# Effects of Particle Size of Dielectric and Operating Time through Nonthermal Plasma on Fuel Characteristics of Refined Fuel from Oily Sludge

## TL;DR

This study explores how nonthermal plasma can refine oily sludge into usable fuel by adjusting particle size and treatment time, improving energy recovery.

## Contribution

The novel contribution is optimizing nonthermal plasma refining of oily sludge using dielectric particle size and treatment time to enhance fuel quality.

## Key findings

- Pretreatment with solvent extraction improves oily sludge properties before plasma refining.
- Dielectric-barrier discharge plasma outperforms other types due to direct sludge contact and increased treatment area.
- Optimal conditions (dielectric ratio 2/1, 8 min, 100 μm particles) yield highest heating value and lowest residual carbon.

## Abstract

The refining processes of oil refineries, waste lubricants
replaced
by maintenance plants of gasoline and diesel vehicles, and mechanical
lubricants of various types of ships produce oily sludge with different
complex components, including varying amounts of water, hydrocarbons,
metal rust, solid residues, inorganic compounds, and other components.
The high heavy content of the sludge results in its high kinematic
viscosity, and it exists in a liquid state close to a solid state
at ambient temperature. Although the composition of oily sludge is
complex and difficult to separate, its heating value can still reach
9000 cal/g, which is about 80% of the heating value of gasoline or
diesel. Therefore, it has a great recycling value. This study therefore
intends to develop oily sludge refining technology and establish an
economical treatment process by nonthermal equilibrium plasma. The
pretreatment technology of solvent extraction combined with filter
filtration was used to extract and separate the oily part of the sludge
containing hydrocarbons from the oil sludge. Two types of nonthermal
plasma, such as DC streamer discharge and dielectric plasma discharge,
were considered for the refining processes. Under operating conditions,
the oily sludge is cracked and intensified to produce liquid and gaseous
fuel products. The gaseous products are condensed and collected into
fuel oil by a vacuum rotary concentrator. The composition and fuel
properties of the fuel refined under different operating conditions
of nonthermal plasma, including dielectric particle size of Al2O3 and action time, were tested. The research results
showed that the pretreatment procedure can effectively improve the
properties of originally discarded sludge at the beginning of the
oil treatment process. In the second part of the experiment, after
comparing different types of plasma reactors, the direct treatment
type of dielectric-barrier discharge (DBD) plasma was found to be
superior because the plasma can directly contact the treated sludge
and extended the plasma treatment range. When quartz glass beads were
added to the sludge, a large number of raised areas were formed on
the surface of the sludge, making it easier to form a tip discharge
for plasma generation and increasing the plasma treatment area. When
the weight ratio of dielectric to sludge, the operating time, and
the particle size were 2/1, 8 min, and 100 μm, respectively,
there is the highest heating value and the lowest residual carbon
content. In addition, the smaller the dielectric particle size, the
smaller the carbonaceous size of the refined oil after the plasma
treatment. As the plasma treatment time increased, the surface of
the oily sludge was carbonized, resulting in a reduction in the plasma
operating range. This research converts waste sludge into a fuel of
precious energy, thus providing an important contribution to the development
and application of energy.