SU883020A1 - Method of producing urea - Google Patents

Description

(Sj) METHOD FOR OBTAINING UREA

,

 The invention relates to an improved method for producing urea, which is used in the production of nitrogen fertilizers. The closest to the invention to the technical essence and the achieved result is a method for producing urea, including its synthesis from ammonia and carbon dioxide, distillation followed by evaporation of the resulting solution to a highly concentrated melt and granulation at the melt temperature in the granulator 125-135 C. Drops The melt at the exit from the granulator is cooled and solidified with a free fall in the upward air flow of the LP.

However, when implementing this method in an industrial granulation tower with a flight height of 30-50 m, it is not possible to obtain a homogeneous particle size distribution. The content of granules with a diameter of 2-3 mm in the initial product is less than 50, which does not satisfy the requirements imposed by agriculture on granulated urea. This is due to the fact that in the granulation process in the granulation tower, liquid urea droplets have a high initial temperature. Therefore, the height of the free fall of droplets in the air must be sufficient for the granules to reach the base of the tower in the opening of the ninth state. Pellets with a diameter up to 1 mm harden in flight almost completely. Granules fraction of a diameter of 2-3 mm have a high temperature at the outlet of the tower,

15 especially during the summer period, therefore the semi-hardened granules are subject to destruction and deformation. As a result, the spherical formula of the granules is distorted, its mechanical strength decreases and the proportion of defective granules increases, which leads to a decrease in the product fraction, heterogeneity of the particle size distribution and deterioration of the agronomic properties of the fertilizer. In addition, there is a sticking of frozen granules to the walls and bottom of the tower, which contributes to the formation of conglomerates and requires cleaning the device. The aim of the invention is to improve the uniformity of the particle size distribution of urea. The goal is achieved by the method of obtaining urea, including its synthesis from ammonia and carbon dioxide, distillation followed by evaporation of the resulting solution to a highly concentrated melt and granulation, the melt being supercooled before granulation to a temperature of 113.7120 ° C. I. Super melting of the melt produced t up to 113.7-120 С in view of the fact that when the temperature of the melt is below 113.7 ° C, there is a risk of its crystallization directly in the granulator, and when the temperature of the melt is above 120 ° С, it is necessary to provide a large height It is designed to cool the liquid droplets from the initial temperature of the melt to the solidification temperature of the droplets. Subcooling of urea melt to 113.7–120 ° С allows partial heat removal (25) from the sprayed melt before dispersing in the granulator. Thus, when implementing the proposed method for producing urea in the granulation process, the free fall height of the liquid droplets is reduced, which is necessary for cooling them from the initial temperature of the melt to the solidification temperature. As a result, the temperature of coarse granules with a diameter of 2–3 mm at the outlet of the tower decreases, which ensures greater hardness and regular spherical shape of the granules in the finished product. The drawing shows a diagram explaining the method of producing urea. An example is r. Conducted urine synthesis from carbon dioxide and ammonia. NHj 18600 kg / h (1), COj, 22000 kg / h (2) in the form of fresh components and 59363 kg / solution of ammonium carbon salts (H) of the composition: NH, kg / h, COg 15000 kg / h As a result of the reaction of CO., (NHg) 2+ HgO, 04 of ammonia passing with an excess, with a degree of conversion of 60%, the melt of urea (C) is released: NH, 37000 kg / h, SO 15000 kg / h, 13000 kg / h The CO (NH) J is 30,000 kg / h and is fed to the distillation II. From site II of the distillation of urea melt, a stream of ammonium salts (G) in the amount of 593 gCh / h, gaseous ammonia (5) for disposal in the amount of 300 kg / h, gaseous ammonia (6) in the amount of 1300 kg / h to obtain ammonia marketable water in node III, dilution of urea (13) in the node. IV evaporation of the composition: NH 580 kg / h, SOD 220 kg / h, 10B07 kg / h, urea 30,000 kg / h, with a total amount of 41407 kg / h. To return part of NHj and COj "to synthesis unit I, from site III evaporation using a system V of the wastewater treatment, a stream of gases (7) of desorption and hydrolysis of the composition: NHj 580 kg / h, CO 220 kg / h water 1570 kg / h. In node III, the evaporation of the urea solution is adjusted to the desired concentration of moisture (0.2). For the operation of the ejectors of the evaporation system, water vapor (8) is introduced into the evaporation unit IV in the amount of 8,700 kg / h. The resulting polluted condensate (9) of the process (condensate of steam steam from the PSC) is processed in the wastewater treatment unit V, from where the purified water (10) is discharged into the sewage system or to biochemistry. Part of the PSC (11) is sent to obtain ammonia marketable water at site III for the production of ammonia water and in the form of a 25-th solution (12) is displayed to the consumer. The finished water (1) of urea composition: HjO 60 kg / h, urea 30,000 kg / h at temperature is sent to the node VI granulation of the product. Supercooling from 140-145 ° C of urea melt to 113.7-120 ° C is carried out at node VII for 90-110 seconds. Then, the melt supercooled in node VII, remaining in the liquid state, is directed to the dispersing device of the granulation tower VIII. The granulation of liquid urea droplets occurs when they are freely dropped in a countercurrent of cooling air having a temperature of 20-30 0 and a feed rate of 0.2-0.5 m / s to the granulation tower. The formed granules (15) are removed from the base of tower VIII, where temperature and content of pellets with a diameter of 2-3 mm are measured in comparison with GOST 208175. The temperature of the melt in the granulator (the initial temperature of the liquid droplets), C 113,

Pellet temperature

at the exit of the tower, ° C

Granule content

fraction diameter

2-3 mm compared

with GOST 2081-75, I The use of the proposed method for producing urea provides an increase in the content of a fraction with a diameter of 2-3 mm on average by 15 compared to GOST 2081-75, which improves the agrotechnical properties of urea and increases the efficiency of its use in agriculture; the increase in the mechanical strength of the granules by S%, which increases the safety of the product during transportation and storage; an increase in the flowability and a decrease in the caking ability of granulated urea, which improves the use of urea in agriculture at the soil application stage. The tests showed that the proposed method provides the technical and economic effect of introducing the invention in the amount of 2-2.5 rubles

80

65 66-70 75

60

50 50

50

Claims (1)

"8830206. To obtain comparative data, granule melting was performed with different initial temperature of the liquid droplets. 125 130 ItO 117 120 LN per ton of granulated urea. DETAILED DESCRIPTION A method for producing urea from ammonia and carbon dioxide, followed by distillation, evaporating the resulting solution to a highly concentrated melt, and granulating, characterized in that, in order to increase the uniformity of the urea granulometric composition, the melt is supercooled before granulation to a temperature of 113.7-120 C. Sources of information taken into account in the examination 1. USSR certificate of authorship If 251571, cl. C 07 C 126/00, 1965 (prototype). -I (381 fi Г -: ь 35-: V-K-, -J- m -