生物质气化发电技术讲座(3)生物质焦油裂解技术

1生物质焦油的特性生物质气化的目标是得到尽可能多的可燃气体产物。但在气化过程中,焦炭和焦油都是不可避免的副产物。焦油在高温时呈气态,与可燃气体完全混合,而在低温(一般低于200℃)时凝结为液态。对于燃气需要降温利用的情况(如燃气用于内燃机发电时),焦油的分离问题显得尤为重要。焦油的存在对生物质气化及其利用会产生不利的影响。首先它降低了气化炉气化效率,气化气中焦油产物的能量一般占总能量的5%～15%,这部分能量在低温时难以与可燃气体一道被利用,大部分被浪费;其次焦油在低温时凝结为液态,容易和水、焦炭等结合在一起,堵塞输…     

生物质炭催化裂解焦油的性能研究

采用管式反应器研究了生物质炭作为焦油裂解催化剂的性能,选用白云石和石英砂作对比试验。通过对焦油转换率、裂解产物、裂解气气体组分和动力学参数的分析对比可知:在所选用的3种材料中,生物质炭作为催化剂的焦油转化率最高,裂解产物中气体所占比重最大,且可燃气体的组分较高,反应动力学参数最小。生物质炭的催化性能显著高于石英砂,稍好于白云石,是一种高效的焦油裂解催化剂。     

生物质气化多联产技术应用研究

生物质气化是指生物质在高温、无氧或缺氧条件下发生热分解,产生可燃气体的过程。国家农业部曾于20世纪90年代在全国多个省份开展了＂秸秆气化集中供气工程＂试点建设,云南昆明、普洱等地共建设秸秆气化站8处,但据云南省农村能源工作站调查,目前基本都处于停运状态,其主要原因在于气化设备技术不成熟、焦油难以处理和综合效益不明显等。     

生物质气化焦油生成碳黑的实验研究

生物质气化焦油有还原NO的作用。在小型管流反应器上进行的生物质气化气焦油还原NO的过程中有碳黑产生,对试验产生影响。碳黑对人体健康也极具危害。虽有研究表明碳黑有还原NO的作用,但其效果不如焦油裂解之后的小分子永久气体还原NO的效果好,因此再燃过程中有必要对碳黑生成进行控制。对几种典型的生物质焦油模型化合物（苯、甲苯、苯乙烯）燃烧生成碳黑的重要起始参数进行实验测定,得到不同再燃温度条件下（900～1400℃）,苯、甲苯和苯乙烯燃烧生成碳黑的起始碳氧比。本试验结果将对含焦油的生物质气化气再燃试验起到指导作用。     

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。     

含焦油生物质气再燃还原燃煤锅炉NOx的试验研究

搭建了10kW上吸式生物质气化炉和20kW煤粉沉降炉组成的生物质气化再燃试验系统,分析了不同再燃条件下含焦油生物质气再燃还原燃煤锅炉NOx的特性．结果表明：气化过程中产生的焦油在再燃过程中会裂解生成高热值的烃类气体,这些烃类气体还原NOx的效果明显;当过量空气系数较小、再燃温度较高时,NOx的还原效率较高,试验中最高还原效率超过80％;采用生物质气化再燃的方式既可以解决焦油难处理的问题,又可以提高生物质能量的转化效率,同时可高效降低燃煤锅炉NOx的排放量．     

催化剂粒径与质量对生物质热解焦油催化裂化反应的影响

针对催化裂化条件对生物质热解焦油处理的影响,以秸秆热解产生的焦油为原料,在固定床焦油催化裂化反应试验台上研究了催化剂作用下焦油催化裂化的过程,并对催化剂粒径和质量等参数对焦油转化效果和催化裂化产物的影响进行了分析．结果表明：减小催化剂的粒径或者增加催化剂质量能促进燃气中高热值大分子气体转化为低热值的小分子轻质气体,从而有效促进焦油裂化,提高燃气产率,降低燃气热值．     

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...     

高热值生物质热解气化技术的探讨

目前生物质热解气化的缺点主要原料不规整、气体热值低、焦油含量高。为克服以上缺点,我们提出了生物质固化、碳化成形、造粒、水煤气气化的工艺设想、,拟用一工艺产生高热值、低焦油的生物气。     

1MW木粉气化发电系统的运行特性分析

通过对海南三亚木粉发电系统的运行状况分析，结果发现：气化过程中所夹带的飞灰以及所生成的焦油是影响发电系统正常运行的主要因素，显热损失和飞灰中没有完全气化的碳损失是导致气化发电系统效率下降的主要原因。同时考查了气化过程中污染物排放情况及添加焦油裂解催化剂对气体成份和焦油裂解的影响，对改进今后生物质气化发电系统的大型化设计具有一定的指导意义。     

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...     

Performance prediction of steam gasification of wood using an ASPEN PLUS thermodynamic equilibrium model

In this article, an equilibrium model based on Gibbs free energy minimisation is presented for steam gasification of biomass in process simulator ASPEN PLUS. Carbon is assumed as fully converted into product gases and no tar content is assumed to be present in gaseous product. The objective is to arrive at the optimum process conditions of gasification. An analysis on the sensitivity of producer gas composition, lower heating value, combustible gas yield, and first and second law efficiencies on gasification process variables including reactor temperature, pressure and steam to biomass mass ratio is also envisaged. Simulations are performed with wood as the biomass material, based on real gas behaviour for product gases and gasifying medium. The predicted results of the model are compared with another Gibbs free energy model formulated using simulated annealing minimisation algorithm. The present ASPEN PLUS model is validated with published experimental results on steam gasification on a fluidised bed gasifier.     

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.     

First and second law thermodynamic analysis of a single and dual-stage ignition biomass downdraft gasifier

The dual-stage ignition biomass downdraft gasifier is an enormous tar reduction technology as against a single-stage ignition biomass gasification. Exergetic analysis of the system guides toward a possible performance enhancement. In dual-stage gasification, around 67.76% of input exergy is destructed in the several components, while 9.16% is obtained as a useful exergy output and 24.34% is found to be as a useful energy output there. The entire unit was assessed with a progressively rising electric load from 15.24 kW to 38.86 kW. The enhanced producer gas quality comes from 57% combustible gas with a higher heating value of 6.524 MJ/Nm³ and tar content of 7 mg/Nm³ after the paper filter, whereas the biomass consumption rate is 58 kg/h at the greatest load with the grate temperature of 1310–1370 °C. The samples of exhaust gas emissions are obtained environmentally favorable. The results even described that the dual-stage ignition biomass downdraft gasifier has significantly greater energetic and exergetic efficiency as compared to the single-stage gasifier.     

Biomass gasification integrated with pyrolysis in a circulating fluidised bed

The use of biomass for energy generation is getting increasing attention. At present, gasification of biomass is taken as a popular technical route to produce fuel gas for application in boilers, engine, gas turbine or fuel cell. Up to now, most of researchers have focused their attentions only on fixed-bed gasification and fluidised bed gasification under air-blown conditions. In that case, the producer gas is contaminated by high tar contents and particles which could lead to the corrosion and wear of blades of turbine. Furthermore, both the technologies, particularly fixed bed gasification, are not flexible for using multiple biomass-fuel types and also not feasible economically and environmentally for large scale application up to 10–50 MW_th. An innovative circulating fluidised bed concept has been considered in our laboratory for biomass gasification thereby overcoming these challenges. The concept combines and integrates partial oxidation, fast pyrolysis (with an instantaneous drying), gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas, in terms of low tar level and particulates carried out in the producer gas, and overall emissions reduction associated with the combustion of producer gas. This paper describes our innovative concept and presents some experimental results. The results indicate that the gas yield can be above 1.83 N m³/kg and the fluctuation of the gas yield during the period of operation is 3.3% at temperature of 750 °C. Generally speaking, the results achieved support our concept as a promising alternative to gasify biomass for the generation of electricity.     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

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。     

Hydrogen-rich gas production by steam gasification of palm oil wastes over supported tri-metallic catalyst

The catalytic steam gasification of palm oil wastes for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor using the newly developed tri-metallic catalyst. The results indicated that the supported tri-metallic catalyst had greater activity for the cracking of hydrocarbons and tar in vapor phase and higher hydrogen yield than the calcined dolomite in catalytic steam gasification of palm oil wastes. A series of experiments have been performed to explore the effects of temperature, steam to biomass ratio (S/B) and biomass particle size on gas composition, gas yield, low heating value (LHV) and hydrogen yield. The experiments demonstrated that temperature was the most important factor in this process; higher temperature contributed to higher hydrogen production and gas yield, however, it lowered gas heating value. Comparing with biomass catalytic gasification, the introduction of steam improved gas quality and yield, the optimal value of S/B was found to be 1.33 under the present operating condition. It was also shown that a smaller particle size was more favorable for gas quality and yield. However, the LHV of fuel gas decreased with the increasing S/B ratio and the decreasing biomass particle size.     

可燃固废焦油处理的研究进展

热解气化技术是实现可燃固废资源化利用的主流技术,有必要对热解气化过程中的副产物焦油进行有效处理。本文介绍了可燃固废焦油的组成、危害及处理方法,对原位处理法、物理法和热化学法等焦油处理技术进行了总结。提出一种将焦油与聚乙烯混合进行加氢处理的方法,利用聚乙烯中富含的氢元素,有望提高焦油利用的经济性。     

An experimental study on air gasification of biomass micron fuel (BMF) in a cyclone gasifier

Biomass micron fuel (BMF) produced from feedstock (energy crops, agricultural wastes, forestry residues and so on) through an efficient crushing process is a kind of powdery biomass fuel with particle size of less than 250 μm. Based on the properties of BMF, a cyclone gasifier concept has been considered in our laboratory for biomass gasification. The concept combines and integrates partial oxidation, fast pyrolysis, gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas. In this paper, characteristics of BMF air gasification were studied in the gasifier. Without outer heat energy input, the whole process is supplied with energy produced by partial combustion of BMF in the gasifier using a hypostoichiometric amount of air. The effects of equivalence ratio (ER) and biomass particle size on gasification temperature, gas composition, gas yield, low-heating value (LHV), carbon conversion and gasification efficiency were studied. The results showed that higher ER led to higher gasification temperature and contributed to high H₂-content, but too high ER lowered fuel gas content and degraded fuel gas quality. A smaller particle was more favorable for higher gas yield, LHV, carbon conversion and gasification efficiency. And the BMF air gasification in the cyclone gasifier with the energy self-sufficiency is reliable.