Experimental Study On Combustion Characteristics Of Sewage Sludge/Bituminous Coal

Sewage sludge is the residue produced by wastewater treatment,but it is also a kind of renewable energy.Coal resources occupy the main part in China's energy structure.Co-combustion of sludge and coal can effectively save the consumption of coal resources,and it is also a kind of effective mean of sludge treatment.In current works,the co-combustion characteristics of sewage sludge/bituminous coal was revealed based on a thermogravimetric analyzer and a lab-scale fixed bed furnace.Based on thermogravimetric experiments and theory analysis,the influence of initial moisture content,heating rate(20?80 K min^-1),blend ratio and oxygen concentration on the combustion characteristics of sludge/bituminous coal were obtained.The results showed that the ignition,burnout and comprehensive combustion indices of the samples increased with increasingly heating rates and sludge ratios.The ignition and burnout indexes of 50SS50C in 40%O₂/60%CO₂ oxy-fuel atmosphere were about 1 and 0.3 times higher than those in air.Between the initial moisture contents of 5.02%and 37.85%,the average activation energies of sewage sludge in mian combustion process ranged from 146.59 to 168.39 kJ mol"1,and the activation energies of sewage sludge increased with increasing their initial moisture contents.The average activation energies of the dry sewage sludge,80SS20C,50SS50C,20SS80C and bituminous coal in the main combustion stage at different heating rates were 165.80,139.24,118.21,82.87 and 68.07 kJ mol^-1,respectively.By conducting experiments in the lab-scale fixed bed combustion system,the influences of sludge ratios,heating rates?non-isothermal burning?and temperatures?isothermal burning?on flame,mass conversion,kinetics and gas emissions of sewage sludge/bituminous coal briquettes were revealed.The results showed that in non-isothermal burning,compared with pure samples,the flame brightness and duration time of sewage sludge/bituminous coal blends increased.NO emission increased with increasing heating rates.Compared with bituminous coal,the average emission of CO and CO₂ of sewage sludge decreased by 212%and 175%respectively at the heating rate of 20 K min^-1,while the average emission of NO increased by 288%.The average activation energies of the sewage sludge,80SS20C,50SS50C,20SS80C and bituminous coal in the main combustion stage were 47.55,40.86,31.69,28.17 and 29.99 kJ mol^-1,respectively.In isothermal burning,the flame duration time of sewage sludge/bituminous coal briquettes decreased with increasing sludge ratios while the flame brightness increased with increasing sludge ratios.The CO emission decreased with increasing temperatures while the CO₂ and NO emission increased with increasing temperatures.The peak of NO and SO₂ emission increased by 0.78 and 10 times respectively when the sludge ratio increased from 20%to 80%at 800 ?.The activation energies of the sewage sludge,80SS20C,50SS50C,20SS80C and bituminous coal in the main combustion process were 30.51,35.03,33.23,41.33 and 36.56 kJ mol^-1,respectively.After adding CaO,the burnout time of sewage sludge/bituminous coal briquettes shortened and the peak of CO,CO₂ and NO emission of bituminous coal decreased by 47.6%,39.4%and 37.5%,respectively.Ash fusion temperatures for bituminous coal and sewage sludge ranged from 1366? to 1508 ? and from 1160 ? to 1230 ?,respectively.CaO made up the most in ash content of sewage sludge and SiO₂ made up the most in ash content of bituminous coal.