低阶烟煤热解过程中氯的迁移释放特性研究

为探明氯元素在低阶烟煤热解过程中的释放机制行为,采用热重红外光谱质谱(TG-IR-MS)联用技术和管式热解炉,考察热解温度、粒径等级、升温速率对陕北低阶烟煤热解过程中氯的迁移转化行为特性的影响,并建立氯迁移释放动力学模型。红外光谱和质谱分析结果表明,陕北低阶烟煤热解气体产物中含氯组分主要为HCl和微量的Cl_2。管式炉热解过程中,相比于粒径和升温速率而言,氯的释放率受温度影响最为显著。在300-800℃,随着温度升高,煤中氯的释放率迅速增大,800℃时氯的释放率为49.5%;半焦中氯的分布率逐渐减小,焦油和热解气中氯的分布率逐渐增大。煤样粒径为3.0-4.0 mm时,氯的释放率达到最大值35.8%;粒径的变化也会一定程度影响热解产物中氯的分布率。提高热解升温速率有利于挥发分的释放,升温速率为15-25℃/min时,煤中氯的释放率变化趋势明显,但过高的升温速率不利于煤中氯的释放。热解焦油中氯元素主要以无机含氯化合物的形式存在,超纯水萃取可明显降低焦油中氯的含量。低阶烟煤中低温热解过程中,氯释放的活化能均在20 k J/mol左右。

Investigation on transferring and release characteristics of chlorine during pyrolysis of low rank coal

In order to reveal the release mechanism of chlorine(Cl) in low rank coal during pyrolysis process, a low rank coal from northern Shaanxi was pyrolyzed at different temperatures, particle sizes and heating rates in a tubular reactor and a Thermo Gravimetric-Infrared-Mass spectrometry (TG-IR-MS) to investigate the transferring and release characteristics of Cl during pyrolysis process. The dynamic model of Cl transferring and release was built based on the process of coal pyrolysis. The results show that the chloric species from the pyrolysis of low rank coal is HCl and little Cl₂, and the temperature strongly influences the release rate of Cl during pyrolysis in the tubular reactor. With the pyrolysis temperature increasing from 300 to 800 ℃, the release rate of Cl increases significantly, reaching to 49.5% at 800 ℃,while the fraction of Cl in the char decreases and the fraction of Cl in coal tar and pyrolysis gas increases gradually. The release rate of Cl has a maximum of 35.8% as the particle size is 3.0-4.0 mm. The particle size also affects the distribution of Cl in pyrolysis products. Moreover, increasing the heating rate is beneficial to the devolatilization, and the release rate of Cl in coal changes obviously as the heating rate is 15-25 ℃/min, but much higher heating rate will result in the decrease of the release rate of Cl in coal. Most Cl species in the coal tar is in form of water-soluble inorganic chlorides, and therefore the ultrapure water can present a better performance to remove chlorides. The release activation energy of chlorine in pyrolysis is about 20 kJ/mol.