添加剂对催化气化工艺中煤灰结渣性及气化性能影响研究

煤催化气化工艺中碱金属催化剂的引入加剧了气化炉的结渣,直接影响了流化床气化炉的正常操作。煤灰的烧结特性是流化床气化炉结渣的主要影响因素之一。通过自制的压差法烧结温度测定实验装置,并结合XRD等分析表征及Factsage热力学软件模拟计算,考察了不同添加剂对煤灰烧结特性及气化性能的影响,并从矿物学角度探讨了添加剂对煤灰结渣特性及气化工艺的影响。结果表明,添加硅铝系添加剂可提高煤灰的烧结温度;相比硅系添加剂,添加高铝系添加剂对改善煤灰的烧结温度效果更明显;高铝系添加剂可作为一种高效的阻熔剂,但因在气化过程中容易同催化剂反应,导致催化剂催化性能降低,对煤的气化活性及催化剂回收率产生不利影响;添加氧化钙添加剂,煤的灰熔温度及烧结温度均增加,随氧化钙含量增加,灰熔点及烧结温度均升高,且对气化活性及催化剂回收率有良性作用;氧化钙可作为改善煤种结渣性的添加剂用于催化气化工艺中,需根据煤种性质及工艺特点确定适宜的添加量。     

添加剂对催化气化工艺中煤灰结渣性及气化性能影响研究

煤催化气化工艺中碱金属催化剂的引入加剧了气化炉的结渣，直接影响了流化床气化炉的正常操作。煤灰的烧结特性是流化床气化炉结渣的主要影响因素之一。通过自制的压差法烧结温度测定实验装置，并结合XRD 等分析表征及Factsage热力学软件模拟计算，考察了不同添加剂对煤灰烧结特性及气化性能的影响，并从矿物学角度探讨了添加剂对煤灰结渣特性及气化工艺的影响。结果表明，添加硅铝系添加剂可提高煤灰的烧结温度；相比硅系添加剂，添加高铝系添加剂对改善煤灰的烧结温度效果更明显；高铝系添加剂可作为一种高效的阻熔剂，但因在气化过程中容易同催化剂反应，导致催化剂催化性能降低，对煤的气化活性及催化剂回收率产生不利影响；添加氧化钙添加剂，煤的灰熔温度及烧结温度均增加，随氧化钙含量增加，灰熔点及烧结温度均升高，且对气化活性及催化剂回收率有良性作用；氧化钙可作为改善煤种结渣性的添加剂用于催化气化工艺中，需根据煤种性质及工艺特点确定适宜的添加量。     

配煤对催化气化工艺中煤灰烧结行为影响研究

针对易结渣煤种,研究不同配煤方式对煤灰熔融特性的影响,在催化气化工况气氛下利用压差法烧结温度测定实验装置对各煤灰进行初始烧结温度测试,并结合X射线衍射(XRD)及Factsage热力学软件计算结果表征分析煤灰的相关物理和化学变化,推测灰中矿物质间的反应及矿物的转变,研究矿物质变迁规律,揭示缓解结渣机理。结果表明,通过将高灰熔点、高硅铝含量煤种同易结渣煤种混配可缓解易结渣煤种的结渣问题,同高灰熔点煤混合可有效提高易结渣煤种灰熔点;混煤工艺不同,对灰熔点及烧结温度影响各异,这主要与催化剂在煤质上分布、催化剂存在形式不同及其与不同煤种中矿物质作用不一有关。     

铝厂污泥对低灰熔点气化型煤熔融特性的影响规律

研究了铝厂污泥在弱还原气氛下对福建建兴矿煤(JX)、永安矿煤(YA)和创宏矿煤(CH)熔融特性的影响,考察了添加铝厂污泥前后JX煤灰在不同热处理温度下的矿物组成变化. 结果表明,JX煤灰熔点低是1000℃以上形成低温共熔物引起的;加入铝厂污泥作为阻熔剂可提高JX煤灰的熔融温度,添加量达6%(w)时(以煤灰基计),可使JX煤灰软化温度提高到1250℃以上,满足气化炉固态排渣对灰熔点的要求;加入阻熔剂后,在1000℃以上JX煤灰内形成了莫来石,莫来石在灰渣中起骨架作用,并延缓低温共熔物形成,从而提高了灰熔点.     

小龙潭褐煤灰烧结温度影响因素的研究

煤灰的烧结温度对流化床气化炉的设计和运行产生重要影响。利用自建的压差法煤灰烧结温度测量装置,探讨了气氛和压力对小龙潭褐煤灰烧结温度的影响。结果表明,小龙潭煤灰在N2,O2,CO2气氛下的烧结温度几乎相同,在还原性气氛（H2,CO）下的烧结温度低于氧化性气氛（O2,CO2）,而在CO气氛下的烧结温度高于H2气氛,混合气氛（V（H2）：V（CO2）=1：1）的烧结温度介于CO2和H2气氛之间,略高于CO气氛下的烧结温度。小龙潭灰的烧结温度随压力的增大而减少,在低压下变化较少,0．7-1．0MPa时烧结温度随压力增大降低明显,之后随压力增大烧结温度降低又趋于缓慢。     

降低鱼卡矿煤灰熔点的试验

水煤浆加压气化技术要求煤灰熔点的流动温度1 350℃,以保证气化炉顺畅排渣。鱼卡矿煤在弱还原气氛下灰熔点的流动温度在1 329~1 379℃,必须加入助熔剂以改变其灰熔融性。通过试验,在原煤中添加质量分数2%~3%的生石灰时,鱼卡矿煤的流动温度可降至1 300℃以下。     

高钠煤灰烧结特性研究进展

中国新疆准东煤具有储量巨大、开采成本低、挥发分高、硫含量低等特点,是优质的动力用煤。但准东煤钠含量高,燃烧利用时易在受热面上形成烧结性积灰,产生严重的结渣,极大限制了高钠煤的开发利用。因此,要实现高钠煤的清洁高效利用,需充分认识高钠煤灰的烧结特性。总结了高钠煤积灰结渣机理,概述了高钠煤灰烧结机制,探讨了二者之间的内在关联。高钠煤在燃烧过程中,煤中碱金属(主要为钠)释放并以Na_2SO_4、NaCl及Na的形式存在于烟气中,与受热面接触并于其上冷凝形成黏性内白层,内白层捕获飞灰颗粒后反应生成低熔点化合物,其烧结温度降低,使锅炉受热面上发生沾污增强型的"沾污烧结"过程。高钠煤灰的烧结过程包含固相烧结、液相烧结和气相烧结3种方式,对煤灰烧结过程的影响因素包括反应温度、化学组成、煤灰粒径、反应气氛、添加剂种类、锅炉设计和锅炉运行工况等。其中添加剂按氧化物种类可分为碱性氧化物和酸性氧化物,一般情况下碱性氧化物可以降低煤灰烧结温度,酸性氧化物可提高煤灰烧结温度。未来对于提高高钠煤灰烧结温度的研究方向可从新型添加剂出发,找到既能固定烟气中的钠,又能与灰渣中的低熔点含钠矿物质反应生成高熔点化合物的单一或混合成分的添加剂。同时,关于钠蒸气对积灰结渣在微观层面上的动态特性的影响机制也需进一步研究。概述了煤灰烧结温度的测量方法,热导率分析法、压力测量法、热机械分析法、筛分法和压降法,其中压降法是目前为止测量烧结温度较为准确的方法。介绍了上海理工大学碳基燃料洁净转化实验室在高钠煤灰烧结特性方面的研究方向,以期为解决燃用高钠煤锅炉积灰结渣问题提供参考。     

石灰石对Shell煤气化的影响

Shell煤气化是当前先进的第二代煤气化工艺,属熔渣、加压气流床气化工艺。煤的灰分、结渣性、灰熔融性等煤质特性对Shell煤气化装置的稳定运行发挥着重要作用。为保证气化炉能顺利排渣,对于高灰熔点的煤,通过添加助燃剂来改变煤的熔融特性成为煤气化工艺的重中之重。探讨了石灰石作为廉价的助燃剂对Shell煤气化的影响。结果表明:添加石灰石后,可降低煤的灰熔融性温度,从而降低了煤灰粘度,降低了煤灰结渣性,保证了装置的稳定运行。     

煤的灰渣熔融特性及其影响因素研究

煤的灰渣熔融特性是决定气化炉结渣情况的重要参数,不仅与煤灰的化学组成有关,还与灰成分的矿物形态有关。本文介绍了煤的灰熔点和相关预测经验公式以及影响灰熔融特性的一般机理,对气化炉稳定安全运行具有一定指导作用。     

高钠煤气化过程中的灰化学研究进展

煤气化是发展煤基大宗化学品及清洁燃料的关键技术，也是实现双碳目标的重要途径。准东高钠煤中碱金属钠含量高，气化过程中碱金属钠释放造成严重的灰释放问题，因此，探究准东高钠煤在气化过程中灰沉积、结渣机理及煤灰流动性对准东煤的清洁高效利用具有重要意义。鉴于此，综述了近年来气化过程中高钠煤的灰化学研究最新进展。总结了煤中钠的赋存形态及含量，阐明了气化过程中钠的迁移转化机制及钠释放导致气化炉受热面造成的灰沉积、结渣问题。由于高钠煤中钠释放主要受气化温度的影响，因此成灰温度不宜高于500℃。气化过程中易生成熔点低的含钠矿物质，降低高钠煤煤灰熔融温度。高钠煤中钙、铁含量高时，煤灰中钙长石及钙铝黄长石在高温下生成低温共晶体、Fe²⁺与煤中矿物质反应形成低熔点尖晶石均是加剧煤灰熔融的重要原因。同时，热转化过程中气氛对高钠煤中矿物演化具有一定影响。高钠煤灰的熔融区间窄，熔融速率快，表明高钠煤灰流动性强，由于Na⁺的离子势较低，O^2-被Si⁴⁺夺取，导致桥氧键断裂成非桥氧键，熔渣网格结构解聚，黏度降低，其熔融机理符合“熔融...     

Effect of different reaction atmospheres on the sintering temperature of Jincheng coal ash under pressurized conditions

The sintering temperature of coal ash is studied to further understand ash behavior. The objective of this study is to obtain a detailed understanding of the effect of the reaction atmospheres on the sintering temperature under elevated pressure. A series of experiments and analyses have been completed using a pressurized pressure-drop measuring device and X-ray diffractometer (XRD) analyzer. The results show that the sintering temperatures decline markedly under all reaction atmospheres with the rise in pressure. The pressure influences the sintering temperatures by affecting the reaction rate and the mineral transformations undergone by the coal ash, as observed from the XRD patterns. The sintering temperatures measured under the reducing reaction atmospheres are lower than those for oxidizing atmospheres. The sintering temperature under N₂ is lower than those under other oxidizing atmospheres. The sintering temperature under the gasification atmosphere is close to those under H₂ and CO atmospheres, whereas the sintering temperature under a H₂ atmosphere is lower than that under a CO atmosphere.     

Agglomeration of coal ash in fluidized beds

The defluidization behaviour of ash derived from Indian coal by combustion in a fluidized bed has been studied. Sintering temperatures for ash in several ranges of particle size were measured with a dilatometer. In agreement with the earlier work on other coals it was found that above the sintering temperature pairs of complementary, limiting values of fluidization velocity and bed temperatures exist which mark the onset of defluidization when the ash particles are heated in a fluidized bed. A linear relation was observed between bad temperature and limiting defluidization velocity. The constants in the corresponding equations were calculated for two size ranges of particles.     

流化床气化技术对煤质的要求

介绍流化床气化技术特点,从煤的分类、工业分析、半焦与CO2反应活性、卤族元素和碱金属含量等方面,分析煤质对流化床气化技术的影响,得出流化床气化适合可气化高灰、高水、高灰熔点的劣质煤,要求煤半焦的CO2反应性高,灰熔点不能偏低,反应温度操作范围尽量大;原料中的卤族元素含量尽量低;碱金属含量低于2%。     

Fundamentals of coal topping gasification: Characterization of pyrolysis topping in a fluidized bed reactor

Coal topping gasification refers to a process that extracts the volatiles contained in coal into gas and tar rich in chemical structures in advance of gasification. The technology can be implemented in a reactor system coupling a fluidized bed pyrolyzer and a transport bed gasifier in which coal is first pyrolyzed in the fluidized bed before being forwarded into the transport bed for gasification. The present article is devoted to investigating the pyrolysis of lignite and bituminite in a fluidized bed reactor. The results showed that the highest tar yield appeared at 823 to 923 K for both coals. When coal ash from CFB boiler was used as the bed material, obvious decreases in the yields of tar and pyrolysis gas were observed. Pyrolysis in a reaction atmosphere simulating the pyrolysis gas composition of coal resulted in a higher production of tar. Under the conditions of using CFB boiler ash as the bed material and the simulated pyrolysis gas as the reaction atmosphere, the tar yields for pyrolytic topping in a fluidized bed reactor was about 11.4 wt.% for bituminite and 6.5 wt.% for lignite in dry ash-free coal base.     

Characterization of low-temperature coal ash behaviors at high temperatures under reducing atmosphere

The coal ash obtained at 815 °C under oxidizing atmosphere was further treated at 1300 °C and 1400 °C under reducing atmosphere. The resultant ashes were examined by XRD, SEM/EDX and FTIR. The results show that the residence time of coal ash at high temperatures has considerable influences on the compositions of coal ash and little effect on the amounts of unburned carbon. The amorphous phase of mineral matters increases with the increasing temperature. The FTIR peaks due to presence of different functional groups of minerals support the findings of XRD, and supply additional information of amorphous phase which cannot be detected in XRD. The ash samples generated from a fixed bed reactor during char gasification were also studied with FTIR. The temperatures of char preparation are responsible for the different transformation of minerals during high temperature gasification.     

Gasification of coal and PET in fluidized bed reactor

Blended fuel comprising 23 wt.% polyethyleneterephthalate (PET) and 77 wt.% brown coal was gasified in an atmospheric fluidized bed gasifier of laboratory-scale. The gasification agent was composed of 10 vol.% O₂ in bulk of nitrogen. Thermal and texture analyses were carried out to determine the basic properties of the fuel components. The influence of experimental conditions, such as the fluidized bed and freeboard temperatures on major and minor gas components and tar content, as well as features of the blended fuel gasification in comparison with the single coal gasification, were studied. In the case of coal with PET gasification, only the fluidized bed temperature showed significant influence on CO, CO₂, CH₄ and H₂ content in the producer gas, whereas the effect of the freeboard temperature was insignificant. In single coal gasification both temperatures had considerable and almost the same influence. The content of minor components, such as ethane, ethylene, acetylene and benzene, was found to be more dependent on the freeboard temperature than on the fluidized bed temperature. It was observed that the higher the freeboard temperatures get, the lower is the concentration of the minor components, with the exception of acetylene. The absolute contents of almost all minor and tar components were approximately three times higher in blended fuel gasification than that in single coal gasification. Finally, partition of carbon (char) and selected metals into bottom and cyclone ash in gasification of both fuels is discussed.     

Technology and economics of coal gasification

The best known commercial coal gasification processes which use oxygen (air) and steam as gasifying media are the gas producer process (normal pressure, fixed bed), Lurgi process (high pressure, fixed bed), Winkler process (normal pressure, fluidized bed) and Koppers-Tetzek process (normal pressure, entrained). Fixed bed and fluidized bed processes are suitable for gasification of noncaking and weakly caking coals with high ash fusion temperatures (> 1200°C). The entrained system is suitable for gasification of any coal. Low-caloric gas (～ 150 Btu/scf) can be produced by the gas producer, Lurgi and Kinkier processes; medium- (～ 300 Btu/scf) and high-caloric (～ 950 Btu/scf) gas by any process. Lurgi and Koppers-Totzek processes are preferred processes for production of synthesis gas at the present time. The costs (/Btu) of production of low-caloric gas are the lowest followed by the medium- and high-caloric gas costs (see Figure 6). The costs of gas production from coal are mainly dependent on the efficiency of the gasification process, scale of operation and the cost of fuel.     

Potassium‐catalyzed steam gasification of ash‐free lignite coal with CO2 capture

The purpose of this research was to study steam gasification of ash‐free coal integrated with CO₂ capture in the presence of a K₂O catalyst for enhancement of the key water‐gas shift reaction and promotion of hydrogen production. To achieve this goal, gasification experiments on ash‐free coal (AFC) were carried out at varying temperatures (600, 650, 675, 700, and 750 °C) with a sorbent‐to‐carbon (CaO/C) ratio of 2 and a catalyst (K₂O) loading of 0.2 g/g (20 weight percent (wt%)) in a fixed‐bed reactor equipped with a gas chromatography analyzer. The sorbent‐to‐carbon (CaO/C) ratio of 2 is based on dry and ash‐free basis. The CaO/C ratio and K₂O wt% were chosen to maximize hydrogen production based on our previously determined optimal values. The AFC was originally extracted from raw lignite coal using organic solvents, which allowed the sorption‐enhanced gasification to be conducted with minimal ash‐catalyst interactions. The effect of temperature on the yield and the initial reaction rate were investigated. The optimal reaction temperature of 675 °C was determined. Carbon balance and final carbon conversions were calculated based on the residue analysis. Activation energy was also calculated using intrinsic kinetics of the reaction. In this study, using AFC offered the potential advantage of operating the gasification process with catalyst recycle.