Auto-thermal chemical looping combustion of sulphur with Fe2O3 oxygen carriers for sulphuric acid production: Thermodynamics

Chemical looping is a novel fuel conversion and material separation technology. It can be applied to obtain sulphur through selective oxidation of H₂S. Further, chemical looping combustion (CLC) of sulphur can generate SO₂ with a high concentration without NO_x formation. The high SO₂ concentration is adjustable and facilitates large-scale H₂SO₄ production. In this study, we examined the thermodynamics of the CLC of sulphur for H₂SO₄ production, which has not been reported previously. We analyzed the effects of reactor temperature and sulphur to Fe₂O₃ oxygen carrier (OC) ratios on sulphur allotrope transformations and on the distributions of reaction products. Moreover, the reactors were operated auto-thermally. Based on this design, we examined the effects of fuel reactor (FR) and air reactor temperatures on the minimum recirculation of the OC, as well as the gas and solid products and heat released from the air reactor. Our results showed that the CLC of sulphur with Fe₂O₃ OC could occur through an auto-thermal process. The FR in a sulphur CLC system should be operated over a temperature range of 800–950°C, with an Fe₂O₃ OC recirculation between 45 and 143 kg/kg_S(s). Furthermore, when the FR was operated in the auto-thermal mode, we achieved 100% SO₂ conversion. The findings of this study may be applied to reactor design for large-scale H₂SO₄ production through CLC of sulphur.     

Co-Fe2O3[104]铁基载氧体优化体系作用下褐煤化学链燃烧特性

前期研究发现高弥勒指数晶面载氧体Fe₂O₃[104]具有高的化学链燃烧反应特性,且Co对煤及其热解中间产物具有催化气化和催化转化作用。通过正交实验优化制备Co-Fe₂O₃[104]/Al₂O₃载氧体体系结构,开展Co-Fe₂O₃[104]/Al₂O₃与褐煤的化学链燃烧,揭示载氧体与褐煤发生化学链燃烧的特性。结果表明:形貌控制制备的高弥勒指数晶面铁基载氧体Co-Fe₂O₃[104]/Al₂O₃(质量分数10%)促进了褐煤化学链燃烧过程中氧的迁移速率以及载氧体的还原程度,进而显著提高了载氧体与褐煤化学链燃烧的反应速率及反应效率。进一步通过CO多循环化学链燃烧反应、XRD和TEM表征了Co-Fe₂O₃[104]/Al₂O₃(10%)的可再生性及反应稳定性。     

温度对载氧体还原过程中汞的析出特性及形态分布的影响

化学链燃烧是近年来提出的一种具有高效、内分离CO₂特点的新型燃烧方式。本文在立式管式炉实验装置上研究了温度对基于Fe₂O₃载氧体的煤化学链燃烧载氧体还原过程中汞析出特性的影响,探讨了不同燃烧温度下燃料反应器（FR）出口烟气组分的变化及其对汞迁移变化的影响。结果表明：在高温条件下（≥ 800℃）,煤中的汞在载氧体还原过程中基本全部析出,180s时基本达到90%,并且随着温度升高而增加;FR出口烟气中的汞主要以单质态（Hg⁰）形式存在,各工况下的单质态汞占烟气中气态总汞比例都在88%以上,随着温度的升高,烟气中Hg⁰/Hg^T略有降低;温度对烟气组分具有影响,随着温度的升高,CO、NO和SO₂浓度上升;对于汞而言,SO₂会抑制Cl及Cl₂的形成从而抑制Hg⁰向Hg²⁺转化,NO会直接或间接促进汞的氧化过程,FR烟气中以CO为主的还原性气氛不利于汞的氧化。     

化学链燃烧中H2S对NiFe2O4氧载体活性的影响机理

采用密度泛函理论方法研究H₂S与NiFe₂O₄（001）完整表面和氧缺陷表面的相互作用机理。结果表明,H₂S在NiFe₂O₄氧载体表面Ni原子位的吸附能比其在Fe原子位的吸附能大。氧缺陷的形成会使H₂S在氧载体表面金属原子位的吸附能增大,并且Ni原子位吸附H₂S的吸附能增加更为明显。因而,NiFe₂O₄氧载体表面的Ni原子位是H₂S的主要吸附位。同时采用热力学方法进一步研究含H₂S的合成气与NiFe₂O₄氧载体之间的反应,发现H₂S与氧载体的反应产物与氧载体的还原程度密切相关。由于铁氧化物的深度还原过程受到热力学限制,H₂S与NiFe₂O₄氧载体反应的主要产物为Ni₃S₂。密度泛函理论方法与热力学方法研究结果均表明H₂S倾向于与NiFe₂O₄氧载体中Ni发生相互作用,这将对NiFe₂O₄氧载体的反应性能产生不利影响。     

Effects of Na2CO3/K2CO3 on Chemical Looping Combustion Using Fe2O3/Al2O3 as Oxygen Carrier

The performance of the Fe₂O₃/Al₂O₃ oxygen carrier modified by the alkali metals, Na and K, was studied by thermogravimetric analysis and in a laboratory-scale fluidized-bed reactor. Different factors, such as the alkali metal content, the alkali metal type, and the interaction between Na and K, were taken into account. Both Na and K had strong catalytic effects on the conversion of Fe₂O₃. A high K content caused serious agglomeration. Increasing the Na content led to slagging because of the low-melting point solid solution. The possibility of agglomeration and slagging was reduced when Na and K were added together. The oxygen carrier with 1.5 wt % Na and 1.5 wt % K had better combustion efficiency and optimal thermal stability. Na and K could enhance the attrition resistance and prolong the lifetime of the oxygen carriers.     

Na2O-Al2O3-Fe2O3系烧结过程中铝、铁的反应行为

以Al2O3, Fe2O3和Na2CO3为原料,对Na2O-Al2O3-Fe2O3系烧结过程中的反应行为进行了详细研究. 基于溶出率与时间、温度的关系,证明Na2O×Al2O3和Na2O×Fe2O3的生成反应动力学都服从Zhuralev-Lesokin-Tempelman模型,表观活化能分别为186.59和80.92 kJ/mol,表明Na2O×Fe2O3比Na2O×Al2O3在动力学上更易形成;Al2O3易与Na2O×Fe2O3反应形成Na2O×Al2O3和Fe2O3,在1273 K烧结30 min,所得熟料Al2O3溶出率达98.51%;Fe2O3对Na2O×Al2O3的形成有双重作用,在1273 K下可加速Na2O×Al2O3的形成,超过1323 K,促使Na2O×Al2O3分解成Na2O和b-Al2O3,且随着温度升高或时间延长,分解程度增高,从而导致熟料中Al2O3溶出率显著降低.     

Multicycle investigation of a sol‐gel‐derived Fe2O3/ATP oxygen carrier for coal chemical looping combustion

Fe‐based oxygen‐carrier particles with attapulgite (ATP) as a support material for coal chemical looping combustion (CLC) have been prepared using a sol‐gel approach. The multiredox characteristics of the prepared Fe4ATP6 (Fe₂O₃ to ATP mass ratio of 40:60) were experimentally examined in a batch fluidized bed reactor at 900°C. The experimental results indicated that the synergistic reactions between ATP and Fe₂O₃ increased the coal conversion. Fe4ATP6 exhibited high reactivity, particularly for low‐rank coals, in the CLC process. The improved pore structure and surface area were responsible for the high reactivity of Fe4ATP6. In 60 redox cycles, H₂ was mainly generated in the outlet gas as the carbon conversion efficiency had reached 95%, and both the coal combustion efficiency and CO₂ capture efficiency were greater than 95%. © 2015 American Institute of Chemical Engineers AIChE J, 62: 996–1006, 2016     

UV/Fe3+/H2O2催化-混凝联合工艺处理络合铜镍废水

采用UV/Fe3+/H2O2催化-混凝联合工艺对难处理络合铜镍电镀废水进行了研究,考察了Fe3+和H2O2初始浓度、初始pH值、温度、反应时间及混凝液pH、混凝剂质量浓度对处理过程的影响,探讨了废水的降解途径和机理.结果表明在体系初始pH=3,温度50℃,H2O2和Fe3+初始浓度分别为1.5×10-4mo1/L、2.5×10-5mo1/L,反应时间60min,混凝液pH=8及混凝剂质量浓度为500mg/L的条件下,废水的COD去除率为96.98%,Cu2+为99.91%,Ni2+为99.92%,处理水达到国家一级排放要求.同时依据GC/MS对X-GN降解最终产物的分析结果,推导出废水的基本降解机理和途径.     

非均相Fe/Al_2O_3催化H_2O_2降解偶氮染料活性黑5

以活性氧化铝为载体,制备了Fe/Al2O3负载型催化剂,用于催化H2O2分解产生羟基自由基氧化降解偶氮染料活性黑5。探讨了pH、H2O2投加量、催化剂投加量等对染料脱色率的影响。结果表明,活性黑5的脱色率随催化剂投加量的增加而升高;随H2O2投加量的增加而降低;Fe/Al2O3/H2O2体系下,活性黑5在pH为2~9之间均有一定的脱色效果,活性黑5的脱色率随初始pH的增加而先增加后减少,其中在初始pH为3时,脱色效果最佳。     

High performance of la‐promoted Fe2O3/α‐Al2O3 oxygen carrier for chemical looping combustion

Iron oxide supported oxygen carrier (OC) is regarded to a promising candidate for chemical looping combustion (CLC). However, phase separation between Fe₂O₃ and supports often occurs resulted from the severe sintering of supports during calcination, which leads to the sintering and breakage of Fe₂O₃ thus the decrease of redox reactivity. In this article, La‐promoted Fe₂O₃/α‐Al₂O₃ were used as OCs for CLC of CH₄ and for the first time found that the OC with the addition of 18 wt % La exhibited outstanding reactivity and redox stability during 50 cycles of CLC of CH₄. Such a superior performance originated from the formation of LaAl₁₂O₁₉ hexaaluminate (La‐HA) phase with not only small particle size but also excellent thermal stability at CLC conditions, which worked as a binder to prevent the phase separation thereby the sintering and breakage of active species α‐Fe₂O₃ were avoided during reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2827–2838, 2017     

CO2气氛下准东煤化学链燃烧特性研究

我国准东煤储量丰富,钠含量高。以高钠准东煤为燃料,CO₂为气化介质,铁矿石为载氧体,基于鼓泡流化床反应器开展准东煤化学链燃烧特性的实验研究,考察了煤粒径、温度、流化风速和煤焦粒径对煤及煤焦化学链燃烧过程中可燃气体逃逸规律的影响;同时研究了煤中矿物质对煤焦气化过程的影响。结果表明,在基于鼓泡流化床实施的煤化学链燃烧过程中,由于煤颗粒和载氧体床料流化特性差异大,存在离析现象;离析影响煤化学链燃烧过程中挥发分和焦炭的转化;较高流化风速可显著增强载氧体与煤/焦炭颗粒的混合,有效改善离析对可燃气体转化的影响,降低可燃气体逃逸,并加快焦炭气化速率;煤焦中的矿物质能够维持煤焦较快的气化速率。     

Migration and emissions of selenium during chemical looping combustion of coal

Selenium is one of the most volatile toxic elements in coal, and its emissions must be strictly controlled. Chemical looping combustion (CLC) is a clean and efficient technology for coal. Herein, the iron-based oxygen carrier (OC) was used as an adsorbent to study the migration and emissions of selenium during the CLC of coal. Due to the oxidation and adsorption of selenium by iron-based OC, most of the selenium was retained in OC or distributed in the CO₂ stream. The proportion of gaseous selenium released into the atmosphere was less than 10%—significantly lower than that from the traditional combustion process of coal, which had a value of 91.79%. The presence of OC increased the distribution phase of selenium, promoted the conversion of gaseous selenium to solid selenium, and reduced selenium emissions in flue gas. During CLC of coal, the fuel reactor (FR) temperature and the number of OC re-oxidation cycles played an important role in the emissions and retention of selenium. The increasing FR temperature increased the gaseous selenium in the CO₂ stream, reduced the particulate selenium absorbed by OC, and reduced the selenium emissions in the atmosphere. After 10 continuous CLC cycles, the selenium concentration in OC increased from 0.889 to 8.20 mg kg⁻¹. The continuous cycling of CLC could realize the enrichment of selenium from coal to OC. Furthermore, the migration and transformation mechanism of selenium during CLC was deduced by experiments and thermodynamic simulation. This research provides a suitable reference for reducing selenium emissions and developing CLC technology.     

UV/Fe3+/H2O2催化-混凝联合工艺

采用UV/Fe³⁺/H₂O₂ 催化-混凝联合工艺对难处理垃圾渗滤液进行了研究， 考察了Fe³⁺和H₂O₂初始浓度、初始pH、温度、反应时间及混凝液pH和混凝剂质量浓度对处理过程的影响。结果表明,在体系初始pH=8、温度40 ℃、 H₂O₂的初始浓度为0.12 mL·L^-1、Fe³⁺的初始浓度为4×10^-4 mol·L^-1、反应时间90 min、混凝液pH＝8及混凝剂质量浓度为500 mg·L^-1的条件下，废水的COD去除率为96.33%,处理水完全达到国家一级排放要求。     

MgCO3·3H2O晶须的制备及其生长机制的研究

以MgCl₂·6H₂O和NH₄HCO₃为原料,CH₃COONa·3H₂O为形貌控制剂,采用沉淀结晶法制备MgCO₃·3H₂O晶须,考察了不同添加量的CH₃COONa·3H₂O对晶须结晶过程和形貌的影响,并研究了晶须在该体系中的生长机制。结果表明：当体系中加入质量分数为0.23%的CH₃COONa·3H₂O时可以成功制备长径比约为30的棒状MgCO₃·3H₂O晶须,CH₃COONa·3H₂O的存在促进了MgCO₃·3H₂O晶须的形成。该体系中晶须的生长过程：首先形成无定形的4MgCO₃·Mg（OH）₂·4H₂O,之后无定形4MgCO₃·Mg（OH）₂·4H₂O逐渐转变为MgCO₃·3H₂O并生长成较大长径比的棒状MgCO₃·3H₂O晶须。这是因为CH₃COONa·3H₂O电离产生的Na ⁺选择性吸附在MgCO₃·3H₂O晶体轴向的（101）晶面,抑制了该晶面生长,而径向晶面生长速率未受到影响,从而促使无定形MgCO₃·3H₂O生长成棒状晶须。     

Fe／Mn／Al2O3催化H2O2降解偶氮染料废水的研究

以活性氧化铝为载体,制备了Fe／Mn／Al2O3负载型催化剂,用于催化H2O2氧化降解偶氮染料活性黑5,探讨了pH、H2O2投加量、染料初始浓度、催化剂投加量等对染料脱色率的影响。结果表明,活性黑5的脱色率随催化剂投加量、H2O2投加量的增加而升高;而随活性黑5初始浓度的增加而降低。当H2O2投加量的增加达到200mg／L后,H2O2投加量的增加对活性黑5脱色效果的影响不显著。Fe／Mn／Al2O3／H2O2体系下,活性黑5在pH为2～9之间均有一定的脱色效果,活性黑5的脱色率随初始pH的增加而先增加后减少,其中在初始pH为3时脱色效果最佳。     

Fe2+/H2O2体系O2生成路径

掌握Fe²⁺/H₂O₂体系O₂的生成路径,可为避免H₂O₂无效分解,开发经济高效的Fe²⁺/H₂O₂体系利用技术指明方向。采用添加自由基捕获剂的方法,探究Fe²⁺/H₂O₂体系内各种自由基对O₂生成速率的影响,进而确定O₂的生成路径。结果表明:Fe²⁺/H₂O₂体系内不会产生大量O₂^-·,O₂^-·不是生成O₂的主要反应物质;O₂^-·被全部捕获后,体系中仍产生大量O₂^-·,但此时无O₂生成,证明生成O₂的反应由·OH和HO₂·两种自由基直接参与。分析认为反应·OH+HO₂·-H₂O+O₂是体系内O₂生成的主要路径。控制Fe²⁺/H₂O₂体系定向生成·OH,抑制HO₂·的产生,是提高Fe²⁺/H₂O₂体系中H₂O₂利用率的有效手段。     

烟煤化学链反应特性及机理分析

在固定床反应器中添加铁基载氧体Fe4Al6和铜基载氧体Cu4Al6,进行巨野(JY)烟煤化学链燃烧实验,通过气相色谱(GC)、红外光谱(FT-IR)等分析了JY煤化学链反应特性及表面官能团演变规律。结果表明,相对于Al2O3,Fe4Al6或Cu4Al6为床料时,JY煤中CO2含量分别提高了52.25%和59.16%,最大碳转化速率分别提高了8.93%和30.36%,Cu4Al6反应效果更好。添加Cu4Al6后,JY煤表面官能团演变进程加快,Cu4Al6对脂肪烃结构、芳香碳骨架和芳香族CH的转化均有明显促进作用。煤中脂肪烃?CH3和?CH2稳定性低、反应速率快,是化学链燃烧初期气相产物主要来源;芳香碳骨架和芳香族?CH稳定性高、反应活性低,反应速率较缓慢,是化学链燃烧中后期气相产物主要来源。     

PVA/Fe2O3磁敏感性水凝胶的制备及性能

采用循环冷冻-解冻方法制备了聚乙烯醇(PVA)/Fe2O3磁敏感性水凝胶. 考察了水凝胶的力学性能、溶胀性能和磁敏感性,并用扫描电镜观察了其表面形貌. 结果表明,当Fe2O3含量为1%(w)时,水凝胶的力学性能最好;水凝胶的溶胀度和脱水率随时间增加有相似的变化趋势,都随磁性粒子含量升高而降低;溶胀性能降低其交联程度增加;PVA和Fe2O3相容性较好;水凝胶在3000 Oe的磁场强度下达到饱和,呈现出很强的顺磁性,磁滞损耗较多,表明具有较好的磁敏感性.