Increasing US diesel fuel production

US refiners are operating in a landscape of growing diesel fuel demand. Figures from the US Energy Information Administration show that over the past 10 years annual distillate fuel oil export from the US has increased dramatically.

This increase in export volumes has been fuelled by demand from Latin America and Europe, which have now become a steady source of revenue for US refiners. Looking ahead to January 2020, when the International Maritime Organization will cut the global sulphur cap from 3.5% to 0.5%, a relatively urgent need for low sulphur distillate molecules, to help meet the ISO 8217 requirement, can also be anticipated.

The combination of these two opportunities means that we can expect continued growth in demand for diesel fuel for the foreseeable future.

Increased demand, coupled with tight refining margins, may encourage US refiners to look for new ways to increase distillate production, without increasing costs or investing in expensive capital projects.

US refiners have traditionally focused on the production of gasoline to satisfy passenger car demand. In contrast, European refiners have largely concentrated on diesel production to meet both light- and heavy-duty requirements. Now, as the need to maximise diesel throughput and profits increases, some of the practices employed by European refiners could be adopted in the US. However, there are regional differences in both operation and infrastructure, which mean there may be some hurdles that must first be overcome.

Market specifications

ASTM D975 specifies US diesel fuel quality while EN590 is used in Europe. These standards have evolved to satisfy local market needs and have several differences. ASTM D975 for instance has no density, total contaminants or oxidation stability limits and has lower distillation (T90%), viscosity, cetane and lubricity requirements than its European counterpart. In addition, US diesel tends to have a lower cloud point (dictated by transport pipeline specifications) than most European diesel.

Both standards make provision for vehicle operability to ensure fuel is fit for purpose in the local market:

Currently, heavier European diesel, which is cost-optimised from a refinery economics standpoint, can be treated effectively with cold flow improver additives to operate effectively over these temperatures. This suggests that elevation of the US T90% distillation specification, to be more in line with European diesel, could be a viable prospect for US refiners to explore.

Cold flow tests

Natural phenomena, related to the wax content of the fuel, can be used as cold flow performance controls. However, both cloud point and pour point tests have shortcomings in relation to assessing vehicle operability. This led to the development of laboratory test procedures e.g. cold filter plugging point (CFPP) and the low temperature flow test (LTFT), which correlate to field test data. However, there are pros and cons for each of these tests.

Since its introduction, the CFPP test (which is included in EN590) has been successfully used to protect both light-duty and heavy-duty vehicles against operability failures in the field during cold conditions. It has helped refineries around the world to optimise their profitability by having a safe correlation to vehicle operability that allows cloud point relaxation. For cold flow additive treated fuels, this test provides robust protection against unacceptable vehicle operability for CFPP values up to 10-12^oC below the cloud point of the untreated diesel fuel.

Concerns remain in the US that CFPP is too optimistic in protecting the predominantly heavy-duty vehicle fleet. That said a combination of CFPP, wax appearance point and cloud point are currently used to release the vast majority of diesel into the US marketplace. There has been discussion within ASTM about changing low temperature operability guidance to a requirement, although there has been no formal action on this proposal to date.

Adopting CFPP as the low temperature operability specification for the release of diesel fuel would mean refiners in the US could let the cloud point of their fuel rise.

Cold flow additives would be used to reduce the CFPP to assure equivalent and consistent low temperature operability performance. This would allow blenders at the refineries to put more heavy fuel streams into the diesel pool, increasing the volume of diesel produced, while minimising the volume of lower value heavy fuel streams.

 

 

 

 

 

Pipeline differences

There are significant differences between Europe and the US in terms of both the way diesel is transported to end users and in the pipeline specifications that apply.

 

 

 

 

 

Compared to their European counterparts, US refiners produce a lighter, fungible diesel fuel to meet diesel pipeline specifications, which are based on cloud point and pour point.

 

Fuel is drawn off the pipeline and may then be further corrected at terminals close to the point of sale. #1 ultra-low sulphur diesel (ULSD) is used for cloud point adjustment and/or additives for CFPP or LTFT adjustment to ensure the fuel is fit for purpose in the local climatic conditions.

In Europe, refineries manufacture diesel suitable for local market climates by successfully applying an operability specification using the CFPP test and CFPP additives. This enables them to elevate the cloud point of their diesel to 10°C above the operability specification. If the US were to adopt a similar practice, the current pipeline specifications serving the southern and mid states (80% of the diesel demand) could elevate diesel cloud point by at least 4°C. This could be done while and still maintaining adequate vehicle operability with the use of cold flow improver additives.

The northern-most states could continue to blend using a combination approach of blending #1 ULSD and/or additives for CFPP or LTFT adjustment to ensure the fuel is fit for purpose.

Cloud point elevation

The current ASTM D975 specification coupled with the fungible diesel pipeline specification employed throughout the US has produced a diesel fuel that serves today’s market well.

There is scope to improve diesel fuel quality and refinery economics at the same time by increasing the cloud point of diesel and by introducing an operability specification.

Cloud point elevation, by incorporating heavier streams into the blending pool, would increase the energy content of the diesel, resulting not only in potential fuel economy benefits but also a possible cetane number boost, depending on blending strategy employed. The resulting debit in natural cold flow performance could be countered by treatment with cold flow improver additives at the refinery to yield an optimised fuel, truly suitable for the US market.

Today, we have a winter diesel fuel which meets the pipeline specifications of -9°C (15°F) cloud point and a -18°C (0°F) pour point. The pipeline specification is employed by the longest finished product pipeline, Colonial, and is tailored for local winter handling in its principal destination of New Jersey. The New Jersey 10^th percentile minimum ambient air temperature guideline is -12°C, which, from a cold flow perspective, is in the temperate range and consequently a 3°C delta between cloud point and operability is extremely conservative. This results in refinery value giveaway in New Jersey and all states to the south and most of the west.

During the summer, these specifications are relaxed slightly (-7^oC cloud point). Moving forward, these summer cloud point pipeline specifications could be adopted year-round, being coupled with a -15°C operability specification in the winter. This fuel would satisfy the needs of the vast majority of the US. Those states requiring further correction for a cold climate would carry on with the current practice of correcting with #1 ULSD or diesel fuel additives.

It is possible to further optimise the strategy of producing a year round -7°C cloud point fuel by producing a -5°C cloud point fuel coupled with the same operability specification.

Realising the benefits

Employing this approach in other regions of the world, most notably Europe, which has similar climatic conditions and similar heavy-duty vehicle architecture to the US, has realised a number of benefits for refiners and end users:

• Increased refinery flexibility to maximise refinery economics
• Minimised cloud point give-away
• Optimised distillation and diesel blending flexibility
• Potential diesel cetane number boost assisting the emissions profile of the diesel automotive pool
• Enhanced fuel economy from heavier diesel
• Increased diesel production to meet growing demand

In our view, this approach could bring potential value to the US refining industry both in terms of capturing a significant amount of value and potentially releasing hundreds of thousands of barrels per day of additional diesel fuel.

Download this article