Low-oxygen enrichment in coal-fired utility boilers

The benefits of oxygen enrichment have been demonstrated in a variety of industrial combustion applications, such as glass melting, steel reheating furnaces, cement/lime kilns, etc. To date, no long-term industrial-scale implementation of oxygen enrichment in boilers has been reported, primarily due to their already high thermal efficiencies, and to the very large scale of these systems – requiring significant amounts of oxygen. In recent years, the topic of oxygen combustion in boilers has experienced a strong comeback, due to the appearance of new drivers. Oxygen enrichment is an effective tool in reducing emissions, and in using low-calorific fuels. Additionally, the increasing interest in carbon capture and sequestration has made the concept of a full oxygen-fired boiler more of a reality, since power generation produces around 30 % of the greenhouse gases. This paper analyzes the use of low-oxygen enrichment in boilers, in terms of operational and economical impact. A literature review of the impact of oxygen in coal-fired systems is presented. Several technological solutions for the low-oxygen enrichment operation are proposed and accompanied by numerical simulation results. In addition, results of comprehensive low-oxygen enrichment tests performed on a 1.5 MW pilot boiler using Illinois coal are reported, including the impact of oxy-combustion on a variety of pollutants, such as NOx and unburnt carbon in ash. Finally, the paper presents the economical aspects related to the technology. It is concluded that the oxy-fired operation may represent an economical way to lower the cost of power generation