Nitrogen Oxide Removal by Coal-Based Activated Carbon for a Marine Diesel Engine

Vanadium-based catalysts are mainly used for marine diesel exhaust denitration. However, their poor catalytic ability at low temperature and poor sulfur tolerance, as well as high toxicity and cost, are big turnoffs. AC (Activated carbon) exhibits good adsorption capacity and catalytic ability in denitration because of its high specific surface area and chemical activity. In this paper, coal-based AC was used for simulating diesel exhaust denitration in different conditions. The results show that the NO removal ability of AC is poor in an NO/N2 system. The NO2 removal ability is excellent in an NO2/N2 system, where NO is desorbed. The NOx removal efficiency is 95% when the temperature is higher than 200 °C in an NO2/NH3/N2 system. When the temperature is lower than 100 °C, AC can catalytically oxidize NO to NO2 in an NO2/O2/N2 system. The near-stable catalytic efficiencies of AC for a slow SCR (Selective Catalytic Reduction) reaction, a standard SCR reaction, and a fast SCR reaction at 300 °C are 12.1%, 31.6%, and 70.8%, respectively. When ships use a high-sulfur fuel, AC can be used after wet scrubber desulfurization to catalytically oxidize NO to NO2 at a low temperature. When ships use a low-sulfur fuel, AC can be used as a denitration catalyst at high temperatures.