Diesel Exhaust Fluid, DEF, is a mixture of urea at 32.5% and deionized water at 67.5%. It is used in vehicles with heavy duty diesel engines to control NOx emissions. The U.S. NOx emission standard of 0.20 grams per brake horsepower hour (0.2 g/bhp-hr) was mandatory for all diesel engines after 2010 with an allowable phase-in period from 2007 to 2009. While there were several options available for diesel engine manufacturers,the one adopted by the medium and heavy-duty truck market to meet this standard was selective catalytic reduction (SCR) technology. SCR allowed diesel manufacturers to tune their engines to improve fuel efficiency and increase torque.
SCR technology was well known for reducing NOx emissions from the combustion gases of coal-fired and gas-fired power plants. The system applied to the exhaust of diesel powered vehicles is illustrated by the following:
As shown above the exhaust gases from the diesel engine first pass through a filter which captures any particulate matter. The same 2010 regulation that established the 0.20 g/bhp-hr NOx standard also set a particulate matter (PM) standard of 0.01 g/bhp-hr. The DEF urea mixture is injected into the exhaust gases as they enter the next stage which contains several different catalysts. First a hydrolysis catalyst converts the urea into ammonia (NH3) and carbon dioxide (CO2). Then over an SCR catalyst, the released NH3 reacts with the NOx to produce nitrogen and water. Any residual ammonia is destroyed over a final oxidation catalyst. The exhaust gases leave the vehicle’s tailpipe essentially PM and NOx free. SCR technology was first used by Nissan Diesel in 2004 to meet Japan’s NOx emissions standards which at that time were the strictest in the world.
Interestingly, NO and NO2, the two nitrogen oxides comprising NOx emissions, that form at the high temperatures of fossil fuel combustion, are not greenhouse gases. So why is it important to control and reduce NOx emissions? Nitrogen oxides contribute to the formation of ozone through their reaction with volatile organic compounds (VOCs) in the presence of sunlight. Breathing ozone triggers a variety of health problems. NOx emissions also contribute to the formation of particulates and acid rain.
Nitrous oxide, N2O, on the other hand, is a greenhouse gas and is the third largest contributor to global warming after carbon dioxide and methane. (See my Feb. 24, 2016 blog, “U.S. is Making Progress in Reducing Methane Emissions.”)
Nitrous oxide, also known as “laughing gas” has a global warming potential (GWP) of 310 and results from both natural and human sources with natural sources accounting for 62% and human sources only 38%.
As shown above, fossil fuel combustion and industrial processes contribute only 10% of the human sources or less than 4% of the total nitrous oxide emissions. Agriculture and soils under natural vegetation are the largest contributors of N2O. The microbial processes of nitrification and denitrification from soil bacteria produce N2O which is released to the atmosphere.
Diesel Exhaust Fluid is produced and marketed by many different companies under different brand names, many of which have “Blue” in the title: AdBlue®, BlueDEF, BlueSky, NOxBlue. One or more of these DEF products are available in the convenience stores at thruway and highway rest stops. Truck drivers need to refill their onboard DEF tanks on a periodic basis. For heavy duty and off-road vehicles the replenishment time is dependent upon several factors such as operating conditions, hours in use, miles traveled, and load factors. For light-duty vehicles, refill is typically done at the same time as the recommended oil change.
Based on a recent study by Integer-Research OCI N.V.’s Iowa Fertilizer Company forecast the North American DEF market to grow at an annual average rate of 17 percent over the 2016 to 2021 time period. (see the below figure from OCI N.V.s March, 2017 Investor Presentation.)
Based on the above projections, the 2021 North American demand for DEF should reach 1.2 billion gallons. At 32.5% the amount of urea required for the North American market in 2021 is estimated at close to 2 million metric tons, about 30% of the urea demand for fertilizer.
The U.S. is not the only country with NOx emissions standards. Other countries, such as Japan, China, Brazil, India and the European Union also have adopted stringent NOx standards. According to a recent report by TechSci Research, “Global Diesel Exhaust Fluid (Adblue) Market By Application, By Storage Solution, By Region, Competition and Opportunities, 2012-2022,” the global demand for DEF should reach 4 billion gallons by 2022.
Demand may be even greater if California’s optional NOx standards are adopted by other states. In October 2014, California’s Air Resources Board released a program for heavy-duty engine manufactures to choose to certify their engines to three optional lower NOx emissions standards: 0.1; 0.05; or 0.02 g/bhp-hr. No change for other pollutants. The preferred option for meeting any or all of the lower standards is enhanced SCR technology. Thus if these stricter standards eventually go into effect, urea consumption for DEF fluids will likely increase faster than the above projections.