Principles of Pre-reforming Technology

Principles of Pre-reforming Technology

Contents

Pre-reforming Flow-schemes

• Feed-stocks • Catalyst handling, loading & start-up

Benefits of a pre-reformer • Case studies • Effects upon primary reformer • Data analysis • Reactor temperature profiles • Catalyst management

Summary

Markets Towns Gas

• Naphtha => Town Gas, reforming & methanation

• Market declining due to NG availability Hydrogen

• Utility/chemical/refinery • C1 though to naphtha => H2 • Feedstock flexibility/smaller primary • Growing market for pre-reforming

Markets (contd) Methanol

• Retrofits, increase output/efficiency • Growing market, technology enabler, big

reactors Ammonia

• Retrofits only GTL

• 1,2 stage • Very big reactors

Contents GBHE pre-reforming background

• Markets • Flow-schemes • Feed-stocks • Catalyst handling, loading & start-up


Summary

Flow-schemes - what does Pre-Reforming do?

What is the aim of a pre-reformer? To react hydrocarbon feed with steam to give a methane

rich product suitable for further downstream reforming.

Pre-reforming works as an adiabatic steam reforming step over a Ni based catalyst.

The basis for the reforming may be considered as the reaction between a hydrocarbon and steam • steam / methane reaction • water / gas shift reaction

Prereformer Installation

Pre- Heating

Re- Heating

Gas/Steam

VSG-Z101 Pre-reformer

500ºC

500ºC 450ºC

Flow Scheme - Desulfurization

Pre-Reforming catalyst is poisoned by sulfur. The performance of the sulfur removal

system is important for the pre-reformer. The sulfur removal system may be designed

in accordance with any well proven system but must achieve less than 0.1 ppm wt sulfur throughout the catalyst life.

Ultra-purification recommended for natural

gas applications

Advantages of Pre-reforming

Fuel savings over stand alone primary reformer Reduced capital cost of reformer Higher primary reformer preheat temperatures Lower involuntary steam production Increased feedstock flexibility Higher activity primary reforming catalyst for naphtha based plants

Lower overall steam to carbon ratios Provides protection for the main reformer Reliable and easy operation




Summary

Feedstock

Following feeds may be fed to a pre-reformer reactor • Natural gas • Refinery Off Gas • Synthesis Gas derived from coal/oil

gasification • LPG’s • Naphtha (up to FBP 240°C) • Kerosene • Methanol • Ethanol

Feedstock Feed Specification Poisons in feed

Sulfur < 0.1 ppm wt Chloride < 1.0 ppm wt * Total heavy metals < 1.0 ppm wt (inc Lead) * Lead < 0.2 ppm wt *

* - inlet purification section

Steam Quality Sodium < 0.2 ppm wt Chloride < 0.1 ppm wt Sulphide < 0.1 ppm wt Silica < 0.1 ppm wt

Feedstock contd For naphtha feeds over pre-reforming

catalyst there are limits on

• Aromatic content – normally 10 wt% • Naphthene content – normally 25 wt%

• When considered together < 40 wt% has

been applied

Feedstock contd

Following feedstock data is required for assessment of performance:

•Gas and LPG feeds •Full composition •Level of impurities

•For Naphtha feeds •PONA analysis •Level of impurities •C/H ratio and molecular weight •FBP




Summary

Pre Reformer Loading Extremely important to achieve a uniform

loading Any zones of low or high voidage will

reduce catalyst life • Check man-way plugs

No meshes should be used in the vessel Thermocouples must be positioned

correctly and height recorded Loading procedure will be provided Loading assistance may be provided

Prereformer Installation

Adiabatic Pre-Reformer Axial flow with Thermowell

Bed of pre-reforming catalyst.

Pre-reformer Start-up

Drying

Heating

Start-up

Reduction

Catalyst Drying

For catalyst subjected to low temperature (ie <0oC)

Dry using Nitrogen 175 to 250°C NG can be used below 200°C 4 to 24 hours Dry air, not suitable for prereduced First start-up of prereduced

Catalyst Heating

Normally heated using nitrogen Absorbed moisture Initial heating rate, 50°C per hour Max temp differential in bed 100°C At 200°C, 70°C per hour Heating till peak 400°C, min 370°C High circ rate, max pd 2 bar

Catalyst Heating continued Warm-up rates Rapid warm-up minimises energy usage/time

Traditional constraints of equipment

Controllability

Limited by mechanical considerations of vessel

Catalyst, 150-170oC per hour

Catalyst Heating contd Limits on impurities * Oxygen 1% vol Carbon Dioxide 1% vol Carbon Monoxide 1% vol Methane 1% vol Hydrogen 1% vol Ethane 100 ppm vol Sulfur 0.1 ppm wt

* For the initial warm up. Lower limits for already activated or prereduced

catalyst

Catalyst Heating contd

Holding at temperature Not recommended

2% hydrogen added

Temperature reduced to 350°C

Catalyst Start-up When operating temperature has been achieved Check for build-up of carbon oxides and hydrocarbons

Addition of 10 mol % Hydrogen

Followed by steam

Introduce process feed, maintain safe S:F ratio

Ensure feed lines are drained and warmed

Vent steam to atmosphere before cutting in

Heating using Natural Gas Using NG as heating medium No impurities Immediate start-up 50°C per hour, max differential 100°C At 200°C introduce steam

• Min S:C 0.3kg/kg at 200°C • Min S:C 0.5kg/kg at 400°C to 450°C • Increase to design feed and S:F

Contents

GBHE pre-reforming background • Markets • Flow-schemes • Feed-stocks • Catalyst handling, loading & start-up


Summary

Process benefits of pre-reforming

Moves reforming load from Primary

Better reformer design • Higher thermal efficiency in radiant box • Raises pre-heat temps before carbon formation

issues • Feedstock flexibility

Reduced steam export • Heat is recovered from duct

Demonstrated using case studies

Process Benefits- Case Study

Case 1 – Base Case – no pre-reformer installed

Case 2 – Pre-reformer installed

Case 3 – Pre-reformer installed and plant rate increased until firing on the reformer is the same as Case 1

Effect of a Pre-reformer on Primary Reformer Performance

Parameter Units Case 1Plant rate % 100Methane slip mol % (dry) 12.84ATE °C 1.8Pressure drop bar 1.26Maximum TWT °C 809Fluegas temperature °C 898Radiant efficiency % 68.7Fuel rate change % 0

Case 2100

12.761.1

1.2880388569.4-8.8

Case 3109

12.791.3

1.4980789868.7

0

Contents

GBHE pre-reforming background • Markets • Flow-schemes • Feed-stocks • Catalyst handling, loading & start-up


Summary

Effect of a Pre-reformer on Primary Reformer Performance

For new plants, there are CAPEX benefits • Can reduce tube count on a new hydrogen plant by over

5% • Fuel usage can be reduced by 8%

For existing plant, excellent revamp opportunity • Additional throughput or feedstock flexibility

In summary • Significant potential economic benefits • Overall benefits plant specific

Effect of a Pre-reformer on Primary Reformer Performance contd

Good performance depends on good design and preparation of the reactor

It is not simply another catalyst bed Guaranteed operation assumes plug flow

through the bed Guaranteed operation relies on good catalyst

management


Travelling (or multi-point) thermocouple

Catalyst Graded

Ceramic Balls Catalyst

discharge nozzle

(alternative)

Catalyst discharge nozzle (typical)


Good performance is achieved through

Even gas distribution Adequate temperature

measurement Thorough pre-commissioning Correct catalyst charging

procedures Good operating practices




Summary

Pre Reforming Data Analysis

Good data is key to understanding performance of the pre reformer

Data includes • Temperatures inlet and outlet the bed • Temperatures through the bed • Gas analysis inlet and outlet bed • Feedstock and steam flows inlet bed • Bed pressure drop trend

Pre Reforming Data Analysis

Careful monitoring of temperatures inlet, outlet and through the bed allows • Problems to be detected early on

Sulfur poisoning, wetting etc • Problems to be resolved before

there has been too much damage caused

• Estimation of residual life




Summary

Reaction Profile Reaction Zone Length

End Of Reaction Zone

Thermoneutral Point

Minimum Reaction

Temperature

Beginning Of Reaction Zone

Preheat Temperature

Tem

pera

ture

°C

Distance through bed

Reaction Profile

end of reaction

zone

methanation and shift reactions dominate

bed shrinkage or deactivation

Tem

pera

ture

°C


endotherm

steam reforming reaction dominates

Reaction Profile

By monitoring relative movement of specific points on the profile, • See if there is sulfur poisoning • See if there is excessive sintering • See if there is mal-distribution

But rate changes will affect positions of profiles

Temperature Profiles - Rate

Temperature Profiles Natural Gas - Effect of Plant Rate

Changes in plant rate affect profile • Increases in rate

Increases the length of profile Decreases the gradient

• Can be mistaken for sintering

Temperature Profiles - Changes in Inlet Temperature

Temperature Profiles Changes in Inlet Temperature

Increases in inlet temperature • Shorten profile length • Steeper profile gradient • Change exit temperature

Temperature Profiles Maldistribution

TI Maldistribution due to

wetting/agglomeration

Temperature Profiles Maldistribution

Maldistribution

Temperature Profiles Natural Gas

Temp

Position along Bed

Std NG

Sintering (Lazy profile)

Poisoning (Flat inlet)

Temperature Profiles Naphtha

Temp

Position along Bed

Std Naphtha

Sintering (Lazy profile)

Poisoning (Flat inlet)

Polymeric Carbon (deepen endotherm)




Summary

Catalyst Management

Draw the pre-reformer catalyst profile weekly

Examine profile and check for • poisoning • carbon polymer formation • sintering

Plot “end of reaction zone” (EOZ or Z90) against time

Catalyst Management - EOZ


Tem

pera

ture

Predicting End-of-Life

The EOZ (or Z90) plot is the most useful tool Waiting for ethane or higher hydrocarbon

slip is too late Ultimate limits are

when feed preheat limitations are reached

when C2+ slip is unacceptable for

reforming catalyst • EOL of VSG-Z101 catalyst often taken to

be when C2+ slip of 2000 ppm v/v of the

wet rich gas.

Summary Successful Pre-reforming requires

• A good catalyst

• Careful Operation/Procedures

GBHE VSG-Z101 catalysts are well suited to withstand operating rigors

And come with the GBHE Experience - the learning which is so essential to well advised operation

Date post:	01-Nov-2014
Category:	Technology
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