BE495086A - - Google Patents

Description

       

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  PROCESS FOR TRANSFORMATION OF GAS HYDROCARBONS9 AND APPARATUS THEREFOR-
This invention relates to the production of clean gas, after enrichment, for distribution in town gas pipelines, from gaseous hydrocarbon material. It relates more particularly to a cyclic process comprising a reaction between a gaseous hydrocarbon and water vapor, known as a transformation reaction, for the manufacture of a gas which is rich in free hydrogen and in products. oxidation of carbon, mainly carbon monoxide (00), and which, by suitable enrichment with a hydrocarbon gas,

   can replace any of the gases produced industrially today and distributed in town gas pipes.



   Natural gas, one of the most common gaseous hydrocarbons, is increasingly available, and in places relatively close to natural gas-producing regions, where the gas is used in its original state, such as collects it, the various combustion apparatuses are constructed and adjusted for its use and it is therefore not necessary to treat or transform the gauze.However, in localities where natural gas was not previously available, various Combustion appliances, such as burners on gas stoves, cooling appliances and heaters, have been constructed and regulated to burn a certain type of industrially produced gas, for example gas in water or coke oven gas.

   If one were to attempt to introduce natural gas into a system with appliances and burners constructed and rated for the combustion of natural gas, the slower burning characteristic of that natural gas would result, if the flame did not go out. not completely, to produce a lazy, smoky flame, which would be dangerous due to incomplete combustion and the release of toxic carbon monoxide.

   Changing all the appliances to adapt them to burning natural gas in its initial state is an expensive operation and would not be practical when there are cold peaks in winter! require an increase in the supply of industrially produced gas having a characteristic

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 combustion faster, because the construction of natural gas distribution pipelines of satisfactory capacity for peak service is prohibitively expensive.

   Consequently, the increasing quantities of natural gas, available as a source of supply to the distribution systems of public utility companies for domestic and industrial uses, have led to the problem of transformation or con - version of natural gas in a product having characteristics suitable for its use as a component of a mixed gas for distribution with gas produced industrially in town gas pipelines. The advantage of such a transformation of natural gas with a view to obtaining suitable combustion characteristics also applies to other gaseous hydrocarbons, such as ethane, ethylene, propane, etc. butane and the like, and to gases rich in hydrocarbons, such as refinery gases.



   The transformation of a gaseous hydrocarbon has heretofore been carried out for the most part by passing it through a coke fire, preferably with a mixture of water vapor. In this way, thermal cracking occurs, with the formation of hydrogen and carbon. However, only a small part, or no part of the carbon contained.

   in the gaseous hydrocarbon, is converted directly to carbon monoxide (CO) in the vapor phase, although some of the deposited carbon can be converted to carbon monoxide and hydrogen by the reaction of water vapor with it. hot coke bed. However, in general, the carbon which is deposited in the bed is consumed by blowing on the window. On the other hand, the carbon which comes out with the gas clogs the gas pipes and the condensing devices and must be removed from the gas by water spray or be electrically precipitated, with considerable additional expense. Furthermore, this carbon is obviously lost to the gas manufacturing process.



   It is known that gaseous hydrocarbons can be reacted with water vapor to release hydrogen and at the same time form carbon monoxide by combining the carbon of the hydrocarbon gas with the carbon dioxide. oxygen from the water vapor, and releasing additional hydrogen from the water vapor, but the existing methods have certain disadvantages.

   For example, catalysts have been employed to allow the reaction to take place at a temperature below that at which thermal cracking occurs to avoid the production of carbon as a final product. The plant hitherto employed for the conversion catalytic hydrocarbons with water vapor is very expensive, It consisted mainly of tubes or. retorts made of quality alloys, filled with catalytic material and heated from the outside in a furnace. Hydrocarbon gases and water vapor are continuously passed through the catalytic material, with production of hydrogen, of carbon monoxide and small proportions of carbon dioxide. As mentioned, the process carried out in such an installation has certain drawbacks.

   Thus, the temperature of the catalyst is maintained by conduction, through the tubes, of heat from the furnace, to provide the heat of formation of the gas and its sensible heat. The conduc- tivity of the catalytic material in the state of particles separate is not high, so that the metal tubes or retorts, if the catalyst is kept at a high temperature, for example from 870 C to 980 C must be brought to a temperature which is not much lower than the temperature maximum safety of the tubes made of the most resistant alloys, and which is necessarily higher than the reaction temperature of the catalyst, In addition, since the particle-to-particle conduction of the catalyst is poor,

   the temperature of the catalyst at the location closest to the wall of the tube or retort is higher than the temperature at the center, giving a non-uniform temperature across the tube or retort. In addition, tubes made of quality alloys are not only expensive and require considerable maintenance costs, but the large number of tubes requires a large number of valve fittings and measuring instruments. flows which, in turn, increase the price of the installation.

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   Because of these difficulties inherent in a continuous process for converting hydrocarbon gas by external heating, various cyclic processes have been proposed from time to time. One of these methods involved the use of a catalyst bed, over which burning gases were alternately blown, to store heat in the catalyst, after which the hydrocarbon was passed. gas and water vapor through the catalyst bed to effect the transformation.

   However, by this method, in order to avoid destruction of the catalyst bed by excessive combustion temperatures, the amount of heat stored in the catalyst bed was limited, which resulted in the vapor d. The colder incoming water and hydrocarbon gas, coupled with the high heat requirements of the transformation reaction itself, rapidly cooled the catalyst bed to temperatures below the reaction temperature and produced variations. As the heat, necessary to bring the reactants to the reaction temperature and for the resulting endothermic reaction, was supplied by the heat stored in the catalyst bed.

   excessively large amounts of catalyst were needed, which is very expensive. In addition, in many of these earlier cyclic processes, relatively large amounts of carbon and other combustible materials were deposited on the catalyst, decreasing its activity and clogging the gas channels through the catalyst bed. .



   The object of the present invention is to obtain a process for the treatment of gaseous hydrocarbon material, in particular natural gas, and of water vapor so as to produce a combustible gas suitable for use as a constituent element of a gas for distribution in town gas pipelines in which industrially manufactured gas has previously been distributed, this process not having the disadvantages of the thermal cracking process or of the catalytic conversion processes currently known.



   Another object of the invention is to obtain a process by which natural gas can be converted economically and efficiently into a clean gas rich in free hydrogen and in which the carbon contained in the hydrocarbon used for the reaction exists at the gaseous state, mainly in the form of carbon monoxide, and in which no appreciable proportion of free carbon or other solid combustible material is formed during the process,
Another object of the invention is to obtain a process for the production of a fuel gas which is free from carbon particles and which can be mixed with another gas so as to:

  produce a gaseous product that can replace water-based gas or coke oven gas produced commercially in utility company gas distribution systems.



   Still another object of the invention is to obtain a relatively inexpensive apparatus of high capacity for carrying out the process described above of a construction in which an existing gas production plant. can be converted easily and economically.



   In accordance with the process according to the invention, a hydrocarbonaceous material which is normally gaseous, that is to say exists in the gaseous state under the conditions of temperature and is catalyzed with water vapor. atmospheric pressure. In addition, air preferably also participates in the reaction. As a result of the transformation or conversion reaction, a gas is obtained which is rich in free hydrogen and containing carbon in the form of. gaseous oxides, mainly carbon oxides (CO-
The process involves the use of a cycle comprising a stage or period of heat storage, in which hot combustion gases -

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 tion, formed by the combustion of a fluid fuel.

   are entrained through a heat storage material and then through a catalyst bed for the transformation reaction, i.e. a catalyst for the endothermic reaction between gaseous hydrocarbons and vapor. water, so as to heat the heat storage material and the catalyst by direct contact with the combustion gases, - and a stage or period of transformation, in which the gaseous reactants, i.e. the hydrocarbon gas and the water vapor, or hydrocarbon gas, water vapor and air are heated by the heat accumulated in the heat storage material and then react in the presence of the catalyst.

   Such a mode of operation may be referred to as a cyclic process, thus, in part of the cycle, fluid fuel is burned in a combustion chamber and the hot products of combustion are passed through a zone filled with material. heat storage and then through a zone containing the catalyst, to store heat therein and provide the heat necessary for the process.

   In the other part of the cycle, the reaction hydrocarbon gas, mixed with water vapor, and in the preferred embodiment also with air is passed first through the containing zone. the heat storage material, which serves as a pre-heating zone, to raise the temperature of the mixture to the reaction temperature, and then through the zone containing the catalyst, in which the reaction takes place, in producing a clean gas, in which the hydrogen of the reaction hydrocarbon has been set free and the carbon of this by-carbon has been combined with the oxygen of the water vapor (and of the air, if one uses this), so as to form carbon monoxide and carbon dioxide.

   It will be seen that before the reactants are brought into contact with the catalyst, they are mixed and preheated uniformly in a preheating zone containing the heat storage material, which is heated by the gases. of combustion in the period of the cycle corresponding to the heat storage.

   As will be discussed more fully below, the gas produced during the period of the cycle corresponding to the transformation reaction, will be, before distribution as town gas, mixed with a predetermined portion of hydrocarbon. normally gaseous to give the desired calorific value,
The method also includes certain advantageous arrangements, whereby the hot products of combustion, used for the heat storage during the cycle period corresponding to the heat storage, are controlled so as to maintain the heat storage. catalyst in a high state of activity, and by which the products of combustion, advantageously constituted by products of incomplete combustion, formed during the period of heat storage,

   are mixed in determined proportions with the transformed gas, produced during the period of the cycle corresponding to the transformation reaction, so as to give a gas mixture having characteristics suitable for distribution in regions supplied with industrially manufactured gas, after enrichment by a hydrocarbon gas,
As, in the process according to the present invention, the heat supply is from the inside with respect to the heat storage material and the catalyst bed, tubes or retorts, heated from the outside. and expensive, are not required to contain the catalyst, and one or two large refractory lined vessels to determine the combustion chamber, heat storage enclosure, and catalyst bed,

   will suffice to constitute a plant with a large production capacity., In addition, since the combustion gases and the reaction gases follow the same paths in the same direction during the respective parts of the cycle, no Expensive valves to operate in a hot state which have given rise to numerous problems in some prior gas production systems. A small number of large pipes will replace the manifolds with the multiple connections required for an installation with many tubes or retorts.

   The control devices are likewise simplified, and the cyclic change of valves can be produced by the established automatic control method.

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 for many years in the gas-to-water art. In addition, the cycle system is more sensitive to thermal control, because temperatures can be set within minutes, unlike a furnace. continuously heated tubes or retorts, for example, which requires considerable time to make the desired changes.

   As the reactants are preheated to reaction temperatures before reaching the catalyst bed, extensive and rapid temperature changes in the catalyst bed are suppressed and smaller amounts of catalyst are required than would be required. the case if one relied on the heat stored in the catalyst mass, to heat one or more of the reaction gases to the reaction temperatures and also to provide the heat necessary in the endothermic reaction.



   Another advantage of the method described lies in the ease with which existing installations for the production of gas with carburized water can be suitably and rapidly transformed so as to be able to be used with the method according to the invention.



   The accompanying drawing schematically shows an apparatus in which the method according to the present invention can be carried out.



   In this drawing, 1 shows a chamber lined with a refractory lining, which may be the superheating apparatus of a common gas-to-water installation with appropriate modifications appearing from the drawing. 2 represents the combustion chamber, which may simply be an enclosure preceding the heat storage zone 3. This heat storage zone 3 consists of heat accumulating refractory bodies, such as refractory bricks arranged in stacks in the usual way, in 14 or in pieces of refractory material 15, arranged at random or, as shown in the drawing, in a combination of these two means.

   The heat storage material can be supported by a vault made of refractory bricks 16 The heat storage zone 3 advantageously consists of layers of different refractory parts supported on a vault formed by a stack of bricks, the parts located closest to the stack being relatively coarse pieces and supporting a thicker layer of smaller pieces, advantageously of a material of better thermal conductivity, such as sintered silicon carbide.

   The catalyst bed is shown at 4 and can be supported by a vault 17 made of refractory bricks. 5 and 6 respectively represent the air and fluid fuel supply conduits for combustion intended to heat the appliance, and 7 represents the valve of the chimney through which the gases having been used for heating can be evacuated. in the atmosphere, or be brought to a boiler heated by these gases (not shown) before being discharged into the atmosphere.



  The supply lines for the natural gaseous hydrocarbon and the water vapor, intended to be introduced into the pre-heating zone at a place close to the combustion zone, so that the reactants pass through the bed of preheating material and the catalyst bed in the same direction as the hot combustion products, are shown at 8 and 9, respectively, and the air supply line for the treatment, if used, is shown in 10. The gas leaves the reaction chamber via line 11, passes through washing box 12 and goes via line 13 to the storage location. In accordance with the known manufacturing procedure. gas,

   the gas leaving the reaction chamber for storage may pass through a boiler heated by the combustion gases (not shown) before reaching the washing box.



   The operation is, as specified, cyclical and the method first comprises a heating or blowing period, during which air and a combustible fluid are admitted through lines 5 and 6, respectively, the combustion taking place in the combustion chamber. combustion chamber 2. The hot combustion gases pass through the pre-heating or heat storage zone 3, which brings it to a temperature above the

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 temperature necessary for the transformation reaction, and then pass through the catalyst bed at a somewhat reduced temperature, and can then be discharged through the valve 7 of the stack.



  After the installation is heated to operating temperature, - the valve 7 of the chimney is closed and the pipes 5 and 6 for supplying air and fluid fuel are also closed. At the same time, the conduits 8 and 9 are opened to admit respectively the gaseous hydrocarbon and the water vapor intended to react with the hydrocarbon. If desired, and in accordance with the preferred embodiment, air can also be admitted for treatment by opening line 8.

   The use of this air has the advantage of helping to maintain operating temperatures, to keep the temperature variation to a minimum and to increase the gas production of the apparatus. These reaction gases are subjected to preliminary heating, substantially up to the reaction temperature - which, as will be discussed more fully below, will be a temperature below that at which the thermal cracking takes place - by their passage. through the pre-heating or heat storage zone, absorbing heat therefrom.

   After leaving the preheating zone or heat storage zone, the reaction gases enter the catalyst bed, where the following typical reactions take place (during the transformation of natural gas) (1) with steam. 'water: CH4 + H2O = 3H2 + CO 49.45 calories per mol-gr.



  (2) with air: CH4 + 1/2 O2 + 1.9 N2 2H2 + CO + 1.9N2 = 7.33 calories per mol-gr.



   Although the drawing shows only one device, it is understood that an installation comprising two or three of these devices can be used by following the same general principles described above. For example, it is possible to use the carburizing apparatus and the superheating apparatus of a current installation for the production of gas with carburized water, these apparatuses being connected at their lower part by an open pipe. carrying out the process according to the invention with this installation, it is possible to admit the fluid fuel and the air to the upper part of the carburizing apparatus, where the combustion takes place, the hot products of the combustion descending through the 'carburetion device,

   passing through the conduit connecting this to the booster heater and rising through the preheating and catalysis zones, as described. Similarly, in such an installation, the reaction hydrocarbon gas, water vapor, and process air if used, can be admitted to the upper part of the fuel apparatus, descend through the carburizing apparatus, pass through the pipe connecting this to the lower part of the superheater and ascend through the preheating and catalysis zones, as described.

   Any stack contained in the carburizing apparatus will function as part of the preheating zone. Similarly, in a three apparatus plant, also employing the generator of a common gas production plant at the same time. If water is fueled, the generator can serve as a combustion chamber, and the various materials can be admitted into the generator, going to the upper part of the carburetion apparatus through the open pipe connecting the upper parts of the generator and from the carburizing unit, then from the latter to the superheating unit, as described therein.



   It will further be understood that, in accordance with the current gas production procedure, steam purges can be carried out, and preferably carried out between the periods of the cycle corresponding to the heating and to the production of gas, or between the periods of the cycle corresponding to gas production and heating, or both. These purges, as is well known in the gas manufacturing art, serve to rid the system of unwanted gases, which can contaminate the produced gas, or serve to discharge useful residual gases back to the environment.

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 right of storage.



   Catalysts for the endothermic reaction of gaseous hydrocarbons with water vapor to produce gas mixtures comprising free hydrogen and carbon monoxide, with varying proportions of carbon dioxide, are well suited. known. The catalysts most frequently proposed for this purpose are metals of the iron group, with nickel and cobalt based catalysts usually being preferred, although other high melting point metals have also been employed. , such as vanadium, chromium, platinum and the like. With regard to nickel and cobalt, nickel-based catalysts have usually been employed, because the reaction is easier to control and nickel-based catalysts are less expensive.



   Frequently, a suitable refractory support is employed, on the surface of which the catalytic material is deposited or through which it is distributed. Hardly reducible oxides, such as alumina, silica, magnesia, calcium oxide, titanium oxide, chromium oxide, oxides of rare earth metals such as, for example, thorium oxide, cerium oxide and / or others, may be present. Compounds such as chromates can be employed.



   A process for the preparation of the catalyst comprises precipitating the catalyst as a salt on a finely divided support material, calcining to produce the oxide of the catalytic metal, agglomeration in the form of balls or balls. or shaping to other shapes by extrusion from a paste of the calcined material, and reducing the oxide at elevated temperature to a metal catalyst, either as a phase in the preparation of the catalyst or after it was installed in the gas treatment plant.

   In the preparation of another type of catalyst, pre-shaped refractories, such as alumdum balls and the like, are impregnated with a salt of the catalytic metal, and the shaped bodies thus impregnated are then calcined to form the oxide. of the metal, which is then reduced. The catalyst employed can be produced by any desired process which does not form part of this invention.



   The gaseous hydrocarbon material, transformed during the period of the cycle corresponding to the production of gas, may consist of normally gaseous hydrocarbon material, such as for example methane, ethane, propane and / or butane. Corresponding unsaturated hydrocarbons can be present in any desired concentration, for example in the form of ethylene, propylene, butylene, etc. The other conditions being the same, it is preferable to employ a saturated hydrocarbon material, preferably. a paraffinic material Natural gas, which consists mainly of methane, and refinery oil gas, which consists mainly of methane and ethylene, are among the hydrocarbon materials that can be used.

   Natural gas is particularly preferred as the reaction hydrocarbon because of its readily available.



   As regards the fuel employed during the period of the cycle corresponding to the heat accumulation, it may consist of any fluid fuel, i.e. gaseous or liquid fuel.



  Gaseous hydrocarbons, such as those mentioned above, and more especially natural gas, are particularly satisfactory, although a gaseous fuel which is not rich in hydrocarbons, such as petroleum gas, can also be employed. water, gas generator and the like. Liquid hydrocarbons, such as fuel oil, gas oil, gasoline, kerosene, tar and the like can also be employed, if desired. In the event that a liquid fuel is employed, a common spray or vaporizer can be used to aid combustion.



   The proportions of reaction gas hydrocarbon and water vapor, employed during the cycle period corresponding to the transformation reaction, generally vary between about 0.8 mol and about 5 months, and preferably between about 1.5 and about. 2.5 mols of water vapor per 1 mol of carbon in the reaction hydrocarbon ,, When

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 air bends during the period of the cycle corresponding to the reaction of
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 transformation, we can reduce the proportion of water vapor to 1-hydrocarbide and we can go down to:

   about 0.8 mol of water vapor per 1 mol of carbon in the reaction gas hydrocarbon.
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 As mentioned., In accordance with the preferred embodiment of the process, a little air is employed during the cycle period corresponding to the transformation reaction. The proportion of air thus employed will be lower.
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 less than about 2 mols from this # Í. polish 1 mol of carbon in the gaseous hydrocarbon reaction., and, in most cases., will be less than en-
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 about 1 mol of air per 1 mol of carbon in the reaction hydrocarbon. Preferably, the proportion of air, employed during the period of the cycle corresponding to the transformation reaction, is between approximately 0.1 and approximately 0.6 mol of air per 1 mol of carbon in the reaction hydrocarbon.



   With regard to the temperature conditions employed during the cycle, the reactants, as mentioned, should be heated to substantially the reaction temperatures by passing them through the heat accumulating zone and prior to their being. passage through the catalysis zone. The main considerations are therefore that the reaction gas hydrocarbon, while being heated to a sufficient degree to achieve substantially complete reaction thereof in the catalysis zone, should not be.
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 not heated to a degree where there is a significant thermal cracking ... "" 1g thereof, with formation of any amount of carbon in the preheating zone.

   The exact temperature conditions determining these considerations will depend in part on the particular reaction hydrocarbon gas employed. It has been found, for example, that when natural gas is converted, the average temperature of the material d The heat build-up in the pre-heating zone should not exceed approx. 1095 C, nor should it drop below approx. 760 C.



  In other words, the heat-storing material will have., At the start of the
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 period of the cycle corresponding to the transformation reaction, a temperature which should not be higher than about 1095 ° C., at the end of the period of the cycle corresponding to this reaction of tq: .zsfor..at .on9 a temperature which must not be lower than approximately 760 C. In order to ensure a period of transformation of reasonable length, when it comes to the transformation of natural gas ,. the average temperature of the heat accumulating material at the start of the cycle period corresponding to the transformation reaction will not be less than about 815 ° C.

   Due to the fact that the hot combustion gases, during the cycle period corresponding to the heat build-up, pass first through the heat build-up material and then through the catalyst zone, the Catalyst temperature at any one time will normally be somewhat lower than the average preheating zone temperature, and generally the temperatures in the catalyst bed, at the start of the transformation period. in the case of the transformation of natural gas and with reference to the temperature limits mentioned above, will not exceed about 980 C and may, -down to about 705 C.

   In the case of the transformation of gaseous hydrocarbons heavier than methane, it
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 It may be advantageous to employ somewhat lower temperatures in the preheating zone to avoid thermal cracking, since the conversion of hydrocarbons heavier than methane may not require temperatures as high as when they are 'is the transformation of methane. Thus, for the conversion of hydrocarbons heavier than methane, temperatures as low as about 537 ° C. can be employed in the pre-heating zone.



   With particular reference to the cycle period corresponding to the heat build-up, the present process is carried out, as mentioned, by burning a fluid fuel and passing the hot products of combustion in series through. the heat accumulation zone and the catalysis zone. The period of the cycle corresponding to the heat accumulation can be carried out by burning the fuel with an ex-

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   these air, or with -j.1 the quantity of air insufficient to assure complete combustion, or with just the quantity of air theoretically necessary for complete combustion, as long as the heat accumulating material and the catalyst are brought to the necessary temperatures.

   However, according to a preferred embodiment of the process, at least the last part of the period of the cycle corresponding to the heating is carried out by burning the fuel with an insufficient quantity of air to ensure complete combustion, thus generating products. combustion substantially free of free oxygen and having a significant content of hydrogen and carbon monoxide in addition to their carbon dioxide, water vapor and nitrogen content. This ensures that the catalyst is maintained in a highly active state.

   The proportion of air employed during a heat storage operation of this type will usually be less than 95% of that theoretically required for the complete combustion of the particular fuel employed, and may drop to about 70%. of that required for complete combustion. The products resulting from combustion supply heat to the heat storage material and the catalyst by direct contact therewith, without danger of oxidation of the metal catalyst.



  Preferably, the combustion, during such a heat storage operation, is incomplete enough to produce combustion products which are reducing with respect to the oxide of the metal catalyst, in order to promote combustion. presence, at the start of the part of the cycle corresponding to the transformation reaction, of contact surfaces of highly active elementary metal catalyst, instead of the oxide of this metal catalyst, while at the same time obtaining a good practical yield in the use of fuel. So,

   the amount of air employed during such a storage operation is preferably between about 85% and about 93% of that theoretically required for complete combustion of the particular fuel employed.



   As indicated above, according to a preferred embodiment of the present process, at least the last part of the cycle period, corresponding to the heat accumulation, is carried out by burning the fuel with an insufficient proportion of air for the heating. Complete combustion, Although the entire period of the cycle corresponding to the heat accumulation can be conducted in this way, it is particularly preferable to conduct the first part of the cycle period corresponding to the heat accumulation by burning the fuel with excess air, so that the combustion gases contain free oxygen, and to conduct the last part of this period of heat accumulation by burning the corner - bustible with an insufficient proportion of air to ensure complete combustion,

   as described. In this case, the proportion of air employed during the first part of the heat accumulation period will usually be at least 2% in excess of that required for complete combustion of the fuel, and may in some cases case go up to about 50% in excess of that necessary for complete combustion. In most cases, an excess of air, in an amount between about 5% and about 15% of that theoretically necessary for the complete combustion of the fuel, gives satisfactory results.

   The use of an excess of air, in the first part of the period of accumulation, of heat, in order to obtain a maximum efficiency of combustion, to shorten the flame and thus to obtain greater heat in the zone of combustion, and also to ensure the removal of any traces of combustible material which may have accidentally settled on the refractory material and the catalyst, However, by the process according to the invention, as already mentioned, very little combustible material is deposited, or not at all. Generally speaking, in this two-stage heat build-up period, the heat build-up stage, in which excess air is used for combustion,

   can extend over a part between approximately 15% and approximately 50% of the total period of the cycle corresponding to the heat accumulation. The remainder of this period of the cycle corresponding to the heat accumulation will, in this procedure, be the stage during which, as described, an insufficient proportion of air is employed to ensure complete combustion.

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   With regard to the gas produced during the period of the cycle corresponding to the transformation of the gas, this gas mainly comprises hydrogen and carbon monoxide, with small but variable proportions of gaseous hydrocarbons and carbon dioxide and with variable proportions of nitrogen depending on the proportion of air used during this period of the cycle corresponding to the transformation. Although this gas is combustible, it does not have the characteristics which would allow it to be used by itself as town gas. For example, its calorific value will be lower than that required for use in town gas distribution systems.

   Therefore, before the gas produced during the cycle period corresponding to the transformation is distributed as town gas, it must be enriched with gas having a higher calorific value than that desired in the mixed gas. Such an enrichment gas may consist of any one of the gaseous hydrocarbons mentioned above and in particular of natural gas.



   However, in many cases the simple enrichment of the gas produced during the period of the cycle corresponding to the transformation with a gas of a higher calorific value does not give a mixed gas having all the characteristics required in a gas. particular region. For example, although one can obtain -a mixed gas, having the desired calorific value, by mixing, for example, natural gas with gas produced during the cycle period corresponding to the transformation reaction, the specific gravity mixed gas may still be less, and / or the ratio of hydrogen to inert components may still be greater than the conditions required in a particular region.

   Or, it may be advantageous to use, as a component of the mixed gas distributed, coke oven gas, due to the fact that the latter is readily available in a particular region. Since the coke oven gas is relatively rich in hydrogen, its mixture with the gas, which is produced during the cycle period corresponding to the transformation reaction and which is also rich in hydrogen, would result in a ratio of the hydrogem and the inert constituents much higher than necessary.



   For these reasons, it is frequently desirable to also mix with the gas produced during the cycle period corresponding to the transformation reaction a determined amount of a gas having a high specific weight and a low ratio of the gas to the gas. hydrogen and inert constituents. Such a gas can be produced by the combustion of a hydrocarbon, preferably in the presence of an insufficient proportion of air to ensure complete combustion. A particularly advantageous gas from this point of view is the product of incomplete combustion obtained during the stage of the heat accumulation period described above during which a fluid hydrocarbon fuel is burned in the presence of a proportion of air. insufficient to ensure complete combustion.

   Accordingly, in accordance with another embodiment of the present invention, at least a portion of the heating gases resulting from the combustion of the fluid hydrocarbon fuel is mixed in the presence of an insufficient proportion of air to ensure combustion. complete during the period of the cycle corresponding to the heat accumulation, with the gas produced during the period of the cycle corresponding to the transformation reaction, so as to obtain a mixed gas which, when enriched, as described herein above, and that it is mixed with coke oven gas, if desired, will satisfy the conditions required in the region where industrially manufactured town gas is used, and which can therefore replace industrially manufactured city.

   According to this embodiment of the invention, although the products of incomplete combustion, formed during the period of heat accumulation of the cycle, can be evacuated and brought to a storage vessel, separate from that to which the combustion is conducted. gas produced during the period of the cycle corresponding to the transformation reaction, it is preferable to conduct the desired amount of these products of incomplete combustion directly to a common storage vessel, in the same manner as this is done for the gas produced during the period of the cycle corresponding to the transformation reaction.

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 mation, that is to say through line 13 passing through line 11 and washing box 12.



   The exact proportions of enrichment gas, and combustion products, if any, and coke oven gas, if used, mixed with the gas produced during the corresponding cycle period to the transformation reaction, to obtain a final gas suitable for distribution as town gas., are subject to variation, not only according to the conditions to be satisfied but also according to the exact characteristics of the enrichment gas, and gas produced during the cycle period corresponding to the transformation reaction, and also combustion products and coke oven gas, if used.

   In general, town gases manufactured industrially have a calorific value of between approximately 4,625 and 5,070 calories per m3, a specific weight of between approximately 0.45 and approximately 0.75 and a ratio between hydrogen and inert constituents included between about 1; 1 and about 6: 1.

   On the other hand, the gas, produced during the period of the cycle corresponding to the transformation reaction, will have a calorific value lower than that mentioned above, for example about 2,670 calories per m3, a specific weight included in or somewhat below the range mentioned above (e.g. 0.35 and a ratio of hydrogen to inert constituents within or somewhat above the range specified above (e.g. 10:

  1). The enrichment gas will have a calorific value well above that required, the natural gas having a calorific value of approximately 9,340 calories per m3, a specific gravity of approximately 0.61 - 0.63, and a ratio of hydrogen to inert constituents equal to zero, since it is usually free of hydrogen.



   The product of incomplete combustion will have a calorific value well below the range mentioned above and which may even be less than 890 calories per m3; its specific weight will be well above the specified range, frequently close to 1; andits ratio of hydrogen to inert constituents will be well below the stated range.



   It will be seen that although the proportions of the various gases to be mixed with each other can vary to a great extent, determining the exact proportions required in any particular case will not present difficulty to the gas technician. and that we can get there by a simple calculation. By varying the proportions of the reactants, in particular the gaseous hydrocarbon and the water vapor, or the gaseous hydrocarbon, the water vapor and the air, used during the period of the corresponding cycle At the transformation reaction, the various characteristics of the resulting gas can be determined as desired.

   In addition to these variables, by varying the proportion of combustion products, such as the products of incomplete combustion formed during the period of the cycle corresponding to the accumulation of heat which can be mixed with the gas produced during the period of cycle corresponding to the transformation reaction, it is possible to act additionally on the characteristics of the resulting mixed gas. In any event, it will be seen that the present invention provides a very flexible process for producing a gas which can replace any industrially manufactured town gas, or which is suitable for being mixed with other gases to satisfy under varying conditions encountered in the town gas industry.



   The invention in its more general aspect, as well as the preferred embodiments described above, will be better understood by the description of the following specific examples, which are given for explanatory purposes only and which are not intended in any way. to limit the scope and the scope of the invention.



    EXAMPLE 1
The reaction apparatus employed is the superheating apparatus of a current installation for manufacturing gas with carburized water, the generator and the carburizing apparatus being omitted; fuel, air, va-

 <Desc / Clms Page number 12>

 afraid of water and the reaction hydrocarbon are admitted to the lower part of the superheater, as shown in the drawing. The reaction apparatus contains 4.075 m3 of pieces of silicon carbide arranged at random, to a depth of 0.685 m, supported on a refractory brick vault, and 8.65m3 of refractory bodies, impregnated with nickel, supported on a refractory brick vault, as shown in the drawing.



   A 1.5 minute cycle was used, of which 44% corresponded to the heat build-up period, 51% corresponded to the gas transformation period, and 5% corresponded to a steam purge.



   During the period of heat accumulation, air and natural gas were admitted to the combustion chamber at the rate of 237.5 m3 per minute and 28.3 m3 per minute, respectively. At this rate, the quantity of air was insufficient to ensure complete combustion. The hot products of combustion passed successively through the heat accumulation zone and the catalysis zone and escaped through the chimney into the atmosphere.



   During the transformation period, natural gas, water vapor and air were mixed and admitted into the enclosure below the pre-heating zone, at the following rates: natural gas, 61.4 m3 per minute; water vapor, 64.8 Kg per minute, air 118.8 m3 per minute. These gases passed through the heat accumulation zone, where they were heated to reaction temperatures, and then through the catalysis zone, where the transformation reaction took place. The transformed gases were conducted, passing through the washing box, to the storage location.



   During the purge, water vapor was admitted into the combustion chamber at a rate of 120.5 kg per minute, and this water vapor returned to the storage location the residual transformed gases. .



   The cycles continued for 24 hours; the average temperatures during this operation, in the various parts of the reaction apparatus, were as follows - lower part of the heat accumulation zone ...... 805 C upper part of the zone heat buildup easev 955 C lower part of catalysis zone @ 971 c upper part of catalysis zone @ 840 C
The gas, produced during the period corresponding to the transformation reaction, had the following composition and characteristics:

   lighting elements 0%
CO 14%
H2 41.6%
CO2 4.4%
CH4 5%
C2H 2.7%
02 0.5%
N2 31.8% calories per m3 2483 specific weight 0.602 ratio: hydrogen / inert constituents 1.6
To this gas was mixed natural gas, having a calorific value of 9,245 calories per, in a proportion sufficient to give a mixed gas having a calorific value of 4,715 calories per m3. The mixture consisted of 67% of the gas. above and in 33% natural gas and pos-

 <Desc / Clms Page number 13>

 besides a calorific value of 4.715 calories per m3, a specific weight of 0.607 and a ratio of 1.11 between hydrogen and inert constituents.



    EXAMPLE 11
In this example, the same apparatus was used as for Example I. However, the cycle had a duration of 3 minutes, 34% of which corresponded to a period of heat accumulation, during which the products of combustion were discharged through the chimney into the atmosphere, - 16% of which corresponded to a period of heat storage, during which natural gas was burned with an insufficient proportion of air to ensure complete combustion and the products resulting from this incomplete combustion was taken to a storage area, passing through the washing box, - 45% of which corresponded to a transformation period, - and 5% of which corresponded to a steam purge.



   During the heat accumulation period during which the combustion products were discharged through the chimney into the atmosphere, air and natural gas were admitted into the combustion chamber at the rate of 304.8 m3 and 28 , 3 m3 per minute, respectively, and were burned.



  During the period of heat accumulation during which the products of incomplete combustion were brought to the storage location, air and natural gas were admitted into the combustion chamber at the rate of 242, 3 m3 and 27.7 m3 per minute, respectively, and were burned
During the transformation period, natural gas, water vapor and air were admitted into the enclosure located in front of the heat accumulation zone, at the following rates: natural gas, 70.7 m3 per water vapor timer, 99.7 kg per minute; air, 44.6 m3 per minute.

   During the purging, 104.6 kg of water vapor per minute was admitted into the combustion chamber and discharged the resulting transformed gas to the storage location.



   The cycles continued for 24 hours, the average temperatures during this operation in the various parts of the reaction apparatus were as follows. lower part of the heat accumulation zone ...... 981 C upper part of the heat accumulation zone ...... 1015 C lower part of the catalysis zone ....... ...... 957 G upper part of the catalysis zone ............. 803 C
The mixed gas, produced as a result of the transformation period and that part of the heat accumulation period during which products of incomplete combustion were carried to the storage location,

   had the following composition and characteristics
Lighting elements @ 0%
CO 12.0%
H2 40.7%
CO2 5.4%
CH4 7.3%
C2H6 1.0%
O2 0.3%
N2 32.4% calories per it? 2456 specific gravity 0.604 ratio: hydrogen / inert constituents 1.08

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Natural gas was mixed with this gas having a calorific value of 9,200 calories per m³ in a proportion sufficient to obtain a mixed gas having a calorific value of 4,715 calories per m³. For this purpose, a mixture consisting of 33.5% natural gas and 66.5% of the gas described above was required.

   This mixture had, in addition to a calorific value of 4,715 calories per m 3, a specific weight of 0.61 and a ratio of 1.02 between the hydrogen and the inert constituents.



  EXAMPLE III.-
Using the same apparatus as that employed in Examples 1 and II, a cycle of 3 minutes was applied, of which 59% corresponded to a period of heat accumulation (during which the fuel was burned in the presence of a insufficient proportion of air to ensure complete combustion and the products resulting from the combustion were taken to the storage area via the washing box), - 36% of which corresponded to the transformation period, - and of which 5% corresponded to a steam purge.



   During the period of heat accumulation, air and natural gas were admitted into the combustion chamber at rates of 166 m3 and 18m7 m3 per minute, respectively, and were burned. During the transformation period, natural gas, water vapor and air were admitted into the enclosure located in front of the heat accumulation zone, at the following rates: natural gas, 68 m3 per minute ; water vapor, 81.5 kg per minute: air, 29.7 m3 per minute. During the purge, 90.6 kg of water vapor per minute were admitted into the combustion chamber, and forced the residual transformed gas to the storage location and eliminated any danger due to the presence of an explosive mixture. at the start of the next period of heat accumulation.



   The cycles continued for 24 hours; the average temperatures during this operation in the various parts of the apparatus were as follows: lower part of the heat accumulation zone @ 961 C upper part of the heat accumulation zone @ 994 C lower part of the catalysis zone ............. 925 C upper part of the catalysis zone ... 788 C
The mixed gas, produced as a result of the transformation period and the heat accumulation period, was conducted to the storage location, and it should be noted that at no time was it vented from gases in the atmosphere.

   The resulting mixed gas had the following composition and characteristics:
Lighting elements ................. 0%
CO 9.1%
H2 27.5%
CO2 6.4% cH4 9.5%
C2H6 0.0%
02 0.4%
N2 46.6%
Calories per m3 1993 specific gravity 0.72 ratio:

   hydrogen / inert constituents 0.52
To increase the calorific value of this gas to that required in the particular example considered, natural gas was mixed with this gas.

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 rel, having a calorific value of 9,200 calories per m³ so that the. proportion of natural gas amounted to 378% of the resulting gas mixture. of enriched gas mixture had, in addition to a calorific value of 4.715 calories per m3, a specific weight of:

   : 368 and the ratio of the hydrogem to the inert constituents, remained at 0.52 of enriched gas was then mixed with coke oven gas, - having a calorific value of 4.715 calories per cubic meter, 3 a specified weight. - that of 0.48 and a ratio of 3.72 between the hydrogen and the inert constituents in a sufficient proportion to increase up to 1.1 the ratio of the mixture between the hydrogen and the inert constituents. This required 22 parts by volume of coke oven gas per 100 parts by volume of the enriched gas.



   The final gas mixture then had a calorific value of 4,715 calories per m3, a specific weight of 0.662 and was suitable for distribution as town gas.



   It is understood that, without departing from the scope of the invention, numerous modifications can be made in the choice of the reaction gas hydrocarbon, the fuel gas and the mixture gases, as well as in the proportions of the reaction gases and of the mixture gases.



   CLAIMS.



   1. Cyclic process for the manufacture of a constituent of a combustible gas suitable for distribution in town gas distribution systems, - this process consisting, in a period of the cycle, in burning a fluid fuel and passing the hot products of combustion successively through a bed of heat-accumulating material to accumulate heat therein, then through a bed of catalyst for the endothermic reaction between gaseous hydrocarbons and water vapor , in order to accumulate heat therein, - and, in another period of the cycle., to pass a normally gaseous hydrocarbon and water vapor (and possibly air) through this bed of matter of heat accumulation,

   to heat these gases to pass the hot gases through this catalyst bed, to transform these gases into a gas rich in hydrogen and carbon oxidation products, - and to collect this gas rich in hydrogen and carbon oxidation products.


    

Claims (1)

2. Process according to Claim 1, characterized in that the proportion of water vapor used is between approximately 0.8 and approximately 5 months thereof for 1 mol of carbon in the gaseous hydrocarbon, and the catalyst. consists of nickel. 3. Process according to Claim 1, characterized in that the proportion of water vapor used is between approximately 0.8 and approximately 5 months thereof for 1 mol of carbon in the ganous hydrocarbon, the pro- portion. portion of air employed is less than about 2 months of ceuli-cik per 1 mol of carbon in the gaseous hydrocarbon., - and the catalyst consists of nickel. 4. Method according to claim 1, characterized in that the combustion of the fluid fuel is carried out, during the period of the cycle corresponding to the heat accumulation, with an excess of air. 5. Method according to claim 1, characterized in that the combustion of the fluid fuel is carried out during the period of the cycle corresponding to the accumulation of heat, with just the proportion of air theoretically necessary. to ensure complete combustion. 6. Process according to claim 1, characterized in that this combustion is carried out with an insufficient proportion of air to ensure complete combustion. 7. Method according to claim 1, characterized in that, at least during the last part of the period of the cycle corresponding to the <Desc / Clms Page number 16> EMI16.1 combustion of a hot fuel for acclimatization of heat, this combustion is carried out in pr'se? 3ce:. '"#} 6 insufficient air proportion to ensure complete cobuNt.on. 8. Process according to the reve.ccic.â-, ion 1., ceracûérisë in this cue 'da: .2s the period of the cycle corresponding to the a, ccuaL = heat lation, we first burn the combustible fluid in the presence of an excess of, 'Ji1, then in the presence of a proportion of insU: -fisé air;:; 6 to ensure complete combustion. 9. Method according to claims 1, 6, 7 and 8, characterized in EMI16.2 this is carried out to a storage location at least part of the products of incomplete combustion, as they leave the catalyst bed, during the period of the cycle corresponding to the heat accumulation, and these products of incomplete combustion with the gas, rich in hydrogen and in carbon oxidation products, leaving the catalyst bed, during the EMI16.3 period of the corresponding cycle 'Ci- the reaction of tra.1J.Sfoltion. 10. A method of manufacturing a combustible gas, suitable for being distributed in a town gas distribution system serving devices regulated for the combustion of industrially manufactured gas and having combustion characteristics determined in advance, - this pro - granted consisting in preparing a gas rich in hydrogen in a cyclic process EMI16.4 that, in which, in a period of. cyclea ro, burns a flàid3 combustible and the hot products of combustion are passed through a bed of heat accumulating material, to accumulate heat therein, and then to EMI16.5 through a bed of catalyst for the thermal reaction between gaseous hydrocarbons and water vapor, in order to accumulate heat therein, - and, in another period of the cycle, u normally gaseous hydrocarbon and water vapor (and possibly air) through this bed of heat storage material, to heat these gases, and then è. through this catalyst bed, to effect the transformation of hydrogen and water vapor (and possibly air) in a gas rich in EMI16.6 hydrogen and carbon oxidation products, - and to enrich this gas., rich in hydrogen and carbon oxidation products by mixing it with a proportion of a normally gaseous hydrocarbon having a EMI16.7 their l if .... 'll desired dl, "i - = -'- de ... their calorific higher than that desired in ¯-3 gases so as to produce a mixed gas having comparative combustion characteristics. bles with the combustion characteristics determined in advance of the industrially produced gas, so that the resulting mixed gas can be distributed in this town gas distribution system. 11 The method of claim 10, wherein at least the last part of the combustion of the fluid fuel is carried out in the presence of an insufficient proportion of air to ensure complete combustion and it is brought to a point of 'storing at least a part of the products of incomplete combustion, leaving the catalyst bed, during the first period of the cycle, - and mixing the gas rich in hydrogen and carbon oxidation products, obtained during the second period of the cycle , with these products of incomplete combustion and with a gas having a calorific value greater than that desired in the resulting mixture, in proportions suitable for producing the mixed gas which can be distributed in a town gas distribution system. 12. Apparatus for the manufacture, by a cyclic process, of a gaseous component, rich in hydrogen and in carbon oxidation products, of a gas suitable for distribution in town gas distribution systems, by the catalytic reaction of a gaseous hydrocarbon with water vapor (and possibly air), - this apparatus comprising a EMI16.8 combustion, a bed of matter? accumulation of heat and a bed of catalytic material arranged one after the other in enclosures freely communicating with each other, - means for introducing, during a predetermined time interval, a. combustible mixture of gaseous fuel and air in this combustion chamber, - means for introducing, during a predetermined time interval, a hydrocarbon <Desc / Clms Page number 17> normally gaseous and water vapor (and possibly air) in this bed of heat-accumulating material, from a location adjacent to the combustion zone, - and means for removing gaseous products from this bed of catalytic material.