Spray-dry desulfurization of flue gas from heavy oil combustion

An experimental investigation on SO2 removal in a pilot scale spray-dryer from the flue gas generated by combustion of low-sulfur heavy oil is reported. The facility is equipped with an oil burner producing 60Nm3/h of flue gas with SO2 concentration up to 1200mg/Nm3, depending on the oil sulfur content. A lime-water slurry was sprayed through an ultrasonic two fluid atomizer in the spray-dry chamber and the spent sorbent was collected downstream in a pulse-jet baghouse together with fly ash. Flue gas was sampled in different points in order to measure the desulfurization efficiency after both the spry-dry chamber and the baghouse. Parametric tests were performed to study the effect of the following variables: gas inlet temperature, difference between gas outlet temperature and adiabatic saturation temperature, lime to sulfur ratio, and average size of lime particles in the slurry. The average droplet size in the spray was also characterized, because of its influence on the total desulfurization efficiency. Results indicated that spray-drying is an effective technology for the desulfurization of low-sulfur fuel oil flue gas, provided operating conditions are chosen carefully. In particular the lowest gas inlet and outlet temperatures compatible with baghouse operation should be selected as well as a sufficiently high lime to sulfur ratio. The attainment of a small lime particle size in the slurry is critical for obtaining a high desulfurization efficiency.