Typical Chinese Coals Research Articles

Application of gaseous fuel reburning for controlling nitric oxide emissions in boilers

An experimental study was performed on a 36 kW th down-fired furnace in order to obtain a wider and more detailed knowledge of the influence of the key parameters on the gaseous fuel reburning process when typical Chinese coals served as the primary fuel. The experimental results show that both above 50% nitric oxide reduction and low carbon loss can be obtained when reburn zone residence time is about 0.6 s–0.9 s, gaseous reburn fuel percent is about 10%–15% and average excess air coefficient of reburn zone is about 0.8–0.9. According to the optimizational reburning operating parameters, a 350 MW e coal-fired boiler was retrofitted for reburning application. The retrofitted boiler had about 0.7 s reburn zone residence time and about 2 s residence time after the burnout air was injected. The results of the demonstration on the full-scale boiler showed that the nitric oxide emission was about 235 mg/Nm 3 (O 2 = 3%, dry) from the retrofitted boiler and above 60% nitric oxide reduction efficiency could be achieved with no adverse effects on the boiler operability when the coke-oven gas used as the reburn fuel. This successful demonstration project filled the gaps in the gaseous fuel reburning application on 300 MW e grade unit boiler in China and showed that the values of the optimizational reburning parameters obtained from experiments could be successfully applied to the designing, retrofitting and optimizing for the gaseous fuel reburning process.

Experimental studies on gasification of the Shenmu coal char with CO2 at elevated pressures

The gasification rates of Shenmu coal chars with CO2 were experimentally studied with a pressurized ther- mo-gravimetric analyzer (PTGA). Shenmu coal is a typical Chinese coal, and the coal char was prepared by a fixed- bed reactor in nitrogen at 900 o C. The experiments were carried out in the dynamic heating segments from 750 o C to 1,000 o C, and the reaction pressure increased from 0.1 MPa to 3.1 MPa with pure CO2. The external diffusion resistances were minimized by increasing the flow rates and decreasing the thickness of sample layer before the test, to ensure the reactions were under kinetic control. The results show that the gasification rates increase proportionally to the 0.1 power of the CO2 partial pressure. The unreacted-core shrinking model was applied to predict the reaction rate by chang- ing the molar fraction of CO2 at 0.6 Mpa and 1.6 Mpa total pressures, which showed a good match with experimental data.

Effect of Volatile−Char Interaction on the NO Emission from Coal Combustion

To clarify the effects of volatile-char interaction on the redistribution of fuel-N to N2 during devolatilization and the reduction of NO through gas-solid reactions during combustion, two types of experiments were performed on a novel reactor. The separate combustion of volatile and char and the combustion of entrained pulverized coal, and the formation of NO was examined between 800 and 1100 degrees C by using four typical Chinese coals with different ranks. The effect of volatile-char interaction on fuel-N conversion to NO during combustion was elucidated through comparing the NO emissions from the two types of combustion experiments. The results show that the volatile-char interaction is more important in the redistribution of fuel-N to N2 during devolatilization than in the reduction of NO over 900 degrees C, and a contrary conclusion is obtained below 850 degrees C for all used coals. A specific parameter has been proposed to characterize the relative importance of the volatile-char interaction in the redistribution of fuel-N to N2 during devolatilization to the interaction in the reduction of NO to N2 during simulataneous combustion of volatile and char. The results are of significance for minimizing the NO formation in industrial combustion processes.

Pressurized Pyrolysis and Gasification of Chinese Typical Coal Samples

This paper aims to understand the pyrolysis and gasification behavior of different Chinese coal samples at different pressures. First, the pyrolysis of four typical Chinese coals samples (Xiaolongtan brown coal, Shenfu bituminous coal, Pingzhai anthracite coal, and Heshan lean coal) were carried out using a pressurized thermogravimetric analyzer at ambient pressure and 3 MPa, respectively. The surface structure and elemental component of the resultant char were measured with an automated gas adsorption apparatus and element analyzer. It was observed that higher pressure suppressed the primary pyrolysis, while the secondary pyrolysis of coal particles was promoted. With respect to the resultant solid char, the carbon content increased while H content decreased; however, the pore structure varied greatly with increasing pressure for different coal samples. For Xiaolongtan brown coal (XLT) char, it decreased greatly, while it increased obviously for the other three char types. Then, the isothermal gasification behavior of solid char particles was investigated using an ambient thermal analyzer with CO2 as the gasifying agent at 1000 °C. The gasification reactivity of solid char was decreased greatly with increasing pyrolysis pressure. However, the extent of change displayed a vital relation with the characteristics of the original coal sample.

Distribution and Occurrence of Arsenic in Two Typical Chinese Coals

Two complementary methods, float-sink experiment and sequential chemical leaching were used to probe into the occurrence of arsenic in two Chinese coals: Yima (YM) and Datong (DT). Flow injection-hydride generation atomic fluorescence spectrometry was employed to measure the arsenic content in parent coals as well as the size and density-fraction samples. Float-sink experiment indicated that the heavy density fractions were enriched mineral containing arsenic in two bituminous coals studied, as confirmed by the sequential chemical leaching method. Sequential chemical leaching revealed that sulfide arsenic was the primary mode of occurrence (> 50%), stable form also abounded in coal with content between 30 and 40%, and a small amount of arsenic took the occurrence of organic form.

Ash particle formation during O2/CO2 combustion of pulverized coals

The present paper was addressed to ash particle formation during O2/CO2 combustion of pulverized coal. Three typical Chinese coals were burned in a drop tube furnace to generate ashes under various combustion conditions. The residue ash particles were measured with Malvern technique. The fine ash particles collected by a low pressure impactor were subjected to the analyses of size distribution and elemental composition to study the fine ash formation. The impacts of O2/CO2 combustion on ash particle formation were explored through extensive comparisons between O2/CO2 combustion and O2/N2 combustion. It was found that O2/CO2 combustion did not significantly affect the size distribution of the residue ash particles but did significant affect the mass and composition size distributions of both the submicron particles and the fine fragmentation particles. Nevertheless, O2/CO2 combustion did not change the formation mechanisms of the submicron particles and the fine fragmentation particles.

Computer-Controlled Scanning Electron Microscopy (CCSEM) Investigation on the Heterogeneous Nature of Mineral Matter in Six Typical Chinese Coals

The heterogeneous nature of mineral matter in six typical Chinese pulverized coals has been quantitatively characterized using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and calcite form the bulk of the mineral matter. Minor minerals, such as dolomite, ankerite, rutile, nonstoichiometric iron sulfides, and gypsum, are also detected in some samples. The particle-size distribution of the included minerals is generally finer than that of the excluded ones in a certain coal. As a consequence, the coal rich in included minerals has more small mineral particles. Regarding the association of individual mineral species, the proportion of included to excluded kaolinite varies with coal greatly. Other minerals are, however, principally excluded in nature. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements. Apatite is the major form of P in only one of the coals studied. Ti is mainly present as rutile and kaolinite.

Predicting coal ash fusion temperature based on its chemical composition using ACO-BP neural network

Coal ash fusion temperature is important to boiler designers and operators of power plants. Fusion temperature is determined by the chemical composition of coal ash, however, their relationships are not precisely known. A novel neural network, ACO-BP neural network, is used to model coal ash fusion temperature based on its chemical composition. Ant colony optimization (ACO) is an ecological system algorithm, which draws its inspiration from the foraging behavior of real ants. A three-layer network is designed with 10 hidden nodes. The oxide contents consist of the inputs of the network and the fusion temperature is the output. Data on 80 typical Chinese coal ash samples were used for training and testing. Results show that ACO-BP neural network can obtain better performance compared with empirical formulas and BP neural network. The well-trained neural network can be used as a useful tool to predict coal ash fusion temperature according to the oxide contents of the coal ash.

04/01586 A mathematical modelling technique for gaseous and solid fuel reburning in pulverised coal combustors: Dimitriou, D. J. et al. Fuel, 2003, 82, (15–17), 2107–2114

An experimental study was performed on a 36 kWth down-fired furnace in order to obtain a wider and more detailed knowledge of the influence of the key parameters on the gaseous fuel reburning process when typical Chinese coals served as the primary fuel. The experimental results show that both above 50% nitric oxide reduction and low carbon loss can be obtained when reburn zone residence time is about 0.6 s–0.9 s, gaseous reburn fuel percent is about 10%–15% and average excess air coefficient of reburn zone is about 0.8–0.9. According to the optimizational reburning operating parameters, a 350 MWe coal-fired boiler was retrofitted for reburning application. The retrofitted boiler had about 0.7 s reburn zone residence time and about 2 s residence time after the burnout air was injected. The results of the demonstration on the full-scale boiler showed that the nitric oxide emission was about 235 mg/Nm3 (O2 = 3%, dry) from the retrofitted boiler and above 60% nitric oxide reduction efficiency could be achieved with no adverse effects on the boiler operability when the coke-oven gas used as the reburn fuel. This successful demonstration project filled the gaps in the gaseous fuel reburning application on 300 MWe grade unit boiler in China and showed that the values of the optimizational reburning parameters obtained from experiments could be successfully applied to the designing, retrofitting and optimizing for the gaseous fuel reburning process.

Fluorine distribution characteristics in coal and behavior of fluorine during coal combustion : Qi, Q. et al. Huagong Xuebao (Chinese Edition), 2002, 53, (6), 572–577. (In Chinese)

In this paper the Concentrations of fluorine in typical Chinese coals are determined by the pyrohydrolysis/FISE method.The distribution characteristics of fluorine in coal are obtained.The correlation between fluorine and ash,the probable mode of occurrence of fluorine in coal are discussed.Fluorine concentration ranges between 17-3145?μg·g -1 and the mean value is close to 200?μg·g -1 .Good correlation between fluorine and ash content suggested that fluorine is present in these coals in inorganic mineral species.Fluorine emission characteristics during coal combustion are studied systemically in tube furnaces for the first time.The influence factors on fluorine emission and the relationship of fluorine emission with coal type,combustion temperature,retention period and combustion atmosphere are obtained and the production mechanism of gaseous fluorine during coal combustion are proposed.Experimental results indicate that fluorine emission appears to begin at 573-673?K and emission rates reaches about 96% at above 1473?K.Gaseous fluorine is probably originated from fluorine occurring as organic forms or adsorbed inorganic form in coals at low temperatures,and appears to come mainly from fluorine occurring as inorganic salt forms in coal at high temperatures.

Catalytic reduction of SO 2 during combustion of typical Chinese coals

The catalytic effects of doping agents on SO 2 emission as well as the coal combustion behavior were investigated by thermogravimetry. All experiments were carried out in a flowing air atmosphere at a heating rate of 20 or 30 °C/min up to 1000 °C. The doping agents employed were NaCl, CaCl 2, FeCl 3, FeCl 2 and Fe 2O 3. The experimental results show that the agents added in coal reduce SO 2 emission of coal, with CaCl 2 being the most effective. The doping agents work with different mechanisms. The catalysis of NaCl, CaCl 2, and Fe 2O 3 promotes the reactions between SO 2 and the minerals in coal, and enhances the sulfur retention capacity of coal ash, thus decreasing SO 2 concentration in flue gas. They have weak effects on the combustion behavior of the coal. FeCl 3 and FeCl 2 have strong effects on coal combustion behaviour. They accelerate the combustion and improve the ignition of the char subsequently formed, increasing SO 2 concentration in flue gas in the region from 300 to 520 °C. However, they reduce the total amount of SO 2 emission during combustion. The reduction of SO 2 yield by FeCl 3 and FeCl 2 mainly results from the Fe 2O 3 created from them at high temperatures.

Preparation of fullerenes from coals

Fullerenes have been prepared from 14 typical Chinese coals by arc plasma evaporation in helium. The purpose of this work is to identify inexpensive sources of carbon to substitute high purity graphite used commonly for fullerene synthesis. The results show that it is possible to prepare fullerenes from Chinese coals, and the yields and the components of fullerenes are related to the properties of raw coals. Because coal contains weak covalent bonds linking macromolecular, large fragments other than C 1 and C 2 units can exist in the arc plasma. This implies that large fragments may play an important part in forming fullerenes. Meanwhile the C 70 content in the crude fullerenes from coals is higher compared with that from high purity graphite under the identical experiment conditions, which may be attributed to the unique chemical structure of coal derived carbons. The fullerene yields from some de ashed coals are comparable to that obtained from graphite under similar experimental conditions.

Emissions of organic hazardous air pollutants during Chinese coal combustion

This paper provides a general investigation of the emissions of organic hazardous air pollutants (HAPs) during the combustion of several typical Chinese coals. First, the distribution of four types of HAP, i.e., aliphatics, cyclic hydrocarbons, monoaromatic compounds and PAHs, in the CH 2Cl 2 extracts of six Chinese coals were studied and the influences of the extractive times and coal varieties were also evaluated. Second, the partitioning of these HAPs in the flue gas during coal combustion in a small-scale reactor were investigated, depending on oven temperatures (500 °C, 600 °C, 700 °C, 800 °C, 900 °C) and coal varieties. The behaviors of HAP in the combustion flue gas were compared with those in the CH 2Cl 2 extracts. Finally, combustion was conducted at given conditions in two laboratory-scale reactors: a fluidized bed and a fixed bed. Two coals (Shengmu bituminous coal and Xunhuan anthracite coal) and one coke were considered in this case. The HAP partitioning both in flue gases and in ashes were evaluated and compared between the two combustors.

Influence of coal nature and structure on ash size formation characteristic and related pollutant emissions during CFB combustion

The size distribution of coal particles in a Circulating Fluidized Bed (CFB) boiler plays a crucial role in the complicated combustion, heat exchange and pollutant emissions in such a plant. Therefore, it is fundamental to study the different factors having influence on the size distribution of coal particles. Above all, the coal itself and in particular, the coal comminution phenomenon is a very influent factor. In the frame of this work, the coal nature (elementary composition) and coal internal structure (mineral components) are studied in detail. At this intermediary stage, experiments on three typical Chinese coals on a 1.5 MWt CFBC pilot plant have been made. Some primary fragmentation tests have also been made in a small lab scale fluidized bed reactor. The results from the hot pilot test show i) the variation of coal ash distributions and other CFB performance data due to the cyclone and the coal characteristics and ii) the variation of desulfurization efficiency with limestone. Whereas the bench scale primary fragmentation test, likely linked to the caking propriety of a coal, does not seem to change considerably the char size distribution.

Determination of Optimum Blending Ratio During Coal Blends Combustion

This paper reports the experimental research on combustion and pollution properties of several typical Chinese individual coals and coal blends and the methods determined optimum blending ratios. Thermogravimetry analysis technique and a drop-tube furnace were used to investigate the ignition and burnout behavior and NOx emission characteristics. Ash chemical composition and fusion temperature was also measured. The effects of the blending ratios on ignition, burnout, slagging and NOx emissions have been analyzed. The fuzzy logic approach has been used to determine the optimum blending ratios based on experimental data which provide a scientific basis for design and operation of power station blending coal. Calculation results were comparable with that of results obtained from combustion test carried out in a boiler simulator furnace.

Preparation of fullerenes using carbon rods manufactured from Chinese hard coals

We report a feasibility study of producing fullerenes (C 60 and C 70) using carbon rods manufactured from Chinese coal which is one of the cheapest natural resources of carbon. A DC arc method is employed using coal-derived carbon rods as electrode materials. The carbon rods are prepared from seven typical Chinese hard coals including bituminous coals and anthracite. The results show that all Chinese coals tested can be used to produce significant quantities of fullerenes. Their yields are strongly affected by the methods of preparing carbon electrodes and the parameters of the arc process, which are directly related to the coal properties and characteristics. Our results show that the two-step carbonisation method is significantly better than the one-step hot-pressing method with regard to the fullerene yields, as such the two-step method is recommended for fullerenes production from Chinese coals. It is found that the fullerene yield increases as the carbon content in coal increases and as ash content in coal decreases. This suggests that the mineral matter in coals could somehow inhibit the fullerenes production. An interesting linear relationship between the C 60/C 70 ratios and the volatile matter content in Chinese coals is also noted.

Comparison of sulphur retention by coal ash in different types of combustors

During coal combustion, a part of the total sulphur in coal will be retained as solid compounds in ash. In the present paper, the retention of sulphur by ash of typical Chinese coal used for electric power generation was correlated with the contents of alkaline elements relative to sulphur in the parent coal. Comparison was performed among the capabilities of sulphur retention by coal ashes in laboratory ashing procedure, pulverised coal-fired combustor and fluidised bed combustor (FBC). It was shown that calcium plays a dominant role in sulphur retention of laboratory-prepared ash and the sulphur retention percentage increases with the increase of Ca/S molar ratio of the parent coal, while the contributions of other elements are limited. The sulphur retention behaviour in pulverised coal-fired combustor is significantly different from that in laboratory ashing procedure. The contribution of calcium is reduced markedly, while the roles of the other alkaline elements are obviously enhanced. Using the literature data from foreign coals, it was found that the sulphur retention in FBC is comparable with that in laboratory ashing procedure. It was suggested from the results obtained in this study that the sulphur retention of laboratory-prepared ash can be applied to fluidised bed combustion because the behaviour of calcium is similar to that of lime in FBC.

Characterization of coals utilized in power stations of China

The petrographic composition of 21 types of typical Chinese coals obtained directly from the power stations was analyzed. The vitrinite reflectograms of them were measured and shows an obvious difference from that of single rank coals, which suggests that the coals utilized in the power stations have the characterization of a blended coal in terms of coal rank. The index S M has been developed to describe the occurrence of mineral in the coals and the results show quite a difference in the occurrence of the mineral for the coals studied. The petrographic constituents of different size fractions were analyzed for three coals and showed little systematic change with the particle size, but revealed the trend that the large particles contained much more of the higher rank coal and the small particles contained much more of the low rank coal.

Trace Elements in Chinese Coals and their Partitioning During Coal Combustion

This paper gives a detail investigation about the trace elements (TEs) in typical Chinese coals, TEs partitioning during combustion and their different environment impacts. Firstly, it is determined that the contents of 9 TEs (As, Be, Cd, Co, Cr, Cu, Ge, Ni, Pb) and 3 sulfur species (sulfate SO4, sulfide S2− and Organic S0) in 7 density fractions of Qingshan bituminous coal, and the TEs occurrence mode is studied with Solari (1989) model. Moreover, the contents of 12 TEs (including above-mentioned 9 TEs and Mn, V, Zn) in 7 Chinese typical coals are determined and che-momelric methods (factor and cluster analysis) are used to investigate the TEs combination in these coals. Secondly, 8 fly ashes with 4 sizes are sampled during Qingshan bituminous coal combustion in a thermal power plant. Higher temperature and reducing atmosphere are found to enhance greatly the metals enrichment in the submicron and micrometer panicles. An enrichment coefficient is used to describe the TEs partitioning in the fly ash size-fractions and the results are discussed according to three factors: TEs combination in coals, combustion condition in a combustor. and fly ashes size. Finally it is also studied, by the sequential extraction analysis, that the TEs speciation in ashes (dregs and fly ashes) from Qingshan bituminous coal combustion, in order to assess reasonably the TEs environmental impacts.

99/03292 The UK new and renewable energy program

An experimental study was performed on a 36 kWth down-fired furnace in order to obtain a wider and more detailed knowledge of the influence of the key parameters on the gaseous fuel reburning process when typical Chinese coals served as the primary fuel. The experimental results show that both above 50% nitric oxide reduction and low carbon loss can be obtained when reburn zone residence time is about 0.6 s–0.9 s, gaseous reburn fuel percent is about 10%–15% and average excess air coefficient of reburn zone is about 0.8–0.9. According to the optimizational reburning operating parameters, a 350 MWe coal-fired boiler was retrofitted for reburning application. The retrofitted boiler had about 0.7 s reburn zone residence time and about 2 s residence time after the burnout air was injected. The results of the demonstration on the full-scale boiler showed that the nitric oxide emission was about 235 mg/Nm3 (O2 = 3%, dry) from the retrofitted boiler and above 60% nitric oxide reduction efficiency could be achieved with no adverse effects on the boiler operability when the coke-oven gas used as the reburn fuel. This successful demonstration project filled the gaps in the gaseous fuel reburning application on 300 MWe grade unit boiler in China and showed that the values of the optimizational reburning parameters obtained from experiments could be successfully applied to the designing, retrofitting and optimizing for the gaseous fuel reburning process.