Rohit Vedhara, managing director at Singapore-based Aum Energy, argues the case for using DME – dimethyl ether – as a possible alternative to diesel in truck vehicles.
Dimethyl ether (DME) is the simplest ether compound, with a chemical formula of C2H6O. It is a clean, colourless gas at ambient temperatures, but can be liquefied under a moderate pressure. This makes DME quite similar to propane and LPG for handling purposes.
DME has been used for decades as an environmentally-benign propellant in aerosols as it is non-toxic and is easily degraded in the troposphere. It is also used as an LPG blending component and is now moving into the diesel replacement market.
China produces four million tonnes of DME per year, 90% of which goes into LPG blending. Other plants have been built in the USA, Sweden, Korea and Japan and a new plant is currently being built in the Caribbean. Whilst China’s focus on DME originated from its desire to create value from its coal resources, Aum Energy believes that it is natural gas that will become the predominant feedstock as DME starts to be used to replace diesel, especially in North America.
Several companies have developed considerable interest in DME as a clean diesel alternative, including Volvo, Itochu, Mitsui and Mitsubishi.
This recent quote from Olof Persson, the chief executive of Volvo Group, sums up a continued belief in DME: “…when it comes to other segments, particularly longer hauls, we continue to believe DME shows tremendous promise,â€? he noted. “Converting natural gas to DME is an innovative way to address many of the distribution, storage and fuelling challenges otherwise presented by natural gas – particularly LNG – as a heavy truck fuel….Volvo will continue to work with this technology and if the industry were able to get the critical mass of production volume needed, DME could really be a game-changerâ€?.
The emissions-related benefits of DME as shown by Volvo certainly point to zero particulates, lower NOx, zero SOx (sulphur dioxide) and 10% lower CO2 emissions, but with the equivalent fuel efficiency against a diesel engine.
Isuzu has been working on DME since 2001 and has focused on city buses and short-haul trucks. It states that DME for Euro VI can be achieved with a simpler configuration than with a diesel engine. A DME engine with an EGR fitted has similar characteristics to a CNG vehicle from a CO2 perspective, with higher thermal efficiency. It has a 4x better distance and time-to-fill ratio than CNG and even better than diesel.
Aum Energy has a basic market offer scaled at 11 mmscf/day (million cubic feet per day) of feed for the LPG market and 16.5 mmscf/day for the diesel replacement market. These sizes produce 200 and 300 tonnes/day of DME respectively. A gas-methanol-DME unit can be built in just over two years, with all of the component parts being proven.
According to the International DME Association, interest in DME as an alternative fuel is high following Volvo and Mack Trucks’ announcements that they plan to produce heavy-duty trucks running on DME in the USA. California has approved the use of DME as vehicle fuel. In 2014, DME became the first biogas-based fuel to receive approval from the EPA for inclusion under the Renewable Fuel Standard, making it eligible for valuable RIN credits based on EPA findings that the fuel achieves a 68% reduction in GHGs when the feedstock is biogas.
Other significant milestones include the U.S. DOE’s confirmation of DME’s status as an ‘alternative fuel’ as set forth in the Energy Policy Act of 1992; the publication of specifications for DME fuel by both the ISO and the ASTM and the State of Washington’s inclusion of DME in a fuels incentive programme.
Elsewhere, Ford and the German Government are leading a 3-year programme to understand the advantages of using DME as a fuel for passenger cars. Based on trials using the Ford Mondeo, the collaboration seeks to ascertain the full manufacturing and supply costs of DME; the fuel efficiency as well as the benefits from an emissions perspective.
When developed on a commercial scale, DME can be supplied at a discount to diesel. With a relatively straight-forward manufacturing process and low operational costs, DME can be introduced in a hub-spoke system with cornerstone projects being built in key locations (such as in northern California and around the major shale formations in the USA) and then gradually being interlinked. DME has increasing relevance for Europe given air quality issues in the major cities.
With an EV solution not being feasible and the operational issues around using LNG, DME stands out as the future fuel of choice for the trucking industry.
– Rohit Vedhara, managing director at Aum Energy.