Devolatilization Zone Research Articles

Thermal Decomposition of Pure Waste and Binary Mixtures

In this study, the thermal decomposition of pure organic residues - coffee grounds, sugarcane bagasse and orange juice residues - and their binary mixtures with coffee grounds were analyzed. The results of thermogravimetric analyses at 10 °C/min under an oxidizing atmosphere showed that sugarcane bagasse and coffee grounds had individually higher reaction rates in the devolatilization zone, while orange juice residues burned more quickly in the combustion zone. There were significant mass interactions between the coffee grounds and orange juice residues in the binary mixtures, which led to higher reaction rates in the combustion of the mixture than in the pure residues. In the mixture of coffee grounds and sugarcane bagasse, there were no significant mass interactions. These encouraging findings can optimize the generation of bioenergy from these wastes and their mixtures, therefore, one must understand the different interactions during thermal decomposition to then develop sustainable strategies for utilizing biomass.

Thermokinetic study of coconut husk pyrolysis in the devolatilization zone using volatile state approach

Thermokinetic study of coconut husk pyrolysis in the devolatilization zone using volatile state approach

Optimization of the Air Distribution in a Biomass Grate-Fired Furnace

This study utilized a combination of FLIC(1D3.2C) and FLUENT(2021R2) software to optimize the primary air distribution along the grate and the performance of a straw briquette combustion furnace of a 7 MW unit in China used to produce hot air for drying grain. Three air distribution modes, namely front-enhanced, uniform, and rear-enhanced modes, were analyzed to determine their effect on the flue gas components above the grate, the temperature field in the furnace, and the nitrogen oxide concentration at the furnace outlet. The results of the calculations showed that the NOx emissions for the front-enhanced, uniform, and rear-enhanced modes were 133.5 mg/Nm3, 104.4 mg/Nm3, and 76.6 mg/Nm3, respectively. It was found that the rear-enhanced mode can expand the biomass drying, devolatilization, and combustion zone, thus improving the furnace combustion performance and decreasing NOx emissions. These findings can provide useful guidance for optimizing biomass chain-grate-firing furnaces.

Hazardous maize processing industrial sludge: Thermo-kinetic assessment and sulfur recovery by evaporation-condensation technique

In the present work, a detailed thermo-kinetics of hazardous sulfur-rich sludge generated from the corn processing industry was performed for acquiring the optimum parameters for the efficient recovery of sulfur using the evaporation-condensation technique. Sulfur in the sludge was found to be 79 ± 3% (wt%) as estimated by the Bureau of Indian Standards method. A weight loss of 77 ± 3% was found in the active devolatilization zone from ≈ 200–400 °C. The online FTIR confirmed the evolution of mainly sulfur vapors (S8) along with some sulfur dioxide (SO2) and disulfur (S2). The thermogravimetric data (TG) was used to evaluate the kinetic parameters with the help of model-free methods, and Z-master plots determined additional insight into the reaction mechanism. Furthermore, the calculated activation energy (Ea) was used to determine the thermodynamic feasibility. The average Ea values appraised by FM, FWO, sDAEM, and ST models were 55.43, 72.04, 62.33, and 62.67 kJ mol−1, respectively. Overall, 91.2% of sulfur was successfully recovered at 400 °C, having 99 ± 0.5% purity. The approximate cost analysis of the sulfur recovery process was also estimated to check the economic viability. Recovered sulfur could be directly used for industrial and agricultural applications without any further purification.

Self-ignition potential assessment for different biomass feedstocks based on the dynamic thermal analysis

Abstract Despite many advantages of the utilization of biomass as a renewable energy source, certain bottlenecks during biomass plant operation can be identified. Transport and collection of biomass as well as non-uniform material characteristics are issues related to decreasing efficiency of logistics and fuel manipulation which can also cause economic problems with biomass collection, transport, and storage. Since biomass is an especially reactive fuel, this has raised concerns over its safe handling and utilization. Fires, and sometimes explosions, are a risk during all stages of fuel production as well as during handling and utilization of the product. This paper presents a novel method for assessing ignition risk and provides a ranking of relative risk of ignition of biomass fuels. Tests within this method include physical and chemical properties of biomass, thermal analysis measurements, and the calculation procedure steps which were made using characteristic temperatures from thermogravimetry recordings. The results of thermogravimetry analysis were used for determination of tangent slope of the mass loss rate curves in devolatilization zone at considered heating rates for all tested samples. Linear interpolation of the data obtained by tangent slope analysis and used heating rates may provide unique straight line for each sample in the ignition testing. Thermogravimetry index of spontaneous ignition (TGspi) is obtained for all samples based on newly established formula. By varying gradient of linear dependence of self-heating coefficient against reference temperatures, mass and heat transfer limitations for various biomasses were discussed. The proposed method is accurate as well as relatively simple and quick, enabling determination of data necessary for design and application of appropriate measures to reduce fire and explosion hazard related to operation of biomass.

Physicochemical characteristics of hazardous sludge from effluent treatment plant of petroleum refinery as feedstock for thermochemical processes

The physicochemical characteristics of hazardous petroleum sludge (PS) become reasonably important when it used as feedstock in thermochemical processes for energy generation. Present work aimed at investigating the physicochemical characteristics of PS before and after soxhlet extraction. The soxhlet extraction was performed using petroleum ether, hexane, toluene, and benzene as solvent, among which hexane yields maximum amount of liquid. Therefore, PS before and after solvent extraction using hexane was characterized using proximate, ultimate, TGA/DTG/DTA, FTIR, XRD, and SEM-EDX analyses, while liquid extracted from PS was characterized by GC–MS analysis. Results revealed that moisture and volatile matter of PS decreased from 23.31 to 9.98 wt % and 65.10 to 62.71 wt %, respectively, while fixed carbon increased from 9.16 to 23.21 wt % after soxhlet extraction. Thermogravimetric analysis (TGA) suggested four distinctive zones during thermal decomposition of PS. Kinetic triplets (activation energy, frequency factor, order of reaction) for major devolatilization zone of organic compounds for raw and filtered PS was found to be 27.80 kJ/mol, 63.802 min−1, 0.07 and 35.01, 272.91, 0.11, respectively. TGA indicated that sludge can be processed by pyrolysis in the temperature range of 250–650 ℃. Many value added chemicals were identified in liquid extracted from PS among which phytol (50.72 %) was the most abundant.

A Two-Dimensional Study on the Effect of Anisotropy on the Devolatilization of a Large Wood Log

In this work, a two-dimensional (2D) model for wood particle drying, devolatilization, and char conversion is presented and validated against experimental studies of devolatilization of a large, dry, cylindrical birch wood log. The wood log’s internal distributions of temperature, solid species densities, gas density, and gas species mass fractions, together with the internal pressure and the gas flow velocities in radial and longitudinal directions, were studied. It was found that the internal pressure peak significantly depended on the permeability of char. The velocity profiles changed as the pressure wave traveled radially inward in the same manner as the devolatilization zone. The wood log internal pressure was not only dependent on wood and char permeabilities but also depended on the devolatilization rate, which itself is a heat-controlled conversion stage. In addition to the study on wood anisotropy, which can be accounted for in detail by the presented 2D model, the authors compared the 2D results to results obtained from a corresponding 1D version of the model, where only radial heat and mass transfer properties were used. It was found that even though the predictions of the 2D model were in better agreement with experimental observations than the 1D modeling results, for these parameters, 1D models can still be used without too much loss in accuracy. Finally, the paper concludes with a clear recommendation of when higher dimensional models should be used and when they should not.

Catalytic Steam Reforming of Biomass-Derived Tar over the Coal/Biomass Blended Char: Effect of Devolatilization Temperature and Biomass Type

Catalytic tar steam reforming over char was conducted in a two-stage fixed-bed reactor. This reactor was divided into two zones: the “devolatilization zone”, where the biomass tar is released, and ...

Thermogravimetric analysis and the fitting model kinetic evaluation of corn silk thermal decomposition under an inert atmosphere

The thermal behavior of corn silk pyrolysis under nitrogen atmosphere has been studied through the thermogravimetric analyzer. The drying process of the original sample was performed by means of an oven at 100°C for 90 minutes. The dry sample subsequently ground and sieved for a mesh size of 60. Approximately 11 mg of the sample was weighed into the crucible. The constant heating program of 10°C/min was imposed on the sample start from room temperature till to 900°C. The 50 ml/min of nitrogen was continuously flowed into the inner of the chamber to ensure the inert conditions. The differential fitting model of Arrhenius was occupied to evaluate the kinetic parameters. The result shows that corn silk was decomposed into the three stages during the pyrolysis process. These three stages initiated by the dehydration process from room environment till to 154°C and then followed by the most massive degradation of an organic component in the main devolatilization zone at the temperature range of 154-514°C and finally rest of material was undergoing slow decomposition till to 900°C. The respective activation energy (E), logarithmic of the pre-exponential factor (log A) and reaction order (n) of the corn silk pyrolysis were 207.37 kJ/mol, 19.15/min and 5.2.

Experimental Analysis on Thermal Characteristics of Argan Nut Shell (ANS) Biomass as a Green Energy Resource

Argan nut shell (ANS) is one of the most abundant agricultural by-product in the southwestern of Morocco. This study aims to focus on thermal characteristics of ANS biomass for alternate energy production. Physicochemical studies were done to characterize biomass-based material. Moreover, thermal degradation characteristics and kinetic parameters were assessed under pyrolysis and oxidizing conditions by means of thermogravimetric methods. Fundamental tests involving particle combustion of ANS and coal were carried out, and a comparison was performed. The results exhibit a heating value of 20.63 MJ kg -1 and negligible amount of nitrogen and sulfur. Furthermore, ANS follows the usual structural decomposition of lignocellulosique biomass, while coal reveal a discrete devolatilization zone. In addition, combustion tests show a significant burning period and high particle temperature. This experimental research is intended to provide a reference data of ANS biomass in engineering applications.

Burning characteristics of Victorian brown coal under MILD combustion conditions

In this work a vertical furnace is used to investigate the MILD (Moderate or Intense Low-oxygen Dilution) combustion characteristics of pulverized Victorian brown coal. This paper reports the effect of turbulence on the volatiles’ release and reactions under vitiated co-flow conditions as well as the impact on the pollutants’ formation and emission. Loy-Yang brown coal from the Latrobe Valley, Victoria, Australia, with particle sizes in the range of 53–125µm, is injected into the furnace using CO2 as a carrier gas through an insulated and water-cooled central jet. The bulk jet Reynolds number was varied from Rejet = 5527 to Rejet = 20,000. The furnace walls as well as co-flow temperature and local oxygen concentrations are controlled by a secondary swirling burner using non-premixed natural gas combustion. The co-flow in the furnace was operated with an O2 concentration of 5.9% (db by volume). Detailed measurements of in-furnace temperatures and chemical species are presented and discussed, together with visual observations and CH chemiluminescence (CH*) imaging at the bottom, middle and top parts of the furnace. The CH* signal intensity is found to be significantly lower at the top part of the furnace which is an indication of slow rate of the heterogeneous combustion of char particles. The largest amount of CO concentrations are measured for the highest jet velocity (i.e., Rjet = 20,000) case which implies that with increasing turbulence there is a better mixing and a broad devolatilization zone is formed which produces more CO. The measured NO emission for any case was less than 125 ppmv (db at 3% O2) which provides evidence to the potential benefits of MILD combustion application to Victorian brown coal towards reducing NO emission. Complementary CFD model helped in shedding light on the flow field, turbulence intensity, volatiles’ release rate, combustion of volatile matters, and overall carbon consumption inside the furnace for the three cases. It was found that increasing the jet Reynolds number increases the volatiles release rates and decrease the rate of overall carbon consumption.

Kinetics of Poplar Short Rotation Coppice Obtained from Thermogravimetric and Drop Tube Furnace Experiments

This article concentrates on the kinetics of poplar short rotation coppice obtained from thermogravimetric and drop tube furnace (DTF) experiments. Three poplar samples were studied, specifically, clone AF8 from two different plantations, one located in Italy (AF8-I) and another located in Portugal (AF8-P), and clone AF2 from a plantation located in Portugal. Initially, the combustion behavior of the three clones was evaluated by thermogravimetry. For the devolatilization zone, the thermogravimetric experiments yielded apparent activation energies of 109.7, 117.7, and 118.6 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. For the char oxidation stage, the apparent activation energies were 267.4, 252.0, and 264.3 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. Subsequently, the combustion behavior of the clone AF8-I was examined in a DTF. The data reported includes gas temperature and particle burnout measured along the DTF for five wall temperatures (900, 950, 1000, 1050, and 1100 °C). Th...

Pulverised wood combustion in a vertical furnace: Experimental and computational analyses

Experimental and numerical investigations of pulverised wood flames in a laboratory vertical furnace are carried out. The aims are to study the fundamental structures of pulverised wood flames, to identify the basic reasons that cause the emissions of unburned volatiles and particles, and to provide experimental data for model validations. Three different fuel particles are investigated; the particle effective diameter ranges from 0.02mm to 1.2mm and the length is about 5 times the diameter. Rather high emission of unburned hydrocarbons and carbon monoxide are recorded in the experiments. It is found that pulverised wood flames have similarities to gas premixed flames; distinct zones are found in pulverised wood flames – preheat zone, drying and devolatilization zone, oxidation zone and post-flame zone. The mechanism of heat transfer to the preheat zone of pulverised wood flames is rather different from the gas flames. The former is by virtue of radiation from the walls and the flames to the fuel particles; the latter is by diffusion (molecular and turbulent diffusion) from the reaction zone. This makes the emissions from pulverised wood flames rather sensitive to the particle size and combustor/burner configurations. An important feature of pulverised wood flames found in the experiments is the effect of particle devolatilization on the dispersion of the particles. A model is developed to account for this dispersion effect.

Investigation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln With Potential Energy Saving Considerations

Calcined coke is a competitive material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is exhausted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. To help improve the energy efficiency and reduce natural gas consumption of the calcining process, a 3D computational model is developed to gain insight of the thermal-flow and combustion behavior in the calciner. Comprehensive models are employed to simulate the moving petcoke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The following parametric studies are conducted: rotation angles, tertiary air injection angles, devolatilization zone length, discharge end gas extractions without injecting natural gas, variations of coke bed properties (thermal conductivity and heat capacity), and coke bed sliding speed. A total of 19 cases have been simulated. The results of studying the effect of tertiary air injection angles show that employing 15 deg tertiary air injection angle provides the best calcining condition than using 30 deg and 45 deg injection angles by achieving a higher coke bed temperature and less coke fines entrainment and attrition rate. In an attempt to reduce natural gas consumption, employing gas extraction at the discharge end successfully draws the hot combustion gas from the tertiary air zone towards the discharge end without burning natural gas. The coke bed temperature between 6 and 21 m from the discharge end is successfully raised 10–100 K higher, but discharge end temperature is reduced 150 K without burning natural gas. The extracted gas at 1000 K is too low to be returned to the kiln, but it could be used to preheat the tertiary air.

Toward the Control of the Smoldering Front in the Reaction-Trailing Mode in Oil Shale Semicoke Porous Media

Results of an experimental investigation on the feasibility of propagating a smoldering front in reaction-trailing mode throughout an oil shale semicoke porous medium are reported. For oil recovery applications, this mode is particularly interesting to avoid low-temperature oxidation reactions, which appear simultaneously with organic matter devolatilization in the reaction-leading mode and are responsible for oxidation of part of the heavy oil. The particularity of this mode is that, contrary to the reaction-leading mode largely studied in the literature, the heat-transfer layer precedes the combustion layer. This leads to two separated high-temperature zones: (i) a devolatilization zone (free of oxygen), where the organic matter is thermally decomposed to incondensable gases, heavy oil, andfixed carbon, also called coke in the literature, without any oxidation, followed by (ii) an oxidation zone, where thefixed carbon left by devolatilization is oxidized. The transition from reaction-leading to reaction-trailing mode was obtained using low oxygen contents in the fed air. It is shown that two distinct layers, the heat-transfer layer and the combustion layer, propagate in a stable and repeatable way. The decrease of the oxygen fraction leads to a decrease of the smoldering temperature and to strongly limit the decarbonation of the mineral matrix. The CO2 emissions are limited. Regardless of the front temperature, all of the fed oxygen is consumed and all of thefixed carbon is oxidized at the passage of the smoldering front.

Distribution and burning modes of char particles during combustion

The distribution and burning modes of various types of char produced from typical Chinese coals in a one-dimensional combustibility evaluation furnace were investigated. The results suggest that the char types formed in the devolatilization zone represent the initial distribution, with no significant combustion taking place. Corpohuminite and textinite in lignite appear to have thermal behaviour similar to inertinite during pyrolysis. Highly vesiculated cenospheres are rarely developed in lignite and semianthracite, due to their poor thermoplasticity. The percentages of different char types generally decrease during combustion although the different reaction rates, further fragmentation and internal burning may also result in the reverse change in some cases. The burning modes of various char particles are associated with the changes in external morphology and internal structure, cenospheres usually burn in a constant-diameter mode, while fragments tend to burn in a constant-density mode. Solid char shows two different burning modes: constant-density and mixed modes. Solid char burning in the mixed mode is considered to be depleted more quickly than that burning in the constant-density mode.

Foam‐enhanced devolatilization of polystyrene melt in a vented extruder

AbstractVented extruder devolatilization (DV) of PS melt containing 6,000 ppm styrene was studied by scanning electron microscopy (SEM) and video photography. Vacuum DV of a polymer is accompanied by foaming, which starts instantaneously upon supersaturation of the stretched melt and is enhanced at higher speeds of the vented extruder screw. As the volatiles are removed from the melt, foaming gradually ceases, starting with the pushing flight of the screw. The experimental installation design allowed us to quench the polymer melt in the DV zone at various stages of the process. Samples taken from four areas of the channel width were investigated by SEM. Bubble nucleation in the melt appears to take place mainly in the border area adjoining the gas phase. In the shear field caused by screw rotation, large bubbles become noticeably elongated. Their surface, as well as the free surface of the melt, is covered with blisters, 1–100 μm in size. Microblisters are often concentrated in areas subjected to stretching. Calculations of cooling due to volatile evaporation and of heating due to viscous dissipation near a growing bubble shows that the process of foam‐enhanced DV of a PS/styrene system can be regarded isothermal if the initial volatile concentration does not exceed approximately 1%.

Kinetic Modeling of Fuel-Nitrogen Conversion in One-Dimensional, Pulverized-Coal Flames

Abstract A detailed reaction mechanism for converting fuel nitrogen to nitric oxide and molecular nitrogen in gas flames is used to model nitrogen chemistry in fuel-rich coal-dust/oxidizer flat flames. In the devolatilization zone a simplified pyrolysis model is used and a hydrocarbon oxidation scheme supplement the nitrogen reactions. The predicted distributions of nitrogenous species (HCN, NH3, NO and N2) are compared to time-resolved experimental data obtained for two stoichiometrics and coal-types. The model accounts for the radical removal on particle surfaces, and various heterogeneous reactions for reduction of NO are considered. In the devolatilization flame zone the coal-N conversion mechanisms appear to be augmented by physical and chemical processes occurring in the vicmity of the devolatilizing particles. The current analysis supported by other investigations indicate that processes such as formation of fuel-rich volatile clouds and heterogeneous reduction of NO on surfaces of coal-particles a...

Variation of char reactivity during simultaneous devolatilization and combustion of coals in a drop-tube reactor

Intrinsic reactivities and activation energies are presented as a function of reaction conditions and carbon conversion for five coal chars produced in situ in the devolatilization zone of a simulated one-dimensional pulverized coal flame environment in an electrically heated drop-tube reactor. Oxygen partial pressures varied from 0.01 to 0.09 atm and gas temperatures from 1123 to 1573 K. Carbon conversion rates were determined by elemental analysis of solid material collected along the axis of propagation. The intrinsic activation energies obtained varied from around 135 kJ mol −1 in the initial char combustion stage to 220 kJ mol −1 towards the end of reactor, where the remaining solid burned with little volatiles evolution. Results are presented indicating that a transition from regime II to regime I conditions takes place over the experimental conditions investigated. The intrinsic reactivities were further compared with the rate of elemental hydrogen release from the particles.

DEVOLATILIZATION STUDIES ON A BITUMINOUS COAL UNDER VARIOUS GAS ENVIRONMENTS

ABSTRACT Devolatilization of a bituminous coal was studied in the temperature range 3 50°C to 550°C and at two pressures: 30 psig and 375 psig. Three separate particle sizes were investigated: (−2, +l),(−4, +3) and (−9, +6) mm. The runs, lasting up to 30 minutes, were carried out under two different types of flowing gas environments: a synthetic gas mixture of composition similar to that entering the devolatilization zone from the gasification zone below in a fixed bed gasifier, and containing 3% steam by volume; and, a helium-steam mixture, also containing 3% steam by volume. The gas evolution rates from devolatilization show a peak at 5–10 minutes from the start of a run and then gradually taper off to zero as the run progresses. The concentration of methane in the off-gas stream is observed to be higher in the helium runs. There, however, is no significant effect of gas environment on the molecular weights of the tar, which show a maximum in the range 300–500. The tar yields, however, are higher for th...