Sludge has a complex composition

which usually contains trace elements(such as heavy metals) with higher mass concentraiton than the coal used by power plants. In this study

a test of sludge and coal co-combustion was conducted on a 600 MW tangentially-fired boiler to investigate the migration and transformation behaviors of heavy metals

As and Se. Under the conditions with and without sludge

the samples of coal

sludge

limestone powder

slag

fly ash

desulfurization gypsum

desulfurization wastewater and stack gas were collected and analyzed. Mass concentrations of trace elements in different input and output materials were measured and the mass flows were calculated. Furthermore

the increasing risk of environmental emission of heavy metals

As and Se induced by sludge addition was predicted. The obtained results indicate that

most of the trace elements transferred into slag and fly ash. The enrichment rates of volatile elements such as Hg

Cd

Pb

As and Se in desulfurization gypsum were significantly higher than that of non-volatile elements such as Zn

Ni

Co

Mn and V in desulfurization gypsum. About 30% of the released Hg which has the highest volatility was captured by the desulfurization system.The addition of small quantity(1%) of sludge did not significantly affect the mass concentrations and mass flow rates of 10 heavy metals

As and Se in output materials including slag

fly ash

desulfurization gypsum and stack gas. The measured mass concentrations of Hg in flue gas were lower than the emission limit of Emission Standard of Air Pollutants for Thermal Power Plants(GB 13223—2011). It was suggested that

the mass concentrations of heavy metals

As and Se in sludge

coal and stack gas should be regularly monitored to avoid large increase of emission levels.