US2685562A - Coke oven with electrically controlled gas recirculation means - Google Patents

Description

F. TREFNY Aug. 3, 1954 COKE OVEN WIT H ELECTRICALLY CONTROLLED GAS RECIRCULATION MEANS Filed Oct. 11 1950 INVENTOR. FRANZ TREFNY iib l ll.

ATTORNEY Patented Aug. 3, 1954 UNITED STATES PATENT OFFICE COKE OVEN WITH ELECTRICALLY CON- TROLLED GAS RECIRCULATION MEANS 1 Claim.

The present invention relates to a method of operating coke ovens, and more particularly coke ovens of the type consisting of a battery of horizontally extending parallel chambers.

In ovens of that type, gas collecting cavities are provided above the chambers for the purpose of collecting the gaseous and volatile constituents of the coal, one such cavity being coordinated to and communicating with each horizontal chamber. 7

It is the object of the present invention to increase the yield of benzene and other compounds oi. the aromatic class contained in such volatile coal constituents.

More particularly, it is an object of the present invention to provide a simple and efiicient method whereby coke ovens of the conventional types may be so operated as to substantially increase the benzene production thereof, such method requiring no substantial changes in the design or in the equipment of the coke ovens of the standard types whereby the improved method may be readily practised in any existing coke oven plant.

Numerous propositions have been made and reduced to practice for creating such thermal conditions in the gas discharge ducts and gas collecting means of various kinds of coke ovens as will result in an increased yield of benzene, toluene, phenol, tar and similar volatile constituents of coal. It has been found that too low temperatures favor the production of undesired aliphatic compounds, whereas excessive temperatures result in a cracking of the hydro-carbons entailing a reduction of the yield. Therefore, the maintenance of a temperature in the gas collecting cavities of 700 to 800 centigrade is deemed desirable, corresponding to 1290 to 1470" F., respectively.

For this purpose prior to my invention means have been provided adapted to rapidly discharge the vapors from beneath the ceiling of the gas collecting cavities and for cooling such vapors thereby precluding an excessive overheating of the volatile constituents. On the other hand it has been found that by heating the distilled vapors subsequent to their discharge from the gas collecting cavities, if carried out during a pre-determined phase within the period of operation of the coke oven, the yield of benzene may be increased. In order to secure within the gas collecting cavities a uniform temperature conducive to an increased yield of valuable byproducts, arrangements have been made prior to-the present invention for returning to the gas collecting cavities an adjustable fraction of the discharged gaseous and volatile constituents in a cool condition. Also, means have been provided for periodically changing the connections of the distributing ducts, cooling means or heating means during the operation of the coke oven, such ducts etc. servicing either the individual chambers of a battery-or groups of such chambers.

In all such cases the operations efiective to control the temperature and, consequently, to influence the yield of benzene etc. were carried out in accordance with a pre-determined schedule, such schedule being designed to fit the kind of coal to be coked, the type of oven and, in the first line, the duration of period of operation of the oven, the schedule being based on laboratory tests and practical test runs, such operations comprising for instance the setting of valves or throttles for governing and changing the connection of the discharge ducts and the return ducts. The coke oven when run in accordance with such pre-designed schedule was expected to yield a maximum of valuable byproducts, such as benzene etc;

In running a coke oven of the type in which part of the gaseous and volatile constituents discharged from the gas collecting cavities is permitted to cool and is then returned to such cavities, it has been the practice to determine once for all how the throttling valves provided in the distributing ducts are to be set and over what period of time such ducts are to be opened, such determination being based on a measurement of the temperature in a test run. lhis practice was based on the presumption that a schedule resulting in a substantially uniform and appropriate temperature during the test run would guarantee similar uniform temperatures in'the gas collecting cavities in subsequent runs performed under substantially the same conditions.

In another process in which the distilled vapors are re-heated after discharge from the gas collecting cavities and in which at certain times during the run additional heat is supplied, whereas at other times the gases are cooled, the times of the required changes in the operation affecting the thermal treatment of the gases were determined by test runs for any given set of conditions, such as a particular brand of the coal, a particular type of oven and a particular range required for a-run. Once such schedule had been pre-determined by a test run, it was then retained for the practical operation of the coke 3 oven. When such prior processes based on fixed schedules are applied to a coke oven of the type consisting of a battery of parallel chambers, as long as the oven i charged with the same brand of coal, each chamber will be invariably controlled in any subsequent run of th coke oven in exactly the same manner with respect to the times at which heat is supplied, the gases are sucked ofi, the gas collecting cavities are reheated and cooled, distilled vapors are returned thereto etc. By such a mode or" operating in accordance with a pre-determined schedule, the conditions controlling the yield of the desired icy-products in the gag collecting cavities could be so improved as to substantially increase the yield of such products. Moreover, it was found that with the same kind of coal, the same yield will be obtained when the same schedule is applied to th coke oven. That experience sup ports the opinion generally entertained by experts conversant with the operation of coke ovens prior to my invention that the conditions of operation controlled by .ich a schedule designed on the basis of temperature measurements in test runs are the best possible conditions resulting in a maximum yield of valuable lay-products. I have found, however, that such an opinion is erroneous in that the thermal conditions existing in the various gas collecting cavities are invariably subject to uncontrollable factors causing fluctuations and departures, even tho the fixed schedule be strictly adhered to and even tho the oven be charged with the same kind of coal in successive runs. Such fluctuations will adversely affect the yield of the valuable lay-products. The existence of such fluctuations was not known before I discovered the same. Probably, they escaped discovery because generally they extend uniformly over the diilerent gas collecting cavities and chambers of a battery and over th difierent periods of operation, whereby the same average yield will be attained, that being the yield regarded as the best attainable result prior to my invention. Nobody realized, however, that such yield, while appearing to represent an optimum, corresponds in truth to an average value only, considerably reduced by the temperature fluctuations in the gas collecting cavities.

I have found that the temperatures existing in the gas collecting cavities allotted to different horizontal chambers of a coke oven are liable to differ considerably, sometimes by several hundred centigrades, in the same phase of the operation, such differences being due to accidental conditions, such as the quantity of the charges of difierent chambers, differences in the water content and the grade of the different charges etc. rather than due to an unequal application of heat.

None of the prior art methods of operating coke ovens were capable of coping with this situation. More particularly, it is impossible to preclude such undesirable temperature fluctuations where the coke oven is run in accordance with a fixed schedule. Therefore, it was not possible prior to my invention to obtain the optimum yield of hydro-carbon by-products.

The present invention is based on the discovery of the existence of such hitherto unavoidable fluctuations of the temperature and of the departure thereof from the desirable range of temperatures and it is based on the realization of the impossibility to cope with such fluctuations when operating coke ovens in accordance with a predetermined fixed schedule, in controlling the application of heat, the discharge, the return and the cooling of the gases etc.

According to my invention the fluctuations of temperature are eliminated by steadily controlling the oven in dependence on the temperature existing in the individual gas collecting chambers during any productive run thereof (as distinguished from a trial run), whereby the thermal conditions will be maintained conducive to a maximum yield of the valuable by-products. In other words, the prior practice of adhering to a fixed schedule in controlling the factors determining the temperature existing in the gas collecting cavities is abandoned and such factors are steadily controlled during any run of the coke oven in dependence on the temperatures actually existing in the gas collecting cavities. Therefore, any tendency of the temperature existing in any particular gas collecting chamber to rise above or to drop below the optimum range of temperatures and to thus adversely affect the yield, will be immediately discovered and compensated for by a suitable adjustment of one or more elements, such as throttles, valves, burners, or the like, determining the temperature.

As a result, the re-setting of the various throttles, valves etc. controlling the temperature existing in the various gas collecting cavities will take place at unpredictable times other than those that could be fixed by a schedule, thus resulting in a truly optimum yield considerably exceeding the yield which prior to my invention Was deemed to be the best possible result, the adverse influence of uncontrollable factors on the yield being eliminated.

For the purpose of my invention temperature detecting elements referred to hereinafter detectors are installed in some or all of the gas collecting cavities allotted to the horizontally extending parallel chambers of the coke oven battery, such detectors indicating the thermal condition of any particular cavity and permitting of a control that guarantees any required, correction of the temperature. The elements controlling the temperature such as valves, throttles and the like may be operated manually or automatically by means of regulating equipment well known in the art.

In lieu of the summary control of the coal battery during a run the present invention provides for an individual control of the thermal conditions existing in the gas collecting cavities with the aid of detectors.

For the purpose of measuring the temperature existing in any gas collecting cavity, numerous kinds of instruments equipped with suitable indicating means may be used, for instance thermoelements, resistance thermometers etc. A detector which has been found to be particularly satisfactory consists of two rods or tubes having different ccefiicients of expansion, said rods being rigidly connected at one end thereof, the free ends being relatively movable. Such free ends will assume a relative position depending on the temperature. Such relative displacement of the free ends is utilized to operate pairs of electrical contacts. By relative adjustment of the contacts, the temperature may be determined at which any pair of contacts will be closed or opened. A detector of that type is inexpensive and is capable of withstanding rough treatment and, therefore, superior to such measurin instruments as millivolt meters or the like.

For the purpose of the present invention detectors of the kind just described are preferred in which one of the two rods or tubes consists of a ceramic material, whereas the other rod or tube is made of metal, the two rods being coaxially arranged. Preferably, only such part of the inner element is made of a material differing regarding its coefficient of its thermal expansion from the outer element as projects into the gas collecting cavity. As a result, only such temperature will be effective to operate the contacts depending on the longitudinal adjustment of the same, as actually exists in the gas collecting cavity, whereas the temperature existing in the wall of such cavity being subject to accidental fluctuations will not be liable to effect the operation of the contacts.

In the accompanying drawings I have illustrated a preferred type of detector and two coke ovens of well known types equipped with such temperature detectors for the purpose of practising my novel method. In the drawings:

Fig. 1 illustrates a vertical section thru the top of a as collecting cavity of a coke oven of the type consisting of a battery of horizontally extending parallel chambers, the top of the cavity being provided with a detector, such section being taken along line |--I of Fig. 4, the central part of said section being omitted.

Fig. 2 is a sectional plan view on a smaller scale of a coke oven of a type provided with a single manifold collecting vessel.

Fig. 3 is a sectional plan view similar to that of Fig. 2 of another type of such coke oven provided with two manifold collecting vessels, such section being taken along line 3-3 of Fig. 4.

Fig. 4 is a vertical sectional view taken along line 4-4 of Fig. 3.

The coke oven illustrated in Figs. 3 and 4 comprises a block of refractory material enclosing a battery of horizontally extending parallel chambers 36, 31, 38, 39 and 40. Above each of the chambers there is provided within the block a gas collecting cavity 3|, 32, 33, 34 or 35 respectively, which communicates with its chamber thru a plurality of ducts 4| distributed lengthwise of the chamber. Within the partitions separating the individual chambers 36 to 40, heating flues ar provided which for sake of simplicity have not been shown in the drawings. The chambers are charged with coal and are then heated by the supply of hot gases to such flues. The gaseous and volatile constituents driven out of the coal will flow thru the ducts 4| into the cavities 3| to 35. From there such gaseous and volatile constituents are discharged thru pipes 42 into a manifold vessel 43 connected by pipes 44, 45 and 46 to a fan 4! and from there thru a pipe 48 to another fan 49. The two fans will maintain a partial vacuum in the vessel 43 and will thereby withdraw the gases and vapors collected in the cavities 3| to 35. Within the pipe 46 a cooling apparatus 50 is inserted. A part of the cooled gases flowing thru pipe 48 is returned thru a pipe 5| to a second manifold vessel 52 communicating thru ducts 53 with the cavities 3| to 35. The quantity of cool gases thus returned into the gas collecting cavities 3| to 35 may be controlled by suitable adjustment of a butterfly valve indicated at 54. Moreover, the quantity of.

gases withdrawn from the gas collecting cavities may be controlled by suitable adjustment of a butterfly valve 55 provided within the tube 45.

Hence, it will appear that the average temperature existing in all of the gas collecting cavities may be raised by throttling the flow thru pipe 45 and/or pipe 5| while, inversely, the average temperature existing in the gas collecting cavities 3| to 35 may be lowered by unthrottling the flow thru pipe 45 and/or pipe 5|. Hence, the average temperature existing in the gas collecting cavities may be arbitrarily determined by suitable adjustment of the valve 54.

.An individual control of the temperatures existing in the different cavities 3|, 32, 33, 34 and 35 is similarly afforded by suitable adjustment of throttling devices 56 provided in pipes 53 and of throttling devices 51 provided in pipes 42.

Within a cycle of operation of such coke oven, that is to say within the so-called run, the function of the two manifold vessels 43 and 52 may be exchanged. For that purpose pipe 45 communicates with pipe 5| thru a pipe 58 containing a butterfly valve 59 and pipe 48 communicates with pipe 44 thru a pipe 60 containing a butterfly valve 5|. By closing valves 54 and 55 and by more or less opening valves 59 and 6|, the fans 4! and 49 will be effective to withdraw the gases from the gas collecting cavities 3|-35 thru the manifold vessel 52 and pipe 58, while cooled gases may be returned to the cavities thru pipe 44 and manifold vessel 43.

As stated above, the coke oven described so far with reference to Figs. 3 and 4 is well known in the art. For the purpose of the present invention, I have equipped each gas collecting chamber 3l-35 with two temperature detectors indicated at M, one being provided near either end thereof. Any of these detectors may be connected with an indicator which will immediately apprise the operator of any departure of th temperature from its normal range. When such abnormal condition arises, the operator may immediately so control the butterfly valves as to counteract the temperature fluctuation and as to maintain the temperature within the normal range. Sinc the coke oven, the various valves described and their function and operation is well known to anyone skilled in the art, a detailed direction stating which valves should be operated in any such case and how they should be operated is deemed dispensable herewith.

The coke oven illustrated in Fig. 2 differs from that shown in Figs. 3 and 4 in that a single manifold vessel I! is provided from which the gases are withdrawn by a fan It) thru a cooling apparatus I9, part of the cooled gases being returned by fan I3 and manifold pipe l2 to the cavities 2|-25, the butterfly valve l8 being pro vided to control the overall temperature in the gas collecting chambers, the individual control being aiforded by valves 62 inserted in the outlets of the manifold pipe l2 leading into the gas collecting cavities 2 |-25. In this instance, each cavity is provided with but a single temperature detector located near the outlet end of the cavity.

In Fig. 1 I have shown a preferred embodiment of the temperature detector. A metallic tube 13 closed at its lower end and provided with a flange R at its top is inserted in a hole S, provided in the top wall of the gas collecting cavity and is suitably attached therein, so as to project into the gas collecting cavity. The tube B may have a diameter of 0.5". In the tube B a ceramic tube A is inserted having its lower end rigidly connected with the bottom of tube B and having its upper end rigidly connected with a metal rod C, formed of the same metal as tube B. Preferably, the ceramic tube A has a length corresponding to that part of tube B, that projects into the gas collecting cavity. The upper end of th rod C is linked to one end of a lever 13 which is .pivotally mounted intermediate its ends on a shaft E, .the ends of which are journalled in the walls of a casing K. The free end of lever D carries a contact F made .of tungsten or a similar material. The casing K is rigidly connected with the flange R of tube B and is provided with two seats each slidingly accommodating an adjustable stem P, or Q respectively. The upper end of each .of such stems carries a knob, while the lower end carries a contact L, or M respectively, made of tungsten, or similar material. The lower portion of stem Q is so offset and bent as to hold its contact at in vertical alignment with the contacts F and L. Each of the elements carrying the contacts L, F and M is connected by a suitable wire to a terminal H, O and N respectively provided on the outside of the casing K.

On account of the difierent coefficients of expansion of the ceramic tube A and of the metal tube B, an increase of the temperature will result in an anticlockwise rocking of lever D. When the temperature exceeds a limit previously set by proper adjustment of stem P, the contacts L and F will be closed. When the temperature drops below a certain limit that may be predetermined by suitable adjustment of the stem Q, the contacts F and M will be closed.

While I have described a preferred embodiment of a temperature detector that has been found satisfactory, it will be readily understood that my invention is in no way limited to the use of that particular type of detector, since numerous other ways and means for measuring the temperature existing in the gas collecting cavities are available to anyone skilled in the art.

Preferably, the detector is effective to operate an indicator which will apprise the operator 1' mediately of any fluctuation of the temperature below or above a pre-determined range. I prefer to use a visible indicator, for instance lights of difierent colors. Two such lights and 53 are diagrammatically shown in Fig. 2, the light It being included by cable 15 in a circuit connected to the terminals N and 0, whereas il indicates another light connected to the terminals H and O. The light i6 is green indicating an excessive drop in temperature, whereas light i1 is red indicating an excessive increase of the temperature.

In the embodiment shown in 3, an indicating panel bearing the two signal lamps i it and i ll may be alternatively connected by a doublethrow switch 63 to the detector located near the pipe 53 or to the detector near the pipe 52 of gas collecting cavity 3|. The switch E3 is so set at any time that the detector located at the hotter end of the cavity, i. e. the end from which the gases are withdrawn, controls the indicating panel H6, H1.

In lieu of a single detector capable of controlling both the red lamp and the green lamp, two separate detectors may be provided in close proximity, one controlling the red lamp indicating excessive temperature and the other one controlling the green lam-p indicating insufficient temperatures.

In lieu of visible indicators, acoustic indicators or other indicating means may be provided.

Preferably, tube 13 projects into the gas collecting cavity a distance of about 6. In order to prevent the detector from injury coincidental to the charging of the chamber with coal or to the discharge of the coke therefrom, when the detector, as may be the case in certain types of ovens, projects into the combustion-chamber itself, the upper part of the latter thus constituting the gas-collecting cavity, means may be provided to lift casing K and the tube B connected thereto the requisite distance of for instance 6 and to keep it in lifted position for the duration of the charging or discharging period. Alternatively, tube B may be made so short that it will not project into the gas collecting cavity. In that event, the space inside the hole 5 and the tube 13 located above the ceramic tube A should be filled with a suitable heat insulating material to minimize the undesirable influence of the outside temperature on the operation of the detector.

Preferably, the detector is placed near the discharge end of the gas collecting cavity. Where two manifold vessels are provided, such as 43 and 52 in Fig. 3 which are alternatively operated as discharge vessels and as cooling vessels, preferably, either end of the cavity is equipped with a detector 14 as shown in Fig. 3, only one of such detectors being operated at any time to control the indicator. However, in that event a signal detector located near the center of the cavity may be substituted.

The measuring points may be so distributed over the entire battery that each cavity has at least one detector. In some instances, however, satisfactory results can be obtained by equipping part of the cavities only with detectors, for instance every other cavity or every third cavity. In that event, the cavities equipped with temperature measuring instruments will be interspersed between other cavities devoid of any detectors. Also, the arrangement may be such that any detector may be easily removed from one measuring point and inserted at another measuring point. In cases where cavities Nos. 1, 3, 5 etc. are equipped with temperature detectors, such detectors may be removed and inserted in the cavities Nos. 2, 4, 6 etc. after certain periods of time, for instance after three runs of the oven, such change being repeated continually. In that event, the valves 6?. are pairwise interconnected for joint control, such as the valves 52 allotted to cavities Nos. 1 and 2 or the valves allotted to the cavities Nos. 3 and 4.

While I have shown only one set of indicating lamps in Figs. '2 and 3 coordinated to the utmost left gas collecting cavity 2! or 31 respectively, it is to be understood that an individual indicator is allotted to any cavity equipped with one or more detectors. In order to practise my novel process, the operator must promptly react to the indication and so adjust the different valves 56 or 51 or '52 as to correct the temperature of any cavity where abnormal thermal conditions have been indicated by the visible indicator.

While I prefer to control the temperature by the admission into the cavities of comparatively cool gases, other suitable means may be provided, such as means controlling the heating fiues or burners in order to increase or reduce the heat supplied to the individual chambers.

My novel process consisting in the individual control of the cavities depending on the indication of temperature detectors is applicable to quite different types of coke ovens. The manual control of the diiferent valves or throttles may be replaced by an automatic control. Since numerous temperature regulating systems are well known and available on the market, it is not deemed necessary to illustrate or describe their use for the purpose of the present invention.

the green lights will 9 Broadly speaking, any such system includes power-driven means for adjusting the valves or throttles and means governing such power-driven means and controlled by the temperature detector.

The indicating lights [6, ll, or H6, H1 correlated to the different gas collecting cavities are preferably mounted on a single panel and are designated by numbers enabling the operator to immediately analyse any indication with respect to the particular cavity involved.

A specific mode of the operation of the coke oven illustrated in Figs. 3 and 4 will now be described as an example, but it is to be clearly understood that the same is not intended to limit the scope of my invention, but is capable of numerous modifications falling within the purview of the invention.

When the chambers 36 to 40 have been charged and heated to a degree where the temperatures existing in the gas collecting chambers 32 to 35 will exceed 700 C. indicated by the green lamps H6 being turned off, the valves 6! and 59 are kept closed while the valves 55 and 54 are opened and suitably adjusted. During that period of operation, the switches 63 of which one only is shown in Fig. 3 are set to the position opposite to that illustrated. After an expiration of four hours, valves 54 and 55 are closed, whereas valves 59 and GI are opened and properly adjusted. At the same time the switches 63 are shifted. Whenever the red light H1 is turned on, the operator will more or less unthrottle the duct 53 or duct #2 respectively of that particular cavity by a suitable adjustment of valve 56 or Valve 51 to admit more cool gases to the cavity, thus maintaining the temperature existing therein within the range of from 700 to 800 centigrades, corresponding to 129 to 1470 F. respectively.

Where a coke oven of an old type not yet pro vided with means for admitting cool gases to the gas collecting cavities is to be operated in accordance with my improved process, the temperature will be controlled by the application of heat at difierent levels of the chambers. As soon as an excessive heat is indicated in the gas collecting cavity by a red lamp, the operator will throttle the fuel supply to the burner on the upper lever. When the green lamp is turned on, however, it will increase the fuel supply to such burner.

A coke oven of the kind shown in Figs. 3 and 4 may also be operated in the following manner:

In the preliminary stages of a run only comparatively cool gaseous and volatile constituents will discharge from the gas collecting cavities. Such gases must be first re-circulated thru hot cavities. For that reason the cavities are first connected with the manifold vessel 43 or 52 respectively opposite to the discharge vessel. Since the temperature is still below the normal range, be turned on. As soon as any cavity reaches the normal range, the green light co-ordinateri thereto will be turned off. Now the operator connects the cavity with the other manifold vessel closing the communication with that previously connected. Upon further rise of the temperature, the latter may in some cavities cause the red lights to be turned on. Thereupon the operator will re-connect such cavities with the cooling vessel $3 or 32 respectively, whereby the temperature will be immediately reduced and the red light be turned ofi. Should the temperature drop below the desired 10 range, the green lamp will indicate the necessity of throttling the supply of cool gases.

My invention is equally applicable to ovens of the type in which the cooling gases are supplied from sources exterior to the coke oven.

Should the observation of the various detectors indicate a marked tendency of some cavity or cavities towards an excessive or insuliicient temperature, a remedy will be found in the simple step of increasing or decreasing the charge of the coordinated chamber in the following runs. Similarly, such tendency can be counter-acted by a suitable control of the heat supplied to the dues.

Having now described the nature of my novel process, I shall quote some figures illustrative of the result obtained in some instances with prior procedures in contrast to my novel process.

Case 1.With the battery comprising 50 horizontal chambers and with a single manifold vessel for the discharge of the gaseous and volatile constituents, a coke coal having 20% of volatile constituents was processed, the coal having a grade in which 75% would pass a sieve of 12 meshes per inch and having a water content of 10%. Each chamber has a capacity of 11 tons wet coal or 10 tons dry coal. A single run takes 20 hours. The average temperature in the gas collecting cavities was found to be 1000 centigrades. The yield of raw benzene amounted to 6,000 grams per ton dry coal.

Case 2.The same battery is provided with two manifold vessels in accordance with Figs. 3 and 4, one serving for the direct discharge of the gases and the other one serving to discharge some of the cavities indirectly thru other cavities, if desired with an intermediate cooling by injected ammonia water. Each cavity may be selectively connected with either manifold vessel by operation of valves, such as valves 55 and 51. Hence, gases which are too cool may be readily heated by conducting them thru hotter gas collecting cavities, whereas gas having insufiicient temperatures may be cooled by the admixture thereto of cool gases. By means of such operation a maintenance of the temperature between 700 and 800 centigrades is aimed at. In practice, part of the gas collecting cavities are equipped with thermometers indicating the rise of the temperature beyond the 700 limit coincidental to the completion of the initial heating phase. Upon such indication cool gases are admitted to all of the cavities until the development of hydrocarbons ceases. Hence, in this process cool gases are conducted to the cavities after the oven has been run for about five hours, such operation continuing for another eleven hours. Then the admission of cool gases is discontinued, since they might be adversely alfected. With such a schedule in which the cavities are connected for the first five hours with the cooling vessel only, from the sixth to the sixteenth hours with both vessels and in the last four hours with the discharge vessel only, the yield of raw benzene will increase to 6,600 grams per ton of dry coal. This process controlled in accordance with a fixed schedule is typical of the prior art.

Case 3.Now the same battery is operated in accordance with my invention, detectors being applied which will automatically watch any individual cavity. Independently of the length of the initial period, any cavity will be individually governed and will remain connected with the cooling manifold vessel until 700 C. are attained. When reaching a temperature between 700 and 11 800 C., the cavity is connected with the discharge vessel only. When this temperature is surpassed, the cavity ill be connected with bothv manifold vessels. soon as the temperature drops be neath the 90 limit, the supply of cool gases is reduced 0 entirely out oif. With this process which is strictly based on a continual measure ment of the temperatures, the yield of raw benzone increases to 7090 grams per ton dry coal.

While I have described my invention with reference to some specific forms thereof, I Wish it to be understood that the same is in no way limited to the details of such specific forms, but is capable of numerous modifications within the scope of the appended claim.

What I claim is:

A coke oven comprising a plurality of horizontally-extending, parallel, heated coking cham hers, a gas-collecting cavity communicating with each chamber, separate thermo-detectors mounted in at least a plurality of said cavities, means for individually exhausting the gaseous and volatile constituents that collect in each of said cavities, means for cooling said exhausted gaseous and volatile constituents, separate means for returning to each cavity cooled constituents, electrically operated temperature indicating means for each of said plurality of cavities, each- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,116,641 Reppekus May 10, 1938 2,260,111 Caldwell Oct. 21., 1941 2,458,489 Pinehard Jan. 4, 1949 2,5413% Van Ackeren Feb. 13', 1951 2,580,121 Nash Dec. 25, 1951 FOREIGN PATENTS Number Country Date 419,125 Great Britain Nov. 6, 1934 100,552 Germany Dec. 23, 1949

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