A method for utilising a silencer unit and an arrangement for applying the method in a large diesel engine

Abstract: A method for utilising a silencer unit (1) attached to an exhaust tube (2) in a large diesel engine, and an exhaust gas system for applying the method in practice, in which the silencer unit (1) includes a substantially hollow, preferably cylindrical, body member (1a), inside of which a set of sound silencing porous elements can be fitted, said elements including a flow channel (5) for the exhaust gases and being arranged in successive order in the flow direction of the exhaust gases longitudinally of the body member (1a) so that the exhaust gases are let through the flow channel (5) of each element one after the other. The elements are installed inside the body member in the axial direction from one end thereof one at a time and are supported to the inner mantle surface of the body member (1a). In the flow direction upstream of the body member (1a), the exhaust tube (2) is provided with means (10) for feeding a medium containing ammonium, urea or the like reagent applicable for catalytic depuration into the exhaust gases. In addition at least one of the elements in the body member is selected so that, in a cross-sectional plane of the body member, it covers the whole flow area of the exhaust gases and provides an exhaust gases depurating, catalytic reaction especially for decreasing the NOx-content of the exhaust gases.

Description: This invention relates to a method according to the preamble of claim 1 of adapting a silencer unit of a large diesel engine, and an exhaust gas system according to claim 3 for applying the method in practice. Large diesel engines refer here to such engines which may be used, for example, as main or auxiliary engines in ships or in power plants for the production of heat and/or electricity. In diesel engines it is conventional for some kind of a silencer to be connected to an exhaust pipe to reduce the noise caused by the engine. Furthermore, in many countries the environmental standards and laws have become more strict requiring the purification or depuration of exhaust gases. Depending on the fuel used, measures have, in particular, been taken to decrease the contents of nitrogen oxides (NOx-content) of exhaust gases. Perhaps the best solution to the NOx problem is the so called "SCR" (selective catalytic reduction) process, which is based on reducing nitrogen oxides by injecting ammonia upstream of a catalyst. The supplied ammonia may for instance be in liquid form, under pressure without water or under normal atmospheric pressure as a water solution including 25% ammonia. Urea can also be used for the reduction process. A reduction process for reducing the NOx-content of exhaust gases in an internal combustion engine is disclosed in US-A-4,403,473. In practice the noise reduction and purification of exhaust gases are conventionally achieved by leading the exhaust gases successively through a silencer and a separate SCR unit. This requires an expensive and space requiring construction which causes problems especially when a depuration arrangement has to be installed in a narrow space following the silencer in an engine. To some degree it has also been understood to combine the noise reduction and depuration functions. For example, in WO-A-93/24744 two stationary silencer units are built in a uniform housing and a separate element is arranged between them which provides catalytic depuration of the exhaust gases. This solution results in a rather complicated construction which is stationary and so cannot be easily modified to cater for different needs of exhaust gas depuration. US-A-3,556,735 also discloses combined silencing and purifying functions for an internal combustion engine. However, there is no suggestion of converting a silencing system to a system with catalytic depurating properties. An aim of the invention is to provide a novel solution to the noise reduction and purification or depuration of exhaust gases which on the one hand makes it possible to achieve sound silencing and on the other hand allows the depuration process to be modified in a simple way in view of the different depuration requirements of the exhaust gases. In particular it is an aim that the modifying can also be accomplished afterwards in accordance with subsequently appearing needs for the depuration of the exhaust gases. A further aim is to provide a solution providing an uncomplicated construction which is advantageous with regard to costs and space requirements (i.e. apparatus can be made cheaply and as small as possible). According to one aspect of the invention there is provided a method as claimed in the ensuing claim 1 of adapting a silencer unit of a large diesel engine. The invention is based on the comprehension that an SCR element for depurating exhaust gases also has a substantial sound silencing property. Accordingly when depuration is required, conventional sound silencing elements can easily be replaced by exhaust depurating elements without increased need for space or greatly weakened sound silencing. With increased depurating requirements for the exhaust gases several, preferably all, of the original sound silencing elements can be replaced by catalytically depurating elements. According to another aspect of the invention there is provided an exhaust gas system in a large diesel engine, the system being as claimed in the ensuing claim 3. Thus, by providing the body member and the sound silencing elements with a construction and a support in accordance with the invention, the sound silencing elements can be selected according to need in each case. In addition they can easily be mutually changed and replaced. Thus afterwards, in a subsequent installation with increased depurating requirements for the exhaust gases, several, preferably all, of the essentially only sound silencing elements can be replaced by the catalytically depurating elements. The body member may be cylindrical which is of advantage in view of the construction thereof and provides effective treatment of the exhaust gas flow. The sound silencing elements of the system that do not essentially affect depuration of the exhaust gases include a flow channel for the exhaust gases. Further the body member is provided with a flame arrester known as such, located in the flow direction upstream of the elements so that it covers the flow channel. The flame arrester can be implemented in many different ways and it can be arranged also to be a part of the first sound silencing element in the flow direction. The catalytically depurating elements for their part cover in the cross-sectional plane of the body member the whole flow area of the exhaust gases. In addition they are arranged at a small distance from each other. In this case the body member, correspondingly, is provided with a set of apertures passing through the mantle thereof and which are arranged to open between the catalytically depurating elements so that compressed air can be fed through the apertures for accomplishing purification of the elements. Thus soot, dust and other impurities which accumulate on the honeycomb structures of the catalytically depurating elements during operation and which decrease the depurating process when deposited in layers can be removed. Correspondingly it is feasible that some of the apertures are used to suck those impurities removed by the compressed air away from the body member. Embodiments of the invention will now be described, by way of example only, with particular reference to the accompanying drawings, in which:- Figures 1 is a sectional view of a silencer unit according to the invention for attachment to an exhaust tube and having a set of sound silencing elements inside; Figure 2 is a sectional view taken on the line 11-11 of Figure 1; Figure 3 is a sectional view of the silencer unit of Figure 1 but with the sound silencing elements omitted; Figure 4 is a sectional view of the silencer unit of Figure 1 which has been modified for depuration of exhaust gases by replacement of the sound silencing elements by exhaust gas depurating elements and by providing the exhaust tube with feeding means for ammonium or urea; and Figure 5 is a sectional view taken on the line V-V of Figure 4. In the drawings reference numeral 1 indicates a silencer unit attached to an exhaust pipe or tube 2 of a large diesel engine (not shown) and including a hollow body member la and a detachable cover element 1b. The inner surface of the body member la has bar-like guiding and support members 3. The body member la encloses a set of sound silencing elements 4 (see Figure 1) or 7 (see Figures 4 and 5) which are supported against the inner wall or mantle surface of the body member la by making use of the guiding and support members 3. Exhaust gas flow is indicated by arrows in Figures 1 and 4. Within the scope of the exhaust gas system according the invention, the silencer unit 1 can be provided with removable, porous sound silencing elements 4, as shown in Figure 1, including a flow channel 5 for the exhaust gases, which do not substantially affect the depuration of the exhaust gases. Thus, these elements essentially provide a sound silencing solution which is cost advantageous for engine applications but in which depuration of the exhaust gases is not a necessity. In this embodiment, the lower part of a perforated duct associated with, and defining, the flow channel 5 together with the closed end of this duct serve as a flame arresting element for preventing exhaust gases from entering directly into the flow channel 5. The duct can easily be removed at the same time as the sound silencing elements 4 are removed. On removal of the cover 1b, the sound silencing elements 4 can easily be drawn out from the end of the body member 1a, for example for service or for replacement. If, however, there is a need also for depurating the exhaust gases, especially for decreasing the NOx-content of the exhaust gases, the elements 4 can be replaced by exhaust gas depurating elements 7, which are with advantage so-called SCR elements, as illustrated in Figure 4. In this arrangement, in the flow direction upstream of the body member 1a, the exhaust tube 2 is provided with means 10 for feeding into the exhaust gases a medium containing ammonia, urea or the like reducing reagent applicable for catalytic depuration. Hence, the changed need for depuration of the exhaust gases can, in a simple way, be taken account of by re-equipping the silencer unit 1 within the scope of the system according to the invention but without compromising, however, the sound silencing requirements. Feeding of the reagent can in practice take place also from quite a distance, e.g. several meters, from the silencer unit 1. As seen in Figures 3 and 4, a ring element 11 can be arranged in the lower part of the body member 1a to prevent the exhaust gases from entering the empty spaces (cf. Figure 5) between the exhaust gas depurating elements 7 and the body member 1a. At the same time the ring element 11 supports the elements 7 in the axial direction. The exhaust gas depurating elements 7 are arranged so that a small gap 8 is left therebetween. Spacer rings 6 can be used for the purpose of keeping the elements 7 apart from each other. The body member la is provided with a set of apertures 9 penetrating the wall or mantle thereof and arranged to open into the spaces between the spaced apart catalytically depurating elements 7 so that compressed air can be fed therethrough for removing impurities deposited on the elements 7 during operation of the engine. In this case some of the apertures 9, for instance the apertures on the opposite side of the body member 1a, can with advantage be used to remove from the body member 1a, by suction, any impurities removed by the compressed air. It is clear the body member 1a does not have to be cylindrical and other shapes, for instance a body member with a square formed cross section, would do as well depending on the possible practical problems set by the manufacturing technique for the form of the catalytically depurating elements 7. The invention is not limited to the embodiments shown but several modifications are feasible within the scope of the attached claims.

Claims: A method of adapting a silencing system of a large diesel engine to a silencing and catalytically depurating system in which a silencer unit (1) is attached to an exhaust tube (2) of the diesel engine and includes a substantially hollow body member (1a) and a set of sound silencing first elements (4) fitted inside the body member (1a) and arranged in successive order in the flow direction of the exhaust gases longitudinally of the body member (1a) so that the exhaust gases are passed through each element (4) one after the other, characterised in that the first elements (4) are supported against an inner mantle surface of the body member and can be removed one at a time from one end of the body member, in that in the flow direction upstream of the body member (1a) the exhaust tube (2) is provided with means (10) for feeding into the exhaust gases a medium, preferably containing ammonia, urea or the like reagent, applicable for catalytic depuration, and in that by withdrawing one or more first elements from said one end of the tube and by introducing one or more elements one at a time into the tube through its said one end, at least one of the said elements (4) is replaced by at least one catalytically depurating second element (7) which, in a cross-sectional plane of the body member, covers the whole flow area of the exhaust gases, is supported against the inner mantle surface of the body member and provides an exhaust gases depurating, catalytic reaction for decreasing the NOx-content of the exhaust gases. A method according to claim 1, characterised in that at increased depurating requirements for the exhaust gases several, preferably all, of said sound silencing first elements (4), including flow channel devices (5) for exhaust gases, are replaced by said catalytically depurating elements (7) which cover the whole flow area of the exhaust gases. An exhaust gas system in a large diesel engine including a silencer unit (1) to be connected to an exhaust tube (2) of the engine and comprising a hollow body member (1a), and a set of elements, which can be installed inside the body member (1a) in successive order in the flow direction of the exhaust gases and through which the exhaust gases are arranged to be conducted, characterised in that the body member (1a) is provided on its inner mantle surface with elongate guiding and support members (3), to which said elements can be supported so that the elements can be installed one at a time one after the other from one end of the body member (1a) axially to their intended in use positions and can be removed one at a time from said one end of the body member, in that the said elements included in the system include sound silencing first elements (4) having no substantial effect on the composition of the exhaust gases and second elements (7) applicable for catalytic depuration of the exhaust gases, which, in a cross-sectional plane of the body member (1a), covers at least substantially the whole flow area of the gases, wherein for depuration of the exhaust gases in the flow direction upstream of the body member the exhaust tube is provided with means (10) for feeding into the exhaust gases a medium, preferably containing ammonia, urea or the like converting reagent, applicable for catalytic depuration, and in addition at least one of said elements in the body member is a second element (7) so that it provides an exhaust gases depurating, catalytic reaction for decreasing the NOx-content of the exhaust gases. A system according to claim 3, characterised in that the body member (1a) is substantially cylindrical. A system according to claim 3 or 4, characterised in that at increased depurating requirements of the exhaust gases several, preferably all, of the said first elements (4) are arranged to be replaced by the said second elements (7). A system according to any of claims 3 to 5, characterised in that each of the sound silencing first elements (4) includes a flow channel (5) for the exhaust gases. A system according to claim 6, characterised in that the body member (1a) is provided with flame arrester means located in the flow direction upstream of said elements so that it covers said flow channels (5).

Inventors: SVAHN PETER, SVAHN, PETER
Applicants: WAERTSILAE NSD OY AB
Application year: 1995
Main classification: F01N3
IPC codes: F01N3, F01N1, F01N7, F02B3, B01D53