Investigation On Co-thermal Charateristic Of Sewage Sludge And Coffee Grounds And The Effects Of AlCl₃/CaO Conditioner On The Acid Gas Emissions During Combustion Of Sludge

Sludge incineration/pyrolysis is a heat treatment method with the advantages of reduction,harmlessness,and resource utilization.It is necessary to add supplementary fuels to maintain the heat cycle during the thermal treatment process of sludge due to high water content and ash content,and low calorific value of the sludge,.Coffee grounds is considered a ideal biofuel because of high production,low ash content,and high calorific value.However,there is limited research concerning the co-thermal of sludge and coffee grounds is unclear.Besides,although a lot of conditioners remain in the deep-dewatered sludge,there exits no study about analyzing the effect of residual conditioners on acid gas emissions during the thermal treatment of sludge.This work focuses on the thermal conversion behavior of sludge and coffee grounds,and discusses the effect of Al Cl₃ and Ca O conditioning on acid gas emission characteristics.The main research contents are as follows:（1）Artificial neural network（ANN）modeling was applied to thermal data obtained by non-isothermal thermogravimetric analysis（TGA）from room temperature to 1000°C at three different heating rates in air to predict the TG curves of sewage sludge（SS）and coffee grounds（CG）mixtures.A good agreement between experimental and predicted data verified the accuracy of the ANN approach.The results of co-combustion showed that there were interactions between SS and CG,and the impacts were mostly positive.With the addition of CG,the mass loss rate and the reactivity of SS were increased while charring was reduced.Measured activation energies（Ea）determined by the Kissinger-Akahira-Sunose（KAS）and Ozawa-Flynn-Wall（OFW）methods deviated by<5%.The average value of E_a(166.8 k J·mol^-1 by KAS and 168.8 k J·mol^-1 by OFW,respectively)was the lowest when the fraction of CG in the mixture was 40%.（3）（Co-）combustion characteristics of sewage sludge（SS）,coffee grounds（CG）and their blends were quantified under increased O₂/CO₂ atmosphere（21,30,40 and60%）using a thermogravimetric analysis.Observed percentages of CG mass loss and its maximum were higher than those of SS.Under the same atmospheric O₂concentration,both higher ignition and lower burnout temperatures occurred with the increased CG content.Results showed that ignition temperature and comprehensive combustion index for the blend of 60%SS-40%CG increased,whereas burnout temperature and co-combustion time decreased with the increased O₂ concentration.Artificial neural network was applied to predict mass loss percent as a function of gas mixing ratio,heating rate,and temperature,with a good agreement between the experimental and ANN-predicted values.Activation energy in response to the increased O₂ concentration was found to increase from 218.91 to 347.32?k J·mol^-1and from 218.34 to 340.08?k J·mol^-1 according to the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods,respectively.（3）The gaseous emissions during blend fuel combustion were investigated by TG-MS.Results show that the gas emissions of different fuels show different characteristics.When CG was added into SS combustion,the SO₂ emission appeared co-effect during the co-combustion of mixture.Besides,the composition of the solid residues was examined by XRF,and their impact on environment was evaluated.It was found that the CG has a well potential to lower the risk of fouling and slagging.This investigation aimed to afford a fully understanding for the combustion progress and its implication for environment.（4）（Co-）pyrolysis characteristics of sewage sludge（SS）,coffee grounds（CG）and their blends were quantified under increased N₂/CO₂ atmosphere（0,25.2,48.8,73.2 and 100%）using a thermogravimetric analysis.Under the same atmospheric CO₂ concentration,both higher maximum mass loss rate and burnout temperatures,and lower peak temperature occurred with the increased heating rates.Results showed that mass loss rate of third stage for the blend of 70%SS-30%CG increased,whereas there was no change in the residual mass of the residue with the increased CO₂ concentration.The apparent activation energy E_a of the second stage showed a non-additive effect.When the CO₂ was 48.8%,the average value of the second stage E_a calculated by DAEM was 362.33 k J·mol^-1.Py-GC/MS results showed that the content of hydrocarbon products in the gaseous phase of SS and CG pyrolysis is the same,but the pyrolysis gaseous product of CG contained a large number of acid compounds.Co-pyrolysis of SS and CG could optimize the distribution of pyrolysis gaseous products and selectivity.（5）The emission characteristics of acid gases during the co-combustion textile dyeing sludge were quantified at different Al Cl₃ and Ca O conditioning mixing ratio and different furnace temperature using a flue gas analyzer and one-dimensional solid-bed furnace（tube furnace）.Results showed that under the same incineration temperature,the average emission concentration of SO₂ increased with the increase of Al Cl₃ addition amount,while NO_x and H₂S showed a non-additive effect.The emission concentration of NO_x,SO₂ and H₂S showed a downward trend with the increase of Ca O addition amount.Compared to Ca O,the addition of Al Cl₃conditioner promotes the escape of NO_x,SO₂,and H₂S during the combustion of textile dyeing sludge.With the increase of incineration temperature,the average emission concentrations of NO_x,SO₂,and H₂S showed an upward trend during Al Cl₃-textile dyeing sludge.At 800°C,Al Cl₃ had the weakest promotion effect on the NO_x precipitation during the incineration of dyeing sludge.For Ca O-textile dyeing sludge,the inhibition effect of temperature on Ca O was dominant when Ca O content is 5%and 10%.While the addition amount of Ca O reached 15%,the effect of the addition amount on Ca O was dominant.From 800°C to 850°C,the inhibitory effect of Ca O on the SO₂ emission was most obvious.In addition,800°C is the optimum temperature for inhibiting H₂S generation and emission during combustion of Ca O-textile dyeing sludge.