| The developing 2nd generation Pressurized Fluidized Bed Combustion Combined Cycle (PFBC-CC) power generation technology features the state of the art among the current Clean Coal Technologies (CCT) in a new concept of challenging the traditional coal complete gasification. Recognizing the fact that wild gasification of coal in fluidized bed gasifiers hinders the further promotion of gasification efficiency, a new concept is proposed that the coal is gasified in a carbonator first and then is burnt in a higher efficient combustor of PFB that is an optical way to utilize the coals with complete utilization and friendly environmental effect. In a result, the re-combustion of gasified coal-chars play a very important role in the 2nd PFBC-CC technologies for pursuing higher overall power generation efficiency. For the purpose of evaluating the effects of coal-char combustion and studying the coal-char combustion characteristic and providing the data base of designing parameters for industrialized PFBC boiler, the gasified coal-chars from both an industrial atmospheric fluidized bed gasifier and a pilot scale pressurized spouted fluidized bed gasifier were collected for better understanding the superficial features of the coal-chars and its pore structures. The pressurized combustion characteristic of coal-chars was systematically conducted in a bench-scale pressurized fluidized bed combustor. The effects of operational conditions on coal-char combustion efficiency were also experimentally tested. Finally, the coal-chars were fed into a pilot scale of heat input 1 MWt pressurized fluidized bed combustor to verify its utility combustion effects.The coal and coal-char samples from atmosphere and pressurized partial gasification were measured by nitrogen adsorption at 77K. Their specific surface areas were determined based on BET model. The average pore size, total pore volumes, pore specific surface areas and pore size distributions were statistically obtained by using BJH theory. The results showed that more abundant pores and larger specific areas and pore volumes were formed after partial gasification. Two peaks were found in distribution curves of the coal-char pore specific surface area and pore volume; the first peak corresponds to a pore diameter of a little less than 2 nm, the second of about 3.8 nm. Such a result implies quick increase of the specific surface areas of less than middle pores and forming a lot of larger than middle pores. It was concluded that gasification at elevated pressure could largely accelerate the pore formation and its further development comparing to gasification at atmospheric condition.The influential factors on pore structure of coal-chars were discussed based on the analytical results such as operating condition, coal-char size and coal-char proximate analysis. In atmospheric gasification process, devolatilization of volatile matters and pyrolysis played a leading role to form the abundant pore structure of coal-chars. While in pressurized gasification process, it was the gasification reaction of char that played an additional and dominant positive impact on promoting formation and development of the coal-char pore structure. An assumption could be derived from the variation of coal-char sizes that there maybe exist an optimal coal-char size range that made abundant porosity and bigger pore specific areas to enhance the gasification reaction. In this study, the optimal range of particle size is about 1mm～1.5mm for atmospheric gasification and about 0.5mm～1mm for pressurized gasification. Moreover, applying the Scanning Electron Microscope (SEM) technique into viewing the microscopic surface configuration ofcoal-chars, it further confirmed that the pressurized gasified coal-chars have more developed pore structures than the atmospheric gasified coal-chars.The systematical experiments on pressurized combustion characteristic were done in a bench scale test facility for two kinds of gasified coal-chars along with bituminous coal from which the coal-chars were produced. The same cola-chars were also tested in a pilot scale PFBC test rig to verify their utility combustion effect. The results showed that the system pressure and combustion temperature exerted different impacts on combustion of coal and coal-chars. Generally, the combustion temperature and efficiency increased with increasing of the system pressure. When pressure approached to 0.5MPa, the combustion efficiency of coal increased slowly but the combustion efficiency of coal-char continued going up which represented potential advantages of coal-char combustion for the 2nd generation pressurized fluidized bed combustion system because it is usually run at higher pressure much more than the experimental pressure. Under operational condition of low pressure, excess air coefficient affected the coal-char combustion efficiency more; however, under operational condition of a little higher pressure of the test case, the pressure turned to pay a dominant affection to the combustion efficiency. The optimal excess air coefficient was better less than 1.5 for most test runs. At elevated pressure, the combustion efficiency also varied greatly with changes of initial stationary height of bed material in the bench scale spouted fluidized bed. It increased first and then decreased with ever increasing of the initial stationary height, which showed that there existed an optimal height of 280～320mm in the operation condition of this paper. The combustion temperature was dependent on many run parameters such as coal feeding rate, excess air coefficient, system pressure, initial bed height, air temperature, and so on, which directly affected the combustion efficiency of coal-chars. Higher temperature made the coal-chars burnt completely as a result of speeding up the combustion reactions between air and coal-chars and thus benefited the combustion efficiency. At the system pressure of 0.5MPa, the coal-char combustion efficiency reached 94.73% in the bench scale pressurized spouted fluidized bed test facility and 99.20% in the pilot scale 1 MWt PFBC test rig, which indicated the advantage of coal-char combustion at elevated pressure.
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