SU682510A1 - Method of the automatic control of a process of recuperation of unreacted ammonia and carbon dioxide - Google Patents

Description

30-50% exceeds the required amount in the disposal zone. In these cases, an excess of contaminated ammonia is mixed with a pure fraction recycled to the synthesis, containing not more than 0.005 days. %, which leads to an increase in carbon dioxide content in return ammonia to 0.05 wt. % and above and the emergence of non-beats in the operation of the unit.

The drawing shows a device that implements the proposed method. High-pressure distillation gases (16–20 kgf / cm) with a temperature of 130-160 ° C are supplied via conduit 1 to a washing column 2 irrigated with high-concentration ammonia water from a conduit 3 and a weak solution of ammonium salts from a pipeline 4 from a low pressure distillation stage . The column 2 is equipped with a heat exchanger 5 through which cooling water circulates. The temperature in the lower part of the column is 90-100 ° C, in the top - 45-50 ° C. In the process of absorption and condensation of high-pressure distillation gases, a concentrated solution of ammonium carbon salts (UAS) is formed, which is returned to the synthesis at pipeline 6. Gaseous excess ammonia with a small amount of carbon dioxide (0.05-0.1 wt.%) Through pipeline 7 It goes into the condenser 8, designed to carry out the first stage of the fractional condensation of ammonia at a temperature of 40-45 ° C, sufficient to condense the main amount of carbon dioxide and the gas phase. As a result, the return ammonia, which is channeled through the pipeline 9 to the next condenser and further to the synthesis, is almost completely free of carbon dioxide (0.005 wt.%).

The carbon dioxide-contaminated ammonia fraction with a content of 0.1–0.2 wt. % from condenser 8 through line 10 is directed to the irrigation of column 2. When the disturbances occur, the material and heat balance of column 2 changes, including the amount of gaseous ammonia flowing through pipe 7. In order to ensure the efficiency of the process of separation and purification of ammonia, the irrigation of the column 2 is accordingly changed, taking into account its total load on ammonia.

The component composition and magnitudes of the material flows shown in the diagram are determined from the material balance equations of the urea production unit taking into account the mathematical models of each apparatus, in particular the flow through pipeline 1 as a result of calculating the material balance of the high pressure distillation unit pressure distillation. The following dependencies are used to calculate column 2:

/ 1.00658 Р-777.47 / Г-0.005088 RF-2.289,

(P where / is the fugacity of ammonia;

T and P - absolute temperature and pressure in the apparatus.

Q.,. N, exp2,303 (-6,697 + 1405.8) 7 - f

+ 1,202Хм-г, + 1,, o, (2)

where L Нз-constant equilibrium ammonia;

 and n, o-mole fractions of ammonia and water in the equilibrium phase. Calculation of the material balance of the column

2 is performed by means of a control computational mask (CCL) 11, into which all necessary information is entered (shown by dash-dotted lines) from temperature sensor 12, pressure sensor 13 and flow sensors 14, 15. Sensor signal 14 is multiplied by a factor proportional to the end of the ammonia water. The CCM of a non-periodical, in accordance with the cycle of obtaining information and calculating the material balance (for example, once every two minutes), determines the amount of gaseous ammonia at the output of column 2, forms a proportional signal, which is issued as a task to the local flow controller 16 the control valve 17 on the water supply line to cool the water to the condenser 8. At the same time, to compile the oscillation of the thermal conditions of the lower part of the column 2 while controlling the flow rate of the contaminated ammonia fraction Using the temperature sensor 18, the middle part of column 2 (bottom of the packing) is corrected for temperature. This is also necessary in order to reduce the transient interplay when generating a control signal, for example, the duration of the ACL operation cycle is taken into account.

The valve 17 controls the flow of cooling water, changes the amount of ammonia to be liquefied in the first zone of fractional condensation. In the absence of a CCM, the sentence is

The method can be implemented on local means. For this purpose, flow sensors of 19 distillation gases, 20 solutions of weak UAS, 21 solutions of strong UAS, composition gauges (content

ammonia), 22 in distillation gases, 23 in a solution of weak AAS, 24 in a solution of a strong AAS, 25 in concentrated ammonia. The signal from each flow sensor is multiplied by the signal from the corresponding composition sensor using function blocks 26, 27, 28, 29 that generate signals proportional to the amount of ammonia in each stream. Output signal of the algebraic block 30

This is a task for the controller 16.

Claims (2)

1. USSR author's certificate No. 452558, cl. C 07C 127/04, 1972. 2. Sinev K. N. and others. Production of carbamide. M., “Himi, 1970, p. 165-167. R