Co-combustion Of Sludge Research Articles

Energy conservation – A novel approach of co-combustion of paint sludge and Australian lignite by principal component analysis, response surface methodology and artificial neural network modeling

Abstract Paint sludge is a waste with potential carcinogens, and its disposal via landfilling, incineration and conversion to other materials is limited. For proper disposal, paint sludge was investigated by thermogravimetric study and was blended with lignite in 70:30, 60:40, 50:50 percentage ratios respectively. Kinetics was computed by Freeman–Carroll and Sharp–Wentworth methods and the activation energy was found in the range of 126–175 kJ/kg and 18–75 kJ/kg respectively. The solid-state reaction mechanism was investigated by Kennedy–Clark and Coats–Redfern methods and was validated by master plot method. Second-order reaction mechanism (F2) was followed by paint sludge up to 0.5 conversion and after that it followed two-dimensional diffusion–reaction mechanism (D2) in the degradation process. Blending of paint sludge with lignite coal shifted the reaction mechanism of contracting volume (R3) up to 0.5 conversions and after that, it followed the same mechanism (D2) in the co-combustion process. The percentage contribution of paint sludge in the thermal degradation of blends was 70.71% and was confirmed by principal component analysis. Response Surface Methodology (RSM) revealed the optimum degradation zones and its empirical relations with temperature and blend ratios respectively. Artificial Neural Network (ANN) modeling suggested four models with multi-layer perception carrying 22 neurons fit for the study.

Evolution of trace elements and polluting gases toward clean co-combustion of coal and sewage sludge

To promote the sustainable use of sewage sludge (SS), its mono-combustion and co-combustion with coal were characterized in this study. Co-combustion was performed with varying mass ratios, where the difference between co-combustion and the linear summation of their individual mono-combustion were mainly investigated. Here we systemically elucidated the evolutions of polluting materials including trace elements and polluting gases during co-combustion. We found that the substantial heat emitted by coal combustion can speed up sludge fixed carbon combustion at 400–600 °C. What’s more, during co-combustion, the trace elements can be chemically bonded and fixed to the aluminosilicate structure of kaolinite. When the mixing mass ratio (sludge to coal) was 3:1, the presence of coal could not only reduce the emission of SO2, CH4S, COS and CS2 but also stabilize the trace elements in the bottom slags, especially for Cd, Pb and Ag. On the basis of the results, the principles for realizing a sustainable and clean co-combustion of sludge and coal were further identified from the respects of calorific value improvement, solid waste utilization and environmental pollution mitigation.

Effect of Sludge Pellets Addition on Combustion Characteristics and Ash Behaviour of Municipal Solid Waste

Co-combustion of sewage sludge and municipal solid waste (MSW) in grate furnaces (GF) is a promising method to meet strict environmental requirements and reduce construction costs given its high market share in China. However, considering the high ash content and low heat value of sludge, co-combustion of sludge and MSW in GF may lead to combustion instability and an increase of fly ash (FA) production, which further aggravates ash deposition and corrosion of heating surfaces. Besides, semi-dried sludge powder with tiny particle size may cause dust explosion and increase the clinker ignition loss of slag ash due to the leakage in grates. In this study, semi-dried sludge powder is compressed into pellets through a rotary ring die granulator to investigate the effect of sludge pellets addition on gaseous pollutant emissions, combustion characteristics and ash behavior (e.g., ash fusion temperature and the clinker ignition loss of slag ash). The results show that the ratio of FA produced from sludge pellets incineration is lower than that of sludge powder. The clinker ignition loss of slag ash of sludge pellets increases with the increase of its compressive strength. The highest clinker ignition loss under the low combustion temperature is 11.9% which is far beyond the limit (5%) for GF. The addition of desulfurizer (CaO, mass ratio: 1%) in sludge pellets is found useful to reduce sulfur dioxide emission with the maximum 84% desulphurization rate at the combustion section. The decrease of ash flow temperature from co-combustion of sludge and MSW is less than 10 °C compared to that from mono-combustion of MSW, which suggests that co-combustion of sludge with the mixing ratio of 10% in municipal solid waste incinerators (MSWI) has little impact on fly ash slagging characteristics. The ash characteristics and gaseous pollutant emissions during co-combustion of sludge pellets and municipal solid waste are investigated.

Effect of Phosphorus Concentration on Alkali and Heavy Metals Transformation Under Agglomeration/Defluidization During Fluidized Bed Simulated Sludge Co-combustion

Agglomeration occurs during municipal sewage sludge (MSS) fluidized bed co-combustion which might affect heavy metal distribution in the bottom ash. A study on the mobility and speciation of heavy metals accompanied with agglomeration behavior and phosphorus addition should be noticed during the MSS co-combustion. The aim of this study was to evaluate the total content and speciation of heavy metals (Pb, Cd and Cr) during the MSS fluidized bed co-combustion by chemical sequential extraction and thermodynamics Equilibrium Calculation. Results indicated that the effect of phosphorus on the agglomeration/defluidization as the function of inhabitation and promotion. Distribution of heavy metals (Pb, Cd and Cr) show similar trends with the presence of a lower ratio of P/Na: the relative concentration of heavy metals in solid phase with the increased of phosphorus. In addition, the relative concentration of heavy metals in solid phase show the raise tendency with the increased of phosphorus under the circumstance of the higher ratio of P/Na due to the formation of the lower-melting-points compounds like NaPO3, the proportion of Pb and Cr residual form increased. While the percentage of Cd residual form reduced with the increasing of the amount of phosphorus. This phenomenon can be contributed by the H3PO4 would priority to react with Al2O3 and reduced the form of a stable compound CdO-Al2O3. Defluidization behavior is found with various P/Na ratios which resulting significantly different influences on particle agglomeration. High-melting-point compound, Na3PO4 (1613 K), is observed to inhibit Na2O-SiO2 formation at lower P/Na ratio. On the contrary, defluidization time decreases with increasing the P/Na ratio due to low-melting-point species Na-phosphates, NaPO3 (900 K) was formed in system.

Co-combustion of residual forest biomass and sludge in a pilot-scale bubbling fluidized bed

In this work, the co-combustion of residual forest biomass from eucalyptus and its blend with different amounts of primary and secondary sludge from the pulp and paper industry was studied in a pilot-scale bubbling fluidized bed reactor. The main objective was the determination of sludge addition influence on the overall process and on the composition of the exhaust gases, with emphasis on chlorine emissions, namely present in the solid phase (fly ashes) and in the gaseous phase (hydrogen chloride), and nitrogen oxides emissions. The co-combustion process of residual forest biomass with primary sludge (up to 5% in mass) and secondary sludge (up to 10% in mass) was successfully demonstrated as a valid energy valorization option. Except specific cases, no significant emissions increase of nitrogen oxides, carbon monoxide or hydrogen chloride were found with the addition of sludge. In fact, hydrogen chloride emissions decreased, potentially due to an increase in the chlorine retention in ashes caused by the high inorganic content present in the sludge. This high inorganic content can also lead to a significant increase in ash production during the combustion process. Thus, consequently, without proper maintenance, significant ash accumulation along the combustion system may occur, which can decrease the process efficiency and cause equipment damage.

Numerical simulation and experimental analysis on nitrogen and sulfur oxides emissions during the co-combustion of Longyan anthracite and sawmill sludge

The cold flow, co-combustion, SO2 and NO emissions’ simulation of dried sawmill sludge (DSS) and Longyan anthracite (LYA) in a CFB pilot device were implemented by using Euler-Euler method, the emissions of SO2 and NO were studied in experiments. The cold flow simulation results showed that air-particle phases finally reached stable flow conditions and backflow occurred in the pilot device. The coal mono-combustion simulation results indicated that when the combustion calculation was stable, the maximum furnace temperature tended to be stable. The co-combustion simulation results were conformed to the relevant combustion theory. The distributions of gas component concentrations of O2, CO and CO2 were reasonable in the furnace. Molar concentrations of CO, CO2, SO2 and NO in dense zone of co-combustion were higher than those of firing LYA separately, outputs of SO2 and NO were accelerated in co-combustion, both of which indicated that the addition of DSS could strengthen and promote the combustion of LYA. Both the simulation and experiment results showed that SO2 and NO mainly released during the early combustion stages, SO2 emission in co-combustion were all lower than that in LYA mono-combustion. In this research, NO concentration was far below the national emission standard. The reasons for low NO emission were deduced.

Experimental Studies on Co-Combustion of Sludge and Wheat Straw

This work presents studies on the co-combustion of sludge and wheat straw (30 wt % sludge + 70 wt % wheat straw). Prior to the combustion experiment, thermogravimetric analysis was performed to investigate the combustion characteristic of the blended fuel. Results indicated that the blended fuel could remedy the defect of each individual component and also promote the combustion. Co-combustion experiments were conducted in a lab-scale vertical tube furnace and the ash samples were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM). Thermodynamic calculations were also made to study the interactions that occurred. Addition of sludge could raise the melting point of wheat straw ash and reduce the slagging tendency. Co-combustion also restrained the release of K and transferred it into aluminosilicate and phosphate. Transfer of Pb and Zn in the co-combustion was also studied. The release and leaching toxicity of the two heavy metals in the co-combustion were weakened effectively by wheat straw. PbCl2(g) and ZnCl2(g) could be captured by K2SiO3 in wheat straw ash particles and generate silicates. Interactions that possibly occurred between K, Zn, and Pb components were discussed at the end of the paper.

A Study of Sewage Sludge Co-Combustion with Australian Black Coal and Shiitake Substrate

Co-combustion technology can be a gateway to sewage sludge valorization and net CO2 reduction. In this study, combustion characteristics of sewage sludge, Australian black coal, shiitake substrate, and their blends were analyzed via thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy. The ignition temperature, burnout temperature, flammability index (C), and combustion characteristics index (S) of the fuels and their respective blends were estimated. Kinetic parameters were also estimated using the Coats-Redfern method. The results showed that the oxidation of the blends had two distinct stages. Synergistic effects existed for all the blends, with negative ones occurring at temperatures between 300 and 500 °C and positive ones during the char oxidation period. In the first oxidation stage, both C and S indexes increased with sludge addition to the coal. However, they decreased with sludge addition in the final oxidation stage. The catalytic effect of the sludge and the shiitake was pronounced in the final oxidation stage and it resulted in a decrease of activation energy. As for the pollutant emissions, the results showed that NOx and SO2 emissions decreased for 25 wt.% sludge addition to the coal. For the sludge-shiitake blends, NOx and SO2 emissions decreased with increasing shiitake addition. The single-pellet combustion results showed that ignition delay time reduced with increasing sludge/coal ratio but increased with increasing sludge/shiitake ratio. The volatile combustion duration decreased with the addition of sludge and total combustion time decreased sharply with increasing sludge ratio.

Co-combustion of Municipal Sludge and Zhundong Coal: Ash Formation Characteristics

ABSTRACTZhundong coal (ZD), which has a high content of Na and low ash fusion temperature (AFT), causes a serious problem of slagging in boilers. P-rich municipal sludge has suitable properties for managing problems with alkali metals, but its insufficient utilization makes sludge management harder. Thus, co-combustion of municipal sludge and ZD may be a suitable approach to solve the problems. Different proportions of sludge were added to ZD at 900°C in different contents of O2 in a laboratory-scale tube furnace experimental system. The transformation of the minerals, the AFTs of residual ashes, and changes of the sodium retention ratio were investigated, respectively. The test results indicate that the ash fusibility of ZD and the sodium retention ratio can be improved because of the generated high-melting-point phosphates, such as Ca2.71Mg0.29(PO4)2, Ca5(PO4)3(OH), Ca9Fe(PO4)7, and Ca9MgNa(PO4)7. With increases in the proportion of sludge in blended samples, the AFTs increase, but the extent of the increase tends to be reduced. Modified sludge with a lower SiO2/Al2O3 ratio is more favorable for the improvement of the AFT. It is observed that 20% oxygen is the most suitable environment of those tested for co-combustion, avoiding the disadvantages of excessively high or low oxygen content.

Thermodynamic Equilibrium Simulations of Thallium Distributions in Interactions with Chlorine, Sulfur, Phosphorus, and Minerals During Sludge Co-combustion

Effects of interactions among chlorine (Cl), sulfur (S), phosphorus (P), and minerals on thallium (Tl) distributions were simulated using thermodynamic equilibrium conditions during the sludge co-combustion. Our results showed that Tl mainly existed in the forms of Tl2O3(s) and Tl(g) and did not react with SiO2, Al2O3, CaO, Fe2O3, and TiO2. Cl generated TlCl(g) and Tl(g) which in turn promoted Tl volatilization. S produced Tl2SO4(s), thus inhibiting Tl volatilization. P existence had no influence on Tl volatilization. With the couplings of Cl + S, S + P, and Cl + S + P, the reactions between single minerals and Tl were mainly controlled by S but P and Cl. With the Cl + P coupling, Cl controlled the reactions between the minerals and Tl, while P and the minerals had no significant impact. With the coupled minerals of SiO2 + CaO + Al2O3, S exerted a more influence than did Cl and P on the distributions of Tl, thus preventing Tl emissions.

Environmental assessment by dynamic full-field synergy model in co-combustion of coal and sludge with high water content

The management of industrial sludge generated considerable interest for environmental protection. The cost associated with the treatment of sludge with high water content is considerably higher before the discharge of a clean effluent. In order to reduce this cost, this study developed the co-combustion of coal and sludge with high water content in a 220 t/h boiler, to tackle the sludge and control the 502, NOx, and CO2 emissions from the boiler. The idea at the basis of this study was to directly eject the sludge with high water content into the boiler. A dynamic full-field synergy model was developed to perform the environmental assessment, which considers the dynamic characteristic and the full-field synergy over two co-combustion fields. Industrial field data were used to validate the model. It was found that boiler efficiency decreased only by 0.1% with sludge ejection, while flue gas moisture was almost unvaried. The SO2 and NOx emissions were reduced by 14.27% and 8.23% respectively, if compared with emissions without co-combustion of coal and sludge. The results are attributed to the improved synergy effects. The drive forces of liquid and solid particles are the dominant steps for the fluid flow field transformation between the W-shape and the M-shape. The dynamic full-field synergy model, presented in this study, allows the characterization of co-combustion with 92% water content and a nozzle diameter of 1.5-3.5 mm. It accurately describes the full-field synergy effects of the field number over two, a result that could not be obtained by the conventional multi-field synergy model. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.

Arsenic Partitioning Behavior During Sludge Co-combustion: Thermodynamic Equilibrium Simulation

Using the computation method of thermodynamic equilibrium, effects of sewage sludge (SS) co-combustion conditions and interactions with Fe2O3, SiO2, CaO and Al2O3 on migration and transformation of arsenic (As) were simulated in oxy-fuel (CO2/O2) and air (N2/O2) atmospheres. Arsenic mainly existed as As(s), As4(g), As2O5(s), As4O6(g) and AsO(g) and volatilized more easily in reducing than oxidizing atmosphere. Increased O2 concentration slowed down the formation rate of AsO(g), thus reducing the volatilization rate of As. With the increased pressure, the conversion rate of As2O5(s) into As4O6(g) accelerated. In the multi-chemical system of SiO2, Al2O3 and CaO, As reacted with CaO and Al2O3 to form AlAsO4(s) and Ca3(AsO4)2(s) which inhibited As volatilization. SiO2 prevented As from reacting with CaO to generate Ca3(AsO4)2(s). Fe2O3 affected reactions between Al2O3(CaO) and As which inhibited As volatilization. In the whole SS co-combustion system, As reacted with O2 but had a weak affinity with Cl and with no arsenic chlorides observed.

Pollution emission and heavy metal speciation from co-combustion of sedum plumbizincicola and sludge in fluidized bed

Abstract The co-combustion of sedum plumbizincicola and sludge is becoming increasingly popular due to its environmental and economic benefits. Here, combustion experiments are performed in a large-scale fluidized bed at different temperatures. Results show that in flue gas, CO and NOx exceed the emission standard and should be controlled by denitrification system before discharge. Three-ring polycyclic aromatic hydrocarbons (PAHs) are found to be the major organic pollutants, but no six-ring PAH is detected in the combustion process. The emission concentrations of Cd, Zn, and Pb are below the standard. With increased temperature from 700 °C to 1000 °C, the concentrations of total PAHs, NOx, and Zn increase. The proportion of residual fraction in Cd for bottom ash increases from 16.82% to 44.03%. The proportion of exchangeable and carbonate-associated fractions in fly ash increases from 15.18% to 19.78%. The dominant phase in Zn and Pb is the residual fraction. With increased temperature, the leaching rates of Cd, Zn and Pb increase with different extents. Leaching rates in fly ash are less than those in bottom ash (except for Cd at 900 and 1000 °C). Cd and Zn show medium risk to environment in fly ash and bottom ash. Pb presents no risk to the ecosystem in fly ash and low risk in bottom ash. The co-combustion is suitable for the disposal of S. plumbizincicola and sludge in China.

Co-combustion of paper sludge in a 750 t/d waste incinerator and effect of sludge moisture content: A simulation study

Co-incineration with municipal solid waste (MSW) is an efficient method in disposal of paper sludge (PS). CFD technology was adopted to verify the possibility of different blending ratio of sludge to combust with MSW in a 750 t/d waste incinerator, and to predict the impact of different moisture content of sludge on co-combustion. In this paper, the reliability of the numerical model is verified by comparing predicted results with operating data; the sludge which contain 30%, 40%, 50%, 60% and 67% moisture content were blended with MSW by the mass proportion of 5% (wet basis, the same below), 10%, 15%, 20% and 25%. The simulation shows that mass residual on bed increases from 19.8% to 27.6% with the mass percentage of sludge rising from 5% to 25%; as the moisture content in sludge increased, the volatiles release and fixed carbon burning are both delayed. The solid gasification efficiency has a negative correlation with blending ratio of sludge and moisture content of sludge. The NO emission is observed to be positively correlated to the percentage of sludge and the highest is not higher than 162 mg/Nm3. Raw paper sludge with high content of water will aggravate coking and corrosion on rear flue wall because of local high temperature. The result indicates that co-combustion of 25 wt% sludge (up to 67% moisture) with MSW is feasible which maintains the furnace temperature, mass residual and several pollutants in allowable range. However, partially dried paper sludge is more proper for incinerator in the consideration of mitigating corrosion. The current work greatly help to understand the effect of paper sludge and its moisture content in large-scale waste incinerator.

Oxy-fuel co-combustion of sewage sludge and wood pellets with flue gas recirculation in a circulating fluidized bed

Oxy-fuel co-combustion of waste sludge and biomass with flue gas recirculation was conducted to observe the combustion characteristics and enrichment of CO2 using a 30kWth circulating fluidized bed. The combustion reaction was accelerated and the ignition time was shortened by increasing the blending ratio of wood pellets and oxygen mixing ratio. The best combustion performance was observed at a 30% blended biomass ratio, with 23% oxygen mixing rate as oxy co-combustion with respect to heat recovery and enrichment of CO2; this study included experiments with ranges of 0 to 70% for the blending ratio and 21 to 30% for the oxygen mixing ratio. With flue gas recirculation at 60%, the oxy-fuel co-combustion of sludge with biomass was optimized in high enrichment of CO2 (over 90%) with less pollutant emissions, specifically 0.91% CO and 14ppm NO.

Rice husk and sewage sludge co-combustion ash: Leaching behavior analysis and cementitious property

The co-combustion of sewage sludge with rice husk is expected to become a trend because of its economic and environmental benefits. In this work, the ashes and its cementitious forms were investigated. The leachability characteristic of heavy metals and mechanical properties in cementitious forms was evaluated. The stabilization/solidification (S/S) mechanism of cementitious forms was also studied. Results showed that the leachability of heavy metals in co-combustion ashes decreased by an average of 30% after the hydration process. Non-crystal hydrates gradually formed and the compact structure hydrates became apparent in RSCA30 after 28 d (relative to SSMA30 and OPC1). The chemical speciation of heavy metals is transformed into immobilization state after hydration. In general, ashes from the co-combustion of rice husk and sewage sludge are beneficial to the development of cementitious materials.

Sludge Acts as a Catalyst for Coal during the Co-Combustion Process Investigated by Thermogravimetric Analysis

Sewage sludge in China has the characteristics of low organic content and low heating value compared with other developed countries. Self-sustaining combustion of Chinese sludge cannot be achieved when the moisture content is high. Co-combusting a small amount of sludge in the existing coal-fired boilers is a usual sludge disposal method in China. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis of a bituminous coal, three different sewage sludges, and their blends have been carried out. Fitted curves by linear calculation and actual curves of blends were compared to study the interaction between sludge and coal in their co-combustion process. The results indicate that the interaction between the two fuels takes place during the devolatilization and combustion period. Sludge acts as a catalyst for coal during the co-combustion process because of the large amount of inorganic salts contained in the sludge. Co-combustion of coal and sludge is more efficient than single burning of the two fuels.

Experimental study on combustion and pollutants emissions of oil sludge blended with microalgae residue

Experimental study on co-combustion of oil sludge (OS) and microalgae residue (MR) was conducted with a thermogravimetric analyzer and a designed fluidized bed reactor system. Combustion process of OS blended with MR could be divided into four stages, water evaporation, volatiles release and combustion, fixed carbon combustion and minerals decomposition. With MR ratio increasing, combustion performance of the mixture became better. MR addition can help improve the combustion performance of OS. NOx and SO2 concentrations increased firstly and then decreased with the increase of combustion temperature which ranged from 800 to 1100 °C. With the increase of excess air ratio α, NOx and SO2 emissions increased. Generally, NOx and SO2 emissions decreased with MR ratio increased at 800 °C, which is caused by the catalysis effect of ash and heavy metals in OS. OS blended with MR could both improve combustion performance and help reduce NOx and SO2 emissions during OS combustion, which provides an effective approach to massive synergistic disposal of waste resources.

Novel utilization of conditioner CaO for gas pollutants control during co-combustion of sludge and coal

CaO is a traditional desulfurizer used in coal combustion, and it is also a widely applied chemical conditioner in sewage sludge dewatering. In this study, the feasibility of co-combustion of CaO-conditioned sludge (Sc-CaO) and coal was discussed, including combustion characteristics and gas pollutants emission. The results show that adding 30% Sc-CaO into co-combustion strengthened the procedure of devolatilization and volatiles combustion (220–380°C). But the main combustion performance (430–600°C) was still similar to that of coal. Conditioner CaO could capture almost all the SO2 during sludge mono-combustion and 15.8–48.4% of SO2 during co-combustion. Meanwhile, conditioner CaO also contributed to N2O catalytic reduction and mitigated the NO increase caused by the co-effect of raw sludge and coal at 900°C. Compared with physical additive CaO, conditioner CaO distributed evenly in sludge matrix and partially bonded to carbon, which was benefit to SO2 adsorption and N2O reduction. At the same time, the increase of NO was more mild than that caused by physical additive CaO. This study shows that co-combustion of Sc-CaO and coal is a suitable and promising technology for clean disposal of sewage sludge.

Combustion performance and slagging characteristics during co-combustion of Zhundong coal and sludge

Zhundong coal (ZDc) with a very large reserve is faced with severe problems of slagging and fouling during combustion in boilers because of the high-Na content. Sludge, the by-product of urban sewage treatment, is also faced with the problem in utilization. In this study, the co-combustion of ZDc and sludge was investigated in a laboratory-scale experimental apparatus before further studies in larger-scale setups. The experimental results confirm an interaction between ZDc and sludge during co-combustion, which was mainly caused by the Na catalytic action and improved the combustion performance of the co-fuels. The catalytic effect was particularly significant at low sludge mixing ratios. The reactions between Na-based compounds in ZDc and Si/Al/P-rich minerals in sludge, forming high-melting-point phosphates and aluminosilicates, not only increased Na retention in residual ash reducing the risk of fouling on tail-heating surfaces in boilers, but also raised the ash fusibility of the co-fuels avoiding low-temperature sintering. Even so, to prevent slagging, the high combustion temperature above 900 °C should be avoided during co-combustion because of the high Na retention in residual ash. Moreover, the high heavy metal retention in residual ash decreased the pollution caused by heavy metal volatilization during sludge combustion.