Syngas synergies
But there is another side to the natural gas story, one which has its roots in the 1920s. By reacting natural gas with steam or oxygen, the methane that constitutes natural gas can be ‘reformed’ to produce a mixture of carbon monoxide and hydrogen, known as syngas. Around 80 years ago, two German professors, Fischer and Tropsch, discovered that syngas can be converted into hydrocarbons in the form of waxy paraffins, which in turn can be upgraded with hydrogen to produce clean liquid fuels, such as diesel and kerosene (see diagram below). The basic technology for ‘gas to liquids’ (GTL) was thus established and has been the focus of much enhancement ever since, leading to a large commercial scale GTL plant being scheduled to come into operation this year in Qatar, with others planned or proposed.
Converting natural gas into useful ultra-clean liquid fuels is an attractive prospect, particularly where the gas resource is effectively ‘stranded’ in a remote location, making the conventional routes to market – by long distance pipelines or conversion to liquefied natural gas (LNG) for shipment by sea – uneconomic. Of the estimated 6000 trillion cubic feet of gas reserves in the world, about one third is considered to be stranded.
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‘Our approach is based on the view that syngas, the intermediate stage between gas and fuels, is a very flexible product,’ says David Robertson, vice president leading BP’s GTP programme. ‘While GTL technology is central to our strategy, there are technologies which could be developed to take syngas in other directions, for example by conversion to methanol for manufacturing a range of chemicals and fuels, to hydrogen, to industrial alcohols, to synthetic liquefied petroleum gas (LPG), or to naphtha and thence to olefins or other petrochemicals. When you consider that syngas can also be produced from other feedstocks, notably through the gasification of coal or from biomass – and BP is looking at these too – the flexibility of syngas becomes even more apparent and the GTP opportunities expand.’
Among the main targets for application of GTP technology are the large gas resources held by national oil companies.
‘Our customers, the host governments, are interested, we believe, in GTP as this would bring more investment into their countries, helping to create a downstream industry while introducing new skills and boosting employment,’ adds Robertson. ‘And this interest is no longer confined to their stranded gas reserves, but also to more accessible gas resources, thereby making GTP complementary to pipelines and LNG as part of an integrated offer.’
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Enthusiastic as he and BP’s GTP team are for GTP’s business potential, Robertson is also cautious. ‘This is a great opportunity but we are under no illusions about the technical risks involved. The conversion technologies are difficult, the economics are challenging – GTP facilities are technically more complex than LNG plants and equally capital intensive – and the remote locations of GTP plants will add further logistics challenges. But we have embarked on accelerating an existing GTP programme, adding more focus to it, and are committed to building up skills and capabilities in the development of GTP technology, licensing, projects, operations and overall business. The GTP value chain is a long one and even large companies like BP can’t go it alone. Working with partners is a key aspect to success.’
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‘The goal is to develop a suite of processes for GTP, rather than GTL alone, which will differentiate BP from its competitors. But the technologies for doing this will not happen overnight.
‘Toward this goal we are pursuing several technology avenues in parallel, focusing on the Fischer-Tropsch (FT) process in different configurations, optimisation of catalysts which are being tested at both laboratory and pilot plant scale, and sophisticated computer modelling for heat management in the process reactors. Looking further ahead, there are also other advanced chemical reaction options being worked on within BP’s university partnerships – the findings are confidential at present – which are showing great promise.’
Currently the priority area is the FT process. Griffiths points out that while BP has proprietary designs for the reforming and hydrotreatment stages in the GTL process, these stages are also commercially available in the market and hence do not lie on the critical path towards building a full scale GTL plant, an important step in BP’s longer term plans. And it is the conversion of syngas by the FT process that unlocks the route to clean fuels and chemicals.
BP’s involvement with FT development goes back 20 years, leading to its flagship demonstration John P Collins GTL plant located in Nikiski, Alaska (Frontiers, December 2002). Since it came on stream in 2002, the 300 barrels per day plant – incorporating compact reformer, fixed bed FT reactor and hydrotreater, designed by BP and strategic partner Davy Process Technology – has been running according to a technology development plan and has operated through several Alaskan winters.
The Nikiski programme has required an investment of over $500 million to date and is scheduled to continue operation in support of BP’s GTP aspirations, beginning with a full-scale GTL plant. Font Freide makes the observation that as BP has shown itself to be capable of successfully constructing and running a GTL plant in remote Alaska, with temperatures down to -20˚C in a region subject to earthquakes and volcanic eruptions, the company can do it anywhere. But he also notes it has not been all plain sailing and problems have been encountered and ironed out along the way – which is precisely what the demonstration plant was meant for.
Equipped with such valuable experience, the team’s intent now is to unlock the potential of the FT process still more. To this end, a new ‘next generation’ fixed bed FT pilot plant is planned to be built at BP’s Hull Research and Technology Centre (HRTC) in the UK. The plant will test catalyst formulations and optimise process steps to develop a more advanced fixed bed process. The new pilot is scheduled to come into operation next year.
Sophisticated slurry
HRTC, located in BP’s acetyls chemicals facility at Saltend, provides a specialised and unique setup for BP, the facility having a large supply of clean syngas on tap and also having extensive experience of operating pilot plants – some 15 years ago, BP’s FT fixed bed was put through its paces here at pilot scale to provide the design basis for Nikiski. But for the last three years, a different type of FT process has been under trial at HRTC in the form of an advanced slurry process, conceived by BP and now being evaluated under the BP-Davy Process Technology partnership.At the heart of the process is an FT slurry reactor, quite different from the fixed bed process. In the FT fixed bed, the catalyst which promotes conversion of syngas to paraffins is packed inside tubes with the gas passing through them; the reaction is highly exothermic and the reactor must be designed to remove heat quickly. In the slurry reactor, the catalyst is dispersed in the liquid paraffin wax product within a large vessel with bubbles of syngas passing through it, creating a three-phase slurry (see diagram on page 23). The slurry of catalyst particles and paraffin wax product is constantly removed from the vessel by pumping around a loop, where excess heat is removed in an external heat exchanger, the catalyst and product are separated, and the catalyst returned to the reactor.
‘A key factor is the ability to manage the heat generated by the syngas conversion reaction,’ says Chris Sharp, project leader for the FT slurry development. ‘Our catalyst is capable of very high syngas conversion rates and in a slurry bed we can take better advantage of this as we are able to remove heat quickly – the heat transfer is much higher for a well mixed slurry than for a packed bed of solids. The end result is significantly higher catalyst productivity than that of the fixed bed.’
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‘Among the critical factors are the sizes of the catalyst particles and the syngas bubbles,’ adds Sharp. ‘To ensure we achieve high conversion and a slurry that flows, the catalyst particles must be small compared to the fixed bed catalyst, which is on the millimetre scale. The small size presents a challenge in the filtration stage to separate such small particles from the liquid paraffin wax without blinding the filter. We have developed a very effective filter to do this.’
Much has been learned from the pilot trials and the cobalt-based catalyst has now been optimised to give the best combination of conversion productivity, selectivity – getting the right products – and life span.
BP is confident it can run a stable slurry process over the long term giving high productivity, with many potential benefits compared to an FT fixed bed, including reduction in catalyst volume, higher liquids production, a smaller plant footprint and consequently lower capital costs, although Sharp also points to the fact that the fixed bed has the advantages of no moving parts nor catalyst separation stage. The company has initiated a design study for a full-scale demonstration plant to enhance understanding of the technology scale-up and to confirm cost and logistics advantages, a necessary step in the GTL game as shown by the success of Nikiski.
‘The microreactors allow us to rapidly test catalyst formulations in-house and for long run times,’ says Barry Nay, a specialist in catalyst discovery and development and another veteran of BP’s GTL research programme who, along with Font Freide, came up with the original concept for the advanced slurry reactor.
‘We can simulate real FT process conditions for both fixed bed and slurry reactors working with actual real-size catalyst pellets to provide us with valuable information on catalyst activation, operation and deactivation. Microreactors are very effective in screening new catalysts at much lower cost than using a pilot plant, and certainly with much lower risk than trying out catalysts on the Nikiski scale – the microreactors are around 0.25m-tall compared with the 20m-high fixed bed at Nikiski.’
The design of the reactors is the result of long experience accumulated within BP – a set of four ‘Mark 1’ microreactors was built in 2001 which were operated by Davy Process Technology as part of the build-up for Nikiski. The new microreactors in Sunbury are fully automated, enabling the hardware to be operated in multiple ways, for example by controlling temperature profiles or automatically adjusting process conditions to achieve a preset syngas conversion target. Members of the GTP team can ‘dial in’ remotely to monitor the state of play in a catalyst trial from their laptop computers. The reactors are modularised and fully mobile so that they could be quickly transported to other locations if required.
Academic acceleration
Two more microreactors are being built now to support research being carried out at Dalian Institute of Chemical Physics (DICP) in China – BP’s co-operation with DICP and also Tsinghua University under the BP-funded ‘Clean Energy: Facing the Future’ programme is now in its fourth year, investigating various fundamental aspects of gas conversion (Frontiers, April 2003).DICP has over 20 years’ experience in technology development, much of it useful for GTP, with particular expertise in scaling up laboratory experiments to pilot plants. BP’s GTP team is working in partnership with DICP scientists in a joint development project based on a catalyst breakthrough in syngas conversion. This exciting project is still in the early stages but may move to pilot plant scale in the near future.
BP has another important university programme in the USA, where the Methane Conversion Co-operative (MC2) at the University of California at Berkeley and the California Institute of Technology (Caltech) is dedicated to methane conversion research. The $20 million, 10-year collaboration is now in its sixth year (Frontiers, April 2004).
‘When we launched the MC2 programme, the primary drive was towards “blue skies thinking” – the longer term breakthroughs in discovering new catalysts for methane conversion,’ explains Theo Fleisch, distinguished advisor within BP and director of the MC2 programme. ‘But with momentum gathering in the commercial marketplace for GTL and GTP, we have accelerated the programme so that the 50 people in the two university teams are now mainly focused on delivering the beginnings of new catalyst technology and products in the shorter term, say in five years from now.’
‘There is no doubt the pace of conversion technologies is quickening all around us,’ adds Fleisch. ‘Compared to just a few years ago, you could rightly say that GTP is no longer a concept for a future business – it’s happening right now, today, in the shape of GTL plants in Qatar and Nigeria, large methanol plants in Trinidad, Chile and Oman among others, and coal-based methanol and dimethylether – an LPG alternative – plants in China.’
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‘The Atlas plant has given us valuable experience in a full scale GTP venture,’ concludes Robertson. ‘Combining this with the expertise and practical know-how flowing from our wider GTP development programme, plus BP’s recognised capability in managing world scale projects, puts BP in a strong position to offer the industry a fully integrated GTP portfolio.’
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