Elemental mercury vapor capture by powdered activated carbon in a fluidized bed reactor

A bubbling fluidized bed of inert material was used to increase the activated carbon residence time in the reaction zone and to improve its performance for mercury vapor capture. Elemental mercury capture experiments were conducted at 100 °C in a purposely designed 65 mm ID lab-scale pyrex reactor, that could be operated both in the fluidized bed and in the entrained bed configurations. Commercial powdered activated carbon was pneumatically injected in the reactor and mercury concentration at the outlet was monitored continuously. Experiments were carried out at different inert particle sizes, bed masses, fluidization velocities and carbon feed rates. Experimental results showed that the presence of a bubbling fluidized bed led to an increase of the mercury capture efficiency and, in turn, of the activated carbon utilization. This was explained by the enhanced activated carbon loading and gas-solid contact time that establishes in the reaction zone, because of the large surface area available for activated carbon adhesion/deposition in the fluidized bed. Transient mercury concentration profiles at the bed outlet during the runs were used to discriminate between the controlling phenomena in the process. Experimental data have been analyzed in the light of a phenomenological framework that takes into account the presence of both free and adhered carbon in the reactor as well as mercury saturation of the adsorbent.