3. Power and H2 production from various Feedstocks

#### 3.1. Integrated systems from low-rank coal by syngas chemical looping

#### 3.1.1. The characteristics of low-rank coal as energy source

Based on the current status of H2 production, fossil fuel occupies dominant portion as the primary substance with more than 90% share [22]. In terms of sustainability, fossil fuel has a drawback in the issue of energy reserve. Hence, fossil fuel with abundant reserves is favorable for this system. One of the fossil fuel fit with this condition is low-rank coal (LRC). Besides the long-term reserves, LRC exhibits other advantages, including high concentration of volatiles, high reactivity, low sulfur content, and relatively low mining costs [23]. However, due to high inherent moisture content and readsorption behavior of the humidity, the drying of LRC is very challenging due to the energy intensive process [24]. Thus, an investigation based on EPI technology to effectively manage the heat circulation is carried out to develop an integrated system which can accommodate least expensive LRC for large-scale MCH production with optimum energy efficiency [25].

and thermal energy for the power generation. The by-product of CO2 generated in the chemical looping is sequestered to keep the clean energy of the integrated system, while the desired products of chemical looping are discharged to the combined cycle module and the hydrogenation module for the generation of electricity and MCH, respectively. The MCH is prepared in the liquid phase. Hence, the compound can be easily transported to the specified place. The generated electricity from the combined cycle is partially consumed for the house load operation for the internal processes, but the remainder can be sold to utilities via a connection to a

Integrated Gasification System for Power and Hydrogen Production

http://dx.doi.org/10.5772/intechopen.71841

261

Figure 2. Schematic of material and energy flows in the integrated system.

The drying process is carried out to meet the target of the moisture content of the LRC particle so that the calorific value is increasing and the high gasification temperature can be achieved. In the drying process, equilibrium moisture content significantly affects the immediate environment because the particle of LRC will reach a water concentration equal to the ambient environment. Hence, the temperature, pressure, and relative humidity of the environment, as well as the partial vapor pressure, determine the moisture content. Among any methods used for high moisture content drying process, the superheated steam exhibits numerous advantages, including the energy efficiency, high capacity, and has been widely investigated for drying scheme [30]. Thus, by employing the superheated steam as the drying method, the drying and gasification modules were developed, as shown in Figure 3. The relationship between the relative vapor pressure, p=po, and the equilibrium moisture content, M, can be

Initially, the discharged heat produced in the chemical looping module and the high energy compressed steam is employed to preheat the high moisture content LRC particles (D1) in HX1 and HX2, respectively. Subsequently, the preheated LRC particles undergo drying process to omit the water content inside the particles. The type of dryer applied in this system is the

ð1Þ

power grid.

3.1.3. Analysis of integrated system

3.1.3.1. Drying and gasification

approximated by Eq. (1) [31].

Another issue for the utilization of LRC is the large amounts of CO2 emission, in which the plant has to be coupled with the CO2 separation (capture) and sequestration facility. For the CO2 capture, several technologies are available, including membrane, algae-based uptake, cryogenic, and chemical looping [26]. The latter is considered as the most potential method for the sequestration of CO2 due to high capability of CO2 capturing and high conversion efficiency.

Some investigations have been carried out to study the production of H2 from coal. An integrated system consisting of hydrogasification, electrolysis, and electricity generation has been carried out by Minutillo and Perna [27] to produce synthetic natural gas. However, as the conventional process integration was adopted to develop the proposed system, the result of their study obtained relatively low energy efficiency due to significant losses of exergy. Another integrated system consisting of shell-type gasification, chemical looping, and electricity generation has been carried out by Xiang et al. In their proposed system [28], overall heat circulation was excluded, as the system adopted the pinch technology for heat recovery. Therefore, the system exhibits low energy efficiency. Moreover, Cleeton et al. carried out an integrated system with the combination of chemical looping and steam-coal gasification [29]. After the parameter evaluation, the delivered system showed energy efficiency up to 58%. However, if the effort of exergy optimization was applied, the energy efficiency of the system can be improved significantly.

#### 3.1.2. Integrated system development

The schematic flow of energy and material of the integrated system is shown in Figure 2. Here, the dotted and solid lines represent electricity and material/heat flows, respectively. At the beginning of the process, the moisture content of raw LRC particles is extracted by the drying module. The product of this module is the high calorific value of LRC as the result of low moisture content. Next, the dried LRC particles are converted to syngas by the gasification module. The produced syngas is thus fed to the chemical looping module to generate H2, CO2,

Figure 2. Schematic of material and energy flows in the integrated system.

and thermal energy for the power generation. The by-product of CO2 generated in the chemical looping is sequestered to keep the clean energy of the integrated system, while the desired products of chemical looping are discharged to the combined cycle module and the hydrogenation module for the generation of electricity and MCH, respectively. The MCH is prepared in the liquid phase. Hence, the compound can be easily transported to the specified place. The generated electricity from the combined cycle is partially consumed for the house load operation for the internal processes, but the remainder can be sold to utilities via a connection to a power grid.

#### 3.1.3. Analysis of integrated system

#### 3.1.3.1. Drying and gasification

3. Power and H2 production from various Feedstocks

3.1.1. The characteristics of low-rank coal as energy source

optimum energy efficiency [25].

260 Gasification for Low-grade Feedstock

can be improved significantly.

3.1.2. Integrated system development

efficiency.

3.1. Integrated systems from low-rank coal by syngas chemical looping

Based on the current status of H2 production, fossil fuel occupies dominant portion as the primary substance with more than 90% share [22]. In terms of sustainability, fossil fuel has a drawback in the issue of energy reserve. Hence, fossil fuel with abundant reserves is favorable for this system. One of the fossil fuel fit with this condition is low-rank coal (LRC). Besides the long-term reserves, LRC exhibits other advantages, including high concentration of volatiles, high reactivity, low sulfur content, and relatively low mining costs [23]. However, due to high inherent moisture content and readsorption behavior of the humidity, the drying of LRC is very challenging due to the energy intensive process [24]. Thus, an investigation based on EPI technology to effectively manage the heat circulation is carried out to develop an integrated system which can accommodate least expensive LRC for large-scale MCH production with

Another issue for the utilization of LRC is the large amounts of CO2 emission, in which the plant has to be coupled with the CO2 separation (capture) and sequestration facility. For the CO2 capture, several technologies are available, including membrane, algae-based uptake, cryogenic, and chemical looping [26]. The latter is considered as the most potential method for the sequestration of CO2 due to high capability of CO2 capturing and high conversion

Some investigations have been carried out to study the production of H2 from coal. An integrated system consisting of hydrogasification, electrolysis, and electricity generation has been carried out by Minutillo and Perna [27] to produce synthetic natural gas. However, as the conventional process integration was adopted to develop the proposed system, the result of their study obtained relatively low energy efficiency due to significant losses of exergy. Another integrated system consisting of shell-type gasification, chemical looping, and electricity generation has been carried out by Xiang et al. In their proposed system [28], overall heat circulation was excluded, as the system adopted the pinch technology for heat recovery. Therefore, the system exhibits low energy efficiency. Moreover, Cleeton et al. carried out an integrated system with the combination of chemical looping and steam-coal gasification [29]. After the parameter evaluation, the delivered system showed energy efficiency up to 58%. However, if the effort of exergy optimization was applied, the energy efficiency of the system

The schematic flow of energy and material of the integrated system is shown in Figure 2. Here, the dotted and solid lines represent electricity and material/heat flows, respectively. At the beginning of the process, the moisture content of raw LRC particles is extracted by the drying module. The product of this module is the high calorific value of LRC as the result of low moisture content. Next, the dried LRC particles are converted to syngas by the gasification module. The produced syngas is thus fed to the chemical looping module to generate H2, CO2, The drying process is carried out to meet the target of the moisture content of the LRC particle so that the calorific value is increasing and the high gasification temperature can be achieved. In the drying process, equilibrium moisture content significantly affects the immediate environment because the particle of LRC will reach a water concentration equal to the ambient environment. Hence, the temperature, pressure, and relative humidity of the environment, as well as the partial vapor pressure, determine the moisture content. Among any methods used for high moisture content drying process, the superheated steam exhibits numerous advantages, including the energy efficiency, high capacity, and has been widely investigated for drying scheme [30]. Thus, by employing the superheated steam as the drying method, the drying and gasification modules were developed, as shown in Figure 3. The relationship between the relative vapor pressure, p=po, and the equilibrium moisture content, M, can be approximated by Eq. (1) [31].

$$\frac{p}{p\_o} = 1 - \exp\left[-2.53(T\_b - 273)^{0.47} \left(\frac{M}{(100 - M)}\right)^{1.59}\right] \tag{1}$$

Initially, the discharged heat produced in the chemical looping module and the high energy compressed steam is employed to preheat the high moisture content LRC particles (D1) in HX1 and HX2, respectively. Subsequently, the preheated LRC particles undergo drying process to omit the water content inside the particles. The type of dryer applied in this system is the

Figure 3. Schematic of drying and gasification modules.

fluidized bed owing to the benefit in the uniform temperature distribution and heat transfers, an extensive area of the contact surface, and proper particle mixing [32]. The immersed heat exchanger (HX3) is furnished inside the fluidized-bed dryer for the superheated steam process.

The next step is the gasification process, which produces combustible gases, including H2, CO, and CH4. Series of reactions are involved in this process, including the water-gas shift, Boudouard, and oxidation, as well as methanation. Due to the necessity of high gasification temperatures, dry-feeding gasification is employed in the system instead of slurry-feeding gasification [33]. Here, a dual-circulating fluidized bed (gasifier and combustor) is furnished to achieve higher carbon conversion efficiency and conversion rate [34].

After the gasification, both of the raw syngas and flue gas are fed into SEP1 and SEP2 for removal of ash and slag by the ceramic particulate removal which exhibits high efficiency under hightemperature conditions [35]. Table 1 summarizes the conditions assumed for LRC drying and gasification study.

The effect of steam-to-fuel ratio during gasification is evaluated to define the optimum combination of steam and fuel. Two different steam-to-fuel ratios (0.9 and 1.4) are investigated to confirm the optimum ratio for the performance of the chemical looping system. Table 2 shows the composition of the syngas resulting from different steam-to-fuel ratios.

oxygen carrier in the system, the syngas chemical looping is employed due to the beneficial in the solids handling and energy efficiency. The oxygen carrier exhibits no direct contact between atmospheric oxygen and the fuel during the combustion process; hence, the highpurity CO2 can be immediately separated without any further handling, which thus promotes an efficient and clean energy conversion. Thus, due to the excellent mechanical properties, large capacity content of oxygen carrier, and the high conversion of syngas and steam, the

Table 2. Composition of syngas generated using a dual-circulating fluidized bed with varying steam-to-fuel ratios.

0.820 0.063 0.486 0.255 19.1

0.9 1.4

0.762 0.066 0.415 0.270 28.7

Figure 4 represents a process flow diagram for the chemical looping and combined cycle modules. The chemical looping module is developed from three connected reactors: reducer (RED),

iron-based materials are applied as the recirculated oxygen carriers [36].

Component Value Note

100 60 18 1, 2, 3, 4 2.0 900 19.33

65.53 3.75 0.84 25.22 0.38 0.05 4.23

1173 1123 0.9; 1.4 2.0 Olivine 0.37

Produced syngas Steam-to-fuel ratio

At moisture content of 18 wt% wb

263

http://dx.doi.org/10.5772/intechopen.71841

Integrated Gasification System for Power and Hydrogen Production

Drying conditions Coal flow rate (Mg h�<sup>1</sup>

)

)

Initial moisture content (wt% wb) Target moisture content (wt% wb) Fluidization velocity Udry/Umf,dry Mean particle diameter (mm) Bulk density (kg m�<sup>3</sup>

Heating value (MJ kg�<sup>1</sup> HHV)

LRC ultimate analysis

Gasification conditions Combustion temperature (K) Gasification temperature (K) Steam-to-fuel ratio

H2 (Nm<sup>3</sup> kg-fuel�<sup>1</sup> daf) CH4 (Nm<sup>3</sup> kg-fuel�<sup>1</sup> daf) CO (Nm<sup>3</sup> kg-fuel�<sup>1</sup> daf) CO2 (Nm<sup>3</sup> kg-fuel�<sup>1</sup> daf)

Steam content in produced gas (vol%)

Bed material

LRC mean particle diameter (mm)

Mean bed material diameter (mm)

Table 1. LRC drying and gasification conditions.

C (wt% db) H (wt% db) N (wt% db) O (wt% db) S (wt% db) Cl (wt% db) Ash (wt% db)

#### 3.1.3.2. Chemical looping and combined cycle

Among any methods, direct chemical looping and syngas chemical looping are the typical methods for the chemical looping. However, due to the utilization of the metal oxide for


Table 1. LRC drying and gasification conditions.

fluidized bed owing to the benefit in the uniform temperature distribution and heat transfers, an extensive area of the contact surface, and proper particle mixing [32]. The immersed heat exchanger (HX3) is furnished inside the fluidized-bed dryer for the superheated steam process. The next step is the gasification process, which produces combustible gases, including H2, CO, and CH4. Series of reactions are involved in this process, including the water-gas shift, Boudouard, and oxidation, as well as methanation. Due to the necessity of high gasification temperatures, dry-feeding gasification is employed in the system instead of slurry-feeding gasification [33]. Here, a dual-circulating fluidized bed (gasifier and combustor) is furnished

After the gasification, both of the raw syngas and flue gas are fed into SEP1 and SEP2 for removal of ash and slag by the ceramic particulate removal which exhibits high efficiency under hightemperature conditions [35]. Table 1 summarizes the conditions assumed for LRC drying and

The effect of steam-to-fuel ratio during gasification is evaluated to define the optimum combination of steam and fuel. Two different steam-to-fuel ratios (0.9 and 1.4) are investigated to confirm the optimum ratio for the performance of the chemical looping system. Table 2 shows

Among any methods, direct chemical looping and syngas chemical looping are the typical methods for the chemical looping. However, due to the utilization of the metal oxide for

to achieve higher carbon conversion efficiency and conversion rate [34].

the composition of the syngas resulting from different steam-to-fuel ratios.

gasification study.

3.1.3.2. Chemical looping and combined cycle

Figure 3. Schematic of drying and gasification modules.

262 Gasification for Low-grade Feedstock


Table 2. Composition of syngas generated using a dual-circulating fluidized bed with varying steam-to-fuel ratios.

oxygen carrier in the system, the syngas chemical looping is employed due to the beneficial in the solids handling and energy efficiency. The oxygen carrier exhibits no direct contact between atmospheric oxygen and the fuel during the combustion process; hence, the highpurity CO2 can be immediately separated without any further handling, which thus promotes an efficient and clean energy conversion. Thus, due to the excellent mechanical properties, large capacity content of oxygen carrier, and the high conversion of syngas and steam, the iron-based materials are applied as the recirculated oxygen carriers [36].

Figure 4 represents a process flow diagram for the chemical looping and combined cycle modules. The chemical looping module is developed from three connected reactors: reducer (RED), oxidizer (OXD), and combustor (COM2). In the reducer and oxidizer, a counter current moving bed reactor is employed, while an entrained fluidized bed is furnished for the combustor.

In the RED, the compressed syngas is fed as the fluidizing gas. After leaving the RED (C3), the high pressure fluidizing gas is thus recovered by the expander (GT1) for electricity generation. The reactions in the RED assumed to occur during reduction are as follows [37]:

$$\begin{aligned} \text{Fe}\_2\text{O}\_3 + \text{CO} &\rightarrow 2\text{FeO} + \text{CO}\_2\\ \text{H} &= \text{-} 2.8 \text{ kJ mol}^{-1} \end{aligned} \tag{2}$$

iron particles (C9), is fed to the OXD in which the oxidation takes place with the steam as reactant to produce highly pure H2 (C16). The reactions inside the OXD in the presence of

Integrated Gasification System for Power and Hydrogen Production

http://dx.doi.org/10.5772/intechopen.71841

The generated H2 is discharged to the hydrogenation module for further process, while the metals move to the COM2 for recirculation. The reaction inside the COM2 is shown below.

The reduction process is performed by the discharged heat from the combustion process implanted inside the metal oxide. The high energy from compressed flue gas is expanded for electricity generation in GT3 and ST1 by employing combined cycle. The conditions of chem-

The conditions during toluene hydrogenation and the schematic flow diagram are shown in Table 4 and Figure 5, respectively. The heat generated from the exothermic reaction of hydrogenation is applied as the heat source for electricity generation in the steam turbine (ST1). The theoretical gravimetric and volumetric hydrogen concentrations in MCH under ambient con-

Figure 6 indicates the effect of drying fluidization velocities to the compressor and blower duties, net generated power, and power efficiency. These values are carried out using a steamto-fuel ratio during gasification and a basic chemical looping pressure of 0.9 and 3 MPa, respectively. A compressor (CP4) is prepared after the gasification module to pressurize the

Based on the calculation results, there is barely significant shift in the compressor duty as the compression work is almost constant at 1.8 MW. On the other hand, the duty of blower is increasing as the fluidization velocities during drying are uprising. Here, the blower duty

the fluidization velocity is increased to 4 Umf,dry. As high amount of energy is required for the high duty of the blower, a rapid fluidization velocity during drying results in a lower total

Figure 7(a) presents the effect of different steam-to-fuel ratios to the amount of H2 generated, H2 production efficiency, net generated power, and the total efficiency, while Figure 7(b) presents the effect of different steam-to-fuel ratios to the amounts of produced H2 and MCH. These values are carried out using a specific fluidization velocity during drying and a basic

ditions are 6.2 and 47%, respectively [39]. The hydrogenation reaction is as follows:

ical looping and combined cycle modules are explained in Table 3.

ð7Þ

265

ð8Þ

ð9Þ

ð10Þ

) is 0.7 MW and rise to 2.7 MW when

excess steam can be written as follows:

3.1.3.3. Hydrogenation

efficiency.

3.1.4. Performance of integrated system

syngas into the pressure of chemical looping.

at the lowest fluidization velocity (Umf,dry, 1.28 m s�<sup>1</sup>

$$\begin{aligned} \text{FeO} + \text{CO} &\rightarrow \text{Fe} + \text{CO}\_2 \end{aligned} \tag{3}$$

$$\begin{aligned} \text{Fe}\_2\text{O}\_3 + \text{H}\_2 &\rightarrow 2\text{FeO} + \text{H}\_2\text{O} \\\\ \text{H} &= 38.4 \text{ kJ mol}^{-1} \end{aligned} \tag{4}$$

$$\text{FeO} + \text{H}\_2 \rightarrow \text{Fe} + \text{H}\_2\text{O} \tag{5}$$

$$\Delta \text{H} = 30.2 \text{ kJ mol}^{-1} \tag{5}$$

$$4Fe\_2O\_3 + 3CH\_4 \rightarrow 8Fe + 3CO\_2 + 6H\_2O \tag{8} H = 897.18 \text{ kJ mol}^{-1} \tag{9}$$

The formation of by-products, including Fe3C and carbon soot due to Boudouard reaction has been noticed in the continuous operation in RED. However, efforts to diminish the formation of Fe3C have been performed in previous studies, including the modification of iron-based oxygen carrier with CeO2 and exhaustive selection of the used iron-based oxygen carriers [38].

CO2 and steam are generated during the reduction step and then leave the reducer for the cooling process in preparation for separation (CD1). The separated CO2 (C7) is then compressed and ready for the sequestration purposes. Other product from the reduction step, the

Figure 4. Process flow diagram of the chemical looping and combined cycle modules.

iron particles (C9), is fed to the OXD in which the oxidation takes place with the steam as reactant to produce highly pure H2 (C16). The reactions inside the OXD in the presence of excess steam can be written as follows:

$$\text{Fe} + \text{H}\_2\text{O} \rightarrow \text{FeO} + \text{H}\_2\tag{7}$$

$$\Delta \text{H} = \text{-30.2 kJ mol}^{-1} \tag{7}$$

$$\text{3FeO} + \text{H}\_2\text{O} \rightarrow \text{Fe}\_3\text{O}\_4 + \text{H}\_2\tag{8}$$

$$\Delta \text{H} = \text{-60.6 kJ mol}^{-1} \tag{8}$$

The generated H2 is discharged to the hydrogenation module for further process, while the metals move to the COM2 for recirculation. The reaction inside the COM2 is shown below.

$$\begin{aligned} \text{4Fe}\_3\text{O}\_4 + \text{O}\_2 &\rightarrow 6\text{Fe}\_2\text{O}\_3\\ \text{4H} &= \text{471.6 kJ mol}^{-1} \end{aligned} \tag{9}$$

The reduction process is performed by the discharged heat from the combustion process implanted inside the metal oxide. The high energy from compressed flue gas is expanded for electricity generation in GT3 and ST1 by employing combined cycle. The conditions of chemical looping and combined cycle modules are explained in Table 3.

#### 3.1.3.3. Hydrogenation

oxidizer (OXD), and combustor (COM2). In the reducer and oxidizer, a counter current moving bed reactor is employed, while an entrained fluidized bed is furnished for the combustor.

In the RED, the compressed syngas is fed as the fluidizing gas. After leaving the RED (C3), the high pressure fluidizing gas is thus recovered by the expander (GT1) for electricity generation.

The formation of by-products, including Fe3C and carbon soot due to Boudouard reaction has been noticed in the continuous operation in RED. However, efforts to diminish the formation of Fe3C have been performed in previous studies, including the modification of iron-based oxygen carrier with CeO2 and exhaustive selection of the used iron-based oxygen carriers [38]. CO2 and steam are generated during the reduction step and then leave the reducer for the cooling process in preparation for separation (CD1). The separated CO2 (C7) is then compressed and ready for the sequestration purposes. Other product from the reduction step, the

Figure 4. Process flow diagram of the chemical looping and combined cycle modules.

ð2Þ

ð3Þ

ð4Þ

ð5Þ

ð6Þ

The reactions in the RED assumed to occur during reduction are as follows [37]:

264 Gasification for Low-grade Feedstock

The conditions during toluene hydrogenation and the schematic flow diagram are shown in Table 4 and Figure 5, respectively. The heat generated from the exothermic reaction of hydrogenation is applied as the heat source for electricity generation in the steam turbine (ST1). The theoretical gravimetric and volumetric hydrogen concentrations in MCH under ambient conditions are 6.2 and 47%, respectively [39]. The hydrogenation reaction is as follows:

$$\text{C}\_7\text{H}\_6 + 3\text{H}\_2 \rightarrow \text{C}\_7\text{H}\_{14} \tag{10}$$

$$\Delta\text{H} = \text{-} 20\text{S}.0 \text{ kJ mol}^{-1} \tag{10}$$

#### 3.1.4. Performance of integrated system

Figure 6 indicates the effect of drying fluidization velocities to the compressor and blower duties, net generated power, and power efficiency. These values are carried out using a steamto-fuel ratio during gasification and a basic chemical looping pressure of 0.9 and 3 MPa, respectively. A compressor (CP4) is prepared after the gasification module to pressurize the syngas into the pressure of chemical looping.

Based on the calculation results, there is barely significant shift in the compressor duty as the compression work is almost constant at 1.8 MW. On the other hand, the duty of blower is increasing as the fluidization velocities during drying are uprising. Here, the blower duty at the lowest fluidization velocity (Umf,dry, 1.28 m s�<sup>1</sup> ) is 0.7 MW and rise to 2.7 MW when the fluidization velocity is increased to 4 Umf,dry. As high amount of energy is required for the high duty of the blower, a rapid fluidization velocity during drying results in a lower total efficiency.

Figure 7(a) presents the effect of different steam-to-fuel ratios to the amount of H2 generated, H2 production efficiency, net generated power, and the total efficiency, while Figure 7(b) presents the effect of different steam-to-fuel ratios to the amounts of produced H2 and MCH. These values are carried out using a specific fluidization velocity during drying and a basic


Table 3. Conditions and assumptions for chemical looping and the combined cycle.


Generally, the increase of chemical looping process pressures leads to increase in both the net

Figure 6. Effect of fluidization velocity during drying (at a steam-to-fuel ratio during gasification and basic chemical

Integrated Gasification System for Power and Hydrogen Production

http://dx.doi.org/10.5772/intechopen.71841

267

Besides the high potential in the pharmaceuticals, industrial materials, and food production, microalgae own a high potential for the energy source [40]. Among other biomasses, microalgae are very exceptional due to its excellent growth rate, ability to grow in a harsh environment, and highly efficient solar energy conversion [4]. Currently, many products of fuel are derived from the microalgae, including bio-oil, biohydrogen, and biodiesel [41]. However, as the microalgae grow in an aqueous environment far from the industrial or residential area, it has to be planted remotely and transported to the designated area for the utilization of microalgae

3.2. Integrated systems from microalgae by supercritical water gasification

generated power and the power generation efficiency.

looping pressure of 0.9 and 3 MPa, respectively).

Figure 5. Process flow diagram of the hydrogenation module.

3.2.1. The characteristics of microalgae as energy source

Table 4. Conditions assumed for toluene hydrogenation.

chemical looping pressure of 2 Umf,dry and 3 MPa, respectively. Generally, the higher H2 production efficiency and power generation are both achieved in the steam-to-fuel ratio of 0.9 instead of 1.4. The produced H2 amount and net generated power at a steam-to-fuel ratio of 1.4 are 4.3 t h�<sup>1</sup> (H2 production efficiency of 66.5%) and 24.1 MW (power generation efficiency of 11.2%), respectively. These values rise up to 4.6 t h�<sup>1</sup> (with a H2 production efficiency of 71.9%) and 26.3 MW (with a power generation efficiency of 12.2%), when the steam-to-fuel ratio is set at 0.9.

Figure 8 Shows the effect of basic chemical looping pressure to the net generated power and power generation efficiency. These values are carried out by applying a fluidization velocity during drying and a steam-to-fuel ratio during gasification of 2 Umf,dry and 0.9, respectively.

Figure 5. Process flow diagram of the hydrogenation module.

Figure 6. Effect of fluidization velocity during drying (at a steam-to-fuel ratio during gasification and basic chemical looping pressure of 0.9 and 3 MPa, respectively).

Generally, the increase of chemical looping process pressures leads to increase in both the net generated power and the power generation efficiency.

#### 3.2. Integrated systems from microalgae by supercritical water gasification

#### 3.2.1. The characteristics of microalgae as energy source

chemical looping pressure of 2 Umf,dry and 3 MPa, respectively. Generally, the higher H2 production efficiency and power generation are both achieved in the steam-to-fuel ratio of 0.9 instead of 1.4. The produced H2 amount and net generated power at a steam-to-fuel ratio of 1.4 are 4.3 t h�<sup>1</sup> (H2 production efficiency of 66.5%) and 24.1 MW (power generation efficiency of 11.2%), respectively. These values rise up to 4.6 t h�<sup>1</sup> (with a H2 production efficiency of 71.9%) and 26.3 MW

Figure 8 Shows the effect of basic chemical looping pressure to the net generated power and power generation efficiency. These values are carried out by applying a fluidization velocity during drying and a steam-to-fuel ratio during gasification of 2 Umf,dry and 0.9, respectively.

(with a power generation efficiency of 12.2%), when the steam-to-fuel ratio is set at 0.9.

Component Value Note

1073 2.0–4.0 100 2 99.99

1023 2.0–4.0 99.99 10

1473 2.2–4.2 10

90 1473

Reducer

Oxidizer

Combustor Temperature (K) Pressure (MPa) Air excess at outlet (%)

Temperature (K) Pressure (MPa) Syngas conversion (%) Iron particle diameter (mm) Produced CO2 purity (%)

266 Gasification for Low-grade Feedstock

Temperature (K) Pressure (MPa) Produced H2 purity (%) Excess steam at outlet (%)

Gas turbine (F-class)

HRSG and steam turbine

Inlet pressure (MPa)

Turbine polytrophic efficiency (%) Maximum turbine inlet temperature (K)

Turbine polytrophic efficiency (%)

Maximum turbine inlet temperature (K) Minimum outlet vapor quality

Table 3. Conditions and assumptions for chemical looping and the combined cycle.

Component Value Reaction temperature (K) 473 Operating pressure (kPa) 130

Catalyst particle size (mm) 0.3 Particle sphericity 0.5

Table 4. Conditions assumed for toluene hydrogenation.

Catalyst Ni-Mo/Al2O3

Besides the high potential in the pharmaceuticals, industrial materials, and food production, microalgae own a high potential for the energy source [40]. Among other biomasses, microalgae are very exceptional due to its excellent growth rate, ability to grow in a harsh environment, and highly efficient solar energy conversion [4]. Currently, many products of fuel are derived from the microalgae, including bio-oil, biohydrogen, and biodiesel [41]. However, as the microalgae grow in an aqueous environment far from the industrial or residential area, it has to be planted remotely and transported to the designated area for the utilization of microalgae

Figure 7. Effects of the steam-to-fuel ratio on (a) net generated power, power generation efficiency, produced H2, H2 production efficiency, and total efficiency and (b) produced H2 and MCH amounts (Udry = 2 Umf,dry, basic chemical looping pressure = 3 MPa).

in the large scale. To this, a process chain from the microalgae cultivation to the H2-based MCH for LOHC generation can solve the transportation and storage issues of the large-scale utilization of microalgae.

For the investigation, an alga species with ability to grow rapidly in normal condition and rich protein is necessary. To this, Chlorella vulgaris is selected as a sample for system evaluation. [42]. The properties of Chlorella vulgaris, including the results of proximate and ultimate analyses are listed in Table 5.

consuming process, which tends to absorb a huge portion of energy and create a lowly energyefficient system [45]. To this, the EPI technology can tackle the challenge of the high energy issue of the SCWG, and leads to a novel process for the large-scale utilization of microalgae into LOHC.

) 18.49

Figure 8. Correlations of net generated power and power generation efficiency with basic chemical looping pressure

64.1 13 21.1 7 15

Integrated Gasification System for Power and Hydrogen Production

http://dx.doi.org/10.5772/intechopen.71841

269

45.8 7.9 7.5 38.7

The basic schematic energy and material flows of the integrated system consists of SCWG, H2 separation, hydrogenation, and the combined cycle. Figure 9 explains the detailed schematic

3.2.2. Integrated system development

(Udry = 2 Umf,dry, steam-to-fuel ratio = 0.9).

Chemical composition Protein (wt% db) Fat (wt% db) Fiber (wt% db) Ash (wt% db)

Carbohydrates (wt% db)

Calorific value (dried, MJ kg�<sup>1</sup>

Ultimate analysis Carbon (wt% db) Hydrogen (wt% db) Nitrogen (wt% db) Oxygen (wt% db)

Property Value Moisture content (wt% wb) 90 Dry solid content (wt% wb) 10

process flow diagram of the proposed integrated system.

Table 5. Proximate and ultimate analyses of Chlorella vulgaris.

Among any candidates in the thermochemical process, gasification owns the highest rank due to its conversion efficiency [43]. There are two gasification methods widely used, the conventional thermal gasification and supercritical water gasification (SCWG). The former requires drying process to low moisture content before the gasification, while the latter is performed in the aqueous state, in which drying process is avoidable [44], and more favorable for the gasification of microalgae, owing to its high moisture content (70–90 wt% wb) [16]. However, SCWG is an energy

Figure 8. Correlations of net generated power and power generation efficiency with basic chemical looping pressure (Udry = 2 Umf,dry, steam-to-fuel ratio = 0.9).


Table 5. Proximate and ultimate analyses of Chlorella vulgaris.

consuming process, which tends to absorb a huge portion of energy and create a lowly energyefficient system [45]. To this, the EPI technology can tackle the challenge of the high energy issue of the SCWG, and leads to a novel process for the large-scale utilization of microalgae into LOHC.

#### 3.2.2. Integrated system development

in the large scale. To this, a process chain from the microalgae cultivation to the H2-based MCH for LOHC generation can solve the transportation and storage issues of the large-scale utiliza-

Figure 7. Effects of the steam-to-fuel ratio on (a) net generated power, power generation efficiency, produced H2, H2 production efficiency, and total efficiency and (b) produced H2 and MCH amounts (Udry = 2 Umf,dry, basic chemical

For the investigation, an alga species with ability to grow rapidly in normal condition and rich protein is necessary. To this, Chlorella vulgaris is selected as a sample for system evaluation. [42]. The properties of Chlorella vulgaris, including the results of proximate and ultimate

Among any candidates in the thermochemical process, gasification owns the highest rank due to its conversion efficiency [43]. There are two gasification methods widely used, the conventional thermal gasification and supercritical water gasification (SCWG). The former requires drying process to low moisture content before the gasification, while the latter is performed in the aqueous state, in which drying process is avoidable [44], and more favorable for the gasification of microalgae, owing to its high moisture content (70–90 wt% wb) [16]. However, SCWG is an energy

tion of microalgae.

looping pressure = 3 MPa).

268 Gasification for Low-grade Feedstock

analyses are listed in Table 5.

The basic schematic energy and material flows of the integrated system consists of SCWG, H2 separation, hydrogenation, and the combined cycle. Figure 9 explains the detailed schematic process flow diagram of the proposed integrated system.

#### 3.2.3. Analysis of integrated system

#### 3.2.3.1. Supercritical water gasification of microalgae

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

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 gasification conditions and produced syngas composition.
