1. Integration of Supercritical Water Gasification and
Combined Cycle Processes for Microalgae
Mumbai, December 10-12, 2013
M. Aziz, T. Oda, T. Kashiwagi

2. Microalgae Utilization
Superiority of microalgae compared to terrestrial one (high efficient solar energy
conversion and nutrient acquisition, effective CO2 absorption, etc.)
Numerous microalgae utilization (energy, feed-stock, etc.)
Microalgae utilization processes
Problems :
 Lack of matured technologies for utilization
 Low energy-returned on energy-invested (EROEI)
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3. Microalgae Gasification
Conventional
thermal gasification
• High temperature (about 900ºC)
• Drying required
Gasification
Utilization of microalgae for
power generation can be an
option in the future electricity
supply, especially providing the
base load electricity
Supercritical
water gasification
• Supercritical condition
• No drying required
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4. Proposed Utilization Process
Integration of Supercritical Water Gasification
and Combined Cycle Processes
Carbon neutral
process
Outline of the material and energy circulation in the proposed system.
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5. Supercritical Water Gasification
 Thermochemical conversion utilizing supercritical water properties
•
Pressure > 22.1 MPa
•
Temperature > 374 ºC
 Produced syngas: CO, hydrogen, methane, etc.
 Advantages
•
Lower water density  decrease in static relative dielectric constant
•
Significantly lower hydrogen bond
•
Higher gasification efficiency
•
Single homogeneous phase of fluid
•
Faster chemical reaction
•
No drying required
 Disadvantages
•
Higher energy to provide high pressure and temperature
•
Requires further technological development
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6. Enhanced Process Integration
 Huge energy consumption in process utilization
 The conventional energy recovery technology cannot recover
significantly the energy involved in the process
Advanced System = Exergy Recovery + Process Integration
Enhanced Process Integration (EPI)
Characteristics of EPI
- Exergy rate elevation and its recovery
- Optimal and effective heat coupling (sensible, latent, etc.)
- Integration with other processes to minimize exergy destruction
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7. Concept of Exergy Recovery
Exergy Recovery
Heat Cascade
T
Qheat exchange
Qheat exchange
T
T1
T1
Effluent
Effluent
Tb
Tm in
Tb’
Tb
Feed
Tm in
Feed
T0
T0
Q
Q
T-Q diagram of SHR process
T-Q diagram of self-heat exchange process
Based on pinch technology
Maximum heat recovery/circulation
No effective heat coupling
Effective and optimal heat coupling
Large exergy destruction
Minimum exergy loss
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8. Integrated Conventional Gasification
Drying
Gasification
Combined cycle
Schematic diagram of integrated conventional gasification and combined cycle
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9. Integrated Conventional Gasification
Process flow diagram of integrated conventional gasification and combined cycle
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10. Proposed Integrated SCWG and CC
Gasification
Combined cycle
Basic schematic diagram of proposed integrated SCWG and combined cycle
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11. Proposed Integrated SCWG and CC
Exergy elevation
Highest energy
recovery
Process flow diagram of proposed integrated SCWG and combined cycle
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12. Calculation Conditions
Proximate and ultimate analysis of Spirulina sp.
Properties
Proximate analysis (wt.% db)
Moisture
Ash
Volatile matter
Fixed carbon
Ultimate analysis (wt.% db)
Carbon
Hydrogen
Nitrogen
Sulfur
Oxygen
Calorific value (MJ kg-1)
Value
Gasification condition
8.04
6.98
68.15
16.83
42.83
6.02
4.09
0.49
46.57
18.5
Assumptions during calculation
1.
2.
3.
4.
5.
The minimum approach temperature in all heat
exchangers is 10 K
The flow rate of microalgae is 1 ton h-1
Fresh microalgae has a moisture content of 90 wt.%
wb
The adiabatic efficiency of the compressor and
turbine (steam/gas) are 87% and 90%, respectively
Heat loss is neglected
Properties
Gasifier pressure (MPa)
Gasifier temperature (C)
Gasification efficiency (%)
HX min. temp. approach (C)
HX pressure drop (%)
Pump efficiency (%)
Fluidizing particles
Particle diameter (mm)
Density (kg m-3)
Void fraction
Gasification products (mol %)
CO
C2H6 and C3H8
CH4
CO2
H2
Gasification catalyst
Catalyst to sample ratio
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Value
25
700
100
10
2
90
Alumina particles
100
3,400
0.5
3.1
4.9
18.1
27.8
46.1
Ru/TiO2
2
12

13. Results – Gasification Efficiency
Correlation between the amount of steam flown into SCWG reactor with net
generated electricity and total electricity generation efficiency
•
•
High electricity generation efficiency could be achieved (up to about 50%)
As the amount of steam flowing to SCWG reactor decreases, the generated
electricity and generation efficiency increases accordingly
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14. Summary
1. Microalgae has a very potential for energy utilization. Unfortunately, its
high moisture content leading to difficulties in transportation, storage,
thermal efficiency, etc. Hence, innovative technology is required to
increase its energy efficiency
2. Gasification of microalgae could be achieved through conventional
thermal gasification and supercritical water gasification
3. Integrated supercritical water gasification and combined cycle based
on the enhanced process integration has been developed well
4. The total energy efficiency could be increased leading to its high
opportunities for application
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15. Close
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