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EP-4605345-B1 - PROCESS FOR OPERATING AN AMMONIA SYNTHESIS AT PARTIAL LOAD AND AMMONIA SYNTHESIS CAPABLE OF OPERATING AT PARTIAL LOAD

EP4605345B1EP 4605345 B1EP4605345 B1EP 4605345B1EP-4605345-B1

Inventors

  • REINKE, MICHAEL
  • KLEIN, HARALD
  • SCHWARZHUBER, JOSEF
  • Fahr, Steffen

Dates

Publication Date
20260513
Application Date
20231018

Claims (15)

  1. A process for the synthesis of ammonia (18), in which a gas mixture (make-up gas) (1) comprising hydrogen and nitrogen is provided in a first operating mode with a flow rate that is above a threshold value and in a second operating mode with a flow rate that is below this threshold value in order to form an ammonia synthesis gas (5) which is reacted in an ammonia reactor (R) in at least one first catalyst bed (K1) and in a second catalyst bed (K2), connected to the first catalyst bed, to form a synthesis product (16) containing ammonia, wherein in a cooling device (E3) arranged between the first catalyst bed (K1) and the second catalyst bed (K2), non-reacted ammonia synthesis gas (8) is used as a cooling agent in order to reduce the temperature of an ammonia synthesis gas (12) partially reacted in the first catalyst bed (K1) before it is forwarded to the second catalyst bed (K2), wherein in the second operating mode, the higher the flow rate of the provided make-up gas (1), the greater the reduction in temperature of the partially reacted ammonia synthesis gas (12), characterized in that the cooling of the ammonia synthesis gas (12) partially reacted in the first catalyst bed (K1) is carried out in indirect heat exchange against provided ammonia synthesis gas (8).
  2. The process according to claim 1, characterized in that the provided ammonia synthesis gas (5) is reacted into the synthesis product (16) in the ammonia reactor (R) in more than two catalyst beds (K1, K2, K3) passed through in series, wherein a cooling device (E2, E3) is arranged between each two immediately adjacent catalyst beds, in which provided ammonia synthesis gas (7, 8) serves as a cooling agent in order to cool the ammonia synthesis gas (12, 14) partially reacted in one catalyst bed in indirect heat exchange before it is forwarded to the following catalyst bed.
  3. The process according to any of the claims 1 or 2, characterized in that at least a part of the provided ammonia synthesis gas (5) is fed to the first catalyst bed (K1) in the second operating mode in the bypass (22, 23) to the cooling device(s) (E2, E3).
  4. The process according to claim 3, characterized in that at least a partial flow (21) of the provided ammonia synthesis gas (5) is heated (E10) against the synthesis product (16).
  5. The process according to claim 4, characterized in that the ratio of the part of the ammonia synthesis gas (5) used as cooling agent (7, 8) in the cooling device(s) (E2, E3) to the part led via bypass (22, 23) around the cooling device(s) (E2, E3) is changed depending on the amount of provided make-up gas (1), wherein the less make-up gas (1) is provided, the smaller said ratio is.
  6. The process according to any of the claims 1 to 5, characterized in that the synthesis product (16) is withdrawn from the ammonia reactor (R) and cooled in several cooling stages (E4, E5, E1, E7, E8, E9) in order to condense out ammonia and produce a two-phase mixture of substances (17) which is separated in a separator (D) into a liquid phase (18) consisting predominantly of ammonia and a gas phase (19) consisting largely of hydrogen and nitrogen and containing residues of ammonia that has not been condensed out, wherein the gas phase (19) is returned to the ammonia reactor (R) as recycle gas (2) and is mixed with the make-up gas (1) consisting of hydrogen and nitrogen to form the ammonia synthesis gas (5).
  7. The process according to claim 6, characterized in that in the second operating mode, a partial flow (22) of the synthesis product (16) is separated upstream of at least one of the plurality of cooling stages (E4, E5, E1, E7, E8, E9) and is fed into the separator (D) without further cooling.
  8. The process according to any of the claims 1 to 7, characterized in that hydrogen and/or nitrogen required for the provision of the make-up gas (1) is generated using electricity that is obtained directly from renewable sources such as wind or solar power plants, or as surplus electricity from the public grid.
  9. An apparatus for the synthesis of ammonia (18), comprising a device with which a make-up gas (1) can be provided for forming an ammonia synthesis gas (5), an ammonia reactor (R) in which at least a first catalyst bed (K1) and a second catalyst bed (K2) connected to the first via a cooling device (E3) are arranged, via which the provided ammonia synthesis gas (5) can be reacted to form a synthesis product (16) containing ammonia, a feed device via which ammonia synthesis gas (5) can be fed to the first catalyst bed (K1) as feed (9) and to the cooling device (3) as a cooling agent in order to lower the temperature of the ammonia synthesis gas (12) partially reacted in the first catalyst bed (K1) before it is forwarded to the second catalyst bed (K2), and a control device via which the extent of the temperature reduction can be adjusted depending on the provided amount of make-up gas (1), characterized in that the cooling device (E3) is designed as a heat exchanger in which ammonia synthesis gas (8) used as cooling agent can be warmed up in indirect heat exchange against partially reacted ammonia synthesis gas (12) before being fed in the first catalyst bed (K1).
  10. The apparatus according to claim 9, characterized in that the ammonia reactor (R) is designed with more than two, preferably with three catalyst beds (K1, K2, K3), each of which is serially connected to each other via a cooling device (E2, E3).
  11. The apparatus according to any of claims 9 or 10, characterized in that the apparatus has a line (22, 23) via which at least a part of the provided ammonia synthesis gas (5) can be supplied to the first catalyst bed (K1) in a bypass to the cooling device(s) (E2, E3) arranged between the catalyst beds (K1, K2, K3), wherein the size of the bypass flow can be adjusted via the control device.
  12. The apparatus according to claim 11, characterized in that a cooling device (E10) is arranged downstream of the last catalyst bed (K3) in the flow direction, with which at least the partial flow of the provided ammonia synthesis gas (5) guided in the bypass can be heated against the synthesis product (16) to be cooled in indirect heat exchange.
  13. The apparatus according to claim 12, characterized in that the cooling device (E10) arranged downstream of the catalyst bed (K3) arranged last in the flow direction is located within the jacket of the ammonia reactor (R).
  14. The apparatus according to any of claims 9 to 13, characterized in that downstream of the ammonia reactor (R) a plurality of cooling devices (E4, E5, E1, E7, E8, E9) and a separator (D) are arranged in series, by means of which ammonia can be condensed out and separated from the synthesis product (16) containing hydrogen and nitrogen components in addition to ammonia and by means of which a liquid phase (18) consisting predominantly of ammonia and a gas phase (19) consisting largely of hydrogen and nitrogen and containing residues of ammonia that has not been condensed out can be obtained, wherein the separator (D) is connected to the ammonia reactor (R) in such a way that the gas phase (19) can be returned to the ammonia reactor (R) as recycle gas (2) and can be mixed with the make-up gas (1) consisting of hydrogen and nitrogen to form the ammonia synthesis gas (5).
  15. The apparatus according to any of claims 9 to 14, characterized in that the apparatus comprises a device for generating hydrogen and nitrogen for providing the ammonia synthesis gas (5), in which device hydrogen and/or nitrogen can be generated using electricity that is obtained directly from renewable sources such as wind or solar power plants, or as surplus electricity from the public grid.

Description

The invention relates to a process for the synthesis of ammonia, in which a gas mixture comprising hydrogen and nitrogen (make-up gas) is provided in a first operating mode with a flow rate above a threshold value and in a second operating mode with a flow rate below this threshold value to form an ammonia synthesis gas, which is reacted in an ammonia reactor in at least one first and a second catalyst bed connected to the first to form an ammonia-containing synthesis product, wherein unreacted ammonia synthesis gas is used as a coolant in a cooling device arranged between the first and the second catalyst bed to lower the temperature of a partially reacted ammonia synthesis gas in the first catalyst bed before it is passed on to the second catalyst bed, wherein the temperature of the partially reacted ammonia synthesis gas is lowered more in the second operating mode the larger the flow rate of the provided make-up gas. Ammonia is one of the world's most produced chemicals. It serves primarily as a raw material for the production of fertilizers, but is also gaining increasing importance as an energy carrier and hydrogen storage medium. On an industrial scale, it is synthesized almost exclusively from nitrogen and hydrogen using the Haber-Bosch process. In the Haber-Bosch process, an ammonia synthesis gas consisting primarily of hydrogen and nitrogen, in which the two substances are present in the stoichiometric ratio of 3:1 for ammonia synthesis, is fed into an ammonia reactor at a pressure between 80 and 300 bar and a temperature between 300 and 450°C. With catalytic assistance, it undergoes an exothermic reaction to form ammonia. However, due to thermodynamic limitations, the reaction is incomplete, resulting in a synthesis product that contains significant amounts of hydrogen and nitrogen in addition to ammonia. The process is carried out at a temperature between 400 and At 450°C, the synthesis product leaves the ammonia reactor and is subsequently cooled in a series of heat exchangers to separate ammonia by condensation and to obtain a recycled gas consisting largely of hydrogen and nitrogen, containing residual uncondensed ammonia. This recycled gas is then returned to the ammonia reactor in a synthesis cycle to increase the ammonia yield and is mixed with a hydrogen and nitrogen make-up gas to form the ammonia synthesis gas. Ammonia reactors are typically designed as adiabatic multi-bed reactors comprising at least two fluidically connected catalyst beds through which ammonia synthesis gas flows serially, undergoing stepwise conversion to the synthesis product. A cooling system is arranged after the first and before each subsequent catalyst bed. This system removes the heat of reaction from the gas mixture obtained by the reaction in the upstream catalyst bed, cooling it before it is transferred to the downstream catalyst bed for further conversion. Unreacted ammonia synthesis gas, which needs to be warmed, serves as the coolant in this type of intermediate cooling. Depending on whether the heat is transferred directly or indirectly to the ammonia synthesis gas, the reactors are referred to in technical circles as adiabatic quench cooling (AQC) or adiabatic indirect cooling (AIC) reactors, respectively. The hydrogen required for the production of the make-up gas is still predominantly obtained from hydrocarbons, which are reformed into a hydrogen-rich synthesis gas, producing carbon dioxide in the process. The climate-damaging carbon dioxide is separated and either released into the atmosphere or disposed of through sequestration, which requires considerable financial and technical resources. To overcome these disadvantages, increased efforts have recently been made to produce hydrogen without carbon dioxide, for example, through the electrochemical decomposition of water using an electrolyzer, and to use it for the formation of the make-up gas. The electricity required for ammonia production is obtained directly from renewable sources such as wind or solar power plants, or as surplus electricity from the public grid, which is why it is not available at a constant output. Since the operation of the Because the electrolyzer and any air separation unit used for nitrogen production can be adapted relatively easily and quickly to fluctuating conditions, and because the production quantities of hydrogen and nitrogen are approximately proportional to the electrical power, the flow rates of hydrogen produced in the electrolyzer and nitrogen produced in the air separation unit vary with the amount of available electrical current. Consequently, the flow rates of make-up gas and ammonia synthesis gas frequently and for extended periods fall below half the values required for full-load operation of the ammonia synthesis unit. Unlike an electrolyzer and an air separator used for nitrogen recovery, the ammonia reactor and the synthesis cycle can only be adjusted very slowly and to a limited extent to fluctuatin