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

An Fe-Zr oxide (Fe2O3 and ZrO2) modified by K2CO3 was prepared as the oxygen carrier (denoted as K3-Fe70Zr30) to examine the effects of temperature and char mass/oxygen carrier (OC) ratio on 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°C, and the reaction rate increases sharply above 750°C. The reduced oxygen carrier begins to react with steam at 400°C, and the concentration of hydrogen significantly increases above 500°C. The results of isothermal experiments indicate that the reaction rate is accelerated with increasing reaction temperature. However, the H2 production yield decreases as the temperature rises when the ratio of CO/CO2 volume ratio increases. In addition, with the increase of char/OC ratio, the ratio of CO/CO2 in the outlet gas increases. As a result, the hydrogen production firstly increases and reaches a maximum value of 1.734 L/g, and then decreases. The activity of oxygen carrier can keep stable during the first 2 redox cycles, but decreases in the 3rd one. The activity can be renewed by the supplement of K2CO3, suggesting that the decreased activity of oxygen carrier can ascribe to the loss of K2CO3.