emerging trends in hydrogen

1.1.

Emerging Trends in Syngas and H

BY

EH Stitt, PEJ Abbott, BJ BJ Crewdson

CatCon 2000:

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Emerging Trends in Syngas and Hydrogen, EH Stitt, PEJ Abbott, BJ Cromarty & BJ Crewdson (Synetix) PagePresented at CatCon 2000: 12-13 June, 2000, Houston, TX 2 of 20

2. INTRODUCTIONThe generation of, what is today recognizable as synthesis gas dates from the first quarter

of the last century, with the deployment of the classical Haber Bosch process in 1917. Thisprocess, which essentially remained commercial into the 1950s, comprised reacting coke withsteam to produce hydrogen via endothermic reaction (1), followed by the moderatelyexothermic water gas shift reaction (2)

C + H2O ⇒⇒⇒⇒ CO + H2 (1)CO + H2O ⇔⇔⇔⇔ CO2 + H2 (2)

In order to sustain the reaction temperature the reactor was periodically blown with air.The gas arising from this cyclic process was rich in hydrogen. It was this approach togenerating syngas that underpinned the developments in the 1920s of the Haber process forammonia manufacture (which required the addition of further nitrogen) and of the FischerTropsch process for the conversion of coal to liquid fuels, both initially in Germany.

The concept of activating methane via reactions analogous to steam reforming of methanewere also first investigated in the first quarter of the 20th century, also in Germany where theessential configuration of the primary reformer was established. In 1931 Standard Oil built aplant to generate hydrogen from refinery off-gases at Baton Rouge; the reforming reactiontook place over a catalyst in vertical tubes in parallel rows in a radiant, fired furnace.

The process was considerably improved by ICI, who developed the fundamentalengineering data for the design of the furnace, improved the catalyst formulation andintroduced a desulphurization step to protect the catalyst, using zinc oxide. The process wasused to produce hydrogen from off-gases for coal hydrogenation plants which ICI built in 1936and 1940. A number of plants were built by other companies based on the same technologyand catalyst; all using a natural gas feedstock. Natural gas was not at this time a readilyavailable feedstock, but as more refineries were built other hydrocarbon feedstocks, such asnaphtha, became increasingly available.

By the 1950s it was clear that if naphtha could be steam reformed economically then thiswould provide a cheap source of hydrogen for refinery applications and petrochemicals, aswell as ammonia manufacture and of syngas for methanol synthesis. Work in ICI at this timeled to a more stable catalyst, operated at economic steam ratios without excessive carbonformation and resistant to poisons.

In 1959 ICI started up the first large-scale pressure steam reformer using naphtha as afeed. This plant and technology became the forerunner to over 400 plants subsequentlylicensed around the world in areas where natural gas was not readily available.

From 1959 to present, development of the catalyst has allowed plants to be run at higherpressure and temperature, using feedstocks with different hydrogen : carbon ratios and theprocessing of unsaturated and aromatic containing feeds.

In the last 25 years the increased availability of natural gas has resulted in its use as themain feedstock for steam reforming; and this is likely to remain so for the foreseeable future.The developments here have built on the engineering of the naphtha reformer, but withdevelopment of the catalyst for longer life, higher activity, reduced carbon formation and withimproved physical attributes.

The last 5 years have however seen a further shift in emphasis. While the use ofreformed gas has historically been dominated by hydrogen manufacture for commercial use,and for ammonia and methanol synthesis this may not remain the case. Two "new"applications of syngas are becoming of increasing importance:� manufacture of liquid fuels from remote, marginal or stranded natural gas - so called "gas-

to-liquids" or GTL - where Fischer Tropsch chemistry is currently the favoured route, and� generation of hydrogen from natural gas liquid fuels to power mobile and stationary fuel

cells.These applications both require the generation of syngas from a gaseous or vaporised

feedstock. They have provided new impetus and led to a major revisit of technology to


manufacture syngas and hydrogen. This presentation will review current and future marketrends as well as current developments in processes and reactoors for the generation ofsyngas and hydrogen.

3. REACTION ROUTES TO SYNGAS AND HYDROGENThere are, in essence, two means to generate syngas from a hydrocarbon fuel. These

are (exemplified for methane):� steam reforming CH4 + H2O ⇔⇔⇔⇔ CO + 3H2 ∆H = +206 kJ/mol (3)� selective oxidation CH4 + 2

1 O2 ⇒⇒⇒⇒ CO + 2H2 ∆H = - 36 kJ/mol (4)

All syngas manufacturing routes are based on one or both of these, idealized, catalyticreactions. Note importantly that the reforming reaction is equilibrium limited and highconversion is thus favoured by high temperature. It is important also to note the opposingthermochemistry of these reactions - with the steam reforming reaction being highlyendothermic whereas the partial oxidation reaction is slightly exothermic. In steam reforming,an excess of steam is used to suppress carbon formation but also beneficially serves toreduce the adiabatic temperature fall.

The reality for the oxidation reaction is of course that it has a propensity, if uncatalysedand not oxygen limited, to give the fully oxidized products, thus increasing the exotherm. Thiscan be summarised by the following reactions� partial combustion CH4 + 2

3 O2 ⇒⇒⇒⇒ CO + 2H2O ∆H = - 519 kJ/mol (5)

� total combustion CH4 + 2O2 ⇒⇒⇒⇒ CO2 + 2H2O ∆H = - 802 kJ/mol (6)Given this, it is easy to theoretically envisage systems where the heat of reforming is

balanced by combustion or oxidation. The significant differences between alternate processesrelate to the nature of the oxidation and combustion, the extent to which they are decoupled(spatially, temporally) and the relative reliance on each reaction.

In both reforming and oxidation reactors the water gas shift reaction will occur:� shift reaction : CO + H2O ⇔⇔⇔⇔ CO2 + H2 ∆H = - 41 kJ/mol (7)

At the temperatures prevailing in either type of reactor this reaction is fast and non-catalytic and will probably be near equilibrium. The reaction, as shown, is slightly exothermicand therefore high temperatures encountered in oxidation or reforming will push conversion infavour of CO.

The other important side reactions are those leading to the formation of carbon. Inreforming these are as follows� disproportionation 2CO ⇔⇔⇔⇔ C + CO2 ∆H = -172 kJ/mol (8)

(Boudouard reaction)� decomposition CH4 ⇔⇔⇔⇔ C + 2H2 ∆H = +75 kJ/mol (9)

In oxidation conditions, carbon forms due to soot formation mechanisms and oxidativedehydrogenation of the hydrocarbon. In either case the formation of carbon species issuppressed by use of steam. The control of carbon formation is important in all forms ofsyngas generation for reasons not only of catalyst longevity but also materials of construction.


4. CONVENTIONAL STEAM REFORMING

The overall flowsheet for steam reforming is dependent on the required end product.Figure 1 shows a generalised flowsheet - that is in fact the flowsheet for the generation ofammonia synthesis gas. In ammonia manufacture the purpose of the secondary reformer is toadd heat but also a convenient means to introduce the nitrogen. Clearly in the case ofmethanol or FT, only the primary reformer is required. For hydrogen generation thesecondary reformer would normally be omitted. The key and common feature of all theflowsheets is the large, fired box reformer.

While this is the most commonly used approach for all the applications mentioned, it has anumber of disadvantages:� it has a large weight and footprint, and is capital intensive� it is slow to start up and shut down and involves manual operations� the gas composition is more hydrogen rich than is ideal for either methanol or Fischer

Tropsch synthesis� it is unsuitable for a floating or mobile facility due to weight and size, sensitivity to motion

and safety hazard potentialThere is one further important factor to appreciate. Cost analysis of either a methanol or a

Fischer Tropsch gas-to-liquids plant indicates that the syngas generation section comprises50-70% of total capital cost. In order therefore to achieve significant cost reductions andlocation flexibility a significant shift in the underpinning reactor technology and its cost base isrequired.

As a result of the above considerations there has been considerable effort to explore andimplement alternative means to generate syngas. The earliest of these efforts were motivatedby the desire to reduce the cost base of ammonia, methanol and refinery hydrogenmanufacture, but more recently have been dominated by the requirements of gas-to-liquidsand fuel cells.

5. APPLICATIONS AND MARKETS FOR SYNGAS & HYDROGENAs a preamble to considering the alternate syngas technologies it is worth reviewing the

demands of both the conventional and the perceived "new" applications. These will beconsidered in approximately the reverse order of scale.

5.1. Gas-to-LiquidsThere are a number of potential scales and environs, and the monetization of remote and

marginal gas through chemical conversion to is generally associated with Fischer Tropsch

Fig 1 : Basic Reforming Set-up

STEAM

HYDROCARBON FEED

FUEL

FEEDPURIFICATION

PRIMARYREFORMER

SECONDARYREFORMER

HIGHTEMPERATURE

SHIFTLOW

TEMPERATURESHIFTAIR


synthesis. In general, for Fischer Tropsch, a syngas with a H2 – CO ratio of approximately 2 isrequired (as for methanol). There are a limited number of FT plants operating, mostly in SouthAfrica (Sasol and Mossgas) but also one in Malaysia (Shell). The Sasol plants are of coursefed with coal derived syngas. The common thread in GTL is that the gas is frequentlyassumed to have little nominal value. While this is certainly true for marginal gas it may not bethe case for large remote gas fields.� Natural gas in Alaska. An opportunity for GTL to generate replacement for crude, as oil

production declines, as a means to maintain liquid throughput of the main (trans-)Alaskanpipeline economic beyond the current horizon of 2008-2012. This is a motivation behindthe significant sums of US government investment in both novel routes to syngas as wellas FT itself. This application requires extremely large plants; probably several timeslarger in syngas capacity than any existing operating single train reformer.

� Remote large gas fields elsewhere such as the Middle East, Africa, Caribbean, North Sea,China etc. It seems most likely that the next world-scale plant will be built in one of theseareas. These split effectively into onshore and offshore. For onshore units the sizeconsiderations are probably similar to those for Alaska. For offshore, the limits areeffectively imposed by the "platform" based nature of the unit. This puts a significantemphasis on size and weight, although the offshore processing unit may be barge ratherthan production platform based.

� Marginal Gas. Gas associated with oil fields that is predominantly flared as a wasteproduct at present. Environmental pressure, resulting in legislation in some areas, willpush for this gas to be used beneficially (or reinjected into the field). The gas rateassociated with this application is probably lower than for remote gas. Some of theapplications are offshore.There is a clear future driver to extract value from remote and marginal gas where an

economic case can be made and where environmental factors dictate. This will become areality over the next 5-10 years. There are of course ongoing studies for alternatives to GTL.These include liquefaction, electric power (gas-to-wire) and others. GTL per se may nothappen. The future imperative to process and beneficially exploit remote and marginal gas ishowever beyond question. The key therefore lies in whether GTL can be made the mostcompetitive and hence most favoured option. Helped by the more favourable price of oil, GTLprojects are now gathering momentum.

5.2. Refinery HydrogenCurrently, the major users of hydrogen (excluding the ammonia and methanol industries)

are refineries, consuming most of the hydrogen manufactured worldwide. On refineries, thehydrogen required mostly comes from two sources, catalytic reformers and ‘on-purpose’hydrogen plants. In excess of 85% of hydrogen production from ‘on purpose’ units is stillgenerated using hydrocarbon steam reforming technology.

Environmental regulations for cleaner fuels continue to march remorselessly forward. InEurope, the year 2005 has been set as a deadline for new specifications for motor gasolineand diesel, and similarly tight limits are being adopted in the US. The European regulationsare shown in Table 1.

Table 1: Clean Fuel Regulations in Europe.MaximumLevels

CurrentSulphurppm

2000/1SulphurPpm

2005Sulphurppm

CurrentAromatics%

2000/1Aromatics%

2005Aromatics%

Gasoline 500 150 50 - 40 35Diesel 500 350 50

Some countries are in fact introducing tax benefits to bring forward the 2005 date as far assulphur goes. Regulations in the rest of the world will inevitably follow trends in the US andEurope. The effect of these regulations on a refinery hydrogen balance is significant. Therewill be a greater demand for hydrogen in hydrocracking and hydroprocessing, especially fortreating the diesel and FCC gasoline product streams. There will also be a tendency for lesshydrogen to be available as a by-product from catalytic reforming, where units are operating atlower severity to reduce aromatics production. Figure 2 shows how anticipated specificationchanges in Europe can be expected to affect the hydrogen balance (also assumes that a lowpolyaromatics/high cetane spec. for diesel will be adopted).


The numbers presented inFigure 2 should be treated with alittle caution and almost certainlyrepresent an upside (that is fromthe viewpoint a catalyst orhydrogen supplier – thusconversely the or downside if youare a refiner). There a number ofreasons why hydrogen growth mayfall below the trendline shown.� The technology developments

in desulphurisation options forFCC gasoline and diesel arecontinuing to reduce hydrogenrequirements

� Refineries are making valiant efforts to avoid spending money to build hydrogen plants.Self help measures here include hydrogen management, hydrogen recovery and clubbingtogether to use spare hydrogen from adjacent facilities.

� The low diesel specification on PNA or a higher cetane specification may or may not beadopted; this is a decision due inn the autumn. The balance of probability is that this willnot be legislated, with a consequent reduction in projected hydrogen requirement.Choices for meeting the increased hydrogen demand include new capacity, revamping

existing capacity and purification and recovery of hydrogen from other refinery streams. Thereis much debate in the industry at present as to how the regulations can be achieved in eachparticular refinery – however there is no doubt that over the next 5 years a large amount ofextra hydrogen production will be required. This scenario faces refinery operators when theycan least afford it. Refinery margins are low and being squeezed. Cash is not easily availableto expand hydrogen production. In terms of hydrogen plant size, this will depend very much onlocation and who builds the plant. In the US, over the past 5 years, there has been a trend tobigger hydrogen plants being built by Industrial Gas producers, supplying the H2 into apipeline system. In Europe, the refineries are more dispersed and smaller, and it is more likelythat there will be a larger number of smaller H2 plants.

The next “hot topic” once the sulphur and VOC issues have been addressed is likely to beCO2 emissions from the Refinery. In terms of Syngas, this can have an impact, since theproduction of hydrogen does lead to a significant output of CO2 from a conventional SMR.AGHR technologies may therefore have an additional benefit in that they have lower CO2emissions overall per unit of H2 produced.

For diesel, the issue of diesel particulate matter is also a topic of concern, but it is notobvious how this links to hydrogen demand or technology.

5.3. MethanolA second traditional user of syngas technology, with the vast majority of the world’s

methanol plants being based on traditional fired steam reformers. The future of methanol iscurrently a little uncertain. Two major factors are influencing this.

The trend now appears set against the use of MTBE as a gasoline additive. A number ofStates in the USA have already put plans in place to phase out its use over the next 3-5 years.MTBE through the 1990s accounted for 25-30% of methanol usage and the probable loss of aportion of that market is having a significant effect on the future expectations of the methanolproducers; an industry that historically swings between glut and high margins is being pushedtowards a downwards path unless alternative uses for methanol can be found.

There is however potential good news on the horizon. Methanol is a very effective meansof fixing hydrogen into the liquid state. Specifically it has use as a liquid hydrogen source forautomobile fuel cells. Opinion is however currently divided amongst the interested parties infuel cells: fuel cell producers, automobile companies and fuel processing technologycompanies, oil companies. The last are almost single minded in their support for using agasoline or diesel fraction. A number of the car companies are, by contrast, stronglysupporting the methanol lobby, primarily on the basis that it is the easiest to “reform” into therequired hydrogen. Even this is not uniform however and other automobile companies appearthe lean towards gasoline. The energetics do not clearly distinguish. The environmental

Fig 2 : Effect of European Fuel Specification Changeson Hydrogen Requirements.

3000

3500

4000

4500

5000

5500

1999 2000 2001 2002 2003 2004 2005

MM

SCF

D (N

m3/

hr)

(3.4 million)

(6.2 million)


burden of the higher C / H ratio, and thus higher CO2 emissions of gasoline or diesel clearlyfavour the use of methanol. It is far from clear which will prevail. If it is methanol, then this willprovide an enormous boost to that industry and in due course encourage increasedproduction. As a measure of the possible tonnages involved, the American Methanol Instituteestimates1 that 10 million Fuel Cell Vehicles will consume 13-14 million tons of methanol perannum. Compare this with the current global methanol market of 30 million tons. It canclearly be seen that the uptake of Zero Emission Vehicles in California alone, if based onmethanol fed fuel cell vehicles, would have a major impact on the world methanol market.This increased commoditization of methanol within the fuel market is however likely to puthigher efficiency and cost minimization demands on the methanol manufacturers.

The final potential influence lies in Norsk Hydro’s methanol-to-gasoline (MTG) process2.This is an alternate GTL route to FT. In the context of the present paper however it does nothave great impact as essentially the same reforming capacity is likely to be slated for GTLirrespective of whether the liquid synthesis reaction is the zeolitic MTG or Fischer Tropsch.

5.4. AmmoniaOne of the earliest users of reforming technology, ammonia production is used to fix

nitrogen into a form from which it can be effectively used as a fertilizer. Nowadays, the mainuse of ammonia is still into the fertilizer industry and thus its production is inextricably linked tothe trends in the said fertilizer market. (Minority uses, amounting to approximately 20% ofammonia use, are for explosives and nylon). The use of inorganic fertilizers in Europe andNorth America has been in decline for 10 years or more. This is a low growth market, withmature technology. The trend is to move production to locations with the cheapest gassupply.

5.5. Reducing Gas Manufacture (Direct Reduction of Iron)The use of a synthesis gas mixture of carbon monoxide and hydrogen is now well

established as a method for the direct reduction of oxides in metals manufacture. Unlike thecases above, the syngas is not required at pressure and so the technology has developedtowards a much lower pressure reforming. The essential reformer design is unchanged,comprising vertical tubes in a fired box, but due to the lower pressure the tubes are largerdiameter and the reforming pellets considerably larger than is the norm in the higher pressureoperations. This market sector appears to command lower margins than the traditionalsyngas markets of hydrogen, methanol and ammonia.

5.6. Fuel CellsThe fuel cell is, simplistically, a device for turning hydrogen into water but generating

electricity as part of the reaction energy. There is a wide range of applications here, dictatednot only by the application and size but also the nature of the fuel cell. Large units (severalMW) are likely to be based on solid oxide or molten carbonate fuel cells. In both of these theoperating temperature is such that internal reforming of a hydrocarbon fuel is realistic,especially for the former. In any case hydrogen demand rate approaches current small-scaletechnology and, even if external reforming were to be applied to these fuel cells, they wouldrepresent a subset. Consequently they are not entirely relevant to the present discussion.

The focus for this presentation is, rather, on smaller units - say < 500 kW to 1 MW .These are most likely to be based at or near ambient operating conditions in the fuel cell.Both the currently commercially available phosphoric acid fuel cell (PAFC) and its probablereplacement ,the polymer electrolyte membrane (a.k.a. proton exchange membrane) fuel cell(PEMFC), operate at relatively low temperatures : approximately 200 and 60-80 C (392 and140-175 F) respectively. As such, generation of the hydrogen must be decoupled. It mayfurther be noted that for the PEM there is sensitivity to CO and hydrogen purification isrequired. There are two distinct applications in terms of scale and priorities

1.1.1. Mobile Power (Cars, Buses, Lorries),The hydrogen will be generated from a liquid fuel (methanol, gasoline ...). The power

rating is likely to be in the order of 20-100 kW and the design emphasis is on compactness,flexibility, automated operation, reliability and rapid start-up. While for methanol fuel adecomposition may seem logical, the development emphasis does appear to be on reformingor partial oxidation3.


1.1.2. Stationary Power UnitsThe power rating will be in the order of 100 - 500 kW and the hydrogen will be generated

from natural gas or a liquid fuel (kerosene, gasoline, diesel). Units rated at up to 250 kW,based on PAFC, have been commercially available for a number of years from IFC(International Fuel Cells) with their own partial oxidation based hydrogen generation system.

1.7. Distributed Syngas and Hydrogen ManufactureThere is a large number of applications and manufacturing processes that require

hydrogen or syngas in much smaller quantities than refineries and methanol plants, Table 2.Traditionally these have taken hydrogen “over the fence” if pipeline hydrogen is available,such as on the US Gulf coast or in large petrochemical complexes. Alternatively the hydrogenhas been sourced as a trailered import.

As an applicationexample, consider atypical edible oilhydrogenation unit thathas a hydrogen demandof approximately 0.25 –0.5 te / day. This is onlyin the order of 1% of thecapacity of a typical(refinery) hydrogen plant.Given the traditionaleconomies of scale insteam reformers, it isclear why it has not beeneconomic for this scale ofuser to install their own hydrohappenstance, this hydrogenstationary fuel cells (100 – 50technologies, particularly for cost compact hydrogen plantthe question of what is the renumber of installations speci

6. SCALES OF OPERATIOThe preceding section ha

users of syngas and hydrogecarbon dioxide. What is clearange of scale, Table 3.Table 3 : Syngas Applica

Gas-to-liquids / FTMethanolRefinery hydrogen

AmmoniaReducing gas (DRI)Carbon monoxideStationary fuel cellsMobile fuel cells

These data indicate a pomagnitude. Given this wide ranges vary. This is indeed tfunction of application rather

Table 2 : Intermediate and Small Scale Uses of Hydrogen

Intermediate-scale Users Small-scale UsersOils and fats hydrogenation AcrylamideAniline Adiponitrile1,4,Butanediol Oxo-alcoholsCyclohexane Butene-1Hydrochloric acid Tetrahydro furanHydrogen peroxide AminesFloat glass Butyrolactum, ButylrolactoneMetals production CaprolactumElectronics industry Cyclohexanol, Cyclohexanone

Fine chemicalsPharmaceuticals

gen unit; hence the large volume of traded hydrogen. By rate is of a similar order of magnitude to that required for0 kW capacity). The development of smaller scale reforming

off-shore and fuel cell applications is promising to deliver a low that may be competitive with trailered hydrogen. This does begal cost of trailered hydrogen. There is however a steady risingfically to deliver hydrogen and syngas to smaller scale users.

Ns given a brief summary of current and possible future majorn. There are of course others, such as the manufacture ofr from the previous section is that the operations cover a wide

tion Typical Plant SizesPlant Capacity Reformer Catalyst

Volume (m3)20,000 Bbl/day 2402,700 te/day 85

5021

te/daymmscfd

12

1000 te/day 301000 te/day 109

40 te/day 2250 kW 0.1

25 kW 0.01

tential for a variation in reformer size over some four orders ofrange, it is to be expected that the design concepts and operatingha case, but the selected operating conditions are generally a than simply of scale of operation, Table 4.


Table 4 : Different Applications Require Different Conditions

Reformer Feed Steam toCarbonRatio

ReformerExit

Temperature(�}C)

ReformerPressure

(atm)

Gas-to-liquids / FT Natural gas 0.6 – 2.0 700 – 1200 20 – 30Methanol Natural gas 2.5 – 2.5 840 – 870 15 – 25Refinery hydrogen Natural gas, off-gas, naphtha 2.5 – 5.5 800 – 870 20 – 35Ammonia Natural gas, naphtha 3.0 – 4.5 775 – 825 35– 45Reducing gas Natural gas, off-gas 1.0 – 2.0 850 – 900 3 – 10Synthetic nat. gas Naphtha 1.5 – 2.0 500 – 550 20 – 35Carbon monoxide Natural gas 1.5 – 2.5 800 – 850 15 – 25Mobile fuel cells Methanol, diesel 1.0 – 10.0 700 – 850 1 – 3

7. OUTLINE OF ALTERNATE TECHNOLOGIESFrom the above it is evident that future demands on syngas and hydrogen generation will

straddle the existing scale of operation. Despite this potential for operation scales varying byseveral orders of magnitude, remarkably similar approaches appear valid across the scaleranges. There are thus a number of distinct, almost generic approaches vying with theconventional fired reformer, and all at varying stages of development.

7.1. Autothermal ReformingThe gas or vapour is burned in air (or oxygen) and the resulting gas passed over a nickel

reforming catalyst (Figure 3), and subsequently a shift catalyst if appropriate. This has beenproposed for both Fischer Tropsch and fuel cell systems, and indeed methanol in the past. Ithas the ostensible advantage of simplicity. This is not however strictly true. The process gasexits the reformer still at elevated temperature (> 800OC, 1470 F) and thus significant heatexchange and recovery duty are required. Large-scale adiabatic autothermal reformers havealready been built in the industry, whether as secondary reformers on ammonia plants or aspre-reformers for the processing of heavier feedstocks. The existing leading catalyst andtechnology suppliers in syngas therefore have considerable experience here.

1.1.1. Use of Air or Enriched AirIn a variation within the theme, the use of air, or enriched air, rather than oxygen has been

proposed for both methanol plants4 and for FT5. Operation is at higher total pressure tomaintain reactant partial pressures. The use of air has the ostensible benefit of removing therequirement for an oxygen plant, reducing cost, but with the knock on effect that the synthesisreactor now includes significant volumes of nitrogen inert thus increasing costs. It is not clearthat the overall cost considerations favour the use of air for either methanol of FT.

1.1.2. Coupled ReactionsIn a further development from the concept of autothermal reforming, a number of

workers6,7,8 have suggested direct heat exchange coupling of oxidation and reforming. Thereactions, both catalysed, occur on opposite sides of a rigid, impermeable barrier throughwhich the heat will transfer. It is not clear how operable these systems will be in terms of localand overall dynamics, steady state multiplicity and working lifetime.

1.2. Partial Oxidation (Thermal).Syngas may be generated by simply burning the methane (or vaporized liquid fuel), in the

absence of a catalyst, under oxygen starved conditions. This does lead to carbon formation,but also very low CO2 content of the product and low methane slip. It leads also to a naturallylow H2 : CO ratio. In practice this requires a dedicated hydrogen plant to operated alongsidein order to achieve H2 : CO = 2. For FT applications the hydrogen plant will probably be basedon conventional fired box steam reforming technology


This technology is believed to be used in the Shell GTL plant at Bintulu, Malaysia, plus aconventional fired steam reformer, fed with FT tail gas, to generate a higher H2 content syngasto adjust the overall H2 : CO ratio upwards.

1.2.1. Fluidized Bed Partial OxidationA similar process to that above has been explored, but using a fluidised bed, with both

catalytic and non-catalytic fluidised particles. The non-catalytic process has been observed bysome to generate excessive soot/carbon. The catalytic approach is however more interestingand has been developed further by BP9. Subsequently Shell10 has developed the noncatalytic route. Neither of these developments appears to be commercial, nor are theybelieved to be still under development

1.3. Catalytic Partial Oxidation.It has been shown that by running at very high space velocity and temperature over a

platinum group metal gauze catalyst or supported on a honeycomb monolith, it is possible toobtain partial oxidation of the methane to CO and hydrogen. Thermodynamically, theformation of CO and H2 is favoured at high temperatures. Feed ratios and/or the shift reactioncan be used to obtain the correct H2 : CO ratio for downstream processing or synthesis. Whileconsiderable work has been done in this area, most notably by Schmidt11, this approachhowever has not been explored beyond the laboratory scale.

Extensive work on catalysed partial oxidation, with a structured or packed bed catalyst isreported in the literature12 but there is currently no known drive for commercialization.

1.3.1. Micro-channel ReactorsIn a similar vein to the work of Schmidt, Tonkovitch et al13 describe a PGM catalysed

micron-channel reactor for partial oxidation of methanol, targeted at fuel processing forautomobile fuel cells. The concept is similar in that residence times are very short but thefocus is on minimizing transport distances in order to minimize diffusional limitation basednon-selectivity.

1.4. Fluidized Bed ReformingExxon has developed a dual-functional fluidized bed process14 where the feedgas is

subject to both oxidation and reforming actions. The oxygen is introduced into the middle ofthe methane/steam fluidized bed. The heat released by the oxidation drives the reformingreactions. The fluidized bed ensures good heat transfer. Operating temperatures lower thanthose typical of the partial oxidation are claimed, leading to improved oxygen efficiency andimproved thermal efficiency. This technology has been demonstrated at scale over a threeyear period

1.5. Compact ReformingThis is a two step process (Figure 4). The net heat generation is by a "secondary"

autothermal reformer, but the exit gas is fed back into a primary, heat exchange reformer (orGas Heated Reformer - GHR) where the incoming process gas plus steam is reformed over aconventional nickel catalyst prior to feeding to the secondary, autothermal reformer. The

SecondaryReformer

Gas +Steam

Air / Oxygen

GasHeatedReformer(GHR)

Fig 4 : Simplified Flowsheet for Combined Reforming

Reformate

Air orOxygen

Gas +Steam

Fig 3 : Autothermal Reformer


primary reformer is thus essentially replaced by a heat exchange reactor based on multipletubes. Originally developed by ICI in the late 1980s15, this technology has been successfullyapplied at the manufacturing scale for ammonia, and more recently over an extended periodat the pilot scale for methanol with an oxygen fired secondary reformer16.

1.6. Membrane ReformingThere is significant effort to try and exploit the separative capability of membranes in

conjunction with the reforming reaction. There are however two distinctly differentapproaches.

1.6.1. Membrane Reforming I - Hydrogen Removal.A palladium membrane is used to remove the hydrogen from the reformate (Figure 5a)

and thus remove the equilibrium barrier17. This has only been achieved to any extent at thelaboratory scale. Major problems remain with obtaining a Pd membrane of sufficient integritybut with sufficient flux. This barrier to success will probably lead to this technique remaining alaboratory and theoretical curiosity for many years.

1.6.2. Membrane Reforming II - Oxygen Separation.A mixed oxide (e.g. perovskite) membrane is used to separate oxygen from air (Figure

5b), and in so doing feed oxygen into the flowing gas stream18. The transport mechanism is infact an electrical counter transport and requires temperatures in the order of 700-800OC(1290–1470�F) to achieve practical transport rates; which is of course in the sametemperature range as required for reforming. The oxygen permeate promotes a partialoxidation reaction, essentially at the membrane surface. It has in fact been found necessaryto use a catalyst in situ to promote the oxidation19. In reality a reduction catalyst may also berequired at the "air face" of the membrane. The eluant from this reactor is then passed over areforming catalyst to maximize methane conversion. This technology is currently the subjectof two major consortia funded projects20; one led by Air Products with USA Government (NISTAdvanced Technology Program) support, the other independently financed and led by Praxairand BPAmoco.

1.7. Adsorptive ReformingWork in Russia in the 1970s (although not published in the west until the 80s-90s)

considered the use of a solid adsorbent to remove CO2 from a reforming or shift reactor, as ameans of pushing the reforming and/or shift reactions towards full conversion. In principle thiswill allow a simplified, even single step, process for the generation of high purity hydrogen athigh methane conversion. This original Russian work21,22 used dolomite as the adsorbent witha thermal swing regeneration; and this idea is now being revisited by Harrison et al23. AirProducts (with DOE support) is also revisiting the idea24 but with a novel adsorbent that canoperate at lower temperatures than the dolomite and be regenerated through pressure swing.Little information is available on this project in the public domain although some technicalinformation is given on prior work with the shift reaction25. The two approaches differ also in

G as +Steam

Figure 5 : Membran e Reactors for Syn gas Genereation

5a) Hydro gen Abstraction 5b) Oxygen Addit ion

ReformingCatalyst

Dense PdMembrane Fi lmPorous Membrane Support

Reformate

Hydro genPermeate

G as +Steam

ReformingCatalystOxidation Catalyst

SolidElectrolyte(Perovskite) Membrane

Reformate

Air

Porous Membrane Support

Oxy

gen

Tra

nspo

rt


the process concept. Harrison is evaluating a fluidized / raining bed approach, similar to theoriginal proposal from the Russian work, while Air Products is using adiabatic fixed cyclingbeds (similar to PSA).

1.8. "Dry" Reforming.The principle here is that CO2 is ostensibly able to fulfil a similar role to steam in respect of

both reforming and carbon inhibition. The dry reforming reaction is:� dry reforming CH4 + CO2 ⇔⇔⇔⇔ 2CO + 2H2 ∆H = + 247 kJ/mol (10)This gives a lower H2/CO ratio than the use of steam, and thus a syngas more suited to

FT is available, and is also of interest as an increased efficiency route to the manufacture ofCO. This is not yet practised commercially and there are development uncertainties in thecatalysis. The recycle of CO2, or its specific use in conjunction with steam is however known.

1.9. Which Development for Which Application?We have already seen that the main drivers in syngas and hydrogen technology are

aimed at diametrically opposed applications in terms of scale and efficiency imperatives.Many of the developments are unsurprisingly explicit.� The development projects for the ceramic (oxygen transport) membrane are specifically

targeted at the GTL type scenario. Commercialization is still some years hence, and littleinformation is available in the public domain as to the progress of the research anddevelopment projects.

� The hydrogen abstraction techniques such as adsorption and Pd membrane are clearlytargeted at hydrogen and thus either commercial hydrogen or fuel cell markets. Bothhowever still face significant obstacles prior to commercialization.

� It is hard to envisage a successful fluidized bed process operating at the small scale, dueprimarily to the problems associated with obtaining solids flow in small tubes or ducts andthus is in reality a GTL or commercial hydrogen process.In essence this leaves four process approaches that seem to be generally applicable and

proven at or near commercial scale:� autothermal reforming (ATF)� compact reforming� partial oxidation (POx)� conventional steam reformingThis is indeed the case, with examples of all being cited for GTL as well as fuel cell type

applications. The compact reforming technology is the most complex in process terms andwill be considered in further detail, with specific reference to manufacturing scale experienceand recent developments that significantly affect its cost base.

8. COMPACT REFORMING TECHNOLOGYThe first compact reforming process, a syngas generation technology that combines

autothermal reforming and a heat recovery based primary reformer, was developed by ICI inthe late 1980s. The first commercial examples were commissioned in ammonia productionplants in the late 1980s. These plants have thus now been operating successfully for morethan 10 years, with a further licensed unit successfully commissioned in 1998 in the USA.This "LCA" (Leading concept Ammonia) technology was later modified, in a joint venture withBHP Petroleum, to feature an oxygen (rather than air) fired secondary reformer for the LCM(Leading Concept Methanol) process which was demonstrated at pilot scale over a three yearperiod from 1994. More recently, improvements to the Gas Heated Reformer have also beentrialled and demonstrated on the same pilot plant and flowsheet simulation work completed toshow the applicability of the reforming technology to FT plants.

8.1. Synetix LCM ProcessIn the LCM process26, Figure 6, a gas - steam mixture heated to 400-450�C (750-840�F)

is fed to the catalyst in the tube side of the GHR. About 25% of the steam reforming reactionis carried out here. The partially reformed gas is then fed to a secondary reformer which isoxygen fired for methanol (or FT) plants. Here the reforming reactions are completed, initiallyby combustion and subsequently by further reforming, and the gas temperature is brought toabout 1,000�C (1830�F) at the exit. This hot gas from the secondary reformer is passed


Tubeside Inlet

Tubeside Outlet

Sheath TubeBayonet TubeScabbard Tube

ShellsideInlet

ShellsideOutlet

Figure 7 : Gas Heated Reformer

through the shell side of the GHR where it gives up its heat to the steam reforming reactionoccurring on the tube side.

In order that this combination can be started up a small catalytic combustion unit isincorporated between the two units. This catalytically combusts and reforms a lowtemperature mixture of gas, steam and air in order to provide a hot gas to heat the GHR to itsstart-up temperature.

1.1.1. Gas Heated ReformerThe GHR, Figure 7, comprises a

number of catalyst filled tubes (scabbardtubes), each with an axial bayonet tube.The feedgas enters through the top of thevessel and into the space between the twotube sheets and then into the scabbardtubes, flowing down the annular catalystpacked space between the scabbard andbayonet tubes, before passing back upthough the bayonet to the top of the GHRwhence it passes to the secondaryreformer. The outside of the scabbard isfinned to maximise heat transfer area andis installed inside an outer sheath tube.The secondary reformer gas is thus forcedto flow over the finned tubes at highvelocity by the sheath, thus enhancing theheat transfer coefficient and reducing thenumber of tubes required for a givenproduction rate.

1.1.2. Secondary ReformerEarly in the development of the LCM process the secondary reformer was seen as a

major technical risk. Oxygen fired reformers have a mixed record in the syngas industries27

where incidents associated with burner failure, refractory defects and waste heat boiler foulinghave been noted. A significant amount of design effort and modelling, including CFD, wasexpended in order to obtain a suitable design for the burner and combustion chamber. Thedesign concepts are based also on Synetix experience in the design of numerous air blownsecondaries on ammonia plants. The design uses the neck region, away from the catalyst

Figure 6 : Combined Reforming with the GHR

Steam

SecondaryReformer

Steam + Gas

Air / Oxygen

GHR

Steam + Gas

Air / OxygenStart-up

Igniter

Gas HeatedReformer


bed, as the combustion zone. Here the mixing of the oxygen and the process gas is moreeasily controlled. The Synetix burner design also ensures minimisation of the gastemperature in contact with the vessel refractory lining. The design is easily scaled and,based on CFD and subsequent experience, it is known that near perfect mixing of the twostreams is achieved before entering the catalyst bed, and thus a uniformity of temperatureprofile and conversion is achieved.

1.2. BHP Petroleum Methanol Research PlantBHP Petroleum is a major producer of oil and gas in Australia with reserves elsewhere in

the world. BHPP operates several offshore oilfields and over the last 15 years hassuccessfully developed the technology of oil and gas extraction and processing using FloatingProduction Storage Offloading (FPSO) facilities. These are essentially converted oil tankersor purpose built barges which are moored to the oil and gas collection risers by a flexiblecoupling. Processing facilities are located above deck and the stabilised crude is stored belowdeck. Associated natural gas is currently flared if the fields are too remote for economicutilization. The FPSO is serviced by shuttle tankers which ship the stabilized crude to itseventual customers. The merits of conversion of remote and marginal gas to a liquid producthave been extensively discussed elsewhere28 and a repetition is not merited here. Clearlyhowever there is interest in extending the FPSO type concept to include conversion of themarginal gas to a viable product. The GHR based reforming is an enabling technology tomake offshore generation of syngas a reality. While actual development by Synetix andBHPP has hitherto focused on methanol, the syngas section of the plant will remainsubstantially the same for a FT unit.

In order to verify and develop the LCM process for offshore operation BHPP first built theMethanol Research Plant (MRP) as an onshore plant located in the outskirts of Melbourne,Australia. The 184 mtpd plant was designed and built primarily for research and developmentbut was nonetheless to be operated as an economically viable commercial facility in supplyinginto the Australian methanol market. The MRP represents therefore the firstcommercialization of the Synetix LCM process and its associated oxygen fired compactreforming technology.

The outline flowsheet for the pilot plant is given in Figure 8. There are a number offeatures other than the GHR - Secondary combination that merit mention:� the natural gas is first purified using Synetix fixed bed low temperature (230�C, 450�F)

absorbents to protect the catalysts� most of the steam is raised in a saturator which recovers heat from cooling synthesis gas

and from the methanol loop. The required steam production from a utility boiler is low.

Purifi er

S aturatorGHR Secondary

Converter

Preheater

Purgeto fuel

Toppi ngColumn

Refini ngColumn

Processcondensate

water

Fusel oil

Natural gas

OxygenSteam

Refinedm ethanol

Purge

Crude m ethanol

Figure 8: Outline LCM Pilot Plant Flowsheet


The saturator also strips hydrocarbons from waste streams for recycle, minimizing liquideffluent

� the distillation section has a standard layout, but includes structured packing rather thanconventional trays to compensate for foreseeable motion on an offshore unit.The MRP was successfully commissioned in October 1994 with a BHPP operating team

supported by a team from Synetix. The plant was running at 100% of flowsheet after 2 weeksand towards the end of 1994 a high trial rate of 200 mtpd was achieved without any impact onproduct methanol quality.

The GHR has performed well from start-up, in fact slightly better in terms of catalystactivity and heat transfer performance than design, and with no evidence of metallurgicalattack. Similarly the secondary reformer has performed excellently. Inspection of the burnerat planned shut-downs has indicated no observable wear and deterioration of the hot face ofthe refractory has also been found to be minimal. The high quality of mixing in the headerspace of the secondary is evidenced by the fact that the exit gas is found to be virtually at thesteam methane equilibrium.

1.3. The Advanced Gas Heated ReformerThe MRP has been useful as a test bed for new ideas over the last few years. Some of

these have been identified out of the BHPP work program to develop their Methanol FloatingProduction Storage Offloading (MFPSO) design concept. There have been operationalimprovements and simplifications as well as hardware design changes. The most significantof these is probably the development of the Advanced Gas Heated Reformer (AGHR).

The AGHR retains many of the essential features of the proven GHR, such as the overallflowsheet, fins and sheath for shellside heat transfer enhancement and the mechanical andprocess design methodology, specifically relating to metallurgy and resistance to metaldusting. A number of aspects of the GHR design were noted that would bear improvement.Specifically these were: the complexity of tubesheet design, the time required for catalystchange, the difficulty of tube replacement and the requirement for multiple reformer shells fora world-scale methanol or FT plant

A clear preference in order to improve simplicity of design was be to negate the need forthe bayonet tube design. One design option that would allow this is the so-called "parallelreforming" type approach to compact reforming, which leads naturally to an open ended tubedesign for the primary reformer. Here the exit streams from the heated reformer and theautothermal reformer are mixed to provide the heat required to sustain the heated reformer.This process is however much less efficient than the Synetix "series reforming" arrangementdescribed herein and thus the preference was to retain the essence of the current flowsheet.The avoidance of the bayonet tube design therefore required inherently a tube sheet at the"hot end" of the reformer; but onethat did not impose thermalexpansion stresses on the tubesand/or tube sheet.

The essential design of theAGHR is shown in Figure 9 29. Thekey element that differs from theGHR is the hot end tube sheet. Thisis ostensibly a standard shell andtube exchanger design with fixedtube sheets except that the tubespass through the lower (hot) tubesheet but are not fixed to it. Thisallows each tube to individuallyexpand and contract withoutimposing stresses on the tube ortube sheet. Leakage from the highpressure (tube, reforming) side to thelower pressure shellside, while safe,is not desirable due to the highermethane content of the tubeside gas.Therefore a seal system is provided

Tubeside Inlet

Tubeside Outlet

S heath Tube

CatalystP acked Tube

Shel lside In let

Shel lsideOutlet

Figure 9 : Advanced Gas Heated Reformer

Seal

Tail Pipe


between the tubes and the lower tube sheet. The seal design is unique and the result ofextensive research and development and has a projected lifetime equal to that of the tubes(10 years).

The simplification of the tube designs allows also a simplification of the mechanical designof the upper tube sheets, with the previous interactions imposed by the bayonet tube designbetween the tubesheets being avoided. The benefit here is that the AGHR can be scaled upto a methanol plant size equivalent to 5,000 mtpd in a single reformer shell. Indeed designinvestigation indicates that the limiting factor is fabrication techniques rather than themechanical design limit of the tubesheet. There are further benefits of the AGHR. Theremoval of the bayonet and the resulting tubular rather than annular catalyst bed givessignificant gains in ease of maintenance and catalyst charging and discharging. Tubereplacement is also much simplified. The main benefit however is a significant reduction inthe cost of the AGHR relative to the GHR due primarily to the simplification of fabrication, andto the reduction in materials required; the increased volume of catalyst per tube due to theremoval of the bayonet is also however a significant factor.

In the pilot unit. it was possible to directly replace the GHR with the AGHR in a shut-downin 1998. This was done as part of the ongoing R&D program. The cost savings of the AGHRin fabrication were proven to be as predicted and upon commissioning the operationalefficiency validated the success of the seal design (no methane leakage from tube toshellside). The plant was tripped and restarted a number of times in the first few monthsoperation to ensure that the sliding seal did not bind or seize. The vessel has been openedand the seals inspected. They showed no signs of wear or deterioration.

2. REFORMING FOR FISCHER TROPSCHThe optimal syngas for FT synthesis is at 20 - 30 bara (290-435 psia), with an H2/CO ratio

exit the syngas generation plant section of 2.0 - 2.1. FT is also favoured by low concentrationsof all of CO2, CH4 and N2. Many similarities exist between the synthesis gas requirements ofFT and methanol syntheses. Clearly, all of the oxygen based processes are applicable,namely POx, ATR and GHR processes. Note that conventional steam reforming will generatea H2/CO ratio higher than required for FT stoichiometry and is thus really not ideal on its own.

2.1. Features of Oxygen Based Routes to FT SyngasBased on published studies30,31 and internal work it is possible to build a comparison of

the main features of the three key alternate routes to FT syngas, Table 5. These data showthat the GHR based process gives not only the highest carbon efficiency but also the lowestoxygen requirement and lowest CO2 emission.

Table 5 : Key Features of Oxygen Based Routes to FT Syngas

Process route PartialOxidation

AutothermalReforming

Compact GHRReforming

Steam : carbon ratio 0.2 0.6 – 1.4 0.6 – 2.5Syngas H2 : CO ratio 1.85 - 1.95 2.0 – 2.1 2.0 – 2.1Oxygen : gas ratio 0.64 0.55 – 0.63 0.48 – 0.51Syngas CO2 (%) 2.0 – 2.5 2.0 – 4.0 0 – 0.5Syngas CH4 (%) < 0.1 0.3 – 2.0 0.2 – 2.0Conversion efficiency to CO (%) 94 88 98Notes : 1) POx route is more costly because it needs additional steam reforming to achieve H2 / CO ratio of 2 2) Data based on CO2 recycle. Tail gas recycle is more economic but basic principles still hold

2.2. Gas Heated Reforming for FT SyngasSynetix has been working to develop the AGHR and related technology to a Fischer

Tropsch flowsheet – Leading Concept Liquids or "LCL" 32. An outline flowsheet is shown inFigure 10, where the reforming scheme is essentially the same as that described above formethanol (LCM). The key features are described below:� The natural gas is purified at low temperature using proprietary fixed bed absorbents.� A tail gas recycle is used to give CO2 and H2 presence in the gas at the GHR feed. This

reduces the tendency to carbon laydown and leads to a lower H2 : CO ratio at thereforming section exit as well as increasing the overall efficiency of the process.


Alternately or in addition, an adiabatic pre-reformer may be used to increase CO2 and H2levels at the GHR inlet.

� Energy for the saturator is provided from the syngas cooling.� The combined gas passes to the two step reforming section comprising the AGHR and the

secondary reformer. The layout is similar to the LCM process with the exit gas beingreformed typically to equilibrium at 25-30 bara (360-435 psia) and 1000�C (1830�F).

� The gas leaving the AGHR shell side is cooled successively by pre-heating the reformerfeed, saturator water circuit heating and finally against cooling water.

� The FT synthesis section reacts the CO and H2 to give hydrocarbons and water with someCO2, oxygenate and light gas by-production at around 20 bara (290 psia). Thepossibilities for layout, catalysts, reactors and flowsheet for the FT synthesis section aredescribed elsewhere and detailed discussion is not appropriate here.

� Unconverted "tail gas” is the source for recycle CO2 and H2. The remainder is used asfuel.

2.3. Comparison of GHR with Autothermal ReformingA more detailed comparison between compact reforming approach of the GHR technology

with the ostensibly simple autothermal reforming (ATR) has been made based on detailedprocess simulations. There are of course a number of features in common. Both requireoxygen that is reacted with the process gas, in the presence of steam, prior to passing over acatalyst. The inherent feature of the GHR technology is that the combustion takes place at alower temperature, explained simply by the fact that, for the same exit temperature(equilibrium conversion) less endothermic reforming takes place downstream of thecombustion in the GHR flowsheet than in an autothermal reformer alone. That is, thecombustion heat is more effectively recovered through the convective heat transfer that occursin the GHR. This difference is at the root of the process differences that are summarised inthe Table 6. In summary� The GHR flowsheet produces around 7.5 – 12.5 % more FT liquid product from the same

gas feed rate.

Fig.10 : LCL Process : Fischer Tropsch Flowsheet with AGHR Reforming (with tailgas recycle)

Purif ica tion

GHR &

SecondaryNATURALGAS

OXYGEN

WATERFTPRO DUCT

Proc ess s tea m

FT Stea m,

Sa tura tor

GHRInt erchange r

FT LOO P

Membran e

H2 to fuel

H2 to H/C

Ta ilgasRe cy cleCompressor

Tai lgasPurgeto fuel


� The GHR flowsheet requires only 77 – 84 % of the air separation duty of ATR ATRrequires more power in the process, but as a penalty also generates more steam andtherefore has a tendency to export more power

� The emission of CO2 from an AGHR plant is 54 – 63 % lower than for the ATR.

Table 6 : Comparison of O2 Fired GHR and Autothermal Reforming FT Processes

AGHR DifferenceUnits High S/C Low S/C ATR AGHR at

High S/CAGHR atLow S/C

Feed rate MMSCFDk(Nm3)/hr

169189

160179

183205

-7.5 % -12.5 %

Product rate Bbl/day 20,000 20,000 20,000 – –Steam/carbon – 2.0 0.6 0.6 x 2.3 –CO2 emission mtpd 1,306 764 2,052 -33 % -63 %Oxygen rate mtpd 3,387 3,111 4,015 -16 % - 23 %C efficiency % 84 89 78 + 8 % + 14 %Power export* MW 21 26 57 - 63 % - 54 %* Assumes that fuel gas is combusted to produce superheated steam which is used to generate power

All of these factors affect the unit capital cost. While the GHR + Secondary is moreexpensive than a single (but larger) autothermal reformer for the same FT product duty, theabove analysis indicates that other sections of the plant are considerably smaller. Overall theLCL process has a lower capital cost than the ATR based process in addition to the ongoingoperational benefits from the AGHR based flowsheet.

2.3.1. Effect of CO2 EmissionsOne operational advantage of the GHR lies in a higher carbon efficiency and lower CO2

emission. While this may not appear important in the overall context of gas at a marginalvalue this will probably not remain so. Resulting from the various international protocolagreements, taxes on CO2 emissions may become reality. For example, Norway has alreadysuggested a CO2 emission levy for offshore operations equivalent to $48/te. The GHRapproach allows a 54 – 63 % reduction in CO2 (depending on the steam : carbon ratio andquantity of oxygen used). This translates, for a 20,000 bpd FT plant, into a potential annualsaving of $ 19 – 23 million; or $2.7 – 3.2 per barrel.

2.4. GHR Development for FT SyngasThe key to improving the economics of gas heated reforming based syngas generation for

GTL lies primarily in reducing the operating steam - carbon ratio (S/C). The main calculationsin this paper are based on an S/C of 2.0 and 0.6. The former is within the known operatingwindow for the existing metallurgy and catalyst and is thus proven.

This can be reduced to 1.5, offering significant benefits, as can be inferred from the dataabove. The existing metallurgy is believed to be satisfactory, although this does need runningon a plant to be demonstrated. A steam ratio of 0.6 would give further significant benefits incost. This is an achievable target for the catalyst (activity at lower temperatures) and thus theprocess is feasible at this reduced steam-carbon ratio. The main development requirementhere is however on the shellside, but it is believed the process could be operated at a steam-carbon ratio of 0.6 at the conclusion of a metallurgy development program.

As an alternate approach to syngas generation using the GHR, the concept of a flue gasheated reformer has been developed33. This is intended to give options for replacing theoxygen fired secondary, and thus because air is used in the burner for the fluegas, avoids thecost of the oxygen plant without incurring the penalty of high nitrogen concentrations in thesynthesis loop.

3. REFORMING FOR FUEL CELL HYDROGENThere is considerable effort, both actual and reported in this area. A significant input is

being made by companies and academics not previously active in the syngas or reformingarea. Unsurprisingly however, the solutions being proposed generally comprise a mix of POx,


ATR and compact reforming, with of course shift and CO removal steps downstream to give ahydrogen rich stream that can be fed to the PEM fuel cell. In truth, the catalysts being used forthe trial units are for the main part supplied by the existing leading catalyst suppliers into thesyngas industry. A number of examples of published developments are briefly reviewedbelow.� International Fuel Cells has been marketing a stationary 250 kW phosphoric acid fuel cell

unit, with built in fuel processor for a number of years, with over 100 units installed world-wide. While an early patent34 proposes a swing process, reminiscent of Haber Bosch,with two fixed beds alternately oxidizing and reforming, their installations are based on atubular reformer heated from the shell side by a hot gas35 which includes spirally finnedtubes and a sheath to promote the heat transfer. IFC has also produced a smallerprototype for automobiles.

� Ballard Power, in work related to stationary fuel cells of 100 - 250 kW, also conclude that asteam reforming system is preferable, and in common with IFC describe a tubular heatedreformer36, what in effect appears to be a single or several tube with firing and counterflowof the resulting flue gas. The heating gas is a mixture of the exhaust anode and cathodegases.� The above can be considered as either fired reformers or, where the conbustion is

carried out externally, as gas heated reformers, where the hot gas is fluegas ratherthan process gas, and are similar in reactor concept to the proposal of Synetix33 forsyngas generation.

� AD Little, in a project funded by the DOE and PNGV (Partnership for New GenerationVehicles) developed a POx based system for automobile application. The preference forPOx over ATR or a heated reformer appears to be based simply on maintenanceconsiderations37, despite recognising the efficiency advantages of a reforming process.As an aside, AD Little has spun off a new business, Epyx, to market the resultingtechnology

� Johnson Matthey favours the autothermal reformer approach, specifically in theconfiguration of their Hotspot reactor or reformer38. Toyota also favours the steamreforming route39.

� Argonne National Labs, in DOE - PNGV sponsored work on fuel processors forautomobiles, favours a combination of oxidation and reforming (viz. small autothermalreformer) for reasons of cost and efficiency, and has configured the system specifically toobtain rapid start40.From the above, incomplete summary, it can be seen that a wide variety of applications is

proposed. It is clear that the drivers for automobile and stationary applications are not thesame, other than capital cost minimization. The stationary systems favour reforming. In thecontext of fuel cells there is a need to move the balance of oxidation vs. reforming towardsreforming in order to obtain maximum hydrogen yield and hence also fuel efficiency. Howeverfor automobiles simplicity, robustness and size are the dominating drivers. With thisexception, the general thrusts are similar to those for GTL despite the difference in scale,noting however that while for GTL the question is how far a technology will scale up, for fuelcells, and especially automobile applications, the problems are scaling down (orminiaturization).

4. CONCLUSIONSWhile syngas and hydrogen markets and technology are often considered mature, this is

not entirey true. There are significant changes occurring in the markets for syngas andhydrogen, many of these actually driven by changing energy needs and environmental drivers.Most significant amongst these are:� the potential growth in the need to monetize stranded and process marginal gas through

gas-to-liquids (viz. Fischer Tropsch or methanol-to-gasoline) technology,� the changing specification of gasoline and diesel with not only increasing hydrogen

processing requirement but also the apparent phasing out of MTBE (with the knock onimpact into methanol markets)

� the potential growth of fuel cell powered vehicles and the need for hydrogen rich fuels(methanol or gasoline) to be processed on-board to generate hydrogen. Clearly if


methanol is to be the fuel of choice then this will impact in a major style on the methanolindustry

� the potential growth of fuel cell distributed electricity generation with the associated needto process locally the gas (or liquid fuel) to generate hydrogen.

� The development of cost effective small scale hydrogen generation technology from thefuel cell applications may lead to growth in distributed manufacture of hydrogen andsyngas for chemicals applications beyond ammonia and methanol.As a direct result of the perceived future changes and challenges in syngas and hydrogen

markets, there is significant effort world-wide aimed at developing technology for syngasgeneration, with the primary alternative goals of gas-to-liquids and fuel cell hydrogen. Theleading technologies are based on steam reforming and/or partial oxidation, with partialoxidation, autothermal reforming and compact (two step) reforming being the leadingcontenders for all applications.

The development and performance of the Synetix two step, compact reforming processbased on a primary gas heated reformer and a secondary autothermal reformer has beenconsidered in details. With regards to this "GHR" based technology the following have beenestablished.� The GHR is a proven reforming technology, with over 10 years operating experience at

commercial scale.� The gas heated reformer provides a compact reformer design, with excellent heat transfer

design, suited to small and very large scale reforming applications.� The GHR produces the optimal gas composition for Methanol and Fischer Tropsch� In GTL duties, the GHR based process has a lower oxygen requirement than POx or

autothermal reforming.� The GHR process also leads to lower CO2 emissions and a lower power export

� The GHR process has a small footprint, low weight and has a competitive capital cost� Continuing development of the GHR is aimed at achieving further reductions in operating

and capital costs:� development work will focus on operability at lower steam to carbon ratios.� this requires development of metallurgy and catalysts plus continued flowsheet

optimisation.

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Catalysis Today, 36 (3), 265-272 (1997)19 Sammells AF: Catalytic Membrane Reactor Improvements for Syngas and Gas to Liquids:

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emerging trends in hydrogen

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