Portland Cement as a Regenerable Sorbent for the Removal and Recovery of SO sub 2 in the Fluidized-Bed Combustion of Coal

摘要

A sorbent which solves most of the problems for the removal of sulfur in the Fluidized Bed Combustion (FBC) of Coal has been developed. The sorbent is based on the use of calcium silicate which is contained in commercial grade Portland cement. The Portland cement is hydrated and agglomerated in a drum type pelletizer to form particles in the size range required for operating FBC units. These are subsequently cured and dried into hard durable pellets which can be directly used in the FBC. Pellet formation is a low energy process. Laboratory measurements have been obtained on the rate and capacity of absorption of SO sub 2 using simulated combustion gases. The sulfated cement pellets have also been regenerated to reform the sorbent and produce a concentrated SO sub 2 gaseous stream. In the overall process, the SO sub 2 will be reduced to sulfur for disposal or for market use. The cement sorbent has been put through more than 10 cycles of absorption and regeneration with little loss of reactivity. Laboratory attrition studies indicate minimal loss of sorbent (less than 3% per cycle). The sorbent is effective up to a temperature of over 1000 exp 0 C in FBC, which would significantly improve the overall power production efficiency of the plant. Portland Cement Type III (PC III) sorbent can readily remove 90% of the sulfur from a high sulfur (4%) coal. Thermodynamic and laboratory pressurized TGA tests indicate that PC III will be effective in pressurized fluidized bed combustion (PFBC) units since the sulfation rate is not decreased under higher CO sub 2 partial pressures compared to limestone. The equilibrium concentration of SO sub 2 on regeneration of PC III is much higher than for limestone. Another important advantage of Portland cement sorbent is that it is produced under quality controlled conditions and is not subject to the variability of natural deposits of limestone with respect to composition, reactivity and capacity for SO sub 2 removal. (ERA citation 06:031114)