Dynamic simulation for mode switching strategy in a conceptual 600 MWe oxy-combustion pulverized-coal-fired boiler

• Dynamic model of a conceptual oxy-combustion PC boiler is established.
• Switching from air-combustion to oxy-combustion and then back is realized.
• Manipulating oxygen, air and RFG flows with different ramp rates is an effective way.
• The switching processes can be accomplished within 17 min.
• Dynamic behavior of material and energy flows during mode switching is gained.

Oxy-fuel combustion as a promising CO2 capture technology is ready for commercial demonstration. Dynamic simulation of oxy-combustion system, which is essential for gaining its dynamic characteristics, can help to evaluate and improve process design, and develop control system and operational strategies. This paper focuses on dynamic simulation of a 600 MWe oxy-combustion pulverized-coal-fired boiler. The steady-state model using a pseudo coal to substitute real coal is firstly established, validated, and then transformed into the dynamic model which uses pressure driven solution. Mode switching processes between air-combustion and oxy-combustion are particularly investigated for reasonable and effective switching strategy. It is found that manipulating oxygen and recycled flue gas streams with different ramp rates of corresponding valve positions during different switching stages while manipulating air stream with a constant ramp rate of air valve position throughout the switching process could be an effective switching strategy. The switching time of 17 min could realize a stable mode switching either from the air-combustion to the oxy-combustion or from the oxy-combustion to the air-combustion. The dynamic model provides powerful tool to study the dynamic behavior and mode switching characteristics of oxy-combustion boiler.