This research was intent for finding relationships among physical and/or chemical properties of sorbents and their sulfur capture capability at a fluidized bed condition. Three limestones and two seashells were chosen as a SO2 sorbent. Characteristics of sorbents were evaluated based on atomic absorption spectrophotometer, scanning electron microscope and mercury-penetration porosimeter analyses. Their sulfur capture capabilities were measured on a fluidized bed test system at 800, 850, 900 and 950 8C. Conversion of the sobents was computed and analyzed depending on the sorbents' morphology and microstructure analysis. Results showed pore size and specific surface might have large influence on sorbents' sulfurization ability in the range of 800-950 8C.

This paper mainly studies the separation mechanism of a square cyclone at high inlet solid concentration. It is shown that the separation mechanism is very different from that at low inlet solid concentration. A phenomenon called two-instantaneous separation exists, which has never been found in square cyclone experiments before. This phenomenon has bearing on the limit load of gas-solid flow, and the part exceeding the limit load will be separated instantaneously after entering the square cyclone. A model called two-instantaneous separation is introduced in this paper as well as the calculations of limit load and separation efficiency, which can be used in the design and research on a square cyclone for circulating fluidized bed boiler.

A method based on fractal geometry is suggested to simulate the porous structure of calcined limestone, in which a model similar to the Menger sponge is employed for the porous calcine. The bulk fractal dimension is calculated on the basis of the experimentally obtained pore-size distribution density. The effects of various factors (such as particle size, calcination tempera-ture and environment, etc.) on the porous structure (i.e. on its bulk fractal dimension) are studied. Combined with the results of sulfur-removal experiments and theoretical analysis, it is concluded that optimum utilization will be achieved when limestone is calcined to a structure with bulk fractal dimensions between 2.53 and 2.65. This fractal dimension is calculated under normal conditions and may provide an alternative ranking index for calcium-based sorbents.

A new system has been developed for clean and highly efficient utilization of coal. The coal is first gasified and the fuel gas is then used for industrial purposes in town gas or as a fuel for gas turbines. The char residue from the gasifier is burned in a circulating fluidized-bed combustor to generate steam for power generation, process heating, refrigeration, air conditioning, etc. The ash is used to produce construction materials. Metals such as vanadium and uranium can be extracted if the metal contents of coal are sufficiently high. An important system component is the combined gasifier-combustor. Experiments show that the system can produce gas and steam simultaneously. The gas heating value is 10-14MJ/Nm3 and the fuel conversion is over 90%. The system has low emissions and low cost. A demonstration system has been constructed at the Yangzhong Thermal Power Plant in Jiangshu Province of China. It produces 3,500Nm3/h of dry gas and 75mt/h steam. The CFB boiler has been in commercial operation since April 1995. It has high efficiency, good fuel adaptability, and a high load turndown ratio.

A mathematical model is developed to evaluate the performance of sulfur retention by limestone in circulating fluidized beds. The model considers particle movement and attrition, calcination and initial pore size distribution, pore plugging and cyclone performance. Percolation scaling theory is used to determine the accessible reaction surface area of the sorbent particles. The model predictions are in good agreement with the experimental data.