Alkali retention/separation during bagasse gasification: a comparison between a fluidised bed and a cyclone gasifier

Biomass fuelled integrated gasification/gas turbines (BIG/GTs) have been found to be one of the most promising technologies to maximise electricity output in the sugar industry. However, biomass fuels contain alkali metals (Na and K) which may be released during the gasification processes and cause deleterious effects on the downstream hardware (e.g. the blades of gas turbines). Much research has therefore been focused on different kinds of gas cleaning. Most of these projects are using a fluidised bed gasifier and includes extensive gas cleaning which leads to a high capital investment.

Increasing alkali retention/separation during the gasification may lead to improved producer gas quality and reduced costs for gas cleaning. However, very little quantitative information is available about the actual potential of this effect. In the present work, comparative bench-scale tests of bagasse gasification were therefore run in an isothermal fluidised bed gasifier and in a cyclone gasifier to evaluate which gasification process is most attractive as regards alkali retention/separation, and to try to elucidate the mechanisms responsible for the retention.

The alkali retention in the fluidised bed gasifier was found to be in the range of 12–4% whereas in the cyclone gasifier the alkali separation was found to be about 70%. No significant coating of the fluidised bed's bed material particles could be observed. The SEM/EDS and the elemental maps of the bed material show that a non-sticky ash matrix consisting of mainly Si, Al and K were distributed in a solid form separated from the particles of bed material. This indicates the formation of a high temperature melting potassium containing silicate phase, which is continuously scavenged and lost from the bed through elutriation.     

旋风器进口回转通道分级效率模型

提出了一种新的旋风器进口回转通道的横混分级效率模型 ,分析了等截面和变截面两种通道的分级效率模型形式 ,并与已有的回转通道分级效率模型进行了比较。模拟结果表明 ,该模型能更合理地描述旋风器回转通道内气固两相的分离能力     

双气路循环流化床压力平衡的实验研究

在Φ800mm×12000mm流化床装置上,用多点压力测量仪对双气路循环流化床各部分的压力分布进行了实验。实验结果表明,颗粒单循环回路的压力平衡图与装置的运行状态、颗粒的循环量密切相关。整个颗粒的循环回路压力曲线呈双8字缠绕式,随质量流率的减少形状发生畸变;补气循环回路与不补气循环回路的压力分布相似,但料腿沉降段的压力降低;提升管内没有明显的稀密相交界面,而料腿内存在着稀密相的交界面,料腿下部的高密度移动床是保证流化床正常运转的必要条件。     

旋流板分离器分离性能实验研究

在实验室冷模实验装置上考察了空速和液气比对旋流板分离器总压降和分离效率的影响,为旋流板分离器的工业应用提供了依据。     

应用FPGA的静电除尘电源控制器设计

为了提高除尘效率以及系统的安全可靠性,针对采用微机控制方案抗干扰能力弱的问题,设计应用了现场可编程门阵列(FPGA)技术的静电除尘电源控制器,并介绍了以Cyclone系列的EP1C12Q240C6芯片为控制核心,采取二折线火花跟踪控制算法,应用VHDL硬件描述语言实现的静电除尘电源控制器的系统结构和工作原理。通过实验室的全面仿真测试及实际电路的实测,证明了方案的可行性,为静电除尘电源控制器的新型产品开发提供了基础。     

直径450mm旋流细筛的研制

φ450旋流细筛应用于拜尔法砂状氧化铝生产中的氢氧化铝分级,可同时分出粗晶种、细晶种和粗粒氢氧化铝3种产品．具有体积小、处理能力大、分级效率高等优点．该设备的研制是为满足国内外百万吨级大型氧化铝厂的需要,现已应用于巴西ALUMAR铝厂．     

Flow Pattern and Pressure Drop for Small Long‐Cylinder Cyclones Operating at High Flow Rates

To address the gas flow pattern and pressure drop characteristics for small long‐cylinder cyclones (SLCCs) in the high operating flow rate range, experimental investigation and computational fluid dynamics (CFD)‐based simulation were performed. The pressure drop coefficient depends insignificantly on the Reynolds number at high flow rates. The tangential and axial velocities present the Rankine vortex and the roughly inverted V‐shaped distribution, respectively, similar to those in typical cyclones. The CFD simulation approximated well the experimental data of pressure drop. The pressure drop caused by vortex loss, turbulent energy loss, and resistance loss accounted for 72.5 % of the total pressure drop. The Stairmand model was found to be relatively accurate among the classical pressure drop models for the proposed cyclone. The results may help in the design and applications of cyclone separators and reactors.     

Characterization of multiphase gas–solid flow and accuracy of turbulence models for lower stage cyclones used in suspension preheaters

This study involved the analysis and characterization of the multiphase flow phenomenon inside the lower stage cyclone separator used in the clinker burning process. The analysis was performed using both CFD and experimental research methods. Very few studies are devoted to such types of cyclone separators, which in addition to their basic functions are also responsible for the technological process. Due to the atypical working conditions of these cyclone separators, they are characterized with a complex geometry, which significantly differs from that of the traditional separators.Furthermore, the evaluation of the accuracy and level of reliability of the two models of turbulence closure—k-e RNG and RSM(RANS), and the LES. The results obtained led to the conclusion that for the lower stage cyclone separators, the LES model proved to be the most accurate(both in the case of forecasting the separation efficiency and pressure drop). The performance parameter(in particular the separation efficiency) values obtained for the RSM model were also characterized by high accuracy. The k-e RNG model was characterized by significantly larger deviations.     

旋风除尘器除尘效率的影响因素探讨

旋风除尘器作为常用除尘设备之一,改善旋风除尘器的除尘效率和降低压力损失一直是成为国内外关心的热门话题。本文简要阐明了旋风除尘器的工作原理和分析了流体流动特点,指出了影响除尘效率的各种因素,在改进除尘器构造,提升除尘效率方面有着非常重要的实际价值。     

Influence of vent air valve opening on combustion characteristics of a down-fired pulverized-coal 300 MWe utility boiler

Industrial experiments have been performed on a down-fired pulverized-coal 300 MWe utility boiler with vent air valve opening of 100% and 40%. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution in the furnace, and gas components such as O₂, CO, CO₂ and NO_x in the near-wall region were measured for the first time. The influence of vent air valve opening on coal combustion in the furnace was determined. The results indicate that ignition of the primary air and pulverized-coal mixture is delayed. The position of the gas temperature peak is above the arches. Emission of NO_x is up to 2101 mg/m³ (at 6% O₂ dry) with vent valve opening of 40%.