Improved grate plates are designed to produce multiple eddy currents in the absence of clinker and to provide even greater air distribution when overlaid by clinker. Each grate plate has a plurality of upwardly flaring wells which open to the upper surface on which the clinker bed is supported. Within each well is at least one semi-annular slot providing ingress for cooling air from a remote source. The slot extends only partially around the wall of the well such that air is injected into the well somewhat tangentially to the flaring surface to induce cyclonic motion of the air which is enhanced by the flared conic walls of the wells. Accordingly, the energy imparted the air by injection is diminished by the rotational energy dissipated and the cooling air's initial vertical component of velocity is diminished. Therefore, the vertical velocity of the cooling air through the bed is largely determined by the interstitial separation of the granular material and the heat absorbed by the air, with the initial vertical velocity playing only a minor role. The plates may be provided with removable plugs which can be used to close the airway through all or part of the wells of a grate to adjust the delivery of the air in gross over the width of the grate.
