Mineralogy and Leaching Characteristics of Coal Ash from a Major Brazilian Power Plant

Abstract

A B S T R A C TThe feed coals, fly ashes and bottom ashes collected from seven different units in a major Brazilian PF power plant have been subjected to comprehensive mineralogical, geochemical, and petrographic studies, to investigate the links between feed coal and ash characteristics. Ashes from two of the units were collected while the coal was being co-fired with oil as part of the boiler start-up procedure, allowing the impact of oil co-firing on ash characteristics also to be evaluated. High proportions of unburnt carbon and high proportions of retained sulphur were found in the fly ashes produced during oil co-firing, probably reflecting less efficient combustion and associated lower combustion temperatures. Higher concentrations of a number of relatively volatile trace elements were also noted in these fly ashes, compared to the fly ashes collected from units under normal operating conditions.The fly ashes produced during oil co-firing gave rise to acid pH conditions in water-based leaching tests, in contrast to the alkaline pH associated with fly ashes produced during normal operations. This probably reflects higher SO 3 contents relative to total CaO + MgO for the co-fired ash samples. Many trace elements that are typically mobilised as cations were also more abundant in leachates from the co-fired fly ashes. This is due, most likely, to the more acid pH conditions involved. Despite similar or even higher total concentrations, however, elements that are typically released from coal ash as oxy-anions were less mobile from the co-fired fly ashes than from the normally-fired fly ash materials.

Determination of mineral matter and elemental composition of individual macerals in coals from Highveld mines

“…Similar studies, linking the mineralogy of ashes from pulverized-fuel power stations to the mineral matter in the respective feed coals, have been published by Ward and French (2006) and Silva et al (2010). These and other studies (e.g.…”

Comprehensive characterization of anthracite fly ash from a thermo-electric power plant and its potential environmental impact

“…Silva et al (2010) notice that some elements, namely As, Bi, Cd, Ga, Ge, Hg, Mo, Pb, Sb, Se, Sn, Tl, W and Zn, may have higher concentration in fly ash derived from combustion that is co-fired with oil.…”

“…The combustion of coal in a TPP using co-firing with fuel oil may also have a significant impact on fly ash chemical characteristics (Navarrette et al, 2004;Silva et al, 2010). Silva et al (2010) notice that some elements, namely As, Bi, Cd, Ga, Ge, Hg, Mo, Pb, Sb, Se, Sn, Tl, W and Zn, may have higher concentration in fly ash derived from combustion that is co-fired with oil.…”

“…The LOI in the fly ash is higher than the more usual range for European fly ashes. This may reflect the difficulty of ignition of the anthracite particles within the pulverized coal combustion system, combined with combustion inefficiencies associated with the use of fuel oil as a co-firing medium (Navarrette et al, 2004;Silva et al, 2010).…”

“…The combustion and pollution control technologies used in the plant, including any use of oil co-firing (Silva et al, 2010), may also play important roles.…”