Post on 01-Nov-2014
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Feedstock Purification Flowsheet Options
By:
Gerard B. Hawkins Managing Director, CEO
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
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