Sulfur recirculation for increased electricity production in Waste-to-Energy plants

Abstract

Sulfur recirculation is a new technology for reducing boiler corrosion and dioxin formation. It was demonstrated in full-scale tests at a Waste to Energy plant in Göteborg (Sweden) during nearly two months of operation. Sulfur was recirculated as sulfuric acid from the flue gas cleaning back to the boiler, thus creating a sulfur loop. The new technology was evaluated by extensive measurement campaigns during operation under normal conditions (reference case) and operation with sulfur recirculation. The chlorine content of both fly ash and boiler ash decreased and the sulfur content increased during the sulfur recirculation tests. The deposit growth and the particle concentration decreased with sulfur recirculation and the dioxin concentration (I-TEQ) of the flue gas was reduced by approximately 25%. Sulfuric acid dew point measurements showed that the sulfuric acid dosage did not lead to elevated SO3 concentrations, which may otherwise induce low temperature corrosion. In the sulfur recirculation corrosion probe exposures, the corrosion rate decreased for all tested materials (16Mo3, Sanicro 28 and Inconel 625) and material temperatures (450 °C and 525 °C) compared to the reference exposure. The corrosion rates were reduced by 60-90%. Sulfur recirculation prevented the formation of transition metal chlorides at the metal/oxide interface, formation of chromate and reduced the presence of zinc in the corrosion products. Furthermore, measured corrosion rates at 525 °C with sulfur recirculation in operation were similar or lower compared to those measured at 450 °C material temperature in reference conditions, which corresponds to normal operation at normal steam temperatures. This implies that sulfur recirculation allows for higher steam data and electricity production without increasing corrosion.

Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 1. Fluidized Bed

“…The increase of SO 2 concentration in the boiler can result in lower corrosion rates. 46 The increased concentration of SO 2 /SO 3 in the gas phase in the freeboard section of the reactor led most probably to sulfation reaction. 47−50 During SB combustion, the additive did not significantly affect the composition of the windward side deposit.…”

The Effect of SO2/HCl Ratio on Superheater High Temperature Corrosion

“…Previous work on the impact of sulfur on superheater corrosion attributed the decrease in corrosion to the conversion of metal chlorides (M = Na, K, etc.) present to sulfates [2,8] as shown in reaction 1:…”

“…More recently, Andersson et al investigated the recirculation of SO 2 in full scale testing. By increasing the SO 2 /HCl ratio from about 1/3 to 5/8, significant corrosion reduction was observed for 16Mo3 and Inconel 625, and Sanicro28 [2]. In practice however, the SO 2 /HCl ratio alone does not decrease superheater corrosion.…”

“…Superheater corrosion is a major operating problem for WTE boilers as it causes downtime and periodic shutdowns and accounts for a significant portion of a facility's total operating cost [1]. Additionally, superheater corrosion impacts electricity production by limiting the boiler's maximum achievable temperature, above which the corrosion rate becomes impractically high [2].…”

“…Primary methods refer to process modifications while secondary methods concern material choice. One primary approach which has received more interest as of late for WTE superheater corrosion is the addition or recirculation of sulfur into the flue gas [2]. Previous literature has demonstrated that addition of elemental sulfur into MSW can decrease boiler corrosion [5].…”