GB2096124A

GB2096124A - Production of ammonium nitrate

Info

Publication number: GB2096124A
Application number: GB8209805A
Authority: GB
Original assignee: Didier Engineering GmbH
Current assignee: Didier Engineering GmbH
Priority date: 1981-04-04
Filing date: 1982-04-02
Publication date: 1982-10-13
Also published as: FR2503126B1; SU1367853A3; NL8201440A; DE3113783C2; DE3113783A1; DD202858A5; FR2503126A1; BE892740A; GB2096124B

Abstract

In producing ammonium nitrate by neutralisation of nitric acid with ammonia in a reactor 1 under superatmospheric pressure, the hot ammonium nitrate solution is discharged through a conduit 7 and depressurised in a valve 8 to a pressure at which its boiling temperature is less than the temperature of the solution in the reactor. The solution is then passed through a heat exchanger/evaporator 9 where it is concentrated by evaporation by the heat transferred to it by a circulated ammonium nitrate solution which is discharged from the reactor 1 through a conduit 11 and passed through the heat exchanger 9 and returned to the reactor 1. The vapours and concentrated ammonium nitrate solution are then separated in a vapour separator 10. <IMAGE>

Description

SPECIFICATION Process and apparatus for the production of ammonium nitrate The invention relates to a process for the production of ammonium nitrate by neutralisation of nitric acid by means of ammonia followed by evaporation of the ammonium nitrate solution, and is concerned with that type of process in which the heat of reaction of the neutralisation is used to effect the evaporation and the neutralisation occurs under a superatmospheric pressure. The invention relates also to an apparatus for carrying out such a method.

A process of this general type is described in the publication "HYDROCARBON PROCESS INr', November 1978, pages 169 et. seq. In this process, low pressure steam and process steam are produced in the neutralisation reactor. The process steam, which is under an overpressure of, for instance, 4 bar absolute, is used to effect the evaporation of the ammonium nitrate solution. However, this steam is contaminated with substantial quantities of ammonium nitrate and ammonia. Thus before using the condensate of this process steam it must therefore be cleaned which is very expensive. The term "process steam" is known in the art and refers to steam produced in the reactor by evaporation of part of the water of solution of the nitric acid whilst low pressure or surplus steam is produced in a heat exchanger within the reactor and is thus uncontaminated.

For reasons of safety the maximum temperature of the neutralisation is fixed at 1 80 C or a little above. Accordingly considerable quantities of water must be recirculated, for instance at acid concentrations of above 57% by weight. Furthermore, the concentration of the ammonium nitrate solution produced can only be brought up to ca. 95% by weight when effecting the evaporation by means of the process steam produced in this process itself.

A further such process is the Stengel Process. In this, nitric acid and ammonia are heated and fed to the reactor but the reaction heat is not used for the evaporation.

It is an object of the invention to provide a process of the type referred to above in which no process steam leaves the reactor and in which a high concentration of the ammonium nitrate solution can be achieved by using the heat of reaction.

In accordance with the present invention there is provided a process for the production of ammonium nitrate including neutralising nitric acid with ammonia without process steam production under superatmospheric pressure in a reactor, discharging a first volume of the hot ammonium nitrate solution from the reactor and depressurising it to an evaporation pressure at which its boiling point is less than the temperature of the solution in the reactor, discharging a second volume of ammonium nitrate solution from the reactor and bringing it in heat exchange relationship with the first volume after it has been depressurised thereby transferring thermal energy to the first volume of the ammonium nitrate solution and thus concentrating it by evaporation.

A cleaning of the process steam or of vapours from the neutralisation reactor is unnecessary because they do not occur. A concentration of the ammonium nitrate solution to, for instance 90 to 99.5% and preferably 97.5 or 98% by weight can be achieved by the process without having to use any externally produced steam.

A preferred embodiment of the invention includes controlling the neutralisation temperature by varying the magnitude of the superatmospheric pressure. Thus the over-pressure occurring in the reactor is maintained within permissible limits which is desirable in order to maintain the necessary and permissible pressure in the reactor.

The invention also embraces an apparatus for carrying out such a process and according to the present invention such an apparatus includes a neutralisation reactor and a heat exchanger, in which the secondary side of the heat exchanger is connected to the reactor and arranged so that, in use, ammonium nitrate solution is circulated from the reactor through the secondary side of the heat exchanger and back to the reactor and the primary side of the heat exchanger is connected to the reactor via a depressurisation valve so that, in use, hot ammonium nitrate solution is discharged from the reactor, depressurised to a pressure at which its boiling point is less than the temperature of the solution in the reactor and passed through the heat exchanger and thereby concentrated by evaporation.

Further features and details of the invention will be apparent from the following description of one exemplary embodiment which is given with reference to the single accompanying drawing which is a flow diagram and schematic representation of an apparatus for carrying out a process in accordance with the invention.

A neutralisation reactor 1, which is constructed as a pressure vessel provided with an internal overflow outlet for the main volume, is fed with nitric acid, e.g. of about 65% by weight concentration, via a conduit 2 and with ammonia via a conduit 3. The head space of the reactor 1 for example communicates with a device 4 for controlling the pressure in the reactor which comprises a conduit 5 in which a cooler 6 is connected. In use, steam developing in the head space of the reactor 1 flows into the conduit 5 and is so cooled in the cooler 6 by means of cold water that the pressure in the reactor 1 stays at a desired value of, e.g., between 4 and 8 bar and preferably between 5 and 6 bar absolute.

The ammonia reacts in the reactor 1 with the nitric acid and the resulting ammonium nitrate solution flows out of the head region of the reactor 1 through the overflow outlet and into a main flow conduit 7 and is fed to a vapour separator 10 via a depressurisation valve 8 and an evaporator/heat exchanger 9.

The ammonium nitrate solution in the conduit 7 flows through the primary side of the evaporator 9. Connected to the secondary side of the evaporator 9 is a supply conduit 11 and a return conduit 1 2. The supply conduit 11 includes a transfer pump 1 3 and communicates with the reactor 1 at a point below the overflow outlet. The return conduit 1 2 communicates with the bottom of the reactor 1. Thus, in use, ammonium nitrate solution-but no process steam-is conveyed through the conduit 11 to the evaporator 9 and then returned to the reactor via the conduit 12.

The pressure in the reactor 1 is preferably so adjusted (for example by means of the device 4) that the boiling temperature of the ammonium nitrate solution in the reactor 1 is maintained at between 1 70 and 190'C, preferably about 1 80'C. The ammonium nitrate solution preferably takes up a concentration of about 70% by weight. Accordingly ammonium nitrate solution at about 180"C and preferably between 5 and 6 bar absolute passes into the conduit 7 under the action of the pressure in the reactor 1.In the depressurisation value 8 the pressure of the ammonium nitrate solution is reduced (flashing effect) to a desired pressure, thus achieving a temperature of, for example 105"C. At the same time a subsidiary flow of ammonium nitrate solution is transferred through the secondary side of the evaporator 9 and since this is also at about 180"C it transfers thermal energy to the solution on the primary side thus causing evaporation of water from the main volume and thus concentration of the solution. At the same time the secondary volume is cooled down in accordance with the amount of heat transferred to the main volume.

It is found to be possible to obtain a concentration of the ammonium nitrate solution to about 98% by weight without using any additional thermal energy.

The vapours obtained and the ammonium nitrate solution are then separated in the vapour separator 10 and discharged through conduits 14 and 1 5 respectively. The conduit 14 conveying the highly concentrated ammonium nitrate solution is connected to a storage tank 1 7 via a dip pot (submerged inlet/overflow outlet container) 1 6. The ammonium nitrate solution is then fed from this tank, if required, by means of a transport pump 1 8 for use in a further process, for instance in a granulating installation.

The vapours flowing through the conduit 1 5 are fed to a water cooled condenser 1 9. The condensate is fed into a collecting container 21 via a dip pot 20 and can be withdrawn from this by means of a pump 22. The condensate is suitable for use as process water for the manufacture of nitric acid or similar processes. A vacuum generating facility 23 is provided for conveying the vapours through the conduit 15 into the condenser 19.

The evaporator 9 can be of single or multi-stage type. For a constant evaporation rate the thermal energy requirements of the evaporator are reduced, if it is of multi-stage type. Thus any excess heat can be used in a heat exchanger 24 connected in the return conduit 1 2 for the production of uncontaminated steam.

If a prewarming of the nitric acid and/or the ammonia before the reactor 1 is desired, then suitable heat exchangers 25, 26 can be connected on the primary side in the conduits 2 and/or 3. These can be fed on the secondary side by the vapours flowing through the conduit 1 5. The waste heat from the vapours in the conduit 1 5 can also be used for heating air which is then fed, e.g. to a product granulation installation. In this case the condenser 1 9 is conveniently cooled on the secondary side with air which is thereby warmed. In order to remove the nitrogen compounds contained in the vapours flowing through the conduits a single or multi-stage washer 27 can be disposed in the conduit 1 5.

In one specific embodiment of the invention in which 98% by weight ammonium nitrate solution was produced the operating data (with quantities given in tonnes per hour) were as follows: Inputs 2, 3 to the reactor 1: Nitric acid containing 65% by weight HNO3 at 30"C 50.48 t/h Gaseous ammonia at 10"C 8.88 t/h Outputs 7, 11 from the reactor 1: (7) Ammonium nitrate solution of 70.2% by weight, at 1 80 C and 5 bar abs. 59.36 t/h (11) 32.24 X 103 MJ/h for heating purposes in the evaporator 9 Inputs 8, 11 to the evaporator 9: (8) Ammonium nitrate solution at 70.2% by weight, at 105"C (primary side) 59.36 t/h (11) 32.24 X 103 MJ/h (secondary side) Outputs 14, 1 5 from the separator 10: : (14) Ammonium nitrate solution of 98% by weight, at 157"C 42.52 t/h (15) Vapours at 0.3 bar abs. and 1 70 C 16.84 t/h Condenser 19: Condensate running off at 65"C 16.84 t/h

Claims

1. A process for the production of ammonium nitrate including neutralising nitric acid with ammonia without process steam production under superatmospheric pressure in a reactor, discharging a first volume of the hot ammonium nitrate solution from the reactor and depressurising it to an evaportion pressure at which its boiling point is less than the temperature of the solution in the reactor, discharging a second volume of ammonium nitrate solution from the reactor and bringing it in heat exchange relationship with the first volume after it has been depressurised thereby transferring thermal energy to the first volume of the ammonium nitrate solution and thus concentrating it by evaporation.

2. A process as claimed in Claim 1 in which the ammonium nitrate solution is concentrated to 90 to 99.5% by weight.

3. A process as claimed in any one of the preceding claims in which the neutralisation occurs at a pressure of between 4 and 8 bar absolute.

4. A process as claimed in any one of the preceding claims in which the excess thermal energy of the second volume of ammonium nitrate solution is used for the production of steam.

5. A process for the production of ammonium nitrate substantially as specifically herein described with reference to the accompanying drawing.

6. Apparatus for carrying out a process as claimed in any one of the preceding claims including a neutralisation reactor and a heat exchanger in which the secondary side of the heat exchanger is connected to the reactor and arranged so that, in use, ammonium nitrate solution is circulated from the reactor through the secondary side of the heat exchanger and back to the reactor possibly passing a steam generator and the primary side of the heat exchanger is connected to the reactor via a depressurisation valve so that, in use, hot ammonium nitrate solution is discharged from the reactor, depressurised to a pressure at which its boiling point is less than the temperature of the solution in the reactor and passed through the heat exchanger and thereby concentrated by evaporation.

7. Apparatus for the production of ammonium nitrate substantially as specifically herein described with reference to the accompanying drawing.