Reactor chamber in a fluidized bed reactor

A fluidized bed reactor comprising a reactor chamber defined in part by vertical walls formed by a plurality of adjacent substantially vertically oriented heat exchange tubes joined together by substantially vertical connecting portions extending therebetween which create natural flow paths for particles in the fluidized bed reactor, a lower portion of said walls having a refractory lining applied thereto, said lining having an upper edge formed with a plurality of longitudinally oriented grooves therein in substantial vertical alignment with said vertical connecting portions, said grooves being formed in said upper edge and inclined toward a lower part of said reactor chamber to facilitate downward flow of the particles and to minimize turbulence at the upper end of the refractory lining where said tubes and said refractory lining are joined.