Wet air oxidation studies of coal gasification wastewaters

The kinetics of wet oxidation of coal gasification wastewater were studied. Experimental studies explored the effect of temperature and residence time on the extent of reaction by conducting constant volume batch tests in a 1-liter high pressure autoclave. The extent of reaction was determined by measuring the chemical oxygen demand (COD) and phenol concentrations of the wastewater at various times.The effect of temperature was studied from 205 to 251°C with residence times from 30 to 90 minutes. The experimental data obtained were used to fit Arrhenius expressions of the reactions. A mathematical model consisted of two first-order reactions in series showing a maximum COD reduction of 60% and a maximum phenol reduction of 95%, both at 251°C and a 90 minute residence time. The activation energies for COD and phenol reduction were both found to be 8.0 kcall.     

Modeling and simulation of coal gasification on an entrained flow coal gasifier

In this paper, the recent researches and developments on coal gasification modeling and simulation are described. Numerical models for the three chemical processes such as devolatilization, char gasification, and gas-phase reaction are reviewed and discussed for further development to improve accuracy. Recently the devolatilization models to describe the coal chemical structure with a simple expression have been proposed and validated on the laboratory-scale flames. It is essential to precisely model char gasification reaction as a rate-determining step and the formulation of the active sites sharing by the mixture and the pore structure formation are important in the modeling. It will become significant to take the elementary reactions into account in the gas phase reaction model. Large-eddy simulation of coal gasification on the laboratory-scale entrained flow gasifier is performed to demonstrate the numerical procedure. Results show the predicted temperature distribution qualitatively agrees with the experiment. Moreover, the gas-liquid-solid three-phase reacting flow simulation is preliminarily performed to capture the molten slag flow behavior within the gasifier. It is revealed that the three-phase simulation can give insight into the complex multiphase and multiphysics phenomena taking place within the gasifier to assess the design and the operating condition.     

Inhibition characteristics of coal dust explosion at the gasification atmosphere

The risk of coal dust explosion threatens the safety of coal gasification process. To reveal the inhibition of carrageenan dry-water material (CDM) on coal dust explosion, a 20 L spherical explosive device was adopted to compare with SiO₂ and NH₄H₂PO₄ at the atmosphere of coal gasification. The thermal decomposition behavior and chemical structures of the explosion residues were characterized by synchronous thermal analyzer, X-ray photoelectron spectroscopy and FTIR. The results indicate that the CDM showed the optimal inhibiting effect on 300 mesh and the maximum explosion pressure of anthracite coal dust was reduced to 0.02 MPa with the percentage of 97.53%. At the same concentration, the inhibiting effect of CDM on the coal dust explosion was better than that of SiO₂ and weaker than that of NH₄H₂PO₄. Through the residues analysis, the CDM mainly prevented the volatilization of C-H and consumption of oxygen-containing groups and sulfur-containing groups contributing to the inhibition of coal dust explosion.     

Evaluation of sensor materials for ultrasonic thermometry In coal gasification systems

The success of ultrasonic thermometry, in coal gasification systems depends on the selection of approprzate sensor materzal(s) that can withstand the hostile environment exhibit good. acoustic sen~itivity to temperature and show long-term stability or reproducibility of acoustic properties in the environment. Six candidate materials SS 310, Incoloy 800, sapphire, alumina, spinel and chrome oxide - were selected based on pilot-plant. experience and laboratory studies of materials performance in coal galasification environments. They were exposed in two simulated coal gasification environment, Westinghouse low-Btu (British thermal unit) at 871°C for 15 hand Texaco medium-Btu at 982°C for 15 h. The physical and acoustic properties of the materzals before and after exposure to the gasification environments are presented, together With a discussion on the long-term performance predictions of the materials for ultrasonic thermometry.     

Effect of physicochemical properties of coal gasification fine ash on its wettability

Coal gasification, recognized as one of the most effective coal utilization technologies, will produce a certain amount of fine ash during the high-temperature reaction process. The wettability of gasification fine ash is a critical parameter to characterize the degree of high-temperature reaction and determine the separation efficiency of purification process. In the present work, the effect of physicochemical properties on the wetting behavior of different gasification fine ash is studied. The difference in wettability between particle size and types can be explained by the unique properties of particles (i.e. pore structure, mineral composition, and chemical structure). The results show that with the decrease in particle size, the surface morphology transforms from an irregular shape with a rough surface to a spherical shape with a smooth surface. The pore structure, characterized by fractal surface dimension D_s, presents positive correlations with the contact angle for a single type of fine ash. The mineral composition can just qualitatively assess the hydrophilicity of particles. Only the ratio of hydrophilic chemical structure can be used as a generic parameter to describe the wetting performance. Meanwhile, the wettability of hydrophilic particles can be enhanced by increasing moisture content, but there is no significant effect of moisture content on the wettability of hydrophobic particles.     

Eulerian–Lagrangian method for three-dimensional simulation of fluidized bed coal gasification

A comprehensive three-dimensional numerical model has been developed to simulate the coal gasification in a fluidized bed gasifier. The methodology is based on the multiphase particle-in-cell (MP-PIC) model, which uses an Eulerian method for fluid phase and a discrete particle method for particle phase. Dense particulate flow, mass and heat transfer, homogeneous and heterogeneous chemistry between phases and within the fluid mixture are considered. The dynamics of the particle phase is calculated by solving a transport equation for the particle distribution function (PDF) f. Particle collisions and chemical reactions are solved on a grid cell with particle properties mapped from discrete particles to the grid. Solid mass consumed or produced in reactions changes the size of particles. Simulations were carried out in a coal gasifier with a height of 2.0 m and a diameter of 0.22 m at atmosphere. The calculated product gas compositions compare well with the experimental data. The formation of flow patterns, profiles of particle species and gas compositions, distributions of reaction rates and consumption of carbon mass were investigated under different operating conditions.     

Hardfacing by chemical vapor deposition of components used in coal gasification units

The Bureau of Mines, as part of an interagency agreement with the Energy Research and Development Administration, is investigating the feasibility of hardfacing the critical surfaces of valves and similar devices by chemical vapor deposition. The objective is to increase the life of these components in the abrasive and erosive environment existing in coal gasification units. Various chemical vapor deposition materials such as the refractory metals, carbides and nitrides were considered for this application and are undergoing laboratory investigation and evaluation. The first hardfacing material investigated was tungsten because of the Bureau's previous experience with this material in lining rocket nozzles. Laboratory research indicated that adherent tungsten coatings could not be obtained on the stainless and carbon steels used in value construction unless they were first electroplated with a thin layer of nickel. Tungsten was deposited by hydrogen reduction of tungsten hexafluoride at temperatures ranging from 450 °C to 650 °C. A large reaction chamber 20 in (0.51 m) in diameter with a rotating gas-dispersion apparatus was fabricated. The large unit was used to coat carbon steel valve seats of inside diameter 10 in (0.25 m) with tungsten, and heating of the ball valve seats to reaction temperature was done by induction. Successfully coated valve seats are undergoing evaluation in the low Btu coal gasification pilot plant at the Morgantown Energy Research Center, Morgantown, W. Va. Results of completed and ongoing chemical vapor deposition research are presented.     

煤气化配套空分设备流程的选择

结合煤气化工艺,详细分析了化肥工业、合成甲醇项目、多联产及合成油项目和IGCC发电项目等煤气化装置对空分设备的要求和流程选择,得出了各个项目适用的大型空分设备流程。     

空分设备配合煤气化装置实现气化炉无扰动切换案例分析

以齐鲁比欧西KDON-45000/30000型空分设备为例,介绍通过液氧后备系统与工艺液氧泵并联运行,满足下游装置气化炉3炉并行的氧气需要,实现气化炉无扰动切换,避免了煤气化后续生产装置的负荷调整。详细阐述空分设备配合气化炉无扰动切换的实施原则、安全风险和防范措施、实施案例和效果。     

Mineralogical examination of the entrained-flow coal gasification residues and the feed coals from northwest China

Minerals are the dominant impurities in coal and their changes in gasifiers could cause many problems such as fouling, slagging, and ash deposition. The mineralogy of the coal gasification residues derived from two commercial entrained-flow coal gasification plants from the Ningdong Energy and Chemical Industry Base were determined. A range of minerals were detected by the analyses of X-ray diffraction and scanning electron microscope with associated energy-dispersive X-ray spectrometer (SEM–EDS). The mineral species formed in General Electric (GE) gasification were more abundant than that in the Gaskombinat Schwarze Pumpe (GSP) gasification. The neoformed minerals such as grossular and hedenbergite detected in the residues indicated that the gasification processes share some similarities with magmatism in geological system. The existence of wustite in the GE coal gasification residues indicated the reductive environment in the GE gasifier. Compared to the GSP feed coals, the higher proportions of calcite, pyrite, and siderite and the higher Na contents in the GE feed coals indicated that the ash problems probably happen in the coal-water slurry gasification. Reducing the proportions of those Na-, Ca-, and Fe-containing mineral from the feed coal is necessary for the improvement of the coal gasification process.     

煤气化渣负载Ni@SiO2/TiO2材料的制备及其催化性能研究

采用氢氟酸(HF)对煤气化渣(CGFS)进行改性,用液相还原法制备纳米Ni粒子,通过对正硅酸乙酯(TEOS)的水解得到SiO2,使其包裹在纳米Ni粒子上得到Ni@SiO2材料.以钛酸丁酯(TBOT)为钛源,通过溶胶-凝胶法使Ni@SiO2/TiO2负载在改性后的煤气化渣上从而得到光催化剂CGFS-Ni@SiO2/TiO...     

Preparation of hierarchical porous activated carbons for high performance supercapacitors from coal gasification fine slag

Journal of Materials Science: Materials in Electronics - Coal gasification is an important technology for clean conversion and utilization of coal. The coal gasification slag is the main solid...     

How lean can lean buffers be?

This paper provides a quantitative characterization of the smallest, i.e., lean, buffer capacity necessary and sufficient to attain a desired throughput in serial production lines with identical exponential machines. The development is carried out in terms of normalized buffer capacity and production line efficiency. The smallest normalized buffer capacity required to ensure the desired line efficiency is referred to as the Lean Level of Buffering (LLB). Exact formulas for the LLB in two- and three-machine lines are presented and an approximate expression for the LLB in lines with more than three machines is derived. Along with these analytical results, several qualitative insights into the nature of lean buffering in serial production lines are presented.     

Improving efficiency of CCS-enabled IGCC power plant through the use of recycle flue gas for coal gasification

Clean Technologies and Environmental Policy - CO2 capture from coal-fired power plants is necessary for continued use of coal as a fuel. Proven CO2 capture techniques such as amine absorption and...     

煤气化工程配套“4万”等级空分流程比较

就煤气化工程配套的“4万”等级空分装置与三家气体公司进行了交流。文章介绍了三家公司分别推荐的内压缩流程的特点及流程中一些问题的解决措施 ;最后 ,粗略分析了三种流程的优缺点。     

The stability of arsenic and selenium compounds that were retained in limestone in a coal gasification atmosphere

The aim of this work was to evaluate the stability of arsenic and selenium species retained in a lime/limestone mixture obtained by using limestone as a sorbent for gas cleaning in a coal gasification atmosphere. It was found that the stability of arsenic and selenium species produced by the gas–solid reactions with lime/limestone may be affected by their exposure to air and by their contact with water. The results confirm the conclusions of a previous work in which Ca(AsO₂)₂ and CaSe was postulated as the products of the reaction between the arsenic and selenium species present in a coal gasification atmosphere with lime/limestone. Moreover it was proved that the compounds (Ca(AsO₂)₂ and CaSe) may undergo transformations when the sorbents post-retention are stored or disposed of in air. From the results obtained by XAFS it was possible to identify the Ca₃(AsO₄)₂ produced by the oxidation of the Ca(AsO₂)₂ on the sorbent surface. The XAFS results for selenium showed that the CaSe formed on the sorbent was transformed to form several species, but mainly elemental Se. These changes in the speciation of arsenic and selenium may explain the behavior of the sorbent post-retention during the water solubility test. Although the selenium compounds and the products that may originate from their decomposition in water are not toxic, in the case of arsenic, species like Ca(AsO₂)₂ and Ca₃(AsO₄)₂ may lixiviate, and generate toxic arsenic compounds in solution that could pose a risk when the sorbent is finally disposed of.     

Physical properties and microstructures of residual carbon and slag particles present in fine slag from entrained-flow coal gasification

Fine slag (FS) consists of residual carbon (RC) and slag particles (SP). This paper studies the characteristics of SP and RC separately. SP contain a little of pores and mainly consist of spherical particles most of which are solids. RC have a higher pore surface, more continuous and complete pore structure. The chemical structure of inorganic minerals in SP has the following characteristics: According to nuclear magnetic resonance results, the amounts of network structure Q₄ and Q₃ are more than that of chain structure Q₂ and Q₁. The 4-coordinated aluminum consists of 74% and the octahedral coordination (Al(VI)) takes up only 11%. SP is a heterogeneous material which contain not only inorganic minerals but also organic carbon. C atom associated in chemical way with the inorganic matter within SP matrix. The predominant groups of organic carbon within SP matrix are C-C and C-O. C-O groups organically bound with inorganic elements in SP forming C-O-M (M: inorganic elements) bands. The predominant components in RC are C-C and C-O.     

Criteria for a lean organisation: development of a lean assessment tool

Lean principles have long been recognised as a competitive advantage. Although there are several measures for various aspects of lean production in the literature, there is no comprehensive measure for overall lean implementation in business firms. An appropriate measurement tool is needed to assess the effectiveness and efficiency of the lean implementation throughout the entire organisation. Based on lean research, a comprehensive tool called the leanness assessment tool (LAT) is developed, using both quantitative (directly measurable and objective) and qualitative (perceptions of individuals) approaches to assess lean implementation. The LAT measures leanness using eight quantitative performance dimensions: time effectiveness, quality, process, cost, human resources, delivery, customer and inventory. The LAT also uses five qualitative performance dimensions: quality, process, customer, human resources and delivery, with 51 evaluation items. The fuzzy method allows managers to identify improvement needs in lean implementation, and the use of radar charts allows an immediate, comprehensive view of strong areas and those needing improvement. Practical uses of the LAT are discussed in the conclusion, along with possible limitations.