Sulphur challenge

Unless airlines, the aerospace industry and oil companies act now to reduce the sulphur in jet fuel, legislation could be imposed – with painful consequences.

What is the aerospace industry going to do about cutting the amount of sulphur that is currently used in jet fuel, or Jet A-1 as it is known?

The issue has the potential to deliver a huge and destabilising shock to the aerospace industry, unless airlines, aerospace manufacturers and oil companies take steps now to avert a crisis.

Sustained legislative and technical effort has gone into reducing sulphur in petrol and diesel for cars. The substance, which has lubricating properties in automotive applications, is associated with acid rainpollution and smog formation.

The latest European directive on road fuel will limit the amount of sulphur in all petrol and diesel to 10mg in every kilo, or 10 parts per million, by 1 January, 2009. Indeed, this amount is so low the fuel will be defined as sulphur free. In addition, the directive requires that ‘sulphur-free’ petrol and diesel must be at least available to some extent within the EU no later than 1 January, 2005.

The UK government is supporting this initiative with tax incentives to encourage the use of the product. At the moment, most petrol and diesel products have a sulphur content of around 50 parts per million.

Meanwhile, over 178 million gallons of jet fuel are consumed every day worldwide; this is according to the latest set of figures, 1998. The typical level of sulphur in Jet A-1 is 350 parts per million. The specification for this fuel, which is held by the MoD, allows for a maximum of 3,000 parts per million. So far there has been no legislative attempt to reduce jet fuel sulphur levels.

While oil producers might approve of the lack of interference, the situation has given rise to a false sense of security. UK fuel experts predict that as more pressure is put on oil companies to lower sulphur in road fuels, there will be a corresponding rise in the sulphur allowed to creep into jet fuels.

Refinery capacity to make sulphur-free fuel is limited, and the demand for the less readily available low-sulphur crude oils – the raw material of petrol, diesel and kerosene – will push their price up. Naturally, as there is plenty of headroom on sulphur content limits in jet fuel, the most expedient solution is to let sulphur levels rise in Jet A-1 and concentrate resources on making cleaner road fuel.

Not only will this be bad news for the environment, but also high-sulphur content increases wear and tear on engines, requiring increased maintenance and ultimately reducing the operating life of a turbine. There is now a danger that the EU or a national government could turn its attention to jet fuel and take unilateral action to impose a strict limit on sulphur. It is difficult to see why this will not happen when so much has been done to limit its use on the ground. At present there is notechnical justification for using high-sulphur jet fuel. Unless the industry does something to anticipate the move, an enforced transition could prove painful, with fuel prices rising dramatically.

The issue is likely to come to a head as the EU road fuel directives come into force. There are a few possible routes around the problem, however. Today, all jet fuel is refined from crude oil, but in the future it could be made from natural gas. Oil companies have recently started to use a chemical process that converts natural gas to synthetic crude oil from which a sulphur-free kerosene can be made. Gas to liquid fuels (GTL) are very clean burning, and contain no aromatic hydrocarbons such as benzene. They also create the possibility of designer fuels made for specific engines, but are expensive to produce.

It may become more economic to exploit natural gas in this way, however, as the price of crude oil rises. Still there is a lot of work to be done to establish that synthetic fuels can match the thermal, combustion and storage specifications of conventionally produced Jet A-1.

Most of the large oil companies such as BP, Shell and ExxonMobil had little or nothing to say about their R&D activities, but in a joint venture South African fuel producer Sasol, and ChevronTexaco have both made some progress on GTLs. SasolChevron has started to produce GTL petrol and diesel which it claims gives improved performance and less pollution. It has also been allowed to produce Jet A-1 containing 50 per cent synthetic fuel.

Note: At Penn State University, researchers are working on a new formula jet fuel, made from coal. The fuel, provisionally called JP900, has a high thermal stability and is intended for the next generation of military jet engines that will compress air at ever greater pressures and generate higher temperatures within the engine.