Kinetics determination of calcium carbonate precipitation behavior by inline techniques

• FBRM can determine the rate of CaCO3 formation.
• FBRM provides a real time measurement of the dimension and number of crystals.
• FBRM has proven to be a sensitive method for monitoring the initial stage of process.
• The effect of concentration and temperature on precipitation can be determined inline.
• Supersaturation and temperature have a significant effect on the scale rate.

Calcium carbonate, CaCO3, presents a big problem in oil and gas industry. Scaling in pipes leads to decreases in pressure drops and often to complete blockage. On heat exchanger, it reduces the heat transfer. It could lead to unstable operation which may result in unscheduled shutdown.Precipitation of calcium carbonate is a prerequisite for the deposition of calcium carbonate crystals on an external surface. Hence to understand the scaling process, it is necessary to understand the calcium carbonate precipitation kinetics. This could be achieved through fully controlling the precipitation and deposition processes.Calcium carbonate precipitation is widely studied using various methods. However, the techniques used were based on either solution side information to determine precipitation kinetics or offline size analysis to find growth rate constants. In the present work inline in situ technique based on FBRM (focused beam reflectance measurement, Mettler Toledo) gives direct measurement of number of crystals. The inline image technique by PVM (particle vision and measurement, Mettler Toledo) gives accurate induction period measurements and nucleation kinetics. The method of moments was utilized to determine the crystal size and hence the growth rate.Therefore, a number of experiments were conducted to obtain reliable and reproducible conditions for consecutive precipitation and deposition processes. The data from the FBRM and images from the PVM provided information about the particle count and size. The experiments were conducted in a closed system to reduce the effect of impurities.The effects of the solution composition on the spontaneous nucleation and the crystal growth rate have been examined. From the measurements of the crystal growth kinetic data, the crystal growth rates were estimated which is found to be logarithmic function of calcium ion concentration.Also, the results presented in this paper are for reference or blank conditions only, i.e. no external force or agent was applied during the process of CaCO3 precipitation. Consequently, these reference experiments were used for comparison with prevention methods in the future.

Total number of chord counts versus calcium ion concentrations at 25 °C after 60 min.Figure optionsDownload as PowerPoint slide