Experimental study about plugging in confined impinging jet mixers during the precipitation of strontium sulfate

• Confined impinging jet mixers (CIJM) were intentionally plugged by precipitation.
• Precipitation of strontium sulfate is suitable for plugging experiments.
• During precipitation, pressure drop of three different CIJM types was monitored.
• Plugging affinity was judged by mean normalized pressure drop and its deviation.
• By treating a Y-mixer with ultrasound, influence on plugging was investigated.

Precipitation in industry is frequently used for the manufacturing of fine particles. Stirred tank reactors are used for the production of these precipitates in most processes. Confined impinging jet mixers (CIJMs) are alternative precipitation apparatuses. Compared to stirred tanks, their use enables the production of higher product quality because of more advantageous, well-defined mixing conditions. Nevertheless, CIJMs have not yet found widespread application in industrial precipitation processes because of their tendency to plug. Fluid dynamic behavior of CIJMs depends on their geometry and is of importance for its plugging affinity. The plugging affinity is defined as the ratio between the pressure drop during precipitation and pressure drop during operation under non-precipitating conditions. In this paper, the plugging affinities of different CIJMs are investigated for the case of strontium sulfate precipitation. Strontium sulfate is known for its high plugging affinity. Hence, it is suitable for mixer plugging experiments. A search for conditions causing plugging is made by carrying out experiments at various flow rates and degrees of supersaturation. Three mixer types of similar basic dimensions are compared. Furthermore, the influence of ultrasound on the plugging affinity is investigated. It is found that ultrasound has some capability of protecting CIJMs against plugging.