The basic idea of the gasifier concept is to divide the fluidized bed
into two zones, a gasification zone and a combustion zone. Between these
two zones a circulation loop of bed material is created but the gases
should remain separated. The circulating bed material acts as heat carrier
from the combustion to the gasification zone. The priciple is shown
graphically in Figure 1.
Fig. 1. Basic idea of the gasification process.
The fuel is fed into the gasification zone and gasified with steam. The gas produced in this zone is therefore nearly free of nitrogen. The bed material, together with some charcoal, circulates to the combustion zone. This zone is fluidized with air and the charcoal is partly burned. The exothermic reaction in the combustion zone provides the energy for the endothermic gasification with steam. Therefore the bed material at the exit of the combustion zone has a higher temperature than at the entrance. The flue gas will be removed without coming in contact with the product gas. With this concept it is possible to get a high-grade product gas without use of pure oxygen. This process can be realized with two fluidized beds connected with transport lines or with an internally circulating fluidized bed.