Introduction to Syngas Plant Flowsheet Options
By:
Gerard B. Hawkins Managing Director, CEO
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
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
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
Simplified Steam Reforming NH3 Plant (cont.)
N2
Ammonia synthesis NH3
Converts N2 + H2 => NH3
Syngas compression
H2
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
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
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
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
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
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
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
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
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”
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
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
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
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)
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
!!
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
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
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
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
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
Tem
pera
ture
(oC
)
Natural Gas
Inlet Exit
947 932 887 842 752 662
Temperature ( oF)
Naphtha
Inlet Exit
Carbon
Gas Phase Polymerisation
Steam Reforming Section - Reactions
General reaction scheme
H2O
CxHy CO/CO2/H2
H2O
Olefins Catalytic H2O
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
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
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
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
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
Tubular Steam Reformers
Top fired designs • Technip; Linde; Uhde; Kellogg; Davy;
Lurgi multiple rows of tubes
TUBE
Tubular Steam Reformers
Side designs • Topsoe; Chiyoda; Selas (historic)
long single row of tubes
Side Fired
Tubular Steam Reformers
Terrace wall designs • Foster Wheeler
two cells, each with a long single row of tubes
Terraced wall
Post Reformer Options
Two options • secondary • gas heated reformer
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
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
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
Steam Reforming Section – Secondary Reformer: Ammonia
Most ammonia flowsheets
Ammonia synthesis NH3
Converts N2 + H2 => NH3
Syngas compression
Air = O2 + N2
Secondary reformer
Steam Reforming Section – Secondary Reformer: Ammonia Linde LAC flowsheets
Ammonia synthesis NH3
Converts N2 + H2 => NH3
Syngas compression
N2 from ASU
Secondary reformer
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
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
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
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
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
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)
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
Shift & Hydrogen Purification Sections – Ammonia Plants
Design options – Linde LAC process • use tubular ITS followed by PSA unit
From Steam Reformer PSA H2 ITS
H2O
Purge gas to fuel
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
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
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
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 H2 LTS
H2O
Purge gas to fuel vent
Shift & Hydrogen Purification Sections – Hydrogen Plants
Design options • use MTS followed by PSA unit
From Steam Reformer PSA H2 MTS
H2O
Purge gas to fuel vent
Ammonia Synthesis/Methanol Synthesis
Multi-stage complex converters Various designs
Not considered further in this presentation
Steam Reforming Based Town Gas Processes
Various flowsheets exist • HKCG; CityGas; Dakota Gas • Rely on standard syngas reactor units
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
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
DRI Processes – Types using Steam Reforming
HYL type flowsheets Midrex type flowsheets Lookalikes exist in each category
DRI Processes - HYL III Process Flowsheet
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
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
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
Summary
High level review of syngas flowsheets
Key differences and options highlighted
Increased awareness but many further layers of detail exist