US3738794A - Process and apparatus for preheating powder - Google Patents

Abstract

A process and apparatus for preheating powder is disclosed. The process, useful for heating finely divided particulate material, such as unrefined cement powder, involves feeding the powder to be treated into a cascade of vertical treatment vessels, generally arranged in a vertical direction, the interior of the treatment vessels being in communication with one another. The powder to be treated is released into said cascade arrangement and permitted to fall through the individual treatment vessels under the influence of gravity. Hot combustion gases are passed in an upward direction through the cascade arrangement of treatment vessels in counterflow to the descending powder and is removed at the top of the entire arrangement, this being the point where the feeding of the powder to be treated takes place. A portion of the hot combustion gases which are removed from the top of the cascade arrangement, now cooler than when first fed into the bottom of the treatment vessels, are injected, under pressure, at distributed points along the cascade arrangement, preferably at the mating points between adjacent treatment vessels, through helical ducts which impart to the descending powder a helical component of movement whereby the dwell time in the treatment vessels is increased. An apparatus is described which is used to implement the abovedescribed process.

Description

[22] Filed:

' United States Patent 1' Thelen PROCESS AND APPARATUS FOR PREHEATING POWDER [75] Inventor: Johannes Thelen,Bergisch- Gladbach, Germany [73] Assigneez' Walther & Cie Aktiengesellschalit, Cologne-Delbrueck, Germany July 13, 1971 .211 Appl. No.: 162,041

[30] Foreign Application Priority Data Primary Examiner-William F. ODea AssistantExaminer-Harold Joyce Attorney-Michael S. Striker [57] ABSTRACT A process and apparatus for preheating powder is dis- June 12, 1973 closed.

The process, useful for heating finely divided particulate material, such as unrefined cement powder, involves feeding the powder to be treated into a cascade of vertical treatment vessels, generally arranged in a vertical direction, the interior of the treatment vessels being in communication with one another. The powder to be treated is released into said cascade arrangement and permitted to fall through the individual treatment vessels under the influence of gravity. Hot combustion gases are passed in an upward direction through the cascade arrangement of treatment vessels in counterflow to the descending powder and is removed at the top of the entire arrangement, this being the point where the feeding of the powder to be treated takes place. A portion of the hot combustion gases which are removed from the top of the cascade arrangement, now cooler than when first fed into the bottom of the treatment vessels, are injected, under pressure, at distributed points along the cascade arrangement, preferably at the mating points between adjacent treatment vessels, through helical ducts which impart to the descending powder a helical component of movement whereby the dwell time in the treatment vessels is increased.

An apparatus is described which is used to implement the above-described process.

37 Claims, 3 Drawing Figures PATENTEDJUN I 23973 SHEU 1 87 2 INVENTOR BY JO/MMVZS THEZEN krona-r BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to preheaters, and more particularly to preheaters for heating finely divided particulate materials, such as unrefined cement powder.

2. Description of the Prior Art Preheating apparatus for unrefined cement powder are known in which the waste gases of a combustion furnace are carried upwards in countercurrent to the descending material to be preheated, the material permitted to fall under its own weight through a series or cascade of treatment vessels or inclined sliding surfaces or the like between which the stream of gas flows upwards.

The treatment vessels used in the prior art have generally been ineffective to accomplish efficient heat transfer. As is known, heat transfer from the waste oven gases to the material to be preheated is a function of the quantity of the oven gases, the velocity of the oven gases and the dwell time of the material to be preheated in the gas stream. Also, the mixture of the oven gases and the material to be preheated is essential, the binding of powder particles to one another reducing the mixture of gases and particles and thereby also the heat transfer. The treatment vessels in the prior art have generally contained replacement bodies or have been funnel-shaped, the periodic changes in the crosssectional area along the cascade of treatment vessels have caused the stream of hot combustion gases to undergo periodic changes in their velocity. Thus, as the hot combustion gases rise through a narrowed portion of a treatment vessel, the gases must contract and therefore the velocity rises. Upon expansion is a widened portion of a treatment vessel, the hot combustion gases decrease in their upward velocity. The purpose of this art has generally been to increase the dwell time of the powder to be preheated inside the series of treatment vessels. Thus, the periodic change of velocity, in

the form of a pulsation in ascending direction, causes.

the powder particles, even the coarser particles, to be carried upwards through the narrow sections of at least some of the treatment vessels. Upon entering the widened portion of the treatment vessels, with the decrease in-velocity of the hot combustion gases, most of the particles, particularly the heavier particles, drop back and resume their descending motion. Thus, the time of stay in the stream of gas, or the dwell time, is thereby substantially increased by these temporary upward movements caused by the pulsating ascending gases.

A disadvantage of the arrangement as just described in that the ascending stream of hot combustion gases exert a classifying effect on the material and causes the crude powder fed into the apparatus to be separated into its constituents. The smaller, and therefore lighter, particles have a tendency to be carried upwards with the ascending gases, while the heavier particles are generally little affected by the ascending gases and have limited upward movements. This results in an unwanted circulation of fine particles which carry heat away with them. Thus, the prior-art apparatus for preheating powder has had disadvantages, the amount of heat transfer being limitedor affected by the classifying effect on the constituent particles and the uneven heat thereby.

Another prior-art arrangement has sought to make use of the fact that heat transfer is much greater in a fluidized bed than in an ascending counterstream of gas. To accomplish this, the prior-art apparatus has sought to mkae the hot combustion furnace gases ascend in a spiralling or helical fashion. Complicated cyclone-type treatment vessels have been used to impart helical components of motion to the hot furnace gases directly. This solution, however, leads to a very complicated construction of the preheater which is expensive to produce and difficult to maintain.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the disadvantages of the prior-art apparatus.

According to the present invention, the process and apparatus for heating finely divided particulate material, such as unrefined cement powder, involves feeding the powder into a preheating treatment vessel and allowing it to fall in a downward direction under its own weight. Hot combustion gases are fed at the other end of the treatment vessel, said hot gases being permitted to ascend in a generally upward direction through the treatment vessel in counterilow to the descending pow der. Means are provided, in the regions where the hot combustion gases enter into the treatment chambers, for injecting the gases into the interior of the treatment vessel tangentially to the interior surface of the vessel and in a direction generally perpendicular to the flow of the ascending hot combustion gases. The tangential injection of gases through such means come into contact with the rising hot combustion gases and impart a helical component of movement to the hot ascending combustion gases. In this manner, the hot ascending combustion gases are in spiralling motion in addition to ascending in the treatment vessel. The descending powder, coming under the influence of the spiralling gases, are thereby also imparted helical components of movement and thereby the dwell time of the powder in the treatment vessel is increased.

Thus, the present invention accomplishes improved heat transfer from the ascending hot furnace gases to the powder to be preheated, first by increasing the dwell time of the powder within the treatment vessel, and second by breaking up the streams of descending powder flow as a result of the impartingof spiral components to the descending powder. In effect, the descending streams of powder are broken up and the powder is subjected to substantial turbulence forces in substantially horizontal planes. This, as mentioned above, increases the efficiency of the heat transfer to the material to be preheated.

According to another aspect of the invention, the gases injected tangentially to the interior surfaces of the treatment vessels are cooled furnace waste gases which are at a temperature lower than that of the ascending hot furnace gases introduced at the bottom of the treatment vessels. Furthermore, the cooled furnace waste gases are the same as the hot rising furnace gases which have cooled by the time they have come to the top of the treatment vessel and are recycled into the treatment vessel by such tangential injection. The use of cooled gases, in this manner, prevents the formation of deposits in the treatment vessels. The cooled gases,

being of higher density than the hot ascending furnace gases, initially spiral away from the interior of the treatment vessels along the interior walls thereof and, by their spiralling motion, carrying away material particles which have adhered thereto.

According to a still further aspect of the present invention a plurality of treatment vessels are arranged in cascade in a substantially vertical direction, with the rising hot oven gases being imparted helical components of movement at distributed points along the entire treatment vessel arrangement, preferably at points between individual treatment vessels. In this manner, the velocity of the helical component of the hot ascending oven gases is maintained throughout the entire cascade arrangement of treatment vessels. The value of the helical component of velocity can be controlled by adjusting the velocity of the gases injected tangentially into said treatment vessels, and valve means are provided for making such adjustment so that optimum operating conditions can easily be achieved.

Because the present invention is more efficient by increasing the heat transfer both as a result of increased dwell time of thematerial to be preheated inside'the treatment chambers .and prevention of streams of flow of the material to be preheated through the treatment chambers, the number of treatment vessels used can be reduced for the same amount of heat transfer. The resulting apparatus is very simple in construction and is therefore inexpensive to produce and simple to maintain.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however,

' both as to its construction and its method of operation,

together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a preheater-according to the present invention is generally designated by reference numeral 1.

' Preheater l is shown to be made up of a plurality of treatment vessels 7. Each treatment vessel 7 is generally elongated and consists of two conical surfaces which form the lateral sides thereof. Each treatment vessel 7 has an input opening at the top and an output opening at the bottom thereof. In FIG. 1, the treatment vessels 7 are shown to be arranged in cascade wherein the output openings of adjacent treatment vessels 7 are inserted within the input openings of the next-lower treatment vessel 7, the input openings being generally of greater cross-sectional area than the output openings. In the regions where the treatment vessels 7 meet,

turbulence chambers 6 are provided which also form a seal between the respective adjacent vessels. Turbulence chambers 6 are in communication with the interiors of the treatment vessels, as will be described, and generally consist of convoluted ducts which admit gases from the exterior of the treatment vessels 7 and injects them tangentially to the interior surfaces of the treatment vessels 7.

A feeding hopper 2 is provided above the uppermost treatment vessel 7 for providing a continuous supply of powder or material to be preheated. A measuring or dosing device 3 is placed between the feeding hopper 2 and the uppermost treatment vessel 7 for regulating the quantities of powder or material to be treated within the cascade arrangement of treatment vessels 7. Dosing device 3 can be of the type presently known in the art and does not form a part of the present invention. As indicated in FIG. 1, the dosing device 3 can be simply a bucket wheel which admits fixed quantities from feeding hopper 2 and releases same after a predetermined amount of rotation.

A combustion furnace 4 generates hot gases at temperatures of about 800-l000C. A deflection bend 5 is shown to connect the combustion furnace 4 to the outlet opening of the treatment vessel 7 at the bottom of the cascade arrangement, with a turbulence chamber 6 likewise interposed and sealing this joint.

The hot combustion gases generated in combustion furnace 4 flow through deflection bend 5 and through the cascade arrangement of treatment vessels 7, such ascending motion resulting in said gases entering gasexhaust conduit 8. A cyclone or dust separator 9 is provided in conjunction with gas-exhaust conduit 8 for separating the dust or fine material components from the ascending gas. The purpose of dust separator 9 is, therefore, to filter the exiting gases and remove all the solid dust particles therefrom and returning the same through return channel 9' to the cascade arrangement of treatment vessels 7 for further processing. The gases leaving dust separator 9, now free of dust particles and at a lowered temperature as a result of heat transfer from the ascending gas to the descending powder to be preheated within the treatment vessels, are shown to be removed by exhaust fan 13 through exhaust conduit 10.

In this embodiment, a blower fan 11 is provided which recycles the cooled gases from exhaust conduit 10 by means of duct 10' and feeds said cooled gases to turbulence chambers 6 under pressure in pipes 11 and 12', the pressure in pipes 12 being controlled by control devices 12 which are interposed between pipes 11" and 12. By controlling the pressure in pipes 12', control devices 12 also control the velocity of the cooled gases during passage through turbulence chambers 6. The significance of this will hereafter be described.

FIG. 2 is a cross-sectional view through a turbulence chamber 6 showing the convoluted nature of the duct comprising turbulence chamber 6 and showing the interior of said duct 6 opening tangentially to the interior surface of treatment vessel 7. In this manner, gases entering treatment vessel 7 through turbulence chamber 6, enter treatment vessel 7 tangentially to the interior surface of an inlet opening of a treatment vessel 7 in a direction which is essentially perpendicular to the directions of flow of both the rising hot combustion gases and the descending material to be treated. By such tangential ingress, the gases which enter through turbulence chamber 6 are imparted, upon contact with the interior surfaces of treatment vessels 7, a helical component of movement. The ascending hot furnace gases passing through the lower portions of treatment vessels 7 wherein the turbulence chambers 6 are located, come under the influence of said injected gases through the convoluted ducts of turbulence chamber 6 and, upon contact therewith, are likewise imparted helical components of movement. Since the material to be preheated is nearly constantly under the influence of the ascending gases in treatment vessels 7, helical components of movement are likewise imparted to the material to be preheated. By imparting components of helical motion to the ascending hot gases which are of sufficient magnitude, said helical components are maintained for the entire ascending distance corresponding to the height of treatment vessel 7 until said helical components are again reinforced by the next-higher turbulence chamber 6. By selecting the height of treatment vessels 7, the velocity of the gases injected into turbulence chambers 6, and the number of turbulence chambers 6, preferably uniformly distributed along the cascade arrangement of vessels 7, it is possible to create optimum operating conditions for maximum heat transfer.

Although three treatment vessels 7 are shown in FIG. 1, it is clear that any number of such vessels can be used in forming a preheater 1. However, because of the increased heat transfer resulting according to this method, a smaller number of treatment vessels 7 will generally be required.

Referring again to FIG. 1, the embodiment there shown makes use of the cooled gases leaving gasexha'ust conduit 8 for recycling to turbulence chambers 6. Although the gases present in exhaust conduit 10 will generally exist under some pressure due to the accumulations of rising gases in the treatment vessels 7, the presures in exhaust conduit 10 will not usually be of sufficient magnitude to adequately propel the cooled gases at the desired higher velocities through turbulence chambers 6 for imparting helical components of movement to the materials passing therethrough. Accordingly, a blower 111 is shown to be interposed between turbulence chambers 6 and exhaust. conduit 10 for generating the higher pressures which are required for propelling the gases at higher velocities. Control devices l2-are shown interposed between blower 11 and turbulence chambers 6 for controlling the pressures in pipes 12 and thereby precisely regulating the velocities of the gases in turbulence chambers 6. In a second embodiment as shown in FIG. 3, a preheater l operates in nearly the identical manner as the embodiment shown in FIG. 1, the only difference being the manner in which the requisite pressures required in pipes 11' are provided. Thus, in FIG. 3 pipes 11' are connected to the outflow side of exhaust fan 13 connected to exhaust pipe 14, instead of exhaust conduit 10. Here, exhaust fan. 13 performs a function similar to that performed by blower ll, the requisite pressure being formed in exhaust pipe 14 and therefore also in pipes 11. With this embodiment it is now possible to eliminate blower 11 and thereby simplify the preheater unit 1.

The operation of preheater 1 will now be explained with reference to the embodiment shown in FIG. 1. As explained above, hot furnace combustion gases at temperatures of approximately 800-l000C are generated in combustion furnace 4, these gases passing through deflection bend 5 and into the interior of a cascaded arrangement of treatment vessels 7. A blower 11 propels gases through turbulence chambers 6, provided at the narrowed sections of treatment vessels 7, said propelled or injected gases being at a lower temperature than the ascending hot oven gases. Injection into the interior of treatment vessel 7 is tangential along the inner surface of treatment vessel 7 whereby upon such contact the heated gases acquire helical components of movements in the regions of turbulence chamber 6. The hot oven gases pass through the narrow openings contained within turbulence chambers 6, said hot turbulent gases coming under the influence of said cooler injected gases and, upon coming into contact with same, are likewise imparted helical components of movement. Control devices 12 are adjusted to regulate the initial velocity of the injected gases through turbulence chamber 6, the initial velocity being set at a sufficiently high magnitude so as to impart adequate helical components of movement to the ascending hot gases whereby said helical components maintain their vitality during the entire ascent from the region of the turbulence chamber 6 to the next-higher turbulence chamber 6. In this manner, the helical components of the ascending hot gases are reinforced periodically along the total ascent path of treatment vessels 7 and such turbulent motion of gases is then retained throughout the entire vertical distance of ascent. The material to be preheated, in this example unrefined cement powder, is released from feeding hopper 2 in measured quantities by means of dosing device 3, as shown. The powder, falling under its own weight, now comes under the influence of the hot rising gases, and in particular the helical components thereof, such helical components likewise being imparted to the powder. The resulting direction of flow of the powder as a result of the combination of the helical components and the downward components, is in a downward spiral. The turbulent gas motions, and in particular the high-velocity motions of injected gases through turbulence chambers 6, have the effect of breaking up powder which has a tendency of compacting and also prevent the formation of strands or streams of powder flow. The effective separation and mixing of powder particles with the hot gases results in improved heat transfer to all components of the powder. Also, due to the higher density-of the cooled gases which enter through turbulence chambers 6, said cooler gases will first rise up the wall of the treatment vessels 7, cool the vessel and remove any deposits formed on the interior surfaces thereof, and ultimately combine with the hot rising surface gases and be mixed therewith, now together heating the material which enters the preheater 1. In the preferred embodiment shown in FIG. 1, the process of injecting cooled gases into turbulence chamber 6 is repeated three times at stepwise greater temperatures, the quantity of supplied cool furnace waste gases decreasing in the ascending direction. However, any combination of treatment vessels 7, injection gas velocities, or temperatures of injected gases can be used. Also, in the example illustrated, the treatment vessels 7 are shown to be double cone shaped, but instead of using the upper cone, cylindrical portions may be substituted therefor.

FIG. 1 shows the cooled gases being removed from treatment vessels 7 to be recycled by injection through turbulence chambers 6. However, it is clear that any other source of gas can be used and, although gases which are cooler than the ascending hot gases within chamber 7 are preferred, use of gases for injection through turbulence chambers 6 which are of the same temperature or even hotter than those rising within chambers 7 can be utilized. Use of hotter gases will still accomplish most of the advantages which are set forth for the present invention and are also within the inventive concepts as presently contemplated.

While the invention has been illustrated and described as embodied in an apparatus for heating finely divided particulate material, such as unrefined cement powder, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is set forth in the appended l. A process for changing the temperature of particulate material, such as finely divided unrefined cement powder, comprising the steps of conveying said material along a predetermined confining path through a series of successive treating zones each having an inlet and an outlet with the outlet of each preceding zone in communication with the inlet of the next following zone; passing along said path in counterflow to said ma terial a stream of a gaseous fluid having a temperature different from that of said material whereby the material exchanges heat with said fluid; admitting currents of a gaseous treating fluid into the outlets of at least some of said treating zones so as to impart a helical component of movement to said material; and conveying said currents along said path in counterflow to said material.

2. A process as defined in claim 1; and further comprising the step of exhausting said gaseous fluids from said treating zones.

3. A process as defined in claim 2, wherein the step of admitting currents of a gaseous treating fluid comprises injecting at least a portion of the exhausted gaseous fluids into said treating zones.

4. A process as defined in claim 2; and further comprising the step of separating finer powder components from the exhausted gaseous fluids and returning said- 7. A process as defined in claim 1, wherein the step of admitting currents of a gaseous treating fluid comprises injecting said currents into said zones in a direction substantially normal to said path.

8. A process as defined in claim 1, wherein said currents of gaseous fluid have a temperature lower than that of said stream of gaseous fluid.

9. An apparatus for changing the temperature of particulate material, such as finely divided unrefined cement powder, comprising a plurality of successive treating vessels arranged in cascade fashion and each having an inlet portion and an outlet portion, the outlet portion of each preceding vessel communicating with the inlet portion of the next-following vessel; feeding means for feeding said material into the inlet portion of the foremost vessel for descent thereof towards the outlet portion of the last vessel; inlet means for admitting a stream of a gaseous fluid in the region of the outlet portion of said last vessel so that the stream rises in counterflow to said material; and means for imparting a helical component of movement to said material in the region of each of said outlet portions.

10. An apparatus as defined in claim 9, wherein said means for imparting a helical component of movement to the material comprises a spiral duct communicating with the interior of the vessel, and means for providing pressurized currents of gaseous fluid which enter said vessels through the respective spiral ducts whereby said currents of gaseous fluid enter said vessels having a helical component of movement.

11. An apparatus as defined in claim 9; and further comprising means for removing said gaseous fluid through said inlet portion of said foremost vessel.

12. An apparatus as defined in claim 11, wherein said means for removing said gaseous fluid comprises an exhaust fan, and duct means connecting said exhaust fan with said inlet portion of said foremost vessel.

13. An apparatus as defined in claim 10, wherein said means for providing pressurized currents of gaseous fluid comprises containing means for containing gaseous fluid, a fan, connecting means for connecting said containing means with said fan and said spiral ducts, and a gas control device interposed between said fan and said spiral ducts for regulating the velocity of the currents of gaseous fluid entering said vessels.

14. An apparatus as defined in claim 13, wherein said containing means comprises said inlet portion of said foremost vessel.

15. An apparatus as defined in claim 13, further including a dust separator interposed between said connecting means and said inlet portion of said foremost vessel.

16. An apparatus as defined in claim 13, wherein said fan is an exhaust fan for removing said gaseous fluid from said vessels.

17. An apparatus as defined in claim 13, wherein said fan is a blower fan provided for forcing cooled gaseous fluid through said connecting means into said vessels. It I I. I

Claims (16)

1. 2. A process as defined in claim 1; and further comprising the step of exhausting said gaseous fluids from said treating zones.
2. 3. A process as defined in claim 2, wherein the step of admitting currents of a gaseous treating fluid comprises injecting at least a portion of the exhausted gaseous fluids into said treating zones.
3. 4. A process as defined in claim 2; and further comprising the step of separating finer powder components from the exhausted gaseous fluids and returning said powder components into said treating zones.
4. 5. A process as defined in claim 4, wherein the step of separating finer powder components comprises whirling the exhausted gaseous fluids so as to effect centrifugal separation of said powder components from said exhausted gaseous fluids.
5. 6. A process as defined in claim 1; and further comprising the step of feeding said material into said zones in predetermined amounts.
6. 7. A process as defined in claim 1, wherein the step of admitting currents of a gaseous treating fluid comprises injecting said currents into said zones in a direction substantially normal to said path.
7. 8. A process as defined in claim 1, wherein said currents of gaseous fluid have a temperature lower than that of said stream of gaseous fluid.
8. 9. An apparatus for changing the temperature of particulate material, such as finely divided unrefined cement powder, comprising a plurality of successive treating vessels arranged in cascade fashion and each having an inlet portion and an outlet portion, the outlet portion of each preceding vessel communicating with the inlet portion of the next-following vessel; feeding means for feeding said material into the inlet portion of the foremost vessel for descent thereof towards the outlet portion of the last vessel; inlet means for admitting a stream of a gaseous fluid in the region of the outlet portion of said last vessel so that the stream rises in counterflow to said material; and means for imparting a helical component of movement to said material in the region of each of said outlet portions.
9. 10. An apparatus as defined in claim 9, wherein said means for imparting a helical component of movement to the material comprises a spiral duct communicating with the interior of the vessel, and means for providing pressurized currents of gaseous fluid which enter said vessels through the respective spiral ducts whereby said currents of gaseous fluid enter said vessels having a helical component of movement.
10. 11. An apparatus as defined in claim 9; and further comprising means for removing said gaseous fluid through said inlet portion of said foremost vessel.
11. 12. An apparatus as defined in claim 11, wherein said means for removing said gaseous fluid comprises an exhaust fan, and duct means connecting said exhaust fan with said inlet portion of said foremost vessel.
12. 13. An apparatus as defined in claim 10, wherein said means for providing pressurized currents of gaseous fluid comprises containing means for containing gaseous fluid, a fan, connecting means for connecting said containing means with said fan and said spiral ducts, and a gas control device interposed between said fan and said spiral ducts for regulating the velocity of the currents of gaseOus fluid entering said vessels.
13. 14. An apparatus as defined in claim 13, wherein said containing means comprises said inlet portion of said foremost vessel.
14. 15. An apparatus as defined in claim 13, further including a dust separator interposed between said connecting means and said inlet portion of said foremost vessel.
15. 16. An apparatus as defined in claim 13, wherein said fan is an exhaust fan for removing said gaseous fluid from said vessels.
16. 17. An apparatus as defined in claim 13, wherein said fan is a blower fan provided for forcing cooled gaseous fluid through said connecting means into said vessels.

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