Release Of Volatile Matter Research Articles

Characterisation of coal blends for pulverised fuel combustion

This study evaluates the effect of blending on the combustion characteristics of pulverised coal through the testing of six coals and fifteen coal blends in an isothermal plug flow reactor (IPFR). The aim of the test was to assess whether the combustion behaviour of blends could be predicted from that of the parent coals. For blends of bituminous coals, an additive behaviour was found for ash, volatile matter and calorific value. Other non-standard fuel properties such as the high volatile matter content determined using the IPFR, fuel-N release and char combustion, were found to be additive. The blends of bituminous coals and lignite demonstrated non-additive properties as far as volatile matter release is concerned. It was concluded that the inorganic coal phase is responsible for non-additive behaviour in blends, since the volatile components of the coal mineral matter may undergo reactions with the second blend partner.

Effect of pyrolysis temperature on composition, surface properties and thermal degradation rates of Brazil Nut shells

Changes in chemical and surface characteristics of Brazil Nut shells ( Bertholletia excelsa) due to pyrolysis at different temperatures (350°C, 600°C, 850°C) were examined. For this purpose, proximate and ultimate analyses, physical adsorption measurements of N 2 (−196°C) and CO 2 (25°C) as well as samples visualisation by scanning electronic microscopy (SEM) were performed. Appreciable differences in the residue characteristics, depending markedly on the pyrolysis temperature, were observed. Release of volatile matter led to the development of pores of different sizes. Progressive increases in micropore development with increasing pyrolysis temperature took place, whereas a maximum development of larger pores occurred at 600°C. Furthermore, kinetics measurements of Brazil Nut shells pyrolysis from ambient temperature up to 900°C were performed by non-isothermal thermogravimetric analysis. A model taking into account the significant changes in the residue during pyrolysis, through an increase in the activation energy with temperature and solid conversion, were found to properly fit the kinetics data over the wide range of degradation investigated.

An Experimental Study on the Combustion Characteristics of CWM Single Droplet

As the combustion process of CWM consists of the water evaporation, the release and combustion of volatile matter, and the combustion of char for every particle, it is more complex than that of existent liquid fuel. Though the many studies on CWM combustion have been carried out by the single droplet using hanging methods or the multiple droplet using atomization methods, any report don't presents definite solution about the effects by the initial water evaporation and combustion of volatile. When CWM is suddenly exposed in the high temperature surroundings, the internal water evaporates and then each droplet builds up pores. Besides, porosity rate changes along the temperature of surroundings, the composition ratio of CWM, and the initial diameter of droplet. In result, because it affects the whole combustion rate, the combustion of CWM has complex mechanism as compared with the combustion of liquid or gas fuel. Therefore, concentrating on porous structure of CWM, this study has proceeded to acquire the basic data on the CWM injection combustion and closely examines the effects of the first stage combustion on the whole combustion by measuring the diameter variations, pore rate, mass fraction burned, and the internal temperature changes of CWM droplet. The results demonstrate that of initial mass is reduced during water evaporation and volatile combustion period, and swelling rate, mass faction burned, and density variation are greatly concerned with atomization of CWM etc.

99/00692 Premixed turbulent flame instability and no formation in lean-burn swirl burner

A promising approach to decrease CO2 emissions from blast furnaces during ironmaking is to blow a reducing gas containing hydrogen into blast furnaces from their tuyeres. However, the combustion behavior of pulverized coal in the presence of a hydrogen-containing gas has not been elucidated. In this work, the combustion experiments of pulverized coal using a drop tube furnace were carried out to investigate the effect of H2 gas addition on the combustibility of pulverized coal. The combustion ratio of char particles in the presence of H2 gas (when introduced at a flow rate of 0.10 L/min) was larger than that in the absence of H2 gas. This is because of the enhanced release of volatile matter from coal and the combustion of char due to an increase in the temperature of the coal particles, which was caused by the drastic combustion of H2 gas. The combustion ratio of char particles when H2 gas was added at flow rates higher than 0.21 L/min was considerably smaller than that obtained when H2 gas was not added. It was found that the combustibility of coal was enhanced when an optimum H2 gas flow rate was used.

The laboratory identification of dangerously coking coals

Several coals, varying in the coking pressure they generate, were selected in order to study the coal properties influencing the escape of volatiles from carbonising coal charges. The aims of the work were to contribute to the understanding of the mechanism of internal gas pressure generation and to help identify dangerously coking coals. Volatile matter release rates from coal/sand mixtures and from packed coal beds were studied to assess whether gases could be trapped within fused coal beds. Also, the variation with temperature of the rate of volatile matter evolution and degree of Gieseler plasticity were compared to ascertain whether excessive pressures could be identified with high volatile release rates occurring when specific plastic properties were evident. It was found that the internal gas pressure generated by coals, when carbonised in a small double-wall oven, could be related to data obtained by plastometry and thermogravimetric analysis.

98/01340 Combustion characteristics of rice husk in fluidized beds: Liu, H. et al. Proc. Int. Conf. Fluid. Bed Combust., 1995, 13, (1), 615–618

Some characteristics of rice husk were studied such as the physical and chemical property, fluidization, slagging, agglomeration and pneumatic transportation properties. Chemical reaction kinetics of rice husk, much different from that of coals, was obtained on the basis of thermogravimetric experiments. Experiments were carried out with an accelerated surface area and porosimetry system to examine the microscopic structure change of rice husk and it was compared with that of coal. Combustion tests were performed on a fluidized bed combustor with a cross section of 0.2m by 0.2m. The concept of two-stage combustion of rice husk proposed is that the release of volatile matter and combustion of carbon takes place separately, which is different from that of coal. According to the combustion characteristics of rice husk, a new boiler design combining combustion styles and taking fluidized bed as the main component, is proposed. It has been licensed as a patent.

High-strength graphites for carbon piston applications

Recent studies have shown that carbon pistons are highly thermal-resistant in comparison to pistons made of aluminium alloys and can contribute to lower hydrocarbon (HC) emissions. A graphite piston material has to meet requirements which will be discussed in this paper. The near-net-shape manufacturing process is regarded as a cost-effective approach to producing carbon pistons. This process will be discussed in connection with results of our own material studies. The results include studies on forming, sintering and evaluation of mesophase carbon materials. The mechanical and physical properties of a crucible acting as a piston showed properties comparable to those of a commercial graphite block. Flexural strength of up to 116 MPa and a Weibull modulus m > 20 were found. The thermal conductivity was determined to be ca 105 W mK −1 with an open porosity of 10 vol%. The properties of the powder, the densification and the controlled release of volatile matter during the temperature treatment appear to be the key factors to achieve the high performance of the graphite. Further results are reported on the successful cold isostatic pressed piston blank with a completely reproduced near-net-shape inner contour.

Modelling of volatile product evolution in coal pyrolysis. The role of aerial oxidation

Non-isothermal thermogravimetry has been applied to study the pyrolysis behaviour of coal and its changes as a consequence of aerial oxidation. A mathematical model has been developed to calculate the kinetic parameters of the coal pyrolysis process, which takes into account three different groups of thermal decomposition reactions for fresh coal, and two groups for oxidised coals. The agreement between the model predictions, for any heating rate, and the experimental values was fairly good. The volatile matter release profile of fresh coal can be described using three stages: Stage I (250–475°C), mainly light species are liberated; Stage II (475-575°C), characteristic of bituminous coals, high molecular weight species (tar) and hydrocarbons (primary gases) are evolved, which may lead to melting (metaplast); Stage III (>575°C), secondary gases are produced while undergoing ring condensation and leading to the formation of coke. The decrease in the amount of aliphatic hydrocarbons released in the pyrolysis of oxidised coals implies that stage II is not observed, `mobile' phase is insufficient to allow aromatic planar units to slide over each other, the melting cannot begin, and oxidised coals pass directly to stage III. This causes loss of plasticity and is therefore, responsible for the degradation of coking properties, as a consequence of oxidation. The aromatic fractions, that cannot rearrange, form a poor ordered structure and yield a powdered char.

Operating Parameters to Minimize Emissions During Rotary Kiln Emergency Safety Vent Openings

Certain designs of hazardous waste incinerator systems include emergency safety vents (ESVs). ESVs (also called dump stacks, vent stacks, emergency by-pass stacks, thermal relief valves, and pressure relief valves) are regarded as true emergency devices. Their purpose is to vent combustion gases directly from the combustion chambers to the atmosphere in the event of a failure of other system components. This is done for operator safety as well as to protect the incinerator and other downstream equipment from damage. ESVs are typically required for rotary kiln and hearth incinerators which process a portion of their waste load as bulk solids or contained liquids introduced continuously or in batch charges. Research has been performed at the U.S. EPA on a 73 kW (250,000 Btu/hr) rotary kiln incinerator simulator examining optimum settings of kiln operating parameters so as to minimize emissions during an ESV opening event. Experimental results are interpreted in the light of previous research results on transient "puffs." Mechanisms governing both the release of volatile matter during an ESV event and the subsequent pyrolysis and oxidation in the residual sorbent bed are identified. From a practical point of view, results indicate that alteration of operator-controllable kiln parameters during the onset of certain ESV opening events can have a significant effect on emissions of both organics and hydrogen chloride (HCl). A low air flow rate results in lower emissions of both organics and HCl. This hypothetical low air flow rate could possibly be equal to the flow rate induced by the natural draft coupled with air in-leakage. Rotational speed (RPM) appears to have slightly different effects on organics and HCl. Whereas emissions of HCl are minimized at a very low or non-existent RPM, emissions of organics exhibit a minimum at a low (but non-zero) RPM, with increasing emissions at both zero and high RPM. The use of a small afterburner to simulate an in-stack flare during an ESV event dramatically reduced organic emissions.

Volatile matter release, particle/cloud ignition, and combustion of near-stoichiometric suspensions of pulverised coal

The ignition characteristics of a cloud of pulverised coal flowing in a drop-tube furnace are examined.Cloud ignition is defined at the minimum gas temperature at which significant oxygen consumption occurs. This is accompanied by the generation of carbon dioxide and oxides of nitrogen, and the formation of a visual flame. Cloud ignition occurs at several hundred degrees above that for the ignition of some single coal particles. For three coals the cloud ignition temperature decreased with oxygen partial pressure, but was not sensitive to fuel equivalence ratio or particle size (as has been observed for single particles). For the three coals examined, pyrolysis measurements show the existence of a tar/light hydrocarbon/oxygenmixture at the cloud ignition temperature. On combustion the accompanying temperature increase results in coal burnoffs from 35 to 65% even though the combustible volatile matter prior to the ignition event corresponds to less than 6.5% burnoff. Different trends of tar and methane combustion and soot formation are observed in the experiments as gas temperature and oxygen levels were changed; however, significant tar combustion was always observed at cloud ignition. A mechanistic model is proposed to explain the observations.

An analysis of the ignition of coal dust clouds

The ignition or explosion of coal dust clouds is of interest in the fields of fire safety, and the combustion of pulverized fuel, as well as being a fundamental issue in combustion science. Ignition of coal particles is the result of a complex interaction among different mechanisms including particle heating, devolatilization, heterogeneous oxidation, and gas-phase oxidation and transport phenomena. Both theoretical and experimental studies on single particles have been well developed, with considerable experimental precision and validation of the predictions. However, experiments have shown that the ignition temperatures could be reduced by as much as 300 C due to the concentration (cooperative influence) effect associated with particle clouds. While the authors have observed that the ignition temperature decreases with increasing particle size using a drop-tube technique involving the injection of a small mass ([approximately]2-5 mg) of coal particles, Gururajan has reported that this effect is not clear (for the same fuel) in continuous ignition experiments involving a higher loading of coal. The theoretical analysis of coal dust cloud ignition is limited at present to the case of heterogeneous ignition on the surface of the particles, which does not allow for this effect. This brief communication extends the energy equations ofmore » Krishna and Berlad to include coal volatile matter (VM) release and the homogeneous ignition of VM in the gas phase of the cloud. The effects of particle size on the ignition temperature and ambient oxygen concentration on ignition mechanisms, predicted by this extension, are then examined.« less

Volatile release profiles of some Turkish lignites

Volatile matter determination is one of the most important criteria in coal analysis, because it is used for evaluating coals for utilisation. In this study, using TG curves of twenty-five lignite samples from various coal reserves in Turkey, the volatile release profiles were prepared. In the light of these profiles, the devolatilisation behaviour of the lignite samples was discussed. During the TG studies, 100 mg sample was used and nitrogen was allowed to flow through the system. The temperature was raised with a heating rate of about 40 K min −1 to 1223 K and the volatile matter release of the sample was determined as a function of time and temperature.

Production of amorphous silica and combustible gas from rice straw

Results of the thermogravimetric analysis of untreated and 1 n HCl-treated rice straw reveal that mass loss occurred in three distinct stages: removal of moisture; release of volatile matter and oxidation of fixed carbon. The rate of combustion of fixed carbon of acid-treated straw was faster than that of untreated straw. Studies on the combustion of large samples of straw in a vertical electric furnace showed that both amorphous silica and combustible gas could be produced simultaneously under certain conditions. Acid treatment of straw prior to combustion helped in producing a white ash in a short period. The silica produced at a furnace temperature of 500°C with a maximum bed temperature of 720°C was amorphous in nature. The low-calorie combustible gas could be produced when straw containing 6.5–7.5% moisture was fed to the furnace set at a temperature above 450°C. The flame temperature, as well as the duration of the flame, increased as the bed thickness increased. A furnace temperature of 450°C, a bed depth of 20 cm and a combustion period of 3 h are considered as optimum for the production of white amorphous silica from 1 n HCl-acid-treated straw.

Simultaneous measurement of weight loss by DTG combustion and SO 2-formation for different coals

Burning profiles and SO 2-formation profiles were measured simultaneously for four different coals by slowly heating coal samples in a flow of air in a thermobalance. The profiles of weight loss and SO 2 formation have the same shape with anthracite combustion. The SO 2-formation profiles of bituminous coals usually display two peaks that approximately correspond to the release of volatile matter and combustion of char in the burning profiles. No correlations could be found between either the types of sulphur present in the raw coals or the ratio of volatile matter to fixed carbon and the shape of the SO 2-formation profiles for the bituminous coals.

Thermal analysis of Australian coals—A short review

It is evident that thermal analysis studies of Australian coals are of primary significance in the rationalisation of the various physical and chemical processes inherent in energy generation from these fossil fuels. To data, considerable such data has been accumulated correlating combustion efficiency with the coal primary structure, surface phenomena, included metal ions, volatile matter release profiles, particle size and corresponding char properties. The kinetics of these complex processes are now also modelled.

Studies on thermal decomposition of rice straw

Investigations of the thermal decomposition of untreated rice straw and that treated with HCl and HNO 3 of various concentrations were carried out by thermogravimetry, derivative thermogravimetry and differential thermal analysis. The mass loss occurred in three distinct stages; removal of moisture, release of volatile matter and burning of combustible carbon. The corresponding temperature ranges were 0–200, 275–400 and 400–600°C. The overall thermal degradation of rice straw was found to be an exothermic process.

Investigation of thermal decomposition of rice husk

Studies on the thermal decomposition of untreated rice husk and that treated with HCl and H 2SO 4 of various concentrations were carried out by TG, DTG and DTA. The mass loss occurred in three distinct stages, namely, removal of moisture, release of volatile matter and burning of combustible material. The corresponding temperature ranges for untreated husk were 40–150, 215–350 and 350–690°C. The final temperature of combustion decreased with acid-treatment of the husk. The thermal decomposition of the husk was found to be an exothermic process.

Formation of submicron unburnt carbon and NO x from pulverized coal combustion system

The emission characteristics of the submicron unburnt carbon (S.U.C.) and NOx from the pulverized coal combustion system were investigated using an experimental model furnace which was designed to obtain a practical combustion condition. An analysis of the classified fly ash particles sampled from the flue indicates a high carbon content of ash in the submicron range. A structure of the unburnt carbon in the submicron range resembles the soot formed in the gaseous phase. The concentration distribution of S.U.C. in the furnace shows that it is formed mainly during the release of volatile matter (V.M.). The effect of primary air velocity on the emission of S.U.C. and NOx was investigated. As the burner velocity increases from 12 m/s to 69 m/s, the final level of S.U.C. decreases, whilst that of NOx increases. The concentration distribution of stable species in the furnace indicates that the local reducing region appeared in the combustion zone of V.M. and is responsible for the emission of S.U.C. and the reduction of NOx under the condition of low primary air velocity. The formation mechanism of this local reducing region was determined by measurement of the velocity profile in the furnace and observation of the ignition point. Finally, the aerodynamic effect on both the emission of S.U.C. and NOx can be explained by the air entrainment rate and the ignition point.

156. The release of volatile matter from green coke during calcination as a function of temperature and atmosphere

156. The release of volatile matter from green coke during calcination as a function of temperature and atmosphere

Influence of carbonization conditions on the development of different types of optical anisotropy in cokes

The vitrain components of a series of coal samples were carbonized at temperatures from 400 to 1000°C at different rates of heating ranging from 0.5 to 10°K/min and utilizing soaking times up to 24 hr. Polished specimens prepared from the carbonized products were examined microscopically under polarized light in order to determine the proportions of the various types of optical anisotropy present in them. The variations in heating rate and soaking time were found to exert little significant influence on the anisotropy developed in high-temperature cokes. But in semicokes produced at carbonization temperatures within the plastic range the influence of the carbonization conditions was much more pronounced with the effects being inter-related. Decreasing the heating rate or increasing the soaking time led to the optical anisotropy generally becoming detectable at lower carbonization temperatures. Fast heating rates caused an increase in the rate of transformation of the fine-grain mosaic anisotropy into coarser-grained types of anisotropy and increased soaking time led to enhanced anisotropic development in the semicokes produced at temperatures within the plastic range. The type of anisotropy developed in cokes is closely related to the release of volatile matter and the plasticity developed during carbonization and the conclusion is drawn that the balance between these factors controls the extent of the anisotropic development.