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EP-3727669-B1 - METHOD AND REACTOR FOR PERFORMING EXOTHERMIC REACTIONS

EP3727669B1EP 3727669 B1EP3727669 B1EP 3727669B1EP-3727669-B1

Inventors

  • SPETH, Christian Henrik
  • WIND, Tommy Lykke
  • THOMSEN, Uffe Bach
  • HANSEN, ANDERS HELBO

Dates

Publication Date
20260506
Application Date
20181219

Claims (20)

  1. Method of performing exothermic catalytic reactions comprising the steps of passing a fresh process gas (9) in parallel to at least two cylindrical catalyst modules (1) arranged in stacked order, each containing in series one or more catalyst zones (14,15), at least one of the catalyst zones is cooled by an intrabed heat exchanger (6); exothermically reacting the fresh process gas (9) flowing in axial flow direction through all of the catalyst zones (14,15) to a product gas; in each of the cylindrical catalyst modules (1), cooling the exothermic reacting process gas with the fresh process gas (9) and thereby preheating the fresh process gas by passing the fresh process gas from an outer annular space (2) formed around each of the cylindrical catalyst modules into the intrabed heat exchanger and passing the fresh process gas through the intrabed heat exchanger in indirect heat exchange with the exothermic reacting preheated process gas passing in axial flow direction through the cooled catalyst zone (17); and collecting the product gas (10) withdrawn from the at least two catalyst modules in a central space (4) formed centrally within the at least two stacked catalyst modules.
  2. The method of claim 1, wherein at least one of serial connected catalyst zones (14) is an adiabatic catalyst zone (15).
  3. The method of claim 1, wherein the process gas from a single cooled catalyst zone (17) is passed in series through a single adiabatic catalyst zone (15).
  4. The method of any one of claims 1 to 3, wherein the intrabed bed heat exchanger comprises a plurality of cooling plates (6) forming flow compartments for the fresh process gas in the intrabed heat exchanger.
  5. The method of claim 4, wherein the thickness the cooled catalyst layer between two adjacent cooling plates (6) varies within ± 10%.
  6. The method of claim 5, wherein the thickness of the cooled catalyst layer between two adjacent cooling plates (6) is between 10 and 300 mm.
  7. The method of claim 5, wherein the thickness of the cooled catalyst layer between two adjacent cooling plates (6) is between 20 and 150 mm.
  8. The method of any one of claims 5 to 7, wherein each of the cooling plates (6) is essentially planar.
  9. The method of any one of claims 5 to 8, wherein the cooling plates (6) are arranged in three 120° sections in the cylindrical catalyst modules (1) and wherein all cooling plates in each 120° section are essentially planar and parallel.
  10. The method of claim 9, wherein the essentially planar cooling plates (6) in any of the three 120° sections are non-parallel to the essentially planar and parallel cooling plates (6) in another section.
  11. The method of any one of claims 1 to 10, wherein the fresh process gas (9) is passed through the intra bed heat exchanger in counter-current flow or in co-current flow with the process gas passing through the catalyst zones (14) in each of the cylindrical catalyst modules (1).
  12. The method of any one of claims 1 to 11, wherein the fresh process gas (9) is passed through the intrabed heat exchanger in counter-current flow with the process gas passing through the catalyst zones in each of the cylindrical catalyst modules (1).
  13. The method of any one of claims 1 to 12, wherein the cylindrical catalyst modules (1) have the same size.
  14. A reactor for performing exothermic reactions, comprising within a cylindrical pressure shell (3) at least two parallel operated cylindrical catalyst modules (1) arranged in stacked order, each containing in series one or more catalyst zones (14,15) with a catalyst layer adapted to axial flow, the catalyst layer in the at least one of the catalyst zones (14) is cooled by an intrabed heat exchanger; an outer annular space (2) between the cylindrical catalyst modules (1) and the cylindrical pressure shell fluidly connected to the at least two parallel cylindrical catalyst modules (1); in the at least one cooled catalyst zone (14) feed means(5) for the fresh process gas into the inlet of the intrabed heat exchanger, fluidly connected to the outer annular space (2); the outlet of the intrabed heat exchanger is formed by open ends of the intrabed heat exchanger in the at least one cooled catalyst zone (14); covers closing the at least two parallel cylindrical catalyst modules (1); outlet means from the at least two parallel cylindrical catalyst modules (1), the outlet means from the at least two parallel cylindrical catalyst modules is arranged in a central space (4) formed centrally within the at least two stacked catalyst modules (1).
  15. The reactor of claim 13, wherein at least one of the serial catalyst zones (14, 15) is an adiabatic catalyst zone (15).
  16. The reactor of claims 14 or 15, having a single cooled catalyst zone (14) connected in series with a single adiabatic zone (15).
  17. The reactor of any one of claims 14 to 16, wherein the intrabed bed heat exchanger is a plate heat exchanger with a plurality of cooling plates (6) forming flow compartments for fresh process gas (9) in the intrabed heat exchanger.
  18. The reactor of claims 17, wherein the thickness of cooled catalyst layer between two adjacent cooling plates (6) varies within ± 10%.
  19. The reactor of claim 18, wherein the thickness of the cooled catalyst layer between two adjacent cooling plates (6) is between 10 and 300 mm.
  20. The reactor of claim 18, wherein the thickness of the cooled catalyst layer between two adjacent cooling plates (6) is between 20 and 150 mm.

Description

BACKGROUND OF THE INVENTION Ammonia is of substantial importance for feeding the worlds growing population through its application as feedstock to fertilizer production. Historically, the Tennessee Valley Authority (TVA) type converter was for decades the preferred reactor type for ammonia synthesis and gained foothold already the 1930ies. It is characterized by utilizing axial flow in a single gas cooled catalyst bed. Cooling of the catalyst is obtained by a number of tubes placed vertically in the catalyst bed, ensuring reaction conditions in favor of conversion of an exothermic reaction. Despite a large number of references for this converter type, the design suffered from three important limitations; I) the pressure drop over a single converter escalated as plant capacity increased resulting in high energy consumption, II) high construction costs to build parallel converters in separate pressure shells to overcome the challenge of high pressure drop and III) high recirculation rates (and loop pressures) were generally required to compensate for the mediocre conversion of hydrogen and nitrogen per reactor pass. To comply with a general trend towards building larger single-line capacity plants after the second world war, the idea of utilizing adiabatic radial flow in fixed catalyst beds was introduced. Especially from the 1960ies and forward the radial flow converter gained increasing market shares at the expense of the TVA converter. The common denominator of radial flow reactors is that they generally provide larger cross sectional area for flow and thereby lower average gas velocity as opposed to the cross sectional area and gas velocity obtained by axial flow through the same catalyst mass. This realization facilitated significantly higher ammonia production rates in a single converter and pressure shell while maintaining the pressure drop over the converter below 3 bar. Furthermore, to increase conversion, lowering the required recirculation rate of the loop, quenching of the product gas from a first adiabatic bed by fresh process gas was introduced in the 1960ies by Haldor Topsoe' S-100 converter. The combined quenched stream was then further converted in a second adiabatic bed connected in series with the first bed. Radial flow was applied in both catalyst beds. Further advancements of the radial flow converter emerged by the S-200 converter during the 1980ies and the S-300 converter around year 2000. Instead of quenching, these reactors are equipped with a single or two interbed heat exchangers respectively to provide cooling in-between two or three catalyst beds operated in series, each bed being adiabatic and taking advantage of the radial flow principle. Similar designs include Casale' axial-radial flow converter which also relies on adiabatic fixed catalyst beds operated in series and with interbed heat exchange. The above-mentioned interbed heat exchanger(s) serves the purpose of generating thermodynamic potential for additional conversion of the exothermic reaction after each catalyst bed while simultaneously preheating the incoming fresh process gas to the converter prior to reaching the first catalyst bed. Any improvement related to ammonia reactors must compare its performance to a two or three bed adiabatic converter with radial flow and interbed heat exchange since this converter type is still the preferred choice for large scale ammonia plants. Though serial adiabatic converters with radial flow and interbed heat exchange are still dominant in the market further steps of improvement can be made. It is well-known that the efficiency of a catalyst for any exothermic reaction can be improved by cooling the catalyst to an extent resulting in an operation curve following the maximum reaction rate curve of the given reaction. An adiabatic reactor, providing no cooling, suffers from part of the catalyst mass operating at colder conditions than optimum while other parts of the catalyst bed operates at hotter conditions than optimum. Hence, a natural evolution was made by Casale which introduced a flow converter where cooling of the catalyst bed is obtained by the use of cooling plates wherein some kind of cooling fluid is heated. Such a converter type may in principle provide a higher conversion per catalyst volume due to improved reaction conditions of the catalyst relative to that obtained in an adiabatic bed. This concept is described through a number of patents, such as US 6,946,494 and US 9,028,766. All these patents, describe cooling plates placed in a radial layout inside a cylindrical converter shell and use of radial flow in the catalyst bed to obtain low pressure drop over the catalyst. EP 80270 discloses a reactor suitable for synthesis of ammonia or methanol comprising a catalyst bed equipped with heat exchange tubes providing catalyst fillable space between the tubes over substantially their whole lenghth. Preferably catalyst particles between the tubes and in an uncooled bed down