Comprehensive Combustion Index Research Articles

Co-combustion characteristics and kinetics of meager coal and spent cathode carbon block by TG-MS analysis

As a hazardous waste, the spent cathode carbon block (SCCB) has a high calorific value while it is difficult to fire, its harmless disposal is a major difficulty at present. Herein, a method of mixed combustion of meager coal and SCCB in a pulverized coal furnace for disposal of SCCB is proposed, and thermogravimetric mass spectrometry (TG-MS) is used to characterize the combustion and gas release characteristics. The effects of the heating rate and mixing ratio on combustion are analyzed as well. The result shows that the comprehensive combustibility index and combustion stability index of SCCB-5 at a heating rate of 50 °C/min are both the highest. Abundant oxygen-containing groups in SCCB promote the co-combustion process. The release of hydrogen fluoride is relatively low below 1000 °C so that the use of pulverized coal boilers meets the temperature requirement for disposal of SCCB. The good melting characteristics of ash after mixing sintering also confirm this point. Finally, the kinetic calculation results show that the combustion activation energy is the lowest when the mixing ratio is 5%, which is in good agreement with the experimental results. The highest activation energy values for the combustion of meager coal, SCCB and SCCB-5 are 46.90, 89.39, 59.87 kJ mol−1, respectively.

Co-hydrothermal carbonization of swine and chicken manure: Influence of cross-interaction on hydrochar and liquid characteristics

Swine and chicken manures are abundant solid wastes that can be converted into carbonaceous materials through hydrothermal carbonization (HTC). Owing to their unique biochemical compositions, co-HTC of these two types of manures may have significant implications for the generated products. We investigated the co-HTC of swine manure and chicken manure to understand the influence of the interaction between contrasting manures on the properties of the derived products. The results indicated that co-HTC treatment enhanced the formation of solid product and improved the C and N contents, heating value, and energy yield of the resulting hydrochar. Regarding the ignition temperature and comprehensive combustion index, the combustion properties of the hydrochar were enhanced owing to the mutual effect of the HTC intermediates. Additionally, the interaction of the intermediates significantly impacted the transfer of nitrogenous species and generation of organic acids and organic polymers with fused-ring structures. Therefore, co-HTC processing of animal manures could potentially provide a sustainable pathway for the conversion of animal waste into solid products with improved characteristics compared to those produced by treating the two feedstocks separately.

Co-hydrothermal carbonization of different feedstocks to hydrochar as potential energy for the future world: A review

Co-hydrothermal carbonization (co-HTC) has emerged recently as a promising thermochemical technique that can transfer organic solid residue (e.g., biomass, sewage sludge, plastic, livestock manure) into value-added products (i.e., hydrochar). This advanced mechanism conceals the weakness of hydrochars derived from the hydrothermal carbonization (HTC) of a single feedstock. The co-HTC of various feedstock blends used for hydrochar is reviewed in this article. Biomass/sludge, biomass/plastic, biomass/coal, biomass/manure were the most common feedstock blends. Many studies have found that co-HTC, compared to single feedstock, enhances the yield, ultimate and proximate properties, higher heating value (HHV), thermal behaviors, and overall quality of hydrochars. The synergistic effects of feedstock types, blending ratio, temperature, and residence time are also discussed. The feedstock mixing ratio emerges as the most important variable, followed by feedstock types, temperature, and reaction time. Thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses have made it possible to better understand the thermal decomposition characteristics of hydrochars. In most papers on this subject, the range of combustion temperature and comprehensive combustion index (CCI) has increased. Overall, the physicochemical and thermal behaviors of hydrochar derived from co-HTC make it energy-efficient and environmentally sound by reducing the waste load and avoiding pollution issues. Additionally, several important suggestions have been recommended for future advances being made in co-HTC of feedstocks and its comprehensive application.

Do FeCl3 and FeCl3/CaO conditioners change pyrolysis and incineration performances, emissions, and elemental fates of textile dyeing sludge?

The pyrolysis and incineration performances of sulfur-rich textile dyeing sludge (TDSS) were determined in response to the additions of FeCl3 or FeCl3 + CaO. The emissions of eight air pollutants from the incineration and pyrolysis were systematically identified. The 3-to-8% FeCl3 additions increased the comprehensive combustibility index by 2.14 and 1.62 times, respectively, as opposed to the 5-to-10% FeCl3 + 8-to-15% CaO additions. The CaO addition inhibited the TDSS incineration, while the FeCl3 addition increased HCl emission. NOx, SO2, and H2S emissions decreased initially and increased between 600 and 950 °C. SO2 and NOx emissions rose with FeCl3 but FeCl3 + CaO. FeCl3 catalyzed NOx, while CaO retained SO2. The main pyrolysis gas/liquid products were alkane, alkenes, nitrile, heterocyclic compounds, benzene, and its derivatives. Benzene and its derivatives accounted for 55.33% of the control group and 42.25–57.23% of the treatment groups. The FeCl3 and FeCl3 + CaO additions did not significantly influence the pyrolysis products. The measured versus thermodynamically simulated SOx and HCl emissions were consistent. Neural network-based simultaneous optimizations of the non-linear dynamics of eight kinds of gases pointed to 50% and 14.4% reductions in the emissions and the pyrolytic temperature, respectively, with the 3% FeCl3, relative to the control.

Structural features and combustion reactivity of residual carbon in fine slag from entrained-flow gasification

The carbon content in fine slag during entrained-flow gasification is very high, at present, most of the fine slag was disposed by landfill. It is expected to provide a favorable technology by adding the fine slag to the circulating fluidized bed boilers to participate in combustion reaction. In this study, the gasification fine slags generated from GE, OMB and GSP gasifier, which are typical gasification processes in Ningdong energy and chemical base, was selected for investigation. The structural features and combustion reactivity of the residual carbon in the gasification fine slag were systematically studied by physical adsorption apparatus, laser Raman spectrum and thermogravimetric analyzer. The results showed that the materials in the original gasification fine slag could be divided into cohesive spherical particles, porous irregular particles and isolated large spherical particles, while the acid-washed gasification fine slag was mostly composed of loose fine particles and porous irregular massive particles. Additionally, the particle size of the residual carbon was clustered to 4–8 nm, and the specific surface area and active sites of that decreased orderly as follows: GE>OMB>GSP. The order degree of the residual carbon structure in GE slag was the lowest, and the amorphous carbon structure in it was the highest, while the case in GSP was the opposite. The combustion rate of the residual carbon in GE slag was the fastest, mainly due to its large specific surface area, more amorphous carbon structure and active site, and the comprehensive combustion index of residual carbon in GE slag was 5.26×10−7 %2/(min2·°C3).

Combustion Characteristics, Kinetics, and Thermodynamics of Pine Wood Through Thermogravimetric Analysis.

The thermal conversion of woody biomass is increasingly critical for the development of the energy processing technologies and fire safety engineering. The combustion characteristics, kinetics, and thermodynamics of pine wood were characterized through a thermogravimetric analyzer in the air atmosphere. There were two apparent peaks in the derivative TG curves for pine wood. The combustion process of pine wood was divided into two stages. Therein, the first stage occurring in the conversion degree range of 0-0.6 may be considered a one-step reaction. It was easier for pine wood to decompose under air than under nitrogen. Moreover, the first stage of pine wood combustion may be characterized by the diffusion model g(α) = [1 - (1 - α)1/3]2. The kinetic modeling showed a good agreement between the predicted and experimental conversion degree curves. In addition, the high comprehensive combustion index of pine wood at 10 K min-1 (6.73 × 10-7 %2 min-2 K-3) showed its great potential for bioenergy generation. Besides, both the value of ΔH and ΔS exhibited similar patterns with the activation energy value versus conversion degree, while the ΔG value almost remained at a positive constant with conversion degree. The average ΔH, ΔG, and ΔS value was nearly equal under different heating rates.

Co-combustion performance analysis of a Fujian anthracite with Cunninghamia lanceolate and Mycorrhizal plants

The co-combustion characteristics of Fujian anthracite with two biomasses (i.e. Cunninghamia lanceolata) and Mycorrhizal plants in different proportions were investigated using thermogravimetric analysis. The result showed that first, the co-combustion processes of Fujian anthracite with the two biomasses ( Cunninghamia lanceolata and Mycorrhizal plants) proceeded in three stages, separation and combustion of volatiles, combustion of fixed carbon in the biomass, and combustion of fixed carbon in Fujian anthracite. Secondly with increasing proportion of biomass, the co-combustion of Fujian anthracite with Cunninghamia lanceolata and Mycorrhizal plants shifted to a low-temperature zone, with a lower ignition temperature, shortened burnout time, and growth of both combustibility index ( Ci) and comprehensive combustion index S. Finally, at different mixing proportions, the comprehensive combustion index S during co-combustion of FW with Mycorrhizal plants is always larger than that during co-combustion with Cunninghamia lanceolata; therefore, FW and Mycorrhizal plants exhibit superior comprehensive co-combustion performance to FW and Cunninghamia lanceolata. Analysis of various parameters pertaining to combustion performance shows that the ignition and combustion performance of Fujian anthracite was improved as long as the Fujian anthracite was mixed with around 20% biomass.

Multi-response optimization toward efficient and clean (co-)combustions of textile dyeing sludge and second-generation feedstock

The rapid growth of textile dyeing sludge (TDS) necessitates feeding it back into a circular economy in an efficient and clean way. This study aimed to optimize the clean and efficient operational conditions to co-combust TDS and incense sticks (IS). The (co-)-combustions exhibited four distinctive stages of thermal degradation. According to the master-plots method, the reaction mechanisms of reaction order (F2.4 and F1.5), three-dimensional diffusion (D3), and nucleation growth (A1.5) best explained the four stages, respectively. The interaction between TDS and IS exerted an inhibition effect in the range of 400–500 °C and a facilitation effect in the range of 600–1000 °C. At 300 °C as the main reaction temperature, the main evolved gas and functional groups such as CO2, H2O, CH4, C˭O, C-O, and C-H were detected. The addition of IS improved the comprehensive combustion index, inhibited SO2, but enhanced CO2, HCN, and NOx emissions. CaO in IS enabled Fe to remain in TDS and fixed more S in ash. Multi-response optimizations based on the best-fit artificial neural networks revealed the range of 545–605 °C and the co-combustion of 25% TDS and 75% IS as the cleaner and more efficient operational conditions.

Influence of co-processing of coal and oil shale on combustion characteristics, kinetics and ash fusion behaviour

Combustion characteristics and ash fusion behaviours of Qinghai coal (QH) and Fushun oil shale (FS) and their blends were investigated. It was found that ignition index and burnout index of the blends reached maximum for the blend with 10 wt% FS, while its comprehensive combustibility index remained nearly unchanged when compared with the coal sample. With the increase in heating rates, combustion performance of the samples improved significantly. The statistical analysis demonstrated that combustion temperature contributed significantly (about 73% of the impact ratio) to the thermogravimetric mass loss, followed by oil shale blending ratio and heating rate. In addition, there is noticeable deviation between the experimental and theoretical curves of the blends in the temperature range of 410–480 °C, which indicates the existence of synergistic interactions. Moreover, the lowest apparent activation energy, determined using two model-free integral methods, was found to be 64.1 kJ/mol for the blend with 10 wt% FS. In addition, slag formation and mineral transformation of different samples were determined using the thermochemical database package FactSage 6.3. For the blend with 10 wt% of FS, anorthite, hematite, diopside and quartz were found to be the main crystalline phases at high temperatures. It is shown that the addition of FS mitigated the slagging and fouling tendency of the QH coal combustion.

Self-ignition risk classification for coal dust layers of three coal types on a hot surface

Pulverised coal in industrial sites and their dust can experience spontaneous combustion and self-heating, increasing the risk of fire and dust explosion. The main objective of the present study was to resolve thermal combustibility (as reflected by comprehensive combustibility index [Sn] and kinetic properties) for three types of coal (S1-BN, S2-CY, and S3-JM) through thermal analysis. The Sn values of the samples indicated a degradation in the quality of comprehensive combustibility. Apparent activation energies (Ea) at the initial stage of spontaneous coal combustion (130–300 °C) were decided through Achar and Coats–Redfern methods. Moreover, thermal susceptibility (minimum auto-ignition temperature [MAIT] and thermodynamic parameters) was evaluated using the hot plate method. The MAIT values for the three coal dust layers were 210, 220, and 300 °C. The results exhibited that heat conduction was the dominant heat transfer mode that originated the temperature distribution within the coal dust layer under the subcritical conditions for ignition; while it converted chemical reaction controlled-mode after thermal runaway. Furthermore, the results based on an improved risk matrix approach showed the S1-BN and S2-CY samples had a high self-ignition risk, whereas the S3-JM sample had a moderate ignition risk.

Experimental Study on Co-Firing of Coal and Brewery Wastewater Sludge

The environmental pollution and high energy consumption caused by the coal-dominated energy structure in China have been the focus of attention for a long time. The co-firing of biomass with coal can save coal resources and realize effective utilization of biomass. In this paper, brewery wastewater sludge (SD) and bituminous coal (BC) were blended for an experimental study which aimed to provide basic experimental data and operational guidance as a reference for practical application in power plants. The co-firing characteristics of sludge and bituminous coal were studied. The results show that the burnout temperature and ignition temperature decrease with an increase in the sludge blending ratio. The Comprehensive Combustion Index (CCI) first rises, then decreases, reaching a maximum at about 15%. Compared with the atmosphere with 79% N2/21% O2, under the 79% CO2/21% O2 atmosphere, ignition is delayed and the burnout temperature is higher. Under an O2/CO2 atmosphere, as the O2 concentration improves, the thermo-gravimetric (TG) curve shifts to the low-temperature region, the burnout temperature drops significantly, and the comprehensive combustion characteristics are improved. With an increment of the heating rate, the curve of TG analysis shifts to the high-temperature region and the CCI increases. This study could provide helpful information on practical blending in coal-fired power plants for energy savings and emission reductions.

Effects of pyrolysis upgrading temperature on semi-coke explosibility for blast furnace injection

The purpose of this work is to understand the semi-coke explosion issues and to improve the safety in semi-coke injection. It shows that the higher pyrolysis upgrading temperature is, the lower explosibility of semi-coke powder has. The effects of pore structure and functional groups on explosive properties are evaluated in detail. The surface area is determined to be at least as important as the volatile matter while the volatile matter content is more than 40.7%. The impact of surface area on explosibility is relatively small while the volatile matter content is less than 31.7%. The explosibility of the sample will show a correlation with combustibility when the comprehensive combustion index is in the range of 7.63 × 10−14–8.62 × 10−14. Content of the oxygen-containing functional groups or the carboxyl and ether bond can all reflect the semi-coke/raw coal explosibility accurately to some degree, and the relative content of carboxyl and ether bond is more closely related to the length of return fire.

Valorization of maize silage digestate from two-stage anaerobic digestion by hydrothermal carbonization

This study proposed a novel bioeconomy concept of combining two-stage anaerobic digestion (TSAD) and hydrothermal carbonization (HTC). The maize silage digestate from the acidification reactor (AR) of the TSAD was hydrothermally carbonized at 180, 200, and 220 °C for 30 min. This was followed by the biogas potential test of the process water and the co-digestion test of the hydrolysate (the liquid product from the AR) and the process water (180 °C). The results show that higher HTC temperatures resulted in lower yield, volatile matter content, and comprehensive combustibility index of the hydrochars. The COD, TOC, and specific methane yield of the process water decreased when increasing the HTC temperature. The modified Gompertz equation successfully described the methane formation of the aqueous samples. The process water from HTC at 180 °C obtained the highest specific methane yield (278 mL CH4/g COD). The highest total energy recovery from hydrochar and process water (methane production) was also achieved at 180 °C. The co-digestion test shows the feasibility of circularly coupling TSAD and HTC, while further optimization is still needed.

Deep dewatering of sewage sludge and simultaneous preparation of derived fuel via carbonaceous skeleton-aided thermal hydrolysis

To simultaneously solve problems of high water content and poor fuel performance hindering sludge incineration, carbonaceous skeleton-aided thermal hydrolysis was firstly developed in this study. Results showed that thermal hydrolysis could break sludge particle and release bound water. Sawdust as a typical carbonaceous skeleton improved permeability of sludge, decreased the specific resistance to filtrate significantly and lowered effective thermal hydrolysis temperature from 180 °C to 150 °C. The water content of sawdust-aided 150 °C hydrolysis sludge reached 42.2% after dewatered at 1 MPa. Zeta potential was not always linked to sludge dewatering performance after carbonaceous skeleton-aided thermal hydrolysis. The changes of zeta potential-pH in sawdust-aided thermal hydrolysis at different temperature, which was affected by aliphatic acid and acetic acid derived from sludge and sawdust respectively, were vector sums of that in hydrolysis alone. Zeta potential-pH vector relations and filtrate composition revealed that sawdust could interact with sludge and accelerate thermal hydrolysis reaction. Maillard reaction was the main color reaction in thermal hydrolysis consuming protein and polysaccharide in EPS. There were two stages for the combustion of derived fuel. Thermal hydrolysis could homogenize the sludge and reduce the temperature intervals between two stages. More fixed carbon, higher heating values and comprehensive combustibility index suggested a better combustion performance of derived fuel.

Energy valorization of cow manure by hydrothermal carbonization and anaerobic digestion

The work evaluates the energy recovery from hydrothermal carbonization (HTC) of cow manure through the thermal analysis of hydrochar and the anaerobic digestion (AD) of the process water (PW). The increase of the HTC temperature in the range of 170–230 °C improved solid-fuel properties (higher heating value (16.4–20.1 MJ kg −1 ), fuel ratio (0.19–0.33)) of dairy manure, but less energy can be recovered by its combustion ascribing to reduction of hydrochar yield (65.0–54.0%). Fixed carbon content (12.5–18.7%), and ignition (263–278 °C) and burnout (581–619 °C) temperatures increased with carbonization temperature, thereby reducing risks of fire and explosion. However, the highest value of the comprehensive combustion index, related with good fuel characteristics, was obtained for the hydrochar carbonized at 170 °C. The high organic matter content of the PW allows energy recovery by AD, obtaining the highest methane yield for the PW generated at 170 °C (294 ± 2 mL STP CH 4 g −1 VS added ). HTC led to higher energy recovery than conventional AD of dairy manure (4.1 MJ kg −1 ). The energy recovery by AD combined with the energy content of the hydrochar (13.7 MJ kg −1 feedstock for HTC conditions below 200 °C) accounted around 85% of the total energy content of feedstock, allowing a potential valorization route for dairy manure. • Energy valorization of cow manure by HTC and anaerobic digestion of process water. • Combustion characteristics of hydrochars were studied by thermogravimetric analysis. • Comprehensive combustion index values indicated good fuel characteristics of hydrochar. • Process water obtained at 170 °C showed the highest methane yield and COD removal. • Energy recovery accounted up to 85% of the total energy content of feedstock.

Research on combustion properties and thermokinetic of pulverized coal: raw and pre-oxidized samples

The combustion behaviors of raw and pre-oxidized samples for two pulverized coals (PC) were investigated using a thermogravimetric (TG) analyzer. The mass variations, characteristic temperatures and combustion characteristic parameters, et al. of PC during oxidation combustion were analyzed. The results demonstrated that the ignition temperatures (T i) and burnout temperatures (T b) of pre-oxidized PC were lower than those of raw PC. The total mass losses of the four samples were 91.33, 92.32, 88.85, and 90.02 mass% respectively, which were consistent with the volatile matter and fixed carbon contents (Vad+FCad). The calculated combustion characteristic parameters (the ignition index C i, burnout index C b, and comprehensive combustibility index S n) of pre-oxidized samples were all greater than those of raw samples, which indicated that pre-oxidized PC was more prone to self-ignition than raw PC under the same conditions. The thermokinetic parameters of PC during pyrolysis and combustion were studied by Coats–Redfern method. The apparent activation energy E a of these four PC samples ranged from 45.12 to 55.37 kJ/mol.

Characteristics and thermal behavior of fresh and waste oil blends as supplement in diesel engines

This study deals with the combustion characteristics of base oil-based blends called number 10 lubes (NTLs), a blend of virgin/nonstandard base oils with low taxation petroleum products and/or wastes, used as diesel additive or substitute using thermogravimetric analysis with Fourier Transform Infrared Spectroscopy. Basic compositional analyses (i.e. elemental analysis, calorific value, sulfated ash) were also conducted with relevant methods in an accredited fuel analysis laboratory. In general, samples yielded exceptional characteristics in terms of sulfated ash content. Oxidation reactions were found to compose of one decomposition stage whilst up to three-stages were also observed outstandingly. Thermographs vary slightly in shape and position, similarly shaped to that for mineral oil, base oil or waste engine oil, and exhibited lower mass loss rates at low temperatures when compared to diesel. Quantitatively, combustion reactions occur between 236 ± 42.2 °C and 362 ± 39.0 °C yielding a maximum combustion rate and mass loss of 17.4 ± 3.87%/min and 98.4 ± 1.29%, respectively, on average, with major gases released carbon dioxide, water vapour, and the others complicating the interpretation of spectral bands. The combustion characteristic indices (ignition, flammability, burnout and comprehensive combustion index) also showed the combustion performance in favor of diesel > NTLs > mineral oil > waste engine oil > base oil > waste vegetable oil. Thus, this problem needs to be handled carefully via waste to fuel projects adopting the circular economy approach if sufficient knowledge on all of the technical and market aspects of such fuels would be obtained.

Characterization and Preparation of Furanic-Glyoxal Foams.

Synthetic foams have become an essential industrial product for a great variety of applications. Furfuryl alcohol, as a biomass chemical, was reacted with glyoxal at room temperature to prepare furanic-glyoxal rigid foams, and p-toluenesulfonic acid was used as a catalyst to initiate the reaction. Foams with different molar ratios (furfuryl alcohol/glyoxal) were prepared in this work, and uniform cells foams have been obtained. Their compression resistance, 24-h water absorption, density, and other basic properties were tested. Scanning electron microscopy (SEM) was used to observe the cellular morphology of the foams prepared, thermogravimetric analysis (TGA) helped to understand their thermal and combustion properties, and FTIR and Matrix Assisted Laser Desorption Ionisation Time of Flight (MALDI ToF) mass spectroscopy to explain the structure of the resulting foams to clarify the reactions occurring during foaming. The results show that the compression resistance of furanic-glyoxal foams declined as the furfuryl alcohol/glyoxal ratio decreases also. SEM observations revealed that foams with open-cell were obtained when furfuryl alcohol was added in greater amounts, and more closed cell structures were formed as the proportion of glyoxal increased. TGA results showed that the initial ignition temperature of furanic-glyoxal foams is ~200 °C higher than that of wood, and the smaller comprehensive combustion index S (about 0.15 × 10−7 (%2 K−3 min−2)) indicates that the foam burns slowly and has poor flammability, that is, it is not easy to burn.

Combustion behaviour and chemical structure changes of enzyme-treated coal

As one of the technologies for the improvement in coal quality, biological enzyme technology has received much attention. The enzyme product named 3EC was shown to enhance the power plant performance in our previous full-scale test. In this work, its effect on coal was explored. The results indicated that the enzyme product was beneficial in the removal of organic sulphur from coal, and the catalytic action of 3EC on the cleavage of C–C and C–S bonds was proven based on data from the dibenzothiophene decomposition test. Thus, when it was used to treat coal, the CH3-to-CH2 ratio changed from 0.81 to 0.32 with an increase in treatment time, which indicated that some chemical structures in the enzyme-treated coal changed. Because of these structural changes, the combustion behaviour of coal improved, indicated by the increase in the comprehensive combustion index from 2.958 × 106 to 3.113 × 106 %2 min−2 K−3 and the decrease in activation energy from 32.76 to 30.43 kJ mol−1. In addition, the optimum enzyme treatment time should be 4 days to ensure enough reaction time between the enzyme and the coal.

Combustion characteristics of coal gangue and biomass under an O2/CO2 atmosphere

Oxygen concentration and biomass content are key factors of the combustion of a mixed sample of biomass and coal gangue. Herein, we studied the effect of oxygen concentration and biomass content and their corresponding combustion and kinetic characteristics. Experiments were conducted in a thermogravimetric analyzer under an O2/CO2 atmosphere. Results showed that the fixed carbon combustion temperature, ignition temperature, and exothermic peak temperature decreased with oxygen concentration increased. By contrast, the burning rate of volatilization increased with oxygen concentration increased. The total and maximum loss rates of the sample, the burnout temperature, the exothermic peak temperature, and the comprehensive combustion index S gradually increased. As oxygen concentration increased, the activation energy at the initial stage of combustion gradually decreased, whereas the activation energy at the end of the reaction gradually increased when the oxygen concentration increased. Activation energy could be rapidly reduced after a small amount of biomass was added, whereas the biomass content had no significant influence on the activation energy of the samples at the end of combustion.