Experimental Study of Fuel Pellet Combustion

Abstract

Ash slagging causes serious problems in combustion equipment with fuel pellets having high ash content like peat pellets. To reduce ash clinker formation, some additives and flue gas recirculation were used. Experiments were carried out using peat pellets having moisture content of 17.4% and ash content 7.8%. A primary study in which the effectiveness of additives was studied was carried out in the laboratory scale tube furnace. Flue gas recirculation experiments were carried out in the 50 kW pilot pellet burner.

The results show, that high ash slagging can be effectively avoided with certain additives to fuel. Additives can be easily mixed with raw material during fuel pelletizing. Additives change the relation of basic and acid oxides of the ash.

Kaoline and building lime were used. They both raised effectively ash fusion temperatures. The use of additives raises the fuel price about 5 %.

Also flue gas recirculation reduces effectively combustion temperature and thus avoids ash slagging. Heat transfer in the combustion chamber changes from radiant heat transfer more to convectional heat transfer. The use of recirculation reduces the luminosity of the flame, reduces flame temperature and raises the amount of flue gas volume in the combustion chamber. The fuel burn rate decreases quite rapidly when recirculation is used. For that reason equipment must be dimensioned larger.