Co-combustion Of Coal Research Articles

Experimental investigation of fuel conversion characteristics during co-combustion of solid recovered fuel and coal in a 1 MWth circulating fluidized bed reactor

This study presents experimental results on co-combustion of hard coal and solid recovered fuel (SRF) conducted in a circulating fluidized bed (CFB) reactor with an internal diameter of 0.59 m, a height of 8.6 m, and a thermal load of 1 MWth. The high flexibility of the test facility enables testing of a variety of input materials under changing test conditions. The combustion of various fuel mixes ranging from 100 % hard coal to 100 % waste was tested to assess the impact of varying fuel ratios on the overall combustion process. As the proportion of SRF increased, a reduction in reactor differential pressure and particle density was observed. Moreover, combustion shifts to higher parts in the reactor when the share of SRF is increased. To further investigate the combustion conditions inside the reactor, three in-bed gas measurements were conducted, capturing the horizontal gas profiles of CO2, O2, and CO. An increase in SRF content led to elevated CO and O2 levels, alongside a reduction in CO2, indicating an upward shift in the combustion zone. The behavior is attributed to the higher volatile content of SRF, which is in this experiment roughly 2.5 times the share of volatiles in hard coal and the lower bulk density of SRF. The study concludes by proposing potential strategies for reducing the impact of high SRF content on combustion conditions.

Three-dimensional numerical simulation of coal and papermaking trash co-combustion in a circulating fluidized bed

Circulating fluidized bed (CFB) combustion is a important method of waste treatment with the benefits of harmlessness, recycling, and energy recovery. Using the existing co-firing CFB boiler to dispose of waste can reduce investment in boilers and environmental protection equipment. However, there is currently limited research available on the co-combustion of coal and waste (especially for papermaking trash), and the mechanism of pollutant emissions during unit operation remains unclear. In this work, the co-combustion of coal and papermaking trash in a three-dimensional industrial-scale CFB are investigated by using the Dense Discrete Phase Model (DDPM) method. Both homogeneous reactions (such as fuel particle pyrolysis, combustion, and surface reaction) and non-homogeneous reactions (such as gas combustion and pollutant generation) are considered. The co-combustion characteristics are comprehensively analyzed in terms of gas distribution, chemical reaction rates, and bed temperature under various operating conditions, including fuel mixing ratio, secondary air arrangement, and excess air coefficient. The results are obtained by comparing the distribution profile along the height. By reducing the mixing ratio of papermaking trash, the excess air coefficient, and adjusting the secondary air arrangement in the lower region, an expanding, reducing atmosphere is observed in the vicinity of the fuel feeding point. This, in turn, leads to an increase in CO concentration and a decrease in NO emissions, which is attributable to the interplay of gas distribution, chemical reaction rates, and bed temperature. A reduction in NO gas emissions was achieved by adjusting the secondary air arrangement and the excess air coefficient. Overall, this work provides valuable insights into the co-combustion characteristics of coal and papermaking trash in an industrial-scale circulating fluidized bed boilers.

Experimental study on enrichment of heavy metals by modified mullite during co-combustion of lignite with eucalyptus wood

ABSTRACT Modifying the content of oxygen vacancies (OVs) has emerged as a crucial approach to tailoring silicate's adsorption properties, microstructure, conductivity, and catalytic performance. Some studies have reported the formation of OVs during ammonia treatment. However, there are limited studies on the production of OV-enriched mullite by treating it with N-containing compounds at low temperatures. In this work, formamide, urea, and ammonium acetate were used as ammonia-assisted reduction modifiers to induce oxygen vacancies in mullite at 30 ℃, 60 ℃, and 90 °C. The aim was to enhance the enrichment effect of heavy metals (Cr, Cu, Mn, Ni, Pb, Zn) during the co-combustion of coal and biomass. The modified mullite was analyzed by using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the particle size of mullite decreased, and the concentration of internal Al3+ ions and oxygen vacancies was enhanced. Coal-biomass-mullite combustion experiments were conducted in a tubular furnace at 900 °C, revealing a significant enhancement in the enrichment of heavy metals during the combustion process, particularly when the modification temperature was 60 °C using ammonium acetate as the modifier. This work holds significant importance for developing novel heavy metal adsorbents and the reduction of pollutant emissions from coal-biomass co-combustion in industrial applications.

Effect of Limestone on NO Emission during the Co-Combustion of Semi-Coke and Bituminous Coal

Effect of Limestone on NO Emission during the Co-Combustion of Semi-Coke and Bituminous Coal

Research on mercury re-release model in wet flue gas desulfurization (WFGD) in coal-fired power plants

Mercury (Hg), a toxic heavy metal, has triggered regulations for emission control from coal-fired power plants. It has been found that mercury re-release occurs in WFGD slurry, which is affected by WFGD process parameters. The coal co-combustion with bromide technology proves to be an efficient approach for enhancing mercury removal ratio but the accumulation of introduced bromine in WFGD slurry would impact the re-emission behavior of mercury significantly. Model study is efficient method to reveal the physicochemical processes in WFGD systems. However, previous model studies were carried out under Hg2+ contained simulated slurry systems without consideration of Hg2+ transformation process from gas to liquid phase, and co-combustion with bromide technology was not considered. Here, a model which encompasses droplets motion sub-model, gas–liquid heat transfer sub-model, gas–liquid mass transfer sub-model and the mercury re-release kinetic sub-model is developed and validated against experimental data. The effects of bromine concentration, slurry temperature, pH value and S(IV) concentration were investigated. It was found that introduced bromine has significant inhibitory effects on the re-release of mercury. When the slurry temperature is higher, the absorption rate of Hg2+ is lower and more Hg0 is released. Moreover, the increase in the slurry pH value and S(IV) concentration has certain inhibitory effects on the re-release of Hg0 in WFGD. Above all, the developed model has high prediction accuracy for the absorption of Hg2+ and the re-release of Hg0 in WFGD which is expected to be beneficial for guiding the operation of WFGD systems.

Experimental Study of Agglomeration Formation during Co-Combustion of Coal and Palm Kernel Shell in Fluidized Bed

Abstract Co-combustion of biomass and coal in Indonesia power plants are a key element of the path towards achieving net-zero emissions. However, introducing biomass into a coal-boiler furnace may pose operational challenges. Therefore, this study aims to assess the potential of agglomeration when mixing biomass with a fluidized bed boiler. Complementation simulation tests were conducted by combining coal with various fractions of palm kernel shell (PKS) in a furnace capacity of 5kWth maintained at 850°C within an hour. The initial fuel was 100% coal, gradually increasing the biomass mixture by 5%, 10%, 15%, 20%, and 25%. The results indicated that de-fluidization occurred at 25% of the biomass mixture and to prevent agglomeration, the temperature of the bed was kept below 850°C. The agglomeration test of coal and PKS mixtures was successfully performed in a 5kW lab-scale facility, and the result will be useful for predicting agglomeration phenomena in power plants.

Combustion Process of Coal–Açai Seed Mixtures in a Circulating Fluidized Bed Boiler

This study investigates the effects of the co-combustion of coal and açai seed in circulating fluidized bed (CFB) boilers, highlighting the increase in thermal efficiency and relevance of a less-polluting source of energy. Using the computer software 1.5D CeSFaMB™® v4.3.0, simulations of the co-combustion process of coal and biomass were carried out in a CFB boiler, obtaining results such as the temperature profile, boiler efficiency and emissions. The work acquired data regarding the equipment in real operational conditions, consisting of the fundamental geometric and operational parameters used in the simulation campaign. The thermal and chemical properties of the fuels were analyzed by carrying out proximate, ultimate, heating value, particle size and specific mass analyses. The model validation was achieved by simulating the boiler in its real operating conditions and comparing the obtained results with the real data; the obtained error was below 10%. Simulations with different fractions of açai seed for energy replacement (10% and 30%) were carried out. As a result, an increase in the average temperature of the bed was observed, highlighting the region immediately above the dense bed. An increase in boiler efficiency was verified from 56% to 85% with 10% açai and to 83% with 30% açai seed. Decreases in SO2 and CO emissions with the insertion of açai were obtained, showing that co-combustion is more complete, while CO2 emissions were increased due to the higher quantity of fuel inserted into the equipment. The fossil CO2 emissions were reduced.

Investigation of co-combustion characteristics and kinetics of low-ranked coal and hydrochar derived from cow manure

CO2 emission should be reduced by the effective utilization of low-ranked coal in a coal-based power plant based on co-combustion of coal and biomass. This study investigated the co-combustion behavior of lignite and cow manure using three different kinds of samples: raw lignite coal blended with cow manure (CM-L), raw lignite coal blended with hydrochar derived from cow manure (HCM-L), and co-hydrothermal carbonization (Co-HTC) of lignite coal and cow manure (Co-HCML) using thermogravimetric analysis and a hydrothermal carbonization (HTC) temperature of 200 °C for 60 min. The kinetic parameters were calculated and analyzed using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods. The combustion characteristics were studied of the various kinds of hydrochar mixed with lignite coal. The results showed that the low-ranked coal improved the fuel properties by increasing carbon content and decreasing sulfur through the HTC processes. The activation energy of Co-HCML was the lowest, which is preferable, and therefore it was recommended as the promising process.

Effect of modified Ca-Al adsorbents on heavy metal fixation during co-combustion of coal and coconut shells: Experiments and simulations

As an alternative fuel, bio-waste coconut shells have shown promise in reducing pollution during the co-combustion process. In this study, a novel metal-mineral adsorbent, Ca-Al (Ca5Al6O14), was prepared and physically (ultrasonic) and chemically (ethylene glycol) modified to enhance its adsorption properties. Thermal adsorption experiments investigated the effect of the adsorbents on the fixation of six heavy metals (HMs): Cr, Cu, Mn, Ni, Pb, and Zn. XRD, SEM, BET, and XPS were used to analyze the adsorbents and the adsorption mechanism was investigated by combining lattice oxygen concentration and Factsage simulation calculations. The ecological risk assessment of heavy metals was used to comprehensively evaluate the fixation effects of the three Ca-Al adsorbents at different additive levels. The results showed that the modification significantly changed the morphological characteristics and oxygen activity of the Ca-Al adsorbents, increased the lattice oxygen and chemisorbed oxygen concentration, and laid the foundation for promoting the chemisorption process in the fixation of heavy metals. In combination with the Er (environmental risk factors), adding all three adsorbents reduced Ri (Risk index). Among them, Ca-Al (EG) at 3% had the best effect on Ri. 3% Ca–Al (EG) reduced the Er value of Ni by 49.02%. 5% Ca–Al (EG) reduced the Er value of Cr by 86.01%. 5% Ca–Al (UM) had the best effect on Mn, with a reduction of 46.13%. The addition of 10% Ca–Al (UM) reduced Er of Ni by 50.43%. Considering the practical application in coal-fired power plants, Ca-Al(EG), which exhibits a higher fixation rate at small additions, is more suitable.

Oxy-fuel co-combustion properties and N-containing pollutants release characteristics of biomass/coal blends

Thermal properties and NO release characteristics during oxy-fuel co-combustion of pine sawdust (PS) and Shenmu coal (SM) were investigated based on the effects of various parameters, including atmosphere, temperature, blending ratio, and oxygen concentration in this research. The results indicate that the release of NO decreased with the increasing temperature during decomposition process of PS and SM. The content of N-Q and N-X in semicoke (SC) increased at higher torrefaction temperature. The N-Q and N-X content for SC at the temperature of 1000 °C was 36.9 % and 23.2 %, respectively. When 40 % PS was added to the SM, the NO release amount was significantly reduced by 16.3–23.1 % in the oxy-fuel atmosphere compared to the O2/N2 atmosphere, and the ignition time was reduced from 4.0s to 0.66s. The NO emission initially increased and then decreased as the combustion temperature increased from 800 to 1000 °C. Furthermore, increasing the oxygen concentration from 10 % to 40 % shortens the combustion time and increases the emissions of NO. Conversely, increasing PS blending ratios from 10 % to 40 % decreased NO emission and the conversion ratio. These findings emphasize that adding biomass can effectively improve coal ignition, increase combustion rates, reduce NO emissions, and address the air pollution problems associated with NOx emissions.

Degradation of the protective layer on stainless steel by chlorine variation under high-temperature conditions

This study investigates the impact of various chlorine (Cl) content ratios on the degradation of 304 stainless steel during co-combustion of coal with solid recovered fuel (SRF) at a combustion temperature of 1250 °C. The research specifically focuses on the corrosion potential at 550 °C, which represents the temperature in the superheater area of a power plant. High-temperature corrosion experiments are conducted in a laboratory-scale drop tube furnace to observe initial corrosion during combustion. Analyses include visual examination, mineral analysis, microstructure-based metal analysis, and corrosion rate determination. The results show significant degradation at Cl contents higher than 0.09 wt%. The usual carbide formation at the grain boundaries in 304 stainless-steel does not occur in the short-term tests, as indicated by Cr content remaining above 12 % and Cl content less than 0.06 wt%. In addition, material degradation is due to the Cl reacting with alkali content, damaging the oxide layer and causing pits in the cross-section area of the probe material. This research provides insights into the critical role of Cl in metal degradation and identifies the optimum Cl amount suitable for coal blending in power plants.

Thermodynamics and synergistic effects on the co-combustion of coal and biomass blends

Thermodynamics and synergistic effects on the co-combustion of coal and biomass blends

Study on thermal behavior and gas pollutant emission control during the co-combustion of rice straw-modified oily sludge and coal

Oily sludge (OS) is a solid waste generated from oil industry activities that can threaten the ecological environment and human health if not properly treated or disposed of. In this paper, the thermal behavior and emission of gas products during the co-combustion of rice straw (R) modified OS (OS5-R5) and coal (C) were investigated using an automatic calorimeter and model analysis. The effect of combustion atmosphere and additives on the gas products emission during the co-combustion of C, R, OS5-R5, and mixed fuels were investigated. The results show that as the content of OS5-R5 increased in mixed fuels, the performance of mixed fuels worsened gradually. When the mass content of OS5-R5 is 30 %, the lower heating value (LHV) was about 20 MJ/kg, which is about 16 % lower than that of C, but the comprehensive combustion index had no significant decrease. The additives could control the emission of pollutant gases. The increase of heating rate from 5 °C/min to 20 °C/min resulted in an increase of the overall combustion performance of the mixed fuel by 5.07-time. Similarly, increasing the oxygen concentration from 10 % to 100 % led to a 3.09-time increase in the combustion index of the mixed fuel. The adsorption of polar molecules by montmorillonite was conducive to reducing the emission of pollutant gases. BaO and CaO do not affect NO and NO2 emission control but reduce H2S and SO2 emissions because BaO and CaO could react with H2S and SO2 to form sulfate resulting in reduced emission. The research provides a theoretical basis for OS's safe disposal and efficient resource utilization.

Simulation of Power Generation System with Co-Combustion of Coal and Torrefied Biomass by Flue Gas

Simulation of Power Generation System with Co-Combustion of Coal and Torrefied Biomass by Flue Gas

NO emission during the co-combustion of biomass and coal at high temperature: An experimental and numerical study

Biomass/coal co-combustion presents a promising avenue for reducing carbon dioxide emissions. However, the mechanism of NO generation during co-combustion in pulverized coal-fired furnaces remains unclear. Herein, this study investigates NO emission characteristics at elevated temperatures, emphasizing mechanistic understanding. The experiments and simulations were conducted across temperatures ranging from 1000 °C to 1600 °C. In addition to exploring how fundamental conditions (temperature, oxygen concentration, and biomass blending ratio (BBR)) affect NO generation, the study also investigates the interactions between biomass and coal, as well as between fuel NO and thermal NO. The results indicate that the change in NO production with increasing temperature is non-monotonic, attributable to the combined contribution of fuel NO and thermal NO. Moreover, the interaction between biomass and coal manifests predominantly during the char combustion stage, owing to the disparate combustion characteristics and reactivity of biomass char and coal char. Numerical simulations were highly consistent with the experimental findings, underscoring a reduction in the rate of production (ROP) for major elementary reactions leading to NO formation as the BBR increased, consequently mitigating NO emissions. By integrating experimental insights with reaction kinetics calculations, this study proposes pathways for fuel NO and thermal NO generation during co-combustion at high temperatures, involving precursors such as NCO, HNO, and NH. These findings offer a deeper understanding of the mechanism of fuel NO and thermal NO emission during co-combustion at high temperatures.

Cocombustion of Coal–Water Fuel with Fuel Oil

Cocombustion of Coal–Water Fuel with Fuel Oil

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.

Study of Characteristics and Heavy Metals Migration During Co-Combustion of Coal and Sludge

Study of Characteristics and Heavy Metals Migration During Co-Combustion of Coal and Sludge

Mechanisms for NOx emission control and ash deposition mitigation in sludge-coal blend combustion

This paper introduces the coupled treatment of alkali and alkaline earth metals (AAEMs)-rich coal with ferric sludge as a method to efficiently and economically control sludge NOx emissions and mitigate coal ash deposition through fuel interactions. We utilized a pilot-scale drop tube furnace to quantify NOx emissions and ash deposition, supported by spectral and energy dispersive analyses. The results demonstrated co-combustion controls NOx emissions by catalyzing the reaction between char and NO and the transformation into more stable N-containing functional groups. It also facilitates the formation of harmless N2 instead of NOx by enabling Ca/Fe-based minerals to react with protein and pyrrolic nitrogen. At 950 °C, blending 10% ferric sludge mitigated ash deposition, thanks to the capture and dilution effect of Si/Al/Fe-based minerals in ferric sludge. However, blending ferric sludge aggravated ash deposition of AAEMs-rich coal at 1250 °C, due to the formation of eutectics by Fe-based minerals and Ca/Na-based feldspars. Besides, the control of NOx was reduced at 1250 °C. Therefore, the co-combustion of AAEMs-rich coal with 10% ferric sludge at 950 °C exhibited excellent performance in both emission control and ash deposition mitigation. This study, grounded in the characteristics of minerals, provides a theoretical foundation for the efficient and economical in-situ control of NOx emissions and ash deposition. It advances the development of low-carbon, environmentally friendly technologies for coupled sludge and coal combustion.

Lignite Coal Co-combustion Performance with Banana Tree Waste, Tree Leaves and Cow Dung Manure Blends for Emission Reduction During Power Generation

Lignite Coal Co-combustion Performance with Banana Tree Waste, Tree Leaves and Cow Dung Manure Blends for Emission Reduction During Power Generation