Supercritical water gasification of sewage sludge

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Supercritical water gasification of sewage sludge
Doki Yamaguchi (Ph.D student 3rd
year) Supervisor Dr. Lu Aye
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Outline of presentation

• Introduction
• Research objectives
• Model developments
• Model results
• Concluding remarks

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Environmental issues
Green house gas emission
Sea water contamination
Depletion of resources
Solid contamination
Air pollution
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Available technology and problems
Sludge left over
Ineffective utilization
Expensive process
Long term treatment
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Advantages of SCWG
Water recycling
Rapid treatment
SCWG
High performance
Complete utilization
High hydrogen production
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Research objectives

• To develop computer models, from stoichiometric,
  thermodynamic and kinetic points of view.
• To verify the model with measured and estimated
  data in literature.
• To estimate maximum hydrogen production at
  stoichiometry and equilibrium on SCWG of sewage
  sludge
• To estimate product distribution at equilibrium
  of SCWG reaction of sewage sludge.
• To identify an optimum reaction condition where
  hydrogen is maximized on SCWG of sewage sludge.

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Stoichiometric model development
Stoichiometric equation

• Stoichiometric H2
• H2O requirement
• Potentiality of sewage sludge

Sewage sludge steam reforming reaction
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Thermodynamic model development
Gibbs free energy minimization
Non-idealization

• Operating conditions
• Temperature
• Pressure
• Feed characteristic

• Equilibrium gas composition
• Effects of operating condition
• Optimum condition for H2

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Result Stoichiometric model
0.25
0.20
0.15
H2 production kg/kg-waste (d.a.f.)
0.10
0.05
0
0
20
40
60
80
100
Moisture content wt
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Model verificationTD model
80
60
40
20
0
0
20
40
60
80
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Comparison of materials TD model
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Effects of conditions TD model
Temperature effect
Pressure effect
600 ºC
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Dry gas composition TD model
100
600 ºC
CO2
80
60
CH4
40
H2
20
0
100
700 ºC
80
60
Moe fractions of species -
40
20
0
100
800 ºC
80
60
40
20
0
50
60
70
80
90
99
Moisture content wt
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Concluding remarks

• Sewage sludge is the better material for H2
  production.
• The thermodynamic model enables to predict a
  competitive results to measured data.
• The higher temperatures and moisture contents and
  the lower pressures are favorable to H2
  production.
• Negligible effects of temperature are predicted
  at the moisture content of 99 wt.
• Stoichiometric hydrogen amount can be achieved
  only at 99 wt.

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Future works
Kinetic model development
Reaction mechanisms
Kinetic parameters

• Transient gas composition
• Effect of residence time

Experimental investigation

• Set up experimental equipment
• Validation of models developed
• Modification of models if required