(213c) Modeling of Gas Transport and Adsorption Considering Liquid Generation during 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 evaluated for coal fired power plants to address the decreasing emission regulations currently implemented in the USA and Europe. One removal option is the use of Sorbent Polymer Catalyst (SPC) composite membranes to simultaneously capture and convert flue gas components. W.L. Gore and Associates have developed a unique porous composite membrane based on the combination of adsorbent and catalyst particles with PTFE. This material is being utilized in the GOREâ„¢ Mercury Control System (GMCS) that captures Mercury and SO₂ from industrial flue gas by a selective sorption and catalytic process.

This paper describes the structure of this material and introduces a simple model to describe the mechanisms to capture mercury by chemisorption and convert SO₂ to liquid sulfuric acid. Experimental observations have confirmed that all adsorption and reaction processes can be approximated as first order reaction steps. This simplification leads to an explicit solution to the differential equations at the various length scales including all steps for transport and reaction/adsorption. Two different Thiele moduli result on the two length scales within the active particles and within the SPC membrane that are used to assess the utilization of the particles and the limiting factors for the removal process. The overall removal efficiency is estimated by a mass balance along the flow channels of the modules.

Model results are compared to experimental observations from the lab environment to simulated flue gases to observations of pilot plants using actual flue gases. A comparison between the model results illustrates the shift in limiting process steps between these conditions. This insight can be utilized to optimize the structure and performance of the material under these conditions. Finally, the paper will conclude with illustrating the limitations of this simple model and the steps to improve the model description are described.