A study on the limestone sulfation behavior under oxy-fuel circulating fluidized bed combustion condition

Wei Li 1, Shiyuan Li1,*, Mingxin Xu1,2, Xin Wang 1,2

1 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

2 University of Chinese Academy of Sciences, Beijing 100049, China

Abstract for oral presentation

Oxy-fuel combustion is widely considered as one of the most promising technologies to address this problem. The removal of the SO2 is necessary during the oxy-fuel CFB combustor operation. Limestone sorbent injection is a relatively simple and low-cost process for SO2 capture. Some works have been done about the sulfation of limestone under oxy-fuel combustion condition with TGA and fix-bed combustor. However, the TGA and fix-bed has many limitations owing to its absence of those existing in fluidized bed, such as, simultaneous calcination and sulfation, attrition, thermical shock and crackle.

In order to investigate the limestone sulfation behavior under oxy-fuel circulating fluidized bed combustion condition, experiments were conducted in a circulating fluidized bed in oxy-fuel combustion condition with inlet oxygen concentrations of 40% and the temperature range from 850 oC to 950 oC. During the experiment, a small cage made from stainless steel net containing limestone particles with the size ranging from 2 mm to 3 mm and the weight of 5 g was dipped into the dense zone of the CFB combustor during the experiment. The bed materials could go through the holes on the cage freely, but limestone particles could not escape from the cage. The cage was taken out after the variation of reaction time, and the products were analyzed with X-ray fluorescence (XRF), nitrogen adsorption analysis and scanning electron microscope (SEM). From these analyses, the calcination of limestone, pore structure of the product layer and calcium conversion was studied.

It was found that the formation process of the product layer is completelydifferent between the direct and indirect sulfation and is almost the same during the indirect sulfation under the oxy-fuel and air combustion. However, the temperature and gas compositions all play important roles in determining the pore structures of the product layer during the limestone indirect sulfation process. Under the O2/CO2 combustion condition, the calcium conversion of indirect sulfation is always higher than that of direct sulfation.

Keywords: Oxy-fuel combustion, Circulation fluidized bed, limestone sulfation

Acknowledgement: The authors gratefully acknowledge the support by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDA07030200) and the International Science & Technology Cooperation Program of China (Grant No. 2014DFG61680).

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