NOx Emission in In-line Low-NOx Calciners - A Theoretical Study

Abstract

Abstract - The present contribution is a continuation of our endeavor in developing mathematical models for In-Line Low-NOx calciners. The objective of the present work is to obtain new information about NO formation and reduction in In-Line Low-NOx calciners. So, the influence of the air combustion mixing into the main flow, limestone feed position, limestone feed ratio in the reducing zone, air combustion temperature and fuel type on the level of NO emission in the in-line low-NOx calciners was investigated. The analysis was carried out using a heterogeneous mathematical model based on non-isothermal diffusion-reaction models for char combustion and limestone calcination. The mixing in the oxidizing zone was modeled using a modified Zwietering approach, which supposes that combustion air is gradually mixed into the sub-stoichiometric suspension leaving the reducing zone. The analysis shows that the mixing rate of oxygen into the main flow determines different local oxygen concentrations and different char-N oxidation rates in the oxidizing zone which in turn affect the level of NO emission. The change of limestone feed position in the oxidizing zone modifies very much the temperature in the region up to the feed level and thereby the NO emission. In the case of bituminous coal, changing the limestone feed ratio in the reducing zone corresponds to an insignificant modification of the NO concentration. The increase of the air combustion temperature has a negative influence on NO emission.