The Sulphur Technology Platform

Through the multi-platform Pentagon Model, Shell Global Solutions provides a portfolio of integrated, comprehensive and customised technology solutions to meet refiners’ specific short-term and long-term business goals. Known as the Sulphur Technology Platform, this suite of technologies can help refiners not only survive but thrive in today’s volatile economy and environment by dealing with sulphur in all its forms, including: sulphur in crude; sulphur in all products, from liquefied petroleum gas (LPG) to residue; hydrogen sulphide (H2S); sulphur dioxide (SO2); mercaptans; and solid sulphur.

The Shell Global Solutions licensing portfolio, which includes technologies from key, carefully selected alliances, is a comprehensive portfolio of integrated technologies derived from and fine-tuned using real business challenges that can be customised to meet each refiner’s individual business needs.

Business value

Shell Global Solutions supports refineries through the crucial front-end development phase, where decisions are critical and have a strong influence on the overall project value.

Initial consultancy and extended services throughout the project lifecycle may include:

• Market studies, such as scenario planning and masterplanning to help take a view of the future market and to enable more robust decision making regarding location, feedstock, logistics, process configuration and hardware requirements;
• Front-end development to optimise process design and
  technology selection;
• Implementation support, such as project management support and contractor management to ensure budgets and schedules are met; and
• Start-up and commissioning services to reduce implementation time and organisational effectiveness reviews throughout the project lifecycle.

Shell Global Solutions then works with refineries to provide optimised technical solutions as part of the Sulphur Technology Platform that can help them to reduce the sulphur levels of their products, from gasoline and diesel through to LPG and fuel oil, to meet product specifications. The solutions also enable refiners to remove H2S, SO2 and CO2 from their off-gases to meet their environmental mandate whilst processing opportunity crudes that represent an additional revenue opportunity.

Hydrotreating unit revamp to produce Euro 5 diesel extended with dewaxing technology

One example of an application of the first pentagon (“operational improvements”), allowed the upgrade of an existing diesel hydrotreater. This particular case led to the application of the second pentagon (“short-term revamps”) through phased investment, which enabled the refinery’s long-term competitive positioning in the region and helped it to meet the regional winter grade diesel demand. The regional supply and demand orbit has historically been short of winter grade diesel and forecasted trends show that this shortfall would continue or even grow.

The main objective of the phase I feasibility study was the assessment of the performance of the diesel hydrotreater reactor section to meet the Euro 5 diesel specifications, in combination with a future target capacity increase of 30 per cent compared to design.

The objective of the phase II revamp was the installation of a second stage dewaxing section to achieve a further cloud point reduction of 20˚C and thus produce a winter diesel product for the local market.

The diesel hydrotreater was designed to process straight run diesel and kerosene with a maximum sulphur content of 50 to 350 wppm. A maximum capacity testrun showed that the unit was capable of operating at 115 per cent of the design throughput at the premised feedstock, having a sulphur content of about 100 wppm in the diesel product.

The premised feedstock is a blend of 85 per cent wt straight run diesel and 15 per cent visbreaker gasoil and light catalytic cracked cycle oil (LCO). The unit was further constrained in terms of a maximum pressure differential across the reactor section, set by the fixed speed recycle gas compressor capacity and heat integration limitations.

To achieve a diesel product sulphur content of less than 10 wppm, the installation of an additional reactor downstream of the existing HDS reactor was required, while the increased feed rate would require the installation of a maximum diameter impeller for the diesel hydrotreater feed charge pump, together with the replacement of the pump driver. This solution was a minimum capital expenditure (capex) solution for the refinery, meeting the premised Euro 5 diesel specifications and the target capacity increase of 30 per cent compared to design.

Processing of gas oils, especially when containing LCO, to very low sulphur levels requires hydrogenation of the difficult sterically-hindered sulphur species (dibenzothiophenes) found in the heavy end of the feed.

In order to achieve the required sulphur in product, a catalyst system based around Criterion Catalysts & Technologies ASCENT™ platform DN-3531 and DC-2531 in a sandwich structure was proposed. The nickel molybdenum (NiMo)-based catalyst was applied to reduce the residual nitrogen to low enough levels for the (future) second stage noble metal hydro-isomerisation dewaxing (HDW) catalyst. The cobalt molybdenum (CoMo)-based catalyst had been included to meet the diesel sulphur specification but minimise hydrogen consumption.
 
As an opportunity to minimise investment for the dewaxing expansion in phase II of the revamp project, the heat integration of the reactor section was optimised by the installation of a new hot high-pressure separator (HHPS) scrubber as part of the application of the third pentagon. This combination would make substantial heat available from the new HHPS pump to be used for feed preheat, while at the same time reducing the condensing duty requirement of the high pressure vapour condenser. The pump around could also be used as liquid quench in between the catalyst beds of the new reactor.

For phase II of the revamp project, the hydro-isomerisation dewaxing technology was applied, because of yield advantage over catalytic cracking dewaxing, and integrated within the existing HDS reactor section. The concept of isomerisation dewaxing is based on a catalyst having a zeolite structure, impregnated with noble metal platinum (Pt).

The feasibility study resulted in several benefits to the refinery’s revamp project. By applying the Pentagon Model, the refinery experienced a capacity expansion of 30 per cent and diesel product that met Euro 5 standards through phased capital expenditure without replacement of capital-intensive equipment. The refinery also produced winter diesel grade with a cloud point specification of -25˚C. Lastly the refinery achieved increased diesel yield (optimisation of gasoil stripper in work-up section) and increased unit reliability (reinstate wash water application).

Integrated MHC/HDS Complex

Final Diesel Hydrotreater Flow Scheme post revamp with Dewaxing technology

In an example of the application of the third pentagon (“long-term options”), an integration of mild hydrocracking and diesel desulphurisation units helped to add value to an existing refinery generating Euro 5 diesel quality products and feedstock for the fluid catalytic cracking (FCC) unit.

The main objective of the configuration review was to upgrade heavy gas oil (HGO)/vacuum gas oil (VGO) to diesel while still producing unconverted oil (UCO) as feedstock to the FCC. Another business driver was to hydrotreat excess light gas oil (LGO) to produce diesel. The challenge was to determine the most economical, reliable and robust solution through co-processing or post treatment while meeting diesel Euro 5 specification.

The assessment demonstrated that in an integrated HDT/HCU configuration, the unconverted oil bleed from the common fractionation section to the FCC and the remainder recycled to a hydrocracker unit (operating at higher conversion), would not be feasible at any of the three investigated pressure levels. This was because the sulphur content of the middle distillate (kerosene and diesel combined) could not meet the 10 wppm sulphur specification. Even at the 120 bar pressure level the S-slip in ULSD was estimated at 65 wppm.

For both the single-stage full range MHC and the integrated MHC/HDS configurations, the cetane number specification could not be achieved at the lower pressure levels of 80 bar and 100 bar. The density specification of < 845 kg/m3 could only be met at SOR conditions for the single-stage full range.

At the highest pressure level of 120 bar, all diesel specifications could be met for both these configurations. The middle distillate yield from the single-stage full range MHC configuration compared with the integrated MHC/HDS is around 5 per cent lower due to extra cracking of the LGO feed.

Although the single-stage full range MHC would have the higher operating flexibility of independent turnarounds for maintenance and/or catalyst change compared with the HDS from MHC functions in the integrated MHC/HDS configuration, the higher capital cost involvement for the two MHC reactors versus the HDS and MHC reactors will justify the loss in operating flexibility.

Sulphur Technology Platform diagram

The integrated configuration consists of a single-stage mild hydrocracker (MHC) reactor in once-through operation and in parallel a single-stage hydrodesulphurisation (HDS) reactor in once-through operation. Both reactors operate at the same pressure level. The configuration features common high pressure gas and recycle section, common cold separation section and common work-up section.

The configuration assessments and optimisation studies resulted in several benefits to the refinery project. The refinery achieved its highest diesel and kerosene yields, while meeting Euro 5 standards and producing unconverted oil requirement as feed for FCC. The project utilised low capex involvement whilst optimising energy efficiency and reliability of operations.

The right solution for managing sulphur should develop out of deliberate evaluation of the application of technologies and their integration within a refinery. There are multiple options to deal with sulphur throughout the refinery. Flexibility within an overall refinery approach can increase capability to respond to market variation and clean fuel legislation or more stringent product specifications. Depending on the refiner’s business goals and the existing refinery configuration, unique technical solutions are available at every step of the Pentagon Model that encompass the whole refinery or focus on individual units.

Shell Global Solutions, together with its various alliances, has developed and applied a broad portfolio of integrated and comprehensive technology solutions that refiners can implement. Enabling refiners to increase margins and prepare for more stringent emissions regulations, the Sulphur Technology Platform allows refiners not only to survive, but also to thrive.