which at least partially solves the above-mentioned problem. The basic idea behind the production is to cool the exhaust gas more inside the scrubber to reduce the amount of evaporated water leaving the scrubber along with the exhaust gas. The exhaust gas system according to the invention is defined in the attached utility model requirements and explained below.

An exhaust gas purification system according to the present invention is adapted to purge exhaust gas on board a ship.

The exhaust gas cleaning system comprises a scrubber which is arranged to wash the exhaust gas with a scrubber fluid which is circulated through the scrubber. The exhaust gas purification system further comprises a first heat exchanger, a circulation tank and a purification unit. The first heat exchanger is arranged in connection with the scrubber for cooling the scrubber fluid which is circulated through the scrubber.

- The circulation tank is arranged in connection with the scrubber for supplying the scrubber fluid to the scrubber and for receiving the scrubber fluid from the scrubber. The cleaning unit is arranged in connection with the circulation tank for receiving the scrubber fluid from the circulation tank and for dividing it into a first and a second fraction, where the second fraction is more contaminated, i.e. contains more particulate matter than the first fraction. The exhaust gas purification system is characterized in that it further comprises a heating device. The heating device is arranged in connection with the circulation tank and the cleaning unit for heating the scrubber fluid after it has left the circulation tank and before it is received by the cleaning unit.

The exhaust gas purification system may be provided for purifying exhaust gas from a maritime engine on board a ship, a maritime burner on board a ship or a maritime boiler on board a ship. It should be emphasized that "connected" and "connection" throughout the text mean respectively. "to connect directly or indirectly" and "direct or indirect connection". Similarly, "reception", "supply", etc. throughout the text means resp. "To - receive directly or indirectly and" to supply directly or indirectly ".

DK 202000116 U3 3 Since the scrubber fluid is circulated through the scrubber via the circulation tank in the exhaust gas cleaning system according to the invention, the scrubber is a scrubber with a so-called closed loop. As previously mentioned, a closed loop scrubber is typically operated with a scrubber fluid of fresh water and / or seawater mixed with a suitable alkaline agent.

The cleaning unit may be arranged to receive a constant or an intermittent flow of scrubber fluid from the circulation tank, and the flow may vary over time.

The cleaning unit may comprise one or more separators and / or filters, for example a centrifugal separator such as a high speed separator and / or a decanter and / or a membrane filter.

As mentioned above, the cooling of the exhaust gas in an exhaust gas purification system according to the present invention is increased so that the amount of water of the scrubber fluid evaporated inside the scrubber is reduced.

Such increased cooling of the exhaust gas is achieved by increased cooling of the scrubber fluid circulating through the scrubber by means of the first heat exchanger. Typically, exhaust gas containing more water vapor will, of course, depending on the prevailing ambient air conditions, cause a more visible cloud as it leaves the ship than exhaust gas containing less water vapor. By reducing the amount of water that evaporates inside the scrubber, the amount of water vapor leaving the ship with the exhaust gas will be reduced, which may result in a less visible cloud from the ship.

As described initially for a closed loop scrubber, scrubber fluid replacement may be necessary to control the quality of the circulating scrubber fluid. The scrubber fluid to be replaced can be purified of particulate matter and then discharged into the sea or to a storage tank depending on the prevailing conditions. In order to be discharged, the scrubber fluid must meet certain criteria; do not have a too low pH value and / or a too high turbidity value. Depending on the alkaline agent contained in the scrubber fluid, a lowered temperature of the scrubber fluid may result in a reduced solubility of the alkaline agent and consequently removal of undissolved alkaline agent together with the particulate matter during the treatment of the scrubber fluid in the cleaning unit. This is, of course, a waste of unused chemicals. In addition, the alkaline agent, when again dependent on which alkaline agent is contained in the scrubber fluid, can impart a high turbidity value to the scrubber fluid which can prevent discharge of scrubber fluid.

DK 202000116 U3 4 In that the exhaust gas cleaning system according to the invention comprises a heating device for heating the scrubber fluid after it has left the circulation tank and before it is received by the cleaning unit, the scrubber fluid to be replaced can be heated before it is treated by the cleaning unit. Heating the scrubber fluid can improve the solubility of the alkaline agent, which can prevent the alkaline agent from ending up in the more contaminated second fraction and being spilled. Additionally / alternatively, heating the scrubber fluid may lower its turbidity value, which may allow discharge of the cleaner first fraction of the scrubber fluid.

The exhaust gas purification system may further comprise means for supplying an alkaline agent to the scrubber fluid. Thereby, alkaline agent can be refilled when this is expedient, so that the efficiency of the exhaust gas cleaning system is optimized. The means for supplying an alkaline agent to the scrubber fluid can e.g. placed upstream of the circulation tank and downstream of the scrubber, ie. the refilling of alkaline agent can be done.

The alkaline agent may comprise various chemicals, e.g. magnesium oxide or magnesium carbonate. According to one embodiment of the invention, the alkaline agent comprises magnesium hydroxide, which has the advantage that the degree of crystallization of the sulphate salts formed in the scrubber fluid is relatively low, even at a low temperature of the scrubber fluid.

The means for supplying an alkaline agent to the scrubber fluid may comprise a source of the alkaline agent and a pump for pumping the alkaline agent from the source of the scrubber fluid. The source of the alkaline agent may simply be a container containing the alkaline agent. The pump can be a screw pump which can reduce erosion from any abrasive alkaline agent. In addition, a screw pump is relatively only slightly exposed to clogging.

The exhaust gas purification system may further comprise a measuring device which is arranged to measure a value of a characteristic property of the scrubber fluid, which value may be lower, equal to or higher than a predetermined value. The handling of the scrubber fluid may depend on an output from the measuring device.

The measuring device may be arranged in connection with the heating device and the cleaning unit for measuring the value of the characteristic property of the scrubber fluid, after it has been heated by the heating device and before it is received by the cleaning unit. The handling of the cleaner first fraction of the scrubber fluid may depend on an output from the measuring device.

DK 202000116 U3 The measuring device may comprise a mass flow meter, and the characteristic feature may be a density of the scrubber fluid. The density of the scrubber fluid depends on the salinity of the scrubber fluid.

The mass flow meter can be of any type. According to an embodiment of the present invention, the mass flow meter is a Coriolis mass flow meter, which has the advantage of being an inline mass flow meter.

Alternatively or additionally, the measuring device may comprise a conductivity sensor, and the characteristic feature may be a conductivity of the scrubber fluid. The conductivity of the scrubber fluid depends on the salt content of the scrubber fluid.

The cleaning unit can be connected to the circulation tank for supplying at least something, ie. part of, the first fraction of the scrubber fluid for the circulation tank, if the value of the characteristic is below the predetermined value. If the value is relatively low, then the salinity of the scrubber fluid may be relatively low, and - discharge of the cleaner first fraction of the scrubber fluid may be unnecessary for proper operation of the exhaust gas purification system. The cleaning unit may be arranged to deliver a constant or an intermittent flow of scrubber fluid to the circulation tank, and the flow may vary over time.

The exhaust gas purification system may further comprise a water analysis unit which is arranged to determine a number = 1 of parameter values of the first fraction of the scrubber fluid. The handling of the cleaner first fraction of the scrubber fluid may depend on an output from the water analysis unit. The parameter values determined by the water analysis unit can e.g. be the turbidity, pH and PAH concentration of the first fraction of the scrubber fluid.

The cleaning unit can be in connection with the circulation tank for dispensing at least something, ie. a part of, the first fraction of the scrubber fluid for the circulation tank, if at least one of the parameter values exceeds or is equal to a respective limit value. Thereby, a discharge of the first fraction of the scrubber fluid can be prevented if certain criteria are not met, i.e. if the first fraction is not - err enough, which is an advantage from an environmental point of view. The cleaning unit may be arranged to deliver a constant or an intermittent flow of scrubber fluid to the circulation tank, and the flow may vary over time.

The cleaning unit can thereby be arranged to deliver at least some of the first fraction of the scrubber fluid to the circulation tank, if the value of the characteristic

DK 202000116 U3 6 property is below the predetermined value, and / or at least one of the parameter values exceeds or is equal to a respective limit value.

As mentioned above, the exhaust gas purification system may further comprise a water analysis unit which is arranged to determine a number> 1 of parameter values of the first fraction of the scrubber fluid. In addition, the exhaust gas purification system may be arranged to emit at least some of, i.e. a part of, the first fraction of the scrubber fluid, if each of the parameter values is below a respective limit value, and / or the value of the characteristic is above or equal to the predetermined value. The first fraction of the scrubber fluid can e.g. discharged overboard or to a temporary storage tank for later discharge overboard. Discharged fluid can be replaced with fresh scrubber fluid. Thereby, a salt concentration of the scrubber fluid circulating through the scrubber can be kept sufficiently low for proper operation of the exhaust gas purification system.

The heating device for heating the scrubber fluid before it is received by the cleaning unit may comprise another heat exchanger.

The first and second heat exchangers can be of any type such as e.g. plate heat exchangers or pipe & jacket heat exchangers. The first and second heat exchangers can also be of the same type or of different types.

However, other objects, features, aspects and advantages of the invention will become apparent from the following detailed description as well as from the drawings. Brief Description of the Drawing The invention will now be described in more detail with reference to the accompanying schematic drawing, in which fig. 1 is a block diagram schematically showing an exhaust gas purification system according to the invention. Detailed description FIG. 1 shows an exhaust gas cleaning system 1, which comprises a first - plate heat exchanger 3, a circulation tank 5, a scrubber 7, a heating device 9 in the form of a second plate heat exchanger 9 ', a cleaning unit 11, a water analysis unit 13, a measuring device 15 in the form of a Coriolis mass flow meter 15 'and means 17 for supplying an alkaline agent, here magnesium hydroxide. On the other hand, the means 17 for supplying an alkaline agent comprise a source 19 of, in particular a container containing alkaline agent, here magnesium hydroxide, and a screw pump 21.

DK 202000116 U3 7 Exhaust gas cleaning system 1 is designed to clean exhaust gas EG from a maritime diesel engine 23 on board a ship (not shown).

Inside the scrubber 7, which operates in a conventional manner not further described herein, the exhaust gas EG is washed with a scrubber fluid SF in the form of fresh water mixed with magnesium hydroxide. | accordingly, the scrubber 7 comprises an exhaust gas inlet 25 for receiving the exhaust gas EG from the engine 23 and an exhaust gas outlet 27 for releasing washed exhaust gas EGW. The scrubber fluid SF is supplied from the circulation tank 5 to the scrubber 7 through the scrubber 7 for absorption of pollutants from the exhaust gas EG to purify it, back to the circulation tank 5 and then again to the scrubber 7, etc.

The exhaust gas EG emitted from the engine 23 is very hot, and in order to maintain a suitable temperature of the scrubber fluid SF it is cooled by means of seawater in the first plate heat exchanger 3, which is arranged upstream of the scrubber 7 and - downstream of the circulation tank 5, i.e. . on its way from the circulation tank 5 to the scrubber 7. Due to the high temperature of the exhaust gas EG, water contained in the scrubber fluid SF evaporates when the scrubber fluid comes into contact with the exhaust gas EG inside the scrubber 7. The water vapor formed leaves the scrubber 7 and is discharged from the ship through a chimney together with the purified - exhaust gas EGW. To reduce the visible cloud formed as a result of this moist purified exhaust gas when it is discharged into the atmosphere, the scrubber fluid SF, which is recycled through the scrubber 7, is cooled more than is conventional by means of the first plate heat exchanger 3. Therefore less water evaporates inside the scrubber, which results in less humid purified exhaust gas - and consequently a less visible cloud.

As the scrubber fluid SF is recycled through the scrubber 7, it becomes more and more contaminated. To ensure efficient operation of the scrubber 7, the scrubber fluid must not become too contaminated. Accordingly, some of the scrubber fluid SF is continuously pumped from the circulation tank 5 to the water purification unit 11 to be purified. The cleaning unit 11 is a high speed separator which is arranged to divide the contaminated scrubber fluid into a cleaner first cleaning fraction SF1 and a more contaminated second fraction SF2. The second fraction SF2 is fed to a sludge tank 29 for later disposal. To ensure a sufficient amount of scrubber fluid in the circulation tank 5, it is refilled with scrubber fluid to replace the scrubber fluid pumped away. This refilling may include the addition of clean fresh water outside

DK 202000116 U3 8 Exhaust gas cleaning system 1. | In this case, in order to maintain characteristic properties of the scrubber fluid, which is suitable for proper operation of the exhaust gas system 1, scrubber fluid refilling will typically also include the supply of magnesium hydroxide to the scrubber fluid. Then magnesium hydroxide is pumped from - the source 19 to the scrubber fluid by means of the screw pump 21. The supply of magnesium hydroxide takes place downstream of the scrubber 7 and upstream of the circulation tank

The scrubber fluid refill can alternatively / additionally be “internal”, which means that the cleaner first fraction SF1 of the scrubber fluid SF is led from the cleaning unit 11 back to the circulation tank 5. This will be explained in more detail below.

As previously mentioned, the use of magnesium hydroxide as an alkaline agent makes it possible to cool the scrubber fluid circulating through the scrubber more than is conventional without any problems of crystallization. However, the relatively low solubility of magnesium hydroxide in water can result in scrubber fluid containing undissolved magnesium hydroxide. To prevent such undissolved magnesium hydroxide from being released to the cleaning unit 11 and ending up in the more contaminated second fraction SF2 of the scrubbing fluid SF, thereby being discarded, the scrubbing fluid to be treated by the cleaning unit 11 is heated by means of water from a heat recovery system in the ship, in the second heat exchanger 9 ', which is arranged upstream of the cleaning unit 11 and downstream of the circulation tank 5, i.e. on its way from the circulation tank 5 to the cleaning unit 11. In this heating, undissolved magnesium hydroxide dissolves in the scrubber fluid to instead end up in the cleaner first fraction SF1 of the scrubber fluid SF, where the cleaner first fraction SF1, as previously mentioned, can be returned to the circulation tank 5.

As mentioned above, the more contaminated second fraction SF2 is supplied by the scrubber fluid SF to the sludge tank 29. What happens to the cleaner first fraction SF1 depends on various factors, e.g. the characteristics of the cleaner first fraction SF1. As the scrubber fluid is recycled through the scrubber, the amount of sulfate salts in the scrubber fluid gradually increases. To ensure proper operation of the exhaust gas cleaning system 1, the salt content of the circulating scrubber fluid must not be too high. For this purpose, the density of the scrubber fluid SF to be treated by the cleaning unit 11 is measured by means of the Coriolis mass flow meter 15 ', which is arranged upstream of the cleaning unit 11 and downstream of the second plate heat exchanger 9', i.e. on its way from the second plate heat exchanger 9 'to the cleaning unit 11. If the density is above or equal to a predetermined value, then the salt content in - the scrubber fluid is so high that the cleaner first fraction SF1 of the scrubber fluid should

DK 202000116 U3 9 is drained or discharged from the exhaust gas cleaning system 1 depending on its additional characteristics. However, if the density is lower than the predetermined value, then it is not necessary to drain the first fraction SF1 of the scrubber fluid SF, and the first fraction SF1 is instead returned to - the circulation tank 5 in an "internal" refill of scrubber fluid.

Draining or discharging the first fraction SF1 from the exhaust gas purification system 1 is carried out only if the density of the scrubber fluid is sufficiently high and the first fraction SF1 of the scrubber fluid SF meets certain criteria. The latter is controlled by the water analysis unit 13, which is located downstream of the purification unit 11 and upstream of the circulation tank 5. The water analysis unit 13 is arranged to determine a turbidity value, a pH value and a PAH (polycyclic aromatic hydrocarbons) concentration of the first fraction SF1 of scrub SF. If one or more of the turbidity value, the pH value and the PAH concentration exceeds or is equal to a respective limit value, for example - resp. NTU, 6,5 and 2250 ppb, the first fraction SF1 of the scrubber fluid SF is not drained, and the first fraction SF1 is instead returned to the circulation tank 5 in an “internal” refill of scrubber fluid. However, if the turbidity value, the pH value and the PAH value are all lower than the respective limit values and the density of the scrubber fluid is sufficiently high, the first fraction is drained or discharged from the exhaust gas purification system 1 overboard or to a temporary holding tank (not shown) for later discharge, e.g. if the ship is in an area where discharge is prohibited.

The scrubber fluid circulating through the scrubber is thus cooled more than normal, for example to 6 degrees C, to reduce the visible cloud from the ship chimney. To allow such a low scrubber fluid temperature, without disturbing crystallization, magnesium hydroxide is used as the alkaline agent. To prevent undissolved magnesium hydroxide from ending up in the discarded fraction, ie. the second fraction SF2, from the cleaning unit, heats the scrubber fluid to be treated in the cleaning unit by means of the second plate heat exchanger, for example to 35 degrees C, before returning to the cleaning unit. In addition to dissolving undissolved magnesium hydroxide in the scrubber fluid to be treated by the cleaning unit, the heating of the scrubber fluid reduces the turbidity of the scrubber fluid and thus of the first fraction SF1 of the scrubber fluid, so that a turbidity value low enough to allow it to drain or discharge first fraction of the scrubber fluid in a more convenient way can be obtained.

DK 202000116 U3 10 As previously mentioned, the scrubber fluid circulating through the scrubber can be cooled by means of seawater, and, to enable more cooling than conventional, the seawater must of course be sufficiently cooled. The visibility of the cloud is also, as previously mentioned, dependent on the ambient air conditions, as the cloud is typically more visible, e.g. when the ambient air temperature is low. A low seawater temperature is mainly due to a low ambient air temperature, which means that the above exhaust gas purification system is most effective when it is most required.

The components of the exhaust gas cleaning system described above are - connected via a suitable pipeline system, so that they can be connected to each other in the manner specified above. The exhaust gas system described above may further comprise additional components to ensure that they function properly, such as pumps, valves, sensors, additional water analysis units, control units, coupling modules, etc. As an example, the exhaust gas system may comprise a pH meter or sensor between the scrubber and the circulation tank for measuring the pH of the scrubber fluid. This pH meter may be connected to the supply means 17 for supplying magnesium hydroxide to the scrubber fluid when this is expedient. The feed means 17 can also / alternatively be controlled in response to a sulfur dioxide / carbon dioxide ratio for the purified - exhaust gas.

The above-described embodiment of the present invention should be considered as an example only. One skilled in the art will recognize that the embodiment disclosed may be varied in a number of ways without departing from the concept of generation.

As an example, the exhaust gas purification system can be operated with alkaline agents other than magnesium hydroxide, magnesium oxide. In addition, chemicals other than an alkaline agent can be added to the scrubber fluid for an optimized operation of the exhaust gas purification system such as e.g. a flocculant or a coagulant to improve the efficiency of the cleaning unit 11.

The supply means 17 for supplying magnesium hydroxide to the scrubber fluid need not be located upstream of the circulation tank 5 and downstream of the scrubber 11, but may be located elsewhere, for example be directly connected to the circulation tank 5.

In the embodiment described above, the handling of the first fraction of the scrubber fluid is dependent on the density of the scrubber fluid after heating, and

DK 202000116 U3 11 the turbidity value, the pH value and the PAH concentration of the first fraction of the scrubber fluid. | In alternative embodiments, the handling of the first fraction of the scrubber fluid may depend on only one or two of these parameters, additional parameters and / or other parameters. The scrubber fluid need not comprise fresh water and an alkaline agent, but may instead comprise seawater and an alkaline agent or a combination thereof.

The flow of scrubber fluid from the circulation tank to the cleaning unit does not have to be continuous, but can be periodic and take place at regular intervals, or if it is only expedient.

The first plate heat exchanger 3 does not have to be placed upstream, i.e. in front of the scrubber and downstream, ie. after the circulation tank, but can instead be placed downstream of the scrubber and upstream of the circulation tank.

The heating device 9 does not have to be in the form of another plate heat exchanger 9 °, but can have any shape.

The heating device 9 can e.g. instead / in addition include an electric heater.

the scrubber fluid to be treated by the cleaning unit 11 does not need to be heated by water from a heat recovery system in the ship, but can be heated by hot water or steam from any suitable source.

The measuring device 15 does not have to be in the form of a Coriolis mass flow meter 15 ', but can have any shape. The measuring device 15 can e.g. instead / in addition include a conductivity sensor.

It should be emphasized that a description of details which are not relevant to the present invention has been omitted and that the figures are purely schematic and not drawn to scale.

Claims (15)

DK 202000116 U3 12 Utility model requirements Exhaust gas purification system (1) for purifying exhaust gas (EG) on board a ship, which exhaust gas purification system (1) comprises a scrubber (7) adapted to wash the exhaust gas (EG) with a scrubber fluid (SF) which is circulated through the scrubber (7), a first heat exchanger (3) arranged in connection with the scrubber (7) for cooling the scrubber fluid (SF) circulating through the scrubber (7), a circulation tank (5) arranged in connection with the scrubber (7) for - supplying the scrubber fluid (SF) to the scrubber (7) and for receiving the scrubber fluid (SF) from the scrubber (7), and a cleaning unit (11) which is arranged in connection with the circulation tank (5) for receiving of the scrubber fluid (SF) from the circulation tank (5) and for its division into a first and a second fraction (SF1, SF2), where the second fraction (SF2) is more - polluted than the first fraction (SF1), which exhaust gas purification system (1 ) is characterized in that it further comprises an opv armature device (9) arranged in connection with the circulation tank (5) and the cleaning unit (11) for heating the scrubber fluid (SF) after it has left the circulation tank (5) and before it is received by the cleaning unit (11). Exhaust gas purification system (1) according to claim 1, further comprising means (17) for supplying an alkaline agent to the scrubber fluid (SF). Exhaust gas purification system (1) according to any one of the preceding claims, wherein the alkaline agent comprises magnesium hydroxide. Exhaust gas purification system (1) according to any one of claims 2-3, wherein the means (17) for supplying an alkaline agent to the scrubber fluid (SF) comprises a source (19) of the alkaline agent and a pump (21) for pumping the alkaline agent from the source (19) to the scrubber fluid (SF). Exhaust gas cleaning system (1) according to claim 4, wherein the pump (21) is a screw screw. Exhaust gas cleaning system (1) according to any one of the preceding claims, further comprising a measuring device (15) arranged to measure a value of a characteristic of the scrubber fluid (SF), which value may be lower, equal to or higher than a predetermined value. DK 202000116 U3 13 Exhaust gas cleaning system (1) according to claim 6, wherein the measuring device (15) is arranged in connection with the heating device (9) and the cleaning unit (11) for measuring the value of the characteristic of the scrubber fluid (SF), after it has been heated by the heating device (9) and before it is received by the cleaning unit (11). Exhaust gas cleaning system (1) according to any one of claims 6-7, wherein the measuring device (15) comprises a mass flow meter (15 °), and the characteristic feature is a density of the scrubber fluid (SF). Exhaust gas purification system (1) according to claim 8, wherein the mass flow meter (15) is a Coriolis mass flow meter. Exhaust gas cleaning system (1) according to any one of claims 6-7, wherein the measuring device (15) comprises a conductivity sensor and the characteristic feature is a conductivity of the scrubber fluid (SF). Exhaust gas cleaning system (1) according to any one of claims 6-10, wherein the cleaning unit (11) is in communication with the circulation tank (5) for supplying at least some of the first fraction (SF1) of the scrubber fluid (SF) to the circulation tank (SF). 5), if the value of the characteristic is below the predetermined value. Exhaust gas purification system (1) according to any one of the preceding claims, further comprising a water analysis unit (13) arranged to determine a number = 1 of parameter values of the first fraction (SF1) of the scrubber fluid (SF). Exhaust gas cleaning system (1) according to claim 12, wherein the cleaning unit (11) is in communication with the circulation tank (5) for supplying at least some of the first fraction (SF1) of the scrubber fluid (SF) to the circulation tank (5), if at least one of the parameter values exceed or are equal to a respective limit value. Exhaust gas purification system (1) according to any one of claims 6-11, further comprising a water analysis unit (13) arranged to determine a number> 1 of parameter values of the first fraction (SF1) of the scrubber fluid (SF), wherein the exhaust gas purification system (1) is arranged to discharge at least some of the first - fraction (SF1) of the scrubber fluid (SF), if each of the parameter values is below a respective limit value, and / or the value of the characteristic is above or equal to the predetermined value. Exhaust gas cleaning system (1) according to any one of the preceding claims, wherein the heating device (9) comprises a second heat exchanger (9 °).