Introduction To Syngas Plant Flowsheet Options
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High level introduction Mainstream syngas = steam reforming processes Ammonia; methanol; hydrogen/HyCO Town gas Steam reforming; low pressure cyclic Direct reduction iron (DRI) HYL type processes; Midrex type processes
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Introduction To Syngas Plant Flowsheet Options
- 1. Introduction to Syngas Plant Flowsheet Options By: Gerard B. Hawkins Managing Director, CEO
- 2. Syngas Flowsheets – Presentation Coverage High level introduction • Mainstream syngas = steam reforming processes Ammonia; methanol; hydrogen/HyCO • Town gas Steam reforming; low pressure cyclic • Direct reduction iron (DRI) HYL type processes; Midrex type processes
- 3. Introduction In each case, various plant flowsheets exist • either: original design • or: resulting from uprate/revamp Preferred flowsheets have evolved over time • influenced by plant size
- 4. Simplified Steam Reforming NH3 Plant H2O H/C feed H/C purification Removes impurities (S, Cl, metals) Steam reforming Converts to H2, CO, CO2 + H2O + CH4 H2O Shift WGS reaction: H2O + CO <=> CO2 + H2 H2 Hydrogen purification Removal of CO, CO2 + maybe CH4
- 5. Simplified Steam Reforming NH3 Plant (cont.) N2 Ammonia synthesis NH3 Converts N2 + H2 => NH3 Syngas compression H2
- 6. Simplified Steam Reforming H2 Plant H2O H/C feed H/C purification Removes impurities (S, Cl, metals) Steam reforming Converts to H2, CO, CO2 + H2O + CH4 H2O Shift WGS reaction: H2O + CO <=> CO2 + H2 H2 Hydrogen purification Removal of CO, CO2 + maybe CH4
- 7. Simplified Steam Reforming HyCO Plant H2O H/C feed H/C purification Removes impurities (S, Cl, metals) Steam reforming Converts to H2, CO, CO2 + H2O + CH4 H2O CO2 recycle to reformer feed H2/CO Liquid CO2 Removal
- 8. Simplified Steam Reforming MeOH Plant H2O H/C feed H/C purification Removes impurities (S, Cl, metals) Steam reforming Converts to H2, CO, CO2 + H2O + CH4 H2O Syngas compression Purge gas to feed or fuel Methanol synthesis MeOH Converts CO/CO2 + H2 => MeOH
- 9. Hydrocarbon Purification Section Historically – up to three parts • Hydrogenation or hydrodesulphurisation catalytic breakdown of organic sulphur compounds to H2S (also RCl to HCl) • Chloride removal (only if Cl present) - absorb HCl • Sulfur removal - absorb H2S Additionally – a fourth optional part • Ultrapurification Various designs depending on • feed composition; plant design
- 10. Hydrocarbon Purification Section H/C feed HDS Breaks down organo-S and RCl H2 HCl absorption Removes HCl by chemical reaction H2S absorption Removes H2S by chemical reaction Ultra- purification Polishes out trace S impurities
- 11. Hydrocarbon Feed Hydrogenation Sulfur Removal Chloride Removal Hydrocarbon Feed Sulfur Removal Hydrogenation Hydrocarbon Feed Hydrogenation Chloride Removal Sulfur Removal Hydrocarbon Purification Section - Typical Flowsheet Examples
- 12. Hydrocarbon Feed HDS ZnO Ultrapurification Hydrocarbon Purification Section - Ultrapurification Used with ZnO at usual operating conditions • ZnO removes bulk of sulfur (H2S) • Follow with a layer of ultrapurification for polishing
- 13. Hydrocarbon Purification Section - Flowsheet Different variants found across syngas plants HDS usually installed • Occasionally left out when total S is low and organo-S is very low (< 2 ppm as mercaptan, RSH) HCl removal less usual • More common in refinery H2 plants using off gas feed H2S removal always present
- 14. Hydrocarbon Purification Section - Flowsheet H2S removal – single bed or lead/lag ? • Single bed found where H2S (or total S to HDS) is low and predictable • E.g. gas purified to a pipeline spec’n of << 10 ppm • Bed must be a realistic size to last T/A interval • Otherwise lead/lag: design bed life 6 – 12 months Ultrapurification • Special situations – NOT for all • AND not installed in all the “special situations”
- 15. Hydrocarbon Purification Section – Flowsheet (cont.) Ultra-purification applications • Pre-reformers • Natural gas fed steam reformers stressed high heat flux; low steam:carbon ratio • Naphtha fed steam reformers low steam:carbon ratio • Precious metal steam reforming catalysts • GHRs
- 16. Steam Reforming Section - Options Generally • feature tubular reformer (“primary”; “steam reformer”) • may include 2nd or 3rd stage to the reforming section pre-reformer • part of initial design or later retrofit post reformers • two types usually considered • secondary • gas heated reformer
- 17. Steam Reforming Section - Options H/C feed Pre- reformer Converts to H2, CO, CO2 + H2O + CH4 Secondary reformer Drives CH4 slip down + other fact0rs H2O Steam reformer Converts to H2, CO, CO2 + H2O + CH4 H2O Air or O2 Ammonia: Optional Normal Usual Hydrogen: Optional Normal Rare HyCO: Optional Normal Rare Methanol: Optional Normal Rare
- 18. Steam Reforming Section - Options What proportion of plants feature all three parts ? Many ammonia plants • Topsoe units with pre-reformer (e.g. India) • Uprate options which add a pre- reformer for capacity and efficiency gains (e.g. ABF; Kemira)
- 19. Steam Reforming Section - Pre- reformer Single adiabatic reactor • upstream of the steam reformer • uses high activity Ni based catalyst Converts hydrocarbons to methane, CO, CO2 and H2 • Eliminates C2 and higher hydrocarbons from feed • Makes life easy for the steam reformer !!
- 20. Steam Reforming Section - Pre- reformer: Why ? High efficiency/low energy plants Low steam export – benefit if steam not required Smaller and high heat flux reformers • Lower reformer capex (offset by pre- reformer capex) Simplified and robust steam reformer operation Means to deliver feedstock flexibility (not only means) between lighter and heavier feeds
- 21. Steam Reforming Section - Pre- reformer: Why Not ? Additional equipment • Capex (offset by smaller reformer ?) • Opex (catalyst; maintenance; ….) Complicated and delicate pre-reformer operation • Easily damaged expensive catalyst Low steam export – problem if steam export valued/required Economics suggest that pre-reformer is not the only solution if feedstock flexibility is required
- 22. Process Steam Hydrocarbon Feed HDS Reformed Gas Fuel ZnO Steam Generation and Superheating Combustion Air Pre-heat Pre-reformer Steam Reforming Section - Pre- reformer: Scheme without Re-heat
- 23. Process Steam Hydrocarbon Feed HDS Reformed Gas Fuel ZnO Steam Generation and Superheating Combustion Air Pre-heat Pre-reformer Steam Reforming Section - Pre- reformer: Scheme with Re-heat
- 24. Steam Reforming Section - Pre-reformer: Why or Why Not Re-heat ? Endothermic steam reforming at inlet (both beds) Methanation causes exotherm with naphtha 525 500 475 450 400 350 Temperature(oC) Natural Gas Inlet Exit 947 932 887 842 752 662 Temperature(oF) Naphtha Inlet Exit
- 25. Carbon Gas Phase Polymerisation Steam Reforming Section - Reactions General reaction scheme H2O CxHy CO/CO2/H2 H2O Olefins Catalytic H2O
- 26. Steam Reforming Section - Tubular Steam Reformers Design based upon • overall strongly endothermic reaction requires large heat input • process gas through catalyst filled tubes • tubes located in fired furnace Various designs dependent on process designer and plant
- 27. Tubular Steam Reformers - Ammonia Designs • 200 - 500 tubes arranged in rows • downflow usually upflow rare • capacity range (approximate) 500 – 3300 mtpd • differing designs favoured by certain contractors top fired side fired terrace wall
- 28. Tubular Steam Reformers - Hydrogen Small plant design - usual • 6 - 40 tubes arranged in a circle • upflow and upfired • single central burner offered by Axsia-Howmar, Howe-Baker, Hydrochem, Glitsch • other geometries are found • capacity range (approximate) 500 - 16000 Nm3/h 0.5 - 15 MMSCFD
- 29. Tubular Steam Reformers - Hydrogen Larger designs • 50 - 500 tubes arranged in rows • downflow usually upflow rare • capacity range (approximate) 10 - 150 kNm3/h 10 - 125 MMSCFD • differing designs favoured by certain contractors top fired side fired terrace wall
- 30. Tubular Steam Reformers - Methanol Designs • 400 - 900 tubes arranged in rows • downflow usually upflow rare • capacity range (approximate) 2000 – 5000 mtpd • differing designs favoured by certain contractors top fired side fired terrace wall
- 31. Tubular Steam Reformers Top fired designs • Technip; Linde; Uhde; Kellogg; Davy; Lurgi multiple rows of tubes TUBE
- 32. Tubular Steam Reformers Side designs • Topsoe; Chiyoda; Selas (historic) long single row of tubes Side Fired
- 33. Tubular Steam Reformers Terrace wall designs • Foster Wheeler two cells, each with a long single row of tubes Terraced wall
- 34. Post Reformer Options Two options • secondary • gas heated reformer
- 35. Steam Reforming Section - Secondary Reformer To Waste Heat Boiler Process Steam Hydrocarbon Feed HDS Fuel Steam Generation and Superheating Combustion Air Pre-heat Air/Oxygen
- 36. Steam Reforming Section – Secondary Reformer Introduction Three key components • Burner Design • Mixing Volume • Catalyst All must be designed correctly to maximize performance Air/Oxygen Steam Reformer Effluent To Waste Heat Boiler
- 37. Steam Reforming Section – Secondary Reformer: Ammonia Ammonia plants fire the burner with AIR • Adds O2 AND N2 N2 is inert in secondary (more or less) & through shifts/CO2 removal/methanation N2/H2 + residual CH4 go to • Compression & NH3 synthesis loop Burner air provides the N2 required for NH3 synthesis Thus – secondaries are common in NH3 plants
- 38. Steam Reforming Section – Secondary Reformer: Ammonia Most ammonia flowsheets Ammonia synthesis NH3 Converts N2 + H2 => NH3 Syngas compression Air = O2 + N2 Secondary reformer
- 39. Steam Reforming Section – Secondary Reformer: Ammonia Linde LAC flowsheets Ammonia synthesis NH3 Converts N2 + H2 => NH3 Syngas compression N2 from ASU Secondary reformer
- 40. Steam Reforming Section – Secondary Reformer: H2/HyCO/MeOH H2/HyCO/MeOH plants must fire with O2 • N2 is not required in the process • N2 cannot be tolerated in the process Source of O2 required • Local air separation unit (ASU) may not be available • Over-the-fence from industrial gas company may be expensive • Construction/operation of ASU adds cost & complexity THUS - O2 fired secondary's are less common
- 41. Steam Reforming Section – Secondary Reformer: MeOH NOTE: Lurgi MeOH process design features O2 fired secondary • Includes “mega-methanol” process Lurgi relatively successful in recent years THUS - O2 fired secondaries are relatively common in MeOH industry area
- 42. Steam Reforming Section – ‘GHR’ Post Reformer Retrofit Steam Hydrocarbon Feed HDS Fuel Steam Generation and Superheating Combustion Air Pre-heat Reformed Gas Process Additional gas + steam feed Gas Heated Post- Reformer Waste Heat Boiler HDS Preheat Mixed Feed Preheat
- 43. Steam Reforming Section – ‘GHR’ GHRs are used in other ways • E.g. full replacement of the primary reformer Various designs exist from Air Products, Technip, Topsoe, Kellogg as well as Johnson Matthey
- 44. Shift & Hydrogen Purification Sections Consider shift + purification together • design options are intimately linked Historically preferred designs linked to available catalyst/absorbent technology Not required on HyCO and MeOH plants
- 45. Shift & Hydrogen Purification Sections Water gas shift reaction Purification • Either: CO2 removal and methanation (NH3 & old H2) COx + H2 => CH4 + H2O yields ~96 % H2 • Or: PSA unit (newer H2) yields 99.9+ % H2 CO + H2O CO2 + H2 (+ heat)
- 46. Shift & Hydrogen Purification Sections – Ammonia Plants Designs feature HTS and LTS beds in series with inter-cooling HTS From Steam Reforming Liquid CO2 Removal LTS H2O CO2 feed to urea plant Methanation H2 COx + H2 => CH4 + H2O
- 47. Shift & Hydrogen Purification Sections – Ammonia Plants Design options – Linde LAC process • use tubular ITS followed by PSA unit From Steam Reformer PSA H2ITS H2O Purge gas to fuel
- 48. Shift & Hydrogen Purification Sections – Hydrogen Plants Designs 1970s to mid-1980s • LTS catalyst developed • HTS and LTS beds in series with inter-cooling HTS From Steam Reforming Liquid CO2 Removal LTS H2O CO2 to vent Methanation H2 COx + H2 => CH4 + H2O
- 49. Shift & Hydrogen Purification Sections – Hydrogen Plants Older plants built up to ~1970 • pre-date LTS catalyst development • two HTS beds in series with inter-cooling HTS From Steam Reforming Liquid CO2 Removal HTS H2O CO2 to vent Methanation H2 COx + H2 => CH4 + H2O
- 50. Shift & Hydrogen Purification Sections – Hydrogen Plants Designs since mid-1980s • PSA units improved significantly • HTS followed by PSA unit From Steam Reforming PSA H2 HTS H2O Purge gas to fuel vent
- 51. Shift & Hydrogen Purification Sections – Hydrogen Plants Design options • include additional LTS before PSA unit favoured in some large new plants (>105 kNm3/h or 90 MMSCFD) HTS From Steam Reforming PSA H2LTS H2O Purge gas to fuel vent
- 52. Shift & Hydrogen Purification Sections – Hydrogen Plants Design options • use MTS followed by PSA unit From Steam Reformer PSA H2MTS H2O Purge gas to fuel vent
- 53. Ammonia Synthesis/Methanol Synthesis Multi-stage complex converters Various designs Not considered further in this presentation
- 54. Steam Reforming Based Town Gas Processes Various flowsheets exist • HKCG; CityGas; Dakota Gas • Rely on standard syngas reactor units
- 55. Cyclic Town Gas - Process Outline Reactor design features • hydrocarbon, O2(air), steam feeds • packed bed of catalyst • burner in top of reactor Burner provides heat • increases temperature of catalyst bulk • partial combustion of the hydrocarbon Catalyst provides reforming and shift activity
- 56. Cyclic Town Gas - Process Outline Hydrocarbon feed varies • natural gas to naphtha • may contain sulphur (ie not desulphurised) Catalyst becomes deactivated • C & S • Fe scale • regeneration may be required • regen can be part of process (eg cyclic TG plants) or physical cleaning
- 57. DRI Processes – Types using Steam Reforming HYL type flowsheets Midrex type flowsheets Lookalikes exist in each category
- 58. DRI Processes - HYL III Process Flowsheet
- 59. DRI Processs - Features of HYL III Steam Reformer Natural gas feedstock Downflow + down-fired Typical conditions • S/C ratio 1.9 - 2.5 • pressure 6 - 7 barg • exit temperature 840°C (1545°F) • methane slip 2.0 - 2.5 mol % (dry) Steam reformer catalysts • same types as HyCO (+H2/NH3/MeOH) plants • feed purity to < 0.1 ppm S required
- 60. DRI Processes - Typical Midrex Process Iron Oxide Direct Reduced Iron Exhaust Stack Flue Gas Natural Gas Feed Gas Main Air Blower Combustion Air Process Gas Compressor Reformer Top Gas Scrubber Cooling Gas Compressor Reducing Gas Scrubber Top Gas Reduction Zone Shaft/ Reduction Furnace Cooling Zone
- 61. DRI Processes - Features of Midrex Type Reformer Natural gas feedstock Upflow + up-fired Typical conditions • From recycle gas CO2 ~15 mol %; CO ~15 mol %; H2O gives S/C ~0.6 S required against metal dusting (up to 10 ppm) • pressure 1 - 2 bara • exit temperature 930°C (1706°F) • methane slip 1.0 mol % (dry) Specialized S tolerant reformer catalysts
- 62. Summary High level review of syngas flowsheets Key differences and options highlighted Increased awareness but many further layers of detail exist