SO2 Removal Efficiency in Fluidized Bed Combustor Burning Coals of Different Sulfur Content

Coal represents over 94% of the fossil energy resources in China, and has played an important role in the country’s explosive economic development over the past decades. Unfortunately, due to various reasons, air pollution from utilization of coals has been a recognized problem for many years. In recent years, with the air emission standards becoming more stringent, coals with sulfur content higher than approx. 1% , which represents over 40% of the Chinese coal reserves, has been limited for use.

For clean and efficient utilization of high sulfur coals, sulfur removal experiments in the fluidized bed combustion were carried out for coals having sulfur content from 0.56% to 3.68%. Limestone with a preferred particle size distribution was used as a sulfur sorbent. Experiments were conducted for combustion temperatures from 800-950℃ with a calcium-to-sulfur ratio (Ca/S) of 2.0-3.0. It is interesting to find out that the SO₂ removal efficiency increases with the sulfur content for given Ca/S and temperature. As the sulfur content is higher than 1.5%, the SO₂ removal efficiency can stably attain above 98% at Ca/S=2.5, resulting in a SO₂ emission of less than 50 mg/Nm³. For the coal with a sulfur content of 3.68%, the SO₂ emission was reduced to 18.2 mg/Nm³ (i.e. 99.6% removal efficiency) at Ca/S=2.5, which is lower than the Chinese new ultralow SO₂ emission requirement of 35 mg/Nm³. Therefore, it can be concluded that with advanced fluidized bed combustion technology, high sulfur coals can be utilized environmental friendly and cost effectively.