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.

A novel technique, the back-propagation (BP) neural network, is presented for predicting the ash fusion temperature from ash compositions for some Chinese coals instead of the traditional techniques, such as the ternary equilibrium phase diagrams and regression relationships. In the applications of the BP networks, some modifications to the original BP algorithm are adopted to speed up the BP learning algorithm, and some useful advice is put forward for the choice of some key parameters in the BP model. Compared to the traditional techniques, the BP neural network method is much more convenient and direct, and can always achieve a much better prediction effect. q 1998 Elsevier Science Ltd. All rights reserved

In developing a mathematical model for a CFB boiler we use earlier work. Our model includes mathematical descriptions of the underlying physical and chemical processes. It has been applied to simulation of a 12 MW CFB boiler. The calculations agree well with test results.

An external heat exchanger (EHE) is believed to be a viable way to solve the heat transfer surface arrangement and furnace temperature control to scale-up of circulating fluidized bed (CFB) boilers. A new concept of EHE is developed in this paper. The flow of hot solid particles diverted from the standpipe is controlled by pneumatic (aeration airflows of recycle device or EHE), not the mechanical valve that is in popular use in many CFB boilers. The major feature of this EHE system is that it avoids the use of the mechanical valve that causes heavy erosion and high cost. An in-series connection between the EHE and the recycle device (i.e. the recycle device is on top of the EHE) is proposed. Experiments completed in cold test rigs show that the solid mass flow rate diverted from the standpipe to the EHE or the loop seal may be controlled well by adjusting the fluidizing air of the overflow part of the loop seal, the fluidized air of the fluidized chambers of the EHE and the aeration airflow to the standpipe. In addition, the new EHE has been validated successfully in a 12 MWe CFB boiler.

A two-dimensional particle population balance model has been developed for the particle size and density distributions in a circulating fluidized bed (CFB) boiler furnace based on analysis of particle properties and the core-annulus hydrodynamic model. The model, incorporating modules to consider fuel particle fragmentation, char combustion, particle attrition and gas-solid separation, is part of an overall model developed earlier by the authors to simulate the operation of a 12MW CFB boiler. The model predictions for particle population in a CFB furnace agree well with the measurement data.

A 0uidized bed reactor with 3kgh−1 throughput operating at an atmospheric pressure with an inert atmosphere at 773K has been used to produce bio-oils from the wood feedstocks such as Pterocarpus indicus, Cunninghamia lanceolata, and Fraxinus mandshurica, as well as from rice straw. The best oil-producing characteristics were for P. indicus and the worst were with rice straw. These data were used to design a larger scale unit of 20kgh−1 throughput, and to estimate the production costs at an industrial scale. The quality of the bio-oil produced remains poor, and a combination of high value products and energy applications are needed for pro7tability.