Lubricity From Sulphur Under 15 PPM?

By BRETT WINBERG

Production of ultra low sulphur diesel (ULSD) is scheduled to begin in June of next year in the United States . Refiners have many plans to produce ULSD, which vary in complexity from plant to plant. Using their tailored methods, each refinery will provide a portion of the total ULSD demand within the U.S. markets.

However, some refiners are still concerned with their ability to deliver the product. These concerns range from the method of production to the pipeline transportation system. Other refiners are struggling with routinely optimizing these new assets once the project is complete and the first shipment of ULSD is produced. Other countries have initiated ULSD production and have experienced startup, operational and production problems.

Clean fuels production is a worldwide initiative with some regions ahead of the USA in implementation, and still others are behind U.S. initiatives. The worldwide refining community recognizes the key role clean fuels play in the improvement of the environment. The refining industry has successfully faced many such challenges by delivering continually cleaner, low cost transportation fuels to the consuming public.

The “clean fuels” title is used to cover a wide range of fuel characterizations for different initiatives: reduce sulphur levels, add oxygenates, reduce aromatics, increase octane or cetane and meet additive package requirements. Selected from this wide-ranging criterion are the specific issues and factors surrounding the refinery requirements to produce 100% highway ULSD according to USA regulations. Several options exist for the refiner to produce ULSD. Selecting the best option involves carefully weighing many important issues:

The refiner’s goal is to produce an ULSD that not only meets the regulatory requirements of 15ppm sulphur, but also the additional commercial requirements of a high quality product. High severity hydro treating is known to produce color-unstable products. A variety of reasons are given for the occurrences of poor product color stability, but one common factor is the reactor outlet temperature.

As reactor outlet temperature is increased during the run, a temperature is reached for all feeds where the product color becomes unstable. This temperature is a function of many factors including feedstock type, feedstock endpoint, catalyst type, and reactor outlet hydrogen partial pressure. At reactor outlet temperatures as low as 680ºF, diesel begins to become color sensitive.

New designs need to remain below this temperature and revamp operations need to carefully consider the consequences of exceeding 680ºF. Although color is not a regulatory specification, it is a “workmanship” issue and poor color stability will adversely affect customer satisfaction.

Lubricity (or boundary lubricity) has been defined as “a liquid's intrinsic ability to prevent wear on contacting solid surfaces in the absence of any hydrodynamic lubricating films”. With only 15-ppm sulphur in our future, this may mean more downtime issues within your fuel system. This property has been a concern due to problems experienced with accelerated jet engine failures for low sulphur jet fuels.

The problems were linked to severely hydro treated jet fuels having both low sulphur and low aromatics contents. Sulphur is the main factor of lubrication in today’s diesel fuels and with tighter guidelines and pressures within the fuel system… these will create component failures in many applications that are using newly designed diesel fuels.

Wise operators will assure they have a back up system for getting the lubricity your fuel system requires to stay productive and fully operational. Source: KBC Advance Technologies.

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