The present invention refers to a plate package for a plate heat exchanger, which includes at least two plate modules each including at least two heat exchanger plates, which each has a primary side and a secondary side and is compression-moulded to extend at at least an intermediate plane, an upper plane and a lower plane with respect to the primary side, which planes are substantially parallel to each other. Said two heat exchanger plates are permanently connected to each other in such a way that the heat exchanger plates form an inner first space between the secondary sides of the heat exchanger plates. Said plate modules are mounted adjacent to each other and form a second space between each other. Each heat exchanger plate includes a first porthole and a second porthole, which are arranged to permit communication with the first space. Each first and second porthole is defined by a port edge and surrounded by ring groove, which is adapted to receive a gasket member and provided at the primary side at a distance from the port edge. The ring groove is formed by a bottom, which is substantially positioned at the level of said intermediate plane, an inner lateral limitation that extends upwardly from the bottom towards the port edge and around the bottom, and an outer lateral limitation that extends upwardly from the bottom away from the port edge and around the bottom. The invention also refers to a plate heat exchanger with such a plate package, and a plate module for a plate package according to the initial portion of claim 16.
Such plate packages are frequently formed by plate modules with two heat exchanger plates which are welded to each other, and are frequently used in applications where there is a first aggressive medium, or a very high pressure, and a second medium which does not attack the gasket members. Sometimes the second medium may also lead to a risk for fouling in such a way that there must be a possibility to open the plate package for cleaning of the second spaces between the pairs of welded heat exchanger plates.
An important advantage with a plate package with such pairs of welded plates is that the welds, which replace the gaskets in every second plate interspace around the heat exchanging surface of the heat exchanger plates, reduce the need of gasket replacement and enhances the security. All gaskets in the plate package can however not be replaced by weld joints if the plate package is to be openable for access to the heat exchanging surfaces in the second spaces for mechanical cleaning. The second space between the pairs of welded plates must be sealed by means of gaskets and this is also true for the first and second portholes mentioned above. The ring gasket which is provided around each of these portholes puts a limit to the performance of the first space, but since the ring gasket has a relatively small volume of material it may be manufactured in a material of high quality without increasing the costs for the heat exchanger too much.
The ring groove on the heat exchanger plates, which is used today in plate packages of the kind initially defined, has the disadvantage that they do not in a reliable manner maintain the gasket in a proper position in the ring groove even if ring gaskets of high quality are used. The outer lateral surface of the ring groove is intermittent, which means that the ring gasket can partly be pushed out of the ring groove since the atmospheric pressure prevails outside the outer lateral surface and since the pressure in the porthole is substantially higher than the atmospheric pressure. This means that the first aggressive medium may leak out of the plate package. Such a risk for leakage is not acceptable, especially when the plate package is used in applications with cooling agents such as freon or ammonium hydrate. At high temperatures, the most gasket materials soften and then the pressure may press the gasket out through the opening so that a significant leakage arises, a so-called gasket blowing.
GB-A-2 080 930 discloses a plate package for a plate heat exchanger. The plate package includes a plurality of plate modules, which each includes two heat exchanger plates welded to each other and forming a first inner space between the heat exchanger plates. The plate modules are stacked on each other and form a second inner space between each other. Each heat exchanger plate includes a first porthole and a second porthole, which are arranged to permit communication with the first inner space. Each such porthole is defined by a port edge and surrounded by a ring groove, which receives a ring gasket and is provided at a distance from the port edge. The ring groove is formed by a bottom, a first continuous lateral surface extending upwardly from the bottom away from the port edge and around the bottom, and a second continuous lateral surface extending upwardly from the bottom towards the port edge and around the bottom.
DK-B-151 915 discloses another plate package for a plate heat exchanger, which includes a plurality of plate modules each enclosing a first inner space. The plate modules are stacked on each other and form a second inner space between each other. Each plate module includes a first porthole and a second porthole, which are arranged to permit communication with the first inner space. Each such porthole is defined by a port edge and surrounded by a ring groove, which receives a ring gasket and is provided at a distance from the port edge. The ring groove is formed by a bottom, a first continuous lateral surface extending upwardly from the bottom away from the port edge and around the bottom, a second continuous lateral surface extending upwardly from the bottom towards the port edge and around the bottom.