MXPA98003526A - Process and process unit for the preparation of amoni synthesis gas - Google Patents

Abstract

A process and a process unit for the preparation of ammonia synthesis gas from a hydrocarbon feed supply, which comprises reforming with primary and secondary catalytic vapor in the feed supply sequence in an exchange steam reformer. primary heat and in a subsequent secondary reformer, where an effluent stream of primary steam reformed gas is heated by indirect heat exchange with a hot product effluent from the secondary reformed gas prior to the introduction of the reformed gas with primary vapor in the secondary reformer

Description

PROCESS AND PROCESS UNIT FOR THE PREPARATION OF GAS OF SYNTHESIS OF AMMONIA The present application relates to the preparation of ammonia synthesis gas. More particularly, the invention relates to a process and a process unit for the preparation of this gas, which comprises a primary and secondary steam reforming sequence of a hydrocarbon feed supply in a primary steam reformer. of heat exchange, and in a subsequent adiabatic reformer. The ammonia synthesis gas is conventionally prepared by subjecting a hydrocarbon feed of natural gas or of higher hydrocarbons to endothermic steam reforming reactions in a tubular fire steam reformer, by contacting it with a steam reforming catalyst. The primary reformed gas is then fed to a secondary adiabatic reformer, where part of the hydrogen and residual amounts of hydrocarbons from the gas are partially oxidized with air or with air enriched with oxygen in the presence of a secondary reformer catalyst. From the secondary reformer, the raw ammonia synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide is formed during the reaction of the feed supply in the above steam reforming reactions, and nitrogen is introduced into the gas through the addition of air in the secondary reformation step. The heat required for the primary endothermic steam reforming reactions is normally supplied by combustion of a fuel on the combustion gas side of the primary steam reformer, where the catalyst is arranged in tubes that extend vertically through the reformer . To reduce fire work and fuel consumption in the primary reformer, it has also been suggested to provide a part of the heat by using an effluent stream of steam reformed gas as a heat source. This process and reactor are mentioned in U.S. Patent No. 5,429,809, where heat is partially supplied by the hot combustion gas for the fuel being burned, and partially by an effluent of hot product in an exchange reactor. Heat from bayonet tube. The general object of this invention is also to reduce the fire work and the fuel consumption in sequence of the steam reforming of primary heat exchange and the secondary reforming, for the preparation of the ammonia synthesis gas from a supply of hydrocarbon feed.

In accordance with the above, an object of the invention is to provide a process for the preparation of ammonia synthesis gas from a hydrocarbon feed supply, which comprises the steps of reforming with primary and secondary catalytic vapor in sequence the power supply in a primary heat exchange steam reformer and in a subsequent secondary reformer, where an effluent stream of primary steam reformed gas is heated by indirect heat exchange with a hot product effluent from the secondary reformed gas before the introduction of the reformed gas with primary steam in the secondary reformer. A further object of the invention is to provide a process unit for use in the above steam reforming process. Accordingly, the process unit comprises a primary heat exchange steam reformer connected with a secondary steam reformer, and a feed / heat exchanger configured upstream of the secondary steam reformer, such that a current Steam reformed hydrocarbon feed supply effluent from the primary heat exchange steam reformer is heated by indirect heat exchange with the hot product effluent from the secondary steam reformer.

The term "heat exchange steam reformer", as used herein, before and in the following description, refers to a steam reformer wherein the heat necessary for the primary steam reforming reaction to occur in a Fixed bed of primary steam reforming catalyst is partially provided by a hot combustion gas and by the heat contained in the primary reformed gas, by passing both gases in a heat exchange relationship with the catalyst bed through the reformer. In this reformer, the heat of the reformed gas is recovered from a reforming temperature typically of about 800 ° C, to a lower level of typically about 600 ° C of exit temperature. The equilibrium temperature at the entrance to the secondary steam reforming step is the temperature of the primary reformed gas at the outlet of the primary steam reforming catalyst bed, typically greater than 800 ° C. When primary heat exchange steam reformers are used in a primary and secondary steam reforming sequence, without preheating the primary reformed gas, the temperature of the primary reformed gas at the inlet to the secondary reformer, however, is lower, due to the indirect heat exchange with the process gas in the primary reformer. This results in a lower feed conversion in the secondary steam reforming step. In order to obtain the desired stoichiometric composition of the secondary reformed crude ammonia synthesis gas, and a low hydrocarbon content in the gas, as required in the following ammonia synthesis process, the equilibrium temperature of the primary reformed gas in a primary heat exchange sequence and a secondary reformation without preheating the primary reformed gas, must be higher to compensate for the lower conversion of the hydrocarbon feed in the secondary reforming step. By combining the invention of a secondary reformer and a feed / effluent heat exchanger, the temperature of the reformed gas with primary steam that has cooled below the equilibrium temperature in the heat exchange reformer rises to the temperature of the reaction, as required in the secondary reformer, through indirect heat exchange with the effluent of the hot product from the secondary reformer. In this way, the fuel consumption in the primary reformer is conveniently reduced by recovering excess heat in the reformed gas with secondary steam in the feed / effluent heat exchanger. Compared to conventional primary-secondary steam reforming, this results in a correspondingly lower exit temperature of the crude ammonia synthesis gas produced from the steam reforming section. The lower outlet temperature from the reformer section, and the reduced fuel consumption in the primary reformer, result in an overall improvement of the consumption figures in the reformer section. The invention will be described in greater detail in the following description, with reference to the drawings, in which the single figure shows a simplified flow diagram of a process according to a specific embodiment of the invention. When the process according to a specific embodiment of the invention is operated, the feed gas 2, for example natural gas and steam, is introduced into a primary heat exchange reforming reactor 4 at a temperature of 450 ° C. Reactor 4 is a conventionally designed bayonet tube reactor comprising, within a pressure cover 6, one or more reactor tubes consisting of an outer sheet tube 8, closed at its outlet end, and concentrically surrounding to a bayonet tube for internal heat exchange with open ends 10. A space between tubes 8 and 10, it is filled with primary reforming catalyst 12. The feed 2 that passes through the outer tube 8 and the catalyst 12, is reformed primary steam by its contact with the catalyst 12. The heat necessary for the endothermic vapor reforming reactions proceed on the catalyst 12, it is supplied by the hot combustion gas obtained by burning the fuel in a lower burner 14, by passing the hot combustion gas along the wall of the outer tube 8, in a heat conduction relationship with the feed that reacts in the tube 8. The supplementary heat is supplied by the hot primary reformed effluent gas 16 from the catalyst 12 leaving the catalyst at an outlet temperature of 800 ° C, and passing through the inner tube 10 in a heat conducting relationship with the feed gas which reacts in the catalyst 12. The temperature of the primary reformed gas 16 decreases from way up to 600 ° C. The gas 16 is then passed to the feed / effluent heat exchanger 18, where the temperature of the gas 16 is raised to 800 ° C by indirect heat exchange, the hot secondary reformed gas 20 being removed from the secondary reformer 22 at a temperature of 975 ° C. The secondary reformer 22 is a conventionally designed adiabatic reformer, wherein the reheated primary reformed gas 16 is partially oxidized with air 24 in the upper portion of the reactor, and subsequently secondary reforming is made by its contact with a secondary reforming catalyst configured as a fixed bed 26 in the lower portion of the reactor 22. The secondary reformed gas 20 is removed from the bottom of the reactor at a temperature of 975 ° C, and cooled to 825 ° C by indirect heat exchange, as described above.

Claims (2)

1. NOVELTY OF THE INVENTION Having described the foregoing invention, it is considered as a novelty, and therefore, property is claimed as contained in the following: CLAIMS 1. A process for the preparation of ammonia synthesis gas from a hydrocarbon feed supply, which comprises the steps of reforming with primary and secondary catalytic steam in sequence the feed supply in a primary heat exchange steam reformer and in a subsequent secondary reformer, where an effluent stream of reformed gas with primary steam is heated by indirect heat exchange with a hot product effluent from the secondary reformed gas before the introduction of the reformed gas with primary steam in the secondary reformer.
2. 2. A process unit for use in the above steam reforming process, which comprises a primary heat exchange steam reformer connected with a secondary steam reformer, and a feed / effluent heat exchanger configured upstream of the secondary vapor reformer, such that an effluent stream of steam reformed hydrocarbon feedstock from the primary heat exchange steam reformer is heated by the indirect heat exchange with the hot product effluent from the reformer of secondary vapor.