Observation of coal fragmentation in early stages of combustion

Measurements of coal fragmentation in the early stages of combustion were undertaken in the size range of crushed coals for Chinese Dongjin and Indonesian Roto coals. A flat flame burner fed with a premixed mixture of methane, air and partly hydrogen was used for the burning of a single coal particles. A high speed video camera system was used for the observation of coal fragmentation during approximately 80 msec. Fragmentation is consistently observed in the controlled combustion environment over a gas flame temperature range of 1220K–1320K. The data indicate that a single coal particle often disintegrates into two, three, and sometimes more fragments. The dominant mechanisim of fragmentation is that producing two fragments in primary fragmentation. The Dongjin coal breaks up more extensively than the Roto coal with the frequency of fragmentation exhibiting a strong particle size dependence and a weaker gas flame temperature dependence. The mean time of primary fragmentation for the Dongjin coal falls to between 10 msec and 20 msec and does not remarkably vary with particle size and gas flame temperature. The mean time of primary fragmentation for the Roto coal is strongly dependent on the particle size, whilst shows less gas flame temperature dependence.     

The characteristics of pulverized coal combustion in the two stage cyclone combustor

Numerical investigations on air staging and fuel staging were carried out with a newly designed coaxial cyclone combustor, which uses the method of two stage coal combustion composed of pre-combustor and main combustor. The pre-combustor with a high air/fuel ratio is designed to supply gas at high temperature to the main combustor. To avoid local high temperature region in this process, secondary air is injected in the downstream. Together with the burned gas supplied from the pre-combustor and the preheated air directly injected into main combustor, coals supplied through the main burner react rapidly at a low air/fuel ratio. Strong swirling motion of cyclone combustor keeps the wall temperature high, which makes slagging combustion possible. Alaska, US coal is used for calculations. Predictions were made for various coal flow rates in the main combustor for fuel staging and for the various flow rate of secondary air in the pre-combustor for air staging. In-scattering angles are also chosen as a variable to increase residence times of coal particles. Temperature fields and particle trajectories for various conditions are described. Predicted temperature variations at the wall of the combustor are compared with corresponding experimental data and show a similar trend. The in-scattering angle of 20° is recommended to increase the combustion efficiency in the main chamber.     

Effect of ash fraction and particle size on ash deposition during pulverized coal combustion

Coal is an important energy source to increase consumption continuously. However, the ash residues from coal combustion have produced ash deposition that causes slagging and fouling in boilers. The goal of this study is to examine the characteristics of ash deposits (i.e., the effects of the ash fraction and particle size) in pulverized coal combustion. For this study, five coals (Suek, Macqurie, Berau, Lanna and Vitol) are used, which have similar chemical components in the ash but differences in the ash fraction. A Thermomechanical analysis technique (TMA) and Drop tube furnace (DTF) are used to analyze the tendencies in the ash fusibility and deposition with temperature, respectively. Moreover, the size and morphology of the fly ash are analyzed for physical changes by using a particle-sizedistribution analyzer and Scanning electron microscopy (SEM), respectively. In the TMA results, all coal types have a similar fusibility because of the similar chemical components in the ash. The order of the deposited mass is Suek, Macqurie, Berau, Vitol and Lanna in accordance with the ash fraction in the DTF. The ash fraction in coal is a major factor in the ash deposit according to these results. The size of the fly ash changed compared to that of the raw coal according to the results of a particle-size analysis and SEM owing to physical processes such as fragmentation, shedding and coalescence during coal burning. On this basis, a deposition model is developed with the ash fraction and particle size. The model results are in good agreement with the measurements. The results demonstrate that the particle size and ash fraction influence the deposit.

     

用模块化DCS实现燃煤热水锅炉的燃烧控制

石油大学供热微机测控系统选用了模志化ＤＣＳ。本文对硬件系统进行配置;针对燃料控制系统时滞大,耦合性强,随机干扰多的特点,对出口水温采用“等等看”控制算法。对氧含量采用前馈－反馈控制,控制算法中采用了积分分离的ＰＩＤ算法;针对负压对象信号波动范围大等特点,以负压变化趋势来控制引风量的办法。     

高速摄像技术在煤粉燃烧工作状态监控中的应用研究

针对高炉喷煤风口监控手段落后和回旋区耦合传热计算误差大、实时性差等问题，本文以高速摄像机作为测试工具，研究了喷煤高炉风口回旋区煤粉燃烧状态。用图像处理和三基色辐射测温法计算回旋区煤粉燃烧的温度变化和相对亮度变化，监控喷吹到高炉的煤粉粒子燃烧工况。并针对高速摄像机CCD传感器在高温测试过程中由于辐射强度过大易出现输出过饱和电流，导致“图像发白”问题，提出了摄像机快门控制模型，以提高摄像机测温动态范围，实现了风口回旋区温度和燃烧脉动的动态测量。通过现场应用表明，该方法为高炉喷煤提供了有力的测试手段和信息来源，快门控制模型提高了温度测量区间。     

Transient analysis of hybrid rocket combustion by the zeldovich-novozhilov method

Hybrid rocket combustion has a manifestation of stable response to the perturbations compared to solid propellant combustion. Recently, it has revealed that the low frequency combustion instability about 10 Hz was occurred mainly due to thermal inertia of solid fuel. In this paper. the combustion response function was theoretically derived by use of ZN (Zeldovich-Novozhilov) method. The result with HTPB/LOX combination showed a quite good agreement in response function with previous works and could predict the low frequency oscillations with a peak around 10 Hz which was observed experimentally. Also, it was found that the amplification region in the frequency domain is independent of the regression rate exponentn but showed the dependence of activation energy. Moreover, the response function has shown that the hybrid combustion system was stable due to negative heat release of solid fuel for vaporization, even though the addition of energetic ingredients such as AP and Al could lead to increase heat release at the fuel surface.     

On the method for hot-fire modeling of high-frequency combustion instability in liquid rocket engines

This study presents the methodological aspects of combustion instability modeling and pro-vides the numerical results of the model (sub-scale) combustion chamber, regarding geometrical dimensions and operating conditions, which are for determining the combustion stability boundaries using the model chamber. An approach to determine the stability limits and acoustic characteristics of injectors is described intensively. Procedures for extrapolation of the model operating parameters to the actual conditions are presented, which allow the hot-fire test data to be presented by parameters of the combustion chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for designers. Tests with the model chamber, based on the suggested scaling method, are far more cost-effective than with the actual (full-scale) chamber and useful for injector screening at the initial stage of the combustor development in a viewpoint of combustion instabilities.     

Investigations on the effect of measurement errors on estimated combustion and performance parameters in HCCI combustion engine

Several parameters derived from heat release analysis are used for combustion diagnostics and control in internal combustion engines. It is important to tune the input parameters used in heat release calculations, in order to get correct estimation of heat release rate. In this study, tuning of input parameters is carried out by using cumulative heat release calculations of cylinder pressure during motoring. This tuning procedure uses offline iterative processing of motoring in-cylinder pressure data. The tuned parameters obtained from this method can also be utilized for online analysis of combustion parameters. Input parameters used in these investigations are intake air temperature, intake air pressure, phasing between the acquired pressure and crank angle position, compression ratio and scaling factor of heat transfer coefficient. Effect of error in these input parameters on estimated combustion and performance parameters like IMEP, combustion phasing, combustion duration, heat release rate, and maximum mean gas temperature are evaluated. The relative importance of measurement error in input parameters and its maximum expected error in the final results is analyzed in a HCCI combustion engine. Results shows that measurement errors in phasing between pressure and crank angle position, compression ratio and inlet air pressure affect estimated combustion and performance parameters significantly.     

Ignition and combustion characteristics of the gas turbine slinger combustor

This paper describes the ignition and combustion characteristics of a gas turbine slinger combustor with rotating fuel injection system. An ignition test was performed under various airflow, temperature and pressure conditions with fuel nozzle rotational speed. From the test, there are two major factors influencing the ignition limits: the rotational speed of the fuel nozzle, and the mass flow parameter. Better ignition capability could be attained through increasing the rotational speed and air mass flow. From the spray visualization and drop size measurement, it was verified that there is a strong correlation between ignition performance and drop size distribution. Also, we performed a combustion test to determine the effects of rotational speed by measuring gas temperature and emission. The combustion efficiency was smoothly enhanced from 99% to 99.6% with increasing rotational speed. The measured pattern factor was 15% and profile factor was 3%.     

An experiment of the combustion characteristics with laser-induced spark ignition

The combustion characteristics and minimum ignition energies using laser-induced spark ignition were demonstrated for quiescent methane-air mixtures in an optically-accessible, constant volume combustion chamber. Initial pressure and equivalence ratio as well as spark energy were varied in order to explore the flame behavior with laser-induced spark ignition. Shadowgraphs for the early stages of combustion process showed that the flame kernel becomes separated into two, one of which grows back towards the laser source. Eventually after a short period, the two flame kernels developed into two flame fronts propagating individually, which is unique in laser-induced spark ignition. For a given mixture, lower initial mixture pressure and higher spark energy resulted in shorter flame initiation period and faster flame propagation. The results of minimum ignition energies for laser ignition shows higher values than electric discharge results, however, the difference decreases toward lean and rich flammability limits.     

火力发电厂煤粉流量测量技术研究

火力发电厂总燃料量的精确测量是进行锅炉燃烧控制优化的关键难点问题。本文系统地提出了火力发电厂煤粉流量的测量技术,并结合实际应用经验提出各种测量方法的技术要点以及制约点,同时结合工程实践提出了煤粉流量测量技术的发展展望,为进一步研究实践煤粉流量的测量技术奠定了基础。     

Prediction of coal feeding during sintering in a rotary kiln based on statistical learning in the phase space

In alumina rotary kiln production, adjusting the coal feeding rate is the main way to maintain sintering temperature stability during the sintering process, which plays a critical role in improving production quality and reducing energy consumption. In this paper, a novel integrated method (termed PSR-PCA-HMM) is proposed to predict the coal feeding state for optimal control by integrating principal component analysis (PCA) and the hidden Markov model (HMM) based on phase space reconstruction (PSR). First, the thermal signals in rotary kilns are shown to have obvious chaotic characteristics. Second, PSR is utilized to extract the features of the sintering process in a rotary kiln, and PCA is proposed to efficiently reduce the redundancy of the high-dimensional feature space reconstructed by the PSR. Then, considering the nonlinear dynamic characteristic of the sintering process, three HMM models are built to capture the nonlinear dynamic relationship between thermal variables and the corresponding coal feeding state. Finally, the posterior probabilities with respect to the three HMM models are estimated by using the forward algorithm, and the final prediction of coal feeding is determined by the maximized likelihood estimation. Based on field data, the application results indicate that the PSR-PCA-HMM method can significantly improve prediction performance and help realize stable closed-loop control for the sintering temperature.     

Concentration measurement with thermal probe for pulverized coal in the pneumatic pipeline of power plant

The concentration measurement of pulverized coal in a pneumatic pipeline is a challenging issue in power plant. A thermal probe manufactured with abrasion-proof steel was developed for coal concentration measurement in such a situation. The probe generates 15 W of heat. This method is based on the heat transfer between the thermal probe and the gas–solid two-phase flow. Experiments were conducted in a horizontal pneumatic pipeline to assess the accuracy of the thermal probe, where the gas was air and the solid was pulverized coal with mean diameter of 65 µm. The wall temperature of the thermal probe was found to be dependent on both coal powder concentration and air velocity. A new heat transfer correlation was proposed in terms of the modified Reynolds and Nusselt numbers for the gas–solid two-phase flow across the thermal probe. In the range of coal powder concentration from 0.1 to 0.65 kg/kg, the standard deviation is 0.01 kg/kg for the thermal probe. The thermal probe has potential application for concentration measurement of pulverized coal in the pneumatic pipelines of power plants.     

Electron spectroscopic diffraction and imaging of the early and mature stages of calcium phosphate formation in the epiphyseal growth plate

A review of different models of biomineralization in collagen-rich hard tissues shows that further investigations of crystal formation are necessary. The electron spectroscopic diffraction (ESD) mode of operation of an energy-filtering electron microscope offers the possibility of being able to avoid the background from inelastic scattering in selected-area electron diffraction patterns. First experiments on the different stages of mineralization in the epiphyseal growth plate have only indicated the presence of apatite. The ESD mode can be complemented by the electron spectroscopic imaging mode and by elemental mapping of calcium.     

A study of control strategy for the bin system with tube mill in the coal fired power station

The pulverized coal systems with tube mills are widely used in coal fired power plants. As there are many controlled variables and disturbances in this system, and startup and shutdown of the system is frequent and the dynamic characteristic of the controlled plant is also extraordinary, the automatic control system for this kind of pulverized coal system is not ideally implemented for long. The authors of this paper investigated and tested a pulverized coal system with tube mill in Nanjing Thermal Power Station, and based on various different controlled plants and control objectives, proposed rather independent control subsystems. These subsystems can organize a whole automatic control system of pulverized coal system that can be used in different conditions. The control system presented in this paper has worked well since it was put into operation in May 1998, and good economic benefits have been acquired.     

A study on the rapid bulk combustion of premixture using the radical seeding

The objective of this study is the rapid bulk combustion of mixture in a constant volume chamber with a tiny sub-chamber. Some narrow passage holes were arranged to induce simultaneous multi-point ignition in the main chamber by jet of burned and unburned gases including radicals from the sub-chamber, and the equivalence ratios of pre-mixture in the main chamber and the sub-chamber were the same. The principal factors of the Radical Induced Auto-Ignition (RIAl) method are the diameter of the passage holes and the volume of sub-chamber. The relationship between the sub-chamber and diameter of passage hole was represented by the ratios of sub-chamber volume to passage hole volume. The ratios are non-dimensional coefficients for sub-chamber characteristics. As a result, the RIAI method reduced the combustion period, which expanded the lean limit in comparison with SI method.     

Mapping the chemistry of resinite,funginite and associated vitrinite in coal with micro‐FTIR

Micro‐FTIR mapping is a powerful tool for nondestructive, in situ chemical characterization of coal macerals at high resolution. In this study, the chemistry of resinite, funginite and associated vitrinite is characterized via reflectance micro‐FTIR for Cenozoic high volatile C bituminous coals from Colombia. In comparison with the micro‐FTIR spectra of vitrinite and inertinite, the corresponding spectra of liptinite macerals in the same coals are characterized by stronger aliphatic CH_x absorbance at 3000–2800 and 1460–1450 cm^?1, but less intense aromatic C=C ring stretching vibration and aromatic CH_x out‐of‐plane deformation at 700–900 cm^?1. The aliphatic components in resinite have the longest carbon chains and are least branched, bestowing the highest hydrocarbon generation potential on resinite among the three macerals studied. In contrast, funginite exhibits the strongest aromatic character, the highest aromaticity, the lowest ‘A’ factor values and the lowest C=O/C=C ratios among the three maceral groups. Vitrinite generally displays intermediate chemical characteristics. Reflectance micro‐FTIR mapping of coal samples further confirms the aliphatic character of resinite and the aromatic nature of funginite. In addition, chemical mapping of resinite and adjacent vitrinite shows that vitrinite immediately adjacent to resinite displays higher aliphatic CH_x stretching intensity than more distant vitrinite, suggesting that chemical components from resinite can diffuse over short distances into adjacent vitrinite, specifically causing hydrogen enrichment. It needs to be pointed out, however, that the region of influence is localized and limited to a narrow zone, whose extent likely depends on resinite's properties, such as its size and aliphatic material content. This way, the chemical map of resinite and associated vitrinite provides direct evidence of the intermaceral effects occurring during the peat forming stage or during later coalification. No influence of funginite (primarily fungal spores and sclerotia) on the chemistry of adjacent vitrinite has been demonstrated, which is likely due to the highly aromatic structure of this type of funginite.     

Analysis of the combustion instability of a model gas turbine combustor by the transfer matrix method

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. A transfer matrix-based approach is developed in this work for the stability analysis of gas turbine combustors. By viewing the combustor cavity as a one-dimensional acoustic system with a side branch, the heat source located inside the cavity can be described as the input to the system. The combustion process is modeled as a closed-loop feedback system, which enables utilization of well-established classic control theories for the stability analysis. Due to the inherent advantage of the transfer matrix method and control system representation, modeling and analysis of the system becomes a straightforward task even for a combustor of the complex geometry. The approach is applied to the stability analysis of a simple combustion system to demonstrate its validity and effectiveness. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dong Jin Cha received his B.S. and M.S. degrees from Hanyang University in Seoul, Korea, in 1981 and 1983, respectively. He then received his Ph.D. in ME from the University of Illinois at Chicago in 1992, and worked at the US DOE NETL for the next three years as a National Research Council (NRC) Associate. Dr. Cha is currently a Professor at the Department of Building Services Engineering at Hanbat National University in Daejeon, Korea. His research interests include combustion instability of gas turbine for power generation and fluid flows in building services engineering. Jay H. Kim received his BSME from Seoul National University in 1977, MSME from KAIST in 1979 and Ph.D. in ME from Purdue University in 1988. He has joined the Mechanical Engineering faculty of the University of Cincinnati in 1990, and is currently a Professor. Before joining the University of Cincinnati, he worked in industry for six years in Korea and US. His research interests have been in broad areas of acoustics, vibrations and applied mechanics with recent focuses on human/bioacoustics and vibration, gas pulsations and elastic stability. Yong-Jin Joo received his BSME and MSME from Sung Kyun Kwan University in Seoul, Korea, in 1990 and 1992, respectively. Mr. Joo is currently a Project Leader for IGCC Operation Technologies at KEPRI (Korea Electric Power Research Institute) which is the central R&D center of KEPCO (Korea Electric Power Corporation). His research interests include the development of operation and maintenance simulator for power plants including IGCC.     

影响循环流化床锅炉碎煤机锤头和筛板使用寿命的因素及改进措施

从材质和结构两方面分析研究循环流化床锅炉碎煤机锤头和筛板磨损机理,针对磨损的主要原因进行材质和结构的改进,从而提高碎煤机的破碎效率,延长锤头的寿命,减少硬度大的大颗粒燃料在破碎机内留存时间,改进和优化破碎后的燃料粒度级配比例     

Numerical analysis of the combustion process in a four-stroke compressed natural gas engine with direct injection system

In this paper, a numerical study to simulate and analyze the combustion process occurred in a compressed natural gas direct injection (CNG-DI) engine by using a multi-dimensional computational fluid dynamics (CFD) code was presented. The investigation was performed on a single cylinder of the 1.6-liter engine running at wide open throttle at a fixed speed of 2000 rpm. The mesh generation was established via an embedded algorithm for moving meshes and boundaries for providing a more accurate transient condition of the operating engine. The combustion process was characterized with the eddy-break-up model of Magnussen for unpremixed or diffusion reaction. The modeling of gaseous fuel injection was described to define the start and end of injection timing. The utilized ignition strategy into the computational mesh was also explained to obtain the real spark ignition timing. The natural gas employed is considered to be 100% methane (CH₄) with three global step reaction scheme. The CFD simulation was started from the intake valves opening until the time before exhaust valves opening. The results of CFD simulation were then compared with the data obtained from the single-cylinder engine experiment and showed a close agreement. For verification purpose, comparison between numerical and experimental work are in the form of average in-cylinder pressure, engine power as well as emission level of CO and NO. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.