Experimental study on supercritical water gasification of oily sludge using a continuous two-step method

Area of Science:

• Chemical Engineering
• Environmental Science
• Materials Science

Background:

• Oily sludge presents a significant disposal challenge.
• Supercritical water gasification (SCWG) offers a promising route for converting waste into valuable products like hydrogen.
• High oil concentrations in sludge complicate efficient SCWG under mild conditions.

Purpose of the Study:

• To develop and investigate a two-step SCWG method for efficient oily sludge conversion.
• To optimize conditions for high oil removal and carbon gasification.
• To understand the underlying mechanisms of the two-step SCWG process.

Main Methods:

• A two-step process involving a supercritical water desorption stage followed by catalytic gasification using Raney-Ni catalyst.
• Optimization of parameters including temperature, concentration, and time.
• Analysis of wastewater and solid residue composition.

Main Results:

• Achieved 99.57% oil removal efficiency and 93.87% carbon gasification efficiency.
• Minimized wastewater contaminants (4.88 ppm TOC, 0.08% oil) and solid residue carbon (0.88%).
• Demonstrated superior performance of the two-step method over single-step at higher concentrations.

Conclusions:

• The two-step SCWG method is highly effective for treating oily sludge with high oil content.
• The process operates efficiently under mild conditions, yielding hydrogen-rich gas and safe residues.
• This approach provides valuable insights for sustainable oily sludge management.