SO3　removal　efficiency　and　ash　particle　flowability　of　low-low-temperature　flue　gas　systems　(LLTSs)　were　studied.　The　results　indicate　that　when　the　temperature　is　approximately　40　°C　lower　than　acid　dew　point　(Td),　the　SO3　removal　efficiency　reaches　a　maximum.　This　optimum　temperature　is　affected　by　particle　physical　characteristics　and　elemental　composition.　The　SO3　removal　efficiency　increases　as　ash/sulfur　ratio　(D/S)　increases.　However,　when　temperature　is　low,　the　effect　of　D/S　is　weak.　Particle　size　is　also　an　important　factor　for　the　removal　efficiency.　The　adsorption　process　is　a　synergistic　effect　of　physical　and　chemical　reactions.　Chemical　adsorption,　which　depends　on　the　metal　elements,　especially　Al　elements,　helps　fix　the　sulfur　element　on　particle　surface　and　increase　the　stickiness　of　it.　The　agglomeration　of　ash　particles　mainly　happens　between　smaller　particles　or　between　small　particles　and　large　particles.　However,　when　temperature　drops　too　much,　large　particles　will　agglomerate　with　each　other　due　to　the　effect　of　H2O　vapor.　The　particle　flowability　is　greatly　reduced　after　the　adsorption　process.　When　temperature　is　20　°C　lower　than　Td,　the　repose　angle　increased　greatly.　Hence,　the　temperature　should　be　properly　lowered　in　pursuit　of　high　sulfur　oxide　removal　efficiency　and　dust　removal　efficiency.　©　2020　Elsevier　Ltd