US2826397A

US2826397A - Scrubbers

Info

Publication number: US2826397A
Application number: US345156A
Authority: US
Inventors: Lofgren Bror; Oholm Gustav; Gustafsson Rune
Original assignee: Svenska Flaktfabriken AB
Current assignee: Svenska Flaktfabriken AB
Priority date: 1952-03-27
Filing date: 1953-03-27
Publication date: 1958-03-11
Anticipated expiration: 1975-03-11

Description

ATTYS.

RUNE GUSTAFSSON Match 11, 1958 B; LFGREN r-:T AL

' SCRUBBERS 3 Sheets-Sheet 2 Filed March 27, 1953 FIEL 35 VM f AVA S R N M N Orr-Iwo TROS N S :GHF VFO.A m O T ls VU A R T G MS U E BGN. U R

ATTYS.

March l1, 1958 B. LFGREN ETAL 2,826,397

scRUBBERs FIEL.

' INVENTORS BROR LOGREN GUSTAV OHOLM By RUNE GUSTAFSSON United States Patent O scRUBERs Bror Lfgren, Stockholm, Gustav holm, Bromma, and

Rune Gustafsson, Stockholm, Sweden, assigner-s to A B Svenska Flktfabriken, Stockholm, Sweden Application March 27, 1953, Serial No. 345,156

Claims priority, application Sweden March 27, 1952 4 Claims. (Cl. 261-11) The present invention relates to improvements in scrubbers. Scrubbers are frequently used for recovering heat from the discharged ventilatingmedium, especially from the Ventilating medium in driers for sheets of defibrated wood or the like. Such driers frequently work at such high temperatures that the discharged medium will be polluted by substances emanating from the sheets which substances normally are volatilizable at this high temperature.

In recovering heat in driers working at a high temperature for the treatment of sheets of defibrated wood, there are great disadvantages caused by the impurities of the discharging Ventilating medium. Said medium will often carry fibres and dust particles and furthermore resinous gases. When the discharging medium is cooled these impurities are precipitated on the cooling surfaces of the heat exchanger resulting in a decrease of the value of the heat transmission coeicient. Accordingly the heat recovery will be decreased. The resinous gases co-mingled with dust and fibrous particles are difficult to eliminate from the heat transmission surfaces. Said surfaces will be at least partly covered with dirt. During the operation of the scrubbers it has often been proved that ignition easily occurs in these impurities which results in a total destruction of the heat recovering plant. The ignition of the impurities can `be caused by heat gases or sparks emanating from a fire within the drier. It is also possible that a self-ignition occurs in the accumulations of the resinous and the fibrous substances. In order to avoid this, it is known to spray water continuously or discontinuously over the heat transmitting surfaces. In operation of the yconventional heat exchanging plants, however, they nevertheless often have been spoiled by fire, since the quantity of water has been maintained relatively small so as to reduce the heat loss in the medium to a predetermined quantity.

According to the invention the method for heat recovering by scrubbers is characterized by the fact that the Ventilating medium discharged from the drier is passed through S-shaped passages by means of distributing devices in the form of Water traps disposed in its path at least once during its passage through the scrubber and that circulating water (dirty used water) in a known manner is heated and that this water is conducted through a heat exchanger where the water is forced to transmit its heat to fresh water, said fresh water being intended for heating purposes, for instance for heating of ventilating air of a locality.

A modification of the method is characterized by that all or a part of the heated fresh water is drawn olf and is replaced by cold fresh water which is added to the circulated fresh water. According to a convenient embodiment, at least so great a quantity of circulated dirty water is brought to pass through the scrubber that said quantity is able to cool the quantity of discharging Ventilating medium down to about 150 C., even if said Ventilating medium has been heated very high for instance up to 1000 C. by lire.

According to the invention, the Ventilating medium being discharged from the drier is thus led through a scrubber in which a great quantity of airis sprayed. The scrubber can be provided only with spray nozzles or can also be provided with contact surfaces. Said quantity of sprayed water is circulated. From this circulation only Water of such a quantity is drawn olf which corre sponds to the quantity of gas condensed from the discharged ventilatingmedium. In such cases where many impurities are in the Ventilating medium discharged from the drier it is preferred that fresh water be added to the quantity of water circulating in the scrubber in order to lower the concentration of dirt particles in the water. A very great quantity of circulating dirty water must be used in order to make sure that the discharged medium, for instance by a tire in the drier which raises the temperature of said medium, nevertheless can be cooled in the scrubber. The risk of any expansion by a fire is then eliminated. The expansion of flames is prevented by means of one or more S-shaped passages for the ventilating medium through the scrubber.

In heat exchangers of this type water is usually s upplied by a number of spray nozzles in the upper part of a tower.

small drops of water may fall down through the tower in counter'current direction to the medium. The medium is adapted to pass upwardly in the tower from the lower part thereof. The small drops `of water contact each other when falling Jdown through the tower resulting in a diminishing of the contact surface. The efficiency of the tower is therefore limited. A further increase of the height of the tower therefore does not result in any increase of the active contact surfaces. is known in which water is sprayed from two or more levels in order to maintain an effective contact surface over the entire height of the tower. Such apparatus has the disadvantage that the difference of the temperature between the medium and the water is diminished. Furthermore, the contact surface is less etlicient, i. e. the etiiciency of a spray outlet disposed in the lower part of the tower will be less than that of a spray outlet disposed in the upper part of the tower owing to collisions between the drops.

It is therefore an object of the invention to eliminate the above mentioned drawbacks of prior known scrubbers. A scrubber in accordance with the invention is characterized by the fact that the space and the tank of thel scrubber are divided byk means of partitions in two orA more treatment chambers adjacent to each other. The

chambers are so joined that the gaseous medium can beA led in S-shaped passages through the treatment chambers,

the tank of the final treatment chamber being connected" with the spraying device of a previous treatment chamber.

Theltank of the last mentioned `chamber can be connected for lnstance by means of an indirect heat exchanger ar-A.' ranged outside the scrubber with the spraying deviceof the iin'al chamber.

A modified embodiment is characterized by the fact Y to clean the same.

It is thus a primary object of the invention that the' scrubber is divided into two or more separate treatment' chambers and the Vquantityl of water intendedto be ligated The water is distributed in order to obtain a large contact surface for transmitting heat. The separate Prior apparatus Vfirst passes is provided with a closed passageway for the water serving only is led in series through the different chambers of the scrubber in a counter current direction to the gas. In the lower part of the first chamber reckoned in the iiow direction of the gas there is'arranged according to an embodiment of the invention a combined watertrap 'and meansfor distributing ,the medium consisting of ilutes combined with vinverted generally U-shaped troughs, which extend downwardly a predetermined distance into the utes'thus forming -S-shaped passages for the gaseous medium. Such a combined water trap and means for distributing the lmedium can also be arranged in the lower part of the other chambers.

' The invention will now vbe more fully `described in connection with the accompanying drawings showing different embodiments of a scrubber within the scope of the invention.

Fig. 1 shows diagrammatically a section of a scrubber.

Fig. 2 shows in a large scale the yoperation of the water traps shown in Fig. 1.

Fig. 2A is a local section on the line 2A--2A of Fig. 2;

Fig. 2B is a view similar to Fig. 2A of a modification within the scope of the present invention;

Fig. 3 shows a vertical section of a modified type of a scrubber.

Fig. 4 shows in a large scale the water traps shown in Fig. 3.

Fig. 5 shows another modification of a scrubber.

In Fig. '1, 1 stands for Va tank which is connected by means of a pipe 15, a pump 16 and a channel 18 of a heat exchanger 19a with a pipe 4, 5 and spray nozzles 9, which discharge into a distributing means 2 in a scrubber 3. The gaseous medium is blown into the tank 1 by means of a fan 11, the inlet and outlet of which being designated 12 and 13. The outlet of the fan opens into the tank below the level of the iiuid 17. As evident from the drawing, the area of the tank is much greater than that of the scrubber.

The edgel of the outlet from the fan is serrated, toothed or perforated similar to the distributing means 2 as will be closer described' in connection with the distributing means 2 in Figs. 2A and 2B. Such teeth of the edge are designated 2b` in Fig. 2A. The perforation is designated 2b in Fig. 2B. The

designations

19b, 20, 21 and 22 standf for diierent parts of the above mentioned heat exchanger. A conduit for the outlet of the gaseous medium from the scrubber is designated 6. 7 and 8 designate. prior known plate means `for precipitating of water from the discharged medium. The slots of the plate 7 isl located ata greater distance from the centre thanV what corresponds to the diameter of the outlet conduit 6.

The operation of the means 2 for distributing the medium is shown. in Fig. 2. Said means can consist of a numberl ofutes'Z'c in: which there are inverted generally U-shaped troughs 2a extending downwardly partly into' the. fluid 23- (water). In Fig. 2 the operation of the downwardly'v extending edges of thel trough isl shown by the: arrows.` rI'he edges: canbeeither perforated as shown at; 2b' in Fig;. 2B 01T toothed as shown at 2b in Figs. 2 and, 2A. A numberr of featuresican be attained by using the above mentioned arrangements. The accumulated impurities are collected inthe uid of the tank. In oppositionv to employing commonly used nets, there is no risk of clogging. Thezinvention also prevents any chimney draft when the scrubber plant is out of operation or is being started. to a great extent eliminates many violentv tires when'. starting theA driers.

As. a practical example ofthe invention a drier for porous plates of debrated wood can be mentioned in which5 the discharge. rate. ofr the wet medium normally is.25',000 kgJh. ancEthetemperature-about'150`C. When a-reoccursimthedrier, the temperature can momentarily increase to 1000 C. If the corresponding quantity ofA ventilatingmediumzisto be cooled down to 100 C. it'is necessary to. eliminate.- a: heat.. quantity.l ofi This quantity of heat is suicient for a theoretical evaporation of about 10 'tons of water. The (quantity f water in the conventional plant must therefore have at least this value. Owing to practical difficulties it is however nearly impossible to distribute the water evenly over the area of the scrubber. The quantity of the circulating water must therefore be greater, at least twice as great as, and in certain cases even 5 to 10 times as great as the abovementioned quantity of water ofthe plant in order to obtain the desired safety against tire.

The quantity of dirty water can in certain cases be greater than that necessary for preventing re. This is because the quantity of heat which normally is transmitted to the dirty water is great.

The dirty water which is circulated in the above mentioned scrubber can normally not be used directly as water for the manufacture process, nor is such water suited for using in heating elements for preheating air. This is partly due' to the earlier mentioned impurities of the waterv andl partly because the water normally contai-ns aceticacid, tannic acid,y oxalic acid or similar substances which originate from the wood to be dried in the drier. According to the present invention the dirty water heats fresh clean Water in separate heat exchangers. Such heated water can then be usedeither in the manufacturing process or can be circulated through ,theV heating elements in which Ventilating air intended Afor the factory heated.A l l y In. Fig. 3 the inlet ofthe scrubber is designated 31. In this the gas 32 o f high temperature and water 33 of.v high temperature flow in counter current with respect to each other. Fromv the part 31 of the scrubber the gaseousV mediumY is passed through a channel 34 to anotherrpart of the scrubber 35 where after passing through tioned part 35 of the scrubberisvaccumulatedin a tank- 38V and is pumped by means of a pump 39 over to the nozzles 52 of the rst mentioned part 31 of the scrubber whereV the circulated water will. be more heated. They Water which is heated in the part 31 of the-scrubber passes through waiter-trap distributing means 53 and is collected in the tank 40 and is forced to passV a filtering means 41. The water is then pumped by means ofa pump 42 through a channel of a heat exchanger 43. InVA this heat exchanger heat is transmitted indirectly to another quantity ofwater which byv means of a pump 44 is forced through heating elements 45. Said` elements 45 are intendedfor indirectly heating-air which for` instance can be used as Ventilating ai rfor different spaces of the factory and also as Ventilatingvair for driers. The arrow 46 stands for the incomingmixtureofair and gaseous media from a drier. The mixture is forced to pass a water trap andi/or meansA 53 for distributing medium on its way.- from the tank 40 before the mixture reaches the inlet .part31'.of'thel scrubber; Such means EL3 can consist of'a number of flutes 47 combined with a plurality of inverted.'generallyY U-'sh'aped troughs'48 partlyextending into'the flutes. This part of the scrubber is shown in a large scale in Fig'. 4.

Fig. 5- shows -a further-modihca'tion of aA scrubber having an inlet vspace 61 'provided `with onlyy circulating water for the cleaning ofthe gaseousl medium. The gaseous medium i's-then passed-on tothe. main scrubber. which is similar to that'shown in Fig. 3 and has corresponding reference characters followed by. the character a. In this way itis possible to eliminate the disadvantages whiclrcan occur in connection with the impurities. Ihe wateris recircul'ated`in the space 61 by nozzles 62,v a coliecti'ngtank 63,' pipes tflanda pump 65.

The supply water to-the different parts of the scrubber is distributedby means of devices 9',

l

10, 51, 52, .51a and 52u. The distance between suchV1 devices andthe Water'tr'ap and7or means for distributing the medium,

which means are designated 2, 50, 53, 50a, and 53a in the lower part of the scrubber are adapted for getting a good result with respect to heating of the water. The distance should not be less than 1 to 1.5 rn. and not greater than 2.5 m. for an optimum result. The distance is also dependent upon the velocity of the medium through the scrubber. The Value of said Velocity can vary between l and 3 m./sec. depending upon the density of the gaseous medium.

The invention produces the following advantages:

(l) Large eicient contact surface between the heat exchanging media.

(2) Mainly a counter current arrangement with re spect to the heat exchanging.

(3) A rather low height of the heat exchanging apparatus.

(4) A water trap for preventing ames or a iire to pass through the apparatus.

(5) Such impurities, for instance fibres and resinous substances, which originate from the heat source will be washed out and precipitated.

What we claim is:

1. The method of eliminating the risk of fire while recovering by a scrubber heat from a hot ilowing ventilating medium containing flammable Volatile gases from a dryer comprising the steps of spraying water into the upper portion of the scrubber chamber over the entire cross-sectional area thereof at a rate of ilow relative to the ow of the Ventilating medium to be able to cool the medium to a temperature of 150 C. from a temperature of at least 1000 C., collecting said water at an intermediate point in the scrubber to form a water trap, affording discharge of the Water from the trap to constitute the water trap a bath of circulating water, discharging and distributing the hot Ventilating medium into the bath of circulating water in the water trap over the entire cross-sectional area of the scrubber chamber and into the spray of water in the upper portion of the scrubber for direct heat exchange with the circulating water and the spray to cool the Ventilating medium and heat the circulating water, conducting the water heated by said Ventilating medium to a separate heat exchanger and utilizing said water as a secondary heat exchange medium for heating fresh water, and using said heated fresh water for heating purposes.

2. In a scrubber for eliminating the risk of re while recovering heat from a warm gaseous medium containing ammable volatile gases, a vertically disposed treatment chamber having two treatment sections adjacent each other, each section having spray means for non-Eammable liquid mounted adjacent the top thereof, a tank at the bottom of said chamber for collecting the liquid discharged from said spray means and distributing means for distributing said medium over the full cross-sectional area of the section, at least one of said means comprising a plurality of cooperating V-shaped and inverted V-shaped troughs forming a non-flammable liquid trap -below the spray means in said section across the full cross-sectional area of the section to prevent travel of lire through said chamber, means for directing the gaseous medium upwardly successively through said second and tirst sections in an S-like path, whereby the medium is cooled by said liquid and heats the latter, means eiecting cyclic flow of the liquid from the tank of the rst section through the spray means of the second section, and from the tank of the second section through the spray means of the iirst section, to thereby afford circulation of the liquid countercurrent to the gaseous medium, and indirect heat exchange means separate from said chamber to receive the heated liquid from the tank of the second section to remove and recover the heat removed from the gaseous medium prior to the ejection of the liquid through the spray means of the irst section.

3. An apparatus according to claim 2 including a third treatment section having a tank and non-flammable liquid spray means therein, means to direct the gaseous medium through the third, then the second, and finally the first treatment section, and means directly connecting the tank of the third section to the non-ammable liquid spray means of said section, in order to use the circulating non-flammable liquid in said third section only for cleaning the gaseous medium.

4. The method of eliminating the risk of re in scrubbers for recovering heat from a hot flowing Ventilating medium containing ammable volatile gases from a dryer comprising the steps of spraying water into the upper portion of the scrubber chamber over the entire crosssectional area thereof at a continuous rate of flow relative to the ow of the Ventilating medium to cool the medium at least down to a temperature of C. from a temperature caused by a tire and as high as 1,000 C. by deliberately overrating the quantity of said spray Water, collecting said water at an intermediate point in the scrubber to form a plurality of water traps, atording discharge of the water from the traps to constitute baths of circulating water, discharging and distributing the hot Ventilating medium over the entire cross-sectional area of the scrubber chamber by passing the medium through said plurality of water traps and forcing the medium to continue into the spray of water in the upper portion of the scrubber for direct heat exchange with the circulating water and the spray to cool the Ventilating medium and heat the circulating Water.

References Cited in the file of this patent UNITED STATES PATENTS 1,780,563 Messer Nov. 4, 1930 1,793,620 Jacobus Feb. 24, 1931 2,299,130 Dill Oct. 20, 1942 2,365,483 Mode Dec. 19, 1944 FOREIGN PATENTS 970,110 France June 7, 1950