DE1075572B - Device for the production of nitric acid by adsorption of nitrous gases - Google Patents

Description

GERMAN

The invention relates to a device for the production of nitric acid by absorption of nitrous gases; The production of nitric acid according to this process is usually based on the following reaction: Burning ammonia produces nitrous gases with a high NO content, which are then _{oxidized to N 2} O ₃ or NO ₂ in an oxidation chamber and these nitrous vapors are then fed to an absorption device in which they are dissolved in water or dilute nitric acid.

Devices for carrying out this process generally require a lot of effort, since, on the one hand, a number of large towers are usually used for oxidation, their structure requires considerable amounts of stainless metal, and there on the other hand to absorb the nitrous vapors an intensive sprinkling of these towers with the (dilute) acids is necessary, which at the foot the towers caught again and raised in a partially closed circuit with the help of pumps The conveying capacity of stainless steel must be returned and cooled in the process.

Another difficulty is that in the course of absorption due to the associated A partial regression of the nitrogen oxide NO takes place if the temperature increases; the associated losses to avoid and to increase the yield, one has already gone over to the absorption of the nitrous vapors carry out in several successive stages and between these respectively to ensure renewed oxidation of the re-formed N O. However, this causes a further complication and increase in the cost of the system.

Certain improvements have already been described to at least partially overcome these disadvantages to remedy.

Oxidation chambers of small volume and weight have been produced, which pressurized working from several atmospheres and in which the dissipation of the heat developed by one external irrigation with cold water takes place. One of the difficulties that arises is then the achievement sufficient absorption by sufficiently intimate contact between the oxidized Gases and the absorbent acidic solution. In other devices, the working pressure was still increased more, and the volume of the oxidation chambers was increased to the volume between the various Decreased use of a column with absorption inserts. Here, however, the Difficulty removing the amount of heat generated in a small volume from one insert to the other.

Device for manufacturing

of nitric acid by adsorption

of nitrous gases

Applicant:

Societe Chimique de la Grande Paroisse,

Azote et Produits Chimiques,

Paris

Representative: Dipl.-Ing. C. Wallach, patent attorney,
Munich 2, Kauftngerstr. 8th

Claimed priority:
France, dated. July 9, 1953

Marcel Jean, Paris,
has been named as the inventor

The apparatus forming the subject of the invention makes use of the following well-known theoretical ones Considerations from:

The oxidation of nitric oxide at a certain temperature is a reaction, its speed decreases rapidly,

1. if the proportion of N ₂ O ₃ or NO _{2 formed} increases,

2. when the partial pressures of NO and O ₂ decrease.

The oxidation reaction is strongly exothermic.
The heat development results from the following equations:

6NO + 1.5O ₂ = 3N ₂ O ₃ + 63cal, (1)

6NO + 3 O ₂ = 6NO ₂ + 84cal ₃ (2)

while the aqueous absorption of the nitrous vapors is expressed by the following formulas:

3N ₂ O ₃ + H ₂ O = 2NO ₃ H + 4NO + 8.8 cal, (3)
6N O ₂ + 2H ₂ O = 4NO ₃ H-f2NO + 59.6cal. (4)

From these equations it can be seen that if the degree of oxidation is restricted to the formation of N ₂ O _3, the greater part of the amount of heat

9OS 730/439

3 4

During the reaction in the gaseous phase released on rust-free metal, an optimal process is achieved, while the temperature-related adaption to the above-mentioned with the liquid resulting from the absorption on contact achieves behavioral theoretical principles,
is much smaller in terms of size. Under these conditions, according to an advantageous embodiment, the acids no longer need to be cooled. 5 additional cooling devices are arranged

Another advantage of the limitation of the Oxy- net, which on the one hand is used to cool the strong, im dation of the gases consists in the oxidation of the lower part of the column before the acid arrived NO below the highest speed ensures entry into the next lower absorption performance Conditions takes place. use and / or on the other hand for cooling the high-

However, in order to use the nitric acid finally obtained io concentrated nitrous gases before they come into contact with the strong acid in the richest nitrous vapors,
In addition, the device has the following characteristics:
The absorption zones are to be driven out in a single cost of N ₂ O ₃ and the absorbing acid, which is already strongly concentrated with absorption inserts on top of one another, is to be cooled. for an effective subdivision of the gas flow

The invention is based on the object among unites, each division from the neighboring Consideration of the above theoretical and procedural departments through a gas-tight partition Considerations a device is separating.

of the type mentioned for nitric acid production to 20 This column is at its upper part with a create, with the chloride-free amount of water precisely calculated in particular for the absorption proceeds with maximum yield; the device since. When streaming down from a mission water should be as space-saving and efficient as possible forms his and thanks to a correct choice and out-concentrated nitrous vapors, whereby when settling the oxidation volumes of the gases, between 25 tion with the same according to equation (3) which highly effective absorption zones contain an increasingly concentrated nitric acid, only a minimal weight of stainless steel. In the lower zone of the column, the require tallen. The invention thus relates to a reaction (4) occurring. You can then have a cooling Make device for making nitric acid of acid.

by absorption of nitrous gases with the gases coming from an oxidation chamber

successive, one on top of the other, flowed through from the outside on their way to the next oxy-

cooled oxidation chambers, which with absorption chamber form an absorption zone. The Oxyda-

Alternate chambers, the superimposed chambers in a column are expediently replaced by horizontal ones

are arranged differently. superimposed cylinders formed. In these

To solve the problems mentioned and for the purpose of the process, the oxidation takes place according to reaction (1). If, however, the described disadvantages of known methods are to be produced, such a device is to be produced according to a concentrated nitric acid, the development of the invention can partially be designed so that the ratio of reaction (2) in the lower cylinders, in cooling surface to volume, allow the one cooled by external sprinkling, which the nitrous vapors are very concentrated, from one or more consecutively 40 The oxidation cylinders are externally cooled by a connected cylinder sprinkling with water,
In order to reduce the overall height, it is advisable to reduce the oxidation cylinder on both sides of the absorption by arranging the diameter of the cylinder column, with two or more oxidation chambers 45 cylinders from the lower stages can be arranged side by side,
or groups of stages to the upper stages or the dimensions of these oxidation cylinders who-groups of stages increase, and that the individual absorption inserts of the column, taking into account the oxyindividual absorption to be achieved, the degree of decomposition of the nitrous gases as well as the work equivalent to the oxidation chambers a low height pressure and the operational safety calculated in such a way that and have a small volume, separated from each other by the required amount of rust-free metal, gas-tight walls as thin as possible and small with piping.

genes are provided through which the liquid takes under the diameter of the oxidation cylinder

the effect of gravity from one insert from one stage to another from the lower cylinder

can flow to the next. those who receive the richest gases

It is already known that in an apparatus for which the rate of oxidation is greatest

Nitric acid production, which is only the greatest for operation at and the heat developed,

Normal pressure is suitable for the device to down to the upper cylinders, which are very poor gases

sorption of the nitrous vapors and to the respective received, in which the oxidation rate

Oxidation of the gases between the individual absorption is lower, too. The input cylinders must

design steps in such a way that the actual ab- 60 therefore have a large cooling surface with a relatively

Sorption chambers of the intermediate oxy- have moderately small internal volumes, which is why they

dation chambers are spatially separated ^ with a small diameter and thin

Absorption chambers are made in a column stacked sheets.

are arranged and the externally coolable Oxyda- To dissipate the heat of reaction one leaves the tion chambers also lie one above the other. Sprinkles distributed along the cylinders of the upper zone by the 65 The measure provided for the invention, the lung water to flow to the lower cylinders. if Ratio of cooling surface to volume of the external temperature as a result of the heat absorption Irrigation of cooled oxidation chambers along which the water becomes too high, it becomes completely or partially Graduated absorption column, is at the utmost by fresh water or by water, which Simplicity of construction and minimal effort 7 ° the heat of reaction of some upper cylinders

has taken, replaced, whereby the arrangement can work according to the known principle of trickle cooler, and possibly with air injection from bottom to top.

The rich nitrous gases, which have undergone considerable oxidation in the lower cylinders, can experience additional cooling by a brine before being fed to the absorption zone.

Likewise, the already rich acids sprinkling the lower inserts can be artificially cooled, in particular by means of a brine, which in turn z. B. by using the evaporative cooling of the used Ammonia, which must be evaporated to NO before its catalytic combustion, on one low temperature.

The cold acid coming from the last use must be reheated and "bleached" by the action of a stream of air in order to separate out the dissolved N ₂ O ₄ it contains, which makes it unusable for numerous purposes.

Before this treatment, this nitrous acid can expediently its coldness from an overlying one Use to release downward trickling, less cold acid.

The invention is explained below with reference to the drawing.

The nitrous gases resulting from the combustion of 625 kg of ammonia per hour are released by a known device pressurized. They are fed through a line 2 to an exchanger 1, after they have given off most of their sensible heat to a boiler, not shown which delivers 2200 kg of steam superheated to 300 ° C per hour.

The gases cool down in 1 by the exhausted gases coming from the absorption column heat about 200 to 250 ° C.

An additional cooling at 3, which in particular by preheating the boiler feed water as well optionally the feed water of the nitrous gas absorption column takes place, causes the Condensation of the water vapor of the gases coming from the burners, so that the gases are cold and get dry to the inlet of the centrifugal compressor 4, which on the one hand by the relaxation of superheated steam generated by the boiler in the turbine 5 and on the other hand by the expansion which is heated at 1 and driven through the line 7 to 6 post-run gases. Of the In the example chosen, the delivery pressure is 3 atmospheres.

The gases compressed in this way are first conveyed through the line 8 into the oxidation chamber 9, 9 '. If the acid produced is bleached under pressure with the aid of air, which at 11 is fed from the compressor 12 to the inserts 13, this becomes air laden with nitrous vapors conveyed further through the line 10 and with the main flow at the entrance of the first oxidation chamber mixed.

When the bleaching of the acid produced after releasing it to about atmospheric pressure takes place, the air used for this purpose is fed to the inlet of the compressor 4.

The oxidation chamber, the volume of which is of the order of 15 m ³ , can be formed by two simple horizontal cylinders about 9 m long and about 1 m in diameter made of 3 mm thick stainless steel sheet. These cylinders are heavily sprinkled on the outside at 14, 14 'and also contain an internal cooling device for indirect water cooling (tube bundle or cooling coils 15, 15') for the absorption of the from the compression and oxidation of the NO to N ₂ O ₃ -IN ₂ O ₄ resulting significant amount of heat. During the oxidation, a certain amount of weak acid condenses which, under the influence of gravity, flows to a feed suitably selected in the absorption column.

The oxidized and well-cooled gases discharged from 9, 9 ' through line 16 reach the absorption column. They flow through the insert 17 a, which is sprinkled with cold acid, where, when they come into contact with the acid, considerable absorption occurs with the formation of NO ₃ H. This absorption results in the regeneration of a considerable part of the NO, the renewed oxidation of which takes place in the horizontal cylindrical elements 18 a, which are cooled at 19 c by an external sprinkling of water. Thereafter, the gases flow through b the absorbent insert 17, before reaching the 18 & Oxydationselementen. They alternately flow through the absorption inserts 17a, 17 b, 17 c ... 17 n - 1, 17 η (the superimposition of which forms the absorption column) and the oxidation elements 18 α, 18 b, 18 c and then the oxidation cylinders 18 d, 18 e etc.

The absorption column is a vertical component with a diameter of 1.5 m and a height from about 8 to 9 m. It contains fourteen to sixteen absorbent inserts including the two lower ones Bleach inserts.

The oxidation chambers are cylindrical parts with a length of about 8 to 10 m, the lower chambers containing the richest gases being between 30 and 50 cm in diameter. The diameters increase to about 1 m. The cylinders are expediently one above the other in order to facilitate the systematic sprinkling of the cooling water. The four or eight upper cylinders 18 η - 3, 18'w-3, 18 ^ -2, 18'w-2, 18n-l, 18'mI, 18m, 18 ' η can be arranged in pairs, the cylinders being one Pair lying next to each other in the same plane.

It is generally convenient not to use four or six cylinders to stop the oxidation cool, since it is well known that the absorption of the nitrous vapors by the dilute acid solutions occurs an increase in temperature, which can expediently reach 40 to 45 ° C., is favored.

The lower cylinders are expediently cooled with fresh water. The gases emerging from the first oxidation chambers can undergo additional cooling before they return to the corresponding absorption element by flowing through return flow pipes 20 α, 20 & ... immersed in cold brine 21 α, 21 b etc.

Likewise, the acids flowing down from use to use, if their concentration rises sharply and the absorption reaction is clearly exothermic, can be cooled by flowing through elements immersed in containers 22α, 22b ... which are filled with cold brine.

The upper part of the absorption column is sprinkled with about 20001 chloride-free water. This Water can be warm water supplied from the line 23, the contact with the Gas vaporized part is heated again with the wake gases in the preheater 1 and to Energy generation in the turbine 6 contributes.

The evaporation of part of the supplied water causes the cooling of what has remained liquid Part.

The gases coming from the last rows of the non-cooled oxidation cylinders give off their warmth to the absorbent liquid, which heats up a little, causing the absorption on the upper inserts is favored, while the gases cool down on contact with the cold liquid, which favors oxidation in the last cylinders.

Under the above conditions, the nitrous vapor content of the exhausted gases can be brought to less than 0.3%, and about 4000 kg of technical acid with 55% NO ₃ H per hour are obtained at the foot of the column, the amount used being stainless metal is less than a third of that used in a normal absorption system of the same capacity operating near atmospheric pressure.

The space requirement of the system according to the invention is very low, and the pumps for reintroducing the acids into the circuit have been eliminated.

Claims (3)

Patent claims: 1. Device for the production of nitric acid by absorption of nitrous gases, with successive, superimposed, externally cooled oxidation chambers which alternate with absorption chambers which are arranged in a column one above the other, characterized in that the ratio of cooling surface to volume of the cooled by external sprinkling , consisting of one or more cylinders connected in series (18 a to 18 n, 18V) from the lower stages or groups of stages (18 a, 18 b, 18 c) to the upper stages or groups of stages (18, 18'n - 2, n-1, n) decreases in that the diameter of the cylindrical oxidation chambers increases from the lower stages or groups of stages to the upper stages or groups of stages, and that the individual absorption inserts (17 α, 17 b , 17 c ... ) Of the column, which compared to the oxidation chambers have a small height and small volume, ν, οη-each other through thin gas-tight walls de are separated and provided with pipes through which the liquid can flow from one insert to the next under the action of gravity. 2. Device according to claim 1, characterized by additional cooling devices, on the one hand (22 a, 22 b, 22 c) for cooling the strong acid that has arrived in the lower part of the column before it enters the next lower absorption insert and / or on the other hand (20 a , 20 b) serve to cool the highly concentrated nitrous gases before they come into contact with the strong acid. 3. Apparatus according to claim 1, characterized by a supply line (23) for warm water for sprinkling the upper part of the column. Considered publications:
French Patent No. 469,649;
British Patent Nos. 131 029, 527 037. 1 sheet of drawings © 909 73W43S2.60