SORBENT/COAL INJECTION IN A CERAMIC FILTER TO CONTROL POWERPLANT EMISSIONS - ACID RAIN PRECURSORS

摘要

This manuscript provides an update on recent laboratory developments of a high-temperature flue gas filtration technology, in conjunction to sorbent injection. Calcium/sodium-based sorbents are sprayed in the post-combustion zone of a furnace. The sorbent reacts with gaseous forms of sulfur and chlorine (SO_2, H_2, HCl, etc.) in the furnace effluent to form stable salts of calcium. The partially-reacted sorbent is then collected in a high-temperature filter, which is placed downstream of the sorbent injection point, and continues reacting therein for a prolonged period of time. The primary advantage of this technique is that both the likelihood and the duration of contact between the solid sorbent particles and the gaseous pollutants increase, since reaction takes place in the furnace upstream of the filter as well as inside the filter itself. Hence, the sorbent utilization (i.e., the conversion of sorbent CaO to CaSO_4, CaSO_3, CaCl_2, etc.) increases drastically. A preferred filter configuration is a wall-flow honeycomb monolith, made of a high temperature ceramic, such as silicon carbide or cordierite. An additional advantage of the filter is that partially-burned carbon, such as soot, char, tar, etc., is collected therein, where there is sufficient time (several minutes to an hour) for complete combustion of carbon. The filter must be regenerated (cleaned) periodically to remove the collected minerals (ash and spent sorbent). This is accomplished with aerodynamic regeneration, i.e., using bursts of compressed air flowing in the opposite to the flue gas direction. This process is a competitive alternative to existing pollution control methods, such as flue gas desulfurization (FGD) scrubbers, selective catalytic/non-catalytic reduction (SCR/SNCR), baghouses, and electrostatic precipitators. Unlike existing technologies, this technique simultaneously removes SO_2, NO_x, HCl, and particulates.