炼焦煤热解收缩特性对焦炭成块性能影响

在国家“双碳”目标及富氢高炉开发利用背景下,对焦炭在高炉中的性能提出了更高要求。除常规的热态性能指标外,焦炭的块度受到更多关注。炼焦煤的热解收缩性能是决定焦炭成块性能至关重要的因素。对不同变质程度炼焦煤进行2 kg焦炉炼焦试验,分析炼焦煤细度对其焦炭成块性能的影响规律。采用改进的奥亚膨胀仪对8种不同变质程度炼焦煤在300~900℃内的热解收缩性能进行深入研究,探讨了煤热解收缩系数与其收缩动力学特性对焦炭成块性能的影响,并建立热解收缩系数及热解活化能与焦炭平均块度的数学关系,试图通过炼焦煤热解收缩特性对焦炭平均块度进行预测。结果表明,焦炭的平均块度随炼焦煤变质程度的升高呈增大趋势。YK气煤的平均块度较低,仅为38.9 mm。SAJ焦煤和BBG瘦煤的平均块度较高,分别为50.5、48.5 mm。8种炼焦煤中除BBG瘦煤外,当入炉煤细度为75%时,形成焦炭的平均块度最大。BBG瘦煤在细度为85%时,焦炭平均块度最优。在热解过程中,不同变质程度炼焦煤第1收缩峰的收缩系数及收缩所需活化能差别明显。其中低变质程度YK气煤和SYS1/3焦煤热解收缩系数高于8.33×10^(-4)℃^(-1),热解活化能均低于77 kJ/mol;高变质程度煤LH焦煤、SAJ焦煤和BBG瘦煤热解收缩系数低于4.55×10^(-4)℃^(-1),但热解所需活化能均高于106.1 kJ/mol,说明变质程度高的炼焦煤,热解时需要更高的能量才能完成收缩过程。在相同的炼焦工艺下,炼焦煤第1收缩峰的热解收缩系数越大,所得焦炭的平均块度越小,且热解收缩系数与焦炭平均块度有很好线性关系,相关系数为0.90。同时,热解收缩活化能也与焦炭平均块度有较好关联。因此,能够通过热解收缩系数和收缩活化能对不同变质程度炼焦煤生成焦炭平均块度进行有效预测。

Leaching kinetics of low-grade copper ore containing calcium-magnesium carbonate in ammonia-ammonium sulfate solution with persulfate

The leaching kinetics of copper from low-grade copper ore was investigated in ammonia-ammonium sulfate solution with sodium persulfate. The effect parameters of stirring speed, temperature, particle size, concentrations of ammonia, ammonium sulfate and sodium persulfate were determined. The results show that the leaching rate is nearly independent of agitation above 300 r/min and increases with the increase of temperature, concentrations of ammonia, ammonium sulfate and sodium persulfate. The EDS analysis and phase quantitative analysis of the residues indicate that bornite can be dissolved by persulfate oxidization. The leaching kinetics with activation energy of 22.91 kJ/mol was analyzed by using a new shrinking core model （SCM） in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. A semi-empirical rate equation was obtained to describe the leaching process and the empirical reaction orders with respect to the concentrations of ammonia, ammonium sulfate and sodium persulfate are 0.5, 1.2 and 0.5, respectively.