Combustion Experiments Research Articles

Numerical Prediction and Experimental Validation of the Low-temperature Oxidation Characteristics of Coal in a Large-scale Furnace in an Adiabatic Environment

ABSTRACT It is of great significance to study the characteristics of low-temperature oxidation of coal in an adiabatic environment for the prediction and control of coal spontaneous combustion. Coal spontaneous combustion experimentation can better simulate the field conditions and reflect and test the actual process underlying the spontaneous combustion of coal. Numerical simulation methods can provide a systematic solution for research on the dynamic evolution process of coal spontaneous combustion. In this study, a large-scale coal spontaneous combustion test bench was employed to test the oxidation heating characteristics and gas generation laws of Huangling coal samples from 303–443 K, revealing the spatiotemporal evolution characteristics of the gas concentration and temperature fields. Based on the theory of computational fluid dynamics (CFD), a mathematical model of the spontaneous combustion of coal in the adiabatic state is therefore constructed. The evolution law and distribution characteristics of the temperature and gas concentration fields of coal in the experimental furnace are simulated by Fluent. The results indicate that the position of the highest coal temperature in the experimental furnace mainly changed along the central axis and gradually moved down toward the air inlet as the coal temperature continued to rise. Above the critical temperature (353 K), the high-temperature point mobility was high, and only one-tenth of the ignition period could be utilized to travel along with more than one-third of the original distance from the intake side. In the furnace, O2, CO, and CO2 were distributed in the upper and lower layers at different concentration values. The concentration of O2 gradually decreased from the inlet side along the gas flow direction, but the concentrations of CO and CO2 demonstrated the opposite behavior. When the temperature exceeded 120°C, the consumption of O2 and the production of CO and CO2 gases were mainly distributed in the furnace body below 0.65 m. The simulation results are in line satisfactorily with the experimental results. This study provides theoretical support for field index gas and three zone division. The development of the model can improve the existing theory of coal spontaneous combustion and find a more systematic and reasonable criterion for judging coal spontaneous combustion.

NNH mechanism in low-NOx hydrogen combustion: Experimental and numerical analysis of formation pathways

The role of the NNH mechanism in NOx formation is investigated using an atmospheric-pressure jet-stirred reactor (JSR). Two sets of hydrogen combustion experiments are performed over a range of fuel–air equivalence ratios (ϕ = 0.8–1.3). Each experimental series uses a different diluent to maintain the temperature of the JSR recirculation zone while varying the fuel–air equivalence ratio. Nitrogen and argon were used as diluents to control the reactor temperature at 1635 K and 1525 K, respectively. In the fuel-lean region, the NOx increases with the fuel–air ratio until the stoichiometric condition (ϕ = 1) is reached, and then decreases in the fuel-rich region with a further increase in the equivalence ratio. A 2D axisymmetric CFD model is used to examine temperature and species distribution in the JSR and to guide the choice of chemical reactor network (CRN). The CFD modeling shows the NNH is formed in the flame brush for all ϕ, the region of high NNH concentration spreads into the recirculation zone for the fuel-rich conditions. Three different CRN schemes are evaluated to model NOx formation. The nitrogen chemistry of Klippenstein et al. (2011) and Glarborg et al. (2018) show the best agreement with the NOx data. The CRN analysis suggests that NNH is the main contributor in the NOx formation during the fuel-rich combustion. For the fuel-lean conditions, the contribution from the nitrous oxide mechanism is significant.

Modeling Low Intensity Fires: Lessons Learned from 2012 RxCADRE

Coupled fire-atmosphere models are increasingly being used to study low-intensity fires, such as those that are used in prescribed fire applications. Thus, the need arises to evaluate these models for their ability to accurately represent fire spread in marginal burning conditions. In this study, wind and fuel data collected during the Prescribed Fire Combustion and Atmospheric Dynamics Research Experiments (RxCADRE) fire campaign were used to generate initial and boundary conditions for coupled fire-atmosphere simulations. We present a novel method to obtain fuels representation at the model grid scale using a combination of imagery, machine learning, and field sampling. Several methods to generate wind input conditions for the model from eight different anemometer measurements are explored. We find a strong sensitivity of fire outcomes to wind inputs. This result highlights the critical need to include variable wind fields as inputs in modeling marginal fire conditions. This work highlights the complexities of comparing physics-based model results against observations, which are more acute in marginal burning conditions, where stronger sensitivities to local variability in wind and fuels drive fire outcomes.

Combustion of distillery sludge mixed with coal in a drop tube furnace and emission characteristics

Co-combustion of coal with distillery sludge waste (DSW) was investigated in a laboratory-scale Drop Tube Furnace (DTF) plant. This study examined the feasibility of combustion of sludge with coal using preliminary testing methods, such as thermogravimetric, ultimate and proximate analysis followed by combustion experiments. These methods helped to identify burnout efficiency, emitted pollutants, and metal constituents in the bottom/fly ash. The ratios of coal to DSW in the feed was 90:10%, 95:5%, 98:2% and 100:0% by dry weight basis. The vibrator feeder and airflow rate were set at the rate of 1.5 kg/h and 150 L/min with slightly negative pressure. The concentration of gases (i.e. nitrogen oxides (NOx), sulphur dioxide (SO2), carbon mono-oxide (CO), hydrocarbon (HC)) and particulate matter (PM) on DSW combustion was measured and compared with the combustion of coal. The pattern of gaseous emission and combustion efficiency showed high degree linear combinations through Pearson’s correlation coefficient. The decrease in the concentration of PM (76.67 ± 10.41 mg/m3 to 91.33 ± 17.62 mg/m3) and SO2 (444 ± 20.63 mg/m3 to 156.60 ± 12.26 mg/m3), increase in the concentration of NOx (136 ± 15.41 mg/m3 to 387 ± 15.2 mg/m3) and CO (26.15 ± 5.36 mg/m3 to 824.32 ± 43.70 mg/m3), unburnt carbon percentage in the fly ash, and clinker formation were taken into account to optimum the sludge proportion in the DTF under a given set of combustion conditions. Most importantly, an increase in sludge quantity (i.e. 2%, 5%, and 10%) showed a decrease in the burnout efficiency (98.41%, 95.91%, and 92.6%, respectively).

Copper Oxide Spectral Emission Detection in Chalcopyrite and Copper Concentrate Combustion

In this research, the spectral detection of copper oxide is reported from different combustion tests of chalcopyrite particles and copper concentrates. Combustion experiments were performed in a bench reactor. In all the tests, the radiation emitted from the sulfide particle reactions was captured in the VIS–NIR range. The obtained spectral data were processed by using the airPLS (adaptive iteratively reweighted penalized least squares) algorithm to remove their baseline, and principal component analysis (PCA) and the multivariate curve resolution method alternate least squares (MCR-ALS) methods were applied to identify the emission lines or spectral bands of copper oxides. The extracted spectral pattern is directly correlated with the emission profile reported in the literature, evidencing the potential of using spectral analysis techniques on copper sulfide combustion spectra.

Experimental study of volatile organic compounds catalytic combustion on Cu‐Mn catalysts with different carriers

Catalytic combustion is an effective way for volatile organic compounds harmless treatment. In this paper, the synergism between non-noble metal active phase Cu-Mn and Y-zeolite, SiO2, γ-Al2O3, and TiO2 was studied by catalytic combustion experiments and corresponding characterizations; the conclusions as following: Cu-Mn/SiO2 has the best activity and stability, T10 and T90 are 210°C and 298°C, respectively. Benzene can be completely oxidized below 300°C, which is due to the formation of substantial Cu-Mn solid solutions and a large number of Cu2+/Mn3+ ions on the surface of SiO2. The activation energy of C6H6 in CuMn2/TiO2 is 95.50 kJ/mol, while that of the other three catalysts is close, probably 60 kJ/mol. Moreover, the stability of SiO2 is the highest and can be maintained for more than 60 hours. The fundamental reason of catalyst deactivation is the higher diffusion resistance on the surface of the catalyst with small pore size distribution and the lack of surface oxygen, which leads to the lower degree of complete oxidation of C6H6.

A Model for Predicting Arsenic Volatilization during Coal Combustion Based on the Ash Fusion Temperature and Coal Characteristic

Arsenic emission from coal combustion power plants has attracted increasing attention due to its high toxicity. In this study, it was found that there was a close relationship between the ash fusion temperature (AFT) and arsenic distribution based on the thermodynamic equilibrium calculation. In addition to the AFT, coal characteristics and combustion temperature also considerably affected the distribution and morphology of arsenic during coal combustion. Thus, an arsenic volatilization model based on the AFT, coal type, and combustion temperature during coal combustion was developed. To test the accuracy of the model, blending coal combustion experiments were carried out. The experimental results and published data proved that the developed arsenic volatilization model can accurately predict arsenic emission during co-combustion, and the errors of the predicted value for bituminous and lignite were 2.3–9.8%, with the exception of JingLong (JL) coal when combusted at 1500 °C.

Study of pyrolysis and combustion kinetics of oil sludge

ABSTRACT In order to deal with the shortage of oil and natural gas, the supplement energies, such as oil sludge, waste plastics, waste rubber needed to be studied. The pyrolysis and combustion methods have advantages when they are chosen to treat oil sludge. The investigation of kinetics is significantly important to know the kinetic parameters and the reaction mechanisms and to provide important theoretical basis for the process design of pyrolysis and combustion to treat oil sludge. Most previous studies on pyrolysis and combustion kinetics of oil sludge regarded pyrolysis process or combustion process, and rarely split pyrolysis or combustion process to calculate kinetic parameters separately. In this work, the experiment of pyrolysis and combustion were carried out by thermal gravimetric analyzer. After splitting the pyrolysis and combustion processes into two stages, respectively, the methods of Coats-Redfern and distributed activation energy model (DAEM) were used to calculate the kinetic parameters. Based on the results of thermogravimetric analysis, the pyrolysis and combustion process can be divided into two stages. For the pyrolysis process, the first stage is mainly with the evolution of adsorbed volatile hydrocarbon and the rupture of weaker chemical bond and the second stage is the cracking of organic macromolecules. Meanwhile, in the first stage of combustion process, small molecular organic matter in dry basis oil sludge will volatilize and then burn on the surface of the crucible and the gas phase outside the crucible, and in the second stage, macromolecular organic matter will volatilize, pyrolyze and burn, and the diffusion of oxygen into the crucible will cause the fixed carbon to burn. According to the kinetic results of the pyrolysis process, the activation energy of the first stage calculated by the Coats-Redfern model are all less than 40 kJ/mol, and that of the second stage increases from 148.14 kJ/mol to 184.97 kJ/mol with the increase of the heating rate. The results of DAEM model show that with the increase of the conversion rate, the activation energy of the first stage increases from 60.82 kJ/mol to 81.05 kJ/mol, and that of the second stage increases from 120.60 kJ/mol to 237.07 kJ/mol. For the combustion process, the activation energy calculated using Coats-Redfern model decreases from 120.18 kJ/mol to 73.48 kJ/mol in the first stage, and that of the second stage is relatively low. The results of DAEM model show that with the increase of the conversion rate, the activation energy decreases from 129.53 kJ/mol to 62.36 kJ/mol in the first stage and that in the second stage is stable at about 70 kJ/mol.

Analysis of Noisy Radiometer Data from ISS Reduced Gravity Droplet Combustion Experiments

Reduced gravity droplet combustion experiments were performed on the International Space Station (ISS). The data from these droplet combustion experiments have been made publicly available by NASA. These experiments utilized narrow-band and wide-band radiometers to measure thermal radiation heat fluxes from flames. The initial set of radiometers, which were used in 80 experiments, exhibited large noise levels, making interpretation of data from these experiments difficult. The noisy radiometers were replaced by NASA with a second set of radiometers that had significantly less noise. The work presented here is focused on: (1) evaluating methods to “denoise” the data from the initial (noisy) set of radiometers with a goal of detecting flame oscillations; and (2) making these denoising methods available to other researchers who would like to analyze the noisy radiometer data. The denoising efforts employed local polynomial regression analysis with a Gaussian kernel as well as frequency-based low-pass filters. Windowed Fourier transform and wavelet transform approaches were also employed to detect flame oscillations in radiometer data. Comparison of results from these approaches showed that local polynomial analyses and also wavelet transforms can detect the presence of flame oscillations in noisy radiometer data. Uncertainties in the noisy radiometer data were evaluated using a Monte Carlo bootstrapping approach.

Evaluation of Hybrid Rocket Fuel Grain with a Star Fractal Port Using Combustion Experiments

Evaluation of Hybrid Rocket Fuel Grain with a Star Fractal Port Using Combustion Experiments

Impacts of Torrefaction on PM10 Emissions from Biomass Combustion

Typical biomass torrefaction is a mild pyrolysis process under conditions of ordinary pressure, low temperature (200–300°C) and inert atmosphere. Torrefaction is considered to be a competitive technology for biomass pretreatment, but its impacts on the emissions of particulate matter from biomass combustion are worthy of further study. In this paper, three kinds of biomass, i.e., bagasse, wheat straw and sawdust were selected for torrefaction pretreatment and the impacts of torrefaction on the emission characteristics of PM10 from biomass combustion were investigated. The combustion experiments were carried out on a drop tube furnace. The combustion-generated particulate and bulk ash samples were collected and subjected to analyses by various techniques. The results show that torrefaction tends to result in a reduction of PM1 (particulates with an aerodynamic diameter less than 1 μm) emissions from combustion, but the extent of reduction is dependent on biomass type. The reduction of PM1 from the combustion of torrefied biomass is mainly because that the torrefaction process removes some Cl and S from the biomass, thereby suppressing the release of alkali metals and the emissions of PM1 during the combustion process. As for PM1–10 (particulates with an aerodynamic diameter within 1–10 μm), its emissions from combustion of torrefied biomasses are consistently reduced, compared with their untreated counterparts. This observation is primarily accounted for the enhanced particle coalescence/agglomeration in combustion of torrefied biomasses, which reduces the emissions of PM1–10.

Investigation on Structure and Reactivity of Demineralized Coal Under Pressurized O <sub>2</sub>/H <sub>2</sub>O Conditions

Pressure strongly affects the pyrolysis of coal and the subsequent combustion process. In this paper, a pressurized horizontal furnace was used to conduct pyrolysis experiments of demineralized coal at 1000 ℃ under different pressure (0.1-1.5 MPa). And then use pyrolysis char as the initial experimental sample, a combustion experiment at 1000 ℃ with 10 vol% of O2 and 25 vol% of H2O was performed at corresponding pyrolysis pressure. Using N2 adsorption, Raman and X-ray Photoelectron Spectroscopy (XPS) test methods, the changes of carbon conversion and pore structure, carbon skeleton structure and surface functional group structure of different pressure pyrolysis char and its combustion residual char were obtained. A micro fluidized bed reaction analyzer was then used to test the reactivity of char to explore the influence of pressure on the reactivity of char. Pressure can increase the yield of pyrolysis char and promote the conversion of char in O2/H2O conditions. For the pore structure of char, pressure and O2/H2O atmosphere have a positive promotion effect, and have a similar effect on the chemical structure of char. And for the reactivity of char prepared in O2/H2O combustion, the pore structure is dominant.

Numerical investigation on combustion and NOx emissions of a CH4 / kerosene afterburner

Cogeneration groups equipped with gas turbines usually operate with natural gas. The new requirements regarding the flexibility of functioning both with conventional and alternative fuels have led to the development of new solutions. An afterburning installation facilities, on the one hand, the combustion of fuels which can not normally be used in gas turbines, and on the other hand, allows a rapid adaptation of the cogeneration group to the user's variable thermal energy requirements. In some cases, an afterburning installation may contribute to the reduction of NOx emissions. It also increases the group's adaptability to changing environmental conditions, especially during the summer. Having in mind these tendencies and starting from the data collected from the 2xST 18 – Suplacu de Barcau cogeneration plant, this paper presents a numerical analysis of an afterburner in order to switch from natural gas to natural gas / kerosene functioning, with minimal modifications to the existing solution. A 3D steady RANS numerical integration of the Navier-Stokes equations has been carried out using the commercial software ANSYS CFX. For future research work, it will be taken into consideration the use of more complex reaction mechanisms and the variation of the spray angle will be considered. Also, in order to validate the CFD results a combustion experiments campaign will be conducted.

Heat of Combustion Experiment Based on the Ratio of Moisture Content of Infected and Non-Infected Bursaphelenchus Xylophilus

Heat of Combustion Experiment Based on the Ratio of Moisture Content of Infected and Non-Infected Bursaphelenchus Xylophilus

Experimental investigation of the emission behaviour and flame stability of the oxygen and hydrogen enriched methane under acoustic enforcement

The instability changes of oxygen-enriched fuel mixtures under acoustic enforcement in a premixed and swirl supported system were investigated in this study. Different amounts of hydrogen (0%, 10%, 20%) were added to methane used as fuel and oxygen enrichment process (21%, 24%, 26%) was applied in hydrogen-added fuel mixtures. The equivalence ratio was kept constant at 0.7 in experiments conducted under constant burner power and swirl support. Experiments showed that although oxygen enrichment up to 24% ratio increases stability by increasing the laminar flame speed, stability decreases when the oxygen content in the oxidizer was increased to 26%. As a result of increasing both hydrogen ratio in fuel mixture and oxygen enrichment, instabilities grow up with decreasing of Markstein length. In this situation, burning in combustion chamber did not continue under acoustic force. According to the emission values taken during combustion experiments, the addition of oxygen increased NOx emissions due to increased adiabatic temperature and sudden NOx formations, while contributing to the reduction of CO emissions. Although the addition of hydrogen reduces NOx emissions in case of combustion with air (%21 O2), it has increased the CO emissions from 2 ppm to 13 ppm because it triggers instabilities when combined with oxygen enrichment.

Heterogeneous reaction and homogeneous flame coupled combustion behavior of n-decane in a partially packed catalytic bed combustor

The premixed combustion experiments of n-decane were conducted in micro-combustors. The characteristics and mechanism of three combustion modes were studied: homogeneous combustion (HMC), heterogeneous combustion (HTC), and coupled combustion (CC) with both HTC and HMC. The homogeneous flame in CC cases can be established downstream of catalytic bed. The stable combustion range of CC is near the stoichiometric ratio, and the lean/rich limits of equivalence ratio (Φ) are close to the lean limit of the HMC and the rich limit of the HTC respectively. The HTC cases show high CO2 selectivity, and CO2 is the major products even at Φ > 1. The different mechanisms of O2 and n-decane adsorption on the Pt active site have significant effects on the stable limits of HTC. Hot flame in the fire core is followed by warm flame in the HMC cases. When Φ > 0.9, n-decane can’t burn out in so small hot flame that the effect of warm flame becomes obvious, resulting in some combustible species being generated in products. CO becomes the main product instead of CO2 in the HMC cases, when Φ > 1.6. In the CC cases, high n-decane conversion owes to the coupling of homogeneous flame and heterogeneous reaction. The homogeneous flame presents warm flame properties at Φ = 1.3 ~ 1.4, and hot flame properties at Φ = 1. More importantly, compared with HMC and HTC, much longer combustion zone achieved in CC with more even distribution of wall temperature and without obvious hot spots, which is significative to actual applications like the thermo-photovoltaic system.

Experimental and numerical study on measuring solid-propellant pressure-coupled response using an improved rotary valve

A small-scale experimental burner with an improved rotary valve has been designed to measure solid-propellant pressure-coupled response for mean pressures on the order of 2.2–2.9 MPa and oscillating frequencies of 23–161 Hz, within 9% amplitudes. This paper proposes an indirect method for measuring the instantaneous valve area and phase delay angle based on a circular grating system and a corresponding mathematical model, and the validity of which is confirmed by several cold-gas experiments and numerical simulations. The effects of frequency on oscillating pressure, exhaust mass flow rate and pressure-coupled response are studied by carrying out several hot-gas experiments and numerical simulations. The results show that the mean pressure is not affected by the oscillating frequency and maintains at 2.9 MPa. The exhaust mass flow rate of the rotary valve is determined by the instantaneous valve area and independent of frequency. The peak-to-peak pressure is inversely proportional to the oscillating frequency, reducing from 0.539 MPa at 23 Hz to 0.053 MPa at 161 Hz. The magnitude of pressure-coupled response appears to be constant (0.8) at 23–161 Hz, with pressure oscillations lagging instantaneous valve area by 0.504π-0.531π。The study is expected to benefit research on similar rotary valves and can serve as a basis for measuring the solid-propellant pressure combustion response.

Effect of Thermal Exposure on Oil Shale Saturation and Reservoir Properties

The experimental and numerical modeling of thermal enhanced oil recovery (EOR) requires a detailed laboratory analysis of core properties influenced by thermal exposure. To acquire the robust knowledge on the change in rock saturation and reservoir properties, the fastest way is to examine the rock samples before and after combustion. In the current paper, we studied the shale rock properties, such as core saturation, porosity, and permeability, organic matter content of the rock caused by the combustion front propagation within the experimental modeling of the high-pressure air injection. The study was conducted on Bazhenov shale formation rock samples. We reported the results on porosity and permeability evolution, which was obtained by the gas pressure-decay technique. The measurements revealed a significant increase of porosity (on average, for 9 abs. % of porosity) and permeability (on average, for 1 mD) of core samples after the combustion tube experiment. The scanning electron microscopy showed the changes induced by thermal exposure: the transformation of organic matter with and the formation of new voids and micro and nanofractures in the mineral matrix. Low-field Nuclear Magnetic Resonance (NMR) was chosen as a primary non-disruptive tool for measuring the saturation of core samples in ambient conditions. NMR T1–T2 maps were interpreted to determine the rock fluid categories (bitumen and adsorbed oil, structural and adsorbed water, and mobile oil) before and after the combustion experiment. Changes in the distribution of organic matter within the core sample were examined using 2D Rock-Eval pyrolysis technique. Results demonstrated the relatively uniform distribution of OM inside the core plugs after the combustion.

Measurements of pressure broadening of N2 in the anisotropic tensor component of spontaneous Raman spectra

Spontaneous Raman scattering from nitrogen is well-suited for temperature measurements in combustion experiments, especially at high pressure which increases the Raman signal because of the higher density in the measurement volume. In this work we investigate high density effects on the anisotropic tensor component of ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate thermometry in high pressure gases using high-fidelity Raman simulations. We measure the collision broadening for the anisotropic component of spontaneous Raman scattering from room temperature nitrogen over the pressure range 10–70 atm for three gas compositions: pure nitrogen, air, and nitrogen in argon. Line broadening coefficients inferred from these measurements were found to be 14 ± 5% larger than the corresponding broadening coefficients of the isotropic Q branch. Air broadening coefficients were found to be very similar and about 2.5% smaller than nitrogen self-broadening coefficients. Argon broadening coefficients were 25% smaller at rotational quantum number 7 and about 50% smaller at rotational quantum number 21. Additionally, we found that our unmixed line model for the O and S branches gave good fits for all pressures, which indicates that line mixing effects are not significant in the O and S branches over this range of pressures. Using indirect experimental evidence we infer that line mixing effects in the anisotropic component of the Q branch were below the threshold set by our experimental spectral resolution at pressures up to 70 atm at room temperature. Assuming that the anisotropic Q branch lines mix like the isotropic lines results in a small systematic error in the inferred temperature at flame temperatures, with the error increasing slowly with pressure. The bias can be easily removed by modeling the anisotropic spectrum separately from the isotropic spectrum. Line mixing effects should be included in the model of the isotropic part of the Raman spectrum, but can probably be neglected in the anisotropic part of the spontaneous Raman spectrum of N 2 for pressures below 400 atm at flame temperatures.

Combustion of bituminous coal and semicoke with copper salts

This paper examines combustion of coal and semicoke modified by 5 wt% of Cu(NO3)2, CuSO4 and Cu(CH3COO)2. The additives were introduced using the wet impregnation method. Ignition and combustion experiments were performed in a combustion chamber at temperatures of the heating medium varying from 500 °C to 700 °C. The gas-phase combustion products were analyzed using an in-line gas analyzer. It was found that, on average, the use of activating additives contributed to a reduction of the ignition delay time by 1.8 times and a decrease in the minimum ignition temperature by 54–135 °C. An increase in the heating medium temperature resulted in a significant ignition delay decrease (by ~270%). The maximum difference in the ignition delay time between the reference sample and the modified coal (3.4 s) and semicoke (10.4 s) samples was observed at 500°С while using copper nitrate. In the initial stage of combustion, formation of micro-explosions on the samples modified with copper nitrate and acetate was observed. The use of additives contributed to reducing the content of unburnt carbon in the fuel. Addition of copper salts resulted in a significant reduction in the CO production volume and better fuel oxidation to CO2.