Emission Control Using Dimethyl Ether in Marine Applications

Ocean going vessels generate significant pollution. These emissions affect not only those who live near to the water but also people living hundreds of miles inland. The US Environmental Pollution Administration (EPA) demonstrated over several studies the impact of emissions from ocean vessels spreading into the nation from the all coastal regions.

These craft are fitted with diesel engines that produce large quantities of NOx, fine particulate matter (PM2.5), ozone (O3) and sulfur oxides (SOx) that fail to meet the EPA Air Quality Standards. These emissions harm both animal and human populations, which worsen already fragile ecological zones.

Along with the above controlled emissions, maritime engines also emit hydrocarbons (HC), carbon monoxide (CO) and other hazardous air pollutants that are associated with adverse health effects. Furthermore, carbon dioxide (CO2) emissions are higher per power output since older engines are inefficient and use very long chain hydrocarbons (bunker fuel). The International Maritime Organization (IMO) estimates that around 3.3% of global human-made CO2 emissions in 2007 emissions were from shipping, and expects them to increase by as much as 72 percent by 2020 unless an urgent response is made.

A significant amount of our national mobile source emission inventory is made up of large marine and their contribution is only predicted to grow. At the current rate, NOx emissions from ships are projected to more than double to 2.1 million tons a year while annual PM2.5 emissions are expected to almost triple to 170,000 tons a year by 2030.

Maritime Pollution Legislation

The North American Emissions Control Area (NAECA) took effect on August 1st, 2012, mandating the use of 1.0% sulfur Heavy Fuel Oil (HFO) or residual fuel oil for ships within 200 miles of the continent of North America. The Emissions Control Areas (ECA) is mandated under the MARPOL agreement. The MARPOL addresses all forms of marine pollution under 6 annexes. Annex VI entered into force 19th May 2005 with the objective to reduce air pollution from ships.

In general, Annex VI applies to all ships 400 GT and above and to all fixed and floating drilling rigs and other platforms. Annex VI contains a set of requirements for survey and issuance of International Air Pollution Prevention Certificate (IAPP) and regulations regarding:

  • Ozone depleting substances from refrigerating plants and firefighting equipment
  • Nitrogen Oxides (NOx) from diesel engines
  • Sulfur Oxides (SOx) from diesel engines
  • Volatile Organic Compound Emissions from cargo tanks of oil tankers
  • Shipboard Incineration
  • Fuel oil quality

Annex VI of the MARPOL treaty is the main international treaty addressing air pollution prevention requirements from ships. It was implemented in the United States through the Act to Prevent Pollution from Ships, 33 U.S.C. §§ 1901-1905 (APPS). Annex VI requirements comprise both engine-based and fuel-based standards, and apply to U.S. flagged ships wherever located and to non-U.S. flagged ships operating in U.S. waters. Annex VI establishes:

  • Limits on NOx emissions from marine diesel engines with a power output of more than 130 kW (175 H.P.). The standards apply to both main propulsion and auxiliary engines and requires the engines to be operated in conformance with the Annex VI NOx emission limits.
  • Limits on the sulfur content of marine fuels.

MARPOL VI requires a study to be completed by 2018, to determine the availability of fuel oil to meet the global 0.5% sulfur limit specified. The Committee tasked a correspondence group to determine the global availability of 0.5% sulfur fuel oil, which should be submitted to MEPC 68 in 2015 and should address:

  • Any new ECA’s that may be established;
  • Projected global economic activity;
  • Use of alternative fuels (such as biofuels, DME and LNG);
  • Availability of abatement technologies; and
  • Actual and planned refinery capacities

These regulations apply to all ships operating at up to 200 nautical miles off U.S. and Canadian shores, and must meet the most up to date standards for NOx emissions and use fuel with lower sulfur content. This geographic area is designated under Annex VI as the ECA.

For example, regulated diesel engines in U.S. flagged vessels must be up to Annex VI NOx standards, demonstrated by their Engine International Air Pollution Prevention (EIAPP) certificate, issued by the EPA. Some particular vessels are also required to have an International Air Pollution Prevention Certificate (IAPP), which is issued by the United States Coast Guard (USCG). Ship operators must also maintain records on board regarding their compliance with the emission standards, fuels requirements and other provisions of Annex VI.

Figure 1. Sulfur Limits for North American Coastal Waters (200 mile)

Table 1. European Emission Regulations

  Regulation Start date Max. NOx Max. PM10 Max. Sulfur
Inland shipping CCR phase 4 1-1-2016 1.5 g/kWh 0.02 g/kWh 0.001%
Coastal shipping SECA phase 3 1-1-2015 N/A N/A 0.10%
Shipping IMO phase 3 1-1-2020 N/A N/A 0.50%


All U.S. flagged vessels are subject to inspection to check for conformity with Annex VI. Non-U.S. flagged ships are subject to examination under Port State Control while operating in U.S. waters. The USCG or EPA may bring an enforcement action for a violation.

Marine Hybrid Drive

A hybrid marine propulsion system could save up to 25% of fuel intake and reduce emissions along with it. A hybrid propulsion system consists of:

  • A diesel engine
  • An electrical generators
  • An electrical storage device
  • A control system and
  • An electric motor that independently or simultaneously drive a propulsion shaft.

Series and parallel hybrid systems are readily available for both commercial and pleasure craft from suppliers, making economic electric propulsion available to boatyards around the world.

  • A series hybrid has the propeller shaft driven by an electric motor. The conventional engine is mechanically decoupled from the propeller shaft and operates as a generator to provide power electrically to the drive system. All full hybrid vehicles run on the electric motor only, as opposed to parallel hybrids.
  • A parallel hybrid allows the propeller shaft to be driven by both the conventional engine and the electric motor. In a parallel hybrid, when the diesel engine generates shaft power, the electric motor acts as a shaft driven generator providing power to meet the vessels hotel loads. Auxiliary generators and optional electrical storage provide power for propulsion through the electric motor during electric only modes of operation.

Hybrid propulsion is available to vessels that have a duty cycle profile with extended periods of low to medium power requirements. Diesel engines have low efficiencies at these load levels and so the energy storage system uses electrical power stored to move the ship, without requiring the diesel engine. Maritime applications include:

  • All workboats (tug boats, barge boats, ferries)
  • Off-shore and platform supply vessels
  • Research and scientific vessels
  • Fishing boats and
  • Leisure and eco-tourism boats (e.g., whale-watching.)

The key operation principle of a marine hybrid control system is choosing the best power and propulsion option for each situation, meeting the needs of the operator. There are multiple system configurations, providing redundancy, by offering alternate sources of power to the vessel.

In a 2010 comparison study by the UC Riverside for the California Air Resources Board (ARB), analyzed the operation of the hybrid tug, Carolyn Dorothy (using a Caterpillar hybrid system) against her conventional sister tug, Alta June. The study found significant improvements in performance, control and noise levels, with 73% reduction in PM, 51% reduction in NOx and 27% reduction in CO2 compared to a standard diesel.

By optimizing current components and operating diesel engines at peak efficiency, marine hybrid systems can grant customers huge savings in owning and operating costs, as well as reducing fuel consumption and maximizing reliability. Using a hybrid system can increase operating efficiencies as well as meet or exceed increasingly stringent environmental requirements.

Introducing the Fuel of the Future: Dimethyl Ether (DME)

For a long time the search has been on to find a fuel for compression engines that is environmentally friendly, stores easily and transported simply. This has been realized in dimethyl ether, a compound that can be used as a direct substitute for diesel. A number of well-established processes mean dimethyl ether can be readily synthesized from abundant natural gas and biomass feedstock. It is benign, evaporates after a spill, burns smoke free with no sulfur and reduced nitrous oxide.

Unlike compressed natural gas (CNG) or liquid natural gas (LNG), most importantly, DME can be used in compression engines, which substantially impacts the potential applications of this fuel over LNG, CNG, ethanol or methanol. It does not require a particulate filter or a selective catalytic reduction (“SCR”) system, so engines are slightly cheaper but much less complicated than standard diesel engines. They are exempt from the filter cleaning and the “add blue” protocols of modern diesel engines.

DME is a clean, colorless gas that is easy to liquefy and transport. DME holds a significant advantage over diesel fuel because it can also be used in turbines, marine applications, fuel cells, refrigeration and heaters. It has the added bonus of being non-toxic and environmentally low risk; accidental spills cannot poison water, it will not sink into the water table and it will not be absorbed by the soil. Moreover, DME can be exported to Europe from East Coast ports in the Mid-Atlantic region, unlike liquid natural gas (LNG).

Figure 2. DME Production Sequence

Dimethyl Ether Engines Today

After decades of investment in DME engine technology Volvo will introduce it to selected markets in North America during early 2018. Their modified 13 Liter Volvo/Mack (VNL 300 DME) diesel engines run on DME at higher compression ratios and make less noise than conventional engines. Running on DME the trucks will eliminate emission of particulate matter, reduces vibration and minimizes nitrous oxides generated by conventional diesel engines. As well as this, the engines can be more efficient, have better wheel-to-wheel costs and reduced emissions when compared to conventional diesels. The fuel costs will also be lower as DME is not derived from oil, but from natural gas, coal or biomass via a constantly improving process

For marine applications, MAN Diesel & Turbine has developed DME engines. The ME-LGI concept is an entirely new system that can be applied to all MAN Diesel & Turbo low-speed engines, either ordered as an original unit or through retrofitting. With two new injection concepts, the ME-LGI concept greatly expands the company’s multi-fuel portfolio and enables the utilization of more low-flash-point fuels such as DME and propane.

The ME-LGI came about due a desire from shipping interests to operate on alternatives to heavy fuel oil (HFO) and diesel. Propane carriers have already operated at sea for many years and many more propane tankers are currently being built as the global propane infrastructure grows. As the transportation mechanism is the similar, the same ship can carry propane and DME. With a viable, convenient and comparatively cheap fuel already onboard, it makes sense to use a fraction of the cargo to power the vessel with a crucial side-benefit of being better for the environment. MAN Diesel & Turbo states that it is already working towards a Tier-III-compatible ME-LGI version, which can easily run on DME.

DME Hybrid Drive: The Worlds Cleanest Ship Propulsion System

Out of concern for the environmental impact diesel fuels and other factors are having on their coastlines the United States and Canada have agreed to make the marine environment a priority. This means that all flora and fauna that exist above and below the waterline are being considered. If DME was used over diesel, the fallout from the disastrous 2014 Galveston Bay spill and the poisonous 2015 Longueuil spill would have been greatly reduced. Current DME engines include the Volvo 13L (450 H.P. or 335 kW) and the MAN 2 Stroke low speed engine. Companies that currently produce hybrid packages include BAE Hybrid Systems, Steyr Motors, Caterpillar, Komatsu and Rolls Royce.

In combining the electrical and mechanical drives, hybrid propulsion can optimize fuel burn in different operating modes. This efficiency can be increased through the use of permanent magnets. Power can also be recouped with propeller wind milling. Harbor tugs, due to their operating profile are ideal candidates for advanced engines plus battery hybrid propulsion, as are many coastal and short sea vessels.

Figure 3. The Stena Germanica has Been Converted to Methanol

Using DME as the engine fuel eliminates all particulate and sulfur emissions and reduces NOx and CO2 emissions to well below guideline amounts. As with the trucking industry, DME can be transported in propane tanks and in using DME based engines particulate filters, selective catalytic reduction and complex exhaust gas recirculation can be bypassed.

For example, it is calculated that for an inland waterway vessel switching to LNG will cost to €500,000 to €1,000,000 more than a traditional ship. Using a DME hybrid system should cost only slightly more than a regular propulsion system. European prices for bunkered LNG are quoted at between €650 and €750/tonne (bunkered in the ship at 48.63 MJ/kg). This price depends on the LNG market price and bunker location. On a dollar basis, LNG ($/€ at 1.3569) costs are 882 $/t to 1018 $/t. With the DME energy density of 28.88 MJ/kg, DME would be equally competitive at 523 $/t to 604 $/t. Although DME will be slightly more expensive than LNG on an energy basis, DME engines are superior to LNG engines and are much less costly. Advantageously, DME does not need to be vented while in port for more than 4 days.

Bunkering Dimethyl Ether

The propane infrastructure in North America moves 25% of the world’s propane supply with both the United States and Canada having well-developed propane infrastructures. This has tremendous capacity to carry a copious supply of DME with high portability via truck and rail. This is a huge plus for DME over LNG or CNG, as there is complete transportation and loading infrastructure already available.

The two most common means for transporting propane across North America from storage facilities or producers to end-users are pipeline and rail. Transporting long distances via truck is often uneconomical. Dimethyl ether can use the exact same rail tanks cars, highway tankers and pipelines as propane.

Dimethyl ether, like propane can be moved west to east across North American. In order for propane and dimethyl ether to be moved by rail, rail car filling and unloading infrastructure (commonly called “racks” or “terminals”) are constructed at both the origin and the destination. Upstream firms generally own facilities located at an originating production plant, while a downstream firm generally owns facilities at the destination.

Dimethyl ether “racks” can be installed at any port area across the globe, ideally easily accessible by rail or pipeline. Current propane marine terminals are a fraction of the cost of LNG terminals, since they do not involve cryogenic technology. For example, propane-shipping terminals exist in Providence, RI. and Newington, NH, while no LNG ports exist on the Eastern seaboard. Moreover, Texas Eastern Pipeline currently supplies propane export ships loading from the Eastern seaboard. Sunoco has developed the Marcus Hook Industrial Complex, on the banks of the Delaware River, as the preeminent eastern marine hub for propane.

Any DME spill would evaporate before it could penetrate and damage an ecosystem, and unlike LNG, there are no greenhouse gas issues with fugitive emissions. Although some current industry groups support LNG, once study groups take into account the use of the existing and growing seaboard propane infrastructure, DME bunkering is an extremely low cost alternative to LNG bunkering.

Recently, a Conoco-Phillips plan for a 23 million gallon propane storage and export terminal was designed and priced at 40 MM$. The storage tanks would have been 138 ft. tall and safely stored propane all year long, without the need for venting. Desfa SA, a Greek natural gas grid operator, invited firms to bid for the design and construction of a third liquefied natural gas storage tank at its Revithoussa LNG terminal facility near Athens. The tank, expected to cost as much as 115 million Euros (150 MM$), will have capacity of 95,000 cubic meters (25.6 million gallons of LNG). On a volume basis, coastal storage of LNG requires 1.56 $/liter of CAPEX versus 0.47 $/liter for DME or propane. This cost does not include the ongoing cryogenic cooling costs required for LNG.

The Best Marine Fuel, Period

Abstract From Report 10: Department of Shipping and Marine Technology, Chalmers University of Technology, Göteborg, Sweden by Selma Brynolf, Shweta Kuvalekar and Karin Andersson:

The combined effort of reducing the emissions of sulphur dioxide, nitrogen oxides and greenhouse gases to comply with future regulations and reduce impact on climate change will require a significant change in ship propulsion. One alternative is to change fuels. In this study the environmental performance of two potential future marine fuels, methanol and dimethyl ether (DME), are evaluated and compared to present and possible future marine fuels.

Methanol and DME produced from natural gas was shown to be associated with a larger energy use and slightly more emissions of greenhouse gases in the life cycle when compared to HFO, MGO and LNG. Use of methanol and DME results in significantly lower impact when considering the impact categories particulate matter, photochemical ozone formation, acidification and eutrophication compared to HFO and MGO without any exhaust abatement technologies and of the same order of magnitude as for LNG.

Methanol and DME produced from willow or forest residues have the lowest life cycle global warming potential (GWP) of all fuels compared in this study and could contribute to reduce the emissions of greenhouse gases from shipping significantly.

Market Factors Supporting the Rapid Growth of Dimethyl Ether

The following market factors have created a favorable investment environment for the ChemBioPower system:

  • North American natural gas prices are lower and supply is higher since the 2008 financial crisis
  • Refined oil products (diesel & petroleum) remain high in price.
  • North American natural gas prices will continue to remain low due to horizontal drilling and hydraulic fracturing.
  • The North American propane infrastructure is robust and universal. Dimethyl ether can be stored in the same infrastructure and moved anywhere across the continent and into existing marine terminals.
  • The price spread between refined oil products and natural gas will provide an ongoing competitive advantage to plants using natural gas as production inputs, and therefore, liquids produced from natural gas will be competitive with oil distillates for decades.
  • Governments will continue to penalize carbon dioxide, sulfur and particulate emissions. Green facilities that reduce CO2 emissions will emerge as an important component of governmental energy policy and will receive preferential treatment (including tax cuts and credits) from national and local authorities.

This information has been sourced, reviewed and adapted from materials provided by ChemBioPower Inc.

For more information on this source, please visit ChemBioPower Inc.


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