生物质气化焦油裂解催化剂研究进展

将生物质气化转化为气体燃料或化工合成气原料,是生物质清洁高效利用的有效途径之一,焦油是气化的副产物,影响产气品质和气化效率,催化剂对生物质催化气化及焦油裂解效果明显,得到广泛应用。综述了天然催化剂、无机盐催化剂及合成催化剂对生物质气化过程焦油催化裂解效果、反应条件、催化机理。进一步分析了不同催化剂的生物质催化气化性能及研究进展。同时指出对天然矿石催化剂进行改性或大力发展合成类催化剂对生物质气化焦油降解有着良好的前景。     

烘焙提升纤维素类生物质热解气化性能的研究进展

生物质作为唯一含碳的可再生能源受到广泛关注。由于生物质具有含水率高、氧含量高、热值低等特性,在生物质热解气化中存在热转化效率低、焦油含量高、产品气热值低等问题。烘焙预处理对于改善生物质原料特性和提升热解气化性能具有积极的影响。本文阐述了烘焙预处理技术对于纤维素类生物质原料的疏水性、可磨性、元素组成、能量密度以及热解气化中产生的产品气组分、焦油组分、产品气热值等方面的影响。原料经烘焙预处理后疏水性、可磨性增强,热值增加,提升了原料品质。同时,经烘焙预处理的纤维素类生物质原料可明显提高热解气化性能,产品气中可燃气体组分含量、产量以及热值得到提升,焦油含量明显下降,提高了热解气化的产品气燃烧性能和利用品质。下一步应开展烘焙与热解气化耦合工艺及应用模式研究,提高生物质热解气化的整体经济性和产品附加值。     

甲烷及水蒸气对生物质催化气化合成气和焦油的影响

以松木木屑为生物质原料，在两段式反应器上进行甲烷、水蒸气对生物质催化气化影响的实验研究，考察了甲烷与生物质之比α、水碳比S/C对气体产率、碳转化率、焦油产率、焦油组分和露点温度影响的变化规律。结果表明：α从0增加到0.4，合成气中H₂的产率增加了57.4%，甲烷的加入有利于生成富含氢气的合成气；α为0.2时碳转化率最高，为86.9%，焦油产率下降了30.5%，第二、五类焦油的产率达到最低，可见适量CH₄的添加能促进焦油的转化，特别是大分子焦油和酚类的反应。随着S/C的提高，H₂产率升高，CO产率降低；S/C从1增加到1.5，各类焦油的含量均有所降低，当S/C进一步增加到2时，第二、五类焦油含量却有所上升，说明水蒸气可以促进焦油向气体分子转化的反应，但过量的水蒸气抑制酚类和大分子焦油的分解。总之，甲烷和水蒸气的适量添加均可以提高合成气中H₂的含量，降低焦油产率，提高合成气的品质，有利于气化产物的进一步利用。     

国外生物质催化气化催化剂的研究进展

生物质气化技术已在国内外得到了广泛的开发和运用,但由于合成气中焦油含量较高,影响了合成气的品质,限制了生物质气化技术的应用。在生物质气化过程中应用催化剂可以有效的降低焦油的含量,调整合成气组成。对国外生物质催化气化催化剂的研究进展进行了综述,并提出了我国生物质催化气化技术的研究方向。     

生物质化学链气化制取合成气模拟研究

利用Aspen Plus软件建立生物质化学链气化制取合成气模型,对铁基生物质化学链气化制取合成气进行模拟计算,分析气化过程中温度和压力等因素变化对生物质气化制取合成气的影响,探讨了氧载体存在对生物质气化过程的影响.结果表明,H2和CO是生物质化学链气化产生的合成气中最主要的两种产物,气化温度的提高对气化过程是有利的,而压力的提高降低了气化效果,气化温度在800℃～850℃较为适宜;载氧体的存在能显著提高合成气的产率.     

生物质气化中焦油特性及其处理

生物质气化过程中产生的焦油问题对整个气化系统的效率以及最终商业化发展有着重要的作用,焦油的危害在于其冷凝之后对反应设备有较大的腐蚀性而且对后续的反应也有影响。因此,生物质气化过程中去除焦油十分必要。本文综述了气化过程中温度、停滞时间、催化剂种类等因素对生物质气化过程中焦油产量的影响,并且详细介绍与对比了现实工业生产中去除焦油的几种常用方法。     

生物质水蒸气气化制取富氢合成气及其应用的研究进展

生物质水蒸气气化是有效的热化学转化手段,可将原材料转化为富氢合成气,气体应用更加广泛,有替代化石能源制氢的潜在价值。不同的生物质资源气化和产氢能力存在差异,物料的选择对气化制取富氢合成气至关重要,而调整气化操作参数包括反应温度、水蒸气加入量、催化剂和吸收剂等可进一步优化合成气质量,提升氢气含量。本文首先综述了不同操作条件对生物质水蒸气气化制取富氢合成气的影响。其次,介绍了生物质炭气化制取富氢合成气的研究现状,炭气化可制得高品质的富氢合成气,但过程受动力学限制,需要加入催化剂以提升炭气化速率。文中还简述了以钾盐为催化剂时的催化机理,并展望了富氢合成气的应用,包括制备高纯氢应用于燃料电池和制备合成天然气。     

生物质裂解气中焦油转化催化剂的研究现状

生物质裂解气中焦油的存在严重影响了燃气的热值和后续流程，因此焦油转化对生物质裂解制取合成气有着重要的意义，介绍了用于生物质裂解气中的焦油转化的催化剂体系，以及国内外在此领域的研究成果，展望了焦油转化催化剂的发展方向以及急需解决的问题。     

生物质与煤流化床共气化特性研究进展

主要从生物质气化特点、共气化对流化特性及气化特性的影响方面综述了生物质与煤流化床共气化技术的优势,重点讨论了生物质加入对煤气化中燃气组成、热值、气体产率、气化效率、碳转化率和焦油含量等气化特性的影响规律及其协同效应机理,为生物质与煤共气化技术的研发提供重要理论基础。     

原料烘焙预处理对生物质气化的影响综述

简述了生物质原料的物理和化学特性,介绍了现有的生物质气化原料预处理方法,着重阐述了生物质烘焙技术研究现状和烘焙预处理对生物质气化的影响。众多研究结果表明：生物质烘焙预处理能够显著改善生物质的磨粉性能,有效提高生物质的能量密度和堆积密度,同时还能降低生物质的O／C比。最后对原料烘焙预处理在生物质气化中的应用做出了展望。     

Torrefaction of reed canary grass, wheat straw and willow to enhance solid fuel qualities and combustion properties

Torrefaction is a treatment which serves to improve the properties of biomass in relation to thermochemical processing techniques for energy generation; for example, combustion, co-combustion with coal or gasification. The topic has gathered interest in the past two decades but further understanding is required for optimisation of the process thus enhancing economic efficiency, which is crucial to the success of the treatment commercially and within industry. In particular there is a noticeable gap in current literature regarding the combustion properties of torrefied biomass. This study examines torrefaction in nitrogen of two energy crops, reed canary grass and short rotation willow coppice (SRC), and a residue, wheat straw. Product evolution and mass and energy losses during torrefaction are measured using a range of laboratory scale methods. Experiments at different torrefaction conditions were undertaken to examine optimization of the process for the three fuels. Progress of torrefaction was also followed by chemical analysis (C, H, N, O, ash), and it was seen that the characters of the biomass fuels begin to resemble those of low rank coals in terms of the van Krevelen coal rank parameter. In addition, the results indicate that the volatile component of biomass is both reduced and altered producing a more thermally stable product, but also one that produces greater heats of reaction during combustion. The difference between the mass and energy yield was shown to improve for the higher torrefaction temperatures investigated. The combustion behaviour of raw and torrefied fuels was studied further by differential thermal analysis (DTA) and also, for willow, by suspending individual particles in a methane-air flame and following the progress of combustion by high-speed video. It is shown that both volatile and char combustion of the torrefied sample become more exothermic compared to the raw fuels, and that depending on the severity of the torrefaction conditions, the torrefied fuel can contain up to 96% of the original energy content on a mass basis. Upon exposure to a methane-air flame, torrefied willow ignites more quickly, presumably because its low moisture content means that it heats faster. Torrefied particles also begin char combustion quicker than the raw SRC particles, although char combustion is slower for the torrefied fuel.     

Isothermal and Morphological Studies of the Torrefaction of Spruce Wood

The replacement of fossil fuels by biofuel for decreasing the action of greenhouse gases on the global climate is encouraged in industrially developed countries. A promising trend in the refining of waste biomass is torrefaction—a mild pyrolysis process in which biomass is heated to 250–350°C without the access of oxygen at low heating rates; as a result, biocoal with improved chemical and physical properties is formed. The torrefaction (mild pyrolysis at 250–300°C) of spruce stem wood was studied in a fixed-bed reactor at different temperatures. The mass and energy yields of biocoal, its specific heat of combustion, and morphological changes in the biomass structure in the course of spruce wood torrefaction were determined. It was established that the torrefied samples began to decompose at higher temperatures, as compared with the nontorrefied biomass. The torrefied fuel had a higher heat of combustion, which increased with the temperature of torrefaction. Conclusions on the restructuring of test samples and the formation of a porous structure at different temperatures depending on exposure time were made.     

生物质气化过程中焦油裂解的工业应用研究

针对生物质气化过程中产生的焦油,采用高温以及木炭催化的双重功效对其裂解进行了工业应用研究,并考察了一些操作参数的影响。实验结果表明,裂解操作温度控制在800℃以上时,对燃气中的焦油有明显的裂解作用。燃气通过焦油裂解炉后,燃气中夹带的飞灰得到了过滤,一方面降低了后序工序中燃气净化的负担,另一方面飞灰中未完全转化的碳得到进一步的转化,提高了碳的转化率,从而为生物质能的利用开辟了更广阔的前景。     

烟气烘焙对玉米秆可磨性的影响规律研究

可磨性是生物质在现有燃煤机组规模化燃烧利用中必须考虑的问题之一。本文基于固定床反应器对玉米秆进行烘焙预处理,针对生物质单烧和与煤混烧两种技术路线,利用臼式研磨仪、全自动粒径筛分仪、纤维素分析仪和傅里叶红外光谱,研究了不同烘焙气氛、温度对燃料可磨性的影响。结果表明,相比于氮气,烟气能够在更低的烘焙温度下使玉米秆可磨性提升至接近于典型动力用煤,主要是由于烟气中的氧化性组分促进了纤维素、半纤维素的分解。当共磨时,煤颗粒表现出助磨的作用提升了玉米秆的可磨性,在较高温度或烟气烘焙条件下,混样的可磨性近似甚至优于煤。     

Impact of torrefaction on syngas production from wood

Torrefaction is a way to treat biomass before transportation or thermochemical conversion. It can be used to increase the energy content of wood or to facilitate grinding. The purpose of this paper was to quantify the impact of such a treatment on the behaviour of wood during gasification by steam at high temperature to produce syngas. The aspects of both gas yields and reaction kinetics were considered.Beechwood was submitted both to light torrefaction and severe torrefaction, using a specially designed crossed fixed bed reactor. The initial wood and the torrefied woods were first characterised, then gasified in a new laboratory high-temperature entrained flow reactor (HT-EFR) at 1400 °C for 2 s in an atmosphere containing 20 vol% steam in N₂. The syngas produced was then analysed. The experiments were modelled using a thermo-dynamical equilibrium approach.It was confirmed that torrefaction decreased the O/C ratio. The quantity of syngas produced increased with the severity of the torrefaction. The equilibrium approach describes the results satisfactorily.Gasification experiments carried out at a lower temperature - 1200 °C - indicated that the chars from torrefied woods are less reactive towards steam than the char from wood.     

A novel biomass air gasification process for producing tar-free higher heating value fuel gas

Biomass is a promising sustainable energy source. A tar-free fuel gas can be obtained in a properly designed biomass gasification process. In the current study, a tar-free biomass gasification process by air was proposed. This concept was demonstrated on a lab-scale fluidized bed using sawdust under autothermic conditions. This lab-scale model gasifier combined two individual regions of pyrolysis, gasification, and combustion of biomass in one reactor, in which the primary air stream and the biomass feedstock were introduced into the gasifier from the bottom and the top of the gasifier respectively to prevent the biomass pyrolysis product from burning out. The biomass was initially pyrolyzed and the produced char was partially gasified in the upper reduction region of the reactor, and further, char residue was combusted at the bottom region of the reactor in an oxidization atmosphere. An assisting fuel gas and second air were injected into the upper region of the reactor to maintain elevated temperature. The tar in the flue gas entered the upper region of the reactor and was decomposed under the elevated temperature and certain residence time. This study indicated that under the optimum operating conditions, a fuel gas could be produced with a production rate of about 3.0 Nm³/kg biomass and heating value of about 5000 kJ/Nm³. The concentration of hydrogen, carbon monoxide and methane in the fuel gas produced were 9.27%, 9.25% and 4.21%, respectively. The tar formation could be efficiently controlled below 10 mg/Nm³. The system carbon conversion and cold gasification efficiency reached above 87.1% and 56.9%, respectively. In addition, the investigation of energy balance for the scale-up of the proposed biomass gasification process showed that the heat loss could be recovered by approximately 23% of total energy input. Thus, partial fuel gas that was produced could be re-circulated and used to meet need of energy input to maintain the elevated temperature at the upper region of reactor for tar decomposition. It was predicted the heating value of product fuel gas would be 8000 kJ/Nm³ if the system was scaled up.     

Influence of torrefaction on the grindability and reactivity of woody biomass

The use of biomass to produce energy is becoming more and more frequent as it helps to achieve a sustainable environmental scenario. However the exploitation of this fuel source does have drawbacks that need to be solved. In this work, the torrefaction of woody biomass (eucalyptus) was studied in order to improve its properties for pulverised systems. The process consisted in a heating treatment at moderate temperature (240, 260, 280 °C) under an inert atmosphere. The grindability of raw biomass and the treated samples was compared and an improvement in the grindability characteristics was observed after the torrefaction process. Thermogravimetric analysis of the samples was carried out in order to study their reactivity in air. The DTG curves of the torrefied biomass showed a double peak nature. The kinetic parameters were calculated for each reaction stage. The torrefaction process was found to influence the parameters of the first stage, whereas those corresponding to the second remained unaffected.     

生物质低温气化催化剂的研究发展

物质气化技术已在国内外得到广泛的开发和运用,但由于燃气品位较差,焦油较多,限制了生物质气化气的进一步利用.近年来生物质的低温气化催化裂解已引起了国内外的广泛关注.分析了目前使用的各种催化剂对减少生物质气化焦油的生成和改进燃料气品质的作用结果,提出了进一步的研究方向.     

An investigation of the grindability of two torrefied energy crops

The process of torrefaction alters the physical properties of biomass, reducing its fibrous tenacious nature. This could allow increased rates of co-milling and therefore co-firing in coal fired power stations, which in turn would enable a reduction in the amount of coal used and an increase in the use of sustainable fuels, without the need for additional plant. This paper presents an experimental investigation of the pulverisation behaviour of two torrefied energy crops, namely: willow and Miscanthus. A multifactorial method approach was adopted to investigate the three process parameters of temperature, residence time and particle size, producing fuels treated using four different torrefaction conditions. The untreated and torrefied fuels were subjected to standard fuel analysis techniques including ultimate analysis, proximate analysis and calorific value determination. The grindability of these fuels was then determined using a laboratory ball mill and by adapting the Hardgrove Grindability Index (HGI) test for hard coals. After grinding, two sets of results were obtained. Firstly a determination similar to the HGI test was made, measuring the proportion of sample passing through a 75 μm sieve and plotting this on a calibrated HGI chart determined using four standard reference coals of known HGI values. Secondly the particle size distributions of the entire ground sample were measured and compared with the four standard reference coals. The standard fuel tests revealed that temperature was the most significant parameter in terms of mass loss, changes in elemental composition and energy content increase. The first grindability test results found that the untreated fuels and fuels treated at low temperatures showed very poor grindability behaviour. However, more severe torrefaction conditions caused the fuels to exhibit similar pulverisation properties as coals with low HGI values. Miscanthus was found to have a higher HGI value than willow. On examining the particle size distributions it was found that the particle size distributions of torrefied Miscanthus differed significantly from the untreated biomass and had comparable profiles to those of the standard reference coals with which they had similar HGI values. However, only the torrefied willow produced at the most severe conditions investigated exhibited this behaviour, and the HGI of torrefied willow was not generally a reliable indicator of grindability performance for this energy crop. Overall it was concluded that torrefied biomass can be successfully pulverised and that torrefied Miscanthus was easier to grind than torrefied willow.