Temperature-Dependent Fractionation of Particulate Matter and Sulfates from a Hot Flue Gas in Pressurized Pulverized Coal Combustion (PPCC)

Abstract

The development of new highly efficient combined-cycle power plants is fundamentally linked to the development of new hot flue gas purification systems. Hot flue gas purification systems aim to remove particles and newly formed particulate matter from condensation reactions from the flue gas to prevent any damage to the gas turbine. This study focuses on the characterization of particulate matter which was deposited onto the inner walls of flue gas probes in a 1 MW pilot plant for pressurized pulverized coal combustion under slagging conditions (PPCC). The particulate matter in the flue gas stream originates from incompletely separated fly ash particles and particles formed during condensation processes from the hot flue gas. The phase analysis of the materials was done by high-resolution scanning electron microscopy. The combination of wavelength dispersive electron microprobe with a knowledge of the approximate temperature profile through the flue gas probe allowed the definition of dew points of single crystalline phases under the actual pressure conditions from the hot flue gas in the pilot plant. At high temperatures (>1200°C) the deposits on the inner wall of the flue gas probe are mainly fly ash particles which were deposited in the liquid state. With decreasing temperature, CaSO 4 , Na 2 SO 4 , K 2 Ca 2 (SO 4 ) 3 , and K 3 Na(SO 4 ) 2 condense from the flue gas. The ubiquitous occurrence of crystalline Cr 2 O 3 can be traced to high-temperature refractory materials in the boiler and the subsequent particle separator of the pilot plant. At low temperatures some sulfates may decompose and form highly corrosive pyrosulfate melts. The changes in the phase composition of the deposits correlate well with chemical profiles along the flue gas probe.

A New Method to Minimize High-Temperature Corrosion Resulting from Alkali Sulfate and Chloride Deposition in Combustion Systems. I. Tungsten Salts

“…The general research emphasis at present for alleviating such corrosion problems tends to be in a direction of coal, biomass, or municipal solid waste gasification and liquefaction. This then provides an opportunity for synfuel cleanup before combustion. − Another approach utilizes combined cycles that can invoke fuel gas cleanup techniques ahead of a gas turbine. ,− At present, commercial gas turbines tend to be bypassing the problem by operating predominantly with natural gas fuel.…”