SE1500177A1 - Ways to clean exhaust gas from diesel engines from soot, sulfur and nitrogen oxides - Google Patents

Abstract

Summary. A s.k. KEBI scrubbers, equipped with valve cassettes, have in pilot experiments proved suitable as a hand in glove to clean marine diesel engines' exhaust gases from sulfur oxides, because the back pressure is low and easily keeps the overhead engine's entire speed and power register, because these engines are particularly sensitive to high back pressures. The test, which was performed with fuel with increased sulfur content, confirmed a 100% efficient sulfur purification and that the exhaust gases can be carried directly into the scrubber, driven with a washing liquid / gas ratio from 1/1 to 6/1, without clogging problems arising due to soot in the exhaust gases . Therefore, the prior separation of soot particles in e.g. a venturi step, which provides a cost-effective scrubber solution. Additional cost advantages are obtained by the KEBI scrubber operating at high sodium sulphite contents, up to at least 200 g / l, whereby less chemicals and fresh water are consumed, while at the same time reducing space for holding tanks.

Description

15 20 25 30 35 40 contact between the gas and the liquid. The filling bodies used to increase the contact surface can be so-called Rasching rings or Berlsadlar etc. Important properties for these are that they have a large surface area per unit volume and allow passage of the gas and that they must be chemically and mechanically durable.

However, the construction is sensitive to clogging of particles in the gas, especially as diesel engine soot is both sticky and sharp. The dynamics of this construction are also limited.

Instead of filling bodies, so-called bottoms can be used. These are very similar to the columns used in ordinary absorption and distillation and which can be, for example, bell bottom / valve bottom columns or screen bottom columns, where the contact surface between the gas and the liquid is made as large as possible. Bottom columns usually have a wider operating range (L / G) than filler body columns, while valve bottoms have the widest.

A k / ock bottom is a common bottom both in terms of distillation and absorption. The principle is to fill each bottom with as many bell-like valves as possible. When the bells are closed, washing liquid collects on the bottom and when the gas presses from below, the bells open, which gives the dynamics. The problem with this technology is that the scrubber becomes large if enough bells are to fit, as well as its "dead areas" when using overflows, which are areas on the bottoms where the gas and liquid can not come into contact with each other. Bell bottoms are sensitive to soot, which slowly but surely causes the bell valves to harden.

The principle for strainer bottoms is that the washing liquid wets the surfaces of the strainer, at the same time as the gas travels upwards through the heel. To make the arrangement insensitive to gas flow increases and thus pressure drop increases, new variants have seen the light of day, where gas and liquid take different paths for different flows, which, however, only gives a marginal improvement. In summary, screen bottoms do not suit the sensitivity of diesel engines to back pressure, because an optimal mixture of the gas and the liquid requires that the holes / meshes in the bottoms be made as small as possible. When you reduce the size of the holes, the pressure drop across the bottom will increase, so you have to compromise between the pressure drop and the contact surface.

Small holes also cause sensitivity to the soot's clogging ability.

As indicated above, the soot in the exhaust gases is an overriding problem in constructing a functional sulfur scrubber for diesel engines. To get around the soot problem, the flue gases can be purified from soot particles before they are led into the scrubber. The state of the art here is to introduce a so-called venturi stage before the scrubber, Fig. 1. As the name suggests, it is a choke, where liquid in droplet form and gas meet and the probability of the soot particles being trapped by the droplets is high. Such a venturi stage is used primarily for dust / soot separation in a preliminary stage and is supplemented with spray nozzles or filler bodies in stage 2 in the scrubber itself, where the main sulfur reduction takes place with alkali.

Venturin operates at a high gas speed between 30-120 m / s and a water pump pressure to the nozzles of between 25-60 bar. The contact time is short and a high pressure drop results in high energy consumption. The liquid / gas mass flow ratio is limited and rapid variations in gas flows must be limited, although the throttling area of the venturi can be regulated. It should be pointed out here that venturin entails a significant additional cost in space and apparatus costs in the form of pumps, pipes and control equipment, as well as an increased operating cost for operating the liquid and gas flows.

The present invention can solve the above-mentioned problems of exhaust gas purification of diesel engines by having the features set forth in the independent claims.

Many unexpected groundbreaking inventions have a "good story" to tell, so does the present invention. One of the inventors had pioneered soot treatment, using cyclone filters, on large diesel engines for electricity generation in the Middle East and also had a background in separating sludge from liquids. The other inventors in Sweden had done pioneering work in supplying the paper and cellulose industry with special scrubbers for purifying the flue gases of ovens and boilers. One day the parties crossed paths and one gave the other and they realized that the special scrubbers could be adapted to solve the problems of cleaning the exhaust gases, among other things. from ship-based diesel engines, which would become mandatory from 2015.

Detailed description A scrubber can be fixed for a certain process with constant parameters, such as gas flow and pressure drop, and is therefore called a static scrubber.

Scrubbers that can handle a varying gas flow without creating problems in the process are called dynamic. Diesel engines typically run at varying speeds and loads, and the flow of exhaust gases from such an engine therefore varies over time. Diesel engines are also sensitive to variations in downstream back pressure, which can be caused, for example, by long flue gas ducts, or heat exchangers, which are connected to the diesel engine's exhaust outlet and which complicate the exhaust gas passage and thus create a back pressure. A scrubber with ideal back pressure properties for purifying diesel exhaust gases should therefore have a constant pressure drop independent of the flow. In the case of exhaust gas purification of diesel engines, the requirements for a scrubber are thus at its peak, both in terms of ability to cope with varying gas flow and in terms of creating low back pressure.

This document describes embodiments of a scrubber for purifying exhaust gases from one or more diesel engines. Embodiments of the described scrubber meet the requirements for handling a varying gas flow and keeping the back pressure within a permissible range. Embodiments of the described scrubber are also able to purify the exhaust gases without first purifying them from soot, which is a great advantage.

The inventors have realized that a so-called KEBI scrubbers can be adapted to meet the requirements of a scrubber for the purification of diesel exhaust gases, and also of soot-laden ones. A basic construction of a KEBI scrubber is described in U.S. Pat. No. 4,557,875, and includes a type of valve cartridge. During the 25 years it has been in existence, the KEBI scrubber has mainly been used in the paper and cellulose industry for its generally good properties, as the requirement for dynamics in these contexts has been extremely limited. Considering this design or parts of it in a process with high demands on dynamics, and also pressure drops, is therefore a novelty in the industry.

The use of a KEBI scrubber for the purification of diesel exhaust gases has several surprising advantages, which will be described in this document.

The term "KEB |", as used herein, is intended to refer to the use of cassettes, which may also be called inserts or frames, provided with valves having certain characteristics. The KEBI scrubber in US 4,557,875 is equipped with a special kind of rocker valves. However, we do not want to limit ourselves to the exact design described therein, but use the term KEBI as including valves of some other nature, which are described later in this document.

Fig. 1 shows a flow chart of a venturi scrubber, representing the state of the art.

Fig 2 Shows a variant of valve, a so-called flap valve with counterweight and its opening angle of a KEBI cassette.

Fig. 3 shows a flow chart in accordance with a marine embodiment of the invention.

The inventors have realized that the KEBI scrubber has the following properties, from use in the paper and cellulose industry; 10 15 20 25 30 35 40 1) Very high separation of sulfur, in principle 100%. 2) Low pressure drop, which can be kept constant. 3) Reliability and simple regulation. 4) Insensitive to dust and particulate matter. 5) Space-saving and energy-efficient.

The inventors have further realized that these properties, or advantages, are extremely important for cost-effective sulfur scrubbing of diesel exhaust gases, especially on board ships. Stricter rules for emissions of sulfur and particles from shipping (Marpol 2015) have increased the need for more efficient treatment of diesel exhaust in marine environments. For diesel engines that work with different speeds and loads, it is important to have a good degree of separation for sulfur and a low pressure drop across the entire engine register, as the engine's performance is negatively affected already at 1000-1500 Pa back pressure. For both land-based and marine diesel engines, purification solutions with low space requirements, operational reliability and low energy consumption are in demand. Low alkali and freshwater consumption is also high on the wish list, properties where KEBI scrubbers excel, to which we will return.

Against this background, a purification solution based on the KEBI scrubber has recently been tested by the inventors on a pilot scale on board a diesel-powered vessel powered by fuel with increased sulfur content. The test confirmed as good sulfur purification as previously shown by the land-based installations in the paper and cellulose industry. The soot particles also did not create clogging problems, which there was previously uncertainty about, as competing scrubber solutions struggle with this. During the marine test of the KEB1 scrubber, it was run, for a certain part of the time, over the sodium sulphite Na2SO3 concentration (approx. 50 g / liter) which was previously considered a maximum limit, and which other scrubber constructions cannot exceed, e.g. due to the washing liquid becoming viscous due to soot and / or crystal formation. In these "out of bounds" tests, it was surprisingly noted that the KEBI scrubber can easily handle 200 g / liter of sulphite, which directly reduces freshwater consumption. In addition, a surprising side effect was obtained when using the high Na 2 SO 3 concentration, namely that the nitric oxide precipitation increased from a modest 8% to a full 25%. In this document, the terms "washing liquid" and "scrubbing liquid" are used as synonyms unless otherwise explicitly stated.

The KEBI scrubber described herein differs from other scrubber constructions in a number of points. Several of these points are presented below along with important benefits. 10 15 20 25 30 35 40 The heart of the KEBI scrubber is its bottom construction with cassettes, consisting of valves of the flap or blade type, which cover the entire surface of the bottom, except on a smaller frame around each cassette. Thus, there are no dead surfaces as when using bell bottoms. To make the handling of the cassettes smooth, they normally have an area around 0.1 m2. The valves can be made of metal, plastic, plastic composite, rubber, or a combination of these or other equivalent materials. The valves can be rigid and shaft bearing of the flap type, or fixed clamped, of the leaf valve type, flexibly bendable in themselves. The lowest pressure drop and best dynamic properties are obtained if the valves do not have a valve seat surface on the sides perpendicular to the shaft / attachment side.

The pressure drop of the KEBI scrubber over the bottoms can be kept almost constant in such a way that the recirculation flow increases if the gas flow decreases or decreases if the gas flow increases, fig.3. An increased recirculation flow leads to more process liquid accumulating over the bottoms and vice versa, a reduced recirculation flow leads to less process liquid accumulating over the bottoms.

During rapid variations in the gas flow, mainly during throttle application, the diesel engine is protected by the cassette valves immediately opening fully, whereby the pressure drop is momentarily reduced. The maximum opening angle of the valves is normally mechanically limited to 8 ° -30 °, depending on the process and choice of closed or open loop.

The KEBI scrubber is self-cleaning from the accumulation of soot and precipitated sodium sulphite crystals, by the valves moving continuously.

Gas velocity up through the scrubber tower can be varied between 0.5 - 4.5 m / s, which is significantly more than any similar construction. This means a significantly wider working area and enables a freer choice of the cross-sectional area of the scrubber tower. The gas velocity is always evenly distributed over the surface of the bottoms, which contributes to all valves moving with the same frequency and amplitude.

By automatically regulating the recirculation flow in relation to the pressure drop across the bottoms, the pressure drop for the scrubber process and the diesel engine's back pressure can be kept constant, independent of the gas flow, by regulating how much process liquid is above the bottoms.

Due to the design of the cassettes on slide rails in the scrubber and with easily demountable doors, the availability is very high, and it is avoided that the scrubber needs to be by-passed during inspections.

At ev. pump interruption for the recirculation flow, the scrubber retains its function for a minimum of 2 hours, so that the pump has time to be replaced. 10 15 20 25 30 35 40 9. The scrubber is usually designed as a square or rectangular, which is an advantage in tight spaces and to get in as many cassettes as possible. 10. The dust separation is significantly higher than in any known scrubber construction, due to the fact that the process liquid that accumulates over each bottom is whipped into a foam due to the movements of the valves, which means that the probability of the soot getting past several bottoms in succession is extremely small. 11. The sulfur separation will also be extra efficient, e.g. thanks to the combined large wet reaction surface of the valves and their possible counterweight surfaces and their movements which lead to gas being dispersed in the process liquid and process liquid being dispersed in the gas. 12. The low pressure drop is a great advantage in connection with the purification of diesel engine exhaust gases, as these engines are sensitive to high back pressures.

Pilot runs on diesel engine exhaust have shown that the optimum pressure drop across each bottom is between 300 and 500 Pa.

The chemical process in a KEBI scrubber works as in any other type of scrubber, but with the difference that installation and operation become more efficient and easier thanks to the differences and advantages related above.

The following describes the purification of diesel exhaust gases with a scrubber according to an exemplary embodiment: The exhaust gases to be purified are led into the lower half of the scrubber tower. They can advantageously first be cooled in a gas / seawater heat exchanger, since the scrubbing process is more efficient at lower temperatures. Thus, no venturi step is required with its control means nor pump system to prevent soot particles from entering the ice scrubber process.

In the scrubber tower, the above-mentioned bottoms with their cassettes and their valves are mounted in at least one level. An extra, empty level can be set up to have in reserve if, for example, the purification requirements were to be raised in the future. If the KEBI scrubber is set up for closed loop, fresh water is mixed with sodium hydroxide NaOH in a recirculation tank and this mixture is then pumped up the top of the tower to the top bottom, where the liquid is evenly distributed over its cassettes and then leaks down to the next bottom. until the liquid finally ends up in the recirculation tank again. As mentioned above, the pressure drop across the scrubber is kept at least relatively constant, by regulating the recirculation flow. If necessary, the recirculation flow is also cooled.

In the case of purification of diesel exhaust gases, it becomes relevant to recycle washing liquid with a high content of suspended sodium sulphite and soot and it has then been found optimal that the top bottom cassettes are provided with valves with a maximum opening angle, which is greater than the other levels. In this way, the liquid level at this level is reduced and the risk of drops and soot being whipped up against a pre-outlet, drip separator is reduced, and a better pressure drop distribution is obtained over the bottoms, which means greater efficiency and less risk of soot clogging. As the sulfur is scrubbed out of the gas, sodium sulphite Na2SO3 is formed in the scrubber liquid, and as the content increases, a certain part of the scrubber liquid bleeds out to a treatment plant, where the soot is separated into a sludge tank or in the sea. New alkali NaOH and fresh water replace the soaked amount.

If the KEBI scrubber is operated with seawater, the above-described recirculation loop is replaced by a direct supply of seawater at at least two levels in the upper part of the scrubber tower. When the seawater has passed the scrubber, it is led directly back to the lake, over a treatment plant. Before the scrubbed gas leaves the scrubber tower at the top, it passes a "demister" / drip separator, where residual liquid droplets are separated.

Downstream of the drip separator is usually mounted a speed-controlled suction fan, which helps to keep the engine back pressure at a low stable level.

An embodiment of the invention is explained below by means of the flow chart in Fig. 3. The diesel exhaust gases to be purified from sulfur are first cooled in a heat exchanger 1 and then sucked into a scrubber tower 2 through an inlet 3 located in the lower half. The exhaust gases first pass a first bottom 4 consisting of so-called valve cassettes having over them a standing level of process liquid which the gas has to pass after which it then rises to a second identical bottom and finally passes a last bottom 5 and leaves the scrubber tower 2 through a drip separator 6 and further through an outlet 7, connected to a suction fan downstream.

The process liquid leaking downwards in the scrubber tower 2 is collected in a lower reservoir 8 which leads on to a recirculation tank 9 in which new washing liquid is prepared by mixing sodium hydroxide and fresh water. This occurs at the same rate as old washing liquid is soaked to a treatment plant 10a, where the soot sludge is separated out into a holding tank 10b, which is emptied into port after which the effluent consisting of sodium sulphite, which must first be oxygenated to sodium sulphate before being discharged into the sea or sewer .

After a period of scrubbing of the flue gases from a diesel engine, powered by sulfur-containing fuel, the contents of the recirculation tank 9 consist of sodium sulfite and soot particles dissolved in the water. The concentration of soot and sodium sulfite increases all the time, until new washing liquid is mixed and old one is bled out.

A common upper limit is in the range of 45-50 g sodium sulfite / liter of washing liquid.

From the recirculation tank 9, a pump 11 pushes the washing liquid through a cooler 12 up into the upper part 13 of the scrubber tower 2. The pressure drop across the bottoms 4 to 5 is registered by a differential pressure gauge 14, which controls the recirculation flow by means of a control valve 15 and thus regulates the amount of washing liquid. each bottom 4 to 5. With this control the pressure drop is kept substantially constant, independent of the size of the exhaust gas flow and thus independent of the speed and load of the diesel engine. For diesel engines that only run at constant speed and load, the control valve 15 can be operated manually to a certain pressure drop across the bottoms, the scrubber only being semi-dynamic. A faster and more accurate control of the pressure drop across the bottoms can be obtained if the pressure drop is also measured over individual bottoms and the washing liquid is simultaneously flow-regulated to these bottoms individually.

The two heat exchangers 1 and 12 are supplied with cooling water from a seawater pump 16. A KEBI scrubber can also be run in a so-called open saltwater mode, in contrast to the more environmentally friendly closed freshwater mode described above. In the salt water mode, the seawater pump 16 feeds seawater to a maximum of two levels 17 and 18 in the scrubber tower 2, the recirculation loop being deactivated, after which the scrubber water goes directly to the treatment plant 10a, 10b to remove soot sludge and then be deposited in the sea.

What forms the basis of the present invention is that a KEBI scrubber, in pilot runs with scrubbing of the exhaust gases of diesel engines, showed striking and in this context superior properties. A KEBI scrubber has never before been tested for diesel exhaust purification, which will now be a novelty in the industry. Furthermore, it has been shown that the KEBI scrubber is not adversely affected by the sticky and sharp soot that diesel engines produce and that other scrubber constructions have problems with. It has also been found that the KEBI scrubber, by waiting longer to bleed and replacing scrubber liquid in the recirculation tank 9, can handle 4-6 times higher sodium sulfite concentrations than other scrubber types can handle, which saves alkali and fresh water, and reduces the size of the treatment plant 10a , 10b, properties appreciated in marine contexts. The higher sodium sulphite content in the recirculation loop means as an extra bonus that the nitrogen oxide reduction in the scrubber tower 2 increases from the previous maximum of 8% to over 25%.

The bubble and foam process that takes place on top of the KEBI cassettes is an excellent oxygenator if air is supplied to the gas, e.g. under one or more bottoms. In this way, the conversion of sodium sulfite to sodium sulfate is accelerated. 10 15 20 25 30 35 40 10 However, oxygenation must not be driven so far that it affects the sulfur oxide purification.

Thus, in certain embodiments of the KEBI scrubber described herein, the flow of scrubber fluid is controlled so that the back pressure of the KEBI scrubber is kept at least relatively constant and within the predetermined limits of the diesel engine. This ensures that the diesel engine has an adequate back pressure and thus does not have reduced efficiency due to, for example, too high back pressure.

Furthermore, in some embodiments, scrubber liquid with a sodium sulfite content in the range of 50-200 g / l is used, which is significantly higher than usual.

This results in increased purification of nitrogen oxides.

Furthermore, in some embodiments, the valves in the insert or inserts in the top bottom level 5 are set so that they have a maximum opening angle that is greater than the maximum opening angle of the valves in the insert or inserts in the other levels. This means that the level of liquid and foam is lower above this level than above other levels, which can be an advantage, for example, when you do not want to risk the level of foam reaching the drip separator or the outlet from the scrubber. For example, the maximum opening angle of the valves in the insert or inserts in the top bottom level can be adjusted to be about 40% - 60% larger than the opening angle of the valves in the insert or inserts in the other levels.

In some embodiments, the maximum opening angle of the valves is variable and controllable. This can apply to all valves, or to some, eg to the valves in the top bottom level. The valves maximum opening angle can also be controlled separately, eg for different bottom levels. In some embodiments, the maximum opening angle of the valves can be adjusted in the range of 8-30 ° depending on, at the time of construction, the selected physical temperature-dependent maximum gas velocity through the cassettes, where the gas velocity is in the range 0.5-4.5 m / s.

In some embodiments, the maximum opening angle of the valves is adjusted to about 30 ° at a mass flow ratio in the KEBI scrubber between liquid and gas of about 10 (liquid) to 1 (gas).

In some embodiments, a control valve 15 is regulated so that a mass flow ratio in the KEBI scrubber between liquid and gas becomes about 1 to 1, at the highest rated power output of the diesel engine. In some embodiments, the control valve 15 is regulated so that a mass flow ratio in the KEBI scrubber, at closed loop, between liquid and gas becomes about 6 to the idle power of the diesel engine. In some embodiments, air is supplied under at least one bottom so that the sulfur sulfite in the scrubber liquid is oxygenated to sulfur sulfate directly in the purification process. 11

Claims (1)

Method of purifying diesel engine exhaust gases from soot, sulfur and nitrogen oxides, CHARACTERIZED in that the soot-laden exhaust gases are fed to a dynamic or semi-dynamic KEBI scrubber consisting of a scrubber tower (2), provided with at least one bottom level (4), consisting of one or more inserts, on top of which scrubbing liquid is supplied, and where the inserts are provided with one or more valves which open when the gas to be purified presses from below, the gas bubbling up through the scrubbing liquid accumulated on top of the cassettes and purified by contact with it, directly and on the valves' surfaces. The method of claim 1, further comprising that the flow of scrubber fluid is automatically regulated so that the back pressure of the KEBI scrubber is kept constant and within the predetermined limits of the diesel engine. Method according to claim 1 or 2, wherein the scrubber liquid has a sodium sulphite content in the range 50-200 g / l. Method according to one of the preceding claims, wherein the valves in the insert (s) in the uppermost bottom level (5) have a maximum opening angle which is greater than the maximum opening angle of the valves in the insert (s) in the other levels. Method according to one of the preceding claims, where the valves in the insert (s) in the uppermost bottom level (5) have a maximum opening angle that is 40% -60% greater than the opening angle of the valves in the insert / s in the other levels. Method according to one of the preceding claims, where the maximum opening angle of the valves is variable and controllable. Method according to one of the preceding claims, where the maximum opening angle of the valves is adjusted in the interval 8-30 ° depending on, at the time of construction, the selected physical temperature-dependent maximum gas velocity through the cassettes, where the gas velocity is in the range 0.5-4.5 m / s. 12 10 15 20 25 30 35 40 8. 10. 11. 12. 13. 14. 15. A method according to any one of the preceding claims, wherein the maximum opening angle of the valves is adjusted to about 30 ° at a mass flow ratio in the KEBI scrubber between liquid and gas on about 10 (liquid) to 1 (gas). Method according to one of the preceding claims, where a control valve (15) is regulated so that a mass flow ratio in the KEBI scrubber between liquid and gas becomes approximately 1 to 1, at the highest rated rated power of the diesel engine. Method according to one of the preceding claims, where the control valve (15) is regulated so that a mass flow ratio in the KEBI scrubber, at closed loop, between liquid and gas becomes approximately 6 to 1 at the idle power of the diesel engine. Method according to any one of the preceding claims, further comprising that air is supplied / let in under at least one bottom so that the sulfur sulphite in the scrubber liquid is oxygenated to sulfur sulphate directly in the purification process. Use of a dynamic or semi-dynamic KEBI scrubber for purification of soot-laden diesel exhaust gases from soot, sulfur and nitrogen oxides. A dynamic, or semi-dynamic KEB1 scrubber, intended to purify the exhaust gases of diesel engines from soot, sulfur and nitrogen oxides, consisting of a scrubbing tower (2), provided with at least one bottom level (4), consisting of one or more inserts, on top of which scrubbing fluid can are supplied, and where the inserts are provided with one or more valves, which open when the gas to be purified presses from below, whereby the gas can bubble up through the scrubbing liquid accumulated on top of the cassettes and be purified by contact therewith, directly and on the surfaces of the valves. that the scrubber is adapted to purify the soot-laden exhaust gases of diesel engines from soot, sulfur and nitrogen oxides. KEBI scrubber according to one of Claims 13 to 14, in which the valves in the insert (s) in the uppermost bottom level (5) have a maximum opening angle which is greater than the maximum opening angle of the valves in the insert in the other levels. KEBI scrubber according to any one of claims 13-15, wherein the valves in the insert (s) in the uppermost bottom level (5) have a maximum opening angle which is 40-60% larger than the opening angle of the valves in the insert (s) in the other levels. KEBI scrubber according to one of Claims 13 to 16, in which the maximum opening angle of the valves is variable and controllable. KEBI scrubber according to one of Claims 13 to 17, in which the maximum opening angle of the valves can be adjusted in the range from 8 to 30 °, depending on the selected physical temperature-dependent maximum gas velocity through the cassettes at the time of construction, where the gas velocity is in the range 0.5-4.5 m. / s. KEBI scrubber according to one of Claims 13 to 18, arranged so that the maximum opening angle of the valves is adjusted to approx. 30 ° at a mass flow ratio in the KEBI scrubber between liquid and gas of approx. 10 (liquid) to 1 (gas). KEBI scrubber according to one of Claims 13 to 19, arranged so that the recirculation liquid flow into the scrubber is automatically controllable by means of a control valve (15). KEBI scrubber according to one of Claims 13 to 20, arranged so that the control valve (15) is regulated so that a mass flow ratio in the KEBI scrubber between liquid and gas becomes approximately 1 to 1, at the highest rated rated power of the diesel engine. KEBI scrubber according to one of Claims 13 to 21, in which the control valve (15) is regulated so that a mass flow ratio in the KEBI scrubber, at closed loop, between liquid and gas becomes approximately 6 to 1 at the idle power of the diesel engine. 14