Peak Reaction Rate Research Articles

MILD combustion characteristics of a premixed CH4/air jet flame in hot coflow from a bluff-body burner

This numerical study is designated to comparatively investigate premixed CH4/air jet flames from bluff-body (BB) and non-BB (NBB) burners in the coflow of hot exhaust gas. Specifically, traditional combustion (TC) from BB burner (BB-TC), MILD combustion (MC) from BB burner (BB-MC), and NBB burner (NBB-MC) under varying coflow temperatures (TC) and oxygen concentrations (YO2, C) are considered. The flow field, combustion reactions, temperature rise, heat release, along with reaction zone, and pollutant emissions are thoroughly investigated. The findings underscore the feasibility of achieving MILD combustion using the BB burner. Remarkably, the small recirculation zone generated by the BB enhances entrainment and mixing, leading to superior combustion stability and reduced CO emission in the BB-MC case compared to the conventional NBB-MC case. Moreover, the BB-MC case exhibits a higher peak temperature, reaction rate, and heat release rate than the NBB-MC case, albeit with slightly higher NO emission. When compared to the BB-TC case, NO emission from both the BB-MC and NBB-MC cases are significantly lower, particularly under relatively low TC and YO2, C conditions.

Study on the pyrolysis characteristics, kinetics, thermodynamics, volatile products, and chemical reactions of micron polyamide waste, a typical marine plastic microfragment

AbstractThe pollution of waste plastic microfragments to the marine ecosystems is an increasingly serious problem. Pyrolysis is widely recognized as a viable technique for the treatment of such plastic waste materials. The pyrolysis behaviors, characteristic parameters, kinetics, thermodynamics, volatiles, and possible chemical reactions during the pyrolysis of micron polyamide waste (the main component of fishing gear abandoned in the marine environment) are studied in inert atmosphere in the present work. The results show that the pyrolysis of micron polyamide may be regarded as a one‐step reaction. The peak and average reaction rates decrease significantly when the heating rate increases. The calculated kinetic parameters can effectively predict the pyrolysis behaviors of micron polyamide. The pyrolysis of micron polyamide is characterized as an endothermic reaction that occurs non‐spontaneously. Furthermore, the information of volatiles was obtained. The volatiles with higher content were –CH2 groups, CO2, and lactam, and the volatiles with smaller content were: –NH groups, NH3, HCN, H2O, CO, and amide derivatives. In addition, an analysis was conducted to explore the potential chemical reactions.Highlights The pyrolysis of micron polyamide can be considered as a one‐step reaction. The obtained kinetic parameters can well predict the pyrolysis process. Pyrolysis of micron polyamide is a non‐spontaneous and endothermic reaction. Specific volatile products are determined by Fourier transform infrared and mass spectrometry. The chemical reactions that may occur during the pyrolysis have been inferred.

Effect of Raw Materials on Temperature Development during Prereduction of Comilog and Nchwaning Manganese Ores

The effect of raw materials on the temperature development and prereduction behavior of Comilog and Nchwaning manganese ores (3.33–4.00 mm or 11.20–15.00 mm) were investigated in a CO-CO2 atmosphere. Experiments were conducted at a heating rate of 6 °C/min from room temperature to 1000 °C where the ore was mixed with inert material (quartz) in various ratios. A similar heating program gave dissimilar temperature development for Comilog and Nchwaning ores due to differences in oxygen levels and reduction rates. The temperature development, and thus reduction rate, decreased with the increasing amount of inert material in the mix for Comilog ore in size 3.33–4.00 mm. The peak reaction rates observed during reduction were 2.4 wt%/min, 1.0 wt%/min, and 0.8 wt%/min for an ore:quartz weight ratio of 1:0, 1:1, and 1:3, respectively. For Comilog ore in size 11.20–15.00 mm, and Nchwaning ore in both sizes, the temperature development and reduction rates were slightly or insignificantly affected. It was suggested that the effect was low for reactions under a diffusion-controlled kinetic regime.

Thermogravimetric Analysis on Co-Gasification Characteristics of Sludge and Straw under CO2 Atmosphere

To maximize the potential energy utilization of agricultural and forestry wastes and sludge, experimental studies were conducted on the co-gasification characteristics of two types of sludge (municipal sludge, MS; paper-mill sludge, PS) and a typical biomass straw (ST) under CO2 atmosphere. In this paper, the main two stages of the gasification process, the pyrolysis in the low-temperature region and the CO2-gasification in the high-temperature region, were separately studied and analyzed. The experimental results showed that biomass could effectively promote the pyrolysis of the sludge in the low-temperature region and improve the gasification in the high-temperature region. Due to the complex interactions between components, the characteristic parameters presented obvious nonlinear rules during the co-pyrolysis and co-gasification processes. For the MS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature gradually decreased, but the final reaction temperature, the peak reaction rate and the corresponding temperature, and the pyrolysis index gradually increased; (ii) in the gasification process, the initial reaction temperature, the reaction final temperature, and the temperature corresponding to the peak gradually increased. Combined with the reaction kinetics analysis of the co-pyrolysis and the co-gasification processes, 25% may be a reasonable mixing ratio for ST for the MS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (26.58 kJ·mol−1 and 178.29 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). For the PS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature, the peak reaction rate, the temperature corresponding to the peak and the pyrolysis index gradually decreased, but the final reaction temperature gradually increased; (ii) in the gasification process, the initial and final reaction temperatures and the temperature corresponding to the peak gradually decreased, but the peak reaction rate gradually increased. Combined with the reaction kinetics analysis of the pyrolysis and the gasification processes, 25% may be a reasonable mixing ratio for ST for the PS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (64.29 kJ·mol−1 and 301.16 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). These findings can provide useful information for the co-gasification of sludge and straw under CO2 atmosphere.

Kinetic and thermodynamic study of micron waste polypropylene thermal degradation

AbstractHow to properly dispose of waste polymers is a recognized challenge all over the world. Thermal degradation is currently recognized as a promising method for recycling polymer waste into fuels or products with high energy density without polluting the environment. In the present study, the thermal degradation characteristics, kinetics, thermodynamic parameters, and volatiles of a representative and extremely widely‐used polymer (micron waste polypropylene [PP]) pyrolysis in nitrogen were investigated. The results indicate that the thermal degradation of micron waste polypropylene can be considered as a one‐step reaction with merely one distinct peak on the reaction rate curves. The peak and average reaction rates decrease with the heating rate. The most appropriate reaction model to characterize the thermal degradation is g(α) = 1−(1−α)1/4. The average values of activation energy and pre‐exponential factor are 128.76 kJ/mol and 6.79 × 109 min−1, respectively. The kinetic parameters obtained in this study are all larger than those of PP with the particle size of millimeters or larger. The predicted thermogravimetric curves of thermal degradation are in good agreement with the experimental results. The changes of enthalpy, Gibbs free energy, and entropy show that the thermal degradation of micron waste polypropylene is a non‐spontaneous and endothermic reaction. In addition, the concentrations of all volatiles in descending order are: H2O > Esters (COO) > CO2 > Alkanes (CH3) > R2CCH2 > Olefins (CC) > Alcohols (ROH) > Methylene group > CO.

Pyrolytic characteristics, kinetics, thermodynamics, volatile products and chemical reactions of micron polypropylene infiltrated with kerosene

The pyrolysis of polymers infiltrated with combustible liquids is one common behavior in the fire accidents resulted by the leakage and overflow of combustible liquids over polymers. The present study may provide a theoretical basis and guidance for the prediction of fire development, the selection or design of fire detection and the design of ventilation and fire extinguishing systems. In the present study, the thermal decomposition behaviors, kinetics, thermodynamics, volatiles and chemical reactions of micron polypropylene (typical polymer) infiltrated with kerosene (typical combustible liquid) are investigated. It is concluded that the thermal decomposition process of micron PP with kerosene can be divided into two stages, and all stages can be considered as one-step reaction. As the kerosene content increases, the average and peak reaction rates of the first stage increase, while they decrease for the second stage and the whole process. As the heating rate increases, the average and peak reaction rates of the whole process decrease. In addition, increasing the heating rate or kerosene content may result in better combustion performance compared with that of pure PP. The calculated average activation energy, pre-exponential factor and global reaction model of the second stage can well predict the thermal decomposition behaviors of this stage. Thermodynamic analysis shows that the thermal decomposition of micron PP with kerosene is an endothermic and non-spontaneous reaction. The main volatile products contain olefins, alkynes, alkanes, hydrogen, carbon dioxide, carbon monoxide and aromatic compounds. The possible chemical reactions generating the above-mentioned products are deduced.

Effects of liquid accelerant on the pyrolysis behaviors and kinetics of PMMA, a noncharring polymer

AbstractThermal decomposition of solid combustibles infiltrated with combustible liquids (liquid accelerants) is one typical fire behavior in arsons. In the present study, thermogravimetric and kinetic analyses are used to investigate the pyrolysis of one typical noncharring polymer namely polymethyl methacrylate (PMMA) infiltrated with different contents of one representative liquid accelerant namely kerosene. Results indicate that the thermal decomposition process of pure PMMA and PMMA infiltrated with kerosene show a one‐stage and a three‐stage process, respectively. Furthermore, the first and third stages for PMMA infiltrated with kerosene can be both regarded as one‐step reaction. With the increase of kerosene content, the conversion rate ranges of the first and third stages for PMMA infiltrated with kerosene are shortened. The peak and average reaction rates of the first and second stages increase, while the peak and average reaction rates of the third stage decrease. The maximum and average reaction rates for the entire decomposition process also decrease. The average activation energy values for the whole and one certain stage both increase. Moreover, the calculated kinetic parameters can be used to accurately predict the thermal decomposition behavior of PMMA infiltrated with kerosene.

Trans-scale study on the thermal response and initiation of ternary fluoropolymer-matrix reactive materials under shock loading

To investigate the thermal response and initiation behavior of ternary fluoropolymer-matrix PTFE/Al/W reactive materials, a research combining shock loading tests and trans-scale modelling is conducted. On the basis of a good agreement of the numerically simulated and tested shock wave propagation, the significant impact of component ratios and particle sizes on the evolution of mesoscopic temperature, hot-spots and initiation is well characterized and analyzed. Results demonstrate that as the content of W increases, the range of mesoscopic high-temperature area increases and tends to distribute more uniform, while material with smaller W particles causes more intense particle deformation and larger temperature rise. The time to reach the critical temperature shows positive correlation to the content of W, while the critical temperature of hot-spots shows negative correlation to the particle size of W. For PTFE/Al/W of high density, with the increase of W particle size, the reaction rate decrease, however the time to reach the peak reaction rate shortens.

Early-age hydration characteristics and kinetics model of blended cement containing waste clay brick and slag

Low-carbon blended cement was prepared by mixing Portland cement, clay brick powder (CBP) and slag. The early-age hydration mechanism was studied by analyzing the hydration characteristics and kinetics parameters of blended cement with different admixture replacement rate, CBP to slag ratio and temperature. The results indicate that increasing admixture replacement rate accelerates cement hydration and leads to the displacement of exothermic peaks. However, the reduced C3S content in blended cement reduces the peak intensity and reaction rates of NG-I-D (nucleation and crystal growth - phase boundary reaction - diffusion) processes. Slag promotes the nucleation and growth of C–S–H gel slightly more than CBP before the third exothermic peak. Then, the slag reaction in the deceleration period consumes a lot of sulfate ions, resulting in the high third exothermic peak. High temperature provides nucleation driving force to accelerate the cement dissolution and ions migration, thus, the reaction rates of NG-I-D processes are increased as the temperature rises.

Pyrolysis characteristics, kinetics and thermodynamics of the plywood material in high-speed trains

The pyrolysis characteristics, kinetics and thermodynamics of a typical plywood material, namely the Huangjinguomu plywood in high-speed trains in nitrogen were studied in the present study. It was indicated that three peaks occurred in the reaction rate curves. The pyrolysis process can be divided into three stages, namely stage 1: 0<a<0.1, stage 2: 0.1<a<0.7 and stage 3: 0.7<a<1. With the increase in the heating rate, the first and third peak reaction rate decreased, while the second peak reaction rate increased. The average reaction rate in stage 1 and throughout the entire pyrolysis process decreased. The average reaction rate in stage 2 increased. The average reaction rate in stage 3 remained almost constant. The second stage may be nominally considered to be a one-step reaction. The pyrolysis of the Huangjinguomu plywood was a non-spontaneous and endothermic process. The AG value maintained almost constant with the progressing of the thermal decomposition. The average values of AH, AG and AS were 191.55 kJ/mol, 139.29 kJ/mol and 92.93 J/(molK), respectively.

Synergetic energetic kinetics of Mg-Zn alloys and pyrotechnics

Zn has been incorporated into Mg via centrifugal atomization in this work. The prepared Mg-Zn alloys have been characterized via SEM/EDS and XRD. The thermal behavior and combustion of Mg-Zn alloys have been tested by TG/DSC and laser ignition. Then, Mg-Zn alloys have been applied in pyrotechnics with PTFE as the oxidizer, followed by measuring the reactivity and ignition delay. Mg-5%Zn and Mg-10%Zn alloys consisting of α-Mg and eutectic phase (α-Mg and MgZn2) in a high degree of sphericity with evenly distributed Zn were obtained. Thermal behavior characterization indicates that the oxidation of Mg-Zn alloys initiates ∼50 °C earlier than Mg along with a higher oxidation rate, which could be attributed to the lower melting point of MgZn2 and Zn. In addition, the oxidation rate of Mg-Zn alloys is also higher than Mg that is the result of significantly lower apparent activation energy of Mg-Zn alloys than Mg. Due to the great discrepancy of melting and evaporation point between Mg, MgZn2, and Zn, a visible microexplosion phenomenon has been observed during the combustion process of Mg-Zn alloys. Then, Mg-Zn alloys have been applied as the fuel to replace Mg in Mg/PTFE pyrotechnics. The ignition delay of Mg-Zn/PTEE composites is shorter than that of Mg/PTFE, which is due to the easier oxidization initiation of Mg-Zn alloys compared to Mg. Besides, the lower melting and evaporation points of MgZn2 and Zn than Mg can accelerate the combustion of Mg-Zn alloys, leading to the improved peak pressure and reaction rate of Mg-Zn/PTEE. Thus, the lower apparent activation energy of Mg-Zn alloys and the lower melting point of MgZn2 and Zn could promote the energetic kinetics of Mg-Zn alloys synergistically. Above all, the prepared Mg-Zn alloys in this study are ambitious candidates in pyrotechnics for controllable ignition and reactivity kinetics.

Effects of Select Metal Oxides on the Onset, Rate and Extent of Low Temperature Ammonium Perchlorate Decomposition

ABSTRACT Ammonium perchlorate (AP) is the most abundant ingredient in many solid rocket motors and presents a thermal runaway hazard. The addition of metal oxides (MOs) can alter motor performance but may affect decomposition behavior. In this work, a total of 14 MOs, mostly transition metal oxides, were mixed with AP and subjected to isothermal thermogravimetric analysis (TGA). MOs commonly incorporated into AP-based propellants can alter AP decomposition rates, the extent of reaction, and the particle size of the AP itself. Partially decomposed AP showed significant changes in terminal particle size. There is an inverse correlation between MO lattice energy and peak reaction rates of AP/MO mixtures. The objective of this work is not to provide definitive details of mechanisms, but rather to report observations and interactions with a wide variety of MOs, often ones that were not previously reported. The findings have implications for the safe storage of AP and the development of insensitive motors.

Effect of different lithological stone powders on properties of cementitious materials

Abstract As the by-product generated during the production of manufactured sands, stone powder is urgent to be utilized due to the high disposal cost and environmental pollution. The main objective of the research is to clarify the viability of stone powders as partial replacement of cementitious materials for a value-added recycling. The paste and mortar samples incorporating limestone, granite, tuff and quartzite powders with different fineness were prepared, whose properties including setting time, compressive strength, dry shrinkage, pore structure and hydration process were studied. The results showed that the limestone and tuff powders shorten the setting time, while the granite and quartzite powders prolong the setting time of the blended pastes. The compressive strength of the mortars blended with quartzite powder was notably improved with the increase of the specific surface area of stone powders. Stone powders with different specific surface areas could potentially decrease the dry shrinkage of the blended mortars. Increasing the fineness of stone powder could reduce the proportion of harmful pores in cement paste. The peak reaction rate and 72 h heat release were improved obviously when the specific surface areas of limestone, granite and quartzite powder were about 500 m2/kg and was about 700 m2/kg for tuff powder.

Auto-ignition performance of an electrified microreactor with constructal geometries

Common techniques employed to minimize ignition energy of gaseous fuels in micro reactors such as the use of catalyst are being plagued with setbacks. This report demonstrates the use of electric field to sustain combustion, minimize heat loss and enhance reactant mixing in microchannels of varying geometries. We set two defining constructal parameters for serpentine and straight microchannels of 0.05 to 0.25 to investigate geometric effect on the mixing of the reactants. Inlet concentration of propane and oxygen was set at 0.15 mol/dm3 and 0.7 mol/dm3 respectively. Reynolds numbers 400, 470, 530, 600 and 670 corresponding to inlet velocities of 0.06 m/s, 0.07 m/s, 0.08 m/s, 0.09 m/s and 0.1 m/s were used in the straight channel to study the dependence of reaction rate, temperature drop and reactants diffusion on the combustion process. We report that at an inlet temperature of 500 K which was below the propane’s auto ignition temperature of 743 K, the reaction could occur in the presence of a 50 V applied voltage. Increasing constructual parameter (β) yielded an increase in reaction rate and a decrease in temperature drop. At the same constructual parameter, the serpentine geometry displayed a better result with the peak reaction rate of 894 mol/m3s. More so, increase in the Reynolds number and shape factor for the two geometries led to an increase in reaction rate and propane consumption. These findings could be suitably beneficial to provide minimal fuel requirement for miniaturized vehicles and micro-heat engines.

Evaluation of lithium glass scintillation detector responses for tritium production rate measurement in blanket neutronics experiments using the PHITS code

Lithium (Li) glass scintillation detectors were utilized by the neutron response of a 7Li glass subtracted from the neutron response of a 6Li glass to evaluate the tritium production rate (TPR) in the fusion blanket neutronics experiments, which is a so called Li glass method. TPRs in the Li2O blanket and the Li/V-alloy blanket were measured by a 6Li2O and a 6Li2CO3 pellet method, and by the Li glass method in the benchmark neutronics experiment with D-T neutrons at the Fusion Neutronics facility (FNS) of JAERI. TPRs measured by the Li glass method are lower than TPRs measured by the pellet method. The neutron responses of Li glass detectors have been calculated to study the discrepancies of two different methods by using the PHITS code. In the blanket, the neutron spectra change to harder from the backside to the front side of blanket. The reaction rate of several reactions, such as 6Li(n, n’α)D, 7Li(n, n’α)T, 7Li(n, 2n)6Li, and the elastic scattering of 6Li and 7Li increase with the neutron energy. The low-energy neutron peak was considered only for the calculation of TPR from Li glass, which loses the information of the 6Li(n, α)T reaction from high-energy neutron range. In addition, the reaction rate of this peak evaluated by the Li glass method is lower than real TPR of this peak for 6Li glass caused by weakened effect from other reactions. Therefore, the ratios of this peak reaction rate from the Li glass method against the total TPR of 6Li glass were evaluated to be a correction factor to correct Li glass method. After the correction, TPRs measured by Li glass method agree well with TPRs measured by pellet method.

Analysis of chemical pathways and flame structure for n-dodecane/air turbulent premixed flames

This paper analyzes turbulence-chemistry interactions of an n-dodecane-air flame, focusing on the degree to which flame structure and fuel oxidation pathways change in turbulent flames relative to their corresponding laminar flames. This work is based on a lean (ϕ = 0.7) n-dodecane-air flame DNS database from Aspden et al. (2017). The relative roles of dominant reactions that release heat and produce/consume radicals are examined at various turbulence intensities and compared with stretched flame calculations from counterflow flames and perfectly stirred reactors. These results show that spatially integrated chemical pathways are relatively insensitive to turbulence intensity and mimic the behavior of stretched flames. In other words, the contribution of a given reaction to heat release or radical production, integrated over the entire flame, is insensitive to turbulence. Localized analysis conditioned on topological feature of the flame and on temperature is also performed. The former analysis reveals that larger alteration of pathways occurs in the positively-curved regions of the flame. Most significantly, it shows that the thermal structure of the flame is altered, as peak reaction rates and heat release in the low temperature (i.e., below 1200 K) region shift towards higher temperatures with increases in Karlovitz number. This result is particularly interesting given that prior work with lighter fuels (e.g., hydrogen) showed the opposite behavior. Various stretched, laminar flame calculations with altered transport effects were performed for reference. These calculations, using mixture-averaged and Le = 1 transport model, can capture similar shifts towards higher temperatures in laminar flames with increasing stretch. However, the stretch rate and transport values must be tuned to match these shifts in thermal structure differently, depending upon reactions, species, and Ka value. This effect is particularly prominent for low temperature species. Thus, these results show that flames do not simply shift to a Le = 1 thermal structure with high turbulence intensity, as previously suggested, but there is interplay between altered scalar diffusivity and stretch effects.

Combustion characteristics of lignite char in a fluidized bed under O2/N2, O2/CO2 and O2/H2O atmospheres

As a possible new focus of oxy-fuel work, O2/H2O combustion has many advantages over O2/CO2 combustion, and has gradually gained increasing attention. The unique physicochemical properties (thermal capacity, diffusivity, reactivity) of H2O significantly influence the char combustion characteristics. In the present work, the combustion and kinetics characteristics of lignite char particle were studied in a fluidized bed (FB) reactor under N2, CO2 and H2O atmospheres with different O2 concentrations (15%–27%) and bed temperatures (Tb, 837–937 °C). Results indicated that the average reaction rate (raverage) and the peak reaction rate (rpeak) of lignite char in H2O atmospheres were slower than those in CO2 atmospheres at low O2 concentrations. However, as the O2 concentration increases, the rpeak and raverage of lignite char in H2O atmospheres significantly improved and exceeded those under CO2 atmospheres. The calculation result for the activation energy based on the shrinking-core model showed that the order of activation energy under different atmospheres is: O2/CO2 (28.96 kJ/mol) > O2/H2O (26.11 kJ/mol) > O2/N2 (23.31 kJ/mol). Furthermore, gasification reactions play an important role in both O2/CO2 and O2/H2O combustion, and should not be ignored. As the Tb increased, the active sites occupied by gasification agent were significantly increased, while the active sites occupied by oxygen decreased correspondingly.

Premixed combustion of low-concentration coal mine methane with water vapor addition in a two-section porous media burner

During the transport of low-concentration coal mine methane (CMM), water mist spraying into the pipeline is used to eliminate the risk of explosion, but it leaves abundant vapor in the methane. This study was aimed to explore the effects of water vapor addition on the low-concentration CMM combustion in porous media. Thereby, a 2D numerical model based on a two-section ceramic foam burner setup with high flame stability was established and multi-step kinetics mechanisms were imported to the model. In this paper, the effects of vapor concentrations on the temperature distribution, flame stability limit, and chemical reaction during low-concentration CMM combustion in ceramic foam were investigated. Results indicate that with the increase of vapor mole fraction in the inlet methane, the overall temperatures in the downstream section of the burner gradually decreased, while the vapor mole fractions were linearly and negatively correlated with the peak temperatures in the burner. A small amount of vapor was involved in the chemical reactions of combustion, and with the increase of vapor mole fraction, more vapor took part in the reactions when the vapor addition into the inlet methane was unchanged. As the vapor mole fraction in the low-concentration CMM increased, the velocity range of flame stability limit was gradually narrowed down. In addition, the lower limit of velocity changed very slightly and maintained at 0.13–0.20 m/s, while the upper limit dropped obviously. The key elementary reactions underlying the effect of vapor on combustion reactions were determined by defining the changing rate of peak reaction rate. Addition of vapor into methane affected the peak rate of each elementary reaction, and altered the area of axial region where elementary reactions occurred.

Autocatalysis in thermal decomposition of polymers

Possibility of replicating polymer decomposition by a single global reaction greatly simplifies pyrolysis modeling. Apparent kinetic parameters are normally derived from the microscale experiments with linear heating program, and the n-th order reaction is routinely assumed thereby strongly affecting the numerical values of the kinetic parameters. In this work, we demonstrate inconsistency of the n-th order reaction assumption and reveal the autocatalytic behavior in thermal degradation of polyethylene, polystyrene and polycarbonate. The autocatalysis manifests itself in non-monotonicity of the conversion function, which markedly increases in a wide range of conversions. Although the iso-conversional approach makes it possible to explicitly recover the conversion function from the measurements, this option has not been used in most of the previous studies. Meanwhile, proper approximation of the experimentally derived conversion function results in excellent replication of the measured reaction rates, with the same kinetic parameters, in a range of the heating rates. Thus developed thermal decomposition kinetic models are provided in this paper for three kinds of polyethylene (LDPE, HDPE, and UHMWPE), seven kinds of polystyrene, polycarbonate, and two kinds of polymethylmethacrylate with different molecular weights. Although the pyrolysis of the polymers with different molecular weights proceeds differently, no systematic correlation of the pyrolysis characteristics (conversion-averaged apparent activation energy, heat of combustion, peak reaction rates and temperatures etc.) with the molecular weight has been observed for polystyrene. Peak reaction rates and temperatures varied in opposite directions for polyethylene and polymethylmethacrylate.

Second-generation sustainability: Application of the distributed activation energy model to the pyrolysis of locally sourced biomass–coal blends for use in co-firing scenarios

While first generation biofuels paved the way for a vision of a renewable energy future, their competition for arable land limited widespread applicability. Second generation fuels, made from a variety of carbonaceous wastes, are considerably more “sustainable” in a land competition sense, but require a higher degree of processing to extract energy. Here we extend the idea of second-generation sustainability by investigating blends of coal and biomasses found within 20miles of coal-fired power stations in the Northeast United States for use in co-firing scenarios that would limit long-range transport of biomass. A commercial high volatile bituminous Pennsylvanian coal was blended at 90, 80, and 50wt% with one of three biomasses: feed corn stover from a local farm, brewer’s spent grains from Redhook Brewery, or cocoa shells from the Lindt chocolate factory. The Distributed Activation Energy Model was applied to analyze the pyrolysis kinetics of the solid fuels and blends, yielding activation energies as a function of mass fraction conversion ranging from 304 to 522kJ/mol for coal, 164 to 304kJ/mol for the biomasses, and 218 to 530kJ/mol for the coal–biomass blends. Overall, the peak reaction rates and temperatures for the primarily biomass decomposition stages were linearly correlated with the percent biomass in the blend. Such an additive scheme did not represent the blends’ kinetics, instead over-predicting the activation energies. Synergy was noted between the fuels, in that the biomass does appear to be promoting the devolatilization of the coal at lower temperatures.