Investigation Of The Combustion And PM₁₀emission Characteristics Of Different Municipal Sludge With Coal

With the rapid development of China's economy,the treatment of solid waste has gradually become an important issue of social concern,and the treatment of sludge is an important task.Although in recent years,sludge treatment has achieved certain results,according to relevant data,it is estimated that the annual output of sludge in 2025 will exceed90 million tons.In the face of increasing sludge production year by year,more reasonable and scientific sludge treatment methods should be sought.At present,the treatment methods for traditional solid wastes like sludge are still mainly sanitary landfills.Although it can be treated effectively,landfilling takes up considerable land resources after all,and improper landfilling can also cause secondary pollution to the environment.However,a large-scale single sludge incineration station currently does not be built,and if it is built,the construction period is long and the construction cost is high.The use of existing thermal power plants for sludge mixing and thermally coupled power generation can not only use the existing boiler equipment,saving construction costs,but also assist in the treatment of sludge and realize the recycling of sludge.However,the co-combustion of sludge and coal also has a series of problems worthy of study and attention,such as changes in fuel characteristics and combustion characteristics after mixing,and the emission of pollutants after mixing,such as NO and SO₂ emissions,especially the impact of particle generation.Therefore,this paper studies the combustion characteristics of different municipal sludge and coal co-combustion and the related issues of tail gas emission and particulate matter generation characteristics during co-combustion.First of all,it is selected that a kind of Shenhua coal and two sludges from sewage treatment plants in the west and east of Yanjiao,and mixed them with static combustion experiments on thermogravimetric and tube furnace benches respectively.These sludge and coal are mixed and burned according to their respective mass fractions.The mixed burning ratio of sludge is 5%,10%,and 20%.Each sludge has two different moisture contents:high moisture content and low.The thermogravimetric heating rate is 20?/min,air atmosphere,and thermogravimetric experiment results show that mixing sludge can improve the ignition performance of coal samples.As the mixing ratio increases,the ignition temperature,burnout temperature,and activation energy gradually decrease;The moisture content of sludge has a certain influence on the combustion process.The S_N of low-water sludge is higher than that of high-water sludge.In samples,the moisture content of sludge can affect the maximum reaction rate and its corresponding temperature.It affects pre-digital factors and activation energy.The co-combustion of sludge and coal shows a positive synergy.Proper blending ratio and moisture content can ensure stable co-combustion of coal and sludge.The exhaust gas emission experiment tube furnace temperature is 900?,the air atmosphere,and the experimental results show that the NO and SO₂ emission characteristics of the two types of sludge mixed with coal are different,and the total NO and SO₂emissions of the West sludge are both required higher than East sludge.The moisture content of the sludge will affect the discharge characteristics.The higher the moisture content of the West sludge,the corresponding increase in NO emissions and the reduction of SO₂emissions;the higher the moisture content of the East sludge,the NO emissions will correspondingly decrease,and the SO₂ will also decrease accordingly.With the increase of the sludge blending ratio,the sludge NO emission will increase correspondingly.For the SO₂ emission of the East sludge,a blending ratio of 10%can maximize the SO₂ emission.On the other hand,two kinds of sludge and coal were mixed and burned on the settling furnace to carry out the particulate matter discharge experiment.The sludge was selected from dehydrated samples,and the sludge and coal were mixed with a certain mass fraction.The mixing ratio of the sludge was 5%,10%,20%and 50%.The temperature of the settling furnace is 1400?,and the air atmosphere is used to collect the particles of each level through the DLPI particle sampling system,and then weigh the mass of each level through a precision balance to obtain the mass size distribution of PM₁₀.Finally,for the collected particulate matter samples,the elemental composition and morphology of the particulate matter were analyzed by X-probe fluorescence spectrometer and scanning electron microscope,etc.,and the corresponding experimental conclusions were obtained.The experimental results show that the samples mixed with sludge can inhibit the generation of PM₁ to varying degrees.When the coal is burned alone,the amount of PM₁ generated is 0.765mg/g.The PM₁produced by the sample mixed with 20%West and East sludge is 0.657mg/g and 0.645mg/g.East sludge has about 20%inhibition and emission reduction effect on PM₁ release,mainly because Si and Al in coal absorb easily gasified elements P,S and Cl,etc.in sludge formed larger particles.There is an interaction between the sludge and coal combustion process,which the Si and Al in the coal and the Ca and Fe in the sludge form larger particles of Ca-Fe-Al-Si,or Ca-Fe-P-Al-Si,transforming from sub-micron particles to ultra-micron particlesand.This interaction will reduce the PM₁ content and increase the particle size distribution.