Activation of Rejected Fly Ash Using Flue Gas Desulphurization (FGD) Sludge

Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon content and large particle size (>45μm).But it is thought that the rejected ash may have potential uses in chemical stabilization/solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity.Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum.As there is no effective usage of both of these two materials,it is of interest to research on the possible activation of rFA using FGD.This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes.Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes.The results show that FGD takes effect as an activator only at late curing ages.Adding Ca(OH) 2 enhances the effect of FGD on activating the hydration of rFA.Also,10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes.The results of the compressive strength measurements correlate well with the porosity results.

Utilization of Thermally Treated Flue Gas Desulfurization (FGD) Gypsum and Class-C Fly Ash (CFA) to Prepare CFA-Based Geopolymer

The feasibility of utilization of flue gas desulfurization （FGD） gypsum and Class-C fly ash （CFA） to prepare CFA-based geopolymer were studied. The results showed that geopolymer made from 90% CFA and 10% FGD gypsum （FGDG） which was thermally treated at 800 ℃ for 1 h obtained the better compressive strength of 37.0 MPa. The micro characteristics and structures of the geopolymer samples of CFA and CFA-FGDG were tested by XRD, FT-IR, and SEM-EDXA after these samples cured at 75 ℃ for 8 h followed by 23 ℃ for 28 d. Both the geopolymer samples of CFA and CFA-FGDG have significant asymmetric stretching of A1-O/Si-O bonds and Si-O-Si / Si-O-A1 bending band. In geopolymer sample of CFA-FGDG, a small quantity of lathy products probably being the ettringite wrapped over the spherical fly ash particle, and the concentration of sulfur is much more than that in geopolymer sample of CFA. It is indicated that FGD gypsum may react during alkali-activated and geopolymeric process.

Experimental study on performance of flow & desulfurisation of a gas-liquid screen scrubber for wet flue gas desulfurization

In the paper, the gas-liquid two-phase flow performance and desulfurisation performance of the gas-liquid screen scrubber were experimentally studied when limestone was used as absorbent. Experiments were carried out at varying the flue gas velocity and slurry flux in concurrent and countercurrent tower respectively. The experimental results showed that the flow resistance of absorber increased rapidly with an increase of the flue gas velocity whether in concurrent or in countereurrent tower, and the up trend of the flow resistance in the cotmtercurrent tower was higher than those in the concurrent one. The influence of the flue gas velocity on the flow resistance of absorber was more than those of the slurry flux density. Whether in the concurrent tower or in the cotmtercurrent one, increasing the flue gas velocity or the slurry flux density would enhance the desulphurization efficiency. The influence of the slurry flux density on the desulfurisation efficiency was greater than those of the flue gas velocity.

Dynamic optimization oriented modeling and nonlinear model predictive control of the wet limestone FGD system

Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(WFGD)system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme.At first,a mathematical model of the FGD process is deduced which is suitable for NMPC structure.To equipoise the model’s accuracy and conciseness,the wet limestone FGD system is separated into several modules.Based on the conservation laws,a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design.Then,by addressing economic objectives directly into the NMPC scheme,the NMPC controller can minimize economic cost and track the set-point simultaneously.The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province,China.The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time.In the meantime,the control scheme satisfies the multiobjective control requirements under complex operation conditions(e.g.,boiler load fluctuation and set point variation).The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.

INTERACTION BETWEEN SO_2 FROM FLUE GAS AND SORBENT PARTICLES IN DRY FGD PROCESSES

Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal efficiency to meet both technical and economic requirements, and for making the best quality byproduct gypsum as a useful additive for improving alkali soil. Among the possible modifications two major factors have been selected for study: (1) favorable chemical reaction kinetics at elevated temperatures and the sorbent characteristics; (2) enhanced diffusion of SO2 to the surface and within the pores of sorbent particles that are closely related to gas-solid two-phase flow patterns caused by flue gas and sorbent particles in the reactor. To achieve an ideal pore structure, a sorbent was prepared through hydration reaction by mixing lime and fly ash collected from bag house of power plants to form a slurry, which was first dewatered and then dried. The dry sorbent was found capable of rapid conversion of 70% of its calcium content at 700℃, reaching a desulphurization efficiency of over 90% at a Ca/S ratio of 1.3. Experiments confirmed that the diffusion effect of SO2 is an important factor and that gas-solid two-phase flow plays a key role to mixing and contact between SO2 and sorbent particles. For designing the FDG reactor, a new theoretical drag model was developed by combination of CFD with the Energy Minimization Multi-Scale (EMMS) theory for dense fluidi-zation systems. This new drag model was first verified by comparing calculated and measured drag values, and was then implemented in simulation of gas-solid two-phase flow in two circulating fluidized beds with different sizes and flow parameters. One riser has diameter and height of 0.15 m×3m and another one 0.2m×14.2m. Their superficial gas velocities are 4 and 5.2 m·s-1, respectively, and the circulating rate 53 and 489 kg·(m-2·s-1). FCC particles were used in both cases. The results show that not only the static pressure drop along the riser height, but also radial distributions of particle volume fraction have been very well predicted in comparison with experiments. The new drag model is expected to shed more light on the further improvement of SO2 diffusion to solid sorbent and optimization of reactor structure.

烧结脱硫石膏的综合利用现状

近年来,烧结烟气脱硫石膏的利用正在被越来越多的人重视,本文在总结国内外烧结脱硫石膏的研究和应用现状的基础上,就其存在的一些问题和发展趋势提出几点自己的看法,并结合脱硫石膏性质提出了一些烧结脱硫石膏的资源化利用途径和建议。

600MW机组湿法脱硫系统除雾器堵塞原因分析及对策

介绍了平板式除雾器的工作原理和结垢种类。针对河北大唐国际王滩发电有限责任公司2×600 MW机组湿法烟气脱硫系统经常出现除雾器堵塞的问题,结合该电厂脱硫系统投产5年来的运行经验,对影响除雾器堵塞和结垢的2个主要因素进行了分析,提出了具体的应对措施。

湿法烟气脱硫吸收塔流场的数值模拟研究

吸收塔设计是实现湿法烟气脱硫技术国产化和自主化的关键。采用Pro/Engineer软件建立吸收塔空塔模型,并利用计算流体力学软件Ansys CFX对吸收塔气相动力流场进行模拟,探讨并比较了不同吸收塔出口形式对其产生的影响,对比了吸收塔内压力、矢量速度分布情况,可为后续吸收塔流场模拟及优化提供指导。

脱硫系统烟气换热器积垢的化学清洗方法

大型火力发电机组脱硫系统的烟气换热器(gas gas heater,GGH)容易积垢堵塞,严重影响锅炉的安全运行,必须对其进行清洗除垢。为此,介绍了清洗火电厂脱硫系统GGH的专用化学WP-T04清洗剂的清洗原理、清垢方法、清洗工艺,并以静态、动态试验验证清洗剂的清洗效果,以腐蚀试验说明清洗剂对脱硫装置无腐蚀作用。该清洗方法在广东某火电厂的应用取得良好效果。

某电厂3×130t/h锅炉氧化镁湿法烟气脱硫关键技术点的设计

提出了3×130 t/h锅炉烟气脱硫的基本设计参数和主要经济技术指标,对氧化镁湿法烟气脱硫的工艺系统组成及工艺流程做了详细说明,着重介绍主要设备的选型和规范。

石灰石—石膏湿法脱硫工艺研究进展

介绍了我国SO2排放状况和控制现状、国内外先进的烟气脱硫技术以及烟气脱硫(FGD)技术在我国的应用情况,并针对当前国内外火电厂运用最广泛的石灰石/石膏湿法FGD工艺技术,详细阐述了这一工艺的原理、典型的工艺流程、系统设备及其作用和特点。

双塔双循环脱硫系统的运行现状分析与优化措施探讨

为满足超低排放要求,需对脱硫系统进行优化和改造,其中双塔双循环技术为可选方案之一。通过现场试验和调研的方式,从脱硫效率、洗尘效率、系统阻力、运行方式等角度,分析了双塔双循环脱硫技术的运行特点。现场试验及实际调研结果表明,双塔双循环脱硫系统具有脱硫裕量较大、运行可靠性高等特点,脱硫效率往往能达到99%以上,同时其协同除尘效果要优于常规单塔单循环系统,是燃中、高硫煤机组超低排放改造技术路线之一。针对双塔双循环脱硫技术设计及运行中存在的主要问题,如循环泵备用数量较多,二级吸收塔氧化风机的利用率不高,一级塔液位下降较快和二级塔液位上升过快,以及系统设计阻力过大等,提出了优化及改进措施。

湿法烟气脱硫系统增容改造技术方案

以某600 MW燃煤电厂石灰石-石膏湿法烟气脱硫系统增容改造为例,介绍了在有限建设场地、主设备利旧等条件下的脱硫系统改造方案,改造后可满足燃用高硫煤时的排放要求,供同类机组改造时参考。

湿式文丘里吸收塔烟气脱硫技术的特点

在燃煤电厂中加设烟气脱硫装置是目前较有效解决燃煤电厂SO2污染问题的方式之一,而吸收塔是主要的脱硫设备,为此,介绍了湿式文丘里吸收塔烟气脱硫的技术原理及其技术特点。实际运行也证明:文丘里吸收塔烟气脱硫的气液传质高,液气比低,无结垢,负荷适应强。

燃煤电厂烟气脱硫湿烟囱特种不锈钢防腐内衬

探讨了湿烟囱的腐蚀特性和防腐选材,通过试验,详细分析了湿烟囱特种防腐内衬超级奥氏体不锈钢XDS-5的耐蚀性能、力学性能及焊接性能,得出了XDS-5是优良的湿烟囱防腐内衬材料的结论,最后介绍了薄板贴衬工艺。湿烟囱乃至整个湿法烟气脱硫系统的合金化有利于系统运行的稳定和可靠,可有效降低设备的生命周期成本。

湿法烟气脱硫系统拆除旁路挡板的方案及实施

介绍了望亭发电厂#14机组石灰石-石膏湿法烟气脱硫系统拆除旁路挡板的方案及实施过程,论述了旁路挡板拆除后脱硫系统启、停及运行过程中存在的问题,针对问题提出了解决方案。

节能增效剂在石灰石-石膏湿法烟气脱硫中的应用

近年来电厂燃用煤中硫的质量分数超过设计值已屡见不鲜。通过湖北华电黄石发电股份有限公司添加节能增效剂试验可以得出,脱硫设施添加节能增效剂后,运行安全、稳定,脱硫效率提升明显且完全可以保证达标排放。在运行中可以停1到2台浆液循环泵,节能效果较好。

湿法烟气脱硫技术在黄埔发电厂的应用

介绍湿法烟气脱硫技术在广州黄埔发电厂的应用,说明其系统构成和化学反应过程。同时指出石灰石石膏湿法烟气脱硫装置的主要特点。

石灰石-石膏湿法烟气脱硫装置的DCS控制研究

石灰石-石膏湿法脱硫技术是目前最成熟的脱硫技术之一,在国内得到了广泛应用。在实际工程运用中,石灰石-石膏湿法烟气脱硫技术控制系统设计是否合理会直接影响系统脱硫效率甚至主机系统的长期安全稳定运行。重点阐述了分散控制系统(DCS)对石灰石-石膏湿法烟气脱硫过程控制的方法。

新型浆液循环方式在双塔双循环脱硫系统中的应用

针对石灰石-石膏法脱硫工艺中双塔双循环技术内部浆液循环和塔间水平衡问题,本文提出了一种较为简洁的双塔间浆液循环方式,并应用于山西某2×350 MW机组烟气脱硫系统。结果表明,一级塔设计脱硫效率87%,二级塔设计脱硫效率97%,简化设计的同时提高了备件替换性;通过设计液位差和强制循环泵建立双塔间浆液循环;一级塔浆液通过浆液循环系统分流至二级塔,二级塔过剩的浆液溢流回一级塔,形成双塔间水平衡体系。187 MW和290 MW两种工况下,启动浆液循环系统后4层喷淋即可达到99.81%的脱硫效率;相对于双塔系统中两塔独立运行,新型双塔循环系统启动6台循环泵即可保证脱硫效率,并减少系统阻力约500 Pa,降低风机电耗400 kW。