Miles Kid

Salicylic acid is produced through Kolbe - Schmitt process - using phenoxide + CO2 -> sodium salicylate and then subsequent acidification to give acid. In these steps I need to mix a powder sodium salicylate at 150 Deg C with Water at 25 deg C to get a slurry. What kind of mixer can I use for the same ? I can use a stirred tank but to calculate the residence time I would need to do pulse experiments, which is not possible to do before hand.