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水泥产业是典型的能源和资源消耗密集型产业,也是仅次于电力行业的第二大CO2、NOx排放源,减排形势严峻[1]。O2/CO2烟气循环煅烧水泥技术是将分离空气制得的高纯度O2与部分再循环烟气混合后通入回转窑和分解炉内助燃,使煤粉在O2/CO2氛围下燃烧,不仅能实现窑尾烟气中CO2的富集和回收,还能降低热力型NOx的排放[2],对水泥行业实现CO2和NOx减排具有重要意义。
许多学者针对煤粉颗粒在O2/CO2气氛下的燃烧特性展开了大量研究。楚化强等[3]利用数值模拟的方法研究了煤粉在空气和O2/CO2气氛下的燃烧情况,结果表明O2/CO2气氛下燃烧火焰温度较低。何先辉等[4]和SHEN等[5]研究表明,在O2/CO2气氛下,煤粉颗粒的完全燃尽时间延长了20%~25%左右。在流化床锅炉方面,有学者通过搭建中小型实验台[6-9]和数值模拟的方法[10-12]进行了O2/CO2燃烧技术的研究,目前O2/CO2燃烧技术已经逐渐应用在电站锅炉上的实际工程中。但是O2/CO2燃烧技术在水泥生产领域的研究还处于起步阶段,仅有少数研究者进行了初步的探索工作。DAVID等[13]通过建立回转窑氧燃料燃烧过程的三维数学模型发现,在同一氧气浓度下, 火焰长度比在空气条件下燃烧的火焰长度短30%~65%,辐射通量提高2~4.5倍,在相同的燃料消耗率下,可以提高熟料的生产率。FRANCISCO等[14]和MARIO等[15]分别以实验和数值模拟的方式验证了现代窑式燃烧器可在不作额外改造的情况下适用氧燃料燃烧。但三者都只单独进行了回转窑的研究,缺少炉、窑一体的研究,没有进一步研究分解炉中NOx的生成情况和煤粉燃烧特性的改变对生料分解产生的影响,无法支持该技术在水泥回转窑和分解炉上的应用。
本研究对某公司2 500 t·d−1回转窑和分解炉进行数值模拟,探讨了O2/CO2烟气循环煅烧水泥技术实现CO2和NOx减排的可行性,对比分析了21%O2/79%CO2助燃工况下与空气助燃工况下回转窑、分解炉的模拟结果,为水泥行业实现O2/CO2燃烧技术的应用提供参考。
Numerical simulation and reliability verification of pulverized coal combustion in rotary kiln and decomposing furnace under O2/CO2 condition
- Received Date: 16/07/2019
- Available Online: 01/05/2020
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Key words:
- O2/CO2 atmosphere /
- numerical simulation /
- rotary kiln /
- decomposition kiln /
- CO2 enrichment /
- denitrification
Abstract: In order to study the feasibility of reducing CO2 and NOx emission by using O2/CO2 flue gas cycling calcinating cement technology, a numerical simulation method was used to study the pulverized coal combustion of the 2 500 t·d−1 rotary kiln and decomposing furnace models under 21%O2/79%CO2 combustion-supporting atmosphere. The simulations results of rotary kiln and decomposition furnace under O2/CO2 combustion-supporting conditions and air-supported combustion conditions were compared and analyzed. The reliability of numerical simulations was also verified by experiments test. The results showed that in comparison with the air-supported combustion conditions, the pulverized coal burnout rate of the rotary kiln and decomposing furnace under O2/CO2 combustion-supporting conditions were 92.41% and 91.15%, respectively, which decreased by 3.06% and 3.51%. The decomposition rate of raw materials at the exit of the decomposing furnace was 90.54%, which decreased by 2.90% and still basically met the production demand. Under O2/CO2 combustion-supporting conditions, NO emission of rotary kiln and decomposing furnace decreased significantly, and the denitrification rates were 74.47% and 11.80%, respectively. The CO2 volume fraction in flue gas increased from 32.23% to 95.35%, and the C capture could be achieved through simple treatment. This study provides a reference for the generalization and application of the O2/CO2 flue gas cycle calcinating cement technology.