# Modeling and Simulation of IGCC Considering Pressure and Flow Distribution of Gasifier
## 4 Results and Analysis
### IGCC System Simulation  
Combining the gasifier model with the power island model, the simulation of the IGCC system is eventually done. The dynamic response of the output power with the same +1% step change in the oxygen flow rate is shown in Figure 9. It is an interesting simulation condition because the flow rate of the fuel increases while the heating value decreases.  
Figure 8: Flow rate dynamic responses with two models (no-pressure model and V-R model).  
Figure 9: Dynamic responses for the output power of the gas turbine and steam turbine.  
Due to the higher oxygen-to-coal ratio, the total heating value of the syngas decreases. Thus, the output power of the gas turbine decreases and achieves stability in about 50 s. It is an extremely quick response speed when considering that the gasifier has already taken about 40 s to reach stability. The results show that the gas turbine has the fastest response speed of all the components of IGCC plant.  
Figure 10 shows the dynamic responses for the main parameters of the gas turbine. The turbine inlet pressure, which represents the pressure ratio, has a similar response trend as the power. This is because these two parameters are both related to the total heating value directly. The outlet flow rate and temperature have an opposite dynamic response. The outlet flow rate increases due to the higher flow rate of the fuel, while the outlet temperature decreases due to the lower heating value.  
The dynamic responses for the output power, the main steam pressure and the enthalpy of the steam turbine are shown in Figure 11. Although the turbine outlet temperature (TOT) decreases, the waste heat from the gas turbine increases, mainly because of the higher flow rate. Due to this reason, the output power finally increases. However, the dynamic response is complicated because the changes of the steam pressure and temperature are opposite. The main steam pressure rises due to the higher waste heat, resulting in a higher mass flow in the steam turbine. The main steam temperature rises for the same reason at first, and then falls because of the lower TOT and higher steam flow rate. Since the inertia of the pressure is much smaller, the quick response of the pressure and flow rate lowers the steam temperature very rapidly. It is the reason why the output power of the steam turbine falls from the 25 th s to the 40 th s. The decreasing speed of the temperature becomes much slower, so that the output power becomes raised again. Finally, the power increases and achieves stability in 120 s, which is much slower than the gas turbine.  
Figure 11: Dynamic response for the steam turbine.  
Figure 10: Dynamic responses for the gas turbine: (a) output power and turbine inlet pressure; (b) turbine outlet temperature and turbine outlet mass flow rate.  
The above analysis shows that the dynamic responses are complicated with the simplified control strategy, mainly because the changes of the heating value and syngas flow rate are opposite. Thus, the design of the IGCC control system should be discussed more in-depth in the future.