Experimental Study Of Sulfur Retention At High Temperature By Compound Sulfur-Fixing Agent Premixed With Low-Sulfur Coal

Compared to the widely-used wet flue gas desulfurization（WFGD）, sulfur retentionduring the low-sulfur coal combustion in the furnace has economical advantage. However,the low utilization ratio of the conventional calcium-based sulfur-fixing agent anddecomposition of the sulfation product CaSO₄at high temperature result in lower sulfurretention efficiency.This paper analyzes the sulfur retention principle at high temperature of severalsulfur-fixing components. Firstly, in the tube furnace, the static sulfur retention experimentsare carried out using different sulfur-fixing components and the compound sulfur-fixingagent, which is mixed by mechanical grinding of sulfur-fixing components in a certainpercentage. Furthermore, in a large（100MW） utility pulverized coal fired boiler, a long-timesulfur retention experiment at high temperature is performed using the compoundsulfur-fixing agent, which is premixed with low-sulfur coal. With the ratio’s increase of thesulfur-fixing components and the compound sulfur-fixing agent, the trends of the sulfurretention efficiency, the SO₂concentration in the flue gas, and the SO₃weight in the ash arestudied. And after the sulfur-fixing components and the compound sulfur-fixing agent areadded in the coal, their influences on the coal combustion and the ash fusion temperatureare analysed.The study of the sulfur-fixing components shows that: Added in a same molar ratio,the sulfur retention efficiencies are higher of strontium salt and barium salt thancalcium-based sulfur-fixing components, but the result is converse when in a equal massratio, and the sulfur retention efficiencies are higher of barium and strontium nitrates thantheir corresponding carbonates both in a constant molar ratio and mass ratio. After addingthe sulfur-fixing components, the SO₃content in coal ash becomes higher. Sr （NO₃）₂andBa （NO₃）₂both can reduce the ignition temperature of the coal, advance the fixed carboncombustion time, and reduce the coal’s burnout temperature. The research of the compoundsulfur-fixing agent shows that: The sulfur retention efficiency is higher in the tube furnacethan in the pulverized coal fired boiler. With the increase of the mass ratio of the compound sulfur-fixing agent, the sulfur retention efficiency grows higher. The more compoundsulfur-fixing agent is added in the coal entering the boiler, the more sulfur will be capturedin the ash,and the less sulfur flies away with the flue gas. Meanwhile, a small portion of thesulfur isn’t able to be detected neither in the ash or flue gas and maybe stay on the heatexchanger’ surface in the boiler. When the compound sulfur-fixing agent is added in a massratio of1%, the CO concentration, the carbon contents in the fly ash and bottom ash are alllower than the blank test, which means the coal combustion is improved and results in theconsumption reduction of standard coal per ton of the steam product. After adding thecompound sulfur-fixing agent, the ash fusion temperature decreases.