US2580121A - Coke oven with gas recirculation means - Google Patents

Description

Dec. 25, 1951 w. NASH COKE OVEN WITH GAS RECIRCULATION MEANS 3 Sheets-Sheet l 'Filed Feb. 19, 1949 Inventor CYRIL zaza/7 /Vvsf/ Attorney Dec." 25, 1951 Filed Feb. 19. 1949.

A c. w. NASH COKE OVEN WITH GAS RECIRCULATION MEANS 3 Sheets-Sheet 2 I Attorney ".Dec. z5, 1951 Filed Feb. 19, 1949 3 Sheets-Sheet 5 Inventor Creu.- @Lawn/W95# Patented Dec. 25, 1951 CQKE OVEN WITH GAS RECIBCULATION MEANS Cyril William Nash, London, England, assigner to The Woodall-Duckham Vertical Retort and Oven Construction Company (1920) Limited, London, England, a British company Application February 19, 1949, Serial No. 77,367 In Great Britain February 24, 1948 6 claims. i

This invention concerns improvements in or relating to coke ovens and has particular reference to batteries of coke ovens of the type described in the speciilcation of United States Patent numbered 1,752,363, in which horizontal ovens are arranged side by side with heating nues on either side of each oven, and in which each of these ovens or each of a group of such ovens is connected with common collecting mains for recovering the gas distilled from the coal being carbonized, the said collecting mains being arranged along both sides of the battery (usually at the crown of the latter) and being connected together by an arched oftake main or cross-duct connected-usually centrally-through a T-joint to a suction main through which the generated gases are removed. l

The ovens are charged to a predetermined level with coal that is to be carbonized, the coal is levelled, carbonized, and then the coke produced is pushed out of the ovens, all according to a predetermined time cycle or sequence and only at the time that the coke is being pushed out of the ovens are the connections of the oven with the gas mains cut o.

It is very desirable to maintain a substantially' uniform temperature throughout the whole depth of the coal bed in each horizontal coke oven in a battery during carbonization of the coal, and various expedients have been tried with little success to achieve this desideratum. As the battery of ovens operates on a time sequence, some ovens will be gassing freely While others in which carbonization is more nearly complete will have more or less stopped gassing. Under the latter condition, there is great danger that the temperature of the oven charge will rise with consequent over-heating of the gas space. Such overheating causes cracking of the hydrocarbon vapours and ammonia which are formed by the .coal carbonization, and thus tends to crack all or part of the by-products and to decrease the value ofv the by-products obtained. Such a cracking operation also acts to form carbon which builds up on the walls of the oven and which interferes with the heat transference from the heating ues to the oven chamber and the proper carbonization of the coal.

It is proposed in the specification of the copending United States patent application No. 627,378 of Koppers Company Inc., now Patent -No. 2,541,794, to control the temperature of the gas and vapour in the space at the top of each oven, while permitting the maintenance of the desired temperature in the coke bed, by effecting a positive circulation of cooled gases through the gas space at the top of the oven in alternating directions so as to maintain a substantially uniform temperature in the gas space. The circulated gases are those contained in the gas spaces of the ovens, the collecting mains and the gas otake mains or arched cross-duct of the battery or group of ovens. about 40 feet long it follows that cooled gases passed into one end of an oven gas space from a gas collecting main increasein temperature as they pass through the gas space so that when the gases reach the opposite end of this gas space their temperature is nearly that of the coke bed. It is for this reason that gases in the said circuit comprising the gas collecting mains, gas oitake mains or cross-duct and the gas spaces of the ovens are alternately circulated in opposite directions, this change of direction being effected at frequent intervalsv so as to bring the cooled gases alternately into the opposite ends of the oven gas spaces in suflicient quantities to maintain a substantially uniform temperature throughout the lengths of these spaces, this temperature being lower than that at which the hydrocarbons and ammonia products will be decomposed.

The alternate circulation of the cooled gases in opposite directions is effected, according to the said Koppers patent application No. 627,378, by means of a pair of independent fans arranged one in each vertical part of the arched oitake main or cross-duct and adapted to circulate the gases therein in opposite directions, automatic timing and switch means being provided so as to bring the two fans alternately intooperation so that first one fan circulates the gases through the oven gas spaces in one direction and then the other fan circulates these gases in the opposite direction whilst the rst fan is at rest,` after which the rst fan comes into operation again and the second fan rests, and so on throughout the operation of the battery or groups of ovens,` it being generally found desirable to effect this reversal of the gas flow direction at about five minute intervals although the duration of these intervals may be varied widely, say between two and sixty minutes, depending for example upon the type of coal being carbonized, the type of coke being made, and the type of gas being produced, it being desirable however to maintain the temperature in the said gas spaces suiilciently low to prevent the decomposition of the by-products being made, as previously explained.

An object of this invention is to provide an im- As the ovenslare usually.

proved means of eiecting an improvement in the said alternate circulation of cooled gases through the gas spaces of the ovens in opposite directions and according to this invention there is provided, in a cokev oven battery, a gas duct which is in communication at opposite ends with the gas collecting mains at the opposite sides of the battery, and a rotary fan or impeller (hereinafter referred to as a fan) which is located in said gas duct for circulating the gasesin the gas spaces of the ovens and the said gas collecting mains alternately in opposite directions, such fan being adjustable as to the position of its fan blades in its gas duct so as to be capable itself of causing the said alternating ow of gases by the change in position of the fari blades without change in its own direction of rotation-i. e. without reversing its motor'.

The said gas duct containing the said fan may be the arched offtake main or cross-duct of the battery but preferably it 'is an additional separate gas-duct arranged in parallel with and bridging the said arched oitake main or cross-duct.

According to a further aspect of the invention, there is provided in combination, a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of the said ovens at the upper parts thereof, offtake mains extending from each of the said collecting mains to a connecting T, a suction main for leading the gas away from said T, an adjustable rotary fan in a gas duct for drawing gases from one of said collecting mains through said oiitake mains and forcing these gases back into the other collecting main and through the gas spaces of the said ovens in one direction and for then drawing gases from the second of the said collecting mains and through the gas spaces of the ovens in the opposite direction to the previous flow, and means for adjusting said rotary fan to alter the position of its blades in its gas duct for causing it alternately to eiiect the said opposite iiow of gases.

According to a further feature of the invention the blades of the said ian are arranged so that their pitches or angles of attack may be adjusted through a range of positive positions, a neutral position and a range ox' negative positions whereby the lan may be adjusted to give a flow of gases in either direction through the said gas duct or so as to produce a static or -no now condition, and whereby the quantitative value of the gas How in either direction can be regulated.

The ian is preferably driven by a uni-directional continuously operating constant-speed electric motor developing suiicient power for the maximum gas ow required, the actual gas flow being varied as desired by adustment of the pitch of the blades of the fan and not by adjustment Y of the running speed oi' the motor.

Variation of the pitch of theblades of the fan may be provided for by mounting each blade for rotational adjustment about its own axis relatively to the fan shaft.

Thus, according to a further aspect of the invention, there is provided in combination a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of the gas spaces of the said ovens at the upper parts thereof, an oitake main leading from each of said collecting mains, a suction main connected to both of said oiltake mains at the ends thereof remote from the said collecting mains, a gas duct bridging the said olftake mains. gas circulating means in said bridging gas duct for circulating gases in said collecting mains and ofl'take mains alternately in opposite directions through the gas spaces of the said ovens, such circulating means comprising a fan in the bridging gas duct having its blades rotatable in its hub to vary and reverse their pitch respectively for effecting a variation in the quantitative flow of said gases thereby, and also to reverse the direction of flow of the gases thereby through the bridging gas duct, means for effecting the variation and reversal of the pitch of said fan blades, and a constant-speed electric motor for driving said fan to run in one direction only.

The rotational adjustment of the blades of the fan may be controlled by any suitable hydraulic, pneumatic, electrical or mechanical means or a combination of such means which itself may be controlled manually or automatically. For example, suitable timing gear may be embodied in the apparatus automatically to control the pitch varying and reversing mechanism of the blades of the fan to eect changes in the quantitative ow of the gas and also the change of direction of the gas flow and, if desired, to provide a Yariable delay or pause between the change-over from gas now in one direction to gas flow,in the opposite direction. For instance, to eiect the said ldelay or pause the said timing gear may provideu for retaining the fan blades, during the reversal of the pitch of the blades, in /a neutral position for a predetermined period )whilst the fan motor continues to run at its synchronous speed, the fan blades thereafter cntinuing to move to the position for reversing the gas iiow.

In an alternative arrangement, the rotary fan may be of the fixed blade uni-,'irectionai type and be mounted in the gas du t for bodily adjustment of the ian blades and their drive shaft through relatively to the duct in order to reverse its direction of thrust, such reversal of the fan as a unitary whole being ellected through any suitabie hydraulic, pneumatic, electrical or mechanical means (or a combination of such means) which may be remotely controlled or controlled through automatic timing mechanism in a manner similar to that above referred to.

In such an arrangement, means may also be providedfor varying the speed of the motor in order quantitatively to ycontrol the gas flow through the gas duct.

According to a still further aspect of the invention, there is provided in combination a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of the gas spaces of the said ovens at the upper parts thereof, an ontake main leading from each of said collecting mains, a suction main connected to both of said oltake mains at the ends thereof remote from the said collecting mains, a gas duct bridging the said offtake mains. means in said bridging gas duct for circuiating gases alternately in opposite directions in said collecting mains and offtake mains and through the gas spaces of the said ovens, said means comprising a rotary fan adjustable as a unitary whole through 180 in said bridging duct to reverse its direction of thrust, means for driving said fan, and means for effecting the adjustment of the'said fan as a unitary whole through 180.

According to a still further feature of the invention. when the fan or fans is or are arranged in a gas duct which is additional to-i. e. which is in parallel with or bridges-the offtake main or cross-duct, a valve or damper may be provided in the oiIta-ke main or cross-duct at the junction of the suction main therewith so as to prevent circulation of the gases in this otake main or cross-duct, such valve or damper being adapted automatically to reverse its position to place opposite sides of the offtake duct into communication with the suction main each time the said fan in the additional gas duct is operated to reverse the ow of the circulating gases.

It will thus Ibe apparent that this invention provides for the use of a single fan itself adapted to provide alternate flow of the gases in each of the two opposite senses orfdirections, thus rendering unnecessary a separate fan for driving the gases in each of the said two directions, and eliminating the braking action such fans tend to impose, when idle, on the gas flowing out through the collecting and exhaust mains. However, although only a single fan of the aforementioned character will normally be used for each of said gas ducts it should nevertheless be understood that if desired two or more such fans may be used, these fans being arranged to operate, and be adjusted, in tandem or unison so as to assist one another.

In order that the nature of the invention and the method of carrying the same into effect may be more readily understood two embodiments of the same will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a fragmentary view, partly in elevation and partly in cross-section, showing diagrammatically the upper part of a coke oven battery with its gas collecting mains, oitake mains and the suction -main therefor;

Figure 2 is an enlarged diagrammatical vertical part-sectional view of the gas collecting fan shown in Figure 1;

Figure 3 is an enlarged vertical sectional elevation diagrammatically showing the blade controlling mechanism of the fan shown in Figure 2;

Figure 4 shows a modication of Figure 1;

Figure 5 diagrammatically illustrates a modied form of fan unit for use in an arrangement such as is shown in Figure 1; and

Figure 6 is a plan of the unit shown-in Figure 5.

In the accompanying drawings, the present invention is shown as applied to a Becker-type coke oven of the kind described in the specification of United States Patent No. 1,752,363.

The coke oven battery is of the horizontal character where wherein a series of ovens, such as the oven\l of which the upper part is shown in Figure 1, are arranged side by side with heating nues (not shown) on opposite sides of each oven. The ovens of such a battery are usually operated as a unit, each of the ovens being connected with gas collecting mains 2 and 3 arranged horizontally one on either side of the battery adjacent the crown 4 thereof and disposed with their lengths perpendicular to the lengths of the ovens I.

The ovens are provided at the oppoiste ends respectively with removable sealing doors 5 and 6.

Each oven I is charged with coal through charging openings I in the crown 4 of the oven after which these openings are sealed. The top oi the coal bed 8, in each case, is levelled by a leveller bar which is inserted through an opening 9 in the door 6 of the oven. A space I0 is thus left between the crown 4 of the battery and the top of the coal bed 8 in each oven and this space is herein referred to as the gas space I0."

The heating nues which are located between the ovens are continuously heated while the battery is in operation and as gases are formed in each oven by the carbonization process these gases rise from the opposite ends of the gas space I0 of the oven and pass upwardly through ascension pipes Il and l2 arranged one adjacent each end of the battery and respectively connected, by intermediate ductings I3 and I4, to the gas collecting mains 2 and 3.

Preferably arrangements are provided whereby, as the gases pass to the gas collecting mains 2 and 3, they are met by sprays of ammonia liquor introduced through appropriate spray pipes (not shown)-which act to cool the gases to a temperature in the region of C. At this stage the generated gases may also be saturated with water vapour to increase their thermal capacity.

The collecting mains 2 and 3 have the lower ends of vertical portions I5 and I6 of an arched offtake main or cross-duct 2| respectively connected thereto, and these vertical parts of the oitake main continue inwardly respectively in horizontal portions II and I8 extending transversely across the top of the battery to a T-joint I9 to which is connected a suction main 20. The arched offtake main 2I is bridged by a gas duct 22 arranged in parallel with the portions I'I and I8 of the oiftake main and connected at its opposite ends respectively to the vertical parts I5 and I6 of this oitake main.

The oitake main or cross-duct 2| is conveniently located approximately centrally between the ends of the battery. but it can be arranged in any other suitable position with respect to the battery, for example at one end thereof; moreover, Where desired two or more of these ofltake mains 2| may be employed at positions spaced along the length of the battery, such oitake mains being connected to separate or to a common suction main.

In order to maintain a more or less uniform temperature in the gas spaces I0 of the ovens whilst retaining the temperature in these spaces below that at which the hydrocarbons and ammonia by-products would be decomposed, cooled gas is circulated through the gas spaces IIJ alternately in opposite directions, and to effect this alternating circulation a rotary fan 23 is located within, and preferably centrally between the ends of, the gas duct 22.

The fan 23 has a plurality of blades-e. g. two, three or more-so arranged that their pitches or angles of attack may be adjusted through a range of positive positions, a neutral position and a range of negative positions whereby the fan may be adjusted to give a ow of gases in either direction through the gas duct 22 or to feather and so produce a. static or no-ow condition and whereby the quantitative value of the gas flow in either direction can be regulated, this being effected by adjusting the pitches or angles of attack of the blades suitably between the maximum positive or negative positions and their neutral positions.

In the examples shown in the accompanying drawings, which as already stated are of a. diagrammatic character, the fan 23 has two diagrammatically opposite similar blades 24 and 25, the roots 26 and 21 of which are rotatably mounted in a cage or hub 28 fixed upon a fan-driving hollow shaft 29. Although the roots 26 and 21 of the blades 24 and 25 are rotatable in the cage 28 they are restrained by any appropriate means against axial movement in this cage.

The shaft 29 is rotatably supported in horizontally spaced bearings 30 and 3| carried by a skeleton supporting structure 32 depending from a housing 34 carried by a vertical trunking 34 built onto the upper side of the cross-duct 22 so that the fan shaft 29 is located coaxially in the gas duct 22.

A constant-speed electric motor 35 is mounted Within the housing 34 and drives the fan shaft 29 through pulleys 36 and 31 and a belt 33 which may be a plain belt or of a multiplesection type as desired.' suitable means (not shown) being provided for appropriately tensioning the belt or belts.

A fan blade pitch-adjusting or feathering shaft 39 is co-axially mounted in the hollow fan-shaft 29 for axial adjustment on the latter and this featheringlshaft projects beyond both ends of the fan shaft..` -The fan end of the feathering shaft 39 carries'a fan-blade feathering head 40 furnished with a pair of racks, 4| and 42 (see Figure 3), arranged opposite each other diametrically of the shaft 29 and parallel to the latter, each of these racks being guided in the cage 28 and meshing with a corresponding toothed wheel fixed coaxially upon the root of the corresponding fan blade 24 or 25, rack 4| meshing with the toothed wheel 43 on the blade 24 being marked in the drawings with a reference 43 and rack 42 meshing with toothed wheel 44 on the blade 25.

The racks 4| and 42 are so arranged with respect to the wheels 43 and 44 that as the feathering shaft 39 is moved axially in one direction in the driving shaft 29, the blades 24 and 25 turn simultaneously and correspondingly in one direction, and as the shaft 39 is moved in opposite directions like rotation of the blades occurs but in a reverse direction so that by appropriately axially adjusting the feathering shaft 39, the blades 24 and 25 can be moved from a maximum positive flow position gradually to a fully feathering or neutral position and then further onwards through gradually increasing negative positions to a maximum flow negative position. Thus. by this means gas can be caused to flow in the gas duct 22 in the direction of the arrows shown in Figure 1 and can subsequently be caused, by reversing the pitches of the blades of the fan, to flow in an exactly opposite direction from that indicated by the arrows. Alternatively the blades can be set in their neutral position sdthat there is a static or no-iiow condition in the duct 22. In addition, by axially adjusting the feathering shaft 39 appropriately, any quantitative value of the gas ow between zero and the maximum capacity of the fan can be achieved in either of the said two directions.

The axial adjustment of the feathering shaft 39 may be effected through a grooved collar 45 xed on the end of the feathering shaft 39 opposite to that end carrying the fan 23, the axial adjustment of the collar 45 being controlled by a pivoted lever 46. This level itself is controlled by any suitable means, for example a hydraulically or pneumatically operated piston, an electric motor and screw or by rods and levers, or the lever 46 may be operated through automatic time-controlled mechanism which may include an electric motor (which can be the fan motor 35) furnished with one or more cams for controlling the action of the lever 46.

The arrangement should preferably be such that the duration of the iiow of gases in either direction along the gas duct 22 can be varied as required. and should also provide for the'variation in the quantitative now of gases from the `duct in either direction as well as for the variation in the period during which the blades of the ian remain in their no-Iiow or neutral position. it being desirable, in some cases, to have me blaues pause in this position for a period and it is desirable that this period should be variable to suit any particular set of circumstances.

The mechanism for actuating the lever 46 for controlling tne operation or the pitch of the fan blades is not illustrated in the drawings as it will be clear that a variety of weil-known sequence-controlling mechanisms can be adapted for the present purpose.

The fan motor 36 is preferably a constant-speed motor which will run continuously whilst the battery of ovens is operating, variation in the quantity of gas ow along the duct 22 being achieved by modification of the settings of the blades 24 and 25 of the fan 23 rather than by variation in the speed of the motor.

To cool the motor 35 and the fan shaft bearings 30 and 3|, the housing 34 is conveniently provided with louvres 4| to admit a certain quantity of air to the housing whilst, if desired, one or more fresh air inlets 46 may be adoitionally provided to admit outside air (which can be under pressure from a secondary fresh air fan-not shown) into the housing 34 for similar cooling purposes, but this cooling air is not conveyed into the gas duct 22 since the skeleton framew'rk 32, the fan shaft 29 and its bearings 30 and 3|, the belt 36 and the mechanism 46 are enclosed by a casing 49. In addition, to the head of the fan 23 is furnished with a spinner 50 and the casing 49 protrudes through a semi-circular flaring 22' which forms a continuation or junction for the gas duct 22 where the casing 49 and the associated parts penetrate into this gas duct.

In the oli'take main or cross-duct 2|, at the T-joint I9, a valve or damper 5| is provided which is adjustable to segregate either the part I6 of the ofitake main or the part I1 of the latter from the suction main 20, and this valve 5| is preferably so coupled with the lever 46 or any other suitable part of the fan blade controlling mechanism that the valve 5| reverses its position each time the lever 46 reverses the direction of flow of gases through the duct 22, thereby ensuring that the upper part of the oitake main 2| is excluded from the recirculating system comprising the gas duct 22, the vertical gas offtake main parts l5 and I6, the gas collecting mains 2 and 3, the ascension pipes and |2 and the gas spaces I9 of the ovens. 'f

It will thus be seen that gas is alternately circulated through the gas spaces I0 of the oven from opposite ends, first in one direction and then in the other direction, the rate of change of the direction of circulation and also the quantity of gas circulated being adjusted to provide for the maintenance of the temperature in the gas spaces below that which will be harmful to the by-products which it is desired to produce by the carbonization process.

A modification of the arrangement above described is shown in Figure 4 of the drawings where two of the fan units shown in Figure l are used in the gas duct 22, these units being marked respectively 34 and 34" in'Figure 4. Otherwise the arrangement is precisely the same as that described with respect to Figures 1 to 3. Where two or more fans are used in the duct 9 22 in this way, these fans are arranged to work in tandem or unison so as to operate together and assist one another.

Figures and 6 show a further modification according to this invention wherein, instead of using a variable pitch fan driven by a constantspeed motor, the fan 52 is of the fixed-blade variety but its housing 34a is mounted for rotation by any suitable means, such as meshing bevel gears 53 and 54, through 180 in the duct 22 so that the fan can beA arranged to propel gas through the duct 22 in either direction therealong-i. e. reversing the position of the fan blades in the duct 22, without changing the direction of rotation of the fan. In this case, variation in the rate of iiow of gas through the duct can be modified to some extent by the rotation of the housing 34 about its vertical axis, but additional variation can be achieved by varyingr the speed of the motor driving the fan. A substantially no-flow condition would arise when the motor had been turned through 90 from the position shown in Figure 1 but a complete stoppage of ilow of the gases through the duct 22 can be achieved by stopping the rotation of the fan altogether.

From the foregoing description, it will be appreciated that apparatus according to this invention enables a proportion of the generated gases (which has not been removed through the suction main but which has been partially cooled by passage through the gas collecting mains) to be recirculated through the gas spaces at the tops of the ovens. When the fan 23 in the gas duct 22 is in the no-flow condition the generated gases do not ow through the gas duct 22; but gas may pass off from both mains 2, 3, in such case, if desired, through the oiitake main 2l direct to the suction main 20, the valve 5I being held in a mid-position at this time.

It will be further understood that the apparatus according to this invention comprises a simplication of that described in the said co-pending United States patent application No. 627,378 of Koppers Company Inc. for carrying out the method of recirculation described and claimed in that patent application.

What I claim is:

1. The combination with a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of said ovens at their crown spaces in the upper parts thereof, an oitake main leading from each of said collecting mains, and a suction main connected to both of said oiitake mains at a position remote from said collecting mains: of a gas duct bridging said offtake mains and by-passing the suction main. means in said bridging gas duct for circulating gases in said collecting mains, through their offtake mains, alternately from one to the other,

' and thence through the gas crown spaces of said ovens alternately in opposite directions, said circulating means comprising a fan having blades rotatable about their axes to vary and reverse their pitch, respectively, for effecting a variation in the quantitative iiow of said gases, and to reverse the direction oi' ow of the gases, respectively, means for effecting the variation and reversal of the pitch of the blades of said fan, and a constant-speed electric motor for driving said fan.

2. Apparatus as claimed in claim l, and which includes an adjustable valve controlling the flow of gases alternately from said otake mains to 10 said suction main, and means to operate said valve to alternate the connection of said two ofitake mains to said suction main in step with the reversal of the pitch of the blades of said fan, for reversal for flow of gases through the said bridging duct.

3. The combination with a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of said ovens at their crown spaces in the upper parts thereof, an offtake main leading from each of .said collecting mains, and a suction main connected to both of said oii'take mains at a. position remote from said collecting mains; of a gas duct bridging said offtake mains and bypassing the section main, means in said bridging gas duct for circulating gases in said collecting mains, through their offtake mains, alternately from one to the other. and thence through the gas crown spaces of the said ovens alternately in opposite directions, said means comprising a rotary fan adjustable through 180 in said bridging duct to reverse its direction oi' thrust, means for driving said fan, and means for effecting the adjustment of the said fan through 180.

4. The combination with a battery of horizontal coke ovens arranged side by side with heating fiues therebetween, gas collecting mains communicating with opposite ends oi the gas crown spaces at the upper parts of said ovens, an oiitake main leading from each of said collecting mains, and a suction main connected to both of the said ofltake mains at a position remote from said collecting mains; of a gas duct bridging the said offtake mains and by-passing the suction main, and fan means in said bridging duct, said fan means comprising an adjustable fan and means to cause said fan to circulate gases cooled in said collecting mains alternately in opposite directions through the bridging duct, from one to the other of the oiitake means, and thence to theirgcollecting mains and through the gas crown spaces of the owens for reverse iiow in alternation therethrough.

5. The combination with a battery of horizontal coke ovens arranged side by side, gas collecting mains communicating with the opposite ends of said ovens at their crown spaces in the upper parts thereof, an oiitake main leading from each of said collecting mains, and a suction main connected to both of said oiitake mains at a position remote from said collecting mains; of a gas duct bridging the said offtake mains and by-passing the suction main, means in said bridging gas duct for circulating gases in said collecting mains, through their oiitake mains, alternately from one to the other, and thence through the gas crown spaces of said ovens alternately in opposite directions, said circulating means comprising a multi-bladed fan having a hub and the roots of the blades rotatably mounted in the hub, a hollow fan shaft on which the hub of the said fan is fixed, an electric motor for driving said fan shaft, a support for suspending the said fan shaft and the fan axially in said bridging gas duct between the ends thereof, gear wheels iixed on the roots of said fan blades, a reciprocable rack for and meshing with each of said gear wheels, a fan blade pitchadjusting shaft housed in said hollow fan shaft for axial sliding movement relative thereto and having said racks attached thereto at the fan end thereof, and means for axially adjusting said pitch adjusting shaft to vary correspondingly the pitches of all the fan blades simultaneously, for

eecting quantitative variation and reversal in 1 1 direction of gas ow through said bridging duct by said gas circulating means.

6. Apparatus as claimed in claim 5, and in which said fan shaft is located coaxially within said bridging gas duct and said electric motor for driving the fan is disposed outside the outer confines of said duct, al1 the parts except the fan blades being housed unitarily in a. housing let into the upper part oi' the said gas duct and closed to the interior thereof.

CYRIL REFERENCES CITED The following references arev ot record in the tile of this patent:

12 UNTTED STATES PATETS Number Number Name Date Yingling July 6, 1948 Koppers Feb. 22, 1921 Becker Apr. 1, 1930 Connors Sept. 30, 1930 Madder Oct. 1, 1940 FOREIGN PATENTS Country Date Germany Dec. 23, 1940 Germany Feb. 27, 1932 Great Britain Jan. 12, 1933

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