
The straight grate consists of a stationary furnace with a moving set of pallet cars travelling through the furnace on a set of rails. The pellets are fed onto the cars and travel along the furnace where they are dried, heated and cooled.
Because the refractory is stationary and not subjected to rotation and abrasion as the rotary kilns refractory’s are, it can be much thicker and keep more heat in the furnace.
The air flow and machine layout is designed to properly indurate all the green pellets and still protect the pallet cars from the high temps of the furnace. To do this, the cars are lined with high temperature stainless steel bars and the sidewalls are also made of high temperature stainless steel. Then the cars are lined with a 70-100mm thick layer of already fired pellets called the hearth layer. These features allow the full indurating temperature to reach all the unfired pellets even the bottom layer without damaging the pallet cars.
The pallet cars are pushed through the furnace by a large sprocket where they are loaded with pellets, then after the pellets are discharged, the pallet cars go around a sprocket at the end of the machine and return to the drive sprocket on a return set of rails.
The cars travel through different temperature zones where the pellets are dried, then pre-heated, then indurated, then finally cooled. There can be multiple burners in some of the zones to allow control of the temperature profile as the cars travel along.