Mechanism and Rates of Hydrogen Cyanide Production in Polyacrylonitrile Incineration Furnaces and Suggesting a Suitable Method for the Removal of Cyanide Gas

Today communities have approved of strict laws for the limits of air pollutants produced by industrial units. Hydrogen cyanide, known as one of the most important and toxic gases, is the exhaust gas from heat treatment of polymers containing nitrile groups, such as polyacrylonitrile (PAN). In this paper, the mechanism of hydrogen cyanide production from polyacrylonitrile pyrolysis has been presented and also the amount of hydrogen cyanide emitted by furnaces producing carbon fiber has been evaluated in a research center in Iran. The amount of released Hydrogen cyanide was measured and presented for two production stages of 150 and 196 carbon fiber and at three different locations; the oxidation furnace, high temperature furnace and before entering the gas purification unit. As expected, the maximum amount of cyanide was observed in HT furnace and the production of the cyanide emission was doubled in 196 carbon fiber mode. The main goal of this paper is to select an appropriate system to eliminate discharged pollutants from the furnaces which is an important issue in the field of combustion and furnace. For this reason, various systems have been surveyed to reduce the amount of hydrogen cyanide. This method has been selected due to the fact that absorption is the appropriate system for removing pollutants with various concentrations in different flows. Furthermore, it is a much less costly method in comparison to the other ones. Moreover, for eliminating hydrogen cyanide by the absorption strategy, a system which consists of two consecutive packed towers is simulated by the aid of powerful Aspen Plus software and Electrolyte NRTL-RK thermodynamic package. The optimum values of operating parameters such as fluid flow, temperature and equipment parameters like the height of the columns were proposed.