US2252810A - Method for carrying out endothermic gas reactions in regenerative gas heaters - Google Patents

Description

llg- 19, l941- H. KOPPERS ET Al. 2,252,810

METHOD FOR CARRYING OUT ENDOTHERMIC GAS REACTIONS IN www REGENERATIVE GAS HEATERS Filed Feb. 6, 1939 Patented Aug. 19, 1941 METHOD FOR CARRYING OUT ENDOTHER- MIC GAS REACTIONS IN REGENERATIVE GAS HEATERS Heinrich Koppers, Friedrich Totzek, and `Willy Linder, Essen, Germany, assignorsfbymesne assignments, to Koppers Company, Pittsburgh, Pa., a corporation of Delaware Application February 6, 1939, Serial No. 254,916 In Germany February 7, 1938 3 Claims.

The present invention relates to the carrying out of endothermic gas reactions at high temperatures, for instance the reaction of methane or methane containing gases with steam in forming carbon monoxide and hydrogen, or similar endothermic processes, where the gas or the gassteam mixture is heated up, in one operating period, to the reaction temperature in regenerative gas heaters, and the chequerwork of the gas heaters is re-heated, in another period, by hot combustion gases flowing in direction counter current .to the gas or gas-steam mixture to be converted.

When carrying out such endothermic reactions it was found that the temperature of the waste gases, which are to be extracted at the lower end by means of a normal cast iron grate, rises more towards the end of the re-heating period. After a certain time of the heating period has elapsed the temperature of the waste gases becomes so high that the castiron grate of the gas heater is vdangerously superheated.

Inorder to eliminate such deficiencies when performing such endothermic gas reactions, which take place at high temperatures in regenerative gas heaters, the invention provides for heating up the chequer work of the gas heater, during the heating period, in the reaction zone on one hand andin the preheating zone on the other hand by means of varying adjustable quantitles of heating gases so that the chequer work is charged with that quantity of heat in the two zones which corresponds to the heat required in each of said two chequer Work zones.

Preferably the invention is practically carried out in such a way that an adjustable part of the hot heating gases from the gas heater is drawn off from the chequer work at a point of increased temperature while the rest of the heating gases passes in the usual way along to the preheating zone up to the grate of the gas heater from where it escapes through the normal waste gas iiue.

Another feature of the invention consists in gradually increasing the quantity of the hot heating gases that is branched-ofi? from the gas heater during each heating period.

We will give now a detailed explanation of our invention.

It may be assumed that the chequer work of a regenerative gas heater is heated up in such a way as is usual for instance with the hot blast stove of the system Ccwper. In this case/the temperature of the chequer work shows practically a straight rise. The disccrdancies from ture. The quantity ofheat absorbed in this temperature zone of the chequer work of the well known hot blast stove corresponds substantially to the heat absorption by the zone. In other Words, such a quantity of heat is drawn of! from the chequer work in the lower zone of the chequer work, also called the preheating zone, as results from the specific heat of the gases and steam to be heated. 'I'his heat quantity practically equals the heat quantity which the heating gases are able to give-oil to the chequer work in heating-up the preheating zone.

As soon as the preheatedgas-steam mixture has reached such va temperature as. is necessary for the reaction, the heat required for the maintenance of the reaction is drawn-off from the chequer Work. Furthermore a certain heat quantity is still further taken off from the chequer work in the reaction zone in order to heat up the gas and gas-steam mixture and the reaction products, respectively, to a higher temperature so that the reaction may be carried out as completely as possible.

The total quantity of the heat drawn off from the chequer work in the reaction zone of the gas heater is considerably higher than the heat quantity which is needed for the normal heating up of non-reacting gases for instance for the hot blast in the `known blast stove. The drop in temperature of the chequer work during the reaction period in the reaction zone is considerably higher than in the corresponding zone of a hot blast stove. The chequer work must therefore be charged with a greater quantity of heat in the reaction zone. This involves a corresponding increase in the volume of the heating gas.

If the gas heater is heated up by leading an increased quantity of hot combustion gases vfrom the top to the bottom of a vertical gas heater through the chequer work much heat will be absorbed at first in the reaction zone owing to the great difference in temperature between the chequer work and the heating media. Therefore the temperature of the waste gas will be low at the beginning of the heating period correspondcould be observed in the heating period of a well constructed hot blast stove. The reason for this fact is that the volume of the heating gases coming from the reaction zone is too large for the heating of the preheating zone where less heat is absorbed. From this it results that a very great rise in the temperature of the waste gases takes place during the heating period.

If one draws off hot heating gases from the Cowper, for instance from a point between the preheating zone'andreaction zone, according to the invention it is possible to control the heat quantities which are supplied by the heating gases in the preheating zone in such a Wall that the highest temperature of waste gases permissible for the cast iron grate can be easily observed. 'I'he hot heating gases removed from the Cowper stove may `be advantageously used for the production of steam which is required for the reaction of the methane containing gas or the like. It is also possible to use the hot heating gases for the preheating of the combustion air or for the heating of other media.

It may be assumed that for the practice of the invention a vertical regenerative gas heater of the type of hot blast stove of the systemfCowper is made use of, wherein a methane containing gas is to react with steam at high temperatures.

The gas to be heated up may enter the'gas heater, at the bottom, with a temperature of 120 degrees centigrade. The maximum temperature which the gas-steam mixture and reaction gas, respectively, shall reach in order'to make the reaction as complete as possible may be l250 C. at the beginning and 1150 C. at the end of the reaction period. This diierence in temperature is due to the drop in temperature of the refractory chequer work'which serves as heat transmitter. As soon as the temperature of the reaction products has arrived at 1150 C. the regenerative system is reversed and the chequer Work of the gas heater is heated up again. This is performed in such a manner that hot combustion'gases are led from the top to the bottom of the gas heater. The temperature of the combustion gases entering the chequer work may be 1540 C. From a certain point of the chequer work zone in which a temperature of the heating gas of about 900 C. prevails, a regulable quantity of hot heating gases is drawn off. 'I'he quantity of the hot heating gases which is removed at this point from the heater may have a ratio of 1:2 to 1:3 to the total quantity of the heating gases entering the 900 C. zone. The exact quantity depends upon the construction of the gas heater, the losses in temperature, the kind of refractory material used and other factors.

AWith the described method of operation the Waste gas temperature rise may be held down to a temperature of from 150 C. to 300 C. and therefore remains far below the maximum which is permissible for the cast iron grate (about 4;00)./l

`It may be mentioned that the temperature of the waste gases leaving the gas heater would rise from 150 to 600 during the heating period in case the total quantity of the heating gases should be made to pass entirely through the gas heaterl without part of the gases being withdrawn from the chequer work zone of increased temperature. as shown in the preceding description of a preferred embodiment of the invention.

A further object of the invention is to provide useful improvements in the method described above in order to utilize the sensible heat of the waste gases leavingvthe gas heater with a compara-tively high temperature, and thus to increase the thermal eiliciency of our process.

The solution of this problem according to our invention consists in mixing the hea ing gases of a comparatively high temperature, that are drawn off from the gas heater, and which have not yet given off entirely their useful heat to the chequer work of the gas heater, which they are not allowed to do because the grate would be stressed too much, completely or partly with cold heating media and advantageously with cold combustion air so that this mixture is used again for heating the regenerative gas heater Where the reaction takes place. Under certain circumstances it is advantageous to provide for a further preheating of the hot mixture resulting from the mixture of hot combustion gases and cold heating media by means of a special gas heater, preferably regenerative gas heater, in order to arrive at the high temperatures which will ensure a high eflciency when carrying out the endothermic gas reactions.

The application of this feature of our invention offers the advantage that one can use a considerable amount of the existing heating gases within the process without extending the plant by means of special, more or less intricate, heat producer plants, such as recuperators, steam boilers or the like.

With the above and other objects and features of my present invention in view we shall now describe a preferred embodiment of our invention on the lines of the accompanying drawing.

On the drawing, a suitable installation for carrying out the invention is shown schematically in Fig. 1, and Fig. 2 likewise shows the grate.

The regenerative gas heater, constructed as a hot blast stove of the system Cowper, in which the- 1 which is connected with the combustion shaft by a pipe 8.

The air regenerator 1 has an air admissionv pipe I0 which joins the regenerator' at the bottom and which is controlled by a valve 9. The pipe I0 is in connection with a fan II. The suction side of the fan II is, on the one hand, connected with a controllable air inlet I3 equipped with a throttle valve I4 by means of the pipe-I2 and, on the other hand, with an outlet I6 governed by a shut-off means I5, which is arranged to communicate with the gas heater I at a certain height above the gas heater bottom in such a way that waste gases of a certain temperature may be drawn oiT from the gas heater.

vThe lower end of the gas heater I is, on the one hand, in connection with the stack flue I9 through the pipe I8 controlled by a valve I1 and',

on the other hand, with a pipe 28 which is'governed by a valve 2I.

The pipe 20 serves for the introduction of the reaction gases or gas mixtures which are to be treated in the gas heater I.

It may be assumed that the gas heater I has been heated up to a desired high temperature, in one` operation period, by means of the combustion of gas and air and the passing of the hot combustion gases through the chequer work. After the `chequer work is heated up the valve 9 is closed, as well as the pipe B through which the gas passes to the combustion shaft 5, and regenerator 1 is shut-off from passing air. Then the valve 2| is opened so that the reaction gas or the reaction gas-steam mixture flows from the pipe 20 into the inside of the gas heater I, packed with refractory chequer work, whereby a previous flushing of the heater can take place if necessary.

The reaction gases ascending in the gas heater I are heated up and react. The reaction products flow through the pipe 3 to the combustion shaft 5, and from there through the pipe 8 and the regenerator 1, and finally escapeat the lower end of the regenerator 1 through a pipe 23 controlled by a valve 22.

The heat still existing in the reaction gases can be utilized in a steam boiler 24 from4 which a pipe 25 leads to a blower 26 to which is connected a washer 21. The cooled and purified reaction gases may then be drawn off at 28 for further use.

As soon as the temperature in the gas heater I has dropped under the permissible degree, the admission of reaction gas through pipe 20 is interrupted by shutting the valve 2l. Then the shut-off valve 22 for the regenerator 1 is closed and the valves 9 and I5 as well as the pipe 6 are opened. The fan II sucks air through I3 and drives it into the regenerator I which has been heated up in the previous operation period by hot reaction product gases. In the combustion shaft 5 the hot air meets the fuel gas from the pipe 8. The combustion is practically finished in the combustion shaft 5, in the dome l and in the connecting pipe 3 sothat only burnt out gases flow into the gas heater I.

The hot gases give their heat off to the chequer work of the gas heater I as they go downwards. A part of the descending gases is sucked through the outlet I6 and the valve I5 by the fan II and driven into the regenerator I together with the air sucked in through I3. The gases leaving the outlet I8 may have a temperature of '700 to 900 C. Then the cold air entering through I3 will probably be preheated to about 250 to 300 C. by the hot waste gas. The fan II has of course to be of such design as to withstand such temperatures.

The 4rest of the waste gases continue to iiow on through the gas heater to the open valve I1 and to the pipe I8 and finally escapes into the stack flue I9.

The following operation period of the plant corresponds to the one which was described at first.

As the fuel gas to be introduced through pipe 6, rich gas (for instance coal distillation gas) or lean gas (for instance producer gas) may be used. In the case of rich gas, the admixing of flue gas to the combustion air is of advantage as the combustion is somewhat delayed and an undue superheating of the refractory lining near the burner is avoided. If, for the heating up of the gas heater, lean gas is used, the gas may be preheated; it is also possible to mix the lean gas j to be preheated with hot heating gases.

At the beginning of the heating period the temperature of the gases leaving the outlet IB is very low according to the invention; The temperature rises however, in accordance with the heating up of the reaction zone to a considerable extent. If necessary the quantity of hot waste gasesadded to the air is gradually increased still more. As the temperature gradually drops down in the regenerator 1, during' the heating period, one can compensate the`lo'ss by increasing the admixture of hot heating gases from I6 to the air. The loss in temperature results from the application of the regenerative principle fori preheating gaseous media.

We have` now described our present invention on the lines of a preferred embodiment thereof but our invention is not limited in all its aspects to the mode of carrying. it out as described and shown, since the invention may be variously embodied within the scopeof the following claims.

We claim:

l. A method of carrying out endothermic gas` reactions at high temperature in a tower-like regenerator having a checkerwork iiller which comprises: heating the gas to be reacted to the reaction temperature by passing the gas up- Y wardly through the checkerwork filler from the bottom to the top of the regenerator tower; preheating the gas in the lower part of the filler and subjecting the gas to endothermic reaction in the upper part of the filler; drawing the gaseous reaction products off from the top of the regenerator and owing them through anl external combustion zone; then reheating the regenerator checkerwork filler by passing hot combustion gases from the external combustion zone into contact with the filler in the regenerator downwardly therethrough; reheating the endothermic reaction zone of the filler in the upper part of the regenerator to a higher tempera-ture than the preheating zone of the filler in the lower part of the regenerator by passing the full quantity of combustion gases from said combustion zone in a stream through 'the endothermic reaction l zone of the filler in the upper part of the regenerator; reheating the preheating zone of the filler in the lower part of the regenerator to a lower temperature than the endothermic reaction zone in the upper part by withdrawing at an intermediate part of the filler a substantial portion of the stream of combustion gases from the regenerator and passing the remaining portion of the stream of combustion gases on through the lower preheating zone in amount controlled to reheat the same to the lower temperature without overheating the lower preheating zone; mixing the combustion gases withdrawn at the intermediate part with relatively cold combustion media for the external combustion zone; passing the mixture into the combustion zone during combustion therein and mixing in the upper part of the filler: 'drawing the gaseous reaction products on! from the top of the regenerator and flowing them through an exter` nal combustion zone and through the checkerwork filler of an external regenerator for preheating combustion media;l then reheating the regenerator checkerwork ller by passing hot combustion gases from the external combustion zone into contact with the filler in the 'regenerator downwardly therethrough; reheating the endothermic reaction zone of the ller in the upper part of the regenerator to a higher temperature than the preheating zone of the ller in the lower part of the regenerator by passing the full quantityl of combustion gases from said combustion zone in a stream through the endothermic reaction zone of the filler in the upper part of the regenerator; reheating the preheating zone of the iiller in the lower part of the regenerator to a lower temperature than the endothermic reaction zone in the upper part by withdrawing at an intermediate part of the iiller a substantial portion of the stream of combustion gases from the regenerator and passing the remaining portion of the stream of combustion gases on through the lower preheating zone in amount con-trolled to reheat the same to the lower temperature,` without overheating the lower preheating zone; mixing the combustion gases withdrawn at the intermediate part with relatively.cold combustion media for the external combustion zone; and passing the mixture of combustion media and combustion gases; withdrawn at the intermediate part through said external regenerator to further heat the mixture with the heat recovered from the gaseous reaction products before the mixture enters the external combustion zone, and thence passing said mixture to said combustion zone and mixing the same with extraneous fuel therein.

3. A method of carrying out endothermicgas reactions at high temperature in a tower-like regenerator having a checkerwork ller which comprises: heating the .gas to be reacted to the reaction temperature by passing the gas upwardly through the checkerwork ller from the bottom to the top of the regenerator tower; preheating the gas in the-lower part of the filler and subjecting the gas tol endothermic reaction in the upper part of the filler; drawing the gaseous reaction products off from the top of the regenerator and iiowlng them through an external combustion zone and through the checkerwork filler of an external regenerator for preator downwardly therethrough; reheating the endothermic reaction zone of the filler in the upper part of the regenerator to a higher temperature than the preheating zone of the ller in the lower part of the regenerator by passing the full quantity of combustion gases from said combustion zone in a stream through thev endothermic reaction zone of the ller in the upper part of the regenerator; reheating the preheating zone of the 1111er in the lower part of the regenerator to a lower temperature than the endothermic reaction zone in the upper part by withdrawing at an intermediate part of the iiller a substantial portion of the stream of combustion gases from the regenerator and passing the remaining portion of the stream of combustion gases on through the lower preheating zone in amount controlled to reheat the same to the lower temperature without overheatingthe lower preheating zone; mixing the combustion gases withdrawn at the intermediate part with relatively cold combustion media for the external combustion zone; passing the mixture of combustion media and combustion gases withdrawn at the intermediate part through said external regenerator to further heat the mixture with the heat recovered from the gaseous reaction products before the mixture enters the external combustion zone, and thence passing said mixture to said combustion zone and mixing the same with extraneous fuel therein; and gradually increasing the amount of the combustion gas that is withdrawn at the intermediate part and mixed with the combustion media to be preheated for combustion as the reheating period progresses and the temperature rises in the upper endothermic reaction zone of the ller in the upper part of the regenerator for the gas reaction, to compensate the temperature drop in the regenerator for further heating the combustion media for the combustion zone.

HEINRICH KOPPERS.

FRIEDRICH TOTZEK.

WILLY LINDER.

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