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