Modeling of Transport and Reaction in Porous Sorbent Polymer Catalyst Composite Membranes for the Removal of Mercury from Flue Gas

Mercury has been identified as a toxic substance that is regulated worldwide to control its emission from industrial flue gas stacks. Several technologies are being developed to address the decreasing emission limits. One of the removal options is the use of Sorbent Polymer Catalyst (SPC) composite materials to simultaneously capture and convert multiple species within the flue gas stream. W.L. Gore and Associates have developed a unique porous composite membrane based on the combination of sorbent and catalyst particles with PTFE. This material is being utilized in the GORE™ Mercury Control System (GMCS) that captures mercury and SO₂ from industrial flue gas by a selective sorption and kinetic process.

The talk will describe the structure of the membrane and the unique transport processes that occur within the porous material for capturing mercury and converting SO₂ into liquid sulfuric acid. A model has been developed to describe the various transport and conversion steps, which elucidates the balance between gas transport and liquid removal. The model incorporates the individual transport steps including a boundary layer in the flue gas stream, transport inside the porous material and the active particles, and a phenomenological description of the kinetics of the mercury chemisorption process.

The kinetic parameters were determined by controlling certain transport steps in laboratory experiments and varying the mercury concentration in the feed gas. The experimental data indicates an apparent first order reaction rate, which leads to an analytical solution for the combined transport and kinetics model through the use of multiple Thiele moduli for the different domains. Utilizing structural parameters for the membrane, the overall model was validated against various sets of experimental data under different limiting conditions. The model is exercised with case studies to elucidate the transport behavior under different realistic operating conditions. The impact of kinetic parameters, the increasing liquid content due to the production of sulfuric acid and fouling on the membrane surface will be highlighted. The talk will conclude with ongoing model improvements and an outlook for future developments.