methanol reformer designs

Gerard B. Hawkins Managing Director, CEO

C2PT Catalyst Process Technology

Three major types of reformer Each tackles the duty in different ways No clear best choice Choice dictated by Contractor history

Top Fired Usually Single box with Multiple rows of tubes. Heat load for a Top fired, is in the top one third of the reforming section. Peak tube wall temperature is is this region Pencil Type Flames required

Side Fired/Foster Wheeler Side Fired Reformers are usually made up of several identical cells, with each having a single row of tubes The aim of the side fired design is to achieve a more even heat flux profile over the length of the tube, by locating burners the full height of the box.

Top Fired KTI Jacobs ( H & G) Kellogg Lummus Uhde

Side Fired Topsoe Selas Howe Baker Chiyoda ICI (Hybrid) Foster Wheeler

Majority of plants have Top Fired Reformers Some have Foster Wheeler Reformers A few have Side Fired Furnaces Lurgi plants often have an oxygen blown secondary A few plants have a pre reformer (Statoil and M5000)

Methanol reformers are large Largest reformer has 960 tubes Two to three times the size of an ammonia reformer Many reformers in the range 600-900 tubes Why is this ? All reforming is done in this reformer There is no secondary Therefore choose the cheapest design and easiest to

scale up Therefore use Top Fired - Why ?

Capital Cost For a reformers of the same size a Top Fired furnace

has less equipment than Side Fired or Foster Wheeler FW and SF duplicate a lot of equipment as there are 2

cells Side fired are generally less heavily loaded - they have

a higher capacity

Operational Costs Top fired have a higher radiant efficiency Typically 50-60% Side fired furnaces have a lower efficiency Typically 40-45% Maintenance Costs Side Fired reformers have more burners By a factor of 5 over Top Fired By a factor of 2 over Foster Wheeler Side Fired refractory temperatures are higher

Name Methanol AmmoniaSteam to Carbon 2.8-3.2 3.0-3.4Pressure (bara) 15-20 30-35Exit 1y Temperature (°C) 860-880 740-780Exit 2y Temperature (°C) n/a 960-980Tube Count 900-1000 300-400Maximum TWT (°C) 900-950 800-850H2 70-73 54-58CO 14-16 10-12CO2 7-9 8-10CH4 2-3 0.1-1.0N2 0-1 22-26

Comparison of Flowsheets Typical Conditions

On most methanol plants we only have a primary reformer

Therefore must minimize methane slip from primary Methane is an inert in the loop Just like ammonia Represents an inefficiency Must be purged out - lose reactants Purge is burned in reformer Typically 2/3 of the reformer fuel (Some plant do sell it !)

Must therefore run at highest outlet temperature There is no secondary to drop slip down to very low

levels A steam to carbon of 2.8 to 3.3 allows MPS to be used

from steam turbine Balances out MPS balance Run at low pressure to minimise methane slip Does increase compression costs

No requirement for nitrogen to be added to the process In fact do not want nitrogen It’s an inert and will reduce loop efficiency Oxygen plants are traditionally expensive Oxygen blown secondary’s have a poor track record Many failures due to poor burner design Many failures due to poor vessel/refractory design Flame temperature is very high (2000°C)

Historically plants were never built with them No need for feedstock flexibility Licensed contractors have their own primary reformer

design - based on JMC design in many cases Topsøe do include them - problems with MgO hydration Similar to ammonia plants Therefore there is no great driving force for inclusion Until now Mega plants are at limit of reformer design

Top Bottom Side Wall

Nearly all heat transfer is by radiation Radiation from the fluegas to the tubes Little direct radiation from refractory to tube Refractory acts as a reflector Radiation from flame to tube at tube top

Tube Support

Pigtail

Burner

Tube

Coffins

Exit Header

Side Fired Furnace

ICI Methanol Foster Wheeler Reformer

Same for both types Nearly all heat transfer is by radiation from flames and

refractory Major portion is from refractory Some from flame (especially in FW) Some from fluegas Heat is transferred from flame to the walls By convection

Typical catalyst is VSG-Z101 Required to prevent carbon formation Heat fluxes are very high 100-160 kW/m² For plants with really high heat fluxes us VSG-Z101 Only two plant shave giant installed Pressure drop is not an issue (no air compressor) Heat transfer and carbon formation ARE issues

Weld

Hot Band

Exit temperatures are higher Therefore inside tube wall temperatures are higher Heat fluxes are higher Top fired between 100-140 kW/m² But some in range 140-160 kW/m² Ammonia plants typically 80-120 kW/m² These conditions favor carbon formation

Several N American Operators had failures at bottom of the tubes

Simulations said lots of margin

New peepholes installed and temperatures measured

Must hotter than expected

Found in Canada Unusual Temperature

distribution Checked using dry

powder Up flow at walls Flame impingement Modelled using CFD

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