Concentrating evaporators – Film type – Moving film
Patent
1996-01-23
1998-11-17
Nessler, Cynthia L.
Concentrating evaporators
Film type
Moving film
159 283, 165115, 165170, F28B 904, F28D 304, F28F 312
Patent
active
058370960
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a falling film evaporator comprising element being formed by to vertical, essentially rectangular heat transfer plates; film along the outer surfaces of the evaporator elements; and discharging formed condensate from the inside.
A well-known falling film evaporator apparatus comprises evaporator elements made of two metal plates so that the plates are attached to each other not only by their edges but also by certain dot-like places. In a complete heat transfer element the flow channel for the heat transfer medium is thereby formed in areas between these dot-like places, i.e. in areas where the plates are separated from each other. This king of elements have been formed by placing a pair of plates between studded support plates, the studs of which define the position of the dot-like fastening spots, dimples, of the heat transfer elements. The plates are then separated from each other by means of internal hydrostatic pressure.
U.S. Pat. No. 3,736,783 discloses an apparatus for manufacturing heat transfer elements, the apparatus comprising a fixed bottom part and an upper part, movable along tracks onto the lower part once a pair of heat transfer plates has been located in the lower part. The fixed bottom part comprises an upwards opening box-like space containing an inflatable bag. A piston plate supported by this bag can be moved vertically. The piston plate in turn supports a studded plate, the studs of which are directed upwards. When the pair of plates has been positioned between the studded plates, it is pressed against the upper part of the apparatus by filling the bag with, e.g. water, causing the piston plate to move upwards. In order to form flow channels, the plates are separated from each other by means of hydraulic pressure, i.e. by directing pressurized water between plates, whereby the plates are separated from each other in other places except at the edges and the dot-like places where the studs prevent expansion and maintain the plates in contact. The plates can be spot-welded to increase strength at the dimples, between which flow channels were formed.
The heat transfer elements described above are often used in evaporators, in which--in case it is falling film apparatus--the liquid to be evaporated is directed to flow along the outer side of the element and steam is directed to flow inside the element in the channels between the dimples. Evaporators often operate in high steam pressures, e.g. about 4 bar, which places a great stress on the dot-like fastening points, and can even break the fastening. Even though the elements are always pressure tested at pressures exceeding the projected operating pressures, it is still reasonable to develop more pressure resistant heat transfer elements. This is especially necessary because of the tendency towards higher operating pressures, because of the advantages brought about by increased steam pressure.
The object of the present invention is to provide a falling film evaporator, with an essentially more pressure resistant evaporator element structure than that of the present designs.
A characterizing feature of an evaporator according to the invention is that the heat transfer plates of each of the evaporator element are jointed together along the upright edges and seam joints, parallel with the upright edges and located within a distance from each other, thus forming tube-like flow channels for steam inside the element.
According to an advantageous embodiment of the invention the seam joints do not extend quite from one to the other end of the plate, but feed and discharge chambers, perpendicular to the seams and thus also to the flow channels, are formed for feeding and discharging steam at the ends of the element. These chambers communicate with the flow channels.
According to another advantageous embodiment of the invention, the seam extends the whole length of the plates. In this case, the chambers for directing steam are formed by joining, preferably by welding, a separat
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Agren Erik
Fagerlind Olof
Hoikkala Juhani
Sannholm Krister
Schonberg Ake
Ahlstrom Machinery Oy
Nessler Cynthia L.
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