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    水泥行业燃烧中碳捕集技术研究及应用进展

    Research and application progress on combustion-based carbon capture technologies in cement industry

    • 摘要: 水泥行业是CO2排放大户,约占全球CO2排放量7%。碳捕集被视为碳中和“兜底”技术,燃烧中碳捕集具有捕集能力强、过程能耗低、捕集成本小等优势。系统梳理了国内外水泥行业布局的燃烧中碳捕集项目,包括直接分离技术4项,富氧燃烧技术12项,钙循环技术4项。直接分离技术通过间接换热捕集生料分解产生的CO2,围绕该技术国外布局了LEILAC项目,核心为直接分离反应器,两期项目设计碳捕集规模分别为2.5万t/a和10万t/a,一期试验表明分离CO2纯度>95%;国内某公司开发了外燃式旋窑技术,正在建设5万t/a碳捕集示范项目。富氧燃烧技术分为部分富氧燃烧、第1代全系统富氧燃烧和第2代全系统富氧燃烧。部分富氧燃烧技术仅在分解炉内实现富氧燃烧,可捕集60%~75%的碳排放。富氧气氛(O2/CO2)下生料中碳酸钙分解受到抑制,分解炉温度需增加60~70 ℃以获得较高分解率。围绕该技术国内已建设2个项目。全系统富氧燃烧技术在回转窑、分解炉内构建富氧气氛,CO2捕集能力90%~95%。第1代全系统富氧燃烧技术通过烟气循环控制燃烧温度,研究表明富氧气氛对于熟料质量无明显影响,通过参数调整可实现回转窑温度分布与空气气氛一致。与第1代相比,第2代全系统富氧燃烧技术取消了烟气循环系统,回转窑温度通过过剩O2控制,研究表明增加O2当量比具有理想的温度控制效果,围绕该技术国外已布局多个项目。由于CaCO3、CaO分别是水泥原料和熟料的主要成分,且预分解工艺包含分解炉,钙循环技术在水泥行业具有天然优势。重点论述了集成钙循环工艺布置及CLEANKER项目工业试验结果,表明碳捕集率20%~80%,在碳酸化炉温度450~750 ℃,随着温度升高CO2捕集效率明显增强,从0增加至最高100%。围绕碳捕集能力、项目规模、能耗及减排成本、技术风险,对燃烧中碳捕集技术进行了对比分析。我国水泥产量占全球约45%,建议加强新技术研发、加快推进技术工程验证、完善相关配套设施。

       

      Abstract: Cement industry is one of the largest contributors to greenhouse gas emissions accounting for about 7% of global CO2 emissions. Carbon capture is considered a “fallback” technology, with combustion carbon capture offering several advantages such as strong capture capacity, low process energy consumption, and low costs. This article systematically reviews combustion carbon capture projects in the cement industry both domestically and internationally, including four projects for direct separation, twelve projects for oxyfuel combustion, and four projects for calcium looping. Direct separation technology captures CO2 produced from the decomposition of limestone through indirect heat exchange. Internationally, the LEILAC project is a key example, with its core being a direct separation reactor. The first phase of the project is designed to capture 25 000 tons of CO2 per year, and the second phase aims to capture 100 000 tons per year. Industrial trials of the first phase have shown that the separated CO2 purity is greater than 95%. Domestically, a company has developed an external combustion rotary kiln technology and is currently constructing a 50000 tons per year carbon capture demonstration project. Oxyfuel combustion technology is divided into partial oxyfuel, first-generation full-sacale oxyfuel, and second-generation full-scale oxyfuel. Partial oxyfuel combustion achieves O2/CO2 combustion only in the calciner, capturing approximately 60%-75% of total carbon emissions. Due to the inhibition of raw material decomposition in the O2/CO2, industrial trial results indicate that the calciner temperature needs to be increased by 60 to 70 ℃ to achieve a higher decomposition rate. Two projects using partial oxyfuel combustion technology have been constructed domestically. Full-system oxyfuel combustion technology creates the O2/CO2 atmosphere both in the rotary kiln and calciner, with a CO2 capture capacity of 90%-95%. The first-generation full-scale oxyfuel combustion technology is based on flue gas recirculation to control flame temperature. Studies have shown that the O2/CO2 atmosphere has no significant impact on clinker quality, and parameter adjustments can achieve a similar temperature field in the rotary kiln with air combustion. Compared to the first generation, the second-generation full-scale oxyfuel combustion technology eliminates the flue gas recirculation system, with the rotary kiln temperature controlled by excess O2. Studies have shown that increasing the oxygen equivalence ratio provides an ideal temperature control effect, and several projects have been laid out. Several features, including CaCO3 and CaO being the main components of the raw meal and clinker respectively, an existing calciner in the production process, give calcium looping technology a natural advantage in the cement industry. This article focuses on the integrated calcium looping process layout and the industrial trial results of the CLEANKER project, which showed a capture efficiency of 20%-80%. Within the carbonator temperature range of 450 to 750 ℃, the CO2 capture efficiency significantly increases with temperature, rising from 0 to a maximum of 100%. A comparative analysis is conducted around carbon capture capacity, the scale of carbon capture projects, energy consumption and abatement costs, and technical risks. China's cement production accounts for about 45% of the global total. It is recommended to strengthen the research and development of new technologies, accelerate the engineering verification of these technologies, and improve related supporting facilities.

       

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