Corrosiveness of Brazilian Candiota Coal

Abstract

Candiota city, in the south of Brazil, is located near the largest reserves of mineral coal of the country. This coal is used for thermoelectric power generation. The extraction of coal from open-cut mines involves operations may generate at least some particulate matter into the atmosphere. These particles retained on the surface of metallic structures exposed to the atmosphere, may adsorb gases such as CO, CO2, SO2 and NO, which, in combination with humid air form corrosive substances, such as HNO3 and H2SO4. This paper aims to evaluate the influence of Candiota coal on the corrosion of buried steel structures and exposed to atmosphere containing particulate matter from coal combustion. The coal sample was characterized by SEM (scanning electron microscopy), thermogravimetric analysis (TGA), surface area analysis (BET method), electrical conductivity (EC) analysis, FTIR and Raman spectroscopy. Corrosion was simulated by exposure of steel samples to coal particles and thermoelectric industrial atmosphere. Electrochemical tests of solutions leached from the coal were conducted by voltammetry to evaluate the soluble compounds corrosiveness. The corrosion rate was determining following the technical standard ASTM G1-90. Localized attacks and corrosion products formations were detected in API 5L Grade B steel exposure to coal. The average corrosion rate for the samples in direct contact to the pulverized coal was 0.15 mm/year, while in samples exposed to the atmosphere from industrial power plant was 0.30 mm/year. It is concluded that API 5L Grade B steel metal structures, exposed to atmospheres rich in Candiota coal and its derivatives, must be properly protected and monitored to avoid future damage caused by corrosion.

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“…Esta última grafia seria facilmente entendida como uma grafia decorrente de um reflexo da fala na variedade do PB, por exemplo, cuja pronúncia ([kéʒu]) é comummente observada em vários dialetos (cf. Cagliari, 1989). Este exemplo mostra como a classificação das FN-C não deve ser feita em abstracto numa língua, mas sim atendendo à variedade linguística falada pela criança.…”

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