Research On After-treatment Technology Of Escaped Methane From Marine Low-pressure Dual-fuel Engine

Compared with marine internal combustion engines,low-pressure dual-fuel engines have lower NOx,SOx and PM emissions and have obvious emission advantages.However,marine low-pressure dual-fuel engines based on in-cylinder premixed combustion have a problem of methane（CH₄）escape.The global warming potential（GWP）of methane is approximately 25times that of carbon dioxide and is an important greenhouse gas.The IMO and other countries around the world have successively restricted the fugitive methane emissions from dual-fuel engines of ships,but the current technology for treating fugitive methane from low-pressure dual-fuel engines is not yet mature.This paper takes the exhaust gas of low-pressure dual-fuel engine as the target,and two technologies of direct catalytic oxidation of escaped methane and plasma coordinated catalytic oxidation of escaped methane are studied.In this paper,through an experimental device for the treatment of escaped methane,the effects of different factors on methane conversion efficiency,CO selectivity and NOX production are studied,the mechanism is analyzed,and the law of action of various factors on escaped methane is obtained.The main research work of the thesis is as follows:（1）Aiming at the problem of escaped methane from marine low-pressure dual-fuel engines,based on the physical properties of methane and related theoretical research on the treatment of escaping methane,an experimental platform for catalytic oxidation of methane was built.On this basis,a method to further promote the treatment of escaping methane using plasma discharge technology was proposed,an experimental platform for escaping methane through plasma promote catalytic oxidation was added as a research platform for thesis.（2）Using the constructed methane oxidation experimental platform,this paper carried out the direct catalytic oxidation of escaped methane technology research,taking methane conversion efficiency,CO selectivity and NO_X production as the research objects,by controlling experimental variables,the influence of reaction conditions,catalysts and other factors on the research objects are studied.Studies have shown that:using Pd/ZSM-5 catalyst,the methane conversion efficiency reaches 97.25%at 400℃.The methane conversion efficiency of Pd/ZSM-5 catalyst is better than Pd/Al₂O₃ catalyst,and better than Pt/Al₂O₃catalyst;increase the catalyst The amount,the initial concentration of methane and the initial concentration of oxygen can increase the conversion efficiency of methane;reducing the gas flow rate will increase the conversion efficiency of methane;CO selectivity and NOx production are very low in the experiment,and the NOx production is most affected by the reaction temperature.（3）Using the constructed methane oxidation experimental platform,this paper researched on the technology of escaped methane by plasma-assisted catalytic oxidation,taking methane conversion efficiency,CO selectivity and NO_X production as the research objects,by controlling experimental variables,the influence of reaction conditions,input power and other factors on the research objects are studied.Studies have shown that:using Pd/Al₂O₃ catalyst with an input power of 20W,the methane conversion efficiency reaches80.975%at 250℃.The synergistic effect of Pd/Al₂O₃ catalyst and plasma is better than Pd/ZSM-5 catalyst and better than Pt/Al₂O₃ catalyst;increasing catalyst noble metal content,catalyst dosage,and initial methane concentration will increase methane conversion efficiency;increasing initial oxygen concentration and gas flow will reduce methane conversion efficiency;CO selectivity and NO_X generation are higher,with input power and methane As the initial concentration increases,the CO selectivity decreases,and the NO_X generation is most affected by the power.When the input power is 70W,the maximum NO_X generation is2704ppm;the experimental results show that the plasma coordinated catalytic oxidation reaction process of escaping methane is divided into two steps.The first step takes place in the discharge area,and the second step takes place on the surface of the catalyst.This paper studied the treatment technology of escaped methane from marine low-pressure dual-fuel engines,and the research results support the control of escaped methane from actual low-pressure dual-fuel engines.