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Introduction to Diesel Exhaust Fluid (DEF)

Santhosh Sorab

Diesel Exhaust Fluid (DEF) is the reactant required to effectively reduce nitrous oxides (NOx) used in SCR technology. DEF is injected into the exhaust chamber, where it converts to ammonia (NH3) and carbon dioxide (CO2). NOx emitted from diesel combustion reacts with ammonia and carbon dioxide in the presence of the SCR catalyst, forming harmless water and nitrogen, which is released into the atmosphere. The rate of consumption of DEF vs. diesel fuel is typically less than 10 percent, which in combination with the desired DEF to diesel refill ratio, determines the required DEF tank size.

SCR technology and the use of DEF to reduce NOx have been widely adopted by the on-highway market over the last six to seven years. Major investments to support the on-highway market have created the necessary infrastructure for manufacture, supply, storage and distribution of DEF. The latest round of Tier 4 interim and Final regulations calls for extending these technologies and DEF infrastructure to off-highway applications like Power Generation, Mining, Marine, etc. Some popular brand names for DEF from the on-highway market are AdBlue®, Air1®, Air-Shield™ and TerraCair®. Air-Shield is the DEF supplied by Cummins Filtration.

Manufacturing and wholesale supply of DEF is well established today in the U.S. Several companies such as Cummins Filtration, Yara, KRUSE GROUP and Potash Corp. supply a wide coverage across the nation. DEF distribution capabilities range from 5,000-gallon tankers to 50-gallon drums and totes. Although the use of DEF is similar across all applications of SCR, the “final mile” distribution and on-site storage could vary by application, site and ambient conditions. Various examples of above- or underground DEF tanks, bulk or disposable methods for storage are already available and established in the marketplace. Technologies around DEF temperature management through heated pipes and lines and insulated tanks have also evolved in the past years and are available for the off-highway market to adapt.

In summary, the DEF usage and SCR technologies have been adopted in the on-highway markets, leading to major investments in DEF production, supply, distribution and storage. With the latest emissions regulations extending to off-highway applications, the power generation market has the opportunity to leverage these infrastructures to effectively apply SCR to reduce the impact on the environment.

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