牛粪热解特性与水蒸气气化制取富氢气体的研究

发布时间：2018-05-06 16:45

本文选题：牛粪 + 热解特性　；参考：《华中农业大学》2017年博士论文

【摘要】：随着人们生活水平的提高,对奶制品、肉制品的需求大幅增加,促进了我国奶牛、肉牛养殖业的规模化发展。牛粪是奶牛、肉牛养殖过程中不可避免的污染物,若大量的牛粪得不到及时处理,不仅会影响养殖场的发展,还会污染周边的环境,对人们的生命健康构成威胁。牛粪中含有丰富的有机成分,具有转化为生物燃料的潜能。热化学方法具有处理效率高,周期短,能够在热处理过程中杀死粪便中病毒细菌,且产生一氧化碳、氢气、生物炭、生物油等高附加值燃料。其中氢气是一种燃烧生成水、清洁无污染的燃料,被认为是能够替代化石燃料的最理想的未来能源之一。本研究拟采用气化技术将牛粪转化为富氢气体,从牛粪热解机理入手,通过试验研究牛粪原位气化和分步气化2种模式下主要工艺参数对产物特性的影响,以实现高效处理牛粪并制备富氢气体的目的。其主要研究内容及结果如下:(1)开展了牛粪热解机理的研究。根据范式洗涤原理对牛粪进行处理获得不同成分组合的洗涤纤维,采用热重分析实验方法探讨牛粪中不同组分洗涤纤维的热解特性。结果表明牛粪中中性洗涤溶解物的含量最大为39.35%,半纤维素和纤维素含量次之,分别为26.24%、24.05%,木质素的含量较低。以纤维素为主要成分的酸性洗涤纤维,热解速率最大,为14.31%/min,强酸洗涤纤维热解速率最小为1.62%/min。牛粪不同组分在热解过程中相互影响而不是简单的叠加,纤维素的加入使木质素的热解速率和温度区间发生变化,半纤维素的存在对纤维素的热解挥发具有一定的抑制作用,使得纤维素的热解速率由14.31%/min降低到7.62%/min,木质素、纤维素和半纤维素三组分的热解存在耦合作用。(2)建立了牛粪热解动力学模型。采用离散分布活化能模型深入分析了牛粪热解特性及其各化学组分之间的耦合关系,对超高、超低升温速率下热解特征进行了预测和对比分析,研究了挥发分析出过程中所对应的起始温度、终止温度、峰值温度以及峰值速率等特征参数随升温速率的变化规律。结果表明牛粪的热解过程可以通过27个主导反应来精准表征,且这些反应可以分成4组分别代表牛粪4组分(中性洗涤溶解物,半纤维素,纤维素和木质素)的热解过程。各组分的分解没有明确的边界,它们相互作用、相互耦合。随着升温速率的不同,各组分之间的这种关联耦合特性亦发生变化。(3)开展了高湿牛粪原位气化制备富氢气体关键工艺参数的研究。以湿牛粪为研究对象,在固定床反应器内采用单因素试验的方法,对不同温度、水分质量分数,升温速率和进料温度条件下原位热解气化产气率、成分、热值,氢气产率和碳转化率的变化进行研究和分析。试验结果表明,随着温度和水分质量分数的增加,氢气的体积百分含量、热解气的产率和热值增加;升温速率和进料温度对氢气的体积百分含量和产气率的影响不显著。湿牛粪的原位气化结果表明牛粪有制备氢气的潜能,氢气的最大产率为536.64ml/g,氢气的含量最高达到了50.57%。原位气化过程中各反应相互重叠,反应复杂且热解产生的挥发分对生物半焦的反应活性和蒸气气化反应有抑制作用。(4)开展了“牛粪低温炭化-半焦高温气化”两步气化制取富氢气体的研究。在低温炭化阶段重点分析操作参数对牛粪低温炭化反应机理的影响,主要采用正交设计研究了温度、含水率、升温速率、进料量、反应时间对产物分布的影响,采用全因素实验设计研究温度和含水率对产物分布和炭特性的影响,采用单因素试验分析温度和炭化时间对干牛粪低温炭化的影响。结果表明温度是影响产物分布和炭特性的主要因素,当含水率固定在75%,随着炭化温度从400℃增加到600℃,固体半焦的产率从47.30%降低到37.70%。含水率的对产物分布有一定的影响,但含水率的影响受温度的限制,且含水率主要改变液体和气体的产率。水蒸气的存在抑制了反应器内重油的二次裂解反应,促进了重油的水蒸气气化反应。温度是影响固体半焦C、H、O、固定碳、挥发份、灰分含量以及半焦热解特性、晶体结构、矿物质含量的主要因素,含水率对牛粪半焦的特性影响不明显。其中600℃条件下制备的半焦C含量高达80.59%。因此以制备半焦为目的的炭化过程中,可以主要考虑温度的影响。(5)进行了两步气化过程中高温气化段的试验研究。主要研究了半焦气化反应机理和操作参数对半焦高温气化产气效果的影响,并选取不同特性的半焦为原料进行气化重整试验,分析半焦对产气效果的影响。试验结果表明:提高气化温度能够增加产气率和产氢率,适宜的水蒸气流速能够促进氢气的产率,高温加热模式有助于制取富氢气体,牛粪灰可以促进半焦气化过程中焦油的产生,但会抑制气化过程,影响气相得率。半焦高温气化的较优的工艺参数为气化温度850℃,水蒸气流速1.66g/min,高温进料方式,氢气的最大产率为1105.30ml/g,氢气百分含量最高达到了59.08%。不同温度制备的半焦在最佳参数下的气化结果表明高温条件制备的半焦有助于氢气的产生,根据氢气产率的大小对原料排序为:BC-500BC-600BC-350BC-400BC-300牛粪,其中BC-300~BC-600分别表示在炭化温度300℃~600℃,反应时间30min条件下制取的牛粪半焦。在相同的气化条件下,牛粪和BC-300在气化过程中的转化率高于BC-500和BC-600,但牛粪和BC-300的产气率低于BC-500和BC-600的产气率。这表明牛粪和BC-300中的组分主要转化为了生物油。因此高温度制备的半焦有利于气化制氢,且能够降低生物油的产率。(6)牛粪的组分和热特性研究表明牛粪具有热化学处理的潜能,可以采用热化学方法处理牛粪。原位气化和分步气化的研究结果表明:a.牛粪具有气化制氢的潜能;b.相比于原位气化,分步气化的方法提高了氢气的产率并减少生物油的产率;c.高温下制备的半焦是较优的气化材料。d.牛粪半焦的气化产氢量优于牛粪气化的产氢量,且半焦气化可以减少生物油的产率;e.850℃的气化温度是半焦气化的适宜温度;f.牛粪半焦的质量是牛粪原料的40%左右,可减少高温段气化装置成本及能耗。因此,牛粪分步气化制取富氢气体是一种处理牛粪污染物、制取富氢气体的有前景的、有潜力的技术。
[Abstract]:With the improvement of people's living standards, the demand for dairy products and meat products has been greatly increased, which has promoted the large-scale development of dairy cattle and cattle breeding in China. Cow dung is an inevitable pollutant in the process of cow and beef cattle breeding. If a large amount of cow dung is not treated in time, it will not only affect the development of the farm, but also pollute the surrounding environment. It is a threat to the health of people. The cow dung contains rich organic ingredients and has the potential to convert into biofuel. The thermochemical method has high treatment efficiency, short cycle, and can kill the virus bacteria in the feces during heat treatment, and produce high added value fuel such as carbon monoxide, hydrogen, biological carbon and bio oil. It is considered to be one of the most ideal future energy sources to replace fossil fuels. This study is intended to convert cow dung into hydrogen rich gas by gasification technology. From the mechanism of cow dung pyrolysis, the main technological parameters of the 2 models of cattle manure in situ gasification and stepwise gasification are studied by experiments. The main research contents and results are as follows: (1) the study of the mechanism of cow dung pyrolysis was carried out. The washing fiber of different composition of cow manure was obtained according to the principle of normal form washing, and the different components washing in cow dung was studied by thermogravimetric analysis. The results show that the maximum content of neutral detergent dissolved in cow dung is 39.35%, the content of hemicellulose and cellulose is 26.24%, 24.05%, and lignin is lower. The acid washing fiber with cellulose as the main component has the highest pyrolysis rate of 14.31%/min and the minimum pyrolysis rate of strong acid washing fiber is 1.62. The different components of%/min. cow dung affect each other in the pyrolysis process rather than the simple superposition. The addition of cellulose makes the pyrolysis rate and temperature range of lignin change. The presence of hemicellulose has a certain inhibitory effect on the pyrolysis and volatilization of cellulose, making the thermal hydrolysis rate of cellulose reduced from 14.31%/min to 7.62%/min and lignin. The pyrolysis of three components of cellulose and hemicellulose has a coupling effect. (2) a kinetic model of cow dung pyrolysis is established. The pyrolysis characteristics of cow dung and the coupling relationship between the chemical components are deeply analyzed by the discrete distribution activation energy model. The characteristics of the thermal solution at ultra high and ultra-low heating rates are predicted and compared, and the volatiles are studied. The results show that the pyrolysis process of cow dung can be accurately characterized by 27 dominant reactions, and these reactions can be divided into 4 groups to represent 4 components of cow dung (neutral detergent solution, semi fiber). The decomposition of vitamin, cellulose and lignin. The decomposition of components has no definite boundary, they interact with each other. With the difference of heating rate, the coupling characteristics of each component also change. (3) the study of the key technological parameters for the preparation of hydrogen rich gas by in situ gasification of high humidity cow dung. In a fixed bed reactor, a single factor test was used to study and analyze the change of gas production rate, composition, calorific value, hydrogen yield and carbon conversion rate at different temperatures, water mass fraction, heating rate and feed temperature. The results showed that the temperature and water mass fraction were found. Increasing the volume fraction of hydrogen and increasing the yield and calorific value of thermal gas, the effect of heating rate and feed temperature on the volume percentage and gas production rate of hydrogen is not significant. The results of in situ gasification of wet cow dung show that the cow dung has the potential of producing hydrogen, the maximum yield of hydrogen is 536.64ml/g, and the highest hydrogen content reaches 50.57%. original. The reaction overlaps each other during the gasification process, and the reaction is complex and the volatiles produced by pyrolysis have a inhibitory effect on the reactivity and vaporization of the biological char. (4) a study on the production of hydrogen rich gas by two step gasification of "low temperature carbonization and semi coke high temperature gasification" of cow dung is carried out. The effect of temperature, water content, heating rate, feed volume and reaction time on the distribution of products was studied by orthogonal design. The effects of temperature and water content on the distribution of products and carbon properties were studied by full factor experimental design. The temperature and carbonization time were used to analyze the low temperature carbon of dry cow dung. The results show that temperature is the main factor affecting the distribution and characteristics of the products. When the water content is fixed at 75%, with the carbonization temperature increasing from 400 to 600, the yield of solid semi coke from 47.30% to 37.70%. water content has a certain effect on the distribution of products, but the effect of water content is limited by temperature, and the water content is main. Change the yield of liquid and gas. The existence of water vapor inhibits the two cracking reaction of heavy oil in the reactor and promotes the vaporization of heavy oil. Temperature is the main factor affecting the C, H, O, fixed carbon, volatiles, ash content and semi coke, crystal structure, mineral content, and water content to cow dung semic. The effect of the characteristics is not obvious. The C content of the semi coke prepared under 600 centigrade is up to 80.59%., so the effect of temperature can be mainly considered during the carbonization process for the purpose of preparing the semi coke. (5) the experimental study on the high temperature gasification section in the two step gasification process is carried out. The mechanism of the semi coke gasification reaction and the operation parameters are mainly studied on the high temperature gas of the semi coke. The effect of gas production is changed, and the gasification reformer test is carried out with different characteristics of the char as raw material. The effect of semi coke on gas production is analyzed. The results show that the gasification temperature can increase gas production rate and hydrogen production rate, the suitable steam flow velocity can promote hydrogen production, and the high temperature heating mode helps to produce hydrogen rich gas. The fecal ash can promote the production of tar in the process of semi coke gasification, but it can inhibit the gasification process and affect the gas phase yield. The better technological parameters of the high temperature gasification of semi coke are the gasification temperature 850 C, the flow velocity of 1.66g/min, the high temperature feeding way, the maximum hydrogen yield of 1105.30ml/g, and the highest hydrogen content reached 59.08%. different temperature system. The gasification results of the prepared semi coke under the optimum parameters indicate that the semi coke prepared at high temperature is helpful to the production of hydrogen. According to the size of the hydrogen yield, the raw material is ordered as BC-500BC-600BC-350BC-400BC-300 cow dung, and the BC-300~BC-600 shows the cow dung semi coke at the temperature of 300 C, ~600, and 30min, respectively. Under the same gasification conditions, the conversion rate of cow dung and BC-300 in the gasification process is higher than that of BC-500 and BC-600, but the gas production rate of cow dung and BC-300 is lower than that of BC-500 and BC-600. This indicates that the components of cow dung and BC-300 are mainly converted to bio oil. Therefore, the high temperature prepared char is beneficial to the gasification of hydrogen and can reduce the bio oil. Yield. (6) studies on the composition and thermal characteristics of cow dung show that cow dung has the potential of thermochemical treatment and can be treated by thermochemical method. The results of in situ gasification and stepwise gasification show that A. cow dung has the potential of gasification for hydrogen; B. is compared to in situ gasification, and the method of stepwise gasification improves the yield of hydrogen and reduces bio oil. The yield of the semi coke prepared by C. at high temperature is better than that of.D. cow dung gasification, and the yield of hydrogen production is better than that of cow dung gasification. The gasification temperature of e.850 centigrade is the suitable temperature for the gasification of semi coke, and the quality of F. cow dung is about 40% of the cow dung raw material and can reduce the gasification at high temperature. Therefore, it is a promising and promising technology to produce hydrogen rich gas by step gasification of cow dung.

【学位授予单位】：华中农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ116.2

【参考文献】