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Evaporation of the ammonium nitrate solution process

 

Out the neutralization is more than 64% of the concentration , the temperature is 110 ~ 125 ℃ ammonium nitrate solution , dried and then flows into the small separator and is under the action of vacuum of 480 to 520 mm Hg , and the solution was then pumped into the continuous section of the evaporator tube is heated , the solution in the tube is heated by steam between the tubes and is vaporized to generate steam emulsion derived from the upper portion of the evaporator section of the tangential direction along the section at high speed into the separator device inside , a rotating motion , the centrifugal force , i.e. the solution flung inner wall of the separator and flow along the wall , after some evaporation , concentration of 75 to 80% , temperature 80 ~ 85 ℃, the lower portion of the separator was then dried pipeline , into a continuous pipeline Sec evaporator is between pipe steam heating ( Sec evaporator using nitric acid byproduct waste heat boiler steam as the heat source ) , the solution is heated and vaporized , the steam generated by the Sec evaporator emulsion upper export into the tangential direction along the inner Sec separator , a gas-liquid separation , the separated concentration of 90 to 92% , the temperature was 110 ~ 120 ℃ seal groove flows into the bottom of the separator via the pipe was then overflow flow solution tank .
 
A secondary steam separators Sec separated , derived from the upper portion of the separator . Convergence in a gas pipe, and then evaporating water into the water jet pump is condensed , non-condensable gas into the mixing tank along with the water .
 
Water flow is: the inner tube of the water , evaporation of water through the pump to the injection pump , and cooling effect , and then recycled into the tank , some of the waste drain.
 
Ammonium nitrate plant was originally 10,000 tons / year ( 100% ammonium nitrate ) design type . After several years of production practice , some changes were made to the original design . The main changes are hereby partially summarized as follows:
 
1, the original design evaporation, crystallization system using steam injection pump , after a period of time, found a steam jet pump to spend a lot of steam , the vacuum is not large temperature setting . Moreover , the operation is relatively cumbersome , through continuous exploration and improvement , and now uses a multi-nozzle shown in Figure 73 water injection process . Water jet pumps and electric water Xun ring vacuum pumps, piston pumps and steam compared to electric jet pump , has a simple structure , operations side variable , reliable and easy to manufacture , maintenance and so on . As a result of the water jet pump , the pump must be eliminated steam jet condenser and the atmosphere of a corresponding ancillary equipment. Meanwhile modify the process after a , Sec evaporation systems share a water jet pump , and the same degree of vacuum process is greatly simplified , and that the operation is more convenient , reliable , and to create the conditions to some evaporation .
 
2 . Under the original design , Sec separator line straight down the feed tube was inserted at the bottom of the slot man solution , which makes the solution flow tube under conditions of non -fat testing, analysis , Sec concentration , sampling is not easy, often due to the heating steam pressure the degree of vacuum is too high or the concentration fluctuations of the tube is too high, clogging or solution in the separator is pumped to run , the lower the downstream tube was no such phenomenon, but these phenomena difficult to find. They bring a lot of difficulties to the evaporation operation . After several years of repeated practice and continuous improvement , the original design of the next feeding tube inserted directly into the bottom of the solution tank to make ammonium nitrate solution was evaporated after the first inflow of liquid seal groove , and then overflow into the melting tank " intuitive cutting ." . That will be the next feeding tube inserted into the liquid seal groove. Sec separator was separated first by cutting down the pipe into the liquid seal groove . And by the liquid seal tank overflow pipe into the solution tank . Such flow conditions and concentration of the solution can be directly observed by the level of the liquid seal groove in the surface and the overflow pipe estuary , Sec sampling is also more convenient. Under Sec material found is not normal or high concentration is too low, it may be timely adjusted promptly . The liquid seal at the lower tank through ammonia, a tube similar to the nozzle and is ammonia , the better , and the acidic solution was evaporated , the fluid seal groove actually played the role of ammonia tank solution tank ammonia can not pass up .
 
It should be noted that under the separator tube to the vertical height of the liquid seal between the grooves of not less than 7 meters , taking the time to prevent the solution .
 
3 . Original design process with a solution pump , dilute solution for playing while driving cycle . However, due to pipeline straight through the small pipe length , solution volume is small. Therefore , the piping and valves , often crystallizes clogging. When used, it often takes time to steam blowing through , very square changed, nor safe. After repeated practice and continuous improvement , the use appears to be very simple " solution self loop" devices. Successfully replaced the original design of the solution pump forced circulation . Thus eliminating the need for a solution pumps and motors , valves and plumbing fixtures attached , greatly simplifying the process . Moreover , the operation is very simple and convenient. Just pick from the top of the overflow pipe liquid seal groove 500 mm at a straight 57 mm long by 3 meters stainless steel drain tube through the re- neutralizer , which constitutes a " solution self- loop" device, when the operation encountered special circumstances require the solution evaporation cycle as long as the solution with a long cork sealed tank overflow pipe outlet plugged . The feed tube in a solution can automatically re- flows into the tube through the solution and refluxed for secondary and evaporated. To be evaporated into normal operation after unplug the cork , and the solution to the solution tank overflow . Return pipe after use , do not blow off steam and will not clog .
 
4 · recovery of ammonia gas on the tank . By-product in the production of ammonia gas in the tank , the amount of ammonia is generally containing 40 to 70% . About 3 ~ 5% of ammonia production, that is, an annual output of 5,000 tons of ammonia fertilizer plant , released a year on gas tank containing ammonia 5000 × 3 ~ 5% ie 150 to 250 tons. A nitrate such as processing , is 300 to 500 tons . Therefore , how to effectively recycle synthesis gas tank release of ammonia , is a very economic significance , worthy of attention problems .
 
Original design, the recovery of ammonia synthesis gas tank is adopted such a program, the tank is mixed with ammonia gas after gas directly together and fed into the reaction with nitric acid . Due to the higher gas tank gas such N2.H2.CH4 content , after mixing, resulting in lower purity ammonia gas , and cause instability in the operation , and the vibration is violent , the loss of ammonia and steam has increased . Practice has proved that this method does not work .
 
After several years of exploration and improvement , use the following methods in the recovery of such a tank of ammonia gas , shown in Figure 74 :
 
That will be sent tanks synthesis gas pressure regulating valve after the two were sent to acid tank through two tanks of gas pipelines. Tank to the bottom of the gas pipeline has been through the acid tank , pipe ejected by segment , tank of ammonia gas that is generated ammonium nitrate solution and nitric acid : unreacted other gases H2.N2.CH4 etc. , emptying the acid tank vent pipe . When operating in the two acid tank can be rotated , ie the production of acid tank with a # , you can pass the acid tank # 2 tank of gas , the production of acid tank with # 2 , # acid tank can pass to a tank of gas . The stirring action from the overflow tank back to the high nitric acid, mixed acid solution of ammonium nitrate in nitric acid tank is relatively uniform , with nitric acid and ammonium nitrate containing dilute ammonia and also to favor the progress of the reaction , the recovery without special care , but also saves stainless steel .
 
Years of production practice prove that the recovery tank of ammonia gas is feasible , of course, there are some really points to be further improved and perfected.
 
5 original design , no ammonia preheater, consider the system back in order to ensure safe production of ammonia and product quality standards, or an increase of ammonia preheater as well. Ammonia can enhance the effect of the temperature 60 ℃, increasing concentration and improve the yield.
 
Ammonia preheater for the ordinary tube heat exchangers.
 
6. One . Sec evaporation phase separator Unicom , the vacuum degree equal.
 
7 . Feed the material crystallized vacuum system also carried out a series of transformation.
 
Because of the above transformation, comprehensive capabilities increased by 50% to an annual 15,000 tons of ammonium nitrate , crystallized capacity can be increased to twenty thousand tons .

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