The grate includes a number of grate lanes arranged side by side between a left and a right side section, neighbouring lanes being connected by a midsection and including a lane section having a number of pivotal grate shafts carrying grate bars. Each midsection includes an upper relatively narrow housing section arranged between grate bars of neighbouring lanes and a lower relatively broad housing section protruding under grate bars of said lanes. The upper housing section of each midsection encloses bearings for grate shaft ends of neighbouring lanes. At least one midsection includes a drive mechanism for pivoting back and forth neighbouring grate shafts in opposite rotational directions and a synchronising mechanism of at least one lane section. An actuator of said drive mechanism and said synchronising mechanism are located in the lower housing section of said midsection.