The faith of fuel bound nitrogen in a solid fuel chemical looping combustion process over oxygen carriers of ilmenite and Fe2O3 supported on Mg-ZrO2
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2016
The formation of NOx from fuel bound nitrogen is of importance to the design of chemical looping combustion (CLC) power plants. This work studies to what extent different nitrogen containing species are formed in solid fuel CLC. The influence of combustion environment (steam level and temperature) and type of oxygen carrier on the formations of nitrogen containing species is mapped. It is also desired to achieve data that can be used to assist partly the selection and the evaluation of CO2 storage sites. The study has been carried out in a lab scale fluidized bed reactor using iron oxide and ilmenite as bed materials. The solid fuel is a wood char containing 1.9 wt.% of nitrogen on dry and ash free basis. Steam is used to gasify the solid fuel in the fuel reactor. The measurements show presence of both nitric oxide (NO) and ammonia (NH3) in the outlet gas stream from the fuel reactor. The inlet concentration of steam and the reactor temperature are both important to formation of NO and NH3. As expected, high inlet steam fractions increases fuel conversion at all temperatures for both oxygen carriers tested. Interestingly, high inlet steam fractions leads to increased NO formation in presence of iron oxide, but to decreased NO formation with ilmenite. This might be explained by the competing reactions between the oxygen carrier and CO and NO and CO in the gas phase. It is concluded that both NO and NH3 are formed however substantial amount of N2 are coming along in the process. In conclusion, the choice of oxygen carrier and operating conditions of chemical looping combustion is crucial to the faith of the fuel bound nitrogen introduced to the process.