What is Ultra-Low Level Sulphur Fuel?

Ultra-low level sulphur fuel is fuel that has been processed to reduce the sulphur content. In many parts of the world, regulations are in place to reduce the sulphur content of fuels for environmental and health benefits.

New regulations will be introduced in the United States in 2017 with the aim of reducing the impact of vehicle emissions on air quality and public health further. The regulations, issued by the Environmental Protection Agency (EPA), will be known as the ‘Control of Air Pollution From Motor Vehicles: Tier 3 Motor Vehicle Emission and Fuel Standards’ (Tier 3).

One of the ways Tier 3 will achieve reduced emissions is by reducing sulphur content in fuels. Most environmental and health concerns around sulphur in fuels initially concerned diesel fuel, as this had a higher sulphur content. Therefore the sulphur dioxide emissions were higher than for petrol. Subsequent regulations in recent years have addressed this situation and Tier 3 does not distinguish between petrol and diesel. The change in sulphur content due to Tier 3 is shown in the table:

Sweet and Sour

The sulphur content of crude oil varies depending on how and where the oil was formed. There are two classes of crude when it comes to sulphur content - sweet and sour. Sweet crude oil (named because it tastes sweeter) has sulphur content below a nominal value of 0.5%. Crude containing sulphur at levels above 0.5% is known as sour crude oil.

The sulphur content of crude oil is economically important. The additional processing needed with sour crude have resulted in higher prices. This isn’t helped by the limited amount of sweet crude resources. Regulations are demanding reduced sulphur content and there is an increasing use of sour crude. Consequently, production costs of fuel will also increase. As a result of additional processing and testing, plants will have to adapt to meet the new regulations, which is discussed in the article: Meeting Tier 3 Requirements with Ease and Precision.

How is the Sulphur removed?

Sulphur is a natural component of crude oil and is present in many different forms, including organic sulphides and disulphides, thiols and thiophenes. It is removed in a process called hydrodesulphurization. The process involves a reaction with hydrogen gas over a catalyst at high temperature (300–450 C) and high pressure (30 – 130 atm).

The sulphur is removed as hydrogen sulphide gas (H₂S), and this can be used as a feedstock for sulphuric acid manufacture.

As the total production costs increase it becomes important to keep the process costs down. Excess sulphur in the process streams can poison the process catalysts. For this reason it is critical to quickly and accurately measure the sulphur content to keep the process optimized. The measurement of sulphur content is discussed further in this article: Total Sulphur Determination in Petro Industry and Refineries – Competitive, More Reliable and Faster than Ever Before.