How to Deal With DEF

December 5, 2015 02:43 AM

Store and transfer Diesel Exhaust Fluid correctly to optimize its performance

Final Tier IV emission standards are the last step in a decades-long transition to dramatically reduce exhaust emissions from diesel engines. The evolution of diesel engines to meet Tier II, Tier III, then Interim Tier IV standards led some farmers to drag their feet on adding Diesel Exhaust Fluid (DEF) storage and transfer systems on their farms.

“This is Final Tier IV. This is the way many diesel engines are going to be fueled from now on,” says Joe Gannon, sales rep for Diamond Oil Company, Des Moines, Iowa. “It’s time to figure out how to properly store and transfer DEF on farms.”

DEF is a blend of purified liquid urea and deionized water that’s injected into the exhaust systems of specially-equipped diesel engines. The non-hazardous solution helps those engines meet the Environmental Protection Agency’s strict Final Tier IV exhaust emission standards.

Proper storage and transfer of DEF is critical to avoid damage to expensive components on Final Tier IV diesel engines. 

“Dirty DEF will plug the special filters in DEF systems on tractors,” says J.J. Hoyle, also with Diamond Oil Company. “Those filters can cost hundreds of dollars to replace.”

To grasp how “clean” DEF must be kept, consider low-sulfur diesel fuel used in Tier III and newer engines is filtered to 2 microns. Fuel-grade DEF is filtered to 1 micron. For reference, a micron is one-millionth of a milli-
meter. Large bacteria and microbes range in size from 1 to 5 microns.

Not only must DEF be clean, it must be chemically correct.

“DEF made with poor-quality urea or unpurified water can have contaminants that cause a chemical reaction and damage catalytic converters,” Hoyle says. “Catalytic converters can cost $12,000 to $20,000 to replace.”

The challenge in developing on-farm DEF storage and transfer systems is two-fold. The first step is determining how much DEF an operation will consume and how much storage capacity is necessary. The second step is identifying storage tanks and transferring equipment that maintains DEF cleanliness and quality.

“People tend to underestimate how much DEF their equipment will use,” Gannon says. “I had a customer rent a 500-hp tractor for disk-ripping, and he initially wanted to just buy 2½-gal. jugs during the rental. He ended up going through seven 55-gal. drums of DEF during the six-week rental. 

“The harder you pull a Final Tier IV engine, the more DEF it uses,” Gannon adds. “That sounds expensive, but DEF doesn’t cost that much, and [using DEF] really improves the power of the machine and the efficiency of how it uses diesel [fuel].”

Because DEF is highly reactive to many metals, it must be stored in stainless steel, polypropylene or high-density polyethylene (HDPE) storage tanks. All pumps, valves and fittings must be DEF-compatible and used only to transfer DEF.

DEF’s physical properties add to the challenge of providing adequate storage. The 32.5% blend of purified urea and deionized water in DEF freezes at 12°F. Diesel engines that require DEF come from the factory with built-intank heaters to prevent DEF from freezing during use in cold conditions and thaw frozen DEF at start-up when machines have been sitting.

“You can freeze and thaw DEF over and over, and it won’t affect its performance,” says Lee Purvis, sales rep for Blue Sky-brand DEF. “But for maximum quality control, you might want to consider heated storage tanks or tanks in heated buildings if you’re going to be using DEF below 12°F.” 

DEF has a shelf life of 24 months, but prolonged exposure to temperatures above 75°F can reduce shelf life. Fresh DEF has a slightly pungent smell of ammonia. After extended exposure to temperatures above 75°F, the ammonia scent grows stronger, indicating nitrogen has vaporized, changing the urea-to-water ratio of the product.

Degraded DEF isn’t harmful to engines, but it’s economically inefficient. Computers on Final Tier IV 
engines constantly monitor the amount of nitrogen in DEF passing through their Selective Catalytic Reduction (SCR) system and increase or decrease the rate of DEF injected into the SCR system to provide adequate nitrogen levels to control exhaust emissions. As a result, engines consume higher rates of “stale” DEF to maintain the correct dosing rate, increasing their operating cost per hour.

While many farmers use 55-gal. barrels or 250-gal. plastic “totes” of DEF before committing to permanent storage and handling systems, some are investing in larger systems so they can buy in bulk.

“A lot of guys are buying a 1,000-gal. poly tank to store DEF, then building a cheap shell of a building around it to keep the sun off,” Hoyle says. “They add a heater on a thermostat so they’ll be able to pump it in cold weather.”  

Fast Facts About DEF

  • Diesel Exhaust Fluid (DEF) is a 32.5% blend of purified urea in deionized water.
  • DEF freezes at 12°F. Freezing and thawing doesn’t affect performance. DEF has a 24-month shelf life.
  • The nitrogen in DEF begins to volatilize into ammonia gas when exposed to sunlight or temperatures above 75°F. Once volatilized, it will not go back into suspension, and the percentage of urea in the product decreases to less than the optimum 32.5%
  • Water can evaporate from DEF storage containers left uncapped or vented to the atmosphere, resulting in an overconcentration of urea in the remaining fluid. 
  • Final Tier IV engines require DEF to be filtered to 1 micron to prevent filters in their Selective Catalytic Reduction (SCR) systems from clogging. (As a reference, microbes and bacteria range in size up to 5 microns.)
  • DEF reacts corrosively with many metals. Storage tanks and transfer equipment must be stainless steel, polypropylene or high density polyethylene (HDPE).
  • DEF is water-soluble. Spilled DEF can be diluted/cleaned up with water. The diluted liquid is essentially liquid nitrogen fertilizer.
  • “Home-brewed” DEF made from fertilizer-grade urea and well-water contains contaminants and chemicals that can clog filters and damage the catalytic converters on engines using SCR to control exhaust emissions.
  • According to John Deere engineers, as little as 1 tsp. of impurities in a 4,800-gal. transport trailer can disqualify a load of DEF for use in SCR engines.


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