At the last New England Fuel Institute (NEFI) show in Providence, R.I.,Boston Steel, a division of Tremcar USA, exhibited a Diesel Exhaust Fluid (DEF) unit. It was specially designed to carry DEF, a liquid, aqueous urea solution that consists of 32.5-percent urea and 67.5-percent deionized water.
SCR Lowers NOx Emissions
To understand the necessity for developing new types of tank trucks, manufacturers need to understand the product being carried. This particular product is standardized as AUS 32 (aqueous urea solution) in ISO 22241. It is a consumable in selective catalytic reduction (SCR) that lowers NOx concentration in the diesel exhaust emissions from diesel engines.
Safer for the environment, new diesel engines are built to use this type of exhaust. These engines can be run with a lean burn air-to-fuel ratio to ensure the full combustion of soot and to prevent exhausting unburnt fuel.
The excess air necessarily leads to generation of nitrogen oxides (NOx), which are harmful pollutants.
Selective catalytic reduction is used to reduce the amount of NOx released into the atmosphere. DEF from a separate tank is injected into the exhaust pipeline, where the aqueous urea vaporizes and decomposes to form ammonia and carbon dioxide.
Within the SCR catalyst, the NOx is catalytically reduced by the ammonia (NH3) into water (H2O) and nitrogen (N2). Both are both harmless, and these are then released through the exhaust.
When it is injected into the hot exhaust gas stream, the water evaporates and the urea thermally decomposes. As companies renew their fleets, the demand for this product will increase.
DEF Corrosive for Tank Trucks
DEF is very corrosive in comparison to all fuel products carried in tank trucks. It must be transported in stainless-steel tanks. The piping is stainless steel or plastic. The pump, the meter system and the emergency valves are stainless steel. The hose and nozzle are plastic. In terms of capacity, the No. 2 fuel used for home heating weights 7.2 pounds per gallon. DEF weights about 9 pounds per gallon.
If we include the weight of stainless steel, much heavier than aluminum, this results to an increase of the GVW of the chassis to handle the load. The capacity of the tank on exhibit was 3,600 USG. This unit was built under 55 000 pounds to respect the federal law on the rear axles and GVWs.
Boston Steel can build larger capacities, but when they are more than 55,000 pounds, haulers have to pay the federal heavy highway vehicle use tax. Nevertheless, haulers could choose to build larger tanks on heavier rated chassis.