3.2.3.2. H2 Separation and hydrogenation

Membrane-based separation is adopted for the H2 extraction from the syngas. This method promotes low energy consumption, simple handling process, and mild conditionings. Among the membrane separation methods, polymeric membrane separation, consists of microporous film acting as a semipermeable barrier, owns the widest commercial application [48]. The assumed conditions during H2 separation and hydrogenation are given in Table 7.

3.2.3.3. Combined cycle and power generation

Table 7. Hydrogen separation and hydrogenation conditions.

Property Value

Figure 9. Schematic diagram of the process flow of the proposed integrated system.

are presented in Table 8.

Separation Type ()

Hydrogenation Pressure (kPa) Temperature (C) Catalyst ()

Sphericity ()

Hydrogen recovery (%) Operating temperature (C) Feed inlet pressure (kPa) Product outlet pressure (kPa) Product H2 concentration (mol%) Product CO concentration (mol%) Product other gas concentration (mol%)

Catalyst particle size (mm)

After the H2 is separated from the syngas, the remaining syngas is employed as a fuel for combustion (COMB) in the combined cycle. Moreover, due to high temperature of the flue gas from the gas turbine (GT), it is thus used to superheat the mixture of syngas and steam from the SCWG reactor. At last, the remaining heat is recovered in HRSG for the steam turbine (ST). The conditions of the combined cycle modules, including combustor, gas and steam turbines

Polymeric membrane

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70 100 800 110.0 0.995 0.000498 0.00448

130 200 Ni-Mo/Al2O3 0.3 0.5


Table 6. SCWG conditions and syngas composition used during calculation.


Table 7. Hydrogen separation and hydrogenation conditions.

#### 3.2.3.3. Combined cycle and power generation

3.2.3. Analysis of integrated system

270 Gasification for Low-grade Feedstock

3.2.3.1. Supercritical water gasification of microalgae

perature distribution, and a high conversion rate [46].

gasification conditions and produced syngas composition.

Property Value

Table 6. SCWG conditions and syngas composition used during calculation.

3.2.3.2. H2 Separation and hydrogenation

SCWG condition Temperature (C) Pressure (MPa)

Fluidization velocity U/Umf () Fluidizing material () Density (kg m<sup>3</sup>

) Particle diameter (mm) Sphericity ()

Carbon conversion efficiency (%)

C2H6 and C3H8 (dry mol%)

Gasification catalyst ()

Syngas composition

H2 (dry mol%) CO (dry mol%) CH4 (dry mol%)

CO2 (dry mol%)

Voidage at minimum fluidization ()

Weight ratio of catalyst to wet algae ()

Due to the supercritical regime of the reaction, the decreasing water density causes a low static relative dielectric constant, hence, weaken the hydrogen bonds and improve the yield of the syngas [13]. Moreover, syngas cleaning can be disregarded due to no formation of NOx or SOx in the process. In the proposed process, a fluidized-bed reactor was selected due to its beneficial characteristics, including better particle mixing, ability to avoid plugging, uniform tem-

For high performance of gasification, a catalyst set of Ru/TiO2 which exhibits H2-rich syngas and complete carbon conversion is injected inside the gasifier. Moreover, fluidizing particles (e.g., alumina) can be proposed to increase the particle dynamics inside the reactor and prevent the production of ash layer and char on the reactor wall [47]. In this study, the flow rate and initial moisture content of wet microalgae are fixed at 1000 t h<sup>1</sup> and 90 wt% wb, respectively. Two gasification pressures are evaluated: 25 and 30 MPa. Table 6 gives the

Membrane-based separation is adopted for the H2 extraction from the syngas. This method promotes low energy consumption, simple handling process, and mild conditionings. Among the membrane separation methods, polymeric membrane separation, consists of microporous film acting as a semipermeable barrier, owns the widest commercial application [48]. The

> 600 25, 30 1, 2, 3, 4 alumina 3400 0.3 0.67 0.45 Ru/TiO2 2

100 46.1 3.1 18.1 4.9 27.8

assumed conditions during H2 separation and hydrogenation are given in Table 7.

After the H2 is separated from the syngas, the remaining syngas is employed as a fuel for combustion (COMB) in the combined cycle. Moreover, due to high temperature of the flue gas from the gas turbine (GT), it is thus used to superheat the mixture of syngas and steam from the SCWG reactor. At last, the remaining heat is recovered in HRSG for the steam turbine (ST). The conditions of the combined cycle modules, including combustor, gas and steam turbines are presented in Table 8.

Figure 9. Schematic diagram of the process flow of the proposed integrated system.

#### 3.2.4. Performance of integrated system

Figure 10 shows the relationship between total energy efficiency, ηtot, and fluidization velocity for different gasification pressures of 25 and 30 MPa. Subsequently, about 3.5 t-H2 h<sup>1</sup> can be converted to MCH by hydrogenation process with toluene. The increase of fluidization velocity leads to lower total energy efficiency. Therefore, gasification carried out under a lower gasification pressure at 25 MPa has better total energy efficiency than that at 30 MPa.

4. Conclusion

Author details

References

delivers the total energy efficiency of 84%.

Lukman Adi Prananto and Muhammad Aziz\*

gen Energy. 2017;42(5):2904-2913

Energy. 2015;40(2):1026-1036

\*Address all correspondence to: maziz@ssr.titech.ac.jp

& Sustainable Energy Reviews. 2014;38:890-902

system. Applied Energy. 2017;204:1138-1147

Institute of Innovative Research, Tokyo Institute of Technology, Japan

Novel integrated gasification systems for coproduction of electricity and MCH from low-rank coal and microalgae have been proposed. Enhanced process integration technology is applied for both systems to minimize exergy losses throughout the integrated system, thus improving the total energy efficiency. However, the models are carried out in the condition of ideal zero heat loss. Therefore, approximately 5–10% of heat losses are necessary to consider for the investigation in the actual case of the systems. For the case of microalgae, the effects of the fluidization velocity and gasification pressure on the total energy and electricity generation efficiencies were evaluated for optimum integrated system, while for the case of low-rank coal, the optimization is subjected to the investigation of fluidization velocity, steam-to-fuel ratio, and the chemical looping pressure. Finally, the integrated system for microalgae is capable to provide more than 60% of total energy efficiency, while the integrated system for low-rank coal

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[3] Aziz M. Power generation from algae employing enhanced process integration technol-

[4] Aziz M, Oda T, Kashiwagi T. Advanced energy harvesting from macroalgae-innovative integration of drying, gasification and combined cycle. Energies. 2014;7(12):8217-8235 [5] Darmawan A, Budianto D, Aziz M, Tokimatsu K. Retrofitting existing coal power plants through cofiring with hydrothermally treated empty fruit bunch and a novel integrated

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The increasing in fluidization velocity leads to more water for the fluidizing steam which thus increases the flow rate of steam exhausted from the SCWG reactor. As a result, the heat available as hot stream in the HRSG decreases, leading to a decrease in actual work obtained from the steam turbine. On the other hand, the increasing of gasification pressure leads to more flow rate of the fluidizing steam under same fluidization velocity. Thus, the increase in gasification pressure finally leads to lower actual work by the steam turbine.


Table 8. Assumed conditions for the combined cycle, including combustion and gas and steam turbines.

Figure 10. Relationship between total energy efficiency and fluidization velocity under different gasification pressures.
