Application of low-temperature thermal treatment for the reduction of mercury content in coal

Abstract

The article describes research carried out on four coals samples (raw coals A and B and enriched coals A and B). The fuels were subjected to low-temperature thermal treatment in order to remove as much mercury as possible while still maintaining high energy quality of the fuels. The lab-scale tests were performed in a fluidized bed column and for chosen coal fraction 500-1000µm. Air and a mixture of carbon dioxide (16%) and nitrogen (the rest) were used as the fluidizing medium that as intended to have similar composition as the synthetic flue gas. The coals were tested for five temperatures of 200, 250, 300, 350 and 400°C.The results indicated that it was possible to remove more than 80% of mercury from coal A (raw and enriched), in CO2 /N2 atmosphere at the temperature of 400°C in the case of coal B, both raw and enriched, the amount of removed mercury at 400°C was roughly 70%. At lower temperature, 350°C, the amount of removed mercury was 70% and 60% for coals A and B, respectively. Apart from the above test the investigation were also carried out in order to determine the loss of volatiles during the thermal treatment of the coals. The results indicated that at 400°C roughly 20% of the volatiles were evolved from the fuel particles. The loss of elemental carbon and fuel higher heating value (HHV) after the treatment were 10% and 8%, respectively.