Embodiments of apparatuses and risers for reacting a feedstock in the presence of a catalyst and methods for installing a baffle in such risers are provided. In one example, a riser comprises a sidewall that defines a cylindrical housing surrounding an interior. A plurality of baffle assemblies is releasably coupled to the sidewall and each comprises a baffle section. The baffle sections together define a segmented baffle ring extending inwardly in the interior.