The automotive urea AdBlue, also known by the generic name Diesel Exhaust Fluid (DEF), is the registered trademark for AUS32 (Aqueous Urea Solution 32.5%). The market of this urea-based, diesel fuel emissions lowering agent has not matured and AdBlue suppliers can expect a year-on-year growth of 40-50% in the coming years.
AdBlue is stored in seperate tank on the vehicle. The usage of AdBlue lies at 3 to 5% of the diesel usage. The oxides of nitrogen formed at combustion are converted into harmless elementary nitrogen and water. This method is called Selective Catalytic Reduction (SCR). As the name AUS32 suggests, AdBlue is made by using urea mixed with demineralized water, resulting in a 32.5% aqueous urea solution.
AdBlue suppliers need to control the quality of each produced batch, which are typically supplied with a quality certificate. In-line concentration measurements are applied in order to ensure the high quality of the product.
A stream of concentrated urea is blended with demineralized high purity water in a mixer. The process temperature is 25-50°C (77-122°F) and the urea mix is cooled after the mixer. The K-Patents Process Refractometer PR-23-GP is mounted in the outlet pipe to control the concentration of the urea mix. The concentration is maintained between 31.8 and 33.2% bw (32.5% optimum) with automatic adjustment of the demineralized water feed.
The lowest freezing point for urea is around -11°C (12°F) at the concentration of 32.5% by weight. The K-Patents refractometer sensor provides an output signal for the control valves of concentrated urea and demineralized water. The urea solution AdBlue 32.5% is transferred to the storage tanks.
The dual connectivity of the two sensors with one transmitter reduces the investment costs, when two or more measurements are needed.