Corrosion of Heat Transfer Materials by Potassium-Contaminated Ilmenite Bed Particles in Chemical-Looping Combustion of Biomass

Abstract

This study discusses the potential corrosion of boiler materials in chemical-looping combustion (CLC) of biomass. The CLC of biomass has the potential to negative CO2 emission in heat and power production. Biomass fuels, however, typically contain compounds of alkali metals, especially potassium and chloride, which may lead to the corrosion of heat-transfer surfaces in the reactors. The influence of potassium-contaminated ilmenite bed material deposits on the corrosion of seven heat transfer materials used in the air and fuel reactors in CLC was studied using one-week lab-scale experiments. Samples with KCl and without any deposit were used as references. After the exposure, the cross-sectional surfaces of the metals were analyzed with SEM/EDX. The results suggested that potassium-contaminated ilmenite might lead to minor corrosion of all studied materials under the oxidizing conditions simulating the air reactor, i.e., 700 °C and dry air. Under reducing fuel reactor conditions, i.e., 450 °C and 550 °C and 50/50 CO2/H2O, corrosion was observed on ferritic steels, especially in the presence of HCl and with KCl deposit. In contrast, samples with uncontaminated and potassium-contaminated ilmenite deposits did not significantly differ from the samples without any deposit. Minor corrosion of ferritic steels was observed at 450 °C, while at 550 °C, the corrosion was more significant. The results suggested that ferritic steels are not suitable for the fuel reactor. Austenitic and nickel-based alloys did not corrode under the test conditions used in this work.

An improved method for feeding ash model compounds to a bubbling fluidized bed – CLC experiments with ilmenite, methane, and K2CO3

“…A series of corrosion tests with K-doped ilmenite has led to this conclusion. 35 Further, Gogolev et al 36 showed with alkali emission measurements in CLC pilot experiments that fuel alkali is largely retained in the ilmenite. They also observed that gas-phase alkali was released mainly in the fuel reactor.…”

“…Thus, ilmenite seemed to stabilize the K released from the fuel and hinder it from further interacting with the boiler surfaces. A series of corrosion tests with K‐doped ilmenite has led to this conclusion 35 . Further, Gogolev et al 36 .…”

Alkali emissions characterization in chemical looping combustion of wood, wood char, and straw fuels

“…Alkali species released to the gas-phase are known to cause fouling and corrosion of heat exchange equipment in contact with the flue gases [ 15,17,18,23,42]. In biomass fluidized bed boilers used for steam production, steam superheaters are operated at temperatures of approximately 400-600 • C, while typical combustion temperatures are maintained in the range of 800-900 • C [15,17].…”

Gaseous Alkali Interactions with Ilmenite, Manganese Oxide and Calcium Manganite Under Chemical Looping Combustion Conditions

“…Ilmenite, an iron-titanium oxide mineral (FeTiO 3 ), has also emerged as a promising OC material due to its attractive properties and is now considered one of the most scrutinized OC materials [48,49]. Ilmenite is a robust and durable OC material that possesses high oxygen-carrying capacity, good chemical stability and low cost, making it a viable alternative to other OC materials [28,[50][51][52].…”