Shenhua Bituminous Coal Research Articles

Influence of calcium chloride on the fine particulate matter formation during coal pyrolysis

This study investigated the influence of CaCl2 on fine particulate matter (PM0.5) formation during coal pyrolysis. Two acid-washed coals were loaded with different amount of CaCl2 by physical impregnation. Pyrolysis experiments were conducted in a flat-flame burner at 1400 K, 1600 K, and 1800 K. The PM0.5 yield was evaluated through the size-segregated sampling with a low pressure impactor (DLPI+). Then, the transformation properties of CaCl2 was analyzed with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the soot properties were analyzed with transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results show that PM0.5 yield is affected by coal type, CaCl2 loading level, and pyrolysis temperature. Loading small amount of CaCl2 can reduce the PM0.5 yield through soot inhibition, while high loading of CaCl2 increases the PM0.5 yield by forming mineral particles, the lowest PM0.5 yield occurs at 1.5 % Ca content. The PM0.5 reduction rate of CaCl2 increases then decreases with temperature from 1400 K to 1800 K. On all tested conditions, the PM0.5 yield of low-rank Zhundong subbituminous coal was lower than Shenhua bituminous coal. The release rate of Ca into PM0.5 is positively related to pyrolysis temperature and CaCl2 loading level. Ca loading decreases the sizes of soot primary particles and agglomerates, and leads to smaller amorphous cores and more disordered graphitic shells in the soot primary particles. CaCl2 loading also causes the dealkylation and deoxygenation of soot. The influence of CaCl2 on soot formation can be summarized as the catalytic effect on soot precursor formation, the enhancement of soot nucleation, and the inhibition of soot coagulation.

Experimental study and kinetic analysis of the impact of ammonia co-firing ratio on products formation characteristics in ammonia/coal co-firing process

Ammonia is a carbon-free, hydrogen-rich fuel, which is considered as an alternative energy source with high utilization potential. Ammonia/coal co-firing in air-staged coal-fired boilers has attracted the attention of a number of academics in order to meet the aim of low carbon and NOx emissions. In this paper, ammonia/coal co-firing experiments were conducted under air-staged condition in a one-dimensional combustion-temperature controlled down-fired furnace with multi-path air inlets at 1100℃. The influence of ammonia co-firing ratio on NO and CO2 emissions, as well as CO and H2S release characteristics, was studied using Shenhua bituminous coal in air-staged and non-staged combustion conditions. Chemical reaction kinetic calculations were conducted to provide a qualitative analysis of the experimental results. Ammonia plays a complex role in the ammonia/coal co-firing process. An effective CO2 reduction was achieved with ammonia co-firing, and it was found that air-staged combustion is also effective for NO emission control in the ammonia/coal co-firing process. Considering the economy issue and NO emission control, 20–30 % ammonia co-firing ratio is recommended. However, ammonia/coal co-firing can greatly promote the coal gasification reaction, which leads to a higher concentration of CO in the reduction zone in air-staged combustion, compared with coal combustion. Meanwhile, ammonia co-firing has a significant inhibitory effect on the release of H2S from coal and will promote the subsequent decomposition process. This study explains the NO release pattern in ammonia/coal co-firing processes based on experimental results and chemical kinetics calculations, which provides a promising technical advancement direction for the coal-fired power plants to achieve a signification reduction of both CO2 and NO emissions.

Effects of Pressure and Coal Rank on the Oxy-Fuel Combustion of Pulverized Coal

Pressurized oxy-fuel combustion technology is the second generation of oxy-fuel combustion technology and has low energy consumption and low cost. In this research, a visual pressurized flat-flame reaction system was designed. A particle-tracking image pyrometer (PTIP) system based on a high-speed camera and an SLR camera was proposed. Combining the experimental system and data-processing method developed, the ignition and combustion characteristics of a single coal particle between 69 and 133 μm in size were investigated. The results indicated that at atmospheric pressure, the ignition delay time of ShanXi (SX) anthracite coal was longer than that of ShenHua (SH) bituminous coal, while that of PRB sub-bituminous coal was the shortest. As the pressure rose, the ignition delay time of the PRB sub-bituminous coal and SX anthracite coal showed a continuous increasing trend, while the ignition delay time of SH bituminous coal showed a trend of first increasing and then decreasing. Moreover, pressure also affects the pyrolysis process of coal. As the pressure increases, it became more difficult to release the volatiles produced by coal pyrolysis, which reduced the release rate of volatiles during the ignition stage, and prolonged the release time and burning duration time of volatiles.

Investigation on the volatile combustion and Fuel-N to NO conversion during pulverized fuel ignition process

The volatile combustion and NO release characteristics of pulverized fuel (PF) flames in an optical flat-flame entrained-flow reactor were investigated by CH∗/NO∗ chemiluminescence imaging. Pyrolyzed bituminous (PB) char with an ultralow volatile content (Vdaf≈10%) and a comparative coal sample of Shenhua (SH) bituminous coal with a high volatile content (Vdaf = 34.2%) were studied under different ambient O2 mole fractions (10%∼30%). The initiation of the combustion region of PB char occurs later than SH bituminous coal, owing to its low volatile contents, a slow devolatilization rate, and homogeneous-heterogeneous ignition/combustion mode. By measuring probed solid and gas samples, the conversion ratios of fuel-N to NO and the releasing ratios of volatile-N/char-N were determined in ignition process. Semi-quantitative NO release integral intensity and volatile combustion intensity results were obtained by integrating the NO∗ or CH∗ chemiluminescence intensity in the corresponding reaction region. The volatile combustion and NO release show good synchronous for Shenhua bituminous coal, which means that the NO releasing originated predominantly and owned higher conversion ratio from the volatile-N in the ignition region. The NO release integral intensity and NO emission of SH bituminous coal decreased with O2 concentration increased from 20% to 30%, which indicates that the enriched-O2 environment is beneficial for high volatiles bituminous to decrease NOx emission in ignition stage. For PB char, NO releasing originated predominantly from the char heterogeneous reactions of char-N in its ignition and combustion late stage.

A particle-tracking image pyrometer for characterizing ignition of pulverized coal particles

In this study, a particle-tracking image pyrometer (PTIP) system, based on a high-resolution high-speed camera and a digital single lens reflex (SLR) camera, was proposed to investigate the ignition characteristics of pulverized coal particles. The goal of the PTIP system was to obtain reliable simultaneous measurements of the velocity, diameter, and temperature of individual burning particles. A modified particle-tracking velocimetry (PTV) algorithm was developed to collect the image sequences of individual particles, and it could weed out defocused particles and other odd particles by low-frequency filtration. Moreover, a template matching method was adopted to distinguish particles undergoing different combustion states (homogeneous volatile combustion or heterogeneous coal/char combustion). The experimental validation was carried out under an O2/CO2 atmosphere in an optically accessible flat flame-supported entrained flow reactor. Particles of Shenhua (SH) bituminous coal, in the size range of 70–133 μm, were combusted in the flue gas with gas temperature of 1400 K and O2 concentration of 20%. The diameter-temperature patterns of particles along their trajectories were discussed. Several criteria based on statistical analysis were adopted to divide the combustion process and obtain the ignition delay time (IDT) and devolatilization duration time (DDT).

CO2 gasification kinetics of Shenhua bituminous coal by isothermal thermogravimetric analysis

AbstractGasification kinetic analysis of three Shenhua bituminous coal samples with various particle size ranges were carried out at three different temperatures (1000, 950, and 900°C) for 30 min using the gasifying agent of CO2 with the flow rate of 40 ml min−1. The average particle sizes for sample A, sample B, and sample C were 43.4, 168, and 293 μm, respectively. Experimental results indicated that there were differences among the weight loss curves of three coal samples with different particle sizes. Furthermore, the differences became larger with the decrease of temperatures. Among the 11 used reaction mechanisms, two‐dimensional growth of nuclei following the Avrami‐Erofeev equation (A2) was proved to be the most appropriate one to fit the gasification data of Shenhua bituminous coal samples, as it can reconstruct gasification curves with high correlation coefficients (R2 > 0.95). The calculated values of apparent activation energy (E) for sample A, sample B, and sample C were 95.9, 79.1, and 69.4 kJ mol−1, respectively. It was also found that the particle size had significant influence on kinetic data. The apparent activation energy decreased when there was an increase of the particle size. The compensation relationship of E and A (apparent pre‐exponential factor) was noted, and the fitted mathematic formula was lnA = 0.1041 E+0.540 28 (R2 = 0.999).

High-temperature pyrolysis behavior of two different rank coals in fixed-bed and drop tube furnace reactors

In order to explore the high-temperature pyrolysis behavior and mechanism, two different rank coals (Shenhua bituminous coal and Baiyinhua lignite coal) were pyrolyzed in fixed-bed and drop tube furnace (DTF) reactors. Pyrolysis gas production was online quantified by a drainage method while the gas composition was detected by the gas chromatography. The physical and chemical characteristics of pyrolysis char were observed by N2 absorption and FTIR. Results show that pyrolysis gas release rate and total production increase with the higher temperature. The gas production of SH coal (618–749 ml/g) is always higher than that of BYH coal (418–510 ml/g) due to its higher volatile content. The main high-temperature pyrolysis gas products are H2 (∼50% vol), CO, CH4 and CO2. Carbon-reduction reaction at high temperatures can further form H2 and CO while the rupture of aromatic heterocyclic ring can generate CH4. High-temperature pyrolysis can greatly remove the coal moisture, develop their pore structures, crack the chemical functional groups (O–H, –CH3, CO, C–O, etc.) and upgrade the coal rank. Different coal structures and pyrolysis heating rates result in various gas evolution and char formation behaviors. Higher heating rate can help to quickly generate large amounts of free radicals and change the pyrolysis behaviors.

Gasification of Shenhua Bituminous Coal with CO2: Effect of Coal Particle Size on Kinetic Behavior and Ash Fusibility

Coal gasification is the process that produces valuable gaseous mixtures consisting primarily of H2 and CO, which can be used to produce liquid fuel and various kinds of chemicals. The literature shows that the effect of particle size on coal gasification and fusibility of coal ash is not clear. In this study, the gasification kinetics and ash fusibility of three coal samples with different particle size ranges were investigated. Thermogravimetric results of coal under a CO2 atmosphere showed that the whole weight loss process consisted of three stages: the loss of moisture, the release of volatile matter, and char gasification with CO2. Coal is a heterogeneous material containing impurities. Different grinding fineness leads to different liberation degrees for impurities. As for the effect of particle size on TG (thermogravimetry) curves, we found that the final solid residue amount was the largest for the coal sample with the smallest particle size. The Miura-Maki isoconversional model was proved to be appropriate to estimate the activation energy and its value experienced a slow increase when the particle size of raw coal increased. Further, we found that particle size had an important impact on ash fusion temperatures and small particle size resulted in higher ash fusion temperatures.

Effects of pyrolyzed semi-char blend ratio on coal combustion and pollution emission in a 0.35 MW pulverized coal-fired furnace

The effects of blend ratio on combustion and pollution emission characteristics for co-combustion of Shenmu pyrolyzed semi-char (SC), i.e., residuals of the coal pyrolysis chemical processing, and Shenhua bituminous coal (SB) were investigated in a 0.35 MW pilot-scale pulverized coal-fired furnace. The gas temperature and concentrations of gaseous species (O2, CO, CO2, NOx and HCN) were measured in the primary combustion zone at different blend ratios. It is found that the standoff distance of ignition changes monotonically from 132 to 384 mm with the increase in pyrolyzed semi-char blend ratio. The effects on the combustion characteristics may be neglected when the blend ratio is less than 30%. Above the 30% blend ratio, the increase in blend ratio postpones ignition in the primary stage and lowers the burnout rate. With the blend ratio increasing, NOx emission at the furnace exit is smallest for the 30% blend ratio and highest for the 100% SC. The NOx concentration was 425 mg/m3 at 6% O2 and char burnout was 76.23% for the 45% blend ratio. The above results indicate that the change of standoff distance and NOx emission were not obvious when the blend ratio of semi-char is less than 45%, and carbon burnout changed a little at all blend ratios. The goal of this study is to achieve blending combustion with a large proportion of semi-char without great changes in combustion characteristics. So, an SC blend ratio of no more than 45% can be suitable for the burning of semi-char.

Experimental study of the flame propagation characteristics of pulverized coal in an O2/CO2 atmosphere

The effects of the pulverized coal concentration, particle size, oxygen concentration, and initial combustion pressure on the flame propagation behavior of pulverized Shenhua bituminous coal have been investigated. The results show that the pulverized coal concentration and oxygen concentration have the same effect on the pulverized coal flame propagation speed. As the pulverized coal concentration or oxygen concentration increases, the pulverized coal flame propagation speed increases. As the pulverized coal particle size increases, the flame propagation speed decreases. Under pressurized conditions, for an oxygen concentration of 70%, the flame propagation speed of the pulverized coal gradually increases with increasing pressure (1–10 atm), and the increase becomes small after 8 atm. For oxygen concentrations of 30% and 50%, pulverized coal flame propagation no longer occurs when the pressure reaches 4 atm. Combined with the combustion parameters determined by thermogravimetry, the flame propagation speed of pulverized coal is positively correlated with combustion characteristics.

Effect of volatile reactions on the yield and quality of tar from pyrolysis of Shenhua bituminous coal

Pyrolysis was an important route for coal conversion and also the fundamental for clean and efficient utilization of coal. As an important product of pyrolysis, coal tar can be used as the raw material for producing premium liquid fuels and high value-added chemicals (benzene-toluene-xylene, naphthalene, phenols, etc.). The products’ distribution and quality were significantly affected by the secondary reaction of volatiles. In this work, Shenhua bituminous coal was pyrolyzed with a two-stage reactor at a relatively low temperature, and the released volatiles underwent secondary reactions at various temperatures and residence time. The yields and quality of coal tar were characterized by gas chromatography–mass spectroscopy (GC–MS) and Fourier transformed infrared spectroscopy (FTIR). The results showed that secondary volatile reactions decrease tar yield but increase gas and coke yield. The volatile reaction results in a decrease in the content of aliphatics and phenols, and an increase in the content of arenes and polar compounds. The volatile reaction includes the following reactions: dehydroxylation, deoxygenation, cleavage of long chain aliphatic structures into short ones, and condensation of aromatic clusters, etc. The higher heating rate of pyrolysis reduces the content of aliphatic and polar compounds while increases that of arenes and phenols in the light tar (HS).

High-temperature pyrolysis behavior of a bituminous coal in a drop tube furnace and further characterization of the resultant char

In order to study the high-temperature pyrolysis behavior of bituminous coal in the drop tube furnace (DTF) and better utilization of the obtained char, a typical Shenhua bituminous coal (SH) was pyrolyzed in a DTF at the temperatures of 1000–1300 °C (100 °C increments). The obtained char was then characterized using BET and FTIR methods, while its combustion, gasification and pollutant emission characteristics were explored by a thermogravimetric analyzer and online flue gas analyzer. Results show that higher pyrolysis temperature leads to more CO and less CH4 for the increased free radical rearrangement by high heating rate and carbon reduction reactions at high temperatures. Pyrolysis generally decomposes the functional groups, increases the volume of char pores, and upgrades the rank of coal. The combustion activation energy increases from 22.99 kJ/mol to 27.42 kJ/mol and the gasification is hindered with the higher pyrolysis temperature. It is notable that the NOx and SO2 emissions of the obtained char combustion are both below 30 mg/s-MJ. High-temperature pyrolysis can enhance the evolution of NH3 and HCN as volatiles, thus decreasing the NOx formation in further char combustion stages while partly decomposing the organic and inorganic sulfur compounds to impact the SO2 emission.

Performance of a 50 kWth coal-fuelled chemical looping combustor

A 50 kWth chemical looping combustion (CLC) reactor for coal has been successfully constructed and operated. A turbulent fluidized bed acts as the air reactor (AR) to achieve high solid circulation rate, while a bubbling fluidized bed operates as the fuel reactor (FR) to guarantee sufficient solid residence time. Two risers are separately connected to the AR and FR to provide the driving force for oxygen carrier (OC) circulation. A four-chamber loop seal (LS) is installed between AR and FR, playing the roles of a gas-sealing configuration and also a carbon stripper to convert unreacted char.Low-cost natural hematite was used as OC and Shenhua bituminous coal was used as fuel. A series of tests was conducted to investigate the performance of the newly constructed CLC reactor under different operational parameters. Effects of temperature, inlet gas velocity and H2O concentration in fluidizing agent, on the performance of the CLC reactor were investigated. The relatively stable pressure drop attained in the FR indicated successful operation of the CLC system. During 120 min continuous running with a bed inventory of 100 kg in FR, the highest CO2 yield reached to 0.91 and the combustion efficiency was 0.86 at 1000 °C.

Fuel Nitrogen Conversion in Chemical Looping with Oxygen Uncoupling of Coal with a CuO-Based Oxygen Carrier

The interest in chemical looping with oxygen uncoupling (CLOU) of coal as a method for CO2 enrichment has increased drastically during recent years. The objective of this work was to experimentally investigate fuel nitrogen conversion in the CLOU process of coal with a CuO-based oxygen carrier in a batch fluidized-bed unit. Three coals of different rank (anthracite, sub-bituminous, and bituminous) and their corresponding chars were used as fuels. Furthermore, experiments of coal combustion under air-fired conditions were performed to recognize the unique pathway of fuel nitrogen conversion in CLOU. Experimental results indicated that NO was formed in the largest amount of total NOx. For the Shenhua bituminous coal that was used, most of the NO, NO2, and N2O from fuel nitrogen was formed during the devolatilization stage of the coal. However, with Xuzhou sub-bituminous coal or Huaibei anthracite as fuels, a certain portion of NO was derived from char-N. Under the current experimental conditions (temperatur...

Co-combustion characteristics of sewage sludge with different rank bituminous coals under the O2/CO2 atmosphere

The effects of sewage sludge (SS) blended ratio, O2/CO2 ratio, and type of bituminous coal on the co-combustion characteristics of SS with bituminous coals were investigated. Thermogravimetric analysis was used to analyze the co-combustion profiles. Results show that TG curve shifts to a lower temperature with increasing SS blended ratio and O2/CO2 ratio. A distinct transition section exists at fixed carbon combustion of the blended fuels stage, and the temperature range of this transition section decreases significantly with increasing O2/CO2 ratio. The combustion property indexes of blended fuel increase with increasing SS blended ratio and O2/CO2 ratio. However, effect of O2/CO2 ratio on increasing the overall co-combustion characteristics becomes smaller when the oxygen concentration exceeds 30 %. Comparing SS blended with Huaibei (HB) bituminous coal, the SS blended with Shenhua (SH) bituminous coal (high-rank bituminous coal) combustion has the good combustion performance.

Field test of coal type adaptability on a 300 MW CFB boiler

Coal type adaptability for CFB boilers is of great importance because it influences whether the unit can operate safely, economically and environmentally when the coal type is changed. Research is carried out on a 300MW CFB boiler located in Longyan power plant, Fujian province by burning three types of coal, i.e. Fujian anthracite, Shenhua bituminous coal and Indonesia lignite. The results show that all the three coals are capable to meet the basic requirement of bed temperature. But the fly ash carbon content and exhaust gas temperature depend on the coal type. Compared with Fujian anthracite, Shenhua bituminous coal and Indonesia lignite tend to possess lower fly ash carbon content and lower exhaust gas temperature under high boiler load, which helps to increase the boiler efficiency. The auxiliary power consumption rates under all the three types of coal are all lower than 4.3% with the successful utilization of lower energy consumption technology based on state specification design theory. Besides, when the fuel is changed from Fujian anthracite to Shenhua bituminous coal and Indonesia lignite, SO2 emission and dust emission decreases, while the NOx emission increases.

Parametric study of reburning of nitrogen oxide for superfine pulverized coal

An experimental investigation of process parameters design by superfine pulverized coal reburning on NOx reduction is carried out in a one-dimensional bench-scale combustion system. Reburning effectiveness for initial levels ranging from 600 to 650ppm is evaluated. It is found that for Shenhua bituminous coal, NOx reduction performance of superfine pulverized coal owns its unique advantage, 50% higher than conventional particle size. Medium reburning fuel fraction (RF20∼RF25) and low oxygen concentration are recommended to be ensured in this experiment. The yield of HCN and CH4 along the furnace axis does not seem to be decisive on the effect of particle size, but is closely related to the effect of reburning fuel fraction. Both exhaust and in-flame measurements are reported in this paper to provide valuable experimental data for practical engineering applications.

Copper-Decorated Hematite as an Oxygen Carrier for in Situ Gasification Chemical Looping Combustion of Coal

Iron ore is a cheap and nontoxic oxygen carrier in chemical looping combustion (CLC) systems. However, iron ore exhibits low reactivity with solid fuels. In this work, hematite decorated with Cu via impregnation was used as an oxygen carrier. Experiments were conducted in a batch fluidized bed reactor using Shenhua (SH) bituminous coal and Gaoping (GP) anthracite as fuels. The effects of Cu loading in the hematite, reaction temperature, supply oxygen coefficient, and coal type on the CLC performance of coal were investigated. It was found that hematite loaded with 6% Cu (6CuHem) had better reactivity with the gasification products (CO and H2) of coal than hematite (Hem) alone. Furthermore, 6CuHem was found to accelerate the gasification rate of GP anthracite char. A reaction temperature higher than 900 °C was conducive to fast and complete conversion of carbon in coal. As the supply oxygen coefficient was increased, the rate of carbon conversion and the combustion efficiency of coal increased. Multiple re...

Coal Consumption for NO Reduction in the Coal Reburning Process in an Entrained Flow Reactor

The ratio of reburn coal to reduced nitrogen monoxide (NO) is defined as the coal consumption. The effects of oxygen, reburn fuel fraction, temperature, coal particle size, and coal type on coal consumption using data from coal reburning in a high-temperature, entrained flow reactor is studied. The results indicate that a high NO reduction efficiency does not necessarily mean low coal consumption. For 71 μm Shenhua bituminous coal, at 1,300°C, 4 and 6% O2, an increased reburn fuel fraction leads to decreased coal consumption. However, at 2% O2, increased reburn fuel fraction leads to increased coal consumption. Increasing volatile content and temperature leads to decreased coal consumption. The effect of temperature on high volatile coal is more notable than on low volatile coal.

Applications of thermal stepwise reactions on the co-gasification of coal and tobacco stems

The objective of this study was to better understand the gasification mechanisms between tobacco stems and coal in a carbon dioxide atmosphere. Shenhua bituminous coal with Chinese tobacco stems were studied using the SDT–MS–FTIR technique, to elicit information from the thermal decomposition curves coupled with the evolved gases analysis. Subsequently, the activation energy of each reaction was calculated. The experimental results show that: (1) there were synergistic effects of mixtures of tobacco stems and coal, while decreasing the gasification temperature of fixed carbon in coal and increasing the reaction rate; (2) the proportion of tobacco stems and coal has an important influence on the gasification reaction; (3) the alkali and alkali earth metals in the tobacco stems play an important role in the cogasification of coal and tobacco stems.