Co-combustion Of Sewage Sludge Research Articles

Co-combustion of municipal sewage sludge and food wastes-derived anerobic digestates: Combustion characteristics, HCl/NO/SO2 emission and ash behaviors

Co-combustion of sewage sludge (SS) and food wastes-derived anerobic digestate (AD) is a promising way of waste-to-energy. Therefore, it is crucial to examine their combustion performance, ash behaviors, and gaseous pollutants emissions during the combustion of AD-SS blends using a thermogravimetric analyzer and a tube furnace combustion system. Results show that obvious interactions between AD and SS are observed in their co-combustion process. In terms of comprehensive combustion index, co-combustion can improve their combustion performance with the decrement of burnout temperature and enhanced combustion reactivity. Higher blending ratio of AD favors the increment of their ash fusion temperature, i.e., from 1109 to 1403oC for deformation temperature due to the formation of high melting point minerals (i.e., Ca9Fe(PO4)7, 2CaO·Al2O3·SiO2). Significant in-situ reduction of NO and HCl as well as self-desulfurization is observed during the combustion of AD-SS blends. Compared to the theoretical values, the emission amount of HCl, NO, and SO2 is reduced by 0.13, 1.39, and 0.35mg·g-1, respectively at 850oC and blending ratio of AD to SS = 0.75:0.25. These phenomena are associated with the reducing environment and reducing substances by their high volatiles as well as the abundant minerals such as CaCO3 and Fe2O3 in AD and SS. However, high combustion temperature is unfavorable for chlorine fixation. This work provides a better understanding of their thermal behaviors, ash characteristics, and gaseous pollutants emission characteristics to realize their stable and clean incineration.

Interaction mechanism and pollutant emission characteristics of sewage sludge and corncob co-combustion

The co-combustion of sewage sludge and biomass has demonstrated significant potential for reducing carbon emissions and realizing the resource utilization of solid waste. In this study, the co-combustion behavior and pollutant emissions of sewage sludge and corncob were systematically investigated using thermogravimetric-Fourier transform infrared spectroscopy-mass spectrometry (TG-FTIR-MS) and a fixed-bed reactor. When the corncob blending ratio reached 30%, the ignition temperature was 179.01 °C lower than that of sewage sludge, and the comprehensive combustion index increased by 13.92 times. The corncob in the mixed fuel dominated the volatiles' release and combustion process. The interaction strength increased as the corncob blending ratio increased. When the corncob blending ratio reached 70%, it promoted the thermal weight loss process of sewage sludge. The release rate of CO2 increased as the biomass ratio increased, and a 30% corncob content could inhibit CO2 emissions. Simultaneously, the interaction between sewage sludge and corncob inhibited the emissions of CO and NO during the co-combustion process, improving the combustion efficiency. This study provides theoretical support for developing the fuel value of sewage sludge, improving the amount of solid waste collaborative disposal, and realizing the leading carbon peak in thermal power industry.

Pollutant Emissions and Heavy Metal Migration in Co-Combustion of Sewage Sludge and Coal

The treatment of sewage sludge has become a global concern. Large amounts of sewage sludge can be disposed of by burning coal-mixed sludge. Thermogravimetric analysis and lab-scale combustion experiments in a drop tube furnace were utilized to study the combustion characteristics, pollutant emissions, and heavy metal migration during the co-combustion of coal and sewage sludge. The results showed that the blended fuels with a sewage sludge content less than 10 weight percent exhibited coal-like combustion characteristics. Additionally, the additional sewage sludge favored the ignition performance of blended fuels. When sewage sludge was added, the SO2 emissions rose to 76 mg/Nm3 under the 10% sludge condition—nearly three times higher than that of coal alone. While NOx emissions stayed mostly unchanged, HCl and HF emissions were very low. Meanwhile, Cr, Cu, and Ni migrated to the bottom ash, and their concentrations were all reduced with an increase in sewage sludge. Pb, Cd, Cr, Cu, Ni, and Hg migrated to the flue gas, mostly in the form of gaseous components. The results provide crucial information in the co-combustion of sewage sludge and coal, with implications in the development and improvement of large-scale, harmless, and resource-recovering techniques for waste sludge.

Investigation on the interaction mechanism during co-combustion of sewage sludge and coal slime: The effect of coal slime type and pretreatment method

Co-combustion of sewage sludge (SS) and coal slime (CS) is the preferred method for mitigating their environmental impact and increasing their added value. However, the interaction mechanism between SS and CS during the co-combustion process has not yet developed a unified understanding. This work aims to obtain the effect of CS types on SS-CS co-combustion and reveal the interaction mechanism between SS and CS based on the influence of pretreatment methods on the interaction. The results showed that during co-combustion, SS reduced the ignition and burnout temperatures, and CS with high fixed carbon content (e.g., XCS) improved the comprehensive combustion characteristics. Principal component analysis showed that the effect of CS on co-combustion was more significant. The interaction between SS and CS mainly occurred within 100–700 °C, in which inhibition and synergism coexisted. The large differences in the interactions before and after de-volatilization and pickling treatments revealed that the volatiles and ash in SS were the main interaction factors. The analysis of the interaction mechanisms showed that the free radicals and heat released from the SS volatiles combustion accelerated the weight loss of CS, but the formation of tars from its incomplete combustion may inhibit the decomposition of CS. The interaction in the fixed carbon combustion stage was mainly caused by SS ash, which can catalyze the combustion of CS fixed carbon, but for the high ash CS (e.g., QCS), the combustion of fixed carbon was hindered by the addition of SS ash higher than 10 %. The final manifestation (synergy or inhibition) of SS and CS interactions was the result of the competitive balance of the above interactive behaviors. This work provides a more comprehensive understanding of the interaction between SS and CS during co-combustion.

Effects of alkali and alkaline earth metals on co-combustion of sewage sludge and coal slime: Combustion characteristics, interactions, and kinetics

The co-combustion of sewage sludge (SS) and coal slime (CS) is a preferred method for their resource utilization, however, alkali and alkaline earth metals (AAEMs) in SS may affect the co-combustion process. In this work, the co-combustion behavior of AAEMs-rich SS and CS was investigated in terms of combustion characteristics, interactions, and combustion kinetics using a thermogravimetric analyzer. Further, the role of AAEMs in co-combustion was evaluated by loading Ca, K, Na, and Mg individually after pickling. The results revealed that co-combustion compensated for the limitations of the individual combustion processes, with SS reducing ignition and burnout temperatures and CS improving the comprehensive combustion characterization. Principal component analysis (PCA) showed that the effect of CS on co-combustion was more significant compared to SS. Significant synergies were observed in the weight loss phase of fixed carbon in the blends with 40%, 50%, and 60% CS ratios, where the peak temperature of fixed carbon combustion was reduced by 9.8 °C, 12.6 °C, and 13.1 °C, respectively, compared to the theoretical values. The effects of AAEMs on combustion were as follows: all AAEMs promoted the precipitation of volatiles except Ca, which showed inhibition of light volatiles; AAEMs had a significant catalytic effect on fixed carbon combustion. The improvement effect of AAEMs on the comprehensive combustion characteristics during co-combustion was Na > K > Mg > Ca. The catalytic effect of Na on fixed carbon was strongest at a loading of 5%, leading to a decrease in the apparent activation energy of fixed carbon combustion by 22.2 kJ/mol and a change in reactor order from n = 1 to n = 1.2 during co-combustion. This work provides a better understanding of the role of AAEMs in SS-CS co-combustion.

Ash Formation and Associated Interactions during Co-Combustion of Wheat Straw and Sewage Sludge

The aim of the present work was to investigate ash formation and associated interactions during the pulverized fuel co-combustion of biomass fuels. Combustion experiments were carried out with narrowly sized wheat straw (WS), sewage sludge (SS), and their blends in a drop tube furnace at 1100 °C and 1300 °C. The resulting residual ash and fine particulate matter (PM10) were characterized with various analyses. It was observed that co-combustion influences size distributions of the residual ash particles and generally generates larger residual ash particles close to those of SS combustion. The interaction of K capture by minerals enhances the melting and consequently increases the production of large and melting ash particles during co-combustion. It was found that blending SS with WS has not only the positive interaction of K capture by minerals from SS ash to significantly reduce submicron ash formation, but also the positive interaction of transforming alkali chlorides into alkali sulfates to reduce the corrosiveness of submicron ash particles. Co-combustion of SS with WS can also reduce the presence of alkali chloride at PM1–10, lowering the propensities of deposition and corrosion of the fine residual ash particles.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

Morphology and phosphate distribution in bottom ash particles from fixed-bed co-combustion of sewage sludge and two agricultural residues

The purpose of this study was to provide detailed knowledge of the morphological properties of ash particles, including the volumetric fractions and 3D distributions of phosphates that lay within them. The ash particles came from digested sewage sludge co-combusted with K- and Si-rich wheat straw or K-rich sunflower husks. X-ray micro-tomography were combined with elemental composition and crystalline phase information to analyse the ash particles in 3D.Analyses of differences in the X-ray attenuation enabled calculation of 3D phosphate distributions that showed high heterogeneity in the slag particles. This is underscored by a distinct absence of phosphates in iron-rich and silicon-rich parts. The slag from silicate-based wheat straw mixtures had lower average attenuation than that from sunflower husks mixtures, which contained more calcium. Calculated shares of phosphates between 7 and 17 vol% were obtained, where the highest value for a single assigned phosphate was observed in hard slag from wheat straw with 10 % sewage sludge. The porosity was notably higher for particles from pure wheat straw combustion (62 vol%), compared to the other samples (15–35 vol%). A high open pore volume fraction (60–97 vol%) indicates that a large part of the pores can be accessed by the surroundings. For all samples, more than 60 % of the discrete (closed) pores had an equivalent diameter < 30 μm, while the largest volume fraction consisted of pores with an equivalent diameter > 75 μm. Slag from sunflower husk mixtures had larger pore volumes and a greater relative number of discrete pores >75 µm compared to wheat straw mixtures.

Synergistic retention of heavy metals and in-situ reduction of NO and SO2 by co-combustion of sewage sludge and coal gangue: A promising approach for contaminant management and emission reduction

This study aims to evaluate the influence of co-firing municipal sewage sludge with coal gangue at 800–1000 °C on the emissions of pollutants such as NO, SO2 and heavy metals (HMs). The results revealed that co-combustion resulted in smoother combustion (e.g., lower ignition and burnout temperatures, and a higher comprehensive combustion index) as well as a reduction in activation energy by approximately 30 kJ/mol when the sewage sludge ratio was above 60%. Moreover, the retention of HMs in the ashes during co-combustion was significantly improved through reactions between the dominant minerals (especially quartz (SiO2), berlinite (AlPO4), hedenbergite (CaFeSi2O6), magnetite (Fe3O4) and gehlenite (Ca2Al2SiO7) with HMs species presented in the wastes, leading to an increase in HMs content by 1 to 3 times. Additionally, in-situ desulfurization and denitration were observed during co-combustion at above 900 °C and below 850 °C, respectively. It is likely that berlinite has a direct impact on NO emissions, while gehlenite, whitlockite (Ca2.86Mg0.14(PO4)2) and diopside (CaMgSi2O8) present in the ashes are associated with the evolution of SO2 during co-combustion. These findings suggest that co-combustion of multiple wastes is a feasible approach for their resource utilization while reducing the environmental impacts associated with solid waste disposal.

Migration and transformation of trace elements during sewage sludge and coal slime Co-combustion

Co-combustion of sewage sludge (SS) and coal slime (CS) could improve the combustion properties of the two materials, however, high levels of trace elements (TEs) can be released from the two wastes, resulting in secondary pollution. The migration and transformation behavior of As, Cr, Pb, Zn, and Mn during co-combustion is explored in current research. The results showed co-combustion could inhibit the emission of Zn, As, Pb, and Mn, and the effect was more pronounced for Zn, As and Mn. Meanwhile, minerals like kaolinite and gypsum were found to generated in the ash from co-combustion but not solo-combustion. Model experiments demonstrated that kaolinite captured As, Pb and Mn, while gypsum captured Zn, As and Mn but facilitated the emission of Pb and Cr. This well explained the distinct TEs emission characteristics between co-combustion and solo combustion. As the temperature elevated, kaolinite in co-combustion ash decomposed and the generation of gypsum was promoted. In this way, the emission ratios of Zn, As, and Mn initially increased but subsequently decreased between 700 and 1300 °C, whereas Pb and Cr emission ratios increased by twofold within the same temperature range. Leaching characteristics and risk assessment code on co-combustion ashes were also conducted in this study. The results indicated a marginal elevation in the risk associated with trace elements (TEs) following co-combustion, provided that all five TEs remained within the limits of national standards.

Transformation of Zn and Cr during co-combustion of sewage sludge and coals: influence of coal and steam.

Combustion experiments of sewage sludge (SS) blended with low-rank coal were conducted through a drop tube furnace (DTF) to explore the effects of low-rank coal type, blending ratio, and steam on the transformation of Zn and Cr. The results showed that the retention rates of Zn and Cr in ash increased from 24.35% and 71.49% for sludge combustion alone to 53.77% and 117.49%, respectively, for coal blended to SS with a mass ratio of 7:3. The greater the proportion of low-rank coal in the fuel, the greater the residual rate of heavy metals in the ash. Meanwhile, rapid diffusion of vapor occupied adsorption sites on metal mineral surfaces, reducing the retention of Zn and Cr in the co-combustion ash. The leaching toxicity analysis of ash showed that the co-combustion ash of SS with coal was free from leaching toxicity hazards in simulated scenarios. The extraction rate of Zn in co-combustion ash increased from 90.72% with hydrothermal acid leaching to 95.46% with microwave-assisted in 2mol/L H2SO4 extract. The extraction rate of Cr in hydrothermal acid leaching was 62.80%, which was much higher than that in microwave-assisted extraction (31.76%).

Ash Transformation during Fixed-Bed Co-combustion of Sewage Sludge and Agricultural Residues with a Focus on Phosphorus.

This work investigates the ash transformation during fixed-bed co-combustion of sewage sludge mixtures with the agricultural residues wheat straw and sunflower husks, focusing on the fate of phosphorus (P) in the resulting ash fractions. The study aims to determine suitable process parameters for fixed-bed combustion of fuels previously investigated in single-pellet experiments. The pure fuels and fuel mixtures were combusted in a 20 kWth residential pellet burner while monitoring the flue gas composition, temperature, and particulate matter formation. Subsequently, the different ash fractions were collected and characterized by CHN, SEM/EDS, and XRD analysis. The results showed that co-combustion of sewage sludge and agricultural residues reduced the formation of particulate matter as well as the formation of slag. Co-combustion of sewage sludge with either agricultural residue resulted in a change in phosphate speciation, displaying higher shares of Ca and lower shares of Fe and Al in the formed orthophosphates as well as amorphous phases containing higher shares of K. The formation of K-bearing phosphates was hindered by the spatial association of P with Ca and Fe in the sewage sludge, the incorporation of available K in K-Al silicates, and the depletion of K in the P-rich melt phase. Compared to mono-combustion, co-combustion experiments showed the potential for improving the combustion performance and reducing the risk of slag formation. The outcome suggests that co-combustion is a feasible path to integrate waste streams in fixed-bed energy conversion with simultaneous formation of phosphates enabling P recovery.

Co combustion of sewage sludge and Turkish lignite: the effect of blending on combustion characteristics

Co combustion of sewage sludge and Turkish lignite: the effect of blending on combustion characteristics

Fate of phosphorus in pulverized fuel co-combustion of sewage sludge and agricultural residues

The fate of phosphorus concerning its distribution in the thermal process and chemical speciation was studied during the co-combustion of sewage sludge with wheat straw and sunflower husks in powder combustion conditions. Co-combustion experiments were performed in a lab-scale entrained flow reactor (EFR) at 1000 °C and 1400 °C. SEM-EDS and ICP-OES analyses were used for studies of deposits collected on a probe, bottom ash, and particulate matter samples collected during experiments. Deposition probe samples were further studied and interpreted using powder X-ray diffraction (XRD) and thermochemical equilibrium calculations (TECs). The inorganic material in the different fuel particles mainly interacted through a molten phase observed on deposition probes. Crystalline P was mainly identified in β-Ca3(PO4)2 whitlockites. TECs support the experimental findings and suggest that a mostly homogenous melt occurs at 1400 °C, whereas Fe-oxides and Ca-phosphates precipitate during the cooling of the formed deposits. It was found that <5 % of incoming P was collected in fine particulate matter (<1 µm), indicating that the majority of P can be found in deposits and bottom ash. This outcome implies that P recovery efforts should be focused on these ash fractions.

Migration characteristics and ecological risk assessment of heavy metals in ash from sewage sludge co-combustion in coal-fired power plants

Co-combustion in coal-fired power plants is one of the main methods to dispose of municipal sewage sludge (MSS). The high heavy metals content of MSS increases the ecological risk of ash from the coal and MSS co-combustion. In response to this problem, the three types of fly ash or bottom ash from MSS co-combustion in the three coal-fired power plants were sampled. The properties of fly ash and bottom ash were analyzed in terms of ash composition, particle size distribution, heavy metals content and leaching characteristics. The potential ecological risks were evaluated using the ecological risk index assessment method. The results showed that the co-combustion of MSS had no significant effect on the ash composition order and heavy metals content order. However, the total content of Cu, Mn, Pb and Zn, Hg in the co-combustion ash was higher than that in the coal-fired ash without sludge blending but did not exceed the risk screening value for soil heavy metal contamination of residential land. Heavy metals showed significant enrichment in fly ash and dilution in bottom ash. The leaching concentrations of Cr and Ni were several times the limit value. The potential ecological risk levels of fly ash and bottom ash were moderate risk and high risk respectively. Cr and Hg were the main contributors to potential ecological risks. The contents of Cr, Hg and Ni need to be paid attention to in the subsequent utilization of coal ash mixed with co-combustion of sewage sludge.

Stable and clean co-combustion of municipal sewage sludge with solid wastes in a grate boiler: A modeling-based feasibility study

Municipal sewage sludge not only has very high moisture content and low heating value but also carries lots of nitrogen, making it difficult to attain stable and clean co-combustion with municipal solid waste (MSW) in existing MSW incinerators. Blending other high-heating value solid waste as assistive fuel in co-firing of sewage sludge and MSW is considered feasible to improve the combustion stability and meanwhile maintain the disposal capacity of the incinerator. This paper numerically investigates MSW co-firing with sewage sludge and industrial solid waste in a moving-grate MSW boiler with a capacity of 750 t/d. The co-combustion stability and nitrogen oxides (NOx) emissions are among the main concerns, different blends of the three solid wastes and under-grate primary air (PA) distributions are probed and compared. First, a validated in-house bed model, comprehensively describing the solid fuel conversion process and heat and mass transfer phenomena on moving grates, is extended to include NOx formation and employed to simulate the combustion of various blends on the grate. Then, the fuel bed model is iteratively coupled with the simulation of the freeboard of the boiler, which is performed using ANSYS Fluent. For the various blends investigated in this study, co-combusting up to 25.6 wt% sewage sludge, with about 14.4 wt% industrial solid waste and 60 wt% MSW in the existing boiler, is feasible and recommended. By properly tuning the under-grate PA distribution, the stable, efficient and clean combustion of the feedstock blend has been achieved. Compared to the original PA distribution, up to 11.54% reduction of NOx emission from the boiler is attained, because of the enhancement of nitric oxide (NO) reduction reactions with ammonia (NH3) and char. At last, an in-depth analysis of co-combusting the recommended blend using the new PA distribution is elaborated. This study provides a valuable reference and guideline for stable and clean co-combustion of sewage sludge and MSW in existing incinerators.

Co-combustion of sewage sludge and Zhundong coal: Effects of combustion conditions on gaseous pollutant emission and ash properties

The combustion of sewage sludge (SS) generates large amounts of NOx and SOx, while that of alkali and alkaline earth metal-rich coals produces slagging-prone ash. To determine whether these problems can be mitigated through the co-combustion of SS and coal, we examined the effects of SS and Zhundong coal co-combustion in a horizontal tubular furnace on the emission of NOx and SOx, analyzing the micromorphology, composition, and pore structure of the produced ash. Sludge content was inversely correlated with SO2 emission but had little effect on NOx emission. A high sludge content promoted the fusion of ash particles, whose size was positively correlated with combustion temperature. Na/Ca-feldspar miscibility led to the fusion of ash particles, facilitating the production of magnesia-iron spinel and complex phosphates to alleviate slagging. The specific surface area of ash was negatively correlated with temperature and was the largest at a sludge content of 20 wt%. The fractal dimensions calculated to examine pore structure complexity and pore surface roughness revealed that the latter parameter was inversely correlated with temperature. A reaction temperature of 900 °C and sludge content of 20 wt% were optimal conditions for gaseous pollutant emissions and ash agglomeration behaviors during co-combustion. Thus, this study provides a theoretical basis for controlling the operation of coal/SS co-fired power plants in terms of pollutant emission, combustion efficiency, and ash slagging.

Construction of iterative algorithm and economic optimization analysis of co-combustion of sewage sludge with coal

ABSTRACT To govern the sewage sludge, which restricts the development of urbanization, the co-combustion of sewage sludge in coal-fired power plants is considered one of the most appropriate methods. Two methods, flue gas dehydration and electric heating dehydration, are used to dry sewage sludge to the target moisture content. And the economic impact of the two methods was evaluated on coal-fired power plants. The boiler efficiency and fuel consumption are obtained by the thermal balance calculation. When the anhydrous sludge ratio was 2% and the water content was 30%, the fuel consumption was 81.11 kg/s and the boiler efficiency was 91.32%. As the water content and the anhydrous sludge ratio increase, the fuel consumption gradually increases, while the boiler efficiency gradually decreases. And the net present value is used to evaluate the economic impact of the co-combustion of sewage sludge in coal-fired power plants. Among them, the maximum NPV value of the flue gas dehydration scheme with a sludge mass ratio of 3% and a moisture content of 40% reached 1163.34 million. Furthermore, the sensitive factors that affect the net present value are obtained as the anhydrous sludge ratio and government subsidies through sensitivity analysis. Combined with the combustion characteristics in the boiler, the recommended range for the moisture content of the sludge is 30%~40%, and the recommended range of anhydrous sludge ratio is 3–5%.

Influence of collaborative disposal of sewage sludge in the fly ash partitioning and PM10 emission from a subcritical coal-fired boiler

Co-combustion of sewage sludge and coal in coal-fired power plants may be a reasonable alternative for intractable sewage sludge. The co-combustion experiments were conducted on a 600 MW subcritical coal-fired boiler to discuss the fly ash partitioning and PM10 emission characteristics. The sewage sludge was sent to the boiler through coal pulverizer with blending ratios of 5 and 10 wt% based on the coal mass. The results showed that the particle size distributions (PSDs) of PM10 present the typical two-peak distribution. The mass yields of PM1 dramatically decreased by 57.83 % and 61.67 % for the 5 % and 10 % blending ratios, respectively, compared with single coal combustion, corresponding to the increase in PM1-10 emissions. The reduced PM1 appears to be transferred toward PM1-10 during co-combustion. The Fe Al-silicate and the Fe-Ca-Si-Al species were formed by the co-combustion of sludge and coal, which were derived from the active Fe-rich fine particles in sludge and mainly mullite and Ca-Si-Al found in coal ash. These transformations can be intensified by the high temperature, intense turbulent flow fields and the consequent frequent contact and collision of minerals in the large capacity boiler to form molten aluminosilicates. Therefore, the condensable Ca and S vapor from coal combustion and fine Si and Al adhere to the surface of molten Fe Al-silicate to form PM1+, which is the main reason for PM1 reduction during co-combustion. In addition, Fe-rich and Ca-rich flocculants in sludge contribute to PM1-10 largely, while some of the fine Al-Si particles are partitioned from PM1 to PM1-10 as captured by the molten aluminosilicates, both contributing to the increased PM1-10 emission after co-combustion.

Investigation of interaction mechanisms during co-combustion of sewage sludge and coal slime: Combustion characteristics and NO/SO2 emission behavior

Co-combustion of sewage sludge (SS) and coal slime (CS) is a promising method to achieve resource utilization of both solid wastes. However, the emission characteristics of NO/SO2 and the interaction mechanisms between SS and CS are unclear. In this paper, the co-combustion characteristics and NO/SO2 emission behavior of SS and CS were investigated using a thermogravimetric analyzer and a tube furnace combustion system, and the interactions between SS and CS were explored. The results revealed the presence of remarkable interactions between SS and CS during the co-combustion. For the combustion characteristics, non-catalytic factors (interaction between volatiles and heat synergy) and catalytic factors (catalysis of inorganic components) controlled the combustion stage of the heavy volatiles and fixed carbon of the blends, respectively, leading to an earlier combustion process. For NO and SO2 emission characteristics, SS-CS co-combustion had significant NO in-situ reduction and self-desulphurization characteristics at 800 °C and 900 °C. The best inhibition occurred at 900 °C and 50 % CS ratio, and NO and SO2 emission amounts were reduced by 0.25 mg/g and 1.37 mg/g, respectively, compared to the theoretical values. At 1000 °C, co-combustion promoted the emissions of both NO and SO2. The interaction mechanisms suggested that the reducing atmosphere created and the reducing gases released by SS combustion promoted the reduction of CS-NO, while the char formed by CS exhibited a significant reduction of SS-NO. In addition, the effect of CS addition on the mass transfer process enhanced the sulfur fixation of inorganic components in SS, which led to the suppression of SO2 production. These findings provide a better understanding of the interactions between SS and CS during SS-CS co-combustion.