Study on Limestone Fines for Desulfurization Completed
Zak Lasemi submitted the final contract report to the Illinois Clean Coal Institute, sponsor of a project studying the economic viability of limestone fines as a source of sorbents. Limestone-based desulfurization processes continue to be an effective strategy in enabling increasing, cleaner use of high-sulfur coal. To be economically viable, high-quality limestone resources need to be available locally and at low cost. One such abundant, yet largely unused resource is by-product "fines" that are produced in all Illinois limestone quarries. Use of quarry fines as a scrubbing agent could provide two major cost-saving advantages: (1) reduced energy cost from grinding, because the material has already been crushed down significantly, and (2) use of this by-product material, which is widely available at quarries at a relatively low cost. Quarry fines vary in quality and have not been previously characterized as a scrubbing agent. The ISGS project scientists conducted a detailed characterization of the fines from 36 representative quarries, especially those located near existing and potential new coal-fired power plants. Sieve analyses indicate that about 50% of the material in the examined quarry fines ranged in particle size from 0.187 to 0.0331 inch (-4 to 20 Tyler Mesh). Mineralogically, quarry fines closely resemble the composition of the parent material. Samples from the northeastern part of the state are predominantly dolomite, and those from the central, western, and southern portions are predominantly limestone. Silica is a major impurity in some of the quarry fines, ranging from 0.11 to 48.26%. However, silica content was less than 10% in the majority of the samples analyzed. Samples with high-silica content are associated with a cherty and siliceous limestone and/or dolomite parent material. Measured relative reactivity of selected quarry fines with respect to sulfur removal under wet flue-gas desulfurization conditions showed significant variation in dissolution performances. Dissolution performance appears to be negatively correlated with the amount of magnesium oxide and silica. The thermogravimetric analyzer (TGA) desulfurization reactivity of selected quarry fines showed higher desulfurization reactivity than was determined for the parent material in earlier studies. The results of this study provide a useful database for the abundantly available by-product limestone fines that could be used as an affordable sorbent for desulfurization in Illinois coal-fired power plants.