Introduction To Syngas Plant Flowsheet Options

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


Cl, metals)

Steam reforming


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


Cl, metals)

Steam reforming


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


Cl, metals)

Steam reforming


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


H/C feed

Pre- reformer


H2O + CH4

Secondary reformer

Drives CH4 slip down +

other fact0rs

H2O

Steam reformer


H2O + CH4

H2O Air or O2

Ammonia: Optional Normal Usual Hydrogen: Optional Normal Rare HyCO: Optional Normal Rare Methanol: Optional Normal Rare


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


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


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


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


Side designs • Topsoe; Chiyoda; Selas (historic)

long single row of tubes

Side Fired


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


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



Syngas compression

Air = O2 + N2

Secondary reformer

Steam Reforming Section – Secondary Reformer: Ammonia Linde LAC flowsheets



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


Liquid CO2

Removal LTS

H2O

CO2 to vent

Methanation H2

COx + H2 => CH4 + H2O


Older plants built up to ~1970 • pre-date LTS catalyst development • two HTS beds in series with inter-cooling


Liquid CO2

Removal HTS

H2O

CO2 to vent

Methanation H2

COx + H2 => CH4 + H2O


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


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



Design options • use MTS followed by PSA unit

From Steam Reformer PSA H2 MTS

H2O


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

Introduction To Syngas Plant Flowsheet Options

Technology

Transcript of Introduction To Syngas Plant Flowsheet Options