Prediction of the Cl_2 and Br_2 content In flue gases

摘要

The paper consists of two parts. In the first part a simple method for the prediction of the emission of molecular halogens was presented. It is based on the calculation of the concentrations of atomic and molecular halogens according to the thermodynamic equilibrium at 1050 deg C. This method can easily be implemented into programs like Aspen plus. We have shown that this procedure is viable for a wide range of conditions and feedstocks. The only restriction identified so far is a quenching rate above approx 5000 K/s starting from temperatures above approx1150 deg C. In the second part a new process was described for selective non-catalytic reduction of molecular halogens (SHR) by the injection of H2 into the burnt flue gas. For reduction of Cl_2 the optimal temperature lies around 700 deg C, and a residence time of approximately 50 ms is required. Reduction efficiencies of at least 99 percent can be achieved without forming unacceptable amounts of CO.Br_2 can also be effectively reduced. As the reduction-kinetics of Bra are slower more residence time is required and more CO is formed. Although these problems appear to be solvable, they might limit the applicability for Br_2. The novel process was at first investigated by numerical modeling and then confirmed by experiments. Some optimization is still required.