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emission. The CFB boiler has achieved significant development in recent years [2 emission can be effectively controlled by adding limestone into the furnace [2 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. To improve the properties of sorbents, several methods were proposed by Ahlstrom Pyropower [2 emission can be reduced by 90% through adding the sorbent into fuel with the Ca/S molar ratio of 2.5 to 4. However, more attention should be paid to the type of fuel and sorbent. A lot of technical methods for emission reduction have been studied and used with CFB boilers to achieve better results. Some CFB boilers adopt 900 °C as the bed temperature to improve combustion efficiency but some researchers, including Ehrlich et al. [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 NOemission. The CFB boiler has achieved significant development in recent years [ 1 ]. SOemission can be effectively controlled by adding limestone into the furnace [ 2 ]. Compared with the pulverized coal boiler, the CFB boiler does not require the construction of expensive wet flue gas desulfurization (WFGD) systems, which would reduce investment and complexity of the whole power plant [ 3 ]. Basu [ 4 ] found that SOemission 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. To improve the properties of sorbents, several methods were proposed by Ahlstrom Pyropower [ 5 ], such as physical grinding of particles, dehydration of spent sorbents with steam or water, slurrying, and reinjection of ash. However, the CFB boiler would be expensively retrofitted by using these technologies. Nowak and Mirek [ 3 ] pointed out that SOemission can be reduced by 90% through adding the sorbent into fuel with the Ca/S molar ratio of 2.5 to 4. However, more attention should be paid to the type of fuel and sorbent. A lot of technical methods for emission reduction have been studied and used with CFB boilers to achieve better results. Some CFB boilers adopt 900 °C as the bed temperature to improve combustion efficiency but some researchers, including Ehrlich et al. [ 6 ], found that desulfurization efficiency reached the best value in the range of 800 to 850 °C. The reaction rate decreased when the temperature increased, while the sulfation rate rose rapidly, which blocked pores of calcium oxides. As a result, the utilization of the sorbent was inhibited. This situation occurred in most commercial CFB boilers [ 7 ]. In these boilers, when the furnace temperature rose above 900 °C, the consumption of sorbent increased. Some countries have very strict environmental standards, such as China which has ultra-low emission standard [ 8 ]. To meet these standards, many efforts have to be made to improve the desulfurization efficiency with relatively low cost. Thus, it is important to find an effective but low-cost sorbent as an alternative to limestone.
10,11,12,2 sorbent at fluidized bed combustion temperatures on a thermogravimetric analyzer (TGA). They found the white mud showed better sulfation capacity than the limestone, as the surface area of the calcined white mud was approximately twice as large as the calcined limestone at the same calcination temperature. Liu et al. [2 sorbent in a 6 t·h&#;1 industrial grate furnace. They found that a nearly 50% reduction in SO2 emission was achieved. Moreover, Yu et al. [2 capture capacity of three industrial wastes, including calcium carbide residue, brine sludge, and white lime mud at &#; °C in a fixed bed. They found that white lime mud gave the highest desulfurization efficiency of 80.4% at °C in coal combustion. All of these results confirmed that industrial wastes containing Ca have the potential to be reused as alternative desulfurizers.A few researchers [ 9 13 ] have carried out research to find a substitute to limestone as the desulfurizer from industrial waste containing Ca. Yin et al. [ 9 ] added red mud to a loose coal and found that the presence of red mud could significantly fix the sulfur with fixation rates over 79%. Li et al. [ 10 ] compared the sulfation behavior of limestone and white mud from paper manufacture as SOsorbent at fluidized bed combustion temperatures on a thermogravimetric analyzer (TGA). They found the white mud showed better sulfation capacity than the limestone, as the surface area of the calcined white mud was approximately twice as large as the calcined limestone at the same calcination temperature. Liu et al. [ 11 ] evaluated white clay, carbide slag, and steel slag as SOsorbent in a 6 t·hindustrial grate furnace. They found that a nearly 50% reduction in SOemission was achieved. Moreover, Yu et al. [ 12 ] investigated the desulfurization performance of several alkaline waste slags, including carbide slag, alkaline slag, waste marble, and limestone in an absorber bottle. They found that both carbide slag and alkaline slag exhibited much higher desulfurization capacity compared to waste marble and limestone. Cheng et al. [ 13 ] compared the SOcapture capacity of three industrial wastes, including calcium carbide residue, brine sludge, and white lime mud at &#; °C in a fixed bed. They found that white lime mud gave the highest desulfurization efficiency of 80.4% at °C in coal combustion. All of these results confirmed that industrial wastes containing Ca have the potential to be reused as alternative desulfurizers.
2) in the production of acetylene. The main component of carbide slag is Ca(OH)2 [2 adsorption by carbide slag and limestone in the fixed bed and found that carbide slag possessed higher SO2 adsorption capacity than limestone at 700 °C. Similar studies were also conducted by Liu et al. [As mentioned above, carbide slag is a promising candidate for the alternative in-bed desulfurizer. Carbide slag is typically a by-product during the hydrolysis process of calcium carbide (CaC) in the production of acetylene. The main component of carbide slag is Ca(OH) 14 ]. More than 40 million tons of carbide slag is produced per year all over the world [ 15 ]. However, carbide slag is difficult to reuse. It is ordinarily landfilled, resulting in land occupation, environmental pollution, and waste of a calcium resource. Carbide slag is likely to contaminate soil and groundwater because it is strong alkaline (pH > 12). Wu et al. [ 16 ] studied SOadsorption by carbide slag and limestone in the fixed bed and found that carbide slag possessed higher SOadsorption capacity than limestone at 700 °C. Similar studies were also conducted by Liu et al. [ 11 ] and Yu et al. [ 12 ], both of which confirmed the potential in desulfurization.
Because the main components of carbide slag are different from limestone, and the particle size of carbide slag is smaller, the desulfurization activity is also different, which may affect its substitution for limestone as a desulfurizer. To our knowledge, most of the studies have been carried out on TGA, fixed bed, or laboratory-scale CFB. Due to the limitations of test conditions, it is not possible to simulate working conditions similar to the real CFB boiler on these devices. Thus these research results may not be applied to directly guide the application of carbide slag on the CFB boiler. So the aim of this work was to study the feasibility of taking the carbide slag as in-bed desulfurizer in large-scale CFB boilers. Calcination and sulfation characteristics of carbide slag were investigated through TGA. 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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Calcium carbide can be introduced into molten steel in the form of blocks, powder, or granules. There are mainly two methods for desulfurizing molten steel: blowing and stirring.
Blowing involves uniformly spraying calcium carbide powder into molten steel using a blowing device. This method excels in desulfurization efficiency and uniform mixing, making it suitable for applications demanding high desulfurization effectiveness.
On the other hand, stirring directly adds calcium carbide material into the molten steel, utilizing mechanical equipment to mix the steel and calcium carbide. This method is simpler and more flexible, suitable for production environments of various scales.
The choice of desulfurization method typically depends on specific production needs, cost considerations, and equipment conditions.
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