1. College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao 266590, P. R. China
2. National Engineering Laboratory of Coal-Fired Pollution Reduction, Shandong University, Jinan 250061, P. R. China
3. Energy Research Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250004, P. R. China