DK150712B - Apparatus for high-pressure synthesis, especially for synthesis of ammonia - Google Patents

Description

150712

The present invention relates to an apparatus of the kind specified in the preamble of the claim for high pressure synthesis, in particular for the synthesis of ammonia, and the apparatus according to the invention is characterized by the characterizing part 5 of the claim.

In high-pressure catalytic reactors for the synthesis of ammonia with several successive catalyst layers, it is known that the gas between the catalyst layers is cooled by exchange of heat in the interior of the reactor with the inflow gas, all layers being axially flowed through the synthesis gas (see Austrian Patent Nos. 216 533, No. 225 722 and No. 215 436).

Also known are plants in which the first catalyst beds are axially flowed, while the long final catalyst layers are flowed radially inside and out (Austrian patent specification 281 8709, in which, inter alia, heat is exchanged with the supplied gas The advantage of this in comparison with the only radially flowing furnaces described in German Patent Specification no.

1,256,205, and by which the gaseous flow alternately from the outside and in and then from the inside out, avoids the formation difficulties in the reduction of the oxide NH 2 synthesis catalyst which occurs by radially conducting the gas externally and inwardly.

Compared to furnaces with purely axial flow, the advantage lies in the smaller pressure loss, which is particularly disturbing in the long end catalyst bearings, while the pressure loss in the relatively modest input catalyst bearings has been considered so low that there would be no any advantage of passing the gas radially through these catalyst beds. On the contrary, it was feared that yield losses would occur in the particularly reactive input catalyst beds, especially when using a small grain size catalyst due to local overheating, especially in the regions of the catalyst beds located near the axis.

Surprisingly, it has now been found that, in comparison with the usual axially flowing furnaces, the synthesis of ammo niak in furnaces with heat exchange in the reactor can be improved by at least 10-13% if all catalyst beds are flowed radially inward from 10 and beyond, and a particle size of less than 3 mm is used.

It is the object of the invention to provide an apparatus which is particularly suitable for carrying out a high pressure synthesis according to the stated guidelines, in particular the synthesis of ammonia.

The apparatus according to the invention is characterized in that each catalyst bed is arranged between two cylindrical perforated metal plates which are concentric with the central means for passing the gas and of which the inner 20 perforated metal plate together with the central means for passing the gas and the outer perforated a metal plate together with the furnace insert housing each forms an inner annulus which serves to supply the gas to the catalyst and an outer annulus which serves to divert the gas, these perforated metal plates being terminated by a container lid and a container bottom, the container lid having a passage for the gas which opens into the innermost annulus near the axis, and the bottom of the container has a passageway for the gas connected to the outer annulus near the furnace insert housing.

In the drawing, an apparatus according to the invention is shown with three catalyst bearings, 2 being the high pressure container and the furnace insert, while 4 is the annular space between the furnace insert and the high pressure container. The gas supplied at 1 flows backwards through the furnace, from where it is fed into the main heat exchanger. The catalyst bearings 6 lie between 5 the concentric annular metal plates 10 and 11 and are separately bounded by a container lid 8 and a container bottom 9. In the container lid 8 there is a gas line 14 in the vicinity of the central means for controlling the gas. In the bottom 9 of the container there are gas passages near the furnace insert 10. The inner annulus 16 serves to supply the gas to the catalyst bed, and the annulus 17 serves to drain the gas from the catalyst bed.

The number 7 is the middle heat exchanger and 18 is gas extracted from the furnace. The number 12 is annular concentric metal sheets welded to the container lids 8 which project into the catalyst filling to prevent a short-circuit of the gas as the catalyst settles. The central means 13 for controlling the gas is, in this furnace construction, a central pipe located at the height of the bottom catalyst bed. After the first intermediate heat exchanger, it consists of a central pipe, around which are arranged two concentric wires of annular cross section. Through the outer ring pipe, the gas is fed to the overlying heat exchanger, from which, after a rotation of 180 °, it is returned again at the level of the first intermediate heat exchanger and from there into the central pipe in which a burner 19 is arranged.

The apparatus according to the invention may also be provided with supply means enabling the supply of fresh cold gas to the pipe space in the heat exchanger 7, which allows a fine control of the temperature in this heat exchanger 7.

The fresh gas which has passed through the annulus between the high pressure vessel and the furnace insert encloses into the tube meal compartment of the main heat exchanger 5 where it is heated by the synthesis gas which is discharged. The gas is passed through the central control means 13 to the upper end of the furnace, thereby passing through both of the intermediate heat exchangers 7 and being further heated. From the upper end it enters via the opening 14 5 of the upper catalyst bed 6 into the inner annulus 16 of this catalyst bed, from which it flows through the catalyst in the radial direction and through the annulus 17 and the gas passage 15 into the middle heat exchanger, where it cooled. Having similarly passed through all the catalyst beds, the gas leaves the furnace via the main heat exchanger 5 and the outlet 18. The invention is further illustrated by the following example.

EXAMPLE

Using the apparatus shown for the synthesis of ammonia, a synthesis mixture of gases 15 of 75000 Nm 2 / h is radially guided from the inside out through 3 catalyst bearings at an overpressure of 310 atm. Before it is put into the oven, does the gas have the following composition? 67.5 vol.% L, 22.5 vol.% N 2, 8.0 vol.% Inert gas, 2.0 vol.% NH3.

The total catalyst volume is 2.2 m 2.

The catalyst is prepared in the furnace from a mixture of ferric oxide (Fe 2 O 2) and 0.5% by weight potassium oxide, 2.8 - 3% by weight alumina, 3.3 - 3.4% by weight calcium oxide and 1% by weight. % magnesium oxide by reduction with a mixture of 25 hydrogen and nitrogen. The average particle size is 2 mm. The ammonia synthesis is carried out at 310 atm and at a temperature of 400-500 ° C. The gas contains 17.81% by volume of NH3 at the furnace exit.