Does Diesel Exhaust Fluid Evaporate?
During SCR, or System Selective Catalytic Reduction, which reduces the nitrogen emissions in diesel engine exhaust, diesel exhaust fluid (DEF) is meant to become a vapor. DEF is made of deionized water and a nitrogen compound called urea. When it is injected into the exhaust from the diesel engine, the heated water evaporates and decomposes the urea to create ammonia.
Next, it contacts a copper catalyst, producing water and nitrogen. This process eliminates 93 percent of the nitrogen oxide, significantly reducing the environmental impact from the engine exhaust.
DEF's tendency to evaporate becomes a problem if it happens before the reduction process begins. DEF should contain 67.5 % deionized water and 32.5 % urea. If evaporation happens while in storage, the percentage of urea increases. This causes problems with SCR, which needs the proper proportion of water to do its work. It also causes DEF to freeze at higher temperatures. The values are not lost when DEF is frozen. Once it is completely thawed, it is useable again. Like water, DEF expands when frozen. This can cause broken containment units and pipes that result in wasted product. To avoid potential issues, you should ensure DEF remains in liquid form at all times.
How To Prevent Evaporation
The first step in preventing evaporation is to monitor the urea concentration of your DEF. You can test your DEF on site with a portable Refractometer. This equipment measures the breaking index of fluid with light in accordance with the standard as defined by (ISO 22241). If you find even a slight change in the urea concentration, investigate the tank immediately for irregularities. You may be able to prevent further evaporation or contamination from occurring and save the product before it's too late.
It is also important to make sure that the fluid is sealed off from the outside world. The better sealed your containment units are; the less likely that water vapor will be able to escape. This also prevents outside contaminants from getting into the stored DEF and spoiling it.
Evaporation, of course, is the result of overheating, so be sure to monitor the temperature of your DEF supplies. Many DEF storage systems come with temperature controls and thermometers. Use these instruments to ensure that the temperature never drops below 32° F. The most effective way to prevent overheating is to store the DEF inside or underground. If you decide to store it outside, be sure to place your containers underground or under a shelter.
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9 年Glen this is another great post regarding an issue that needs more consideration. Three years ago I introduced the idea that DEF dispensed from IBC's would benefit from a collapsible & disposable bladder (similar to wine in a box concept). This bladder could be supported by a modified IBC to insure product purity from airborne contaminates by preventing air inclusion during incremental dispensing. This disposable bag would insure traceability by preventing batch mixing (which occurs each time an IBC is topped off ) and would eliminate the evaporation/condensation cycles that also has an effect on the delicate 67.5%-32.5% water to urea ratio. The IBC drum tote and frame was a brilliant strategy in the infancy of DEF and made bulk distribution and storage possible for the fledgling SCR/Diesel markets and end users. Waiting for underground storage infrastructure would have stifled the concept from ever taking off. The only draw back was the rigidity of the vessel which was not cost effective to return for factory refill and lead to multiple on site refillings, which can and does lead to compromised product purity as the industry continues to grow. The IBC is still of great value to the market, and the bladder concept should be embraced by the industry for a multitude of good reasons. I would prefer these smaller bulk containers over a UST for this vulnerable product (DEF) Consider this: There is no additive that can be introduced to DEF or AdBlue without changing the chemical make up, which voids the certification and purity of the product. A large underground vessel that holds a product made of 67.5% water is a potential breeding ground for microbial and other forms of contamination. Bigger is not always better. Glen I hope your article sparks some open dialog within the industry.