Combustion Characteristics Of Coal Research Articles

06/02012 Combustion characteristics of coal in a mixture of oxygen and recycled flue gas: Tan, Y. et al. Fuel, 2006, 85, (4), 507–512.

06/02012 Combustion characteristics of coal in a mixture of oxygen and recycled flue gas: Tan, Y. et al. Fuel, 2006, 85, (4), 507–512.

Emission characteristics of coal combustion in different O 2/N 2, O 2/CO 2 and O 2/RFG atmosphere

This study investigates the emission characteristics of CO 2, SO 2 and NOx in the flue gas of coal combustion by varying the compositions and concentrations of feed gas (O 2/CO 2/N 2) and the ratios of recycled flue gas. The differences between O 2/recycled flue gas (O 2/RFG) combustion and general air combustion are also discussed. Experimental results indicate that the maximum concentration of CO 2 in O 2/CO 2 combustion system is 95% as the feed gas is 30% O 2/70% CO 2. The average concentration of CO 2 in the flue gas of O 2/CO 2 coal combustion system is higher than 90% and much higher than that of O 2/N 2 coal combustion system. This high concentration of CO 2 is beneficial for the separation of CO 2 from the flue gas by adsorption or absorption technologies. The maximum concentration of CO 2 in O 2/N 2 combustion system is only 34% at the feed gas 50% O 2/50% N 2, the concentration of CO 2 is increased with the concentration of O 2 in feed gas. By O 2/CO 2 combustion technology, higher concentration of SO 2 is produced as the feed gas is 30% O 2/70% CO 2 or 40% O 2/60% CO 2, while higher concentration of NOx is produced as the feed gas is 20% O 2/80% CO 2 or 50% O 2/50% CO 2. The mass flow rates of CO 2, SO 2 and NOx in the flue gas are all increased with the ratio of recycled flue gas except for the feed gas 20% O 2/80% CO 2. The enhanced mass flow rates of air pollutants in such O 2/RFG combustion system are also beneficial for improving the control efficiencies of air pollution control devices. By O 2/N 2 combustion technology, higher concentrations of SO 2 and NOx are produced as the feed gas is 21% O 2/79% N 2. The results also indicate that the formation of NOx in general air combustion system is higher than that in O 2/RFG or O 2/CO 2 combustion system.

Assessment of the effect of high ash content in pulverized coal combustion

The existing literature on CFD-based coal combustion modelling is applicable mainly for coals of low ash content and the calculations are done on an ash-free basis. In Indian coals, the ash content may be significantly higher, up to 40% or more. Studies reported in the literature show that the mineral matter in the coal may have a number of effects on the combustion characteristics. In the present study, a sensitivity analysis is performed, using the CFD code CFX of AEA Technology, on the likely effect of ash content on the char reactivity, oxygen diffusion rate for char combustion and on the radiative heat transfer parameters. The results show that the effect of enhanced char reactivity is negligible whereas reduced oxygen diffusion rates due to a thicker ash layer may result in a significant reduction in char oxidation rates with a resultant decrease in the peak temperature in the furnace. The global parameters such as the peak temperature and the flue gas temperature remain relatively insensitive to the presence of high ash content. These results are consistent with the experimental observations of Kurose et al. [R. Kurose, M. Ikeda, H. Makino, Combustion characteristics of high ash coal in pulverized coal combustion, J. Fuel 80 (2001) 1447–1455].

Thermogravimetric analysis of the co-combustion of the blends with high ash coal and waste tyres

Incineration methods are becoming increasingly important from the view point of the need to minimize the environmental impact of waste tyre disposal. Combustion of waste tyre, one high ash coal and tyre-coal blends with 10, 30 and 50% waste tyre were investigated by means of thermogravimetric analysis (TGA) carried out at 20 K min −1 in the temperature range from ambient temperature to 1273 K. And effects of the mixed proportion between coal and waste tyre on the combustion process, ignition and burnout characteristics were also studied. The results indicate that the combustion of waste tyre is controlled by the emission of volatile matter, the regions are more complex for waste tyre (three or more peaks) than for coal (one peak). Also as compared with the case of burning only high ash coal, the incorporation of waste tyre can improve the combustion characteristics of high ash coal, especially the ignition performance and the peak weight loss compared with the separate burning of waste tyre and coal. Moreover, comparisons of the TG–DTG profiles between experimental and calculational results, it is indicate that there is a comparatively important difference, the co-combustion characteristics is the coupling effect between waste tyre and coal. The data resulting also showed that the co-combustion of waste tyre and low quanlitied coal as fuel is feasible.

Effects of Processing Temperature of Hot Water Drying on the Properties and Combustion Characteristics of an Indonesian Low Rank Coal

ABSTRACT Experiments have been carried out to measure the effect of processing temperature on the moisture content of low rank coal upgraded by the hot water drying (HWD) method. The Berau coal from East Kalimantan, which was used for this investigation, is a sub-bituminous coal with a calorific value of 5324 kcal/kg and an inherent moisture content of 16.13% (air dried basis). Experimental results from this study indicate that at the processing temperature of 300°C the moisture content is reduced to 1.94% and the calorific value is increased up to 6312 kcal/kg (air dried basis). The change in functional groups determined by FTIR analysis and the change in combustion characteristics determined by DTA-TG are discussed for both the raw and upgraded coals.

Combustion characteristics of coal in a mixture of oxygen and recycled flue gas

The combustion of coal in a mixture of pure O 2 and recycled flue gas is one variant of a novel combustion approach called oxy-fuel combustion. With the absence of N 2, this approach leads to a flue gas stream highly enriched in CO 2. For many applications, this flue gas stream can then be compressed and sequestered without further separation. As a result, oxy-fuel combustion is an attractive way to capture CO 2 produced from fossil fuel combustion. When coal is burned in this O 2 and CO 2 rich environment, its combustion characteristics can be very different from conventional air-fired combustion. In CETC-O, a vertical combustor research facility has been used in the past years to investigate the combustion characteristics of several different coals with this variant of oxy-fuel combustion. This included flame stability, emissions of NO x , SO x and trace elements, heat transfer, in-furnace flame profiles and flue gas compositions. This paper will report some of the major findings obtained from these research activities.

05/00546 Pulverized coal combustion characteristics of high-fuel-ratio coals

05/00546 Pulverized coal combustion characteristics of high-fuel-ratio coals

実験室規模の加圧流動層燃焼における窒素酸化物の生成特性―チャーによるＮＯｘ分解―

A laboratory scale pressurized fluidized bed combustion (PFBC) system was designed and constructed to clear the details of combustion of coal in PFBC. This PFBC system allows visual observation of hot fluid-ized bed by using a transparent electric furnace. To simulate the emission characteristics of coal combustion of the full scale PFBCs by this lab-scale PFBC, a new similarity rule was introduced. Volumetric heat input and mean gas residence time through fluidized bed in lab-scale PFBC were adjusted to the values matching those of full scale PFBCs. Motion of bubbles and burning of coal particles and volatiles were recognized by visual observations. Volatiles burned mostly in the bottom region of the fluidized bed. On the other hand, char particles burned uniformly in the bed. Ranges of conversion of fuel-N to NO agreed with those obtained in a full scale PFBC. Thus, it is verified that new similarity rule explained above is useful to simulate the combustion behaviors in full scale PFBC by a laboratory scale small PFBC.Effects of operating pressure and O2 partial pressure in flue gas on NO emission were examined. Linear relationship between O2 partial pressure and NO emission was observed. NO emission was decreased rapidly with increasing in operating pressure at constant O2 partial pressure. This may be caused by an enhance-ment of NO reduction by char particles because of increase in number density of char particle in the bed at elevated pressure. In order to confirm this assumption, initial combustion rate of char in the pressurized fluidized bed condition was measured. Initial combustion rate of char increased with 0.6th power of operating pressure. This means that char number density is increased in elevated pressure condition. One of the major reasons to achieve the low NOx emission in PFBC condition, should be the reduction of NOx by char particles through the bed.

04/01710 Coal combustion characteristics based on the release of carbon dioxide: Zou, X. et al. Ranliao Huaxue Xuebao, 2003, 31, (2), 185–188. (In Chinese)

04/01710 Coal combustion characteristics based on the release of carbon dioxide: Zou, X. et al. Ranliao Huaxue Xuebao, 2003, 31, (2), 185–188. (In Chinese)

04/01176 Combustion characteristics of power coal: Zheng, M. and He, X. Huagong Xuebao, 2003, 54, (3), 374–378. (In Chinese)

Combustion reaction is the most important way of coal conversion,coal's combustion parameter plays an important role in evaluating its ecological and economic indicators.The combustion characteristics are studied in this paper on six types of different rank power coals by thermogravimetric and fourier transform infrared spectrometry technique,respectively.The results show that each characteristic temperature and the temperature at which these gases,such as CO,CO 2 and H 2O released,become small with the decrease of the coal rank,contrarily weight loss of lower rank coal sample between each characteristic temperature increases.CO is generated at a lower temperature while CO 2 is mainly generated at a higher temperature.Both the variation of activation energy and the reaction order pass a maximum as the temperature increases in the combustion process.All the above observations indicate that lower rank coal is easier to combust than higher rank coal.

Pulverized coal combustion characteristics of high-fuel-ratio coals

It is strongly desired for coal-fired power plants in Japan to utilize not only low-rank coals with high moisture and high ash contents, but also high-rank coals with high fuel ratio for diversifying fuel sources and lowering cost. In this study, pulverized coal combustion characteristics of high-fuel-ratio coals are experimentally investigated using an approximately 100 kg-coal/h pulverized coal combustion test furnace. The combustion characteristics are compared to those for bituminous coal. The coals tested are six kinds of coal with fuel ratios ranging from 1.46 to 7.10. The results show that under the non-staged combustion condition, the minimum burner load for stable combustion rises as fuel ratio increases. To improve the stability, it is effective to lengthen the residence time of coal particles in the high gas temperature region close to the burner outlet by using a recirculation flow. The conversion ratio of fuel nitrogen to NOx and unburned carbon fraction increases with increasing the fuel ratio. In addition, as the fuel ratio increases, NOx reduction owing to the staged combustion becomes small, and unburned carbon fraction increment becomes significant. The numerical simulations conducted under the staged combustion condition show that although the numerical results are in general agreement with the experimental ones, there remains room for improvement in NOx reduction model for high-fuel-ratio coals.

04/00601 Combustion characteristics of power coal: Zheng, M. and He, X. Huagong Xuebao, 2003, 54, (3), 374–378. (In Chinese)

04/00601 Combustion characteristics of power coal: Zheng, M. and He, X. Huagong Xuebao, 2003, 54, (3), 374–378. (In Chinese)

04/00017 Study on combustion characteristics of coal by TG-DSC-FTIR: Zou, X. et al. Meitan Zhuanhua, 2003, 26, (1), 71–73 (In Chinese)

To investigate short-term and long-term effects of repetitive peripheral magnetic stimulation (rpMS) on spasticity and motor function.Monocentric, randomized, double-blind, sham-controlled trial.Neurologic rehabilitation hospital.Patients (N=66) with severe hemiparesis and mild to moderate spasticity resulting from a stroke or a traumatic brain injury. The average time ± SD since injury for the intervention groups was 26±71 weeks or 37±82 weeks.rpMS for 20 minutes or sham stimulation with subsequent occupational therapy for 20 minutes, 2 times a day, over a 2-week period.Modified Tardieu Scale and Fugl-Meyer Assessment (arm score), assessed before therapy, at the end of the 2-week treatment period, and 2 weeks after study treatment. Additionally, the Tardieu Scale was assessed after the first and before the third therapy session to determine any short-term effects.Spasticity (Tardieu >0) was present in 83% of wrist flexors, 62% of elbow flexors, 44% of elbow extensors, and 10% of wrist extensors. Compared with the sham stimulation group, the rpMS group showed short-term effects on spasticity for wrist flexors (P=.048), and long-term effects for elbow extensors (P<.045). Arm motor function (rpMS group: median 5 [4–27]; sham group: median 4 [4–9]) did not significantly change over the study period in either group, whereas rpMS had a positive effect on sensory function.Therapy with rpMS increases sensory function in patients with severe limb paresis. The magnetic stimulation, however, has limited effect on spasticity and no effect on motor function.

Numerical analysis of pulverized coal combustion characteristics using advanced low-NO x burner

A three-dimensional numerical simulation is applied to a pulverized coal combustion field in a test furnace equipped with an advanced low-NO x burner called CI-α burner, and the detailed combustion characteristics are investigated. In addition, the validities of the existing NO x formation and reduction models are examined. The results show that a recirculation flow is formed in the high-gas-temperature region near the CI-α burner outlet, and this lengthens the residence time of coal particles in this high-temperature region, promotes the evolution of volatile matter and the progress of char reaction, and produces an extremely low-O 2 region for effective NO reduction. It is also found that, by lessening the effect of NO reduction in Levy et al.'s model and taking the NO formation from char N into account, the accuracy of the NO prediction is improved. The efficiency factor of the conversion of char N to NO affects the total NO concentration downstream after the injection of staged combustion air.

03/02645 Numerical analysis of pulverized coal combustion characteristics using advanced low-NO x burner : Kurose, R. et al. Preprints of Symposia — American Chemical Society. Division of Fuel Chemistry, 2003, 48, (1), 308–309

03/02645 Numerical analysis of pulverized coal combustion characteristics using advanced low-NO x burner : Kurose, R. et al. Preprints of Symposia — American Chemical Society. Division of Fuel Chemistry, 2003, 48, (1), 308–309

Evaluation of Combustion Characteristics of Chinese High-Ash Coals

The combustion characteristics of four Chinese high-ash coals were evaluated by thermogravimetric and surface analysis. Changes in surface area and porosity during combustion were investigated with original (as-received) coals, coal samples before ignition, and chars after burnout. To understand the roles of various ash components, comparative experiments were carried out with as-received, de-ashed, and impregnated coals. SiO2, Al2O3, CaCO3, MgO, Na2CO3, TiO2, K2CO3, Fe2O3, FeS2, FeSO4(NH4)SO4·6H2O, and NH4Fe(SO4)2·12H2O at different concentrations were used as chemical additives impregnated into the de-ashed coals to investigate their influence on coal combustion. Most of these minerals inhibited coal ignitability; only K and Ca were found to promote coal ignition. Fe, Al, Na, and Ca were found to hinder both ignition and burnout of coal. Other ash components demonstrated variable effects on coal ignition and burnout with changing concentrations and species. A full understanding of the different effects of mineral matter is essential to achieve improved performance with high-ash coal applications.

Waterwall corrosion mechanisms in coal combustion environments

When coal-fired boilers are operating with substoichiometric firing to limit NOx formation in order to comply with emission regulations, the reducing environments formed locally in the firing zone or under deposits can result in sulfidation attack and premature failure of components. Carbon and low-alloy steels are the preferred materials for waterwall applications due to their good thermal conductivity, creep strength (up to 550°C) and relatively low cost. However, these materials, with at best low contents of Cr, are also the most susceptible to sulfidation attack. This paper presents the results of an extensive investigation to evaluate the effect of coal combustion characteristics, gas flow in the boiler, sulfidation potential of the environment, and the formation of deposits, on the kinetics of sulfidation in typical boiler materials. An interdisciplinary approach was adopted involving combustion analysis, corrosion studies and computational fluid dynamics along with information on operational boilers. The objective was to provide support for the low NOx retrofit program and to generate authoritative information for utility customers and also to develop a capability to predict potential combinations of coal and combustion conditions which could cause enhanced rates of attack.

Coal structure and reactivity changes induced by chemical demineralisation

The aim of this work was to determine the influence that an advanced demineralisation procedure has on the combustion characteristics of coal. A high-volatile bituminous coal with 6.2% ash content was treated in a mixture of hydrofluoric and fluorosilicic acids (HF/H 2SiF 6). Nitric acid was used either as a pretreatment, or as a washing stage after HF/H 2SiF 6 demineralisation, with an ash content as low as 0.3% being attained in the latter case. The structural changes produced by the chemical treatment were evaluated by comparison of the FTIR spectra of the raw and treated coal samples. The devolatilisation and combustibility behaviour of the samples was studied by using a thermobalance coupled to a mass spectrometer (TGA-MS) for evolved gas analysis. The combustibility characteristics of the cleaned samples were clearly improved, there being a decrease in SO 2 emissions.

Combustion characteristics of high ash coal in a pulverized coal combustion

Combustion characteristics of high ash coal in a pulverized coal combustion

Effects of moisture in coal on pulverized coal combustion characteristics

Effects of moisture in coal on pulverized coal combustion characteristics