FI72300C - Process and apparatus for producing ammonium nitrate. - Google Patents

Description

72300

Method and apparatus for the preparation of ammonium nitrate seedlings

The invention relates to a process for the preparation of ammonium nitrate by neutralizing nitric acid with ammonia 5, which neutralization involves concentrating the ammonium nitrate solution by evaporation, whereby evaporation utilizes the heat of neutralization reaction and the neutralization takes place under overpressure without generating process steam.

10 A similar process is described in Hydrocarbon Processing, November 1978, pages 169 et seq. However, this process produces low pressure water vapor and process steam in a neutralization stage reactor. 20 The maximum temperature in the neutralization is 180 ° C or slightly above for safety reasons, which means that considerable amounts of water must be recycled at acid concentrations higher than, for example, 57% by weight, and the generated process steam can also be recycled. by means of (4 bar abs.) to obtain the concentration of ammonium nitrate solution produced only about 95% by weight.

A similar method is the Stengel method.

In this process, nitric acid and ammonia are introduced into the reactor when heated. The heat of reaction is then not used in the evaporation.

The object of the invention is to provide a process of the quality mentioned at the beginning, in which no process steam is generated and in which a high concentration of ammonium nitrate solution is achieved under the effect of the heat of reaction.

According to the invention, the above-mentioned task is solved by means of the method initially described, so that the pressure of the main stream of ammonium nitrate solution is adjusted to the evaporation pressure, where it is evaporated by means of a side stream of ammonium nitrate solution.

5 No process steam is removed from the neutralization reactor. Instead, a side stream of ammonium nitrate solution is used to evaporate the main stream of ammonium nitrate solution. As a result of the heat exchange between the side stream and the main stream, the latter expands so that its heat-10 state falls below the side stream temperature. In this process, process steam purification or condensation of the neutralization reactor is omitted because these are not required at all. To obtain an ammonium nitrate content of, for example, 98%, it is not necessary to use water vapor generated in an external process.

In a preferred embodiment of the invention, the neutralization takes place under the control of overpressure. In this case, the overpressure generated in the reactor is kept within the permissible limits. This is advantageous for maintaining the required and permissible pressure in the reactor.

Other preferred embodiments of the invention and the features of the device for carrying out the method according to the invention appear from the following description of an embodiment and from the subclaims. The drawing shows a flow chart of an apparatus for carrying out the method according to the invention.

To the neutralization reactor 1, which has been formed as a full-space device with an internal overflow, about 65% by weight of nitric acid is introduced via line 2 and ammonia via line 3. A device 4 for pressure control is connected to the lid of the reactor 1. It has a pipe 5 connected to the condenser 6. The water vapor formed in the upper part of the reactor 1 flows through the pipe 5 and is cooled in the condenser 6 with cold water so that the pressure in the reactor 1 remains the desired, between 4-8 bar abs. at current value.

3 72300

Ammonium nitrate solution is removed from the top of the reactor 1 through the main flow pipe 7 and transferred to the steam separator 10 via the expansion valve 8 and the evaporator heat exchanger 9.

In the main flow pipe 7, the ammonium nitrate solution flows through the heat exchanger 9 in the primary direction. Connected to the heat exchanger 9 on the secondary side is a recirculation line supply pipe 11 and an outlet pipe 12, which also comprises a feed pump 13. The supply pipe 11 starts from the reactor 1 below its upper part. The return pipe 12 terminates in the lower part of the reactor 1. The ammonium nitrate solution, but not the process water of the reactor 1, is thus passed through the recirculation pipes 10 11, 12 and 13.

The pressure in the reactor 1 is preferably regulated by means of a pressure control device 4 so that the boiling point of the ammonium nitrate solution in the reactor 1 is about 180 ° C. The concentration of the ammonium nitrate solution is then about 70% by weight. In the same way, a side stream of ammonium nitrate solution having a temperature of 180 ° C is fed to the evaporator heat exchanger 9 from the secondary side. The ammonium nitrate solution at substantially the same temperature is transferred to the main flow pipe 7. The pressure is then preferably 20 to 6 bar abs. The ammonium nitrate solution passes through the main flow line 7 under the influence of the reactor intrinsic pressure. In the expansion valve 8, the ammonium nitrate solution is subjected to an evaporation pressure at which the temperature of the ammonium nitrate solution is, for example, 105 ° C. In this case, the ammonium nitrate-25 solution evaporates in the evaporator heat exchanger 9. In the vapor separator 10, the phases are separated into an ammonium nitrate solution in the pipe 14 having a concentration of about 98% by weight and into a condensate discharge into the pipe 15. The pipe 14 for transferring the highly concentrated ammonium nitrate solution is connected via a dipping cup 16 to the storage tank 17. From this the ammonium nitrate solution can be led by means of a transfer pump 18 to further processing, for example to a granulation plant.

«4 72300

The condensate flowing through the pipe 15 is led to the condenser 19. The condensate is transferred through the immersion cup 20 to the collecting vessel 21 and can be removed therefrom by means of a pump 21. The condensate is suitable as process water for the production of nitric acid 5 and the like. An empty pump 2 3 is used to transfer the condensate water through the pipe 15 to the condenser 19.

The heat exchanger 9 can be single-stage or multi-stage. If it is formed in several stages, it involves 10 low heat consumption. The excess heat can be utilized in a heat exchanger 24 connected to the return pipe 12 to produce heating steam.

If it is desired to preheat nitric acid and / or ammonia before the reactor 1, suitable heat exchangers 25, 26 are connected to the pipe 2, respectively 3 on the front side. Secondarily, condensate flowing through the pipe 15 at a temperature of about 170 ° C can be fed to them. In order to separate the nitrogen compounds contained in the condensate flowing through the pipes, a single or multi-stage washing 27 can be performed in the pipe 15.

The following summary shows the values obtained in one exemplary case when preparing a 98% by weight ammonium nitrate solution with an ammonium nitrate apparatus.

25

Feed (2,3) reactor (1): nitric acid containing 65% by weight of HNO-j, temperature 30 ° C 50.48 t / h ammonia, gaseous, temperature 10 ° C 8.88 t / h 30

Removal (7, 11) of reactor (1): (7) ammonium nitrate solution, 70.2% by weight, temperature 180 ° C and pressure 5 bar abs. 59.36 t / h 25 (11) 32.24 x 10 ^ MJ / h for heating purposes to the evaporator (9) t! 5 72300

Feed (8,11) evaporator heat exchanger (9): (8) ammonium nitrate solution, 70.2% by weight temperature 105 ° C, primary) 59.36 t / h (11) 32.24 x 10 ^ MJ / h (secondary side) 5

Removal (14,15) separator (10): (14) ammonium nitrate solution, 98% by weight, 157 ° C 42.52 t / h (15) condensate water pressure 0.3 bar abs.

10 temperature 170 ° C 16.84 t / h

Condenser (19): condensate leaving, temperature 65 ° C 16.84 t / h

The heat of discharge from the condensate in line 15 can also be conducted to heat the air used in the product granulation plant.

In this case, the condenser 19 is suitably cooled by air, which then heats up.

Claims (7)

6 72300 1. A process for producing ammonium nitrate by neutralizing nitric acid with ammonia by neutralizing the concentration of the ammonium nitrate solution by evaporation, using the reaction heat formed in the neutralization for evaporation and neutralizing the mixture with an overpressure without producing the process steam, knowing that by means of the side stream (11,12) it is evaporated that the neutralization is carried out between 4-8 bar abs., preferably 5-6 bar abs. depending on the concentration of nitric acid used and thus the water content, so that evaporation corresponding to the total water content in the neutralization vessel is not achieved and that the neutralization is carried out at a temperature of 170-190 ° C, preferably 180 ° C. Process according to Claim 1, characterized in that the ammonium nitrate solution is concentrated to 90 to 99% by weight, preferably 97.5% by weight, by means of a side stream (11, 12). Process according to one of the preceding claims, characterized in that the concentration of the ammonium nitrate solution takes place in one or several stages. Method according to Claim 3, characterized in that the excess heat of the side stream (11, 12) is used to produce heating steam. Apparatus for carrying out the process according to one of the preceding claims, wherein an evaporator heat exchanger is connected downstream of the neutralization reactor, characterized in that the heat exchanger (9) on the secondary side is in a recirculation line (11, 12, 13; 24) 1) and in front of the heat exchanger (9) on the primary side is connected a main flow pipe (7) discharging from the reactor (1), which is provided with an expansion valve (8). Device according to Claim 5, characterized in that the reactor (1) is designed as a full-space device with an internal overflow. 7 72300