A novel calibration method for online determination of nitrogen- to-carbon ratio in urea synthesis

Abstract Online monitoring of urea synthesis plant performance is critical for optimizing production efficiency and product quality. This aim is achieved with accurate ratio control of reactants, which is known as the N/C ratio. The conventional techniques require complex calibration due to harsh process conditions (high temperature, high pressure, corrosive media). This research presents a non-contact, rapid, economical calibration method based on the gamma radiation technique. The calibration for this method is established by using process flow diagram (PFD) data to identify four representative calibration points. These points correspond to fluid compositions similar to the reactor outlet stream, each with a known density. Process water serves as the reference standard, typically applied during plant shutdown periods. By calculating and simulating the expected count rates using Monte Carlo code (MCNPX) for different compositions, a reliable calibration curve was generated. The calculated correlation coefficient for the presented techniques was 0.9995, confirming a high degree of correlation of the data. Also, the mean relative error percentage (MRE%) between the calibration curve based on the MCNPX code and experimental results based on the oscillation technique was measured less 1.55%. Thus, the acquired calibration curve based on the MCNPX code can be replaced with the calibration curve based on the oscillation technique. This innovative approach provides real-time insight into reactor internal conditions and reaction rates, without the need for invasive sampling.