Method for producing ammonium nitrate
Technical Field
The invention relates to a method for producing ammonium nitrate by neutralizing nitric acid with ammonia, in particular to a method for producing ammonium nitrate by neutralizing nitric acid and gaseous ammonia in a tubular reactor.
Background
Nitric acid reacts with ammonia very vigorously to produce ammonium nitrate, and the reaction equation is as follows:
as can be seen from the equation, a large amount of heat is evolved during the reaction, and if the amount of heat evolved by the reaction is not effectively controlled or removed in time, the temperature of the reaction system rapidly increases. Ammonium nitrate can generate violent decomposition reaction at a certain high temperature, a large amount of gas is released, the volume is expanded sharply, and the danger of explosion is generated.
In addition, the amount of heat released by the reaction of nitric acid and ammonia is closely related to the concentration of nitric acid, and the higher the concentration of nitric acid involved in the reaction, the more vigorous the reaction, the more heat released.
The reaction for preparing ammonium nitrate solution is a normal pressure kettle type reaction, i.e. under normal pressure, the neutralization reaction of nitric acid and ammonia is carried out in a reaction kettle. The concentration of the nitric acid participating in the reaction is generally low (45-55%) because the heat generated in the reaction process cannot be removed in time, and if the nitric acid with higher concentration is used, the danger of explosion is generated. Meanwhile, the temperature of the neutralization steam generated in the reaction process of the normal pressure kettle type reaction is low, and the value of recycling is not available, so that the energy loss is caused.
However, in actual production, the concentration of the nitric acid participating in the reaction is always desired to be higher, so that energy can be saved and the production cost can be reduced. For this purpose, research institutes at home and abroad havedeveloped a tubular reactor for reacting ammonia and nitric acid in recent years, that is, nitric acid (higher concentration nitric acid can be used) and gaseous ammonia are introduced into a pipeline with a relatively small diameter in a certain proportion under a pressurized state to react to generate ammonium nitrate, and the ammonium nitrate is sent out from the other end of the tubular reactor. The tubular reactor is used for neutralization reaction of ammonia and nitric acid, and has the advantages of few materials participating in the reaction instantly, short retention time of the materials in a reaction area, avoidance of explosion danger, and capability of recycling heat energy of the neutralization steam generated by the reaction.
However, even if the method is adopted, because the nitric acid with higher concentration (56% -62%) is used for the neutralization reaction, although the reaction materials are few, the heat release is still very violent, and in addition, the reaction is continuously fed, the reaction is controlled improperly, the neutralization reaction is still easy to exceed the critical temperature, and explosion accidents occur.
Disclosure of Invention
The invention aims to provide a method for producing ammonium nitrate, which improves the explosion danger existing in the prior pressurized tubular reaction of nitric acid and gaseous ammonia, prevents the explosion to the maximum extent and realizes the safe production of ammonium nitrate.
The original ammonium nitrate production method is that nitric acid and gas ammonia are led into a tubular reactor through respective feeding pipes to carry out neutralization reaction, reaction products are discharged into a container from the other end of the tubular reactor, and ammonium nitrate solution is obtained after steam is flashed off.
The improvement measure of the invention is that a temperature measuring device is arranged on the tubular reactor to carry out real-time monitoring on the temperature in the tubular reactor; the nitric acid and ammonia feeding pipes are respectively connected with a steam pipe and are provided with a steam control valve; the temperature measuring device is interlocked with the material control valve on the nitric acid and ammonia feeding pipe and the steam control valve on each steam pipe. When the reaction temperature in the tubular reactor is lower than the set control temperature, the material control valves on the nitric acid and ammonia gas feeding pipes are allowed to be opened, the steam control valves on the steam pipes are closed, and the reaction in the tubular reactor is normally carried out. Once the reaction temperature in the tubular reactor reaches the set control temperature, the material control valves on the nitric acid and gas ammonia feeding pipes are immediately closed in an interlocking manner, the reaction materials are cut off, meanwhile, the steam control valve on the steam pipe connected with the nitric acid and gas ammonia feeding pipes is rapidly opened, low-pressure steam is introduced into the tubular reactor, the residual reaction materials in the tubular reactor are washed out, and the occurrence of explosion accidents in the tubular reactor is avoided.
The device is characterized in that a flash evaporation tank is connected behind the tubular reactor, the main function of the flash evaporation tank is two points, one is that the ammonium nitrate solution generated by the reaction is discharged into the flash evaporation tank from the other end of the tubular reactor, and after steam is flashed out, concentrated ammonium nitrate solution is obtained; and secondly, the reacted materials enter a relatively enlarged space, and even if a small amount of materials explode, the energy can be released in a larger space without danger.
However, because a certain amount of concentrated ammonium nitrate solution is accumulated at the bottom of the flash tank, the solution temperature is out of control and exceeds the critical temperature, and the explosion accident is hidden. Therefore, the invention also has further safety protection measures for the flash tank, and particularly, the temperature measuring device is arranged at the lower part of the flash tank and used for monitoring the temperature of the ammonium nitrate solution at the bottom of the flash tank in real time, and meanwhile, a steam condensate pipe is introduced into the flash tank and is interlocked with a control valve on the steam condensate pipe. Once the liquid phase temperature in the flash tank reaches the set control temperature, a control valve on a steam condensate pipe is opened immediately, condensate with lower temperature enters the flash tank, the temperature of the liquid phase in the flash tank is rapidly reduced, and ammonium nitrate solution is diluted to avoid explosion accidents.
The device for realizing the ammonium nitrate production method comprises the following steps:
a tubular reactor;
the front end of the tubular reactor is connected with a nitric acid feeding pipe and a gas ammonia feeding pipe, and material control valves are arranged on the nitric acid feeding pipe and the gas ammonia feeding pipe;
the vapor control valves are respectively connected with the vapor pipe on the nitric acid feeding pipe and the ammonia feeding pipe and are arranged on the vapor pipe;
a temperature measuring device mounted on the tubular reactor;
and a flash tank connected to the rear end of the tubular reactor;
the temperature measuring device is interlocked with the material control valve and the steam control valve.
The device for realizing the ammonium nitrate production method of the invention also comprises:
a temperature measuring device is arranged on the flash tank;
a steam condensate pipe led into the flash tank and a control valve arranged on the steam condensate pipe;
the temperature measuring device is interlocked with the control valve.
The invention adopts multiple safety protection measures for the tubular reactor and the flash evaporation tank in the method for producing the ammonium nitrate by the pressurized tubular reaction of the nitric acid and the gas ammonia, greatly reduces the possibility of explosion and realizes the safe production of the pressurized tubular reaction of the ammonium nitrate.
Drawings
Figure 1 is a schematic diagram of an ammonium nitrate production plant of the present invention.
Detailed Description
One end of the tubular reactor 1 was equipped with a nitric acid feed pipe 3 and a gaseous ammonia feed pipe 4, and material control valves FC1 and FC2 were provided on the feed pipes. Vapor pipes 5 and 6 are respectively connected with the back of the material control valves of the nitric acid feeding pipe 3 and the ammonia gas feeding pipe 4, and vapor control valves HV1 and HV2 are arranged. The tubular reactor 1 is equipped with a temperature measuring device T1, FC1, FC2, HV1, HV2 and T1 interlock. The rear end of the tubular reactor 1 is connected with a flash tank 2, the bottom of the flash tank is connected with an ammonium nitrate conveying pipe8, and a neutralization steam output pipe 9 is arranged above the flash tank. The temperature measuring device T2 is installed at the lower part of the flash tank 2, a steam condensate pipe 7 is led into the flash tank 2, and the T2 is interlocked with a control valve FC3 on the steam condensate pipe 7.
During normal production, the material control valves FC1 and FC2 are opened, the vapor control valves HV1 and HV2 are closed, and nitric acid and ammonia gas enter the tubular reactor 1 through the feeding pipes 3 and 4 to carry out neutralization reaction; the generated ammonium nitrate is discharged into the flash tank 2 from the other end of the tubular reactor; the steam flashed off is discharged from a neutralizing steam output pipe 9 and can be used for other heating devices to recover the heat energy of the steam; the concentrated ammonium nitrate solution is stored at the bottom of the flash tank and is sent out by an ammonium nitrate conveying pipe 8, and the concentration of the ammonium nitrate solution is 76-82%.
The temperature measuring device T1 arranged on the tubular reactor 1 monitors the temperature in the tubular reactor in real time, and once the set control temperature is reached, the material control valves FC1 and FC2 are immediately closed in an interlocking manner, reaction materials are cut off, the steam control valves HV1 and HV2 are rapidly opened, low-pressure steam is introduced, residual reaction materials in the tubular reactor are flushed out, and explosion in the tubular reactor is avoided.
The temperature measuring device T2 arranged at the lower part of the flash tank 2 monitors the temperature of the ammonium nitrate solution at the bottom of the flash tank in real time, once the liquid phase temperature reaches the set control temperature, the control valve FC3 on the steam condensate pipe 7 is opened immediately, the low-temperature condensate is added into the flash tank, the temperature of the ammonium nitrate solution is reduced rapidly, and the ammonium nitrate solution is diluted to avoid explosion.