Abstract The present invention relates to an apparatus for carrying out chemical and physical processes, wherein flowable substances are mixed together, comprising a vertical, cylindrical vessel with inlets and outlets, as well as a central shaft and radial agitator blades arranged on the said central shaft and extending close to the wall. In this context, viewed in the peripheral direction, the agitator blades are curved and are combined in pairs of agitator elements one above the other to form groups, the blades of one element of the group being curved in a radially concave manner and the blades of the other element being curved in a radially convex manner. Fig. 2