SU1696387A1 - Method of ammonia synthesis - Google Patents

Abstract

A method of producing ammonia provides for introducing a nitrogen-hydrogen mixture into a catalyst layer divided into at least two parts by a plane which is perpendicular to the initial gas mixture flow direction. The temperature of the initial gas mixture introduced is 20-250 DEG C, its pressure 10-100 MPa and the temperature of the catalyst before introduction of the inital gas mixture is 420-590 DEG C. The direction of the initial gas mixture introduced into the catalyst is periodically changed to the opposite one. The nitrogen-hydrogen mixture is mixed between the catalyst layers formed during the division of the latter in a ratio of (0.5-1):1 until its temperature gradient between the preceding and subsequent layers of the catalyst does not exceed 20 DEG C. The ammonia generated and the non-reacted part of the nitrogen-hydrogen mixture are extracted from the catalyst layer. The method of producing ammonia enables an end product with a yield of 14-30 % to be obtained.

Description

The invention relates to chemical technology and can be used to synthesize ammonia from a nitric mixture, respected by processing natural or associated gas in enterprises of the nitrogen industry.

The aim of the invention is to increase the yield of ammonia by reducing the overheating of the catalyst.

The method is carried out as follows.

The catalyst layer is divided into two parts, the ratio (0.5-1) 1. between which the gas mixture is stirred to the maximum maximum temperature difference in the gas mixture in the cross section perpendicular to the gas flow, no more than Raadel - from the catalyst bed to two equal the parts correspond to the ratio of volumes 1. The mixing of the gas mixture is carried out in the zone of maximum temperatures which takes about 1/3 of the total volume of the catalyst bed and is located on its central part along the gas flow. The mixing of gas outside the zone of maximum temperatures with a volume ratio of less than 0.5 drastically reduces its efficiency, since the gas temperature here is lower than the maximum one. The terii alignment of the inhomogeneities in the gas mixture by mixing is related to the pressure lottery. When the gas mixture is stirred until the maximum temperature difference in the cross section is reached, which is perpendicular to the gas flow, less than 20 ° C

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Mixing rates increase substantially. With a larger temperature difference in the cross section, perpendicular to the gas flow, after mixing, overheating zones and echoles in the catalyst layers form, reducing ammonia yield by more than 10%.

The process of ammonia synthesis is carried out in non-stationary mode. A gas mixture with a temperature of 20-250 ° C and a pressure of 10-100 MPa is fed to the first part of the catalyst bed along the gas path. Supply of a gas mixture with a temperature below 20 ° C does not lead to an increase in the ammonia yield, and the supply of gas with a temperature of more than 250 ° C leads to a decrease in the ammonia yield due to the formation of a catalyst bed below the optimum temperature, and also a significant reduction in the time between switching directions. feed gas mixture. The efficiency of the ammonia synthesis process at pressures below 10 and above 100 MPa is significantly reduced due to the fact that at low pressures the yield of ammonia is significantly reduced, and at high pressures the cost of equipment is significantly increased. The gas mixture leaving the first layer has a high temperature, differing in cross section, perpendicular to the gas flow, by 15 ° C to 200 ° C. To equalize the temperature irregularities, the gas mixture is stirred until the maximum temperature difference in the cross section, perpendicular to the gas flow, is reached, not more than 20 ° C and is fed to the second part of the catalyst bed.

Due to the fact that the characteristic time for establishing temperature inhomogeneities due to structural heterogeneity of the layer is longer than the time between switching gas supply, mixing the gas mixture between the catalyst layers leads to the formation of uniform temperature profiles in each section of the reactor and, thereby, allows There is no optimal mode of operation of the reactor as a whole.

The change in the direction of supply of the gas mixture to the catalyst bed from inlet to outlet is carried out with a switching period of 1-5 minutes (switching time 0.5-2.5 minutes). With a fixed load, with a decrease in the maximum allowable switching period, the ammonia output is reduced. As the period increases, the heat from the catalyst bed is blown out by the feed mixture and the reactor cools down, the reaction is stopped. The synthesis of ammonia can be carried out with a period of 5-30 minutes, but for this it is necessary to reduce the load on the catepizer in order to maintain a high ammonia yield.

To create optimal temperature regimes, lowering the maximum

temperatures inside the catalyst bed and, thus, increasing the yield of the product, ammonia synthesis is carried out in an unsteady way on catalyst grains 15-30 mm in size. Grains of this size have

0 significantly smaller outer surface per unit volume of the layer as compared to practical grains of size less than 15 mm. Due to this, the heat exchange rate is reduced.

5 filtering gas and a layer, which leads to an increase in contact time required by the time of heating the cold gas to high temperatures. During this time, some of the initial reagents manage to enter into the ammonia synthesis reaction, the partially reacted mixture enters the high temperature zone and the reaction proceeds with a lower heat release, which leads to a decrease in the maximum temperature.

5 To prevent diffusion braking of the reaction inside large grains of the catalyst, there are provided through coaxial holes with a diameter of 3-15 mm. These holes can be either one or the other.

0 large, or several small.

Due to the lowering of the maximum temperature and the smoothing of the temperature profiles caused by the use of a coarse-grained catalyst, the temperature of the reactor approaches the optimum, and the hydraulic resistance of the reactor is significantly reduced.

The use of catalyst grains larger than 50 mm so greatly reduces the intensity of the processes of heat and mass transfer between the filtering gas and the catalyst, so that to maintain a high yield of ammonia, it is necessary to substantially

5 to increase the amount of catalyst, i.e. lower the gas flow rate.

PRI me R 1. A catalyst layer of grains 3-5 mm in size is divided into two equal parts (volume ratio 1) and warmed to

0 500 ° C. The gas mixture containing,%: nitrogen 22; hydrogen 66; inerts 10; ammonia 2, served on the first layer of the catalyst. The temperature of the gas mixture is 20 ° C. pressure 32 MPa. volumetric flow rate 1200.

5 Switching period of the gas flow direction 1 min. Between the catalyst layers, the gas mixture is stirred until the maximum temperature difference in the cross section, perpendicular to the gas flow, is reached, 20 ° C. The average yield of ammonia is 16.1%.

EXAMPLE 2. Same as in Example 1, but the switching period is 30 minutes. Gas displaced heat from the catalyst bed, ammonia synthesis does not react.

Example 3: Same as in Example 1, but the temperature of the gas mixture at the inlet to the catalyst bed is 100 ° C, the switching period of the gas flow direction is 4 minutes. The average yield of EMC is 19.7%.

Example 4. Same as in example 1, but the temperature of the gas mixture at the inlet to the catalyst bed is 250 ° C. The average yield is 19%.

Example 5. As in Example 1, the pressure 10 MPa, the temperature of the gas mixture at the inlet to the catalyst bed is 100 ° C, and the switching zone is 5 minutes. The average yield of ammonia is 10%.

For example, the same as the B example, pressure at 100 MPa. The average yield of ammonia is 32%.

PRI me R 7. Same as in example 3, but the catalyst grain size of 15 mm. The average yield of ammonia is 20.2%.

Example 8, Same as in Example 3, but catalyst grains 50 mm in size. Ammonia yield 16%.

Example 9. Same as in Example 1, t, the gas mixture is stirred until a maximum temperature difference in cross section is reached, which is perpendicular to the flow of gas at 30 ° C. The average yield of ammonia is 14.5%.

PRI me R 10. Same as in example 1, but the layer of catalyst is divided into two parts with the ratio of a smaller volume to a larger 0.3: 1. The average yield of ammonia is 14%,

Example 11. Same as in example 1, but the catalyst layer is divided into two parts with the ratio of a smaller volume to a larger 0.4: 1. The average yield of ammonia is 15%.

Note er. 12. Same as in example 1, but the catalyst layer is divided into two parts with the ratio of a smaller volume to a larger 0.5: 1. The average yield of ammonia is 15.8%.

PRI me R 13. Same as in example 1, but the catalyst layer is divided into two parts with the ratio of a smaller volume to a larger 0.6. The average yield of ammonia is 15.9%,

PRI me R 14. Same as in example 1, but the layer of catalyst is divided into two parts

with the ratio of a smaller volume to a greater 0.7. The average yield of ammonia is 16%.

Example 15. Same as in Example 1, but the catalyst bed is divided into two parts with the ratio of a smaller volume to a larger 0.8. The average yield of ammonia is 16%.

Example 16. Same as in example 1, but the catalyst layer is divided into two parts with a ratio of less than volume to a greater 0.9. The average yield of ammonia is 16.1%.

Example 1. Same. 4iO and in example 1,

nor g e, govuy mix nc ,, to reach; es, .... ch smm m p oh lzkos1i temperatures

at . perpendicular to the rrcvoKy gas

i; W. ;: HELL .a 16.4%.

m p and m e & (by a known method). That xt. what is in group vsne T, but katal.zzztor sa- G0chok yn one sls-s, - ;. gas mixing by medium; to instant. So - v, orzzo-vf g.ri razz / v-4 -nkgl layer / isetora two parts and a ratio of (0.5-) 1 at a temperature difference in the cross section of the cohalker layer 10-20, at the gas temperature at the inlet layer To-killer 20-250 ° C. s also np-t carrying out the process from a catalyst with a grain size of 15-50 mm and so forth, the output increases from 14 to 14.5-32 /%.

About About rm at g, and about about RETTA h n and

Claims (2)

1 Method of synthesis of ".. n.. Aa, including the supply of a hydrogen-hydrogen mixture to the catalyst bed, from hot to 420-590 ° C with a periodic change of -: apoavlen pod h; it is on the contradiction, about i and h h go and with and so. oh, in order to increase the ammonia output, by reducing the overheating of the catalyst, the catalyst layer is divided into two parts in the ratio (0.5-1): 1 m (The gas mixture is mixed before feeding into the second part of the catalyst bed until the maximum temperature difference of the gas mixture is reached in a cross section perpendicular to the gas flow not exceeding 20 ° C. 2. The method according to claim. Characterized in that the process of pulses at a pressure of 10-100 MPa nagalittoe with a grain size of (15-50) mm to the transfer switch psdach 1 gas mixture (1-25) min and gas inlet temperature of 20-250 ° С.