February 2017

Special Focus: Clean Fuels

DME as a diesel alternative in North America

Major trends in the global hydrocarbon processing industry include the regulatory-driven demand for clean, low-emissions fuels. Two decades of global efforts have shown that dimethyl ether (DME) can satisfy these drivers.

Sills, R. A., XTL & DME Institute

Major trends in the global hydrocarbon processing industry include the regulatory-driven demand for clean, low-emissions fuels. Two decades of global efforts have shown that dimethyl ether (DME) can satisfy these drivers.1

DME has been used for many years as an aerosol propellant in cosmetic and other personal and household products, but this represents a small market. DME was first commercialized as a fuel in China as a liquefied petroleum gas (LPG) blendstock for the domestic home cooking/heating market. As a result, it now represents about 5% of global methanol demand.2

This article focuses on the challenges—and the significant progress that has been made—of commercializing DME as a diesel alternative in North America (NA), particularly for heavy-duty trucks. Questions regarding supply, distribution infrastructure, vehicle modifications and market developments will be discussed, as well as the “chicken or egg” challenges that face emerging alternative fuels.

What is DME?

DME is a colorless gas at ambient temperature and pressure. It burns like natural gas in cooking applications, and handles like LPG, as it is a liquid at moderate pressure (75 psig at room temperature). DME is compared to other conventional fuels in TABLE 1.

DME’s health and environmental effects have been evaluated extensively since its development and commercialization as an aerosol propellant for personal care products. DME is thermally stable, and does not form peroxides, deplete stratospheric ozone or contribute to global warming. It has minimal impact on land and water because of its volatility, has a low order of inhalation toxicity, and presents no human hazard relative to systemic toxicity, carcinogenicity, mutagenicity or teratogenicity within occupational exposure limits (1,000 ppm in 8-hr total weight average).3

DME as a diesel alternative

In the 1990s, DME in pure form (“neat”) was recognized as having attractive combustion properties as a potential alternative to diesel. It has a high cetane number and can be used in conventional diesel engines with a modified fuel injection system. DME burns without soot (smoke or particulates) due to a lack of a carbon-carbon bond and oxygen incorporated in the molecule. Without sulfur oxide (SOx) emissions, it is essentially sulfur-free. Engine noise is noticeably lower, as well.

An additional advantage of DME is that it can be produced from a variety of non-crude oil sources, particularly from ample supplies of low-cost natural gas, and biomass. Since DME has a very low viscosity and no natural lubricity, the fuel injection system must be designed to tolerate these fuel properties, and a lubricity additive must be included to protect the fuel injector and fuel pump.

Over the past two decades, extensive global development work has been conducted in Europe, Asia and, more recently, NA. A number of original equipment manufacturers (OEMs), including Volvo, Isuzu, Hino, Nissan, Shanghai Automotive, Navistar and Ford, have tested DME as a diesel fuel in research, trials and demonstrations.

In particular, the Volvo Group has been developing DME as a diesel alternative since the mid-1990s. These efforts include an extensive, large-scale fleet test in Sweden from 2011–2016 that included 10 heavy-duty, Class 8 trucks in commercial operation, accumulating 750,000 on-road miles. This program was part of a bio-DME program that produced DME from paper mill residue, and included a DME distribution infrastructure with four filling stations.

DME can be applicable to virtually all demanding haul applications where fuel consumption is high enough to secure a return on investment (ROI). Initially, Volvo is targeting Class 8 heavy-duty, regional haul trucks, as these return-to-base applications limit concerns for expanded fueling infrastructure during the early phases of this initiative.

The diesel fuel market for Class 8 trucks is significant—approximately 2 MMbpd. Even 10,000 heavy-duty trucks using DME supplied from a world-scale, 1-MMtpy DME plant (1 metric t of DME is equivalent to 395 gal) would represent only a small fraction of the approximately 2 MM diesel-powered, Class 8 heavy-duty trucks in the US.

Fleet tests in NA

Volvo, in partnership with Oberon Fuels, conducted a test program in Beaumont, Texas. The test was conducted from 2013–2015 using three DME 13-liter (13-l) heavy-duty trucks, which were in daily service in East Texas and hauled a range of bulk-liquid cargoes for a total travel distance of 60,000 mi.

The fleet tests and extensive engine development efforts confirmed the attractive benefits of using DME in heavy-duty trucks, showing that:

  • The DME engine is similar to its diesel counterpart. The basic diesel engine remains unchanged, as DME ignites on compression. The main difference is in the fuel injection system, where specific pumps and injectors are required to deliver the fuel to the engine.
  • The exhaust after-treatment system is similar to that used on modern diesel trucks, with the notable exception that the diesel particulate filter (DPF), which weighs about 500 lb, is unnecessary. The removal of the DPF eliminates the need for regeneration and negates DPF-cleaning maintenance requirements. NOx emissions are controlled by existing selective catalytic reduction (SCR). Raw engine exhaust NOx emissions are lower and compliant with US GHG 2014 greenhouse gas (GHG) emissions and fuel economy standards regulations.
  • The fuel tanks resemble propane tanks and require specific seals and materials. The fuel tank is larger due to lower energy density (1.88 gal of DME are energy equivalent to 1 gal of diesel). Two saddle fuel tanks can achieve a range of 700 mi.
  • The DME-fueled trucks achieve the approximate horsepower (hp), torque and overall engine efficiency as a diesel truck. DME fuel economy is on par with diesel, as well.
  • No truck chassis modifications are needed, and the weight penalty is less than 100 lb.
  • Early testing technical challenges included fuel lubricity/additives package; temperature management and vapor lock; and in-tank challenges due to iron oxides from supply chain and oil residues in fuel.

In July 2016, Mack Trucks, the sister company of Volvo Trucks NA, announced that it is partnering with New York City’s Department of Sanitation (DSNY) to explore the use of DME as an alternative fuel in the city’s waste management fleet. The city, which runs the largest municipal sanitation department in the world, will begin assessing DME in a vehicle equipped with a 13-l engine.

DME supply

DME can be manufactured by catalytic dehydration of methanol, followed by distillation, meaning that DME can be produced from a variety of feedstocks, such as natural gas, coal and biomass.1 To produce 1 mt of DME, 1.4 mt of methanol is required.

DME production is a mature technology that is utilized in a number of countries in Asia, Europe and NA. In NA, numerous plants have been built, and more are planned, to produce methanol from ample supplies of low-cost natural gas. Methanol can also be produced from renewable feedstocks, such as biogas from waste feedstocks, landfill solid waste, manure, etc.; and black liquor from pulp mills. Methanex is the world’s largest producer of methanol, and supports the commercialization of DME in other regions, such as Korea, as well as in new markets, such as bitumen recovery in the Canadian oil sands.

FIG. 1. Oberon Fuels’ DME plant located in southern California.

To supply its demonstration programs in NA, Volvo Trucks NA has partnered with Oberon Fuels, the first company to produce DME fuel in NA. Oberon Fuels operates a skid-mounted, small-scale production unit that converts methanol to DME. The company’s first plant, located in the Imperial Valley region of southern California, went online in 2013 (FIG. 1). The plant can produce 4,500 gpd of fuel-grade DME from methanol. The process converts methanol to DME in an innovative catalytic distillation column, and purifies the product to meet fuel specifications.

Distribution logistics: Storage, transport and refueling

Multiple industries have ample experience storing and distributing DME, due to its use as a propellant. DME distributors have stated that DME can be safely transported, stored and handled.4 DME is transported in bulk containers—via truck and railroad tank cars—that are virtually identical to those used for propane, with consideration for the use of appropriate seals and elastomers.

For transfer hoses, DME carriers use a convoluted stainless steel hose manufactured with double-reinforced stainless steel external braiding, which meets similar or higher-working pressure and burst pressure ratings as the LPG hose. Proper grounding and bonding is essential for safe handling of both DME and LPG when filling containers.

Standards and regulations

While DME is a relatively safe product that is environmentally benign, it requires that appropriate standards and regulations are in place, and that safe handling procedures are followed. Over the past decade, the DME community has been working with international and regional standards/regulatory organizations to provide DME producers, engine manufacturers, infrastructure developers and others with references and guidance.5

Since 2009, the International Organization for Standardization (ISO) has published numerous DME specifications, establishing characteristics and testing methods for DME fuel, and providing important benchmarks. The ISO is continuing its efforts to establish additional standards in the near future.

In 2014, the American Society for Testing and Materials (ASTM) International issued ASTM D7901, which covers DME for use as a fuel in engines specifically designed or modified for DME, and for blending with LPG.6 DME can be legally sold as a fuel in all US states. In addition, biogas-based DME is eligible under the US Environmental Protection Agency’s (EPA’s) Renewable Fuel Standard for Renewable Identification Number credits. Washington state has already qualified DME-powered trucks for tax incentives.

Regional developments

Other noteworthy developments include:

  • In Trinidad and Tobago, state-owned National Gas Co. and Massy Holdings, in conjunction with a consortium comprised of Japanese companies, is building a large-scale, 1-MMtpy methanol plant and a 20-Mtpy to 100-Mtpy DME production plant. DME target markets include diesel alternatives, LPG blendstock and aerosol propellant.
  • Ford European Research and Innovation Center is leading a $3.66-MM project to develop the first passenger cars to run on DME and oxymethylene ether, a liquid used as a solvent in the chemical industry. This 3-yr program began in 2015.
  • In 2017, a major multinational automaker is expected to announce a new, multi-year project to develop
    a DME medium-duty truck for NA. 

Path forward

The opportunity to use ample supplies of low-cost natural gas, combined with government-driven policies to utilize renewable resources and consume clean fuels, has created an opportunity for DME to play a pivotal role in NA’s fuels pool. This adoption is not without challenges, but the fuel supply, infrastructure and vehicle logistical challenges faced by many emerging alternative fuels producers can be addressed by the developments mentioned in this article.

Prospects for market growth would be enhanced with more providers for trucks/engines, infrastructure and fuel production. The IDA has adopted a near-term goal of 20 DME engines, including the New York City test, to be engaged in NA commercial demonstrations by 2018. Remaining challenges include:

  • Customer acceptance by fleet owners depends on DME meeting their criteria for vehicle performance, reliability, durability and economical operations, including lifecycle costs, maintenance capabilities, and fuel costs and availability
  • Low crude oil and diesel prices, which are a challenge for all alternative fuels.

As expressed by Rebecca Boudreaux, IDA chair and president of Oberon Fuels, DME as a diesel alternative can move from the demonstration phase to commercialization by harnessing the power of collaboration and contribution. The DME community has its sights beyond heavy-duty trucks and across multiple industries including locomotive, marine transportation and as a fuel for power generation. To achieve these purposes and build the DME ecosystem, the DME community must continue working together, and recruit and encourage new members to become active members.7 HP

ACKNOWLEDGEMENTS

The author gratefully acknowledges the contributions by the members of the International DME Association, particularly Volvo AB, Oberon Fuels, Methanex, Parafour Innovations and Diversified CPC Intl.

LITERATURE CITED

  1. Fleisch, T. H., A. Basu and R. A. Sills, “Introduction and advancement of a new clean global fuel: The status of DME development in China and beyond,” Journal of Natural Gas Science and Engineering, 2012.
  2. Methanex Investors presentation, October 2016.
  3. Creazzo, J., “US dimethylether markets, manufacture, storage and transfer,” 2005.
  4. Frauenheim, W. A., 7th International DME Conference (DME7), Houston, Texas, September 2016.
  5. Zilioli, M., “ISO Standardization of DME Components,” 7th International DME Conference (DME7), Houston, Texas, September 2016.
  6. ASTM International, ASTM D7901—14b, “Standard specification for dimethyl ether for fuel purposes,” 2014.
  7. Boudreaux, R., 7th International DME Conference (DME7), Houston, Texas, September 2016.

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