PLATE HEAT EXCHANGER AND USES OF A HEAT EXCHANGER PLATE

TECHNICAL FIELD OF THE INVENTION

The invention relates to a plate heat exchanger and uses of a heat exchanger plate as presented in the preambles of the independent claims disclosed further below. The invention especially relates to a new manner of manufacturing a plate heat exchanger.

PRIOR ART Heat exchangers with plate structures have already been manufactured for a long time. For enhancing the heat exchange, the heat exchanger plates have typically been very thin, having, for example, a thickness of 0.4 — 0.6 mm. For ensuring the corrosion resistance, the heat exchanger plates have traditionally been manufactured of at least AISI 304, i.e. of stainless steel or of a finer material, such as acid-proof steel. Stainless steels typically refer to steels, which have chromium (Cr) and nickel (Ni) as blend components. Acid-proof steels typically refer to steels, which, in addition to the above-mentioned materials, have molybdenum (Mo) as a blend component. The carbon content in the stainless and acid-proof steel is small, typically 0.02% and the chromium content is typically over 10%, for example 17— 25%.

The heat exchanger plates can also be manufactured of other corrosion resistant materials. Typical known plate materials are for example AISI 316L, i.e. acid-proof steel, titanium, AISI 904L, 254SMO, Duplex.

The materials used in heat exchanger plates are typically costly and often hard to process.

THE AIM AND BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to reduce or even to eliminate above- mentioned problems appearing in the prior art.

An object of the present invention is especially to obtain a plate heat exchanger, the manufacturing of which is inexpensive and easy.

In order to realize the above-mentioned objects, among other things, the present invention is characterised by what is presented in the characterising parts of the enclosed independent claims.

The embodiments and advantages mentioned in this text are in suitable parts applicable to the plate heat exchanger, the use of the heat exchanger plate as well as the method according to the invention, even if this is not always specifically mentioned.

A typical plate heat exchanger according to the invention comprises a stack of plates formed by the heat exchanger plates and a shell surrounding it, wherein - inlet and outlet passages of the first and the second heat exchange medium have been arranged through the shell,

- the inlet and outlet passage of the first heat exchange medium has been arranged in connection with the inner parts of the stack of plates,

- the inlet and outlet passage of the second heat exchange medium has been arranged in connection with the inside of the shell, i.e. with the outside of the stack of plates.

The heat exchanger plates according to the invention are at least mainly, preferably completely, made of carbon steel.

In this text the plate heat exchanger refers to a plate heat exchanger according to the so-called Plate & Shell ™ technology developed by the applicant or a similar plate heat exchanger, which comprises a stack of plates formed by the heat exchanger plates and a shell surrounding it. The stack of plates is formed of several plate pairs. Each plate pair is formed of two heat exchanger plates, which are welded together at least at their outer periphery. Each heat exchanger plate has at least two first openings for the flow of the first heat exchange medium. Adjacent plate pairs are fastened together by welding or by otherwise combining the first openings of two adjacent plate pairs to each other. Thus, the first heat

exchange medium can flow from a plate pair to another via the first openings. The second heat exchange medium is arranged to flow inside the shell in the spaces between the plate pairs.

Inlet and outlet passages of the first as well as of the second heat exchange medium have been arranged through the shell of a Plate & Shell ™ plate heat exchanger or the like. The inlet and outlet passage of the first heat exchange medium has been arranged in connection with the inner parts of the stack of plates, i.e. with the inner parts of the plate pairs. The primary circuit of the plate heat exchanger is thus formed between the inlet and outlet passage of the first heat exchange medium, inside the plate pairs. The inlet and outlet passage of the second heat exchange medium has been arranged in connection with the inside of the shell, i.e. with the outside of the stack of plates, i.e. with the outer sides of the plate pairs. In other words, the secondary circuit of the plate heat exchanger is formed between the inlet and outlet passage of the second heat exchange medium, inside the shell, in the spaces between the plate pairs. Typically, the primary and secondary circuits are separate from each other, i.e. the first heat exchange medium flowing in the inner part of the stack of plates cannot get mixed with the second heat exchange medium flowing in the shell, i.e. outside the stack of plates. Thus, the first heat exchange medium of the primary side flows in the space between every other plate and the second heat exchange medium of the secondary side flows in the space between every other plate of a typical plate heat exchanger according to the invention.

In this context, carbon steel refers to an alloy, which is mainly composed of two elements: iron and carbon. The contents of other materials are small and they don't typically substantially affect the properties of steel. The properties of carbon steel change upon increase of the carbon content so that the when the carbon content is low, the steel is soft and tough and upon increase of the content the steel is harder, but brittler. The carbon content typically varies between 0.05 — 2.1 %. The carbon content of pressure vessel steels is typically 0.2 % or lower. Carbon steel is typically alloyed with boron or corresponding material in order to enhance the strength, cold formability, impact toughness and corrosion resistance.

In this context the refrigerant refers to the circulating medium, i.e. working medium, of vaporization processes used in the refrigerating machinery. Such refrigerants are for example ammonia, carbon dioxide and CFC agents. The brine refers to a liquid circulating in an intermediate system.

Now it has thus been surprisingly found that ordinary carbon steel superiorly suits as manufacturing material of heat exchanger plates for several plate heat exchangers. In several embodiments its corrosion resistance is completely sufficient, even when using thin heat exchanger plates. On the other hand, the heat exchange technology, i.e. the so-called Plate & Shell ™ technology makes it possible to use thicker plate materials than before in heat exchanger plates. Thicker heat exchanger plates resist corrosion better than the thin ones.

One of the greatest advantages of the invention is that carbon steel is inexpensive and its availability in the world market is good. For example, titanium is typically used with a CaCI ₂ solution, which is used as a brine in heat exchanger plates. The availability of titanium has been weak already for a long time and its price is very high and hard to predict.

In one embodiment according to the invention the thickness of the heat exchanger plate is 0.5 — 1.5 mm or 0.7 — 1.2 mm. The thickness of the thinnest duct materials used in connection with heat exchangers is traditionally almost of the same magnitude.

In an embodiment of the invention the heat exchanger plate is grooved or corrugated. The heat exchange performance of a heat exchanger can be adjusted by grooving and corrugation.

In an embodiment of the invention the heat exchanger is a pressure vessel. The pressure bearing parts of the heat exchanger are typically made of materials classified as pressure vessel steels, the carbon content of which materials is

0.2 % at the most. For example the shell, ends, pipeline fittings and flanges of a

heat exchanger can be made of pressure vessel steel. Also the heat exchanger plates can be made of pressure vessel steel.

In an embodiment of the invention the shell and/or the inlet and outlet passages of the plate heat exchanger are made of carbon steel. The carbon steel heat exchanger plates according to the invention and the plate heat exchanger according to the invention are well suited also for those embodiments, in which the shell of the heat exchanger and the parts in connection with it, such as the piping connected to it, are made of carbon steel. The use of one material, which use is as extensive as possible, simplifies the manufacturing.

Embodiments of the invention can, for example, be the use of a carbon steel heat exchanger plate as a heat exchanger plate of a heat exchanger in the following applications: - in an oil cooler, where oil is cooled with a refrigerant,

- in an oil heat exchanger, where oil is heated with liquid or gas,

- in a brine cooler, where brine is cooled with a refrigerant,

- in a cascade heat exchanger, where the primary flow medium is condensing refrigerant and the secondary flow medium is vaporizing refrigerant,

- in an exhaust gas cooler, where gas is cooled with liquid or gas.

The carbon steel heat exchanger plates according to the invention and the plate heat exchanger according to the invention are well suited for those applications, in which the media flowing in the plate heat exchanger do not cause any corrosion or the corrosion is relatively minor. Such applications include, for example, ammonia- oil coolers, CaCI solutions in low temperatures as well as vaporizers and condensers, which have a glycol solution on the secondary side. Other possible objects are for example CO ₂ -NH ₃ cascade heat exchangers as well as hot oil and exhaust gas applications.

The carbon steel heat exchanger plates and the plate heat exchanger according to the invention are well suited for those applications, in which the heat exchange

media to be used are oxygen-free or the oxygen content is insignificant. Such application is, for example, an oil cooler, in which compressor oil flowing in a closed cycle is cooled with ammonia.

The heat exchanger plates according to the invention can, for example, be approximately circles in their form, the diameter of which circles is for example 0.2 — 1.5 meters. The plate heat exchanger according to the invention can, for example, be a substantial circle cylinder in its form, the length of which cylinder can, for example, be 0.5 — 3 meters and the diameter 0.2 — 1.6 meters.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described below in more detail with reference to the enclosed schematic drawing, in which

Figure 1 shows a cross section of a plate heat exchanger according to the invention seen from the side,

Figure 2 shows a cross section of a plate heat exchanger of Figure 1 seen from the end, and Figure 3 shows a heat exchanger plate according to the invention.

DETAILED DESCRIPTION OF THE EXAMPLES OF THE FIGURES

Figure 1 shows a plate heat exchanger 1 , inside the shell 2 of which there has been arranged a stack of plates 3. The flows of the heat exchange media are shown with arrows.

The stack of plates 3 is fastened between the end plates 4a, 4b. The stack of plates 3 comprises plate pairs, each of which is formed by welding two carbon steel heat exchanger plates 5, shown in Figure 3, together at their outer periphery 5a. For the sake of clarity of the figures, the plate pairs are not shown in greater detail. Each heat exchanger plate has two openings 6a and 6b for the flow of the first heat exchange medium, i.e. for the primary circuit. The heat exchange plates are grooved 5b so that there remains a flow channel inside the plate pair from opening 6a to opening 6b. Adjacent plate pairs are welded together at the edges of the adjacent openings 6a and 6b. The openings form flow channels 7a and 7b

passing through the whole stack of plates. Inlet passages 8a and 8b of the first heat exchange medium and outlet passages 9a and 9b of the first heat exchange medium have been arranged at the flow channels 7a and 7b through the end plates 4a and 4b at the ends of the stack of plates. The primary circuit of the plate heat exchanger 1 passes thus via inlet passages 8a and 8b to the inner flow channel 7a of the stack of plates, from there further inside the plate pairs from opening 6a to opening 6b and to the inner flow channel 7b of the stack of plates and along it out of the outlet passage 9a and 9b.

An inlet passage 10a of the second heat exchange medium has been arranged through the upper part 2a of the shell. An outlet passage 10b of the second heat exchange medium has been arranged through the lower part 2b of the shell. Flow guides 11a and 11b have been arranged between the stack of plates 3 and the shell 2, which flow guides force the second flow medium into the spaces between the plate pairs of the stack of plates in the upper part 12a of the plate heat exchanger in the instant vicinity of the inlet passage 10a. On the other hand, the flow guides 11a and 11b allow the second flow medium to exit from the spaces between the plate pairs only in the lower part 12b of the plate heat exchanger, near the outlet passage 10b. The secondary circuit of the plate heat exchanger 1 passes thus from the inlet passage 10a to the upper part 12a of the plate heat exchanger, from there via the spaces between the plate pairs to the lower part 12b of the plate heat exchanger and to the outlet passage 10b.

The thickness of the heat exchanger plate 5 presented in Figure 3 towards the view of the Figure in a perpendicular direction is for example 0.7-1.2 mm.

The embodiment of the Figures can, for example, illustrate an ammonia-oil cooler. In that case, ammonia would be the first heat exchange medium and refrigerated oil, for example compressor oil, would be the second heat exchange medium.

Only one advantageous embodiment of the invention is shown in the Figures. The Figures do not separately disclose facts, which are of secondary importance regarding the main idea of the invention and which are known as such or obvious

as such for a person skilled in the art. It is apparent to a person skilled in the art that the invention is not limited exclusively to the examples described above, but that the invention can vary within the scope of the claims presented below. The dependent claims present some possible embodiments of the invention, and they are not to be considered to restrict the scope of protection of the invention as such.