Combustion and heat transfer characteristics in a combustion chamber of a 13-step grate wood pellet firing boiler

A grate-firing boiler was developed for wood pellet fuel, and its combustion and heat transfer characteristics were tested. The first prototype revealed problems with fuel delivery and residence time. To solve these problems, we quadrupled the number of grates and developed the second prototype with a baffle; however, the volume significantly increased in the second prototype. By examining the space usage in the second prototype, we designed the third prototype with inclined grates, which reduced the number of grates by 25 % and reduced the volume by 20 %. The experimental results show that the third prototype had similar combustion performance to the second prototype with the reduced volume. Furthermore, some grates remained unused in the combustion, and a recirculation flow appeared in the CFD results, which suggests the possibility of additional design improvements.