Effect of Equivalence Ratio on Partitioning of Nitrogen during Biomass Gasification

Gasification of biomass can produce process heat, electricity, liquid fuels, and chemicals without use of fossil fuels. Utilization of biomass and waste products for energy and fuels enables use of energy sources that are renewable, secure, and enable global climate change mitigation. Most feedstocks suitable for gasification contain small amounts of fuel-bound nitrogen (FBN), which converts during gasification to five major products: hydrogen cyanide (HCN), ammonia (NH 3 ), char-bound nitrogen (char N), tar-bound nitrogen (tar N), and diatomic nitrogen (N 2 ). Of these products, NH 3 and HCN are of the greatest concern because they primarily convert into NO x species if the syngas is burned for heat or power applications. They are also potent catalyst poisons during chemical synthesis. Yields of NH 3 and HCN from FBN vary broadly as a result of differences in feedstock properties and gasification conditions. To better understand nitrogen chemistry during gasification, switchgrass was gasified in a bubbling fluidized bed gasifier at 750 °C, while the equivalence ratio (ER) was varied from 0 to 0.4. The results demonstrated that major portions of the FBN can remain bound in the char and tar. This nitrogen can be released to the gas phase as the ER increases, leading to increased yields of NH 3 and HCN.