Jul-2012

Challenges and opportunities of 10 ppm sulphur gasoline: part 1

Prospect of a worldwide standard for ULSG and the challenges of increased heavy crude supplies demand careful consideration and selection of refinery configuration

Delphine Largeteau, Jay Ross, Marc Laborde and Larry Wisdom
Axens

Article Summary

The worldwide refining industry has undergone a major transformation in the last decade due to changes in regulatory and market forces, such as fluctuating crude prices, tighter regulation on product quality and refinery emissions, shifting crude quality and fundamental changes in fuel demands. These forces can be seen clearly in the North American market, where crude quality has become heavier due to increasing amounts of lower-cost heavy, sour Canadian bitumen and where regulations have become more severe by limiting the sulphur level in fuels to 15 wppm in diesel and 30 wppm in gasoline. In addition to these feed and product quality changes, the overall demand for transportation fuels is shifting from a traditionally gasoline-oriented to an increasingly diesel-oriented market.

Regulatory specifications for the gasoline and diesel pool, which are constantly evolving, have been in the forefront of refiners’ challenges in the last 10 years. In particular, the gasoline sulphur and benzene regulations have been the main drivers for the recent remodelling of the refinery configuration. This transformation has been seen all around the world, but particularly in Europe, Asia and North America. Other countries are following the trend and a common worldwide gasoline sulphur specification is on the horizon. Indeed, the overall gasoline sulphur content is likely to level off at 10 ppm across the globe. As a consequence, most refiners will face renewed challenges to be able to meet the new ultra-low-sulphur gasoline (ULSG) specifications. However, in view of other market forces, there may also be new opportunities for refiners.

This article will identify these new opportunities by reviewing the processing options and consequences of such regulation, focusing mainly on North American refineries and drawing on the European and Asian experience of meeting the 10 ppm ULSG regulations. The issues, challenges and opportunities of each option will be presented and discussed. In a second article, a detailed economic assessment of each configuration will be applied in a case study.

Gasoline sulphur regulation
There has been a steady downward trend in the sulphur content of fuels to reduce emissions from cars and trucks. Many countries mandated the production of low-sulphur gasoline (LSG) some time ago, but in recent years regulations in Western Europe, some Asian countries and California in the US have brought in even tighter specifications to lower the gasoline sulphur to 10 ppm.

The different regional approaches to the gasoline sulphur specification set out in Table 1 show a clear trend towards ULSG. Other countries are following the same path to either meet their domestic regulatory specifications or be able to export and sell on the international ULSG market (see Figure 1).

Although the majority of countries still have gasoline sulphur specifications well above 10 ppm, the overall trend clearly shows that in the near future ULSG production will become the norm worldwide.

Current refinery configuration
Refinery configurations vary widely, depending on crude availability, local demand, export markets and regulatory constraints. In the same way, each market has its own set of dynamics and means of complying with the new fuel regulations.

In Europe, regulations for ULSG were adopted early and somewhat influenced by a market demand, which is more heavily skewed toward diesel than gasoline. The options for ULSG compliance were influenced by:
• Processing of relatively light and low-sulphur crude oil
• Relatively good-quality FCC feed (little cracked gas oil such as heavy coker gas oil)
• Undercutting of FCC gasoline to maximise diesel production.

The EU’s 10 ppm ULSG is produced mainly by using moderate severity FCC post-treatment.

Many catalytic feed hydrotreater (CFHT) units installed in Asian refineries were designed to meet modern fuels and emission regulations. As such, many are designed for high desulphurisation levels to meet refinery and SOx regulations from the FCC flue gas, resulting 
in low-sulphur FCC gasoline. Consequently, most refineries in Japan have met the new ULSG limit of 10 ppm by adding low-severity post-treatment units.

In the US, the refinery configuration was influenced by a large demand for gasoline coupled with limited fuel oil outlets, resulting in the installation of bottom-of-the barrel conversion units and high FCC feed sulphur. The US Tier 2 gasoline sulphur and California Air Resources Board (CARB) regulations led to a sharp increase in the number of FCC feed pretreatment and FCC gasoline post-treatment units over a short period of time (see Figure 2). Essentially, all of the US refineries now have pre- and/or post-treatment units to ensure compliance with gasoline sulphur regulations.

FCC pretreatment vs post-treatment
When the Tier 2 regulations were proposed, many were convinced that CFHT would be the solution of choice due to the resulting large improvement in FCC performance. However, the high capital cost requirement for the FCC pretreatment option coupled with low refinery margins resulted in the wide application of FCC post-treatment to reduce gasoline sulphur.

Another factor that can influence the decision between pretreatment and post-treatment is FCC flue gas emissions. Limits on refinery emissions and in particular those from the FCC have led to refinery-specific regulation via consent decrees with the EPA, resulting in much lower SOx and NOx emissions. The “preferred” refinery configuration may well have been different had the limits on emissions and product sulphur been regulated in concert.

More recently, there has been an important trend towards the processing of increasingly heavier crudes, in particular heavy Canadian crude or bitumen. By 2015, there is an expected increase of about 2 million b/d of Canadian bitumen, which will be largely exported to the US as raw bitumen (DilBit) or synthetic bitumen (SynBit) after partial upgrading at the production site. These very heavy crudes are a challenge for processing in existing refinery assets due to a high acid content (TAN), high aromaticity and low hydrogen content, along with very high contaminant content: sulphur, nitrogen, Conradson carbon and metals.