The industrial application
of burning Zhundong coal has been directly
restricted due to severe ash deposition. To attain the wide utilization
for this coal, experiments about the effects of different additives
on ash deposition were conducted in a drop-tube furnace. The properties
of ash deposits were characterized by ICP-OES and XRD, and mineral
properties were also calculated by molecular dynamics from the perspective
of elemental reactions. The results indicate that ash deposition can
be divided into inner layer and outer layer. The deposited layer and
the size of particles under vermiculite additive are looser and bigger
than those under raw coal and kaolin additive. Additionally, ash deposition
for the inner layer is thinner, and ash ratio for the outer layer
is higher under vermiculite additive. The total deposited layer may
be thinner under kaolin additive, but the inner layer for ash deposition
is denser than that under vermiculite additive. Ash deposition for
raw coal is mainly caused by the formation of hematite, magnesioferrite,
anhydrite, and a littlie sodium silicate. Vermiculite additive mainly
promotes the further reaction between calcium oxide with magnesium
oxide, silicon dioxide, causing the formation of high melting point
merwinite. Additionally, vermiculite additive also reduces the formation
of magnesioferrite for the deposit layer. Kaolin additive can mainly
reduce the formation of anhydrite, and accelerate the formation of
anorthite. Furthermore, kaolin additive does not change the types
of iron-bearing minerals for the deposit layer. On the basis of molecular
dynamic simulations, α-Fe2O3 is more easy
to combine with anhydrite, followed by merwinite, and finally anorthite
based on the binding energy and the radial distribution function.
This shows the formation of anhydrite is a key mineral to cause severe
ash deposition for the combustion of Zhundong coal.
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