Compared to diesel, liquefied natural gas (LNG), often used as an alternative fuel for marine engines, comes with significant advantages in reducing emissions of particulate matter (PM), SOx, CO2, and other pollutants. Promoting the use of LNG is of great significance for achieving carbon peaking and neutrality worldwide, as well as improving the energy structure. However, compared to diesel engines, medium- and high-speed marine LNG engines may produce higher methane (CH4) emissions and also have nitrogen oxide (NOx) emission issues. For the removal of CH4 and NOx from the exhaust of marine LNG engines, the traditional technical route of combining a methane oxidation catalyst (MOC) and an HN3 selective catalytic reduction system (NH3-SCR) will face problems, such as low conversion efficiency and high operation cost. In view of this, the technology of non-thermal plasma (NTP) combined with CH4-SCR is proposed. However, the synergistic mechanism between NTP and catalysts is still unclear, which limits the optimization of an NTP-CH4-SCR system. This article summarizes the synergistic mechanism of NTP and catalysts in the integrated treatment process of CH4 and NOx, including experimental analysis and numerical simulation. And the relevant impact parameters (such as electrode diameter, electrode shape, electrode material, and barrier material, etc.) of NTP reactor energy optimization are discussed. The work of this paper is of great significance for guiding the high-efficiency removal of CH4 and NOx for an NTP-CH4-SCR system.
Keywords: CH4 emission; LNG engines; NOx emission; catalyst; marine; nonthermal plasma.