Gas and liquid contact apparatus – With external supply or removal of heat – Heat exchange means at or downstream of contact zone
Reexamination Certificate
1999-05-07
2001-06-19
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
With external supply or removal of heat
Heat exchange means at or downstream of contact zone
C261S153000, C261S157000, C261S161000, C261SDIG007, C165S900000
Reexamination Certificate
active
06247682
ABSTRACT:
THE PRIOR ART
Air cooling towers have been widely used, for example for cooling the water used in a condensation unit of an electrical power plant.
Wet cooling towers are towers comprising a heat exchanger on which water is distributed and in which air and the water counterflow. The air escaping the heat exchanger and the tower is charged in water and forms a visible plume, which is an esthetical pollution. In certain instances, the formation of plume has even to be completely avoided for example when the cooling tower is located near a road or in a city.
In order to solve the problem of plume, various wet-dry type cooling towers have been proposed.
Said wet-dry cooling towers comprises two distinct heat exchangers, namely a first indirect contact heat exchanger for the dry heating of a first air flow, said first heat exchanger having fin tubes in which the water coming from the condensation unit flows, before being sprayed onto a second direct contact heat exchanger having channels in which air and water counterflow so as to form a wet heated air flow. The said first air flow and the wet air flow are then mixed together so as to reduce the formation of plume. The plume abatement by means of wet/dry cooling tower is for example disclosed in the “Technical Paper Number TP93-01” of the Cooling Tower Institute 1993 Annual Meeting, “Plume abatement and Water Conservation with the wet/dry cooling tower” by Paul A. Lindahl et al, the content of said paper being incorporated to this specification by reference.
Such known wet-dry cooling towers have many drawbacks, the major of which are the construction of an expensive specific heat exchanger for the dry heating of air, and the consumption of energy for compensating the pressure loss of the water when flowing through the fin tubes of the first heat exchanger. It means that the investments and the operating costs for such known wet-dry cooling tower are high, whereby industrials are reluctant to use such wet-dry cooling towers.
The present invention relates to a cooling tower that obviates these drawbacks. The cooling tower of the invention does not require the high investments and operating costs required by the dry-wet tower of the state of the art, as the cooling tower has a heat exchanger on which the water to be cooled is distributed and through which said water flows, said heat exchanger being adapted for the dry heating of a first air flow and for the wet heating of a second air flow.
BRIEF DESCRIPTION OF THE INVENTION
The invention relates to a plume abated cooling tower for cooling an aqueous fluid by means of air, said tower comprising:
(a) at least one air inlet;
(b) an air outlet;
(c) an air-aqueous fluid heat exchanger;
(d) at least one means for ensuring an air flow between the air inlet and the air outlet, as well as through the heat exchanger;
(e) a distribution system for distributing the fluid to be cooled on the heat exchanger, wherein the heat exchanger has first channels in which air and the fluid to be cooled counterflow, second channels in which air flows, and a means for avoiding the passage of the fluid to be cooled into the said second channels, said second channels having a heat conductive surface contacting a plurality of first channels.
Advantageously, said tower further comprises a drift eliminator for reducing the water loss by drift due to the air flow, said drift eliminator being located above the water distribution system, in which the means for avoiding the passage of the fluid to be cooled into the said second channels conveys the air escaping from the second channels at least upto a level in the tower located in the vicinity of the drift eliminator, preferably at least to a level in the tower upper the drift eliminator.
According to a preferred embodiment of the tower according to the invention, the first channels are adapted for ensuring a substantially vertical air-fluid counterflow, while the second channels are adapted for ensuring a substantially horizontal air flow.
According to a detail of an embodiment of the invention, the heat exchanger comprises heat exchanger packs with second channels, each pack comprising a plurality of second channels and a plurality of first channels. By using such packs, the construction of the heat exchanger of the tower of the invention is simple and not expensive. For example, a pack is made of several heat conductive plates linked the one to another by fins and/or by substantially perpendicular plates (linking plates substantially perpendicular to the heat conductive plates), preferably heat conductive fins and/or plates, so that between at least a first couple of adjacent plates, the fins define a series of second channels, while between at least another couple of adjacent plates, the fins and/or substantially perpendicular plates define a series of first channels.
In order to reach the highest temperature for the air flowing through the second channels, the said second channels preferably form a part of the heat exchanger adjacent to the said upper face onto the water is distributed or sprayed.
The tower may have one or more air inlets, for example distinct air inlets for the air flowing into the first channels and for the air flowing into the second channels. The tower may also have one or several air inlets and means for guiding part of the air towards the second channels.
Preferably, the cooling tower is provided with a drift eliminator and at least one wall defining an inner chamber in which the heat exchanger and the drift eliminator are located. In said embodiments, the means for avoiding the passage of the fluid to be cooled into the said second channels advantageously conveys the air escaping from the second channels (or at least a part of said air) at least at a distance from the said at least one wall defining the said chamber and/or at least part of the air escaping from the second channels at least substantially along the central axis of the chamber.
In the tower of the invention, the means for ensuring an air flow between the air inlet and the air outlet, as well as through the heat exchanger, is for example, a fan sucking air through the heat exchanger, a plurality of fans sucking air through the heat exchanger, a fan pushing air through the heat exchanger, a plurality of fans pushing air through the heat exchanger, a form of the tower adapted for a natural draft of air through the heat exchanger, or a combination thereof.
The invention relates also to a process for abating plume produced from a cooling tower. In said process, an aqueous fluid is cooled by means of an air flow having an initial relative humidity, the said aqueous fluid being distributed on a heat exchanger having first channels in which air and the fluid counterflow, and second channels in which air flows without counterflow of fluid, said second channels having a heat conductive surface contacting a plurality of first channels whereby heat is transferred from the fluid and air flowing through first channels towards the air flowing in second channels. The air passing through the exchanger is heated and comprises at least one air flow with a relative humidity of at least 99% and at least one air flow with a relative humidity lower than the initial relative humidity of the air. Thereafter, at least one air flow with a relative humidity of at least 99% and at least one air flow with a relative humidity lower than the initial relative humidity of the air are mixed together.
Advantageously, the air flow with a relative humidity of at least 99% passes through a drift eliminator for eliminating from said air flow drifted water droplets.
For example, the air flow with a relative humidity of at least 99% and the air flow with a relative humidity lower than the initial relative humidity of the ambient air are mixed together in a volume ratio air flow with a relative humidity of at least 99%/air flow with a relative humidity lower than the initial relative humidity of the air advantageously comprised between 5:1 and 1:1. The said ratio is advantageously adapted or controlled so that when
Bushey C. Scott
Hamon Thermal Europe S.A.
Hoffmann & Baron , LLP
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