The concentration of urea solution is one of the key factors in SCR reduction system. The concentration of urea solution is generally 31.8-33.3/33.2% according to the domestic and foreign standards.
Chemical reagent method
Indirect method, chemical reagent method is to convert the sample into hexamethylenetetramine salt and ammonium ion after titration with alkali. GB / T696 and the local standards of Beijing and Shenzhen all use this method. This method has less investment, but the operation is tedious and time-consuming. Users need to have some experience in chemical test operation, and can use formaldehyde, sulfuric acid and other solvents, which is harmful to operators and not environmentally friendly. It
J. Kjeldahl method
Indirect method, Kjeldahl nitrogen method is a general nitrogen content detection method, through Kjeldahl nitrogen analyzer to determine nitrogen content, and then converted to urea content. This method takes a long time, and it's not sure where the nitrogen comes from, for example, if melamine is added to the urea solution, the nitrogen content will increase.
Refraction method
The concentration of urea solution was calculated indirectly by measuring the refractive index of standard urea solution and sample solution. Refractivity itself is also the index of vehicle urea solution. The domestic and foreign standards generally stipulate that the refractive index is between 1.3814 and 1.3843. Similar to density, the refractive index of urea solution corresponds to the concentration at a certain temperature. Measuring the refractive index is helpful to verify the concentration and quality of vehicle urea solution, but refraction is not a direct method. If the solution contains other components, it will affect the refractive index.