Abstract
Carbide slag is a waste residue during the production of acetylene. Due to its high content of Ca(OH)2, carbide slag becomes a potential alternative to limestone as the in-bed desulfurizer of circulating fluidized bed (CFB) boilers. In this study, the calcination and sulfation characteristics of carbide slag were investigated by three different facilities, thermogravimetric analyzer (TGA), 1 MWth pilot CFB boiler, and 690 t·h−1 CFB boiler. Pore structures and sulfation behaviors of carbide slag and limestone were investigated for the sake of comparison. The results showed that carbide slag has a lower calcination temperature than limestone. Its calcined product has a better pore structure and desulfurization activity. The carbide slag exhibited a higher desulfurization efficiency than the limestone in the pilot tests. The SO2 emission concentration showed a downward trend with the increase of molar fraction of carbide slag in the desulfurizer. Meanwhile, carbide slag had a better sintering-resistance property, which makes it possible to effectively reduce SO2 emissions even at high combustion temperatures (>910 °C). While the field test results were similar to that of the pilot tests, the desulfurization efficiency of carbide slag with the same Ca/S mole ratio was higher than that of limestone. The fine size of carbide slag particles and the lower separation efficiency of the cyclone on the 690 t·h−1 boiler left the carbide slag with insufficient residence time in the furnace. Therefore, it is necessary to ensure a high separation efficiency of the cyclone if the carbide slag is used as an alternative desulfurizer in furnace.
Highlights
Compared to the other main boiler types of coal-fired power plants, the circulating fluidized bed (CFB) boiler has many advantages, such as wide fuel adaptability, low-cost in-bed desulfurization, and low NOx emission
Basu [4] found that SO2 emission and utilization of sorbents in CFB boilers could be affected by many design and operating parameters, including combustion temperature, circulation rate and bed density, gas and solid residence time, pore characteristics, and sorbent size
Because there was no other limestone with more satisfactory particle size that could be purchased around the power plant of the 690 t·h−1 CFB boiler, this limestone with coarser particle size was selected to be fed into the furnace
Summary
Compared to the other main boiler types of coal-fired power plants, the circulating fluidized bed (CFB) boiler has many advantages, such as wide fuel adaptability, low-cost in-bed desulfurization, and low NOx emission. Li et al [10] compared the sulfation behavior of limestone and white mud from paper manufacture as SO2 sorbent at fluidized bed combustion temperatures on a thermogravimetric analyzer (TGA). Liu et al [11] evaluated white clay, carbide slag, and steel slag as SO2 sorbent in a 6 t·h−1 industrial grate furnace. They found that a nearly 50% reduction in SO2 emission was achieved. The aim of this work was to study the feasibility of taking the carbide slag as in-bed desulfurizer in large-scale CFB boilers. The effects of bed temperature especially the higher bed temperature, Ca/S mole ratio of carbide slag and limestone were explored in two different scale facilities, i.e., a 1 MWth pilot CFB boiler and a 690 t·h−1 CFB boiler
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