Energy-Cost Targeted Self-Optimizing Control And Dynamic Behavior For Oxy-Fuel Combustion Systems

With the development of economy and society,people pays more and more attention to energy saving and emission reduction.As an effective CO₂ capture method,oxy-fuel combustion technology can significantly reduce CO₂ emissions and mitigate the greenhouse effect.However,due to the structural complexity of the power plant system,the transition from traditional air combustion to oxy-fuel combustion brings many challenges to the operation control,energy consumption and economic cost.Aiming to solve the problems of low operation control reliability and high energy-cost penalty,a self-optimizing control method is adopted to design desirable control system for oxy-fuel combustion system.Based on the optimization goal of energy-cost minimization,the new control structures are designed for the boiler island sub-system and CO₂compression and purification sub-system in oxy-fuel combustion.Moreover,dynamic characteristics under different operating conditions and control failures are identified to achieve highly efficient and low-cost operation and to provide certain guidance for the commercial deployment of oxy-fuel combustion technology.For CO₂ compression and purification unit（CPU）,self-optimizing control structures aimed at minimizing energy consumption and economic cost are proposed:based on the specific energy consumption target（Case 1）and the specific economic cost target（Case 2）.The dynamic simulation results show that under the two operating conditions of flue gas flow rate change and flue gas CO ₂ concentration change,the two self-optimizing cases can achieve the goals of low energy consumption and low economic cost.Case 1 is the most suitable control strategy,because its absolute changes in specific energy consumption and specific economic cost are only 14.02%and 10.29%of Case 2.The research results provide a new solution to the energy-saving and efficient operation for CPU process.For oxygen-fuel boiler island system,a self-optimizing control structure is proposed to maximize the operating profit.The designed self-optimizing control scheme was dynamically simulated under three opera ting conditions:load change,oxygen supply purity change and furnace air leakage change.The dynamic characteristics of the operating parameters on the water side and flue gas side are observed to obtain the curve of operating profit over time under the three operating conditions.The results show that the observed parameters fluctuate within the set-point range under all operating cases.More importantly,the operating profit can be kept above 86$/（t coal）,which is significantly higher than that under the reference control structure（the operating profit is almost 0 at steady-state operation）.The results indicate that the self-optimizing control exhibits good reliability and economy during system operation.Based on the proposed self-optimizing control structure,the safety analysis for oxy-fuel Boiler Island under the control failure condition is carried out.The controller failure is applied during the varied operating case to ob tain the corresponding dynamic characteristics.It is found that the failure of the oxygen concentration controller under load change process will cause the parameters variations in the water and flue gas sides.The failure of the oxygen flow rate controller under oxygen supply purity change condition will cause the fluctuation of boiler parameters that a big deviation from the set-point.These results are conductive to discover the operating faults caused by the controller failure during system operation,and can provide a certain guarantee for the safe operation of the oxy-fuel combustion system.