Combustion and Emission Challenges at LKAB

Abstract

Increased production combined with stringent emission regulations and growing energy prices has initiated a number of activities at LKAB to investigate and evaluate alternatives to the company’s current combustion technology and fuels. Reduction of NOx emissions is, for example, one of these activities. The NOx work at LKAB has been going on for the last decade and has included both primary and secondary control measures. Work with primary measures has comprised pre-studies, physical and numerical modelling work, pilot scale and full scale trials in both Straight-Grate and Grate-Kiln pelletizing plants. Secondary measures have consisted of both SCR and SNCR studies. LKAB is also the first and only mining company in the world that have installed an SCR system in an existing Grate-Kiln plant. LKAB’s experimental combustion furnace, that is operated with high excess air ratios (n ≈ 5-6) and high combustion air temperatures (900 – 1300°C), has played a major role in these NOx investigations. It has, for example, been used to evaluate options to reduce NOx-emissions from Straight-Grate pelletizing plants during 2009. Specifically, different combustion configurations were tested including a pre-combustor, secondary air, wateroil mixtures and gas fuel. Except for the use of gas fuels, all these configurations showed a significant NOx-reduction compared to the current reference case. With the precombustor and a secondary air temperature of 450 °C the NOx-emissions could be reduced by approximately 65 %. The NOx emissions can be reduced even further with lower secondary air temperature but with the consequence of higher energy cost.