DE1152217B - Method for producing a heating gas - Google Patents

Description

Method for producing a heating gas The invention relates to a Method for producing a heating gas, e.g. B. a standard-compliant town gas, by catalytic cleavage of gaseous or liquid obtained by distillation Hydrocarbons in the presence of steam and possibly small amounts Oxygen (air). To the heating gas generated in this way, e.g. B. town gas will the requirement made that it is fully interchangeable with standard-compliant town gas, d. H. corresponds to a distillation gas, which in high-temperature coking of coal. The requirement of full interchangeability relates primarily Line on calorific value and density of the generated cracked gas. But also play alongside other burning properties of the gas, for example its ignition behavior, the formation of soot and carbon oxide during combustion, as well as air requirements and flame stability, a certain role.

The production of heating gas through the catalytic splitting of hydrocarbons can be carried out continuously or batchwise. What way of working one expediently chosen depends on the type of starting product and also on the gas output that a splitting device should have. At higher boiling points than gasoline Hydrocarbons are generally used batchwise prefer. Furthermore, one is used in cracking systems that have a higher gas output than maximum should have about 150,000 m> per day, regardless of the type of hydrocarbon consider discontinuous operation.

Recently, the production of heating gas, especially town gas, by catalytic cleavage of light gasoline with a boiling point of around 120 ° C gained a special meaning. This hydrocarbon mixture is suitable for him Particularly good for a continuous split by nature, since the right choice the operating conditions a soot-free and condensate-free cleavage over long periods of time constant activity of the catalyst with economically justifiable Means is to be achieved. Although light petrol, especially with high gas output, nevertheless can also be processed in discontinuous operation on heating gas, is the invention first using the example of the continuous splitting of light gasoline explained in more detail because continuous operation has more severe operating conditions requires. The application of the invention to other starting materials and to the discontinuous Operation will then be dealt with.

The continuous production of heating gas by splitting light Hydrocarbons, e.g. B. mineral spirits, usually takes place in elongated pipes made of high temperature resistant metal, e.g. B. steel, possibly also made of ceramic material, which are heated from the outside with hot flame gases. Located inside the tube a catalyst filling. In general, marketable, relatively highly active catalysts in granular form (20 to 40 mm particle diameter), which contain nickel as the active metal. For technical purposes, the pipes often have a length of 3 to 6 m, which is more or less completely filled with catalyst are. The pipes are hung in a furnace, in which some fuel is burned, so that the heat consumed in the fission is partly due to radiation and partly by convection onto the pipe walls and through them into the Catalyst filling is transferred.

With a correct coordination of temperature, amount of catalyst and Fraction of the starting materials light petrol, water vapor and air can be a cracked gas obtained, which in terms of calorific value and density practically completely through High-temperature coking of coal corresponds to town gas produced. The formation of Soot can be kept practically as small as desired. Unless the light gasoline certain substances directly influencing the catalyst activity (sulfur compounds, high-boiling impurities) in a sufficiently small amount is also one long operating time guaranteed without catalyst regeneration or renewal. That however, gas produced in this way is generally not completely against normal Town gas is replaceable because it still contains certain compounds that are used when it cools down of the cracked gas at normal temperature practically in the full amount in the generated Fission gas remain and affect its burning properties. These organic Compounds consist for the most part of unconverted light gasoline, especially the lower-boiling parts of the same. There is also a certain one Amount of higher hydrocarbons formed in the cleavage, in particular Aromatics and diolefins, present in the cracked gas, and finally are also found most of the aromatics contained in the starting product itself are in the cracked gas again.

The proportion of these compounds in the cracked gas can be up to 80 to 100 g / Nm3 cracked gas. However, practical experience with fission gases has shown that it is necessary for the purpose of full interchangeability with normal town gas is, the content of these compounds in the cracked gas to a value of less than 15 g / Nm3, preferably to less than 10 g / Nm3.

These organic compounds can be removed from the cracked gas. This can be done, for example, by means of an activated carbon filter, if necessary also by washing with oil or by freezing. In any case, there is a special one to carry out the gas cleaning system to be installed downstream of the actual splitting device, which not only increases the investment costs of the actual splitting device, but also requires additional expenses for ongoing operations.

As a particularly effective method of removing the mentioned unwanted Connections is the application of an activated carbon filter, these connections should be for the sake of simplicity in the context of the present description as activated carbon condensates are designated.

Besides the fact that the separation of these A-carbon condensates is special requires structural and operational expenses is also significant, that these condensates, in addition to reducing the yield of valuable gas, represent a pretty worthless product by themselves. You can't get them into the splitting process as they differ under the conditions used in the cleavage process difficult to split soot-free. So at best they provide fuel represents, which can optionally be used to heat the splitting device.

The invention has set itself the goal of the catalytic cracking process to be modified so that a fully exchangeable town gas is produced without it is necessary to have a special device for separating so-called charcoal condensates to be provided. In other words: the splitting process is carried out according to the invention in such a way that that the content of the cracked gas at A-carbon condensate without additional facilities is kept at 15 g / Nm3, preferably below 10 g / Nm- 'finished cracked gas.

One means of reducing the amount of activated carbon condensate would be on the increase in the gap temperature. In fact you can by increasing it accordingly the formation of activated carbon condensate practically no matter the fission temperature. However, increasing the splitting temperature has the disadvantage that, at the same time, the composition of the cracked gas is changed in such a way that the calorific value no longer conforms to the standard. That is due to the fact that at the increased cracking temperature not only the amount of activated carbon condensate, but also the proportion of calorific value hydrocarbons, in particular Methane and ethylene, in favor of the hydrogen and carbon dioxide content.

Another way of suppressing the formation of charcoal condensate would be a higher throughput, based on a constant amount of catalyst, if a higher throughput is even feasible (pressure loss). One higher throughput, combined with an increased temperature, affects the The exchange processes on the surface of the catalytic converter up to a certain extent Degree in the direction of a reduction in the amount of activated carbon condensate, the Influencing the gas quality can be kept within limits. However, it arises An operational difficulty here is that of increased throughput bring corresponding increased amount of heat into the catalyst bed. In the the catalyst bed by the endothermic cracking processes consumed heat must, so far it cannot be taken from the preheated replacement materials themselves the wall part of the cans that is in contact with the catalyst filling is introduced will. The outside temperature that can be reasonably expected of the cans is, however, limited in terms of material, so that this path is also impassable.

There is already a process for the production of carbon oxides and hydrogen Known gas mixtures of gaseous hydrocarbons in which to achieve a uniform distribution of the reactants over the entire cross-section of the Reaction space and to avoid reactions open cooperation of the catalyst between the reaction space and the area in which the gas supply line opens into the reaction chamber, a catalyst is arranged, which in comparison larger grains for the catalyst of the reaction space, d. H. a smaller catalyst surface and larger gaps between the catalyst bodies, i.e. less resistance for gas passage and gas distribution and a lower content of active having making substances in the catalyst carrier.

It is also known to design the catalyst bed so that the catalyst bodies located at and near the inlet end of the catalyst layer have a greater heat retention capacity than the rest.

It has now been found that a fully interchangeable fission gas, that is to say which corresponds to normal town gas in terms of all combustion properties, can be obtained if the spatial concentration of the active centers of the highly active catalyst is at least partially mixed in with the throughput rate remaining essentially the same as in the previous normal case of catalytically practically inactive, heat-resistant, solid substances in a ratio of between about 1: 1 and 1:10 catalyst to inactive solid, while increasing the temperature by 75 to 150 ° C compared to the temperature usually used with the undiluted catalyst (650 to 750 ° C , depending on the load). An active catalyst is to be understood as one which strongly accelerates the conversion of hydrocarbons with water vapor to carbon oxide and hydrogen. Possibly existing catalytic effects of another kind are not taken into account.

The use of the elevated temperature in the procedure according to the invention because of the stronger splitting has the expected effect that the Amount of activated carbon condensate is kept sufficiently small, while the dilution of the Catalyst a shift in the gap equilibria towards a preferred one Formation of short-chain hydrocarbons, mainly those with 1 or 2 carbon atoms per molecule. It is therefore surprising in the procedure according to the invention a simple way of adapting the catalytic conversion of the cleavage products initially essentially thermally split starting material with steam and Oxygen (air) to the degree of decomposition that has changed due to the higher temperature the higher hydrocarbons take place by the thermal fission, which is one too could be described as primary cleavage, in which inactive solid is relocated.

Example I A catalyst filling is located in a can with a total length of 2.1m. The filling consists of a mixture of 15 kg Nickel contact, consisting of spherical bodies 20 to 30 mm in diameter, and 95 kg of basalt gravel with an average grain size of 40 to 50 mm. Above this Filling is still a catalyst-free basalt gravel layer of 20 cm Height. The hydrocarbon, which has been preheated to 300 ° C, is fed into the can from above (evaporated light petrol), the steam preheated to 400 ° C and cold air fed. In the present case, the amount of gasoline vapor was 57.3 kg / hour The amount of water vapor 201.0 kg / hour, the amount of air 22.6 Nm3 / hour. The heating of the tube was adjusted so that an average reaction temperature in the catalyst of 820 ° C prevailed. The amount of cracked gas generated was after deposition of the non-decomposed water vapor 181.5 Nm3 / hour.

The fission gas had the following analysis: Volume percentage CO., .............................. 5.9 C., H., ............................. 0.0 Heavy hydrocarbons ......... 7.5 Oxygen ......................... 0.0 CO ............................... 17.4 H., ................................ 49.7 CH4 .............................. 8.8 N., ................................ 10.7 The upper calorific value of the gas was 4200 kcal / Nm-3, and the density (air = 4 was 0.52.

The carbon gasification degree of the cracking process was at least 0.998.

After cooling to normal temperature, the gas contained A carbon condensate of 8.2 g / Nm3. Of the steam used, 37 kg were for the catalytic conversions consumed. The amount of protective steam was so 164 kg, d. H. 2.8 kg of protective steam per kilogram of light petrol used.

If the split were to be carried out in the usual way, namely using a neat catalyst and an average reaction temperature of about 670 ° C, a soot-free cleavage of the light gasoline would also be achieved to obtain a heating gas with an upper calorific value of about 4000 kcal / Nm3; this However, gas would produce at least about 73 g of activated carbon condensate per normal cubic meter Contain fission gas and therefore not easily full against normal town gas be interchangeable.

An advantageous embodiment of the invention is that one does not exceed the degree of dilution of the catalyst with inactive solid makes constant the entire length of the filling of the pipe serving for the cleavage, as this is provided in example 1, but rather the degree of dilution from the gas inlet side (usually at the top) can be gradually or continuously reduced to the gas outlet side, so that the materials to be cleaved initially after entering the can find a highly diluted catalyst that is very strong in the sense of a predominantly thermal cleavage is effective, while the largely cleaved reaction mixture As the catalyst continues to pass through the can, ever stronger concentrations is suspended, thereby the implementation of the small amounts of possibly still not completely split hydrocarbons or the higher split products is intensified with the water vapor.

The main advantage of this method of operation is that, in spite of the significantly increased throughput, the amount of protective steam (excess steam) can be reduced considerably. Example 11 In a can of the same diameter as in Example I there is a filling, the total length of which is 4.2 m. The filling consists of a total of 125 g of basalt and 75 kg of catalyst. The grain sizes of these materials are the same as in Example I. The filling is designed as follows: top layer (gas inlet) mixture of 46 kg of basalt and 4 kg of catalyst, second layer of mixture of 42 kg of basalt and 8 kg of catalyst, third layer of mixture 20 kg basalt and 30 kg catalyst, lowest layer (gas outlet) mixture of 17 kg basalt and 33 kg catalyst. So there is 50 kg of material in each shift. The average dilution of the catalyst is 1: 1.65; The dilution in the individual layers is 1: 11.5; 1: 5.2; 1: 1.5 and 1.9: 1.

The throughput of light gasoline was 98 kg / hour, of steam 189 kg / hour. and in air 40 m3 / h. The preheating temperature of the steam was 400 ° C., that of the light gasoline vapor was 300 ° C. The pipe was heated in such a way that the following temperatures were established after a stable state had been reached: Top layer ................. 800 ° C Second layer ................. 820 ° C Third layer .................. 800 ° C Bottom layer ............... 780 ° C The amount of fission gas after separation of the undecomposed water vapor was 310.3 Nm3 / hour. The fission gas had the following analysis: Volume percentage CO2 .............................. 4.0 C, H2 ............................. 0.0 Heavy hydrocarbons ......... 7.9 Oxygen ......................... 0.1 CO ............................... 20.3 H, ................................ 47.7 CH4 .............................. 8.7 N 2 ................................ 11.3 The upper calorific value of the gas was 4100 kcal / Nm3 and the density (air = 4 0.53.

As in Example, the degree of carbon gasification was 10.998.

After cooling to normal temperature, the gas contained A carbon condensate of 9.1 g / Nm3.

Of the steam used, 72 kg were used for the catalytic Conversions consumed. The amount of protective steam was therefore 117 kg, i.e. H. 1.2 kg protective water vapor per kilogram of light petrol used.

Compared to example I is the gas line of the can 6811 / o greater and the consumption of protective steam to 429 / o of the corresponding Value of example I has been lowered.

One would use the same amount of undiluted catalyst in the same Using a pipe, not only could one not use the lower charcoal condensate value achieve, but one would also not be able to achieve the high throughput rate, since it would be technically impossible to find the appropriate for the increased throughput Cleavage reactions require heat beyond that of the small volume of catalyst to bring an adapted can surface into the filling.

On the other hand, if one were to use the entire volume, which in Example II with the Mixture of solid and catalyst is met with undiluted catalyst fill out, the high throughput of example II would not be achieved without having to accept a lot of soot formation. Much of the At best, the catalytic converter would serve as a ceramic heat storage mass, which is practical cause unnecessary expense.

The number of stages with the different dilution ratios can be larger or smaller than indicated in example 1I. Also the concentration differences can can be chosen to be much smaller between the stages. If necessary, you can go to Provide a layer on the gas inlet side that only contains the inactive solid, and on the gas outlet side a layer that only contains undiluted catalyst.

Finally, it is also possible to determine the spatial content of the catalyst column at active centers can also be varied by using different catalysts high activity and the less active varieties, seen in the direction of the gas, placed in front of the more active varieties, possibly mixed with inactive solids.

Regarding the solids, it should be noted that one is primarily interested in Water vapor resistance and heat resistance, especially to a certain extent Must place thermal shock resistance. In addition, the substances should have good thermal conductivity own. This is particularly the case with tube gap devices with a comparatively large Pipe diameter important. Materials for this purpose are in addition to lumps of basalt and Alumina shards also rock lumps of other origin, as well as coarse grains of chamotte, Silica, sillimanite, burnt dolomite or magnesite. The in itself low activity, which these substances in relation to the catalytic conversion of hydrocarbons with Occasionally having water vapor has no effect on the actual splitting process.

This was explained using the example of a continuous splitting of light gasoline The invention can be easily applied to discontinuous operation, which is particularly suitable for large gas outputs. The one for the splitting processes The required heat is not continuously fed through the pipe walls, but stored in the filling by direct heating of the mixed filling with hot gases. This heating-up period is then followed by a cleavage period in which the one to be cleaved Hydrocarbon together with the other reactants through the heated Filling is directed. These two periods alternate in the rhythm that with regard to the most constant possible quality of the generated fission gas is required.

As already mentioned at the beginning, the explanation of the invention means using the example of the splitting of light gasoline does not limit the invention this initial good. Rather, all other hydrocarbons can also be used or mixtures of such cleavage according to the procedure according to the invention, however with the restriction that when using hydrocarbon mixtures, the significant amounts of non-evaporable or very high-boiling components contain, in addition to cracked gas, more or less large amounts of solid and high-boiling points Fission products arise that relocate the catalyst, among other things, so that a the preconditions for an operationally simple cleavage process, namely constant one Contact activity, is not guaranteed.

When using methane, natural gas, refinery residual gas or liquefied petroleum gas for the cleavage process according to the invention, it is opposed by the invention the previous way of working did not achieve technical progress in the reduction of A-carbon condensate-like additions in the cracked gas generated, as such substances not formed in disruptive quantities from the respective starting hydrocarbons are or are not included in them. The advantages of the invention in such Rather, starting materials lie in the possibility of increasing the throughput of splitting plants certain dimensions as a result of the enlargement of the heat transfer surfaces (im continuous Operation) or the storage space (in discontinuous Operation) by the neutral filler to increase significantly while at the same time Reduction of the need for protective water vapor that remains undecomposed.

When using hydrocarbons, their boiling ranges are higher than that of light gasoline, such as regular gasoline, heavy gasoline, diesel oil In addition to the advantages mentioned, the typical advantage of light gasoline is added, namely Reduction in the amount of so-called charcoal condensate.

Claims (3)

PATENT CLAIMS: 1. A method for producing a heating gas, e.g. B. a standard with regard to calorific value and density, with by high temperature coking city gas produced by coal fully exchangeable city gas, by catalytic Splitting of gaseous or liquid hydrocarbons obtained by distillation in the presence of water vapor and possibly small amounts of oxygen (air), characterized in that the spatial concentration of the active centers of the per se highly active, preferably nickel-containing catalyst at least partially by admixing catalytically practically ineffective, heat-resistant, solid ones Substances in a ratio between about 1: 1 and 1:10 catalyst to diluent is reduced with a simultaneous increase in the temperature in the dilute catalyst around 75 to 150 ° C compared to that usually used with the undiluted catalyst Temperature (650 to 750 ° C, depending on the load). 2. The method according to claim 1, characterized characterized in that the dilution of the catalyst with inactive solids in takes place in such a way that the spatial concentration of active centers per unit volume stepwise or continuously in the direction of the gas flow prevailing during the cleavage increases. 3. The method according to claim 2, characterized in that catalysts different activity in the form that, in the gas flow direction seen the catalysts with greater activity lagging behind those with lower activity are arranged, with inactive solids optionally being admixed. In Publications considered: German Auslegeschrift No. 1037 626.