Circulating fluidized bed (CFB) technology plays an important role in the utilization of low-grade coal in China. This article reviews CFB combustion technology development in China and summarizes recent achievements. Since 1990 Chinese engineers and researchers have been undertaking work to improve CFB boiler technology. A completely novel CFB boiler design theory was developed and used in the domestic manufacturing of CFB boilers with various capacities. China is the largest supplier and customer of CFB boilers in the world due to the widespread use of CFB boilers. In 2007, the lower energy consumption CFB technology was successfully developed by re-specifying the fluidization state, which reduced the power consumption of forced fans and solved the potential erosion problems on the water wall. Afterwards, in order to increase the electric power generation efficiency, the supercritical CFB (SCCFB) boiler was developed and the first 600 MW SCCFB boiler was demonstrated and put into commercial operation in 2013. The success of the technology is evident with over 80 SCCFB boilers on order with capacities of 350 MW to 660 MW. Chinese scientists and engineers are also developing technology to lower the emissions of CFB combustion to meet the requirements of China's strict emission regulations. This emission reduction is through high-efficiency desulfurization by limestone injection into the furnace and low NO x combustion, ultra-low emission of SO 2 and NO x in the furnace can be realized by improving the bed quality and increasing the solid circulation rate. There is currently further research and design development being undertaken to develop a 660 MW ultra-supercritical CFB (USCCFB) boiler. The new boiler is expected to be operational before 2020 resulting in higher efficiency and lower energy consumption and emissions.

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With the stringent emission regulation taking effect, it is difficult for the conventional desulfurization technology in circulating fluidized bed (CFB) boilers to meet the requirements of ultralow SO2 emission. Therefore, in this paper, the application of natural ultrafine limestone, with a Sauter mean diameter of less than 20 μm, was tested by conducting bench-scale, pilot-scale, and commercial-scale experiments to realize highly efficient desulfurization in CFB furnaces. In the past, such small-size limestone was considered unsuitable for CFB boilers. However, as demonstrated by bench-scale results, the desulfurization performance was clearly superior to that of coarse limestone, especially at low SO2 concentrations. In a 3 MWth pilot-scale CFB boiler, the ultrafine limestone exhibited competent desulfurization efficiency to that of the coarse limestone but clearly less significant catalytic effects on NOx formation. As revealed by field tests in four commercial-scale CFB boilers, when high-efficiency cyclones were applied to CFB boilers, the mass inventory of ultrafine particles was significantly increased and the residence time would be extended accordingly; thus, the ultrafine limestone can be used to achieve high desulfurization efficiency and even ultralow SO2 emission with a favorable Ca/S ratio. Furthermore, a technical roadmap was drawn for the cost-effective control of SO2 emission.

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