PURPOSE: To improve the dispersibility of an additive prior to premixing, and to improve the stability of produced COM, by placing a static in-line mixer before a mixing tank, and adding an additive at the inlet-side of the mixer.

CONSTITUTION: Unloaded COM20 is stirred in the collect tank mixer 14 to prevent the precipitation, and transferred through the pump 3 and the flow meter 4 to the in-line static mixer 8. Immediately before entering into the static mixer 8, the COM is loaded with the additive 23 from the tank 11, dispersed thoroughly by the mixer 8, and stirred in the mixing tank 5 with the stirrer 15 to obtain the loaded COM21. The loaded COM is pumped with the pump 6 to the flow meter 7, redispersed with line mixer 9, and stored in the storage tank 10 as the COM product 22.