# Nitrogen Oxide Removal by Coal-Based Activated Carbon for a Marine Diesel Engine
## 4 Conclusions  
Based on the above experiments on the denitration ability of coal-based activated carbon under different conditions, the paper mainly draws the following conclusions:  
(1) In the range of 15-300 \({}^{\circ}\)C, when the inlet gas is NO/N\({}_{2}\), the removal of NO by coal-based activated carbon mainly depends on the adsorption, and the near-stable denitration efficiency is low. When the inlet gas is NO\({}_{2}\)/N\({}_{2}\), NO\({}_{2}\) is finally converted to NO and desorbs from the surface of activated carbon. However, when NH\({}_{3}\) is added and the temperature is higher than 200 \({}^{\circ}\)C, the NOx removal efficiency is up to 95% in the NO\({}_{2}\)/N\({}_{2}\) system.  
(2) When the inlet gas is 1000 \(\mu\)L/L NO + 5% O\({}_{2}\), the saturated adsorption time of NO for AC at 10 \({}^{\circ}\)C and 50 \({}^{\circ}\)C is 660 min and 500 min, respectively. However, the adsorption saturation time drops sharply with an increase in temperature. When the temperature is above 200 \({}^{\circ}\)C, the adsorption saturation time is less than 10 min. When the temperature is lower than 100 \({}^{\circ}\)C, activated carbon can catalyze the oxidation of NO to NO\({}_{2}\). The conversion efficiency of NO to NO\({}_{2}\) at 15 \({}^{\circ}\)C and 50 \({}^{\circ}\)C is 62.3% and 43.8%, respectively. When the temperature is higher than 100 \({}^{\circ}\)C, the ability of AC for catalytic oxidation of NO is minimal.  
(3) The stable denitration efficiencies of activated carbon with different inlet gas are investigated at 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, and 300 \({}^{\circ}\)C. When the inlet gas is NO/NH\({}_{3}\)/N\({}_{2}\), simulating slow SCR reaction Equation (1), the NOx removal rates corresponding to the three temperatures are 9.1%, 10%, and 12%. When the inlet gas is NO/NO\({}_{2}\)/NH\({}_{3}\)/N\({}_{2}\), simulating the fast SCR reaction Equation (2), the NOx removal efficiencies corresponding to the three temperatures are 53%, 69.2%, and 70.8%, respectively. When the inlet gas is NO/NH\({}_{3}\)/O\({}_{2}\)/N\({}_{2}\), simulating the standard SCR reaction Equation (3), the NOx removal efficiencies corresponding to the three temperatures are 34.6%, 16%, and 31.6%, respectively.  
(4) There are two main methods for the application of activated carbon in the exhaust gas denitration of marine diesel engines. When ships use high-sulfur fuel oil, the exhaust gas cooled after the wet scrubber desulfurization can be passed into the activated carbon to oxidize NO to NO\({}_{2}\), which is more soluble in water. Then the gas can be passed to a wet scrubber for denitration. When ships use low-sulfur fuel oil, the high-temperature exhaust gas can be passed into the activated carbon catalytic reactor. Then NH3 can be injected into the reactor for SCR denitration treatment.  
**Author Contributions:** Conceptualization, Z.W., J.Z. and Y.J.; data curation, H.K. and L.C.; formal analysis, Z.W., H.K.; investigation, Z.W., H.K. and L.C.; resources, Y.J.; writing--original draft preparation, Z.W.; writing--review and editing, J.Z. and Y.J.  
**Funding:** This research was supported by the National Natural Science Foundation of China (51876019, 51579026), Innovative talent support program for University of Liaoning province (LR2017048), and the Transportation Industry High-Level Talent Training Program.  
**Conflicts of Interest:** The authors declare no conflict of interest.