SO retention by highly cycled modified CaO-based sorbent in calcium looping process.

The limestone modified by pyroligneous acid has been proved to have good CO capture behavior in the calcium looping process. In this work, SO retention of the highly cycled modified limestone in the carbonation/calcination cycles was investigated in a thermogravimetric analyzer (TG). The cyclic carbonation/calcination of the modified limestone was performed in a dual fixed-bed reactor and then the cycled modified limestone was sent for sulfation in TG. The effects of sulfation temperature, cycle number, and prolonged carbonation on SO retention of the cycled modified limestone were discussed. The optimum temperature for sulfation of the cycled modified limestone should be in the range of 900-950 °C. The effect of sulfation temperature on SO retention of the modified limestone drops with increasing cycle number. With increasing cycle number from 20 to 100, the sulfation conversion of the cycled modified limestone is stable and can reach ~0.4. The cycled modified limestone exhibits obviously higher SO retention than the cycled raw one for the same number of cycles. The prolonged carbonation increases SO retention of the modified limestone and the raw one after the subsequent cycles. The sulfation conversions of the modified limestone and the raw one at 118 min after 9-h carbonation in the 20th cycle increase 43 and 56 %, respectively. The cycled modified limestone shows a greater SO retention than the cycled raw one after the same prolonged carbonation treatment. The prolonged carbonation increases the pores in 5-20 nm range which is considered the optimum pore size for sulfation of CaO-based sorbent, so it results in an improvement in SO retention of the cycled sorbents. [ABSTRACT FROM AUTHOR]