Study On The Combustion And Pollutant Emission Characteristics Of Coal Blent With Sludge In O₂/CO₂ Atmosphere

Sludge is a solid precipitate which is produced in the treatment of sewage and wastewater.Sludge blending coal combustion is one of the most promising methods for sludge treatment.Oxy-fuel combustion technology is a new high efficiency and low pollution combustion technology.The co-combustion of coal and sludge in O2/CO2 atmosphere can not only effectively deal with the sludge,but also reduce pollutant emission.Thermogravimetric analysis technology has been used in this paper to study and compare the combustion characteristics of the bituminous coal and three common sludge(including sewage sludge,garbage sludge,river sludge)and their blending in O2/CO2 and O2/N2 atmosphere,and the dynamic characteristics of co-combustion are analyzed by dynamic analysis.It was found that the SO2 and NO emission characteristics of three kinds of sludge blent with coal combustion in the atmosphere of O2/CO2 and O2/N2 by the static combustion system of tube furnace.The conventional pollutant emission characteristics of coal blent with three kinds of sludge in O2/CO2 and O2/N2 atmosphere were studied and compared by the static combustion system of tube furnace.First,TGA/DSC 1 synchronous thermal analyzer was used to study the effects of sludge type,oxygen concentration,combustion atmosphere,sludge blending ratio and heating rate on combustion characteristics of coal blent with sludge combustion.The conclusions are as follows:in O2/CO2 atmosphere,the combustion of bituminous coal has only obvious coke combustion stage,while the combustion of sewage sludge and garbage sludge has both volatile combustion stage and coke combustion stage,the combustion of river sludge has only volatile combustion stage.Except for river sludge,the comprehensive combustion characteristics of sewage sludge and garbage sludge are better than coal.With the increase of oxygen concentration,the maximum coke combustion rate increased,burnout temperature decreased,and the comprehensive combustion characteristic index S*increased.The blending ratio of sludge increased,the maximum weight loss rate of volatile sections increased,the maximum weight loss rate of coke section decreased,and the S*value first increased and then decreased With the increase of heating rate,the combustion time of coal blent with sludge is greatly reduced,the average burning rate increased,the index S*increased significantly.Compared with the O2/N2 atmosphere,the ignition temperature and the maximum combustion rate of the samples in the O2/CO2 atmosphere decreased,and the index S*decreased slightly.Through the dynamic analysis,the random nucleation function(n=3)is best suited to the low-temperature combustion of coal blent with sludge,the three-dimensional diffusion function is best suited to the high-temperature combustion of coal blent with sludge.The activation energy E of each sample did not change when the combustion atmosphere and the oxygen concentration changed.It is theoretically possible to use O2/CO2 atmosphere instead of O2/N2 atmosphere for coal blent with sludge combustion.Then,the influence of oxygen concentration,sludge blending ratio,furnace temperature and combustion atmosphere on the SO2 and NO emission characteristics of coal blent with sludge combustion was studied by using tube furnace.The conclusions are as follows:The SO2 yields and conversion rate of coal combustion are much higher than that of each sludge combustion.With the increase of oxygen concentration,the SO2 yields and conversion rate of coal blent with sludge combustion both increased.With the increase of the blending ratio of sludge,the SO2 yields and conversion rate of coal blent with sludge combustion decreased.With the increase of the furnace temperature,the exhalation peak of SO2 from each sample increased,the SO2 yields and conversion rate both increased.In contrast to the O2/N2 atmosphere of the same oxygen concentration,the SO2 yields and conversion rate of each sample combustion in the O2/CO2 atmosphere were reduced,they decreased by about 7%.The NO yields of coal combustion were lower than each sludge combustion,but,due to its low nitrogen content,the NO conversion rate of coal combustion is far higher than that of each sludge combustion.With the increase of oxygen concentration,the NO yields and conversion rate of coal blent with sludge combustion both increased.With the increase of the blending ratio of sludge,the NO yields and conversion rate of sewage sludge and garbage sludge combustion decreased,but the river sludge is the opposite.With the increase of the furnace temperature,the exhalation peak of NO from each sample increased,the NO yields and conversion rate both increased.In contrast to the O2/N2 atmosphere of the same oxygen concentration,the NO yields and conversion rate of each sample combustion in the O2/CO2 atmosphere were reduced significantly,they decreased by about 20%.Finally,it can be concluded that coal blent with sludge combustion in O2/CO2 atmosphere is feasible.The garbage sludge and sewage sludge have higher volatiles and calorific value,lower SO2 and NO yields and conversion rate.They can be used as a good materials blent with coal combustion.And river sludge as a comparison,Its volatile and fixed carbon content is low,and the combustion performance is poor.NO yields is high.It is not suitable to be used as a materials blent with coal combustion.