A cross-draft fixed bed gasifier variant of a so-called co-current fixed bed gasifier where the fuel is fed from the top and the air from the side. The difference from the downdraft version is the product gas outlet on the side opposite of the air inlet. A schematic is shown in Figure 6.6.

The air is introduced in the reactor at high velocity creating a hot zone, also called the hearth, with a temperature above 1500°C due to combustion of part of the char. The remaining char is gasified to CO in the subsequent zone. The heat from the combustion is conducted to the pyrolysis zone where the fresh biomass is pyrolyzed when passing. The cross-draft is generally used for small-scale units and allows for a simple reactor construction due to the small combustion zone and the insulating effect of the fuel and the ash. Due to the high temperature, the concentration of tar in the product gas is low, as shown in Table 6.2, and therefore a fairly simple gas cleaning system can be used after the reactor.