2.2. Coal agglomeration
In this process, fine coal is used to retrieve oil fromoil-contaminated
coarse sediments. Here, oil acts as a binder gluing the fine coal particles
together. As they are hydrophobic, coal particles can be easilywetted by
non-polar liquids such as oil. About 0.1% of residual hydrocarbons can
be removed from crude oil-contaminated sediments through this
process (Rahnama and Arnold, 1993). Remediation of highly oil-
contaminated sediments can be performed with a large amount of
fine coal. The amount of coal required for remediation largely depends
on the sediment grain size and fineness of the coal used (Rahnama
and Arnold, 1993). Typically, the oil content of the sediment determines
the amount of coal appropriate for the formation of extremely hydro-
phobic oil–coal agglomerates. The addition of an excess amount of
coal often reduces the sediment cleaning efficiency due to the deficiency
of the bridging liquid collected between coal particles (Shin and
Shen, 2011).
The remediation of oil-contaminated sediment through coal ag-
glomeration involves four stages, as shown in Fig. 1. At the initial
stage, fine coal particles attach to each other forming layers over the
oil-contaminated sediment surfaces. These layers are compacted in
the next step. During these two stages, oil is adsorbed onto the coal
particles, thus cleaning the sediment. In the third stage, known as the
abrasion stage, a high shear force is applied to detach coal from the
sediment. In the last stage, the oil–coal particles are agglomerated
with liquid-phase agglomeration (Joshi and Lee, 1996).
The coal agglomeration technique is simple and economical. This
technique requires both low pressure and low temperature for recover-
ing oil fromthe sediment (Kasi et al., 1993). The coal agglomeration pro-
cess increases the Btu (British thermal unit) value of the coal. This
technique allows for a high-capacity treatment to be performed effec-
tively in a very short time (Kasi et al., 1993). However, clay-rich
sediments cannot be easily processed with this method, as are low-
boiling-point hydrocarbons in the coal agglomeration process due to
fire hazards (Rainis and Detz, 1983).