## 4 Thermodynamic Performance Comparison and Discussion  
Based on the above experimental results, thermodynamic performance of the whole process is presented in this section. ASPEN PLUS software V8.2 was used for process simulation and the PR-BM method was selected. Next, 1300 \({}^{\circ}\)C and 4 MPa was assumed for GE gasification; 1100 \({}^{\circ}\)C and 2.5 MPa was assumed for char-steam gasification. In the proposed process, part of the coal was sent to the combustion chamber to provide heat to coking and char-steam reaction. The temperature of combustion was 1150 \({}^{\circ}\)C and the temperature of flue gas was 120 \({}^{\circ}\)C. The PSA unit for both processes operated at 5 MPa and the purity of the H\({}_{2}\) product was 99.9%. Three indicators were used to evaluate thermodynamic performance, as shown in Equations (1)-(3). Cold gas efficiency represented the ratio of converting chemical energy of coal into syngas. The coal to hydrogen efficiency denoted the amount of chemical energy of coal converted into hydrogen product. Exergy efficiency stood for the ratio of the exergy of H\({}_{2}\) product to the exergy of feed coal. \[\text{Cold gas efficiency}=\text{Lower heating value of syngas/Lower heating value of coal} \tag{1}\]  
Coal to hydrogen efficiency = Lower heating value of hydrogen product/Lower heating value of coal (2)  
\[\text{Exergy efficiency}=\text{Exergy of hydrogen product/Exergy of coal} \tag{3}\]  
Experimental results of char making process were directly used for char-steam gasification simulation. Further, the simulated results of syngas components agreed well with the experiments presented in Figure 3. A thermodynamic analysis showed that coal to hydrogen efficiency based on chemical regenerative gasification was as high as 71.6% (LHV based), which was far higher than  
Figure 4: Online CO fraction from char-steam gasification at different tempeatures. Figure 5: Online CO\({}_{2}\) fraction from char-steam gasification at different tempeatures. 58.9% of traditional GE gasification-based plant. Moreover, the energy consumption for unit hydrogen production decreased from 183.8 MJ/kg in a traditional plant to 151.2 MJ/kg in this novel process. The efficiency upgrade was mainly caused by the improvement of cold gas efficiency during coal gasification, in addition to being brought by the reduction of power consumption for air separation (Table 4). By recovering the sensible heat of syngas to drive gasification reaction, sensible heat was converted into the chemical energy of syngas and thereby the cold gas efficiency of chemical regenerative gasification was lifted by 5.6%. Adopting steam instead of pure oxygen as an oxidant reduced the power consumption for air separation (Table 5). Thus, the coal input for the auxiliary power generation is reduced, which further helped improve the whole plant efficiency. To disclose the reason for system performance enhancement, exergy analysis is also presented in Table 6. The exergy efficiency of the novel coal to hydrogen plant was 78.5%, which was 13.9 percentage points higher than the traditional plant. It can be seen that the efficiency upgrade was mainly a result of the reduction in exergy destruction of coal gasification, air separation, auxiliary power generation, and heat recovery of syngas units. Eliminating the air separation unit reduced exergy destruction by 3.1 percentages and the coal gasification unit (including char making and char gasification) reduced exergy destruction by 4.3 percentages. Because there is no power consumption for air separation, the exergy destruction in auxiliary power generation unit also decreased by 2.3%. Furthermore, recovery of syngas sensible heat instead of quenching reduced exergy destruction by 2.8%.