生物质气化过程燃气净化技术研究进展

生物质燃气必须经过净化后才能进行使用。文章针对生物质气化过程中燃气净化效率低、焦油脱除困难等问题,对不同种类燃气净化设备（机械式、过滤式、洗涤式和静电式）的优缺点进行了对比研究,并对利用多级设备联合净化燃气的技术措施和方法进行了分析,深入探讨了生物质燃气在净化过程中面临的问题。同时,基于我国农村小型生物质气化站低成本、低能耗、高效率的要求进行考虑,指出开发高效低廉的适用于农村小型生物质气化站的多级燃气净化系统是促进生物质气化集中供气推广的关键技术。     

自燃连续式生物质热解炭气油联产系统燃气净化分离技术工艺研究

在对自燃连续式生物质热解炭化工艺过程和特点分析的基础上,结合生物质热解粗燃气组分特征,采用协同分离和多级净化的设计思路,研究了该热解工艺条件下的燃气净化分离与高值化处理技术路线,主要包括空气富氧化处理、粉尘脱除、焦油与木醋液分离、燃气提质、深度净化等工艺环节,最后分析了该工艺系统涉及的辅助性关键技术问题。该研究可为生物质热解炭气油联产系统的开发提供重要参考。     

生物质热解气化气中焦油生成机理及其脱除研究

生物质气化气中焦油含量高成为制约生物质气化技术商业化发展的决定性因素之一。在对生物质热解气化过程中焦油的生成及其影响因素进行分析的基础上,采取优化炉内结构与炉外气体湿式净化相结合的方法来脱除气体中的焦油,研究开发出气化剂由侧向送入的气化反应炉,以及相应的集喷淋、水浴、水膜、冲激于一体的湿式净化装置。该生物质气化机组所得到的可燃气具有燃气热值高、焦油含量低、操作简单、安全可靠的特点。气化效率可达到 78％,燃气低位热值为 5.4 MJ/m3(玉米秸 ),焦油含量 48 mg/m3, O2含量为 0.7％,主要技术指标均低于有关行业标准。     

电捕焦油器用于生物质燃气净化及燃气允许最高氧含量的研究

焦油清除是生物质气化技术的难点问题,用电捕焦油器除焦是解决焦油问题的根本途径。通过试验,验证了电捕焦油器应用于生物质燃气的效果;计算了典型生物质燃气的爆炸极限;提出了氧含量以1.5%为报警极限,最高允许氧含量不超过2%;建议修改相关标准,为电捕焦油器在生物质燃气领域的应用提供理论依据。     

生物质气化发电燃气焦油脱除方法的探讨

生物质气化发电技术的最大难点之一就是如何除去燃气中含有的焦油等污染物,这些成分会对燃气轮机或内燃机等设备造成一定的影响.因此生物质气化发电过程中燃气焦油的脱除是目前国内外重点研究和解决的课题之一.文章在研究国内外大量有关文献资料的基础上,深入阐述了气化过程中焦油产生的机理、影响焦油生成的因素以及焦油的脱除方法,重点探讨了目前较为有效的焦油热化学脱除方法,即焦油的热裂解和催化裂解方法,以期为生物质气化发电燃气焦油的脱除提供一些思路和参考.     

生物质气化技术面临的挑战及技术选择

生物质气化可实现低品位生物质能的深层次利用,不同地区、不同行业有不同的能源需求和产业结构,应合理选择生物质气化技术。固定床气化技术针对的是中小规模应用,该技术存在的问题包括焦油含量高、规模小、机械化和自动化程度较低、发电效率低等。流化床气化技术针对的是中等及以上规模应用,目前需要解决的问题是热效率低,发电效率低,需要开发高气化效率和无焦油的燃气型气化炉、低热值燃气轮机、高效燃气净化系统,以便采用BIGCC技术。沼气技术是一项生物质综合高效清洁利用的多联产工艺,目前急需开发高效高浓度厌氧消化的沼气发酵工艺和配套的集成设备,培育和筛选高效沼气发酵微生物菌群,简化沼气净化工序,解决沼液、沼渣的利用难题等。生物质快速热解技术是一种高温处理过程,其最大的优点是产物生物油易于储存运输,不存在产品规模和消费的地域限制问题。从工艺特点、经济效益和规模化生产来看,沼气技术更适合处理高含水的养殖业粪便,快速热解技术更适合农作物秸秆的规模化转化,燃气型气化技术更适合社区生活垃圾和农林产品加工废弃物的处理。     

生物质气化发电技术讲座(4)生物质燃气净化技术

生物质气化燃气含有各种各样的杂质,杂质的主要成分列在表1中。各种杂质的含量与原料特性、气化炉的形式关系很大。燃气净化的目标就是要根据气化工艺的特点,设计合理有效的杂质去除工艺,保证后部气化发电设备不会因杂质的存在而导致其磨损腐蚀和污染等问题。(1)燃气高温过滤生物质气化燃气含有大量的微小的焦炭颗粒和灰,由于焦炭的密度和直径都很小,一般旋风分离器难以去除,即使用非常高效的旋风分离器,燃气中的颗粒含量也很难降到5～30g/m3。在这种情况下,比较好的净化方法是过滤。由于焦油在表1燃气中各种杂质的特性杂质种类典型成分可能…     

户用型下吸式生物质气化炉性能研究

由于生物质能具有储量大、环境友好等特点,生物质气化技术尤其是户用型气化技术在我国农村应用值得研究。论文在建立下吸式户用型气化系统上,研究了不同生物质原料的气化性能,如对温度分布、气化效率、燃气热值、燃气产量等,并进行了焦油脱除效率的研究。结果表明,该炉型的气化效率可达70％,燃气热值达到6MJ／m3,燃气中焦油含量降低至20mg／m3。     

生物质气化焦油脱除过程参数优化方法

焦油是生物质气化过程中的有害产物,它会降低燃气品质,对气化设备及后续用气设备产生危害.本文通过对生物质气化过程中影响焦油生成量的因素进行分析,依据最小二乘曲线拟合原理和目标规划理论建立了生物质料木屑气化过程焦油脱除的参数优化模型,在此基础上采用遗传算法对焦油脱除过程优化模型进行参数寻优.计算结果表明,当气化温度为796.6℃、当量比为0.203时,木屑气化的焦油生成量最小.     

生物质流化床气化技术应用研究现状

按所得产品不同,可将生物质气化技术分为制氢、发电和合成液体燃料3大类。文章介绍了生物质流化床水蒸气气化制氢、催化气化制氢和超临界水气化制氢的工艺特点;分析了生物质流化床气化发电的技术、经济可行性;简述了生物质流化床气化合成液体燃料的研究现状;指出气化产出气化学当量比调变、焦油去除问题和合成气净化是生物质流化床气化技术应用的主要瓶颈,认为定向气化是今后研究的主要方向。     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

A review of cleaning technologies for biomass-derived syngas

Syngas from gasification of carbonaceous feedstocks is used for power production and synthesis of fuels and commodity chemicals. Impurities in gasification feedstocks, especially sulfur, nitrogen, chlorine, and ash, often find their way into syngas and can interfere with downstream applications. Incomplete gasification can also produce undesirable products in the raw syngas in the form of tar and particulate char. This paper reviews the technologies for removing contaminants from raw syngas. These technologies are classified according to the gas temperature exiting the cleanup device: hot (T > 300 °C), cold (T < ∼100 °C), and warm gas cleaning regimes. Cold gas cleanup uses relatively mature techniques that are highly effective although they often generate waste water streams and may suffer from energy inefficiencies. The majority of these techniques are based on using wet scrubbers. Hot gas cleaning technologies are attractive because they avoid cooling and reheating the gas stream. Many of these are still under development given the technical difficulties caused by extreme environments. Warm gas cleaning technologies include traditional particulate removal devices along with new approaches for removing tar and chlorine.     

The effects of syngas impurities on syngas fermentation to liquid fuels

Biomass gasification to generate raw syngas used in anaerobic fermentation processes is one of several emerging technologies for the production of biofuels from biomass. The gasification-fermentation process can utilize a wide variety of lignocellulosic biomass such as prairie grasses, wood chips, and paper wastes, in addition to non-lignocellulosic biomass such as solid municipal wastes. Although the primary components of raw syngas used in the fermentation process are CO, H₂, and CO₂, several impurities can also be present. Some of these impurities may interfere with the fermentation process. Since the impurities will depend upon the feedstock, the gasifier type, and cleanup conditions, an understanding of the positive or adverse effects of the impurities on raw syngas fermentation is critical to understand the need for efficient gas cleaning processes required for commercialization. This work describes the impurities generated during gasification and discusses the potential accumulation of impurities in the fermentation media and the associated potential effects on the microbial fermentation process (e.g. cell toxicity, enzymatic inhibition and end product distribution). A wide distribution of impurity solubilities in the media shows that certain impurities, such as ammonia, are more likely to accumulate in the media. Additionally, entrained tar particulates greater than 0.025 ??m, nitric oxide greater than 0.004 mol%, and ammonia in general have an adverse effect on the fermentation process. Therefore, a cleanup system suitable for raw syngas fermentation processes is evident although the degree of cleanup would likely depend upon the feedstock and the associated gasification process.     

Evaluation of sorbents for high temperature removal of tars,hydrogen sulphide,hydrogen chloride and ammonia from biomass-derived syngas by using Aspen Plus

Biomass gasification is a promising technology to produce secondary fuels or heat and power, offering considerable advantages over fossil fuels. An important aspect in the usage of producer gas is the removal of harmful contaminants from the raw syngas. Thus, the object of this study is the development of a simulation model for a gasifier including gas clean-up, for which a fluidized-bed gasifier for biomass-derived syngas production was considered, based on a quasi-equilibrium approach through Gibbs free energy minimisation, and including an innovative hot gas cleaning, constituted by a combination of catalyst sorbents inside the gasification reactor, catalysts in the freeboard and subsequent sorbent reactors, by using Aspen Plus software. The gas cleaning chain simulates the raw syngas clean-up for several organic and inorganic contaminants, i.e. toluene, benzene, naphthalene, hydrogen sulphide, hydrogen chloride and ammonia. The tar and inorganic contaminants final values achieved are under 1 g/Nm³ and 1 ppm respectively.     

Enhanced trace pollutants removal efficiency and hydrogen production in rice straw gasification using hot gas cleaning system

This study investigates the enhancement of tar and trace gaseous pollutants (e.g. hydrogen sulfide (H₂S) and hydrogen chloride (HCl) removal efficiency derived from rice straw gasification using an integrated hot-gas cleaning system. A bubbling fluidized bed gasifier was used by controlling the temperature at 800 °C and equivalence ratio (ER) ranging 0.2 to 0.4. The hot gas cleaning system was operated at 250 °C and designed to combine three types of absorbents including zeolite, calcined dolomite, and activated carbon. Tar, H₂S, and HCl removal efficiency and enhanced hydrogen production were also discussed. The experimental results indicated that light fraction tar removal efficiency was higher than 90% and the overall tar removal efficiency was approximately 70%. In the case of ER 0.4, the syngas tar content was decreased from 71.88 g/Nm³ (without hot gas cleaning system) to 16.53 g/Nm³ (with hot gas cleaning system). The tar removal efficiency is nearly 77% using the hot gas cleaning system. The HCl and H₂S removal efficiency ranged from 94% to 98% and from 80.7% to 83.92%, respectively. In the case of ER 0.3 and with the hot gas cleaning system, the HCl and H₂S concentrations in cleaned syngas gas were less than 40 ppm and 100 ppm, respectively. Meanwhile, the hydrogen concentration of produced gas was also increased from 6.82% to 9.83% with hot gas cleaning system used. It means that the hot gas cleaning system can effectively remove HCl and H₂S from produced gas in gasification, but also it has good potential for improving syngas quality and enhancing gas turbine application in the future.     

Modeling and parametric optimization of air catalytic co-gasification of wood-oil palm fronds blend for clean syngas (H2+CO) production

Syngas production from biomass gasification is a potentially sustainable and alternative means of conventional fuels. The current challenges for biomass gasification process are biomass storage and tar contamination in syngas. Co-gasification of two biomass and use of mineral catalysts as tar reformer in downdraft gasifier is addressed the issues. The optimized and parametric study of key parameters such as temperature, biomass blending ratio, and catalyst loading were made using Response Surface Methodology (RSM) and Artificial Neural Network (ANN) on tar reduction and syngas. The maximum H₂ was produced when Portland cement used as catalyst at optimum conditions, temperature of 900 °C, catalyst-loading of 30%, and biomass blending-ratio of W52:OPF48. Higher CO was yielded from dolomite catalyst and lowest tar content obtained from limestone catalyst. Both RSM and ANN are satisfactory to validate and predict the response for each type of catalytic co-gasification of two biomass for clean syngas production.     

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H₂) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H₂ production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.     

生物质加压气化技术的研究与应用现状

生物质气化气可以替代化石燃料用于发电、供热和用于生产合成反应的化工原料,解决日益严重的能源短缺和环境污染等问题.加压气化具有生产能力大、效率高,可降低单位投资成本,减少焦油的产生,有利于后续发电及合成工艺等诸多优点.文章介绍了压力对气化的影响,加压气化存在的主要问题,加压在生物质和劣质煤等联合气化、定向气化制备合成气、IGCC上应用的研究和应用现状.     

Methanation of syngas from biomass gasification: An overview

Traditional fossil fuel overuse could lead to global warming and environmental pollution. As a renewable energy, biomass energy is a sustainable and low pollution carbon energy, which has a wide range of sources. Syngas production from biomass thermochemical conversion is a promising technology to realize effective utilization of the renewable energy. Syngas produced from gasification could be further converted into value-added chemicals via the method of Fischer-Tropsch synthesis. Syngas and CO₂ methanation could transform renewable energy into feasible transport and high-density energy. However, tar formation and catalyst deactivation are the main problem during the biomass gasification and methanation. This review sheds light on the development of biomass gasification and syngas methanation. Firstly, we presented the common reactors and some other factors during gasification. Secondly, we provide a comprehensive introduction of the advanced active catalyst for gasification and syngas methanation. Finally, some representative large-scale and commercial plants and companies for biomass gasification were compared and discussed in details. Then the prospective developments in combination of gasification and methanation were concluded to give an outlook for biomass gasification and its downstream development.     

Detailed process modeling of a wood gasification combined heat and power plant

We provide the first process simulation able to depict a complete life cycle inventory of a biomass gasification combined heat and power (CHP) plant. The model predicts the detailed mass and energy balances, minor compounds emissions (such as NO_x, SO_x, aromatics, etc.). It is based on a phenomenological approach for dryer, reactors (gasification and combustion) and scrubber modeling. Process units are modeled with Aspen Plus® models completed with dedicated Fortran sub-models when more details are required. The gasifier is a Dual Fluidized Bed (DFB). It is decomposed in three sections, describing the three main mechanisms occurring in the reactor: wood pyrolysis, secondary reactions and char combustion. At the outlet of the gasifier, the complete composition of the syngas is predicted, which includes water, permanent gases, inorganics, particles and tars (phenol, benzene, toluene, styrene, indene, naphthalene, acenaphthylene, anthracene, phenanthrene, pyrene). Simulation results were validated against measurements from a pilot plant and other literature data. A wet conventional syngas cleaning system for gasification plant, including cyclone, catalytic tar cracker, syngas cooler, bag filters, water scrubber and wastewater treatment was considered and modeled. The complexity of tar composition allows a reliable determination of tar dew point. At the outlet of the cleaning system, syngas is burned in gas engines. Gaseous emissions (NO_x, SO_x, etc.) of the gas engines and the DFB combustor are also handled by the model as well as ashes and liquid waste. The predicted electrical and thermal efficiencies are 27 and 39% respectively.