Reaction characteristics research of coal char chemical looping gasification for hydrogen production with an Fe-Zr oxygen carrier modified by K₂CO₃

In this study, an Fe-Zr oxide (Fe₂O₃ and ZrO₂) modified by K₂CO₃ was used as the oxygen carrier (denoted as K3-Fe70Zr30) to analyze the effects of the temperature and the char mass ratio on the gas yield and composition during coal char chemical looping gasification for hydrogen production. The results of temperature-programmed experiments show that the reaction of oxygen carrier and coal char starts at 500 ℃, and the reaction rate increases sharply after 750 ℃; the reduced oxygen carrier begins to react with steam when the temperature reaches 400 ℃, and the concentration of hydrogen significantly increases after 500 ℃. The results of isothermal experiments indicate that the reaction rate accelerates with increasing reaction temperature. However, the ratio of CO/CO₂ volume ratio increases, resulting in the H₂ production decreases as the temperature raises. In addition, an increase in char ratio increases the ratio of CO/CO₂ volume ratio in the outlet gas increases, which leads to the hydrogen production firstly increase and reaches a maximum value of 1.734 L/g, and then decrease. The activity of oxygen carrier can keep stable during the first 2 redox cycles, but it decreases in the 3rd cycle. The activity can be renewed by supplement of K₂CO₃, which suggests that the loss of K₂CO₃ can contribute to the decreased activity.