HEAT EXCHANGER ARRANGEMENT AND A METHOD USED IN A HEAT EX- CHANGER The present invention relates to a heat exchanger arrangement as set forth in the preamble of claim 1, the apparatus comprising a shell flow arrangement for a first heat transfer medium, a channel flow arrangement for a second heat transfer medium, arranged to be at least partially enveloped by the shell flow arrangement, wherein the channel flow arrangement comprises a first part and a second part, in which the heat transfer medium flow directions are approximately opposite to each other. The present invention relates also to a method of condensing condensable components from hot gases, which in- cludes the shell flow arrangement and the channel flow arrangement envel- oped by the shell flow arrangement according to preamble of claim 11.

It is known per se that both particle emissions and, for example, sulphur ox- ide emissions into the atmosphere can be reduced by condensing combustion gases. The condensable components can be condensed by sufficiently cool- ing the exhaust gases. A number of solutions have previously been sug- gested for this purpose. Publication DE 3440266 discloses a solution, in which a heat exchanger has been arranged inside the exhaust gas duct for cooling the gas. This solution is, however, problematic, as the heat ex- changer located in the gas stream may be prone to corrosion and clogging.

It is an aim of the present invention to produce a heat exchanger arrange- ment minimising the problems associated with prior art. It is also an aim of the present invention to produce a method of efficiently and reliably con- densing condensable components. It is a special aim of the invention to pro- duce a heat exchanger arrangement for exhaust gases of an internal combus- tion engine, in which the risk of corrosion and clogging is minimised and the cleaning efficiency of the exhaust gases of an internal combustion engine is improved.

Aims of the invention are mainly achieved as disclosed in the appended claims 1 and 11 and more closely explained in other claims.

A heat exchanger arrangement according to the invention comprises a shell flow arrangement for a first heat exchange medium, a channel flow arrange- ment for a second heat transfer medium arranged to be at least partially en- veloped by the shell flow arrangement. The channel flow arrangement com- prises a first part and a second part, in which parts the flow directions of the heat transfer medium are approximately opposite to each other. The first part of the channel flow arrangement comprises an outer shell at least partially enveloped by the shell flow arrangement and the second part comprises an inner shell arranged at least a partially inside the first part.

The first part and the second part are in flow connection with each other so that the second heat transfer medium can first flow via the first part and thereafter via the second part. This will produce both a compact design and the desired function, in which the second heat transfer medium is warmed as it flows via the second part. Preferably the first part and the second part are formed by concentrically arranged tubes.

This way the heat exchanger arrangement may be constructed to be such that the channel flow arrangement is essentially free of internal heat ex- changer elements. In practise, cooling and re-heating of the second heat transfer medium is effected only through the walls of the first and second part of the channel flow arrangement.

The channel flow arrangement preferably extends through the shell flow ar- rangement and consists of a number of units consisting of first and second parts connected in parallel.

A first header chamber of the second heat transfer medium is arranged on the first side of the shell flow arrangement, the header comprising a medium inlet conduit, and the first part of each channel flow arrangement is in flow connection with the first header chamber by its first end. In addition to this, a second header chamber of the second heat transfer medium is arranged on the first side of the shell flow arrangement, the header comprising a medium outlet conduit, and the second part of each channel flow arrangement is in flow connection with the second header chamber by its one end.

On the second side of the shell flow arrangement is a space to which the first part is connected by its second end and the second part by its first end, the said space comprising at least one outlet conduit for removing the liquid condensed from the heat transfer medium. According to the invention, the first and the second header chambers are arranged next to each other, and the second part of each channel flow arrangement is arranged to extend through the first chamber. This way, the connections for the second heat transfer medium can be arranged on the same side of the heat exchanger.

Flow guides are arranged in the space between the outer shell and the inner shell of the channel flow arrangement for causing the flow of the heat trans- fer medium to rotate around the longitudinal axis of the inner shell. The above described heat transfer arrangement is very suitable for cleaning of exhaust gases of a piston engine subjected to production of power.

In a method of condensing condensable components from hot gases in a heat exchanger according to the invention, the method comprising a shell flow ar- rangement and a channel flow arrangement enveloped by the shell flow ar- rangement, the hot gas is arranged to flow essentially downwards in the channel flow arrangement in the space between the outer shell and the inner shell thereof, simultaneously transferring heat through the shells so that con- densation is effected, subsequent to which the flow direction of the by now partially cooled gas is changed about 180°, whereby the condensed compo-

nents are separated from the gas flow. Further, gas is caused to flow essen- tially upwards in the space inside the inner shell, whereby it is simultaneously warned by receiving heat from the hot gas.

Hot gas is preferably caused to flow essentially downwards in the channel flow arrangement, in the space between the outer shell and the inner shell, while simultaneously transferring heat to both the shell flow and the already partially cooled gas flow in the space inside the inner shell. Subsequent to changing the flow direction of the gas, and after liquid has been separated therefrom, gas is caused to flow essentially upwards in the space inside the inner shell, while simultaneously receiving heat from the hot gas flowing es- sentially downwards in the channel flow arrangement, in the space formed by the outer shell and the inner shell thereof. By means of this arrangement, the gases are first caused to cool so that there is a desired amount of con- densation, and further to heat up to the extent that there is no more conden- sation to an undesired degree. Further, it possible to ensure by means of this arrangement that the temperature of the gases elevates to a level sufficient to cause the gases to rise up, instead of being spread to the close proximity of the plant. This can be achieved without a separate heat source.

According to a specific aspect of the invention beneficial results may be achieved particularly in connection with large piston engine. According to this aspect water is added into the charge of the engine while the engine is run- ning, thus producing vapour-containing exhaust gas. In the method, the va- pour-containing exhaust gas is cooled so that the vapour contained therein is condensed and the solid particles contained by the exhaust gas are made to adhere to the condensed water according to the invention. Preferably water is injected into the combustion air or directly to cylinders of the engine. This way the exhaust gas contains more vapour than the amount of vapour gen- erated in the combustion process, and respectively the amount of vapour condensed from the exhaust gases of the engine is larger than the amount of water generated in the fuel combustion process.

Preferably, humid, vapour-containing exhaust gas is cooled by essentially si- multaneously transferring heat to a cooling medium and the already cooled exhaust gas. This causes the temperature of the exhaust gas to rise, ensur- ing that the exhaust gas rises upwards as it is released into the atmosphere from, for example, a smokestack. Further, according to the invention, this is achieved essentially without additional external energy.

Several benefits are achieved by the invention. The solution is very compact and it can significantly reduce the exhaust gas emissions. Further, separation of condensed liquid is efficient without excessive pressure losses. A solution according to the invention does not foul easily, either, and it is easy to keep clean.

In the following, the invention is disclosed by way of an example, with refer- ence to the appended drawing, in which figure 1 is a schematic illustration of an embodiment of a heat exchanger arrangement in connection with a piston engine plant according to the invention.

The piston engine plant 1 schematically comprises piston engine 6 and heat exchanger arrangement 1.1 in connection with the exhaust gas channel of the piston engine plant. The piston engine can be an engine known as such.

The heat exchanger arrangement 1.1 comprises a shell flow arrangement 2, with the first heat transfer medium arranged to flow therein. The first heat transfer medium acts in this case as a heat receiving medium and it can be, for example, water or air. The shell flow arrangement comprises inlet conduit 3 and outlet conduit 4, through which the first heat transfer medium can be directed via the shell flow arrangement.

The heat exchanger arrangement 1.1 also comprises the channel flow ar- rangement 5 for the second heat transfer medium, which is enveloped by the shell flow arrangement. In the illustrated embodiment the second heat trans-

fer medium is exhaust gas of the piston engine 6. It should be understood that the plant may also include other equipment in the gas flow between the engine 6 and the heat exchanger arrangement 1.1. A number of various un- desired components are generated in the combustion process of the piston engine 6, the amount of which it is advantageous to minimise. These include, e. g. particle emissions, such as soot, and gaseous emissions, such as sulphur compounds. According to the invention, the piston engine 6 is provided with suitable water injection means 6.2 for introducing water or steam into the engine 6. Water can be introduced into the engine in different stages, such as into the engine intake air or directly into the cylinder 6.2 of the engine.

Water is introduced from a water source 6.1, in such a way, however, that water is injected into each cylinder of the engine 6, at the latest. Water can be injected as a liquid, steam or a fuel-water emulsion or a combination of these as desired. Thus, the method enables the humidity of the exhaust gases of the engine 6 to be increased above the level achieved by the fuel combustion process alone. This way the amount of condensable water in the exhaust gases is higher than normally. The amount of the injected water can be controlled e. g. on the basis of exhaust gas temperature by means of main- taining the amount of injected water such that the exhaust gas temperature is a desired lower level compared to situation where water is not injected.

When the water condenses into liquid, solid particles adhere on the surfaces of the liquid and liquid drops condensing on the surfaces of the apparatus. As water is injected into the engine in addition to the water generated in com- bustion, solid particles are also separated more efficiently.

Hot and vapour-containing exhaust gas is directed from the piston engine 6 to the inlet conduit 7 and further through the heat exchanger arrangement 1.1. The inlet conduit 7 is arranged in the first header chamber 5.1 of the channel flow arrangement 5. The first header chamber 5.1 directs hot ex- haust gas from the piston engine 6 to each of the channel flow arrangement 5 assemblies, connected in parallel. This kind of assembly comprises a first part 8 and a second part 9. The first part comprises the outer shell 8.1 en-

veloped by the shell flow arrangement, preferably a tube having a circular cross-section, the tube being in the following called the outer tube. The outer tube 8.1 extends through the shell flow arrangement 2 from its first side 2.1 to the second side 2.2. Another tube, acting as an internal shell 9.1, is ar- ranged inside the tube 8.1, the tube being in the following called inner tube.

The outer tube is in flow connection with the header chamber 5.1, whereby gas can flow from the header chamber 5.1 to the space formed between the outer tube and the inner tube. The outer tube and the inner tube are prefera- bly concentrically arranged in relation to each other.

Gas is caused to flow essentially downwards in the channel flow arrange- ment 5 in the space formed by outer tube 8.1 and its inner tube 9.1 thereof while transferring heat to the extent that condensation takes place in the gas. Heat is transferred basically through plain walls of the tubes. There is a space 5.3 arranged in connection with the second end of the outer tube and on the second side 2.2 of the shell flow arrangement 2. The first end of the inner tube 9.1 is connected with this space as well.

With this construction, the flow direction of the by now partly cooled gas is changed about 180° in space 5.3, whereby the condensed components and separated material from the exhaust gases are separated from the gas flow into space 5.3. Thus, a large amount of condensed water, and with it also detrimental components, can be separated from the exhaust gases. The space comprises at least one outlet conduit 11 for removing the liquid con- densed from the gas. There preferably also is a gas lock 13 arranged in con- nection with the outlet conduit 11.

As the gas contains an elevated amount of condensable vapour, flow guides 12 have been arranged into the space for improving the separation of liquid by causing the flow of the second heat transfer medium to rotate around the longitudinal axis of the inner shell 9.1 and thereby to separate on the inner surface of the outer tube 8.1.

From the space 5.3, gas is arranged to flow essentially upwards in the space inside the inner tube 9. 1. At this stage, the partially cooled gas is heated by the gas flowing countercurrently to it in the space between the outer tube 8.1 and the inner tube 9.1. Each outer tube 8.1 extends both to the first side 2.1 of the shell flow arrangement 2 and further through the first header chamber 5.1 and is connected to the second header chamber 5.2. The sec- ond header chamber 5.2 connects the flow of each outer tube 8.1 and di- rects the combined flow out to further treatment via conduit 10. The header chambers 5.1 and 5.2 are arranged side by side on the first side 2.1 of the shell flow arrangement, whereby the inlet and outlet of the hot gas takes place on the same side of the heat exchanger.

The outlet conduit 11 for the condensed water is preferably in flow connec- tion with the water source 6.1 via channel 11. 1, whereby at lest partly closed process is achieved as far as water is concerned. In that case, water source 6.1 preferably comprises suitable water cleaning apparatuses The invention is not limited to the embodiments described here, but a number of modifications thereof can be conceived of within the scope of the ap- pended claims.