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Integration of Supercritical Water Gasification and Combined Cycle Processes for Microalgae

Mumbai, December 10-12, 2013

M. Aziz, T. Oda, T. Kashiwagi

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Microalgae Utilization

4th ICAER 2013, Mumbai

Microalgae utilization processes

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.)

Problems : Lack of matured technologies for utilization Low energy-returned on energy-invested (EROEI)

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Microalgae Gasification


Gasification

Conventional thermal gasification

Supercritical water gasification

• High temperature (about 900ºC)• Drying required

• Supercritical condition• No drying required

Utilization of microalgae for power generation can be an option in the future electricity supply, especially providing the base load electricity

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Proposed Utilization Process

Outline of the material and energy circulation in the proposed system.

Integration of Supercritical Water Gasification

and Combined Cycle Processes


Carbon neutral process

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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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Enhanced Process Integration


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

Advanced System = Exergy Recovery + Process Integration

Enhanced Process Integration (EPI)

Huge energy consumption in process utilization

The conventional energy recovery technology cannot recover

significantly the energy involved in the process

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Concept of Exergy Recovery


T-Q diagram of self-heat exchange process T-Q diagram of SHR process

T0

Tb’

T1

Feed

Effluent

Tb

Qheat exchange

Q

T

Heat Cascade Exergy Recovery

Q

T

T0

Tb

T1

FeedminT

Effluent

Qheat exchange

Maximum heat recovery/circulation

Effective and optimal heat coupling

Minimum exergy loss

Based on pinch technology

No effective heat coupling

Large exergy destruction

minT

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Integrated Conventional Gasification

Schematic diagram of integrated conventional gasification and combined cycle

Drying Gasification Combined cycle


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Integrated Conventional Gasification


Process flow diagram of integrated conventional gasification and combined cycle

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Proposed Integrated SCWG and CC


Basic schematic diagram of proposed integrated SCWG and combined cycle

Gasification Combined cycle

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Proposed Integrated SCWG and CC


Process flow diagram of proposed integrated SCWG and combined cycle

Exergy elevation

Highest energy recovery

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Calculation Conditions


Proximate and ultimate analysis of Spirulina sp.

Assumptions during calculation

1. The minimum approach temperature in all heat exchangers is 10 K

2. The flow rate of microalgae is 1 ton h-1

3. Fresh microalgae has a moisture content of 90 wt.% wb

4. The adiabatic efficiency of the compressor and turbine (steam/gas) are 87% and 90%, respectively

5. Heat loss is neglected

Properties ValueProximate analysis (wt.% db)MoistureAshVolatile matterFixed carbon

8.046.9868.1516.83

Ultimate analysis (wt.% db)CarbonHydrogenNitrogenSulfurOxygen

42.836.024.090.4946.57

Calorific value (MJ kg-1) 18.5

Properties ValueGasifier pressure (MPa) 25Gasifier temperature (C) 700Gasification efficiency (%) 100HX min. temp. approach (C) 10HX pressure drop (%) 2Pump efficiency (%) 90Fluidizing particles

Particle diameter (mm)Density (kg m-3)

Alumina particles1003,400

Void fraction 0.5Gasification products (mol %) CO C2H6 and C3H8

CH4

CO2

H2

3.14.918.127.846.1

Gasification catalyst Catalyst to sample ratio

Ru/TiO2

2

Gasification condition

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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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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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Close


Thank you very much

Technology

89 aziz