The Effects of Cofiring Natural Gas and Coal on Sulfur Retention in Ash


Under certain conditions, cofiring natural gas with coal has been shown to reduce SOx emissions beyond the reduction expected from simple replacement of sulfur-bearing coal. This enhanced reduction of sulfur emissions, known as sulfur leveraging, is believed to result from increased sulfur capture in coal ash. In this research, experiments with three coals, using size ranges from 90 to 106 µm and 125 to 150 µm, and furnace temperatures of 1300 and 1550 K, demonstrate the extent of sulfur leveraging through increased sulfur retention in ash when cofiring coal and natural gas. Leveraging is shown to be affected by residence time (through particle size) and furnace temperature, while original sulfur form (pyritic or organic) and coal sorbent capacity are shown to have little effect. Results from sorbent activation studies, SEM images, and N2 adsorption measurement of total surface area indicate that the effects of a natural gas flame on ash sorbent reactivity and ash surface area are minimal. Results also indicate that the primary mechanism for sulfur leveraging is the gas phase conversion of SO2 to more reactive SO3, as caused by the natural gas flame. Results from numerical modeling of the furnace environment, particle combustion, and the evolution of sulfur to SO3 support the experimental findings.


Mechanical and Aerospace Engineering

Keywords and Phrases

Coal; Natural Gas; Sulfur Dioxide; Air Pollution; Article; Ash; Combustion; Furnace; Mathematical Model; Particle Size; Priority Journal

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Document Type

Article - Journal

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© 1996 Elsevier Inc, All rights reserved.

Publication Date

01 Aug 1996