However, it showed that probably due to clearances in grate sweeping mechanism the travel speed of burning fuel decreased significantly and burning fuel began to accumulate on the grate preventing the primary air access to upper layers of fuel. The length of grate sweeper run had to be lengthened again. It was experimentally found out that proper run length for grate sweeping with two minutes period is 12 mm. After the mentioned changes of the grate sweeping algorithm and adjustment of the grate sweeping mechanism the peaks of quantities were practically completely eliminated (Fig. 2, on the right).