Large, single train hydrogen plants, with a capacity inthe range of 60 - 200 mmscfd are becoming increas-ingly prevalent. The economies of scale from supply-

ing multiple customers, synergies with energy integrationand proven reliability have all boosted their popularity.

However, the characteristics of large capacity hydrogenplants present greater challenges than medium sized (< 60 mmscfd) plants and demand a different approach intheir design and operation. Such challenges require strongeremphasis on design boundaries, reliability valuation, utilitiesintegration and effective execution strategies, as well as astronger commitment to efficiency, environmental compli-ance and overall economics. Moreover, these large facilitiesgenerally demand tighter execution schedules and rapidcommissioning, while facing the familiar project budget pres-sures and site specific (such as cold climate) constraints.

For Technip and Air Products there are four major chal-lenges that must be addressed in providing large hydrogenplants to the refining and oil sands upgrading industries:

� Leveraging lessons learned from previous large scaleprojects into streamlined project schedules and opti-mised startup/commissioning schedules.

� Optimising the hydrogen/steam/power balances withinthe context of a refinery’s future utility infrastructure,including refinery fuel gas utilisation.

� Implementing design reliability at the lowest justifiedcost, while enlarging scale up envelop.

� Implementing product development and modularisationtechniques learned from small/medium capacity hydro-gen projects.

Drivers for large hydrogenThe growing demand for transportation fuels, increasingpressure for cleaner fuels and higher crude oil prices aresupporting a significant number of refining investments for:processing more sour and heavier crudes; deeper conver-sion capacity such as hydrocracking and residue upgrading;

and oil sands upgrader projects to produce syntheticcrude. Furthermore, in emerging refining markets such asChina and India, as well as the export oriented economiesof the Middle East, several large scale expansions andgrassroots refining complexes are planned. All of thesetrends require large quantities of ‘on purpose’ hydrogengeneration, with inherent prospects for ‘site wide’ energyintegration.

One of the major challenges for refiners today is toassess their current and near term hydrogen demand andsatisfy such demand in a reliable and economical manner.Major refiners worldwide have increasingly outsourced theirrefinery hydrogen needs to third party suppliers throughpipelines or over the fence plants. This enables largehydrogen facilities to serve multiple customers in the same vicinity.

To satisfy refiners’ hydrogen needs reliably and costeffectively, Air Products and Technip formed an alliance in1992 for over the fence hydrogen supply. Under thisalliance, more than 1.3 billion scfd of hydrogen productionhave been installed or placed under contract. Air Productsis scheduled to start up four new large hydrogen plants in2005 and 2006 supplied by Technip (70 - 110 mmscfd),while Technip plans to commission three large hydrogenplants in the next two years, including the largest singletrain plant (200 mmscfd) for Canadian oil sands upgrading.The underlying objective of these projects is to lower theunit cost of hydrogen while meeting the specific needs ofeach facility in terms of synergistic steam power integrationand/or feedstock flexibility.

Economies of scaleOn purpose hydrogen generation plants are capital inten-sive due to high temperature catalytic processing and cus-tomary gas phase purification. The total investment canalso vary considerably depending upon site specific factorssuch as location, feedstock, export steam conditions,

Reprinted from HYDROCARBON ENGINEERING JULY 2005

The largehydrogen

plantchallenge

Sanjiv Ratan, Technip, USA, and William Baadeand David Wolfson, Air Products and

Chemicals Inc, USA, discuss the challengesposed by large hydrogen plants.

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degree of utility integration and reliability needs. For larger hydrogen plants (above 60 mmscfd), the vari-

able costs linked to specific energy consumption costs (feedplus fuel minus export steam per 1000 scf H2) are the majorcomponents of the unit cost of hydrogen. With current highnatural gas or naphtha prices, the energy cost portionbecomes even more significant. The challenge lies in properassessment of the specific refinery’s future hydrogendemand and utility infrastructure to achieve both integratedoptimisation of hydrogen, steam and power on a site widebasis and high utilisation from the first year of operation.

Table 1 provides an overview of the sensitivity of vari-able and fixed costs to plant capacity. Accordingly, empha-sis should be placed on energy efficiency for large plants toimprove the unit cost of hydrogen. A 1% reduction in theenergy costs of a hydrogen plant of 100 mmscfd can resultin approximately US$ 600 000 savings per year based onUS$ 4/million Btu. Thus, for larger hydrogen plants, there isa bigger incentive for incremental investment in extendedheat recovery in addition to that of optimising the flowsheetand operating conditions, which typically has a paybackperiod of two - four years.

Although the capital investment costs are not of primaryimportance for larger plants, their reduction is vital in loweringthe unit cost of hydrogen. Based on economies of scale, thecost of hydrogen produced by a single train large capacityhydrogen plant can be appreciably lowered by the capitalexponent contribution. Figure 1 illustrates the economy of scalereduction in the unit cost of hydrogen from a 50 mmscfd to a110 mmscfd hydrogen plant based on US gulf coast eco-nomics and natural gas pricing of US$ 4/million Btu.

Although economies of scale favour larger plants, thereis a size limit above which a single train plant startsbecoming cumbersome and requires detailed evaluation toestablish the break point for two or more trains. Physicalsize, weight and transportable limits on the equipment,valves and piping as well construction facilities must betaken into consideration. Such limits have progressivelyincreased from 100 mmscfd up to a recent project size of200 mmscfd, due to advances in compacting equipment,equipment design, piping modeLling and modular con-struction concepts.

Facility replacementAs noted, focusing on energy efficiency can yield significantsaving to hydrogen unit costs. The reduction in energy con-sumption of hydrogen plants from the 1960s and 70s canbe more than 10 - 15% (or up to 70 Btu/scf) when compared to modern PSA purification based plants.Accordingly, for an 80 mmscf hydrogen plant, it can provideUS$ 6 million/y of energy cost savings based on US$ 4/million Btu.

For a refinery expansion, there is usually a simultane-ous need for additional hydrogen, steam and electricalpower and this provides an opportunity to reassess theirbalances within the refinery to improve its overall coststructure. In addition, refiners are required to significantlyimprove the environmental emissions performance of sucholder plants and/or create emissions allowances for thenew hydroprocessing project in an overlapping timeframeto comply with clean fuels legislation. As a result of theseevaluations, many refiners have opted for over the fencehydrogen supply instead of refurbishing and/or expandingthem based on the overall shutdown economics.

Design considerationsFor large hydrogen plants, especially above 80 mmscfd,the design basis and margins must be carefully applied toensure both reliable long term performance and cost effec-tiveness. Some investments are easier to justify for largeplants but the equipment scale up for a single train config-uration must be properly devised not only in terms of mate-rial cost, but also taking into account fabrication, provensupply, transportation and site erection. There is an inher-ent need for compacting equipment and piping items and,in doing so, design considerations will include:� Average and critical heat flux in the reformer firebox as

well as the process gas boiler.

� Catalyst space velocities and L/D ratios for reactor sizing.

� Continuous run cycle and the need for ant online catalyst replacement.

� Flow distribution in reactors for lowest turndown.

Reprinted from HYDROCARBON ENGINEERING JULY 2005

Table 1. Hydrogen plant economicsLarge Medium Small(> 60 mmscfd) (20 - 60 mmscfd) (<20 mmscfd)

Variable costs (%) 60 - 80 50 - 70 30 - 50Fixed costs (%) 20 - 40 30 - 50 50 - 70

Figure 2. CFD modelling of large reformer radiant section.

Figure 1. Economies of scale on hydrogen costs.

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� Momentum flux limits and hydraulicpressure drop optimisation for pipe siz-ing.

� Optimisation of heat exchanger surfaceagainst pressure drop.

� Optimisation of PSA H2 recovery (andthe related number of PSA adsorbers).

� Establishing PSA purge back pressurebased upon the criticality of H2 recoveryversus size and the cost of the purge gasfuel circuit.

� ID/FD fan rating and value engineeringof variable speed coupling or variablefrequency drive versus turbine drive.

It is very important when designing verylarge reformers to avoid excessive maldistri-bution of flow and resulting temperatures inthe radiant box. This becomes the limitingfactor when scaling up the reformer.Although single box large reformers are bestserved by multi lane top fired configuration,adding excessive design margins to coverfor the temperature maldistribution both adds to the invest-ment cost and restricts the metallurgical and mechanicallimits, which otherwise can be favourably exploited.

Using CFD modelling and the experience of buildingvery large reformers, improvements on the burner layoutand design of air and fuel manifolds as well as flue gas tun-nel design are applied for achieving uniform heat releaseand its distribution in the large reformer radiant fire box(Figure 2). Such modelling becomes even more importantfor very large radiant boxes since they tend to be deeperand often have higher combustion air preheat levels. Thisnot only increases their volume but also requires extraattention to thermal expansion. The model is also utilised tostudy the flow patterns and heat distribution at low turndown operation, which in some instances can prove to becritical.

For larger scale up of a steam reformer inherently oper-ating at near creep conditions, proper compensation forthermal expansion and related stresses becomes increasingly critical due to increased material growth formaintaining system elasticity. An increasing number of tuberows calls for greater flexibility, especially in relation to theoutlet conditions. This is usually accomplished by employ-ing a long pigtail outlet system design. Technip executesthe total ‘hot system’ of the reformer comprising the feedheader, inlet system, catalyst tubes and the outlet systemas ‘one free floating system’ designed to accommodatesustained worst case thermal stresses. It ensures propermechanical integrity and reliable operating life of the criticalparts under normal operating conditions as well asexpected thermal cycling during several shutdowns andrestarts.

Meanwhile, when designing a large top fired reformer,special attention to the temperature contours in the pent-house is important. Maintaining acceptable working temper-atures for operation or maintenance personnel as well asinstrumentation components is of key importance. Specialsystems have been developed and implemented for achiev-ing penthouse climate control in large reformers, especiallyin tropical locations.

Cogeneration integrationSteam and power can be integrated with a refiner’s hydro-gen needs and integrated with a pipeline system if they arelocated near other refineries or chemical facilities. Further

optimisation of a refinery hydrogen system can be achievedthrough purge streams containing significant concentrationsof hydrogen currently sent to the refinery fuel system.Integrating these streams into the design of a new, largeenergy efficient steam reformer integrated with a gas turbinecan provide opportunities to unlock the value of refinery fuelgas into a new hydrogen and utility supply system. Thevalue is illustrated in Table 2 in the form of an efficient heatrate (Btu/kWh) and competitive capital factor (US$/KW).

Figure 3, meanwhile, illustrates the block flow diagramfor the SMR/Integrated Cogen unit design for high avail-ability of steam and hydrogen. The challenge for AirProducts and Technip was to design the SMR and cogenequipment to be operated independently. The concept wassuccessfully implemented into the ongoing operations forthe past four years at the Port Arthur facility.

To date, Air Products and Technip have installed largeSMRs integrated with cogen units at six refineries in theUSA and Europe. In April, Air Products announced its latestlarge SMR project (100 mmscfd) for supplying hydrogen,steam and power to Premcor’s refinery in Port Arthur,Texas, and Technip will be commissioning a 200 mmscfdSMR integrated with a 75 MW cogen unit for Syncrudeupgrader complex in Canada.

Reliability challenges As designs have advanced and needs changed over thepast years, refiners have come to expect a 99+% onstreamperformance. Refiners are under significant pressure tomaintain high utilisation rates to meet the increasingdemand for product. A lapse in hydrogen supply can havea significant impact on both the refinery’s operations and itsconsumers, such as hydrocrackers, gas oil hydrotreatersand diesel hydrotreaters, and thus on overall profitability.

For instance, a hydrogen plant outage of two hours canresult in a 48+ hour hydrocracker outage, leading to a mar-gin loss in the range of US$ 400 000 - 1 million (based onrefining margins of US$ 10 - 20/bbl). The challenge with

Reprinted from HYDROCARBON ENGINEERING JULY 2005

Table 2. SMR/cogen Integration economicsCost component

Heat rate 5300 Btu/kWhCapital 700 US$/kW

Unit power costat US$ 2.50/million Btu 0.03 US$/kWhat US$ 4.25/million Btu 0.04 US$/kWh

Figure 3. Block flow diagram for SMR / Integrated cogen unit.

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large plants is to constantly evaluate core designs and plantoperations to maintain the highest level of reliability at thelowest justified cost. The focal areas for maximisingonstream availability (time between unplanned outages) andcontinuous operation cycle for large hydrogen plants include:� Reformer design based on computational fluid dynam-

ics (CFD) modelling to maintain proper heat distributionand hydraulics for process performance, long term lifeand reliability.

� Reliable large process gas boiler design selection.

� Catalyst stage of run profiling and online catalystchange over provisions as needed.

� Design criteria and specifications as well as designmargins, prudent material selection and cost effectivesparing philosophy.

� Advanced process control, monitoring and shutdownlogic with fall back modes to minimise avoidable shut-downs (e.g. two out of three voting on critical controlsystems and diagnostic sequences).

� Startup and transient diagnostic sequences to minimiseprocess excursions and trip conditions during processupsets, as well as to enable smooth and rapid restarts.

� Extensive cumulative operational experience andshared expertise from multiple hydrogen facilities.

Construction challengesThe construction of a hydrogen plant requires considerable levelof skilled labour. However, often its availability may be limited.Thus modularisation concepts, which were traditionally appliedto small and medium sized plants, are now used for largerhydrogen plants, not only to shorten execution schedules butalso to enhance construction quality and curtail execution costs.

Efficient construction planning involves multidisciplinaryreviews to establish the detailed prefabrication and modu-larisation strategy while taking into account the equipmentlayout, expansion loops and accessibility. The underlyingobjective is not to maximise the shop fabrication, but to findthe optimum between shop and field work, considering sitelocation; local labour availability; overall project scheduling;engineering and shop man hours; shipping and transportlimits; the costs of the entire routing; rigging facilities; andlocal costs. The challenge is to manage the overall com-plexity of the project using a risk assessment approach todeliver net cost savings upon completion of the project.

Design techniques have been developed to aid in theprogressive evaluation and selection of modularisation andpre-assembly concepts to enable optimisation of shop andfield erection activities, taking into account the site specificsand overall project activity in the area.

Modularisation of a large hydrogen plant mainly con-

centrates on two areas, the reformer and the heat recoverysections, and can result in several different modules,dependent on the project specific factors. The radiant boxpanels with ceramic fibre modules pre-installed can beapplied to minimise lifting and bolting requirements at site.The platforms and ladders can also be sectional prefabri-cated. The penthouse prefabrication can be optimised withthe trusses and walls as pre-assemblies and can includeinlet system components as well as burner piping and man-ifolds in varying proportions (Figure 4). Such modularisa-tion can account for a fairly large portion of the structuralsteel and related field construction.

The convection coils can be pre-assembled into com-pact, dense modules complete with refractory lining andshop hydrotesting, whereas the crossover piping can bespooled in the shop to reduce total field welds. The inletmanifold and outlet system can be harped into shippableassemblies. The refractory lined transfer line can also beshop fabricated with its refractory lining, and supplied aftertesting and painting.

Degree of modularisation of process and heat recoverysections can be established depending upon the size andlayout requirements of the heat exchangers and related ves-sels and the maximum transportable envelop for the modulesfrom ex works to the site. Exchangers, pumps, piping andinstruments can be installed on steel support structures afterfully hydrotested, cleaned and being made ready for commis-sioning at site. Supervision and logistical support during shopfabrication as well as the precommissioning phase is veryimportant to accomplish efficient and quality construction.

For construction in the cold climate zones, the modular-isation strategy must be specifically established, taking intoaccount special logistics, civil works, transportation timewindow and overall construction management. SeveralCanadian locations allow transportation and related han-dling of megamodules, which can prove to be quite effec-tive and proficient for such cold site construction. In recentyears, several large plants have been designed and sup-plied using the modular approach demonstrating improve-ments in logistical safety performance, plant quality, costeffectiveness and project schedule.

ConclusionTechnip and Air Products have sufficiently overcome the chal-lenges of implementing advanced concepts for the successfuldesign, scale up, streamlined execution and reliable operationof large hydrogen plants. Specifically, they have met the largeplant challenges through: leveraging lessons learned from pre-vious large scale projects into streamlined project schedulesand optimised startup/commissioning schedules; optimisingthe hydrogen/steam/power balances within the context of arefinery’s future utility infrastructure, including refinery fuel gasutilisation; implementing design reliability at the lowest justifiedcost; and implementing product development and modularisa-tion techniques learned from small/medium capacity hydrogenprojects.

References1. BAADE, W., JORDAN, R., PATEL, N. and SEKHRI, S., Integrated

Hydrogen Supply - Extend your Refinery’s Enterprise, NPRA AnnualMeeting, New Orleans, Louisiana, AM-01-19.

2. Air Products and Chemicals Inc., Press Release for Hydrogen PlantIntegrated with Cogen facility for Premcor Pt Arthur II, 21st April 2005.

3. HEFELE, D. and DE GEEST, P., NPRA Clean Fuels ChallengeConference, Hydrogen Plant Reliability Presentation CFC 01-210,Houston, Texas, 28th - 29th August 2001.

4. SALYZYN, B., PE. Considerations in the decision to build a singletrain 200 mmscfd H2 plant. Technip/UOP/Synetix Tenth H2 seminar,

San Francisco, June

2002._____________________________________�

Reprinted from HYDROCARBON ENGINEERING JULY 2005

Figure 4. Large reformer modularised penthouse.

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