秸秆气焦油高温裂解实验分析及研究

针对生物质气化过程中产生的焦油,采用高温石英砂固定床对其裂解进行了实验研究,并获取了一些实验参数。实验结果表明,床内温度在800℃以上时,焦油能发生明显的裂解。焦油裂解后,变成小分子烃类,大大降低了焦油含量,气体热值有所下降,但燃气总量有大幅度提高,从而为焦油的处理提供了新的方式。     

生物质闪速热觧工艺

在完全或部分地隔绝氧气的条件下,对生物质原料加热,使原料在高温作用下发生裂解反应的过程,称为生物质的热解。生物质原料通过热化学降解,可以生产出木炭、焦油和可燃气等三类不同形态的产品。     

生物质热解气重整试验平台设计与试验

针对热解气焦油含量高、热值低的问题,文章基于焦油催化裂解和热解气气化重整原理,提出了生物质热解气重整工艺路线,并设计、搭建了生物质热解气重整试验平台,该试验平台主要由热解、催化重整、产品收集、控制系统等组成。以玉米秸秆为原料,在该试验平台上开展了热解气重整试验,试验结果表明:在以石英砂作为惰性材料的条件(高温裂解)下,热解气产率为33.8%,焦油转化率为64.3%;在玉米秸秆炭催化裂解条件下,热解气产率为37.8%,焦油转化率72.6%;高温裂解和催化裂解条件下生成的热解气的热值均达到了17MJ/m3以上。热解气重整试验平台达到了设计目的,为热解气重整研究提供了理论支持和技术支撑。     

CaO催化裂解生物质气化焦油实验研究

以谷壳气化发电产生焦油为研究对象,考查了CaO作为焦油裂解催化剂对其催化裂解的影响。实验研究结果表明:CaO作为焦油裂解催化剂可使焦油裂解率明显提高,在800℃时,其裂解率可由热裂解的28.66%提高到65.60%,焦油催化裂解后可使燃气成份中的H2、CO、CH4以及CO2含量提高。但焦油裂解过程中,其积炭率可达30.51%;扫描电镜显示:因焦油裂解积炭包裹CaO催化剂,易使其催化活性失效,同时由于积炭,使床层压降增加,给焦油催化裂解运行带来困难。     

大颗粒生物质高温热解模型的建立及数值模拟

通过对生物质理化特性和热解机理的深入分析,建立了高温条件下生物质热解模型.耦合生物质热解化学反应动力学方程和传热方程,用四阶龙格库塔法和三角追赶法求解,并将计算结果与文献中的实验数据进行对比.模拟结果表明:在径向位置颗粒中心温度的增加速率比表面的增加速率高;随着颗粒粒径的增加,生物质热解完成所需的时间加长;大分子焦油在1273K以上才开始快速裂解,温度越高裂解速率越快,当温度达到1673K时,大分子焦油几乎裂解完全.     

生物质二次裂解制取氢气的研究

采用生物质热解及二次裂解的方法制取富氢气体.通过对生物质热解产生的气液体成份进行二次裂解,实现热解组分中焦油等含氢化合物的深度转化,提高产品气体中氢气的含量,同时解决了热解产品气中焦油不易去除的难题,得到洁净的富氢气体.实验选用稻壳为原料,分析了热解温度和物料滞留时间等因素对热解气体成份的影响,比较了热解气体和二次裂解气体成份的变化,同时分析了水蒸汽、催化剂等因素对裂解气体成份的影响.实验结果表明,热解温度和物料滞留时间的增加提高了热解气体中氢气的含量,二次裂解、水蒸汽和催化剂的引入都能在一定程度上提高产品气中H2的含量.实验最终表明,氢气体积含量可达到60%以上.     

催化剂对稻壳水蒸气气化特性和焦油转化的影响

使用白云石、橄榄石、菱镁矿作为催化剂,在自行搭建的小型固定床气化炉试验台上对稻壳进行高温水蒸气催化气化和焦油转化实验,研究了气化温度、催化剂种类、镍负载、表观停留时间等因素对稻壳水蒸气气化半焦产率、焦油产率、气体产率以及气体组分的影响.试验结果表明,白云石、橄榄石、菱镁矿都对焦油有一定催化裂解效果,白云石的催化活性高于...     

烟秆裂解实验研究

系统地研究了以烟秆为原料裂解制备生物质焦油的工艺参数,以及原料粒径、裂解温度、添加剂用量对裂解产物组成的影响。结果表明,当裂解温度在550℃左右,原料粒径为0.425～1.000 mm,添加剂凹凸棒土用量为烟秆的100%时,生物质焦油产率最高,为47.9%,而残焦及气体得率分别为17.6%和34.5%。烟秆裂解得到的生物质焦油,其成分复杂。分离提纯生物质焦油中的较大组分尼古丁,可用于医药、食品和饲料、日用化工、染料及电镀等行业,应用前景相当广泛,烟秆裂解具有巨大的开发利用潜力。     

生物质气化气中焦油非催化裂解实验研究

生物质气化是一种环境友好的新能源利用技术,焦油作为生物质气化的副产物,是限制气化技术发展的主要因素.试验针对生物质气化产出气中焦油在700～1 000℃裂解温度区间的裂解特性进行了分析,并提出了焦油裂解产气率的概念.试验表明,焦油裂解气可以成为生物质气化气的有效的能量补充,而且随着裂解温度的升高,焦油裂解产气率增加,焦...     

生活垃圾气化焦油非原位裂解实验研究

通过水平固定床气化炉,模拟生活垃圾气化焦油非原位裂解过程,旨在研究设备运行工况对焦油裂解的影响。结果表明:反应温度是影响生活垃圾气化焦油二次裂解的主要因素,反应温度的升高促进了焦油的裂解转化,焦油转化率由500℃工况下的37.06%升高到了900℃时的82.47%,与此同时焦油三相裂解产物中的固相炭黑随着反应温度的升高产率增加;水蒸气的加入通过消耗焦油裂解副产物固相炭黑从而导致气相产物的增加,同时促进焦油重组反应,且存在最佳水蒸气注入浓度9 vol% N_2,此时焦油转化率为95.91%。     

A study on a multi-stage hybrid gasifier-engine system

This paper presents the results of a study on a multi-stage hybrid biomass–charcoal gasification to produce low tar content gas for engine application using coconut shell as a fuel. The performance of a gasifier-engine system consisting of the hybrid biomass–charcoal gasifier, a gas cleaning/cooling system and a diesel engine is also discussed.

The lowest tar content found in hybrid coconut shell-charcoal gasification was 28 mgNm⁻³. Using a spray tower, producer gas could be cooled down to 40°C; almost tar-free gas was obtained after cooling the producer gas from the hybrid gasifier system. A three-cylinder Perkins diesel engine was tested at a constant speed of 1500 rpm on diesel alone and dual fuel modes of operation. A maximum of 81% of the total heat energy input was replaced by the producer gas at an electricity generation of 11.44 kWe.     

Pyrolysis of coconut shells in a concentric three tubes reactor

To improve energy efficiency, coconut shells were pyrolyzed in a concentric three tubes reactor using a combination of external and internal heating method. Coconut shells were oxidized partially at the bottom of the reactor, and the gas rised through the redhot charcoal packing to be cracked to smaller compounds and burnt by the air. The hot gas diverged outward and flowed down along the outside wall of the second tube before it left the reactor. The higher the temperature and the longer the time of pyrolysis, the less charcoal and light oil, but the more tar were produced. The charcoal obtained was in between that produced from external and internal heating procedures. Under the optimum time of 95 minutes and temperature of 579°C, the products were 19.53% charcoal, 5.22% tar, and 0.16 % light oil.     

Carbonization of Eight Bamboo Species of Northeast India

Abstract

Eight bamboo species of northeast India were carbonized in a laboratory-scale fixed bed reactor at temperature ranging from 300°C to 600°C with a heating rate of 5°C/min, and their mass balance experiments of decomposition products were done at 600°C. At this temperature, the yields of charcoal, tar, gas, and condensable liquid ranged from 23.35–28.25%, 6.46–8.85%, 6.93–10.05%, and 51.98–57.96%, respectively. Fixed carbon content of the charcoal samples varied from 62.10–67.52% indicating their suitability only for domestic use or as a fuel for gasification and not for metallurgical use.     

Gas cleaning for IC engine applications from fixed bed biomass gasification

Gas cleaning for tar and particle removal is necessary for internal combustion (IC) engine applications of producer gas from fixed bed biomass gasifiers which are usually in the capacity range from 100 kW up to 5000 kW. In the present investigation, tar and particle collection efficiencies have been determined in a sand bed filter, a wash tower, two different fabric filters, and a rotational particle separator (RPS) in different test runs with fixed bed gasifiers. Tar adsorption on coke has been investigated in a fixed bed batch reactor. Furthermore data from literature for catalytic tar crackers, venturi scrubbers, a rotational atomizer, and a wet electrostatic precipitator (ESP) are given. Based on the presented gas cleaning efficiencies and the investment cost, an assessment of gas cleaning systems is made for IC engine applications from cocurrent gasifiers. The results show that the postulated gas quality requirements for IC engines cannot be safely achieved with state-of-the-art gas cleaning techniques and that 90% particle removal is easier to achieve than 90% tar removal. Except for the catalytic tar crackers which are considered as an option for applications above several MW and for gases with a high tar level, none of the investigated gas cleaning systems can securely meet a tar reduction exceeding 90%. Therefore one of the key issues for a successful application of biomass derived producer gas from small scale gasifiers is the tar removal, where further development is needed.     

Behavior and mechanisms of Ni/ScSZ cermet anode deterioration by trace tar in wood gas in a solid oxide fuel cell

In order to determine both the criterion for diagnosing the deterioration of Ni/ScSZ cermet anodes in solid oxide fuel cells (SOFCs) by tar contaminants in wood gas and the tolerance limit of tar in wood gas for such anodes, the influence of tar concentration in wood gas on anode deterioration behavior was examined by means of scanning electron microscopy. We found that the anode degradation mechanism consisted of three phenomena: the disappearance of Ni particles, the destruction of sintered ScSZ, and carbon deposition. Furthermore, the Ni particle disappearance occurred at lower tar concentrations than did sintered ScSZ destruction and apparent carbon deposition. Therefore, we propose that the disappearance of Ni particles be set as the criterion for confirming deterioration of Ni/ScSZ cermet anodes in SOFCs by tar. On the basis of this criterion, the tolerance limit of toluene in fuel gas was determined to be 3 g/Nm³ when the operating temperature, steam to carbon molar ratio, and current density were 1073 K, 1, and 0.5 A/cm², respectively. The tolerance limit for tar for the fuel cell constructed herein was one to two orders of magnitude higher than that for internal combustion engines.     

From coal towards renewables: Catalytic/synergistic effects during steam co-gasification of switchgrass and coal in a pilot-scale bubbling fluidized bed

Recent environmental sharp curbs on fossil fuel energy systems such as coal power plants due to their greenhouse gas emissions have compelled industries to include renewable fuels. Biomass/coal co-gasification could provide a transition from energy production based on fossil fuels to renewables. A low-ash coal and switchgrass rich in potassium were selected on the basis of previous thermogravimetric studies to steam co-gasify 50:50 wt% coal:switchgrass mixtures in a pilot scale bubbling fluidized bed reactor with silica sand as the bed material at ∼800 and 860 °C and 1 atm. With the switchgrass added to coal, the hydrogen and cold gas efficiencies, gas yield and HHV of the product gas were enhanced remarkably relative to single-fuel gasification. The product gas tar yield also decreased considerably due to decomposition of tar catalyzed by switchgrass alkali and alkaline earth metals. Switchgrass ash therefore can act as inexpensive natural catalysts for steam gasification and assist in operating at lower temperatures without being penalized by an increase in product tar yield. An equilibrium model over-predicted hydrogen and under-predicted methane concentrations. However, an empirically kinetically-modified model was able to predict the product gas compositions accurately.     

Catalytic decomposition of biomass tars: use of dolomite and untreated olivine

Although biomass is getting increased attention as a renewable energy source, one of the remaining problems still to be solved is the reduction of the high level of tar present in the product gas from gasification of biomass. The purpose of the present work is to study the activity of olivine and dolomite for tar destruction. Some researchers investigated olivine as bed material for biomass gasification. But it is not yet known how tars behave in the presence of olivine and whether olivine has some activity towards tar destruction. A slipstream from a lab-scale atmospheric bubbling-fluidised-bed gasifier (located at ECN) is passed through a secondary fixed-bed reactor where the additives are placed. For easy understanding, the results are represented in terms of the following tar classes; GC-undetectable tars (class 1), heterocyclic compounds (class 2), aromatic compounds (class 3), light polyaromatic compounds (class 4), heavy polyaromatic compounds (class 5). The general observation is that the conversion of all tar classes increases as the temperature was raised from 800 to 900 °C for both additives. The water-soluble heterocyclic compounds can be easily converted by thermal treatment. At the temperature of 900 °C, the water-soluble heterocyclic compounds are completely converted. A 48% decrease in heavy PAHs is observed with pure sand. Addition of 17 wt% olivine to the sand leads to a 71% decrease of PAHs at 900 °C, whereas addition of 17 wt% (pre-calcined) dolomite converted 90%. Also improvement in conversion of other tar classes is observed when olivine and dolomite are added during hot gas cleaning. A total tar amount of 4.0 g m₀⁻³ could be reduced to 1.5 and 2.2 g m₀⁻³ using dolomite and olivine, respectively, at a temperature of 900 °C. Inspite of this reduction in total tar concentration, a limited impact on the tar dewpoint is observed.     

Influences of equivalence ratio,oxygen concentration and fluidization velocity on the characteristics of oxygen-enriched gasification products from biomass in a pilot-scale fluidized bed

The influences of equivalence ratio (ER), oxygen concentration (OC) and fluidization velocity (FV) on the gasification performance in a pilot-scale fluidized bed with capacity of 1 ton biomass (the mixture of agricultural residue) per day were investigated using oxygen-enriched air as gasification agent and high-alumina bauxite as bed material. The characteristics of syngas (lower heating value (LHV), gas yield (Y), carbon conversion (CC) and cold gas efficiency (CGE)), bio-char (LHV and Proximate analysis) and tar (tar yield and LHV) were used to evaluate the gasification performance in this study. The results showed that 0.161 was the optimal ER due to the high quality of syngas produced and relatively lower tar generation with ER changing from 0.115 to 0.243 at OC ≈ 40% and FV ≈ 1.20.29.7% was the optimal OC due to the highest Y and CC and relatively low tar generation when OC varied from 21% to 44.7% at ER ≈ 1.40 and FV ≈ 1.15. Although higher FV could improve syngas quality, it also resulted in the higher tar yield and heavier wear, therefore, the optimal gasification performance was achieved at moderate FV (FV = 1.13). This study proved that oxygen-enriched gasification in a large-scale fluidized bed was an effective option to produce gaseous biofuels with high quality.     

Pyrolysis products from different biomasses: application to the thermal cracking of tar

The purpose of this study was to evaluate the amounts of various pyrolysis products (gases, water, tar and charcoal) from three biomasses (wood, coconut shell and straw) and to suggest a kinetic equation for the thermal cracking of tar at temperatures varying from 400 to 900°C. From the results, a comparative analysis is done for the biomasses, and a kinetic model of thermal cracking of tar is proposed for a residence time ranging from zero to 4s . This can be applied to the purification of gasification gases used as a feed gas to a combustion engine, and so contributes to the design of gasifiers.     

Air gasification of dried sewage sludge in a two-stage gasifier. Part 2: Calcined dolomite as a bed material and effect of moisture content of dried sewage sludge for the hydrogen production and tar removal

In order to produce a clean producer gas, the air gasification of dried sewage sludge was conducted in a two-stage gasifier that consisted of a bubbling fluidized bed and a tar-cracking zone. The kind and amount of bed materials, the kind of additives in the upper-reactor, and the moisture content in the sewage sludge were selected as operating variables in order to investigate their effects on the development of the producer gas characteristics. In our experiments, the gasification of a dried sewage sludge sample containing 30 wt.% of moisture with a combination of calcined dolomite as the bed material and activated carbon in the tar-cracking zone removed the most tar and produced the highest hydrogen concentration. The total tar removal efficiency and the H₂ content in the producer gas from the sample noted above reached 88.4% and 32.1 vol.%, respectively. The LHVs of all the producer gases were high with values above 7 MJ Nm⁻³.