Advances in Gas-to-Liquids Technology at Shell

Advances in Gas-to-Liquids Technology at Shell

G.L. Bezemer

¹ Shell Global Solutions International BV, Grasweg 31, 1031 HW Amsterdam, The Netherlands

Introduction

Shell researchers have been studying the Fischer-Tropsch (FT) reaction for more than 40 years. This contributed to commercial Gas-to-Liquids (GTL) plants in Malaysia and Qatar and ongoing developments for new GTL prospects at various locations. Shell Middle Distillate Synthesis (Shell MDS) in Bintulu, Malaysia, started up in 1993 with a current capacity of 14,700 bbl/d synthetic products. Pearl GTL is situated in Ras-Laffan, Qatar, and started up in 2011. It is the largest GTL plant in the world with a production capacity of 140,000 bbl/d synthetic products. In Shell, research to further improve the economical and technical aspects of the GTL process has been a continuous activity. This has resulted in improved technology for each of the main process steps. In this talk FT related developments will be discussed first. In both Shell MDS Bintulu and Pearl GTL, multi-tubular fixed bed technology is used for the Heavy Paraffin Synthesis (HPS). This technology has proven scale-up benefits and several other differentiating features compared to other reactor types such as slurry reactors. Second main topic will be improvements made in the Heavy Paraffin Conversion (HPC) technology. Afterwards the product slate of the Shell GTL process will be discussed in conjunction with the technology. Finally, an update will be given on the implications of these and other improvements on new GTL plant designs.

HPS catalyst improvements

In Shell MDS Bintulu and Pearl GTL, a multitude of HPS reactors are installed where the chemical conversion of gas into liquids takes place. The catalyst in the reactors can be reactivated in situ several times before it has to be unloaded and reclaimed. The design and early operation of Shell MDS Bintulu was based on the first-generation Fischer-Tropsch catalyst. The second-generation FT catalysts were implemented from 2000 onwards. In the design of Pearl GTL, the full potential of this improved catalyst could be harvested, being a doubled production rate per unit catalyst volume, a heavier product distribution with higher liquid selectivity and lower CO₂ make.

Since the start-up of Pearl, catalyst development has continued resulting in third-generation catalysts with even further improved liquid selectivity and reduced CO₂ production. Besides that, catalyst stability was further increased. Introduction of these third-generation catalysts started in 2014 in Pearl GTL and Shell MDS followed in 2015. In the lecture the performance of next generation HPS catalyst will be discussed and some of the underlying capabilities that were behind the development will be highlighted.

HPC catalyst improvements

The conversion of raw FT product into final products is done in the Liquid Processing Unit (LPU). The LPU can be regarded as the refinery part of the GTL plant. The molecular structure of FT wax is however quite different compared to the crude oil diet of a normal refinery and hence dedicated catalysts and process units were developed for this purpose. In the HPC reactor (de)hydrogenation, isomerisation and cracking reactions are taking place. The noble metal based HPC catalyst designed for Pearl GTL provided excellent product quality. In the lecture improvements in the HPC catalyst system will be discussed with examples shown of stability and selectivity improvements that were enabled by fundamental understanding of the process.

GTL products developments

Shell’s FT synthesis process results in very clean paraffinic hydrocarbons. The unique nature of the molecules makes them very suitable in specialty applications. The very heavy wax produced by the HPS allows the conversion into lubricant baseoils with superior properties compared to oil derived baseoils available in the market. Shell baseoils are used in premium lubricants and enable improved fuel economy during driving. In the lecture a comparison will be made with different baseoil types and the basis of the enhanced performance will be discussed.

Scalable GTL design for new prospects

With the Shell MDS and the Pearl GTL projects, Shell has proven GTL on 15 and 140 kbpd scale. This experience enables the selection of a scale (hence: “Scalable GTL”) that gives the optimum balance of economy of scale versus project complexity and resource requirements. The Scalable GTL design It is based on the latest technology improvements in various areas (gasification, HPS, HPC) and has an optimized cost based on competitive scoping, supply chain transformation & efficient execution. In the lecture the interaction between technology steps and the resulting design will be highlighted.

Conclusions

Almost 100 years after its initial discovery, the Fischer-Tropsch process still receives a lot of attention in academia and industry. In the lecture, four areas where recently significant improvements have been made will be show cased alongside an overview of the Gas-to-Liquids process deployed in Shell MDS Bintulu and Pearl GTL.