Online Alkali Measurement during Oxy-fuel Combustion

Abstract

Coal has been the main fuel in the generation of heat and power for many years and will continue to be so for years to come. Global warming awareness has led to the Kyoto Protocol, which targets the abatement of six greenhouse gases, including carbon dioxide (CO2). For the abatement of CO2 emissions, co-combustion of coal and biomass is an attractive solution. Other mitigation solutions include oxy-fuel combustion followed by Carbon Capture and Storage (CCS). However, co-combustion with coal and biomass in oxy-fuel atmosphere has been found to be conducive to chlorine-induced corrosion, slagging and fouling due to the use of complex fuel mixtures rich in alkali metals and chlorine. In order to address problems such as high-temperature corrosion, slagging and fouling caused by the use of these types of fuel mixtures, an alkali-measuring device is needed. The In-situ Alkali Chloride Monitor (IACM) utilizes UV light and Differential Optical Absorption Spectroscopy to measure gas-phase potassium chloride (KCl). This device has been successfully employed during biomass (wood chips and demolition wood) combustion and waste incineration. To investigate its performance in oxy-fuel combustion, the instrument was mounted on a 100 kW oxy-fuel combustion test unit equipped with a propane burner and a system for seeding of aqueous potassium chloride solution. The unit was operated in air- and oxy-fuel mode and the experiments substantiated the feasibility of online monitoring of gas-phase KCl in the flue gas during oxy-fuel combustion. The employment of an online alkali monitoring device during oxy-fuel combustion has the potential to increase the understanding of the release and capture of alkali chlorides, which in turn opens up for mitigation methods to reduce high temperature corrosion, slagging and fouling. This is a cost-efficient, sustainable solution because it extends the operational time of the boiler, reducing related maintenance costs.