MXPA98002989A - Process and reactor for ammoni preparation - Google Patents

Abstract

A process for the preparation of ammonia at elevated pressure and temperature in an ammonia reactor, which comprises passing a stream of the ammonia synthesis gas process successively through at least three catalyst beds, and reacting the synthesis gas in the beds, to cool in an intermediate way the partially reacted synthesis gas that leaves the catalyst beds, by heat exchange in the heat exchangers configured between each catalyst bed, and to remove an effluent of product rich in ammonia, where the current The process is obtained by combining, before being introduced into a first catalyst bed, a first syngeneating gas feed stream that has been preheated through indirect heat exchange, during the intermediate cooling of the partially converted synthesis gas, a second synthesis gas feed stream that has been preheated by indirect heat exchange with the product effluent, and a third synthesis gas feed stream to adjust the temperature of the process stream, and where the first feed stream is successively passed through the heat exchangers between beds to cool the partially converted synthesis gas

Description

PROCESS AND REACTOR FOR PREPARATION OF AMMONIA FIELD OF THE INVENTION The present invention relates to a process and reactor for the preparation of ammonia from a synthesis gas comprising nitrogen and hydrogen through the passage of the synthesis gas through a number of catalyst beds with intermediate cooling of synthesis gas partially converted between the catalyst beds. In particular, the invention relates to an improved process of the above type and to an ammonia reactor for use in the process, wherein the cooling of the partially converted synthesis gas is carried out by indirect heat exchange with a single stream of synthesis gas cool. BACKGROUND OF THE INVENTION U.S. Patent No. 4,181,701 discloses an ammonia reactor with an upper and a lower catalyst bed, with a central heat exchanger mounted on one of the beds. A stream of process synthesis gas is obtained by combining the separate feed streams inside the reactor; a cover current serving to cool the reactor cover, an exchange current serving to cool the central heat exchanger, and a bypass current for the final adjustment of the process current temperature. Further, indirect cooling of ammonia synthesis gas partially converted into a reactor with more than two catalyst beds is known in the art and is conventionally applied in the industry. In this way, the synthesis gas is indirectly cooled, passing fresh synthesis gas in a number of separate streams to the heat exchangers between the catalyst beds. The streams are introduced through separate tube connections mounted on the reactor deck. The main drawback of the known ammonia preparation processes with the intermediate cooling of the partially converted synthesis gas into a number of heat exchangers between beds with separated gas streams, is the need for numerous inlet elements and a complicated pipe in the ammonia reactor. SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a process for the preparation of ammonia in more than two catalyst beds with intermediate cooling of the partially converted synthesis gas, wherein the gas is cooled between the catalyst beds by exchange of indirect heat, without the above drawbacks of the known processes. According to the above object, this invention provides a process for the preparation of ammonia under pressure and elevated temperature in an ammonia reactor, which comprises passing a stream of ammonia synthesis gas from the process successively through at least 3 beds catalysts, and react the synthesis gas in the beds; cooling in an intermediate manner the partially reacted synthesis gas leaving the catalyst beds, by exchanging heat in the heat exchangers configured between each catalyst bed, and removing an effluent of product rich in ammonia, wherein the process stream is obtained by the combination, before being introduced into a first catalyst bed, of a first synthesis gas feed stream that has been preheated through indirect heat exchange, during the intermediate cooling of the partially converted synthesis gas, a second stream of synthesis gas feed that has been preheated by indirect heat exchange with the effluent of the product, and a third synthesis gas feed stream to adjust the temperature of the process stream, and where the first feed stream is passes successively through the heat exchangers between beds to cool the partially converted synthesis gas. A further object of the invention is to provide an ammonia reactor for use in the process of the invention, with simplified inlet and pipe means, for the distribution of fresh synthesis gas which serves as the cooling medium in the indirect heat exchange with the partially reacted synthesis gas between each catalyst bed. Accordingly, an ammonia reactor according to the invention comprises, inside a cylindrical shell under pressure, at least one first, one second, and one last catalyst bed vertically configured around a common axis, and connected in series; intermediate heat exchange elements configured between each catalyst bed, for the intermediate cooling of a partially converted ammonia synthesis gas from the catalyst bed, by indirect heat exchange with a first fresh ammonia synthesis gas feed stream; feed effluent heat exchange elements configured at the outlet of the last catalyst bed, to cool an effluent stream of ammonia product, by indirect heat exchange with a second feed stream of ammonia synthesis gas; input elements for introducing the first feed stream, and input elements for introducing the second feed stream into the reactor; input elements for introducing a third feed stream of fresh ammonia synthesis gas into the reactor; elements for passing the first, second, and third feed streams to the upper catalyst bed; and elements for combining the feed currents in a process stream, before introducing the process stream into the upper catalyst bed, wherein the elements for passing the first feed stream consist of a passage-way, to connect in series the intermediate heat exchangers, and for passing the first stream from the input element consecutively through the intermediate heat exchange element to the element for combining the feed streams. The invention will be explained in more detail in the following description, with reference to the drawings, in which the single figure shows a pure schematic form of a sectional view of an ammonia reactor in accordance with a specific embodiment of the invention.

Claims (2)

1. DETAILED DESCRIPTION OF THE INVENTION When the invention is operated, fresh ammonia synthesis gas 2 is introduced into an ammonia reactor 4 which is constructed in accordance with a specific embodiment of the invention. The synthesis gas is introduced into three separate feed streams 6, 8, 10, through the inlets 16, 18, and 20 configured in the cover 12 of the reactor. The reactor 4 comprises, inside the cover, an upper catalyst bed 24, a central catalyst bed 26, and a lower catalyst bed 28. Between the beds 24 and 26, and between the beds 26 and 28, heat exchangers 30 and 30 are configured. 32 for cooling a partially converted process stream 37 leaving the beds 24 and 26. A lower heat exchanger 34, configured downstream of the lower catalyst bed 28, serves to cool a product effluent 38 from the bed 28. The gas fresh synthesis is passed in the process stream 36 to the bed 24, and partially converted to the bed 24. The partially converted synthesis gas is then passed to the process stream 37 successively through the beds 26 and 28. By passing through the beds, the nitrogen and hydrogen in the stream react exothermically to produce ammonia and the effluent of product 38 which is rich in ammonia. The product effluent 38 is cooled in the heat exchanger 34 by indirect cooling with the feed stream 8 before being removed from the reactor through the outlet 40. As mentioned hereinabove, the reaction between the hydrogen and the nitrogen proceeds exothermically in the catalyst beds, and the temperature of the process stream rises. Due to thermodynamic reasons, the temperature of the process stream 37 has to be lowered, before being introduced into the beds 26 and 28. In this way the current in the heat exchangers 30 and 32 is cooled, by means of indirect heat exchange with the supply current 6, which is passed in series through the heat exchangers 32 and 30. When passing through the heat exchangers, the supply streams 6 and 8 are preheated by indirect heat exchange as described above . The preheated feed streams are then combined with the process stream 36 upstream of the upper catalyst bed 24. Before entering the bed 24, the temperature of the process stream 36 is adjusted by the addition of a cold feed stream. . NOVELTY OF THE INVENTION Having described the foregoing invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS 1. A process for the preparation of ammonia at elevated pressure and temperature in a reactor of ammonia, which comprises passing a stream of the ammonia synthesis gas process successively through at least three catalyst beds, and reacting the synthesis gas in the beds; cooling in an intermediate manner the partially reacted synthesis gas leaving the catalyst beds, by exchanging heat in the heat exchangers configured between each catalyst bed, and removing an effluent of product rich in ammonia, wherein the process stream is obtained by the combination, before being introduced into a first catalyst bed, of a first synthesis gas feed stream that has been preheated through indirect heat exchange, during the intermediate cooling of the partially converted synthesis gas, a second stream of synthesis gas feed that has been preheated by indirect heat exchange with the effluent of the product, and a third synthesis gas feed stream to adjust the temperature of the process stream, and where the first feed stream is passes successively through the heat exchangers between beds to cool the partially converted synthesis gas.
2. 2. An ammonia reactor, which comprises, inside a pressurized cylindrical cover, at least one first, one second, and one last catalyst bed vertically configured around a common axis, and connected in series; intermediate heat exchange elements configured between each catalyst bed, for the intermediate cooling of a partially converted ammonia synthesis gas from the catalyst bed, by indirect heat exchange with a first fresh ammonia synthesis gas feed stream; feed effluent heat exchange elements configured at the outlet of the last catalyst bed, to cool an effluent stream of ammonia product, by indirect heat exchange with a second feed stream of ammonia synthesis gas; input elements for introducing the first feed stream, and input elements for introducing the second feed stream into the reactor; input elements for introducing a third feed stream of fresh ammonia synthesis gas into the reactor; elements for passing the first, second, and third feed streams to the upper catalyst bed; and elements for combining the feed currents in a process stream, before introducing the process stream into the upper catalyst bed, wherein the elements for passing the first feed stream consist of a passage-way, to connect in series the intermediate heat exchangers, and for passing the first stream from the input element consecutively through the intermediate heat exchange element to the element for combining the feed streams.