Isothermal Combustion Research Articles

Isothermal combustion kinetics of synthetic refuse plastic fuel (RPF) blends by thermogravimetric analysis

Thermal behavior of wastewater sludge, plastic and synthetic blends during combustion process was studied to identify potential of refused derived fuel application. Experiments were conducted in a large-scale thermogravimetric analyzer at temperatures ranging from 400°C to 700°C in the presence of air flow at 8L/min. Isothermal modeling was performed to find system kinetic parameters including combustion reaction rate constant (k), order of reaction (n), Arrhenius pre-exponential factor (A) and activation energy (E). Results revealed that with increase in temperature from 400°C to 700°C, maximum rate of combustion was observed to increase from 1.6%/min to 7.12%/min and 2.09%/min to 21.9%/min for wastewater sludge and plastics, respectively. The corresponding time for maximum weight loss rate was observed to decrease from 15min to 3.1min for wastewater sludge and from 47min to 3.8min for plastic. Thermogravimetric profile and activation energy indicated that refuse plastic fuel blends with higher percentage of plastic required higher activation energy than wastewater sludge from 12.43kJ/mol to 58.60kJ/mol. Experimental results show the potential to explain and predict combustion behavior and activation energy of combustion of wastewater sludge and plastic blends in practical RPF applications.

Effect of the coupling action between volatiles, char and steam on isothermal combustion of coal char

The effects of the coupling action between volatiles, char and the steam on combustion characteristics of coal char were studied in a customized isothermal thermogravimetric experimental system. The results showed that volatiles released during devolatilization played a key role in the combustion. Heat produced by volatiles combustion accelerated the burning rate of pulverized coal, at the same time, volatiles combustion depleted the oxygen surrounding the char particles. With the decrease of the furnace temperature, the acceleration effect on burning rate due to volatiles combustion improved while its impact to oxygen consuming reduced. The influence of volatiles on burning rate acceleration and oxygen depletion appeared to be inversely affected by the coal rank. When oxygen concentration decreased from 21% to 5% in the reactor, the burning process of volatiles and coal char displayed a tendency of separation. In addition, the presence of steam, which increased the burning rate and reduced the burning time noticeably, had a significant impact on the combustion of coal char.

MSW oxy-enriched incineration technology applied in China: Combustion temperature, flue gas loss and economic considerations

To investigate the application prospect of MSW oxy-enriched incineration technology in China, the technical and economical analyses of a municipal solid waste (MSW) grate furnace with oxy-fuel incineration technology in comparison to co-incineration with coal are performed. The rated capacity of the grate furnace is 350tonnes MSW per day. When raw MSW is burned, the amount of pure oxygen injected should be about 14.5wt.% under 25% O2 oxy-fuel combustion conditions with the mode of oxygen supply determined by the actual situation. According to the isothermal combustion temperature (Ta), the combustion effect of 25% O2 oxy-enriched incineration (α=1.43) is identical with that of MSW co-incineration with 20% mass ratio of coal (α=1.91). However, the former is better than the latter in terms of plant cost, flue gas loss, and environmental impact. Despite the lower costs of MSW co-incineration with mass ratio of 5% and 10% coal (α=1.91), 25% O2 oxy-enriched incineration (α=1.43) is far more advantageous in combustion and pollutant control. Conventional combustion flue gas loss (q2) for co-incineration with 0% coal, 20% coal, 10% coal, 5% coal are around 17%, 13%, 14% and 15%, respectively, while that under the condition of 25% O2 oxy-enriched combustion is approximately 12% (α=1.43). Clearly, q2 of oxy-enriched incineration is less than other methods under the same combustion conditions. High moisture content presents challenges for MSW incineration, therefore it is necessary to dry MSW prior to incineration, and making oxy-enriched incineration technology achieves higher combustion temperature and lower flue gas loss. In conclusion, based on technical and economical analysis, MSW oxy-enriched incineration retains obvious advantages and demonstrates great future prospects for MSW incineration in China.

Thermogravimetric Analysis of Coal Char Combustion Kinetics

Four chars prepared from pulverized coals were subjected to non-isothermal and isothermal combustion tests in a thermogravimetric analysis (TGA) device. Three different test methods, i.e., non-isothermal single heating rate (A), non-isothermal multiple heating rate (B), and isothermal test (C), were conducted to calculate the kinetic parameters of combustion of coal char. The results show that the combustion characteristics of bituminous coal char is better than that of anthracite char, and both increase of heating rate and increase of combustion temperature can obviously improve combustion characteristics of coal char. Activation energies of coal char combustion calculated by different methods are different, with activation energies calculated by methods A, B and C in the range of 103. 12–153. 77, 93. 87–119. 26, and 46. 48–76. 68 kJ/mol, respectively. By using different methods, activation energy of anthracite char is always higher than that of bituminous coal char. In non-isothermal tests, with increase of combustion temperature, the combustion process changed from kinetic control to diffusion control. For isothermal combustion, the combustion process was kinetically controlled at temperature lower than 580 °C for bituminous coal char and at temperature lower than 630 °C for anthracite char.

Maximum-efficiency architectures for steady-flow combustion engines, II: Work-regenerative gas turbine engines

In this paper we identify the maximum-efficiency architecture allowed by physics for simple-cycle gas turbine engines. This is achieved by functional minimization of total irreversibility using the attractor trajectory optimization approach developed in the first part of this study. It is shown that maximization of efficiency requires the combustion process to be performed in a part-adiabatic and part-isothermal manner. The optimal split of fuel to be burned between the adiabatic and isothermal segments is determined to be a function of turbomachinery irreversibilities and the turbine-blade temperature limit. The resulting optimal architecture has higher efficiency than both the traditional Brayton cycle (that employs only adiabatic combustion) and a fully-reheat cycle (that employs only isothermal combustion).

Binary Brayton cycle with two isothermal processes

The literature introduced isothermal concept and binary Brayton cycle as two promising methods used to enhance the performance of the gas turbine. Consequently, this work presents a cycle based on the blending of the two methods. This cycle is composed of gas turbine topping cycle with isothermal combustion and air turbine bottoming cycle with isothermal heating. Different parameters affecting the cycle performance have been studied. Simulations demonstrate that the present cycle achieves drastic enhancement in performance. The cycle merits justify its potential utilization for future power generation.

Air-Foam-Injection Process: An Improved-Oil-Recovery Technique for Waterflooded Light-Oil Reservoirs

Summary With the intent of solving problems that emerge at the later stage of waterflooded reservoirs, we study the feasibility of air-foam flooding of waterflooded light-oil reservoirs using the method of physical simulation. Through isothermal combustion experiments, the influence of clay mineral and foam on low-temperature-oxidation (LTO) reactions is investigated qualitatively. Then, the quantitative investigation of water saturation on oxidation rate and O2 consumption rate is discussed. After that, some dynamic foam displacement experiments are also performed, including the singletube displacement experiments of air foam at different water saturations and enhanced-oil-recovery (EOR) experiments of air-foam flooding in parallel tubes. In addition, in order to verify the O2 consumption capacity of the sample oil, a slimtube experiment is conducted. The results show that the presence of clay minerals could speed the process of the LTO reaction, while the presence of foam will slow this process. The LTO reaction is not significantly associated with oil viscosity. The concentration of O2 was near zero when the gas breakthrough occurred. Once the oxidation region reached the outlet, the concentration of O2 suddenly increased, and the effect of O2 consumption became worse. G64-38 crude oil performs better in the process of O2 consumption. The injection of air foam could effectively plug the high-permeability tube and restart the low-permeability tube. This paper could be used as a tool for the successful design of air-foam flooding at a later waterflood stage to enhance crude-oil recovery in light-oil reservoirs.

Standard thermochemical characteristics of formation of triphenylantimony bis(acetophenoneoximate)

For the first time, the energy of combustion Δc U of crystalline triphenylantimony bis(acetophenoneoximate) Ph3Sb(ONCPhMe)2 has been measured at T = 298.15 K using the isothermal combustion calorimeter with a stationary bomb. The standard molar enthalpy of combustion Δc Ho, the standard molar enthalpy Δf Ho, and free Gibbs energy Δf Go of formation of the above oximate have been calculated.

Thermodynamics of tetraphenylantimony acetophenoneoxymate

Abstract In the present research for the first time, the heat capacity of crystalline tetraphenylantimony acetophenoneoxymate Ph4SbONCPhMe has been measured using the methods of precision adiabatic vacuum calorimetry over the range from 6 to 350 K, the standard thermodynamic functions: heat capacity , enthalpy H°(T) − H°(0), entropy S°(T), and Gibbs function G°(T) − H°(0) have been calculated over the range from T → 0 K to 350 K. Low-temperature (20 K ≤ T ≤ 50 K) heat capacity data have shown a chain-layered structure topology of the compound under study. The energy of combustion of the compound has been determined in the isothermal combustion calorimeter with a stationary bomb. The standard thermodynamic functions of formation of crystalline Ph4SbONCPhMe at 298.15 K have been calculated. The differential scanning calorimetry and thermogravimetric analysis studies have shown the compound melts with decomposition and its melting temperature has been estimated. Thermodynamic properties of Ph4SbONCPhMe, Ph5S...

Effect of Temperature on NO Release during the Combustion of Coals with Different Ranks

It is highly important to study the effect of the actual combustion environment temperature in a boiler on NOx formation and its types during the coal combustion. In this paper, a horizontal high temperature tube furnace system was established. Four typical Chinese coals with different ranks including a lignite coal, a high volatile bituminous coal, a high ash bituminous coal, and a low-volatile anthracite coal were employed in a series of isothermal combustion experiments in order to find out the combustion environment temperature in a boiler ranging from 1000 to 1600 °C affecting total NO transient release, as well as thermal NO transient release characteristics under the condition of fast heating. The results show, with the combustion environment temperature increasing, NO generates gradually in advance, the peak of NO appears earlier, and the peak value of NO increases. The effect of the combustion environment temperature on NO release amounts of per unit mass coal samples exhibited the change trend o...

A Comparison of Combustion of Coal Chars in O2/CO2 and O2/N2 Mixtures - Isothermal TGA Studies

Two chars prepared from parent coals of a high volatile bituminous coal and an anthracite coal were subjected to isothermal combustion tests in a thermogravimetric analyser (TGA). The chars were burned in mixtures of O2/CO2 and O2/N2 with O2 concentrations of 3%, 6%, 10%, 21% and 30% and combustion temperature ranging from 723 K to 1163 K. Experimental results show that replacing the inert nitrogen gas in the oxidizer with CO2 has little influence on the measured reactivity of coal chars under conditions of the experiments. The measured reactivity of each char was found to be approximately first order (0.88 – 0.90) to the concentration of O2 in the O2/CO2 mixtures. As char combustion tests were conducted under relatively high temperatures conditions, internal and external effectiveness factors were estimated in order to derive combustion kinetics of both chars. The values of activation energy for both chars, obtained by taking account of both the internal and external effectiveness factors (i.e. with correction), were very much in line with the literature data. The activation energy of the bituminous coal char combustion in O2/CO2 was found to be 96323 (without correction) – 108893 (with correction) kJ/kmol within the temperature range of 723 – 873 K, whereas the activation energy of the anthracite char was found to be 125716 (without correction) – 140486 (with correction) kJ/kmol within the temperature range of 773 – 973 K.

Pyrolysis and combustion kinetics of Fosterton oil using thermogravimetric analysis

Thermogravimetric analysis (TGA) was used to examine the thermal behavior of Fosterton oil mixed with reservoir sand. TGA experiments were performed in nitrogen and air atmospheres at the heating rate of 10 °C/min up to 800 °C. In this study, four sets of TGA runs were performed to examine the thermal behavior of Fosterton whole oil, and the coke sample derived from the whole oil. Similar to previous studies in the literature, we also observed low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO) in the non-isothermal combustion experiment. Higher activation energy values were obtained in reaction regions at higher temperatures. The mean activation energy for whole oil in nitrogen and air atmospheres was 33 and 126 kJ/mol, respectively. Fresh coke samples derived from whole oil were subjected to isothermal combustion at different temperatures from 375 to 500 °C. Arrhenius model was used to obtain the kinetic parameters from the TGA data. From the model, the Arrhenius parameters such as activation energy ( E = 127 kJ/mol) and the pre-exponential factor ( A = 1.6 × 10 8/min) were determined for the coke combustion. The results showed a close agreement between the kinetic model and experimental data for different combustion temperatures. It was observed that the apparent order of combustion reaction for different temperatures approach unity.

Travelling waves of auto-catalytic chemical reaction of general order—An elliptic approach

In this paper we study the existence and non-existence of travelling wave to parabolic system of the form a t = a x x − a f ( b ) , b t = D b x x + a f ( b ) , with f a degenerate nonlinearity. In the context of an auto-catalytic chemical reaction, a is the density of a chemical species called reactant A, b that of another chemical species B called auto-catalyst, and D = D B / D A > 0 is the ratio of diffusion coefficients, D B of B and D A of A, respectively. Such a system also arises from isothermal combustion. The nonlinearity is called degenerate, since f ( 0 ) = f ′ ( 0 ) = 0 . One case of interest in this article is the propagating wave fronts in an isothermal auto-catalytic chemical reaction of order n : A + n B → ( n + 1 ) B with 1 < n < 2 , and D ≠ 1 due to different molecular weights and/or sizes of A and B. The resulting nonlinearity is f ( b ) = b n . Explicit bounds v ∗ and v ∗ that depend on D are derived such that there is a unique travelling wave of every speed v ⩾ v ∗ and there does not exist any travelling wave of speed v < v ∗ . New to the literature, it is shown that v ∗ ∝ v ∗ ∝ D when D < 1 . Furthermore, when D > 1 , it is shown rigorously that there exists a v min such that there is a travelling wave of speed v if and only if v ⩾ v min . Estimates on v min improve significantly that of early works. Another case in which two different orders of isothermal auto-catalytic chemical reactions are involved is also studied with interesting new results proved.

Investigation of sulfur forms and transformation during the co-combustion of sewage sludge and coal using X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to investigate the characteristics and evolution of sulfur (S) in mixtures of bituminous coal and sewage sludge (SS) and their chars during isothermal combustion. Five groups of mixtures with SS content of 0%, 10%, 20%, 30% and 100%, were examined at different burn-off ratios ( β) of 0, 30%, 50%, 70% and 100%. The S in the coal mainly exist as the forms of mercaptan (S1), sulfide (S2), thiophene (S3), sulfoxide (S4), sulfone (S5) and sulfate (S6). During the coal combustion process, the content of S1 and S2 decreased, while that of S3 and S5 increased in the early stage and decreased in the late stage. The S4 content increased throughout the entire process of combustion. Small amount of S6 was detected, showing a fluctuated pattern. The trend of S1, S2, S5 and S6 in SS was alike with that in coal, whereas S4 decreased at the end of combustion. The changing process of S3 in SS was opposite to that of coal, while the composition of S in the mixtures resulted from the mixing of coal and SS. The transformation of each functional group during co-combustion were correlated with their transformation characteristics during the mono-combustion of coal and SS, and no obvious interaction was observed, which demonstrated that the coal-origin and SS-origin sulfur in mixtures kept their own characteristics in the combustion. SS may accumulate on the solid surface as α increase, resulting its significant influence on the evolution of each form of S. When α was low, most of the S-contained functional groups presented the characteristics of coal. The percentage of coal-origin functional groups declined as α increased. The transforming trends of most functional groups were similar with that of SS when α reached 30%.

Thermodynamic properties of pentaphenylantimony Ph 5Sb over the range from T → 0 K to 400 K

In the present research, the temperature dependence of the heat capacity C p ,m ∘ = f ( T ) of pentaphenylantimony Ph 5Sb has been measured between T = (6 and 350) K in the precision adiabatic vacuum calorimeter and from T = (327 to 415) K in the differential scanning calorimeter and reported for the first time. The melting of the sample has been observed within the above temperature range. The melting was accompanied by partial compound decomposition. The experimental results have been used to calculate the standard ( p ∘ = 0.1 MPa) thermodynamic functions C p ,m ∘ / R , Δ 0 T H m ∘ / RT , Δ 0 T S m ∘ / R , and Φ m ∘ / R = Δ 0 T S m ∘ / R - Δ 0 T H m ∘ / RT (where R is the universal gas constant) of crystalline Ph 5Sb over the range from T → 0 K to 400 K. The energy of combustion of the compound under study has been determined in the isothermal combustion calorimeter with a stationary bomb. The standard thermodynamic functions of crystalline Ph 5Sb formation at T = 298.15 K have been calculated.

A Simple Kinetic Model for Coke Combustion During an In-Situ Combustion (ISC) Process

Abstract Although coke combustion studies have long been conducted, the literature is still lacking an accurate understanding of reaction kinetics. To this end, the thermo-oxidative behaviours of Neilburg oil and its asphaltene fraction were examined in the presence of core sand. Thermo gravimetric analysis (TGA) was performed in a flowing atmosphere at the heating rate of 10 °C/min up to 750 °C. Both nitrogen and air were used at a flow rate of 45 ml/min in the experiments. As earlier researchers have observed, at least two main regions of reactions were identified by the thermo gravimetric (TG) and derivative thermo gravimetric (DTG) thermo grams. Various effects, including distillation, low-temperature oxidation (LTO), thermal cracking, middle-temperature oxidation (MTO), high-temperature oxidation (HTO) or combustion, and even mineral decomposition, were observed. In this study, Neilburg oil and asphaltenes were completely cracked in a nitrogen atmosphere at 425 ° C to produce coke. Subsequently, the fresh coke was subjected to isothermal combustion at several temperatures from 374 °C to 519 °C. A two-step oxidation reaction model was applied to describe this combustion process. The chemical reactions were simplified into two oxidations occurring in series. In the first reaction, coke was partially oxidized to form an intermediate product, which was then burned in the second reaction. Based on the TGA data, kinetic parameters were estimated with the aid of custom written software. For comparison, the one-step oxidation reaction model was also employed to predict the combustion process. The two-step oxidation reaction model gave a better fit to the experimental data. It was also confirmed that the coke derived from the Neilburg asphaltenes is reasonably representative of the coke derived from the whole oil. Introduction It has long been recognized that in situ combustion (ISC) might be a potentially effective enhanced oil recovery (EOR) technique, particularly suitable for medium and heavy crude oil-bearing reservoirs, as well as for steam depleted reservoirs. However, the fact that the fundamental reaction mechanisms of the ISC process have not been completely understood makes its field performance prediction unreliable. It is generally believed that there are three major reactions during an ISC process: thermal cracking, low temperature oxidation (LTO) and high temperature oxidation (HTO). Thermal cracking of crude oil, including visbreaking and coking, produces a solid residue on the surface of the reservoir sand grains. The solid residue, or so-called coke, is consumed as the fuel for combustion. LTO reactions, which are typically heterogeneous reactions between the gas and condensed phases, involve the formation of oxygenated hydrocarbons. During an ISC process, LTO is possible if oxygen is present ahead of the combustion front, either due to the oxygen flux being relatively high or due to bypassing of the front by some of the injected oxygen(1). HTO is the heterogeneous (gas-solid) reactions that consume the coke deposited by thermal cracking to produce carbon oxides and water. Some efforts to investigate the oxidation reaction mechanisms during ISC can be found in the literature. An early extensive study was carried out by Dart et al.(2) who tested the combustion rate for oxidation of carbonaceous residues on clay catalyst pellets.

Controlling low-pressure flame conditions by affecting the cold service lines located far from the heated reactor

A study was performed of a low-pressure oxyhydrogen flame in an isothermal regime in the diffusion-controlled region of heterogeneous chain termination. The chain propagation and termination sites were widely separated in space. Controlling the chain loss conditions made it possible to carry out isothermal combustion of the mixture in the diffusion-controlled region and to verify the proposition of the Semenov theory that the propagation of a chain explosion in time near the limit can be described by a linear model. From a comparison of calculated and experimental data, gas-surface interaction with a variable rate constant was found and the range of variation of this constant during one ignition was determined. The large differences between the kinetic curves obtained previously for various modes of chain termination on the wall were found to be related primarily to heterogeneous chain interaction, which governs the gas-phase process in the kinetic region and has a weak effect on this process in the diffusion-controlled region of chain termination.

Explosion limits and runaway criteria: A stretching-based approach

Temperature and concentration evolution in a spatially homogeneous reacting system is described by a dynamical system characterized by a vector field accounting for reaction rates and heat exchange with the surroundings in a lumped way. This article addresses the estimate of the explosion limits and the assessment of runaway criteria in batch reacting systems by focusing on the evolution of the stretching rates along system trajectories. The stretching-based runaway criteria are applied in archetypal systems, such as the Semenov model, and compared with classical sensitivity-based criteria and with other detection methods derived from dynamical system theory. Several other examples are thoroughly addressed, including an isothermal combustion model (the chain-branching model) and the explosion limits in the H 2 – O 2 system.

The influence of thermal annealing on oxygen uptake and combustion rates of a bituminous coal char

The effect of thermal annealing on the combustion reactivity of a bituminous coal char has been investigated with a focus on the role of the formation of surface oxides by oxygen chemisorption. The combined use of thermogravimetric analysis and of analysis of the off-gas during isothermal combustion of char samples enabled the determination of the rate and extent of oxygen uptake along burn-off. Combustion was carried out at temperatures between 350 and 510 °C. Char samples were prepared by controlled isothermal heat treatment of coal for different times (in the range between 1 s and 30 min) at different temperatures (in the range 900–2000 °C). Results indicate that oxygen uptake is extensive along burn off of chars prepared under mild heat treatment conditions. The maximum oxygen uptake is barely affected by the combustion temperature within the range of combustion conditions investigated. The severity of heat treatment has a pronounced effect on char combustion rate as well as on the extent and rate at which surface oxides are built up by oxygen chemisorption. Chars prepared under severe heat treatment conditions show negligible oxygen uptake and strongly reduced combustion rates. Altogether it appears that a close correlation can be established between the extent and the accessibility of active sites on the carbon surface and the combustion rate. Despite the investigation has been carried out at temperatures well below those of practical interest, results provide useful insight into the relationship existing between thermal annealing, formation of surface oxide and combustion reactivity which is relevant to the proper formulation of detailed kinetic models of char combustion.

Thermogravimetric Studies on Pyrolysis and Combustion Behavior of a Heavy Oil and Its Asphaltenes

A thermogravimetric analyzer (TGA) was used to obtain information on the pyrolysis and combustion behavior of both crude oil (Neilburg) and its asphaltenes, each mixed with reservoir sand. Of all the saturate, aromatic, resin, and asphaltene fractions, asphaltenes contribute the most to the formation of coke (fuel). Temperature-ramped as well as the isothermal pyrolysis experiments on whole oil and asphaltenes were analyzed to determine the temperature at which coke formation was maximized. Furthermore, isothermal combustion curves for coke derived from whole oil and asphaltenes were obtained to provide reliable data for calculating the kinetics of the reactions. The classical Arrhenius model was applied, and the activation energy for the combustion of coke formed from pure asphaltenes and from the whole oil was calculated. The results showed that the Arrhenius model fitted the data well in the entire range of temperatures the experiments were conducted. The source material for the coke led to modest differences in its reactivity. The observed activation energy for asphaltenes was 117.7 kJ/mol, and for the whole oil it was 129.5 kJ/mol, which indicates that they were in close agreement. Also, the combustion of coke from asphaltenes showed a reaction order of 0.4 at 375°C, which gradually increased to 0.9 at 525°C. For whole oil, it increased from 0.5 at 375°C to 0.7 at 500°C.