DE747958C - Catalytic oxidation of ammonia - Google Patents

Description

Catalytic oxidation of ammonia In catalytic oxidation from ammonia to nitrogen oxide, it is known to cool the contacts, if necessary by boiling liquids with the generation of steam. The known methods show however, it has various disadvantages. So z. B. either through the reaction mixture Steam is heavily diluted or the gas flow is hindered and throughput is restricted as a result. Furthermore, the temperature profile over the entire contact length is not sufficient controllable, the yield is not optimal, and the heat of reaction is not complete exploited, or the explosion safety especially when processing more concentrated Gas mixtures are unsatisfactory, as is the durability and weight stability the catalytic converters, or finally fresh gas or a component of the fresh gas be added to the reaction mixture again or several times, etc. It has been found that such disadvantages can be avoided and further advantages result if the in particular concentrated gas mixture first through in the heating pipes of a steam boiler or cooler attached contacts and is incompletely implemented and after exiting these pipes through perpendicular or transverse to the direction of flow the gases just spread catalyst zones is passed. So it is according to the invention the ammonia-oxygenbz, w. Ammonia-air mixture first in the z. B. boiler room one Contacts attached to the steam boiler are advantageous while utilizing the sensible heat for steam generation only implemented incompletely, while the remaining conversion in the downstream catalysts takes place. The gas velocities or the free Cross-sections of the heating pipes in the steam boilers can then be designed so that large gas throughputs can be achieved with sufficient heat dissipation at the same time as a result of the flow through the downstream catalytic converters secured full sales. An added benefit is that dar as a result of the only remaining conversion to the downstream catalysts, z. B. Platinum fabrics, which have only a fraction of the expansion compared to before, where: lurcli a substantial saving of space is gained. The excellent explosion safety even when processing explosive gas mixtures and protecting the catalytic converters should be particularly emphasized.

The essential novelty of the invention thus consists in its very definite nature Series connection of the cooled ones that largely subdivide the gas flow Tubes arranged contacts with transverse to the direction of flow of several tubes combined gas stream spreading catalyst zones, d. 1i. so in a whole certain two-stage conduct of the procedure, with the first stage the second stage, on the other hand, deliberately avoiding cooling with one level Surface catalyst is carried out.

The progress achieved in this way is one that was previously not possible Mastery of combustion, especially with high-percentage ammonia-oxygen mixtures. This is not possible if you go for the gradual combustion geometrically and functionally similar contacts connected in series. The functional diversity in the contact arrangement according to the invention results from the fact that the The first catalyst has the task of achieving a high energy zone concentration in the event of incomplete conversion allow and dissipate the heat of reaction, while the second catalyst in essential to complete the reaction among those most favorable for the task Conditions, i.e. in a geometrically coherent arrangement, is used, wherein the question of heat dissipation is no longer of decisive importance.

In known methods there is also the risk that when it slackens one of the contact tubes known to be used in large numbers, the one that occurs as a result incomplete implementation cannot be remedied without further ado, rather it must relevant contact tube only determined in a cumbersome, operation-hindering manner will. In contrast, the two-stage process of the invention has the advantage that such a different work of the contact tubes for the total turnover not harmful; but this undoubtedly means an increase in operational reliability. Compared to the known methods, there are special advantages in processing concentrated gas mixtures, e.g. B. of ammonia with undiluted oxygen, w e, fl in the known procedure the flat and surface catalysts are not resp. can only be cooled less; n. The main part of the heat of reaction is invented (lungsgUinäß made usable at the contacts in the pipes of the steam generator. D: e heat the converted gases is known in l), z. B. by just above the wire mesh Attached Würine exchangers, steam generators and the like, exploited. Ini contrast there are procedures for this. which the overall contact within hülil or. Steam generator pipes is arranged. lower yields because the tube is cooled over the entire length of the contact and thus also on the termination of the reactions in; len already largely implemented. vei-thin gas mixture is extended and on the other hand the advantages over a large area spread contact tissue remain unused. Will nian before the just arranged If the catalysts do not allow the gases to get too hot, the gas mixture is released Leaving the first contacts, further cooling pipes free of catalysts flow through, before it reaches the flat surface catalytic converters. In a particularly simple way this is achieved when the first contacts in the Dainpflzesselrolii-en these do not fill in their entire length, so that part of their length is made of contacts free is. In this part, the intermediate cooling of those leaving the contact part takes place Gases. However, special pipe sections or a special Rölirenlciilil <@ i or. Steam boiler between the steam boiler tubes containing the contacts and the planar ones Flat catalytic converters are switched on. The resulting controllability and disconnection unwanted intermediate reactions are another advantage of the new process.

As a cathode, for. B. o @ vdic contacts, possibly on known ones Contact carriers, such as pumice stone, ceramic masses. Silica, etc., or e.g. B. metallic Contacts can be used on their own or on carriers. Instead of zvlindrischen Pipes inside the steam boiler can also be pipes or pipes distributed over the cross-section, Shafts delimited, separated or connected by water-cooled surfaces of elliptical or circular corrugated etc. or triangular or inelirangigein, z. B. square or rhombic cross-section, use. These cross-sectional shapes may be limited to part of the length of the steam boiler or approximately on the length occupied by the contact. May bring particular advantages such cross-sectional shapes between the z. B. tubes rooms with parallel, planar Boundary surfaces result, z. B. square or rhombic cross-sectional figures. Combustion and cooling space can also be connected to each other. be swapped, d.1 i. the Contacts can also be arranged between the pipes of the steam boiler or cooler, while the pipes or the like themselves are flowed through by the optionally boiling coolant will.

It has been found that when using metallic contacts of is of particular importance that z. B. the steam boiler arranged Apply catalysts in the form of contiguous metal surfaces, e.g. B. as Metal foil, metal pipes or the like. When using several flat surface catalysts one after the other, in the direction of the gas flow, there may also be a reduction in cross section enter.

The connected catalyst metal surfaces installed in the boiler tubes have a stronger cooling or temperature equalizing effect than metal mesh and are also less sensitive to temperature increases than the latter.

Because of the better thermal conductivity of metal surfaces, local Avoided overheating. In the case of pipes made of precious metal contacts, e.g. B. made of platinum or Platinum alloys, there are also lower metal losses. With these cheap The new process combines the excellent effects of connected metal surfaces Properties of metal mesh necessary for the termination of the reaction at a minimum in terms of contact ensure a maximum of sales, and it will result for same Small diameter apparatus throughput.

It has been found that the contact surfaces in the. Pipes of the steam generator can advantageously be made of pure platinum, while after Leaving the steam generator one or more flat contact networks are used, which consist entirely or at least partially of platinum-rhodium alloys. Man used e.g. B. three nets, the first and middle of which are made of platinum-rhodium alloy exist, while the last network in the direction of flow is made of pure platinum is. You can also use nets, the threads of which are partly made of pure platinum and for Part made of platinum alloys, e.g. B. when using only one network.

The method is suitable for working with ordinary as well as especially with increased pressures, where the smaller cross-section the apparatus makes advantageous.

The mounted in the boiler tubes catalysts may be of any shape and extent, and the steam t> or abut therefrom by a gap, slit or the like to be separated..; z. For example, in addition to one or more catalyst tubes with circular or circular corrugated or oval cross-sections, spiral, star-shaped, porridge or polygonal us @ -tv., Optionally cross-sectional shapes arranged one after the other or superimposed, are used. Catalyst tubes are preferably cylindrical or conical in their longitudinal extent and, if required, are provided at their ends with nozzles, widenings or constrictions, sieve-like outlet openings or the like, or are themselves designed as nozzles, sieves or the like. Conical catalyst tubes or steam boiler tubes have the particular advantage that the contact temperature is additionally regulated over the entire length of the tube, e.g. B. can be made practically constant, namely when the gap between the catalyst and steam boiler tube increases towards the larger cross-section, z. B. in the direction of flow of the gases, so that the cooling effect is correspondingly reduced in the case of partially converted gas. A plurality of concentric catalyst tubes can also be used, optionally with one or more reversals of the gas flow direction by r80 °. B. the gas mixture only in the case of the first pipe element, its inside and from the second pipe element, after a partial conversion has already taken place, flushed the inside and outside of the catalyst tube. In this way, the second pipe element or the subsequent pipe sections are operated hotter, so that a temperature drop in the direction of flow that occurs without splitting is largely compensated and the contact in the steam boiler pipes is operated at a practically uniform temperature. The same effect can also be achieved in a contact tube with perforations, slots or the like. If the second or subsequent pipe elements are supplied with colder gas than is withdrawn from the first or preceding pipe element, a distance between two individual pipe pieces is selected so that, if necessary, multiple intermediate cooling occurs through the steam boiler pipes. The amount of each intercooling can be set differently by the individually provided, possibly adjustable individual distance; so that constant temperatures or the desired optimal temperature distribution is achieved over the length of the pipe. With only one catalyst tube, increasing cooling can be achieved by such a conical design of the same or the steam boiler tubes that the gap between the catalyst surface and the steam tube becomes narrower in the direction of flow. If you want to use its inner and outer surface for catalysis over the entire length of the pipe, z. B. cut the contact tube in the longitudinal direction one or more times or provided with holes or slots so that a partial flow of the gas mixture touches the outer catalyst surface.

The new method has further advantages in the processing of such high-percentage ammonia-oxygen mixes up where the explosive limit is reached is exceeded, d. H. for mixtures with more than about i4% NHs, e.g. B. over 30 % NH3. By arranging the first contact masses in the tubes, e.g. B. - a steam generator, so excellent cooling is achieved that the explosive Gas mixtures are prevented, especially since their flow velocities are chosen to be large can be. It has been found that in the case of pipes or the like made of catalyst metal this advantageous only at one of the pipe ends on the outer pipes of the steam generator are attached or hung or are particularly or directly cooled here, while they are otherwise separated from the boiler tubes by a gap. This results in the cooling at the adjacent pipe end forming the gas inlet side designed particularly effective, so that a kickback of the explosive gas mixture is prevented while at the same time in the remaining part of the catalyst tube the necessary reaction temperature is maintained. Particularly effective in terms of It is explosion-proof and kickback-proof when the gas mixture passes through Pipes made of catalyst metal are removed from the steam boiler pipes at the gas inlet end protrude and there z. B. be cooled directly by liquid. It is one Choose a liquid that does not affect the durability of the contacts. With this arrangement can still combine the special mode of operation that in the Space between the catalyst and steam kettle pipe evaporated liquid, e.g. B. water vapor, flows from the pipe cooling at the gas inlet end and only after leaving the contact tubes mixed with the partially converted gas mixture, so that a a diluted mixture reaches the contact network through steam. Will be done beforehand mixing with steam is desired, for. B. the walls of the contact tubes provided with perforations, holes, slots and the like.

Instead of direct purging of the outstanding catalyst ends with z. B. water, the pipe ends z. B. also surrounded by special cooling sleeves or in the openings of a z. B. double-walled cooling plate through which water flows on the inside or such a bundle of cooling tubes or feedwater preheater that is connected to the steam generator o. The like. Are used. The contact tubes can, however, also, especially with the extended pipe end, directly into the openings in the roller plate of the steam generator used or hooked in, e.g. B. using slightly conical Pipe sleeves in the openings of the roller plate, through which the catalyst pipe to the Wall of the roll plate opening is pressed. There is then one inside the sleeve increased flow rate, which in conjunction with the improved cooling the catalytic converter eliminates the risk of kickback.

A special additional steam or gas stream can also be used in the space between the boiler tube and the catalyst to dilute the catalyst tube leaving gas mixture or to regulate the network temperature or after leaving the contacts in the pipes, gas or gas mixture is added, z. B. water vapor in the boiler or by direct cooling of catalyst tubes is produced. A special embodiment is that part of the to be implemented, in particular concentrated gas mixture in the gap between the steam boiler tube and Catalyst tube is introduced and the latter at least on part of its Length washed around the outside, then with the one introduced into the interior of the catalyst tube Gas part is mixed and flows through the flat surface catalyst zones together.

The contact tubes within the tubes of the steam generator can otherwise be designed as desired; In particular, it has often proven to be advantageous for the tubes made of catalyst substance to have a diameter that decreases uniformly or in steps in the direction of flow of the gases, preferably with an enlargement of the gap between the cylindrical tubes of the steam boiler and the catalyst tube. The contacts in the pipes of the steam boiler and the flat surface catalysts behind the steam boiler can consist of the same catalyzing substance or of different types of catalysts, e.g. contact tubes in the steam boiler are made of pure platinum, while the flat catalyst zones behind the steam boiler consist of one or more platinum-rhodium networks with a content of z. B. 5 % rhodium or with z. B. 2. % Ru and i% Rh or Ir.

Another advantageous modification of the procedure is to that the contacts in the tubes of the boiler are divided with or without spacing and the parts are made from the same or different catalyst mass will. Catalyst tubes made of platinum can, for. B. directly .with those made of platinum-rhodium alloys be joined together, or to follow pipe sections made of platinum alloy below Interposition of a spacer made of pure platinum.

The diameter of catalyst tubes made of platinum or platinum alloys is basically not limited; it is used when processing high-percentage gas mixtures advantageously chosen to be about 5 to 15 mm, while the inner diameter of the steam boiler or cooler pipes then z. B. 5 to 20 mm. The length of the catalyst tubes can be dimensioned according to the invention so that at the contact in the steam boiler tubes at least 1/3 of the conversion and at the flat surface contact not more than 1/3 of the conversion is effected.

It has also been found useful to have a certain ratio between to adhere to the diameter of the catalyst tubes and their glowing length, and although the diameter is chosen so that it is at most 111, preferably less than 1J20 of the glowing length of the catalyst tubes. If you turn z. B. contact tubes whose glowing length is 20 cm, according to the invention, a Pipe diameter of about 10 mm used, e.g. B. made of platinum foil with 8 mm 1st W., or Pipes that are in the flow direction in the first third 8 mm in diameter and in the a further two thirds of the pipe length are only 6 mm in diameter. The flow velocity in the pipes is then about twice as long in the last two thirds of the pipe length big than in the beginning.

When burning high-percentage mixtures, it was further recognized as advantageous that the flow rate in the catalyst tubes within the steam boiler per square centimeter tube cross-section is at least zoo, preferably more than 3009 nitrogen per hour. In the case of a platinum tube of 8.2 mm 1. W., which has a cross-section of about 0.53 square centimeters, therefore, 100 to zoo g of nitrogen per hour, that is to say up to 6 kg per day, are passed through if a mixture with 3q. . Volume percent ammonia and 66 volume percent. 98% wants to convert oxygen. If you use z. B. only iooo parallel pipes, so with such an arrangement with a downstream network area of only about a quarter of the previously usual area, ie in combustion elements of only about in diameter, q, up to 6 tons of nitrogen per day can be burned or at 2 m diameter z. B. 16 to 24 tons of nitrogen per day and above. Another advantage of the invention is the possibility of processing high-percentage mixtures reliably in operation in relatively small apparatuses with little need for catalyst gauzes and thus being able to achieve very high throughput rates per m 'of cross-section. Because of the smaller cross-section of the apparatus, the method has advantages especially when working at increased pressure.

The ignition of the flat surface contact zone takes place in a known manner z. B. by means of a hydrogen flame or by an electrical heating device, e.g. B. can also be designed as a current conductor, the catalyst tubes themselves. To the Ignition of the catalyst tubes inside the steam boiler was found to be advantageous the catalyst tubes or surfaces connected to them, extensions and the like. made of catalyst metal on the inlet side and / or outlet side of the gas flow from the steam boiler tubes to let protrude and these outstanding surfaces until the entrance of the Heat reaction. When the reaction has started, the heater is removed or switched off; If required, the protruding ends can also be specially cooled will.

A technically particularly effective design of the catalyst tubes is that they protrude on both sides of the boiler and on the Gas inlet side through a cooling, «, water flow directly or indirectly, z. B. by means of a cooling plate, can be cooled particularly effectively, while the one on the gas outlet side protruding surfaces can be used for ignition. This way it becomes an excellent one Explosion safety achieved because the strong cooling of the catalyst tubes on the Gas inlet side prevents kickback, exploding and the like, while on the other hand the catalyst tubes are easily accessible for ignition. Naturally the ignition can also take place on the gas tistrittsseite if between the special Cooling of the protruding catalyst tube part and your steam boiler e'.n for the Pilot flame or the like. Accessible space is left. The cooling of the or the. Catalytic converter parts protruding from the steam boiler are preferred designed as a feed water preheater.

The steam boiler, in the pipes of which the especially concentrated atmospheric oxygen mixture is implemented incompletely at first, in order to avoid deposition of -innnon nitrate advantageously operated at increased pressure.

The new method is not limited to the aforementioned embodiments. Example An exemplary embodiment is shown by FIGS. 1 to 3. The Roligasgeinisch steps. through the pipe socket i into the lower part of the apparatus. The rooms 2 and 3 are with z. E. Raschig rings made of wire mesh or the like. Filled out. After flowing through these spaces, the gas enters the tubes 4 made of catalyst metal, which are located inside the tubes 5 of the steam boiler 6. The catalyst tubes are, as can be seen from _1b13.3, z. B. in the _lrt shown there in the openings i () of a cooling plate through which Wassur flows. The `1-ace (# inlet is at 17, the water outlet at 18. In the catalyst tubes or the like 4, more than half of the gas 2 is converted, preferably about 2/3, and then flows through the Room 7 in the row g des'Danipfkusseis io. The boiler 10 can also be used, for example, as a feed water preheater. In the boiler 10, intermediate cooling of the hot gas mixture occurs. The gas then flows out of the pipes 9 through a more even layer Flat catalytic converters. Instead of metal fabrics, oxidic catalytic converters can also be used. After passing through the catalytic converters ii, the now completely converted gas mixture reaches the tubes 14 of the steam boiler 13 and, after the desired part of the waste heat has been drained off, into the outflow opening 15.

The catalyst tubes 4 are ignited through the openings 8 in FIG your intermediate part between the kettles 6 and io, namely to the one from the kettle 6 protruding from the top-1en pipe ends of the catalyst roller, z. P. by means of a hydrogen flame. The planar surface catalytic converters ii are ignited through the openings 12, which at the same time serve to observe the temperature of the last.

All three boilers (i, io and 13 can also be interconnected by pipe connections to form a single boiler, e.g. to a steam boiler, the water level of which is indicated by the horizontal line shown between 13 and 14.

Claims (1)

PATENT CLAIMS: i. "experienced in catalytic oxidation tion of ammonia through gradual Incineration of the raw gas characterized in that the raw gas mix first in in in itself bell-annter Way in pipes (5) or the like. A cooler or steam: boiler arranged control ten (4) burns incompletely and the Implementation then after leaving the Pipes at right angles or at right angles to the flow direction of the combined gas flow mes arranged catalysts (ii), z. B. Dralitnetzl #: atalysatoren, v o1 lstand: g through- to be led. : 2. Method according to claim i, characterized marked # l -release the converted gas- gLinisch after the first con cycle zone (4) with a drop in temperature tere contact-free zones (5) and / or (c9) before it passes through the catalytic converter Sators (ii) is directed. 3. The method according to claim t and 2 characterized in that in the raw Ren (5) catalysts made from pure platinum are used and the catalysts (ii) at least partially from I'latin-I @ ho- clittm alloy. 4. The method according to Anspruca 3, characterized marked that the inside of the Darnpfkesselrohre (5) z. B. an- orderly arranged ordered catalysts (4) only on the Entry point of the gas mixture at the Inner wall of the tubes (5) aii :: eyes or at the entry point especially directly become high while in] ü'urigen of the pipes (5) through a gap are separated. 5 .. method according to claim 3 and .1, characterized by: leave the ho intact in the tubes (5) finite or without stand are divided and d: e 7'e: lu atis Oei- chcn or various catalysts stand. 6. The method according to claim i iui #, t =. there- marked by. dar e: ii "1'e1 de Raw gas mixture in the gap between the pipe (5) and catalyst tube (_l) u: ngeiüliri and the latter at least: on one Part of its length was washed by au lien, so- then finite into the interior # .lus katal \ - s @ torrolires introduced Grist (#il verinisrlit is and jointly flows through the catalyst zones (ii). 7. The method according to claim i to 6, characterized in that the catalyst tubes (4) or connected to these. which surfaces, projections and the like of catalyst metal on the inlet and / or outlet side of the gas stream protrude from the cooling tubes (5) and the protruding surfaces to start the reaction in a manner known per se, for B. heated by a flame or electrically and optionally cooled during operation. B. The method according to claim i to 7, characterized in that the steam boiler, in the tubes of which the raw gas mixture is incompletely implemented, is operated. In order to differentiate the subject of the application from the state of the art, the following publications were considered in the granting procedure: German patents. No. 43,5o6, 418,622; Swiss patent documents - 120511, 65 129; Austrian patent specification - 135994, French patent specification. . - 712384, U.S. Patent. . ...... - i 5o8 o61.