Conversion of fuel nitrogen in a dual fluidized bed steam gasifier

Abstract

During gasification, fuel nitrogen is converted into gaseous species, such as NH3, HCN and others. Several materials are gasified in the dual fluidized bed gasification pilot plant in order to assess the conversion of fuel nitrogen. The fuels tested in this study are different kinds of waste wood, bark and plastic residues. The nitrogen content of these materials ranges from 0.05 to 2.70wt.-%. Detailed measurements of NH3, N2, HCN, NO and nitrogenous tars are carried out during the test runs. It is found that the vast majority of nitrogen is present in the form of NH3. There is a linear relationship with high accuracy between fuel nitrogen and NH3 in the producer gas. The nitrogen balance of the dual fluidized bed gasification system shows the distribution of nitrogen in the two coupled reactors of the gasification system. It is assessed that nitrogen conversion occurs almost exclusively in the gasification reactor. Only minor amounts of nitrogen are found in the char, which is transported to the combustion reactor and is converted to NO there. This result provides important information for the gas cleaning requirements when nitrogen-rich fuels are gasified.