Downloaded 2,138 times
Uploaded byGerard B. Hawkins
Ammonia Synthesis Flowsheet - Operator training
The document outlines the ammonia synthesis process, focusing on various technology suppliers and their distinct flowsheet designs, including Uhde, KBR, and Topsøe. It details the steps involved in ammonia production, including feed purification, reforming, and synthesis, as well as the importance of recycle loops in achieving optimal yields. Additionally, it discusses the operational principles, catalyst types, and modern converter designs aimed at enhancing efficiency and minimizing pressure drop.
In this document
Powered by AI
Introduction to ammonia synthesis and operator training by Gerard B. Hawkins.
Modern ammonia production mainly via steam-reforming natural gas. Key suppliers include Uhde, Topsoe, and KBR.
Describes the simplified NH3 plant flowsheet. Highlights purification, reforming, and synthesis loop.
Details typical ammonia plant flowsheet and steam, power systems, including waste heat recovery.
Various ammonia flowsheet designs by Uhde, KBR, Topsøe, and Linde featuring different reformer types.
Variety in flowsheets detailing synthesis mechanisms and key steps like adsorption and NH3 formation.
Explores the synthesis loop and equilibrium concentration impact due to temperature and pressure variations.
Describes mass and molar balances, impact of purge and inerts in the synthesis loop.
Explains hydrogen recovery systems in ammonia loops, catalyst bed temperature control, and heat balance.
Details on catalyst optimization, activity effects, deactivation, and typical operating conditions.
Overview of ammonia converter designs, objectives for efficiency, and specific designs from key companies.
Explains types and features of modern converters, highlighting designs from Kellogg, Topsøe, and ICI.
Discusses equilibrium plots related to ammonia converters and their performance metrics in temperature vs. content.
More Related Content
Similar to Ammonia Synthesis Flowsheet - Operator training
Ammonia Synthesis Flowsheet - Operator training
- 1. Ammonia Synthesis Flowsheet Operator Training By GerardB. Hawkins Managing Director, CEO
- 3. Introduction Most modernammonia processes are based on steam-reforming of natural gas or naphtha. The 3 main technology suppliers are Uhde (Uhde/JM Partnership), Topsoe & KBR. The process steps are very similar in all cases. Other suppliers are Linde (LAC) & Ammonia Casale.
- 4. Simplified - NH3PlantH2O H/C feed H/C purification Removes impurities (S, Cl, metals) Primary reforming Converts to H2, CO, CO2 + H2O + CH4 CO Shift WGS reaction Secondary reforming Combustion + Adiabatic Reforming + Adds Nitrogen Air Ammonia synthesis NH3 Converts N2 + H2 => NH3 Syngas compression Purification CO2 Removal & Methanation
- 6. Ammonia Synthesis Loop Synthesis reaction is equilibrium limited, typically 15 – 20% NH3 at converter exit. Therefore recycle in a ‘loop’ is required. Multi-stage complex converters are required to control bed temperatures. Various designs are used depending on contractor. Liquid Ammonia is recovered by refrigeration.
- 7. Simplified Flowsheet fora Typical Ammonia Plant Natural Gas Steam superheater Air Steam 30 bar Steam Steam raising 350 C 200 C Heat Recovery Steam raising Cooling Cooling Reboiler CO Cooling Preheater Heat Recovery Steam Boiler Process Condensate Quench Quench Liquid Ammonia H Hydrodesulphuriser Primary Reformer Secondary Reformer High Temperature Shift Low Temperature Shift Ammonia SynthesisMethanator Carbon Dioxide Purge Gas Cooling 400 Co 390 Co 2 790 C o 550 Co 1000 Co o 420 Co 150 C o 400 Co 470 C o o 220 C o 290 Co 330 Co 2 CO Removal2 220 bar Refrigeration Condensate Cooling Ammonia Catchpot
- 8. Ammonia Plant Steam& Power System Waste Heat recovery is used to raise HP steam, 100 – 120 bar Steam is used to drive the main compressors • Process air • Syn gas compression + circulator • Refrigeration Pass-out steam is used for process.
- 9. Ammonia Flowsheet Variations 1.Uhde Top fired reformer • Cold outlet manifold design Secondary reformer with internal riser H P loop (200 bar) with radial flow converter • 1 or 2 converters Once-through synthesis section upstream of main synthesis loop for very large capacities (dual pressure Uhde process)
- 10. Ammonia Flowsheet Variations 2.KBR Top-fired reformer • With internal risers Several synthesis loop options: • Conventional 140 bar loop with 4bed quench converter • Higher pressure for large-scale plants • Horizontal converter on modern plants. • KAAP design – 100 bar loop with Ru/C catalyst Braun Purifier flowsheet • Excess air with cryogenic ‘purifier’ to remove excess N2 and inerts from MUG
- 11. Ammonia Flowsheet Variations 3.Topsøe Side-fired reformer Radial flow converter • S-100 2 bed quench • S-200 2 bed intercooled • S-250 = S-200 + boiler + 2nd converter (1 bed) • S-300 3 bed intercooled
- 12. Ammonia Flowsheet Variations 4.Linde LAC (Linde Ammonia Concept) Hydrogen plant + N2 addition from air separation unit Ammonia Casale synthesis loop
- 13. Ammonia Flowsheet Variations 5.ICI (JM) AMV • Large-scale process with excess air, low pressure loop (80 – 110 bar) LCA • Small-scale plant based on GHR technology AMV / LCA technology is now part of JM’s ‘background in ammonia’
- 14. Ammonia Synthesis Mechanism Dissociative adsorption of H2 Dissociative adsorption of N2 - Believed to be the Rate Determining Step (RDS) Multi-step hydrogenation of adsorbed N2 Desorption of NH3
- 15.
- 16. Uhde Dual-Pressure Process C.W.Makeup gas from frontend C.W. Steam Once through converter Synthesis Loop Purge NH3 NH3 NH3 1 2 3 R C.W.Make up gas from frontend C.W. Steam Once through converter Synthesis Loop Purge NH3 NH3 NH3 1 2 3 R
- 17. Effect of Pressureon Ammonia Equilibrium Concentration 0 10 20 30 40 50 60 50 75 100 125 150 175 200 225 250 275 300 NH3concentration% Pressure bara 380 C 400 C 420 C
- 18. Ammonia Equilibrium Diagram 300 (572) 350 (662) 400 (752) 450 (842) 500 (932) 550 (1022) 600 (1112) 650 (1202) 0 10 20 30 40 Equilibrium MaxRate Temperature °C (°F) Ammoniacontent%
- 19. Effect of CatchpotTemperature on Ammonia VLE 0.0 2.0 4.0 6.0 8.0 10.0 12.0 50 75 100 125 150 175 200 225 250 275 300 NH3concentration% Pressure bara 0 C minus 20 C
- 20. Synthesis Loop Principles: MassBalance Overall Loop Mass Balance • On a mass basis: NH3 = MUG – Purge • On a molar basis: NH3 = (MUG – Purge) / 2 because 4 mol -> 2 mol in the NH3 reaction. Converter balance, on a molar basis: NH3 = Inlet gas – Outlet gas
- 21. Synthesis Loop Principles: MassBalance Converter Molar balance: NH3 = Circ Flow x (NH3out- NH3in) 1 + NH3out NH3in is set by P & T of final separator + position of MUG addition (before or after separator).
- 22. Synthesis Loop Principles: Effectof Purge Circulating composition is the same as the purge composition (like a stirred-tank reactor). Inerts (CH4 + Ar) build-up in loop. Circulating gas H / N ratio is very sensitive to MUG H / N ratio because the reaction consumes gas in a 3 : 1 ratio.
- 23. Synthesis Loop Principles: H2: N2 ratio example H / N = 3 : 1 MUG NH3 Purge H2 3000 2700 300 N2 1000 900 100 H / N 3.0 3.0 3.0 H / N = 2.95 : 1 H2 2950 2700 250 N2 1000 900 100 H / N 2.95 3.0 2.50
- 24. Synthesis Loop Principles: Inerts Balance Inerts (CH4 + Ar) concentrate in the loop, typically by a factor of about 10. Note that some of the inerts (10 – 20% of the total) dissolve in the product NH3. A few loops with purified make-up gas have a ‘self-purging loop’ where all the inerts are removed in solution in the product. The NH3 content of the purge at the flowmeter position is required to check the loop mass balance.
- 25. Synthesis Loop Principles: Effect of H2 Recovery Most modern loops have H2 recovery. 2 systems are used, cryogenic or membrane. The overall effect is similar, typically 90% H2 recovery at 90% purity. Overall loop H2 conversion to NH3 increases from about 92% to 98%. MUG H / N ratio changes from 3.0 to approx. 2.85, and returns to 3.0 after H2 addition.
- 26. Synthesis Loop Principles: Control of Catalyst Bed Temperatures Multi-bed design : 2, 3, or 4 catalyst beds with intermediate cooling.
- 27. Synthesis Loop Principles: Converter Heat Balance Older converter designs usually had an interchanger after the final bed to contain high temperatures within the converter. Modern designs typically have no ‘overall’ interchanger because this gives better heat recovery (heat available at a higher temperature) ‘Split converter designs’ further increase the heat recovery temperature.
- 28. 3 Bed ConverterExample 450 C 1. Optimum Catalyst Temperatures 410 C 520 C 415 C 480 C 410 C
- 29. 3 i/c design ‘Cold’Converter 410 C 520 C 415 C 480 C 410 C 450 C 120 C 335 C
- 30. 2 i/c design 410C 520 C 415 C 480 C 410 C 450 C ‘Hot’ Converter 235 C
- 31. 1 i/c design 410C 520 C 415 C 480 C 410 C 450 C ‘Split’ Converter 305 C
- 32. Converter Heat RecoveryExample In all cases the amount of heat recovered is the same, only the available temperatures are different. In all cases, the catalyst bed temperatures are the same: Bed 1 410 – 520 dT = 110 Bed 2 415 – 480 dT = 65 Bed 3 410 – 450 dT = 40 Total Bed dT = Converter dT = 215
- 33. Comparison of 74& 35 Series 30 40 50 60 70 80 90 100 110 120 0 2 4 6 8 10 12 14 Time on line (years) RelativeActivity Severnside LCA Standard Catalyst
- 34. Effect of Sizeon Activity Particle Diameter (mm) 14121086420 RelativeActivity 120 100 80 60 40 0 20
- 35. Effect of Sizeon Activity Smaller pellets = high activity Therefore high production rate or smaller catalyst volume But pressure drop will rise Either axial-radial or radial flow beds are used to minimise pressure drop Radial flow is the basis of many converter internal retrofits
- 36. Deactivation Clean Gas •Thermal sintering Contaminated Gas • Both Temporary and Permanent Poisoning • Oxygen induced sintering • By water, CO and CO2 • Site blocking/Sintering
- 37. Typical Operating Conditions Temperature (o C) 360-520 Pressure (bar) 80-600 Space velocity (hr-1 )1000-5000 Poisons oxygen and oxygen compounds normally < 3ppm
- 38. Catalyst Size Grade Size A1.5-3.0 mm B 3.0-4.5 mm C 3.0-6.0 mm D / E 6.0-10.0 mm G 14.0-20.0 mm
- 39. Catalyst Reduction Max waterin outlet gas during reduction (ppm) Formation of water during reduction of 1te of Catalyst (kg) Pre-reduced Oxidized 1000 3000 25 280
- 40.
- 41.
- 42. Converter Designs Objectives formodern designs are; - low pressure drop with small catalyst particles. - high conversion per pass with high grade heat recovery. Principal types are designed by: Uhde Kellogg (KBR) - conventional, Braun, KAAP Topsoe Ammonia Casale JM (I C I)
- 43. Uhde Uhde designa range of converters: Modern designs use radial flow with inter-cooling & 'split converters' with heat recovery between, - Converter 1 : 2-bed, 1 interchanger - Heat recovery (boiler) - Converter 2 : 3rd bed.
- 44. Uhde 3 bed NH3Converter
- 45. M W KelloggConverter Types 'Conventional' make-up gas and loop layout, refrigeration to low temperature (- 25 C), loop pressure typically 140 - 180 bar. Converters: 4 bed quench ; conventional Kellogg design. Horizontal converter ; • lower cost, low pressure drop, easier installation • 2 bed inter-cooled layout with small catalyst
- 46. Kellogg Ammonia QuenchConverter Outlet Inlet
- 47. Kellogg Horizontal Converter Bed1Bed 2ABed 2B Inlet Outlet
- 48. KBR KAAP Converteris made up of 4 beds First bed uses magnetite catalyst Ru can not be used since temperature rise is too large Lower beds use Ru catalyst Ru catalyst has a carbon support Catalyst developed by BP • Very high activity even at low pressure
- 49. Braun Converter Types Purifier Process gives pure make-up gas - low levels of poisons; H2O, CO, CO2 - Low inerts; no purge from loop Converters : Basically 2-bed intercooled with each catalyst bed in a separate vessel Modern designs may use 3 converters &/or radial flow
- 50. Haldor Topsøe S-Series S-100 :Radial flow 2-bed quench S-200 :Radial flow 2-bed inter cooled S-250 : S-200, heat recovery, 2nd converter with 1 radial flow bed S-300 :Radial flow 3-bed inter cooled
- 51.
- 52. Ammonia Casale AmmoniaCasale - 'axial-radial' concept - radial flow without a top cover on the beds - simpler mechanical design No. of beds & type of inter-bed cooling varies; typically 3 bed, 2 interchanger.
- 53. ICI Types Lozengequench converter : • single bed divided into 3 parts by quench addition • simple concept but suffered high pressure drop ICI AMV Process : • Low pressure loop with H2 recovery at loop pressure • range of converters in use • Terra: ICI 3-bed, 1 quench + 1 intercooler axial flow ICI LCA Process : • Tube-cooled + adiabatic design.
- 54. ICI Lozenge QuenchConverter
- 55. ICI Tube CooledConverter
- 56. ICI TCC EquilibriumPlot 300 (572) 350 (662) 400 (752) 450 (842) 500 (932) 550 (1022) 600 (1112) 650 (1202) 0 10 20 30 40 Equilibrium Max Rate Converter Profile Temperature °C (°F) Ammoniacontent%