燃料乙醇技术讲座(五) 燃料乙醇的储运

<正>燃料乙醇从生产到应用的整个流程如图1所示。在燃料乙醇发酵生产或合成生产中,蒸馏后得到浓度为95%左右的乙醇;通过进一步脱水,即得到水分含量(体积分数)小于0.8%的燃料乙醇;再往燃料乙醇中添加变性剂,使其成为变性燃料乙醇(即燃料乙醇成品);最后,把燃料乙醇成品运输到混配中心,进入应用领域。     

基于平行流铝扁管吸附床传热性能的模拟研究

吸附床是吸附式制冷系统的关键部件。吸附床的换热能力对吸附式制冷系统的各项性能有显著影响。文章针对应用于吸附床的传统换热器和扁管换热器的不足之处,设计出一种新型平行流铝扁管吸附床,并建立了该吸附床的二维传热模型,以温度随时间的变化情况为分析指标,分析翅片的间距、高度、厚度,以及吸附剂体积分数等因素对吸附床传热性能的影响,从而优化调整吸附床的结构,提高其换热性能。分析结果表明:当翅片高度约为70 mm时,吸附床的换热能力达到峰值;当翅片厚度大于1.5 mm时,翅片厚度的增加对吸附床传热性能的影响比较微弱;当吸附剂体积分数由0.25逐渐增大至0.45时,吸附剂的等效传热系数约增加了50%。     

煤与污泥的循环流化床富氧燃烧

结合污泥的特性与富氧燃烧技术的优点,在一个内径为100mm的循环流化床焚烧炉内进行煤与污泥的富氧燃烧试验.试验分析了不同煤泥质量比,在氧体积分数为21%～35%环境下的燃烧特性以及送风含氧量、床层温度对烟气成分的影响.结果表明:不同质量比的燃料在不同氧气氛围的燃烧特性不同;当给料量恒定时,随着送风含氧量的增大,总风量减少,炉膛的温度逐渐升高,烟气中SO2与NOx浓度都呈增大的趋势,这有利于SO2与NOx的脱除;NOx体积分数随床层温度的升高逐渐增加.     

中试规模铁基化学链燃烧的数值模拟

为了研究进气速度对铁基载氧体化学链燃烧的影响,以体积分数各为50%的H_2和CO作为混合气燃料,Fe_2O_3为载氧体,分析了不同进气速度(0.2～0.6 m/s)对化学链燃烧过程中流化质量、气体组分分布、燃料转化率的影响。结果表明:随着进气速度的增加,床层高度提高,床层中气泡体积增大,流化质量提高;气体燃料上升高度和相同高度处燃气摩尔分数均与进气速度呈正比,当进气速度从0.2 m/s提高至0.6 m/s时,CO摩尔分数从1.3%增加至7.2%,H_2摩尔分数从0.2%增加至2.6%,燃料转化率下降。     

皇竹草流态化燃烧粘结特性试验研究

以能源植物皇竹草作为研究对象,利用5 kW鼓泡流化床实验装置,研究床层温度、燃料形状以及燃料中钙元素含量对流化床粘结失流现象的影响.试验结果表明:失流时间随着床层温度上升而缩短;燃料形状对失流时间影响不明显；钙元素具有延长失流时间的作用.床料和飞灰的ICP-OES分析结果表明,床层温度较高时,在床料中K元素较少的情况下也能发生失流现象.     

燃料床特性对炭粉阴燃过程影响的理论预测

建立了自然对流(静止空气)条件下炭粉床一维竖直向下阴燃的简化数学模型,预测了典璎条件下燃料床各特性参数对阴燃过程的影响.结果表明,床层收缩率、碳堆积密度、燃料床孔隙尺寸、氧气在多孔灰层中的扩散率对阴燃传播速度、床层内部温度和阴燃持续时间影响显著;而初始条件、环境条件及燃料和灰的比热容、导热系数等物性参数的影响可忽略不计.     

柴油含水乙醇乳化燃料物性及喷雾燃烧特性研究

试验使用不同配比的柴油含水乙醇乳化燃料,对其理化、喷雾和燃烧特性进行了研究。随着柴油含水乙醇乳化燃料中含水乙醇含量的增加,乳化燃料的密度和运动黏度上升,表面张力略微下降,初始蒸馏温度下降,含氧量升高,十六烷值和低热值降低。试验使用定容燃烧弹,在常温高压和高温高压环境下,对乳化燃料非蒸发喷雾、蒸发喷雾及喷雾燃烧的特性进行了测试。研究结果表明:随着乳化燃料中含水乙醇比例升高,非蒸发喷雾贯穿距和喷雾锥角变化不大;蒸发喷雾贯穿距和喷雾锥角略微减小,但无明显规律,而蒸发喷雾中液相贯穿距离明显增加;燃烧火焰自发光亮度逐渐降低,表征碳烟生成量逐渐减少;在900K环境温度、21%氧体积分数条件下着火滞燃期变化不大。     

乙醇基纳米流体燃料液滴着火燃烧研究

采用挂滴法研究了在高温条件下纳米铝粉质量分数及粒径对乙醇基纳米流体燃料液滴着火特性及燃烧过程的影响.研究结果表明,与乙醇燃料相比,添加50,nm铝粉质量分数为0.5%,和2.5%,的乙醇基纳米流体燃料液滴的着火延迟时间分别降低了0.315,s和0.525,s,着火温度分别降低了12.712,℃和42.214,℃.增大纳米铝粉粒径至100,nm,当添加的铝粉质量分数为2.5%,时,其液滴着火延迟时间比乙醇降低了0.42,s,两种粒径的纳米流体燃料着火温度相近.乙醇及乙醇基纳米流体燃料液滴燃烧火焰分为3个阶段:着火燃烧阶段、火焰熄灭阶段和二次燃烧阶段.随纳米铝粉含量增加,在二次燃烧阶段纳米流体燃料液滴火焰亮点增多,火焰燃烧剧烈,其中含50,nm铝粉的纳米流体燃料比含100,nm铝粉的纳米流体燃料燃烧剧烈.     

富氧燃煤锅炉烟气再循环方式选择与水分平衡计算

在不同的二次烟气再循环方式下,以300 MW富氧燃烧锅炉机组为例,对分别采用直接接触式冷却器（DCC）进行烟气脱水和湿式脱硫（FGD）与DCC串联进行烟气脱硫及脱水的富氧燃烧系统详细计算并比较了烟气中水蒸气体积分数的变化,并计算和比较了各种布置方式下的风机功耗.结果表明：单独采用DCC脱水情况下,锅炉烟气水蒸气体积分数比空气燃烧方式下高10%-15%;二次循环烟气脱水时,锅炉烟气中的水蒸气含量比空气燃烧方式下高约3%;FGD与DCC串联布置时的锅炉流通烟气水蒸气含量略高于采用单独DCC时二次循环烟气脱水的水蒸气含量;电厂循环水温度为30℃时,DCC出口烟气理论水蒸气体积分数为4.28%;单独采用DCC脱水的干烟气循环方式的风机总电耗最小.     

乙醇微型燃烧室燃烧特性的数值模拟研究

为了解决化石燃料储备不足与环境污染问题，生物质燃料作为石油替代能源得到大力提倡，如何合理地将化石燃料替换为生物质燃料且维持设备正常运行成为工程上亟待解决的问题。本文采用CFD软件研究了车载5 kW生物乙醇微型燃烧室的燃烧特性，对比分析了不同功率（0.5~5 kW）和出口温度（840~960 K）时的回流区长度与宽度、回流量、出口温度分布系数（OTDF）、出口NO体积分数等特征参数。结果表明：随着出口温度升高，回流区长度逐渐缩短，回流量减少，出口温度均匀性逐渐变差，出口NO体积分数明显增加；随着燃烧室功率增大，回流区长度变长，回流量增加，OTDF先增大后减小，NO体积分数随着功率的降低而显著升高，最大值出现在1 kW时，达到满负荷时的7倍。因此，为了实现稳定燃烧和减少污染物排放，该乙醇微型燃烧室应在较高的空燃比（即较低的出口温度）和功率下运行。     

生物质合成气发酵生产乙醇的工艺分析

介绍了生物质合成气发酵制备乙醇的工艺过程。采用Aspen plus软件对工艺过程建立模型,模拟计算乙醇的产量。针对影响乙醇产量的主要参数进行了灵敏度分析,结果表明:气化过程中氧气与干生物质质量比对乙醇产量影响显著,且比值为0.4时,乙醇产量最大;而气化过程中过多蒸汽的加入会降低乙醇产量;发酵过程中CO和H2转化率的提高有利于乙醇产量的增加。     

木薯干发酵生产燃料乙醇潜力研究

在实验室条件下研究木薯于发酵生产乙醇的潜力,以期为红薯燃料乙醇项目的生产提供相关参考数据。以粉碎后的木薯干为原料,料水比为1：2．8,糖化所用的复合酶添加量为原料质量的0．4％,在35℃±1℃温度下用酵母活化液（干酵母在33℃±1℃、40倍其质量的2％的葡萄糖溶液中活化60min）发酵原料产乙醇,反应周期为70h。在此工艺条件下．酒精度达22．0％,乙醇产率为48．32％,原料的TS和VS利用率分别为75．22％和80．01％。根据实验研究结果,今后在红薯燃料乙醇项目的运行和技改过程中需要根据实际情况确定适宜的料水比范围;酵母生理活性的高低是影响产酒率的重要因素．应根据生产状况对其进行改进或创新,从而取得自己的知识产权：应通过气相色谱法分析液相产物的成分．同时掌握发酵液的残留糖含量和酵渣组成等情况,为副产物的充分利用和开发附加产品做准备。     

甜高粱制燃料乙醇的原料和工艺

甜高粱生物产量高,适应能力强,被誉为最有希望的能源作物。世界许多国家竞相开发甜高粱制取燃料乙醇的技术。针对甜高粱规模化生产燃料乙醇的重要影响因素,论述了良种选育、栽培技术、储藏技术、生产工艺和综合利用等方面的研究现状,从原料工程和生产工艺的角度阐述了各环节的重要作用．从综合利用的角度评估了甜高粱的制燃料乙醇的技术经济性。     

我国非粮燃料乙醇的原料资源量分析

目前世界燃料乙醇的生产原料约60%为甘蔗或甜菜等糖质原料、33%为玉米或小麦等淀粉质原料,而纤维质原料正日益受到重视。我国可用于生产燃料乙醇的非粮淀粉质原料主要有甘薯、木薯、蕉藕、葛根等。其中蕉藕目前尚未形成产业化生产;葛根原料价格高,不宜作为乙醇原料;甘薯归属粮食范畴;只有木薯是最适宜制燃料乙醇的非粮淀粉质原料。纤维质原料主要包括农作物秸秆、农林废弃物、木屑等,其中农作物秸秆是我国产量最大的非粮燃料乙醇原料。秸秆资源密度考虑,利用区域应主要集中在河南、山东、江苏等地,保守估计这3个省的秸秆量可供生产1117×104t乙醇。目前制约纤维质原料制乙醇的关键瓶颈之一是原料的收集、运输及供应保障,若没有国家大的政策扶持和资金补贴,纤维质原料因缺乏经济可行性而尚不具备工业化生产乙醇的条件。糖质原料主要有甘蔗、甜菜、甜高粱茎秆和菊芋。由于菊芋菊粉附加值高,不宜作乙醇原料;甘蔗、甜菜主要用于糖业,不会作为乙醇原料;从单位土地面积乙醇产量和原料成本、农民种植收益综合来看,甜高粱茎秆是适宜生产燃料乙醇的糖质原料。需要寻求产业化种植模式来落实资源总量,提高资源保障度;另一方面要进一步研究低成本、安全保质的茎秆储藏技术。     

Environmentally benign working pairs for adsorption refrigeration

This paper begins from adsorption working pairs: water and ethanol were selected as refrigerants; 13x molecular sieve, silica gel, activated carbon, adsorbent NA and NB, proposed by authors, were selected as adsorbents, and the performance of adsorption working pairs in adsorption refrigeration cycle was studied. The adsorption isotherms of adsorbents (NA and NB) were obtained by high-vacuum gravimetric method. Desorption properties of adsorbents were analyzed and compared by thermal analysis method. The performance of adsorption refrigeration was studied on simulation device of adsorption refrigeration cycle. After presentation of adsorption isotherms, the thermodynamic performance for their use in adsorption refrigeration system was calculated. The results show: (1) the maximum adsorption capacity of water on adsorbent NA reaches 0.7 kg/kg, and the maximum adsorption capacity of ethanol on adsorbent NB is 0.68 kg/kg, which is three times that of ethanol on activated carbon, (2) the refrigeration capacity of NA–water working pair is 922 kJ/kg, the refrigeration capacity of NB–ethanol is 2.4 times that of activated carbon–methanol, (3) as environmental friendly and no public hazard adsorption working pair, NA–H₂O and NB–ethanol can substitute activated carbon–methanol in adsorption refrigeration system using low-grade heat source.     

Simultaneous cold hydrolysis and fermentation of fresh sweet potato

In recent decades, environmental and economic issues have pushed the production of biofuels worldwide. In this scenario, ethanol is the most produced biofuel. Starch is a potential substrate for this purpose, but the extra cost needed to hydrolyze it into glucose is still a drawback. As an alternative for the expensive and energy demanding conventional hydrolysis process, the cold hydrolysis is being studied. In this process, granular starch degrading enzymes act directly on raw starch granules; therefore, this hydrolysis is carried out below gelatinization temperature. As a consequence, the energy requirement can be significantly reduced. In this work, the cold hydrolysis and fermentation of fresh sweet potato were experimentally studied. For that, it was employed the sweet potato strain BRS Cuia, whose carbohydrate level reaches 28.7%. It can be translated into a potential to produce 185 L t⁻¹ ethanol, or equivalently 7400 L ha⁻¹. The enzymes blend adopted for the hydrolysis stage was Stargen™ 002. The surface response method indicated 200 g L⁻¹ of sweet potato and 45 GAU g⁻¹ of sweet potato as the best balance between high glucose formation rate and low enzyme consume. The 1 h pretreatment that achieved the highest glucose concentration was at 52 °C in the presence of the enzymes blend. Finally, the study of the simultaneous hydrolysis and fermentation showed that the medium supplementation has no significant effect over the fermentation performance, while the pH control is beneficial, improving the ethanol production in 54%.     

Heat and mass transfer in adsorbent bed with consideration of non-equilibrium adsorption

In the solid adsorption refrigeration cycles, the actual adsorption processes are all non-equilibrium. To investigate the heat and mass transfer in adsorbent bed, mathematical model is established and solved by a numerical method. The relations between adsorption temperature, adsorption velocity, adsorption quantity, coefficient of performance (COP), specific cooling power (SCP) and time are discussed during the process of cooling the adsorbent bed. The relations between desorption temperature, desorption velocity, desorption quantity and time are discussed during the process of heating the adsorbent bed. It indicates that there is a peak value for adsorption velocity in the adsorption process and there is also a peak value for desorption velocity in the desorption process. It also shows that the changing rate of the adsorbent temperature tends to let up, and the coefficient of performance value grows nearly linearly in the adsorption process and there is a peak value of SCP in the adsorption process.     

Simulation studies of a vacuum and temperature swing adsorption process for the removal of VOC from waste air streams

A theoretical study of the cyclic combined vacuum and temperature swing adsorption (VTSA) process for removing of volatile organic compounds (VOC) from waste air streams is done on the basis of computer simulation. The VTSA system consists of two adsorption columns with a fixed bed of activated carbon. The adsorption cycle for each column is operated in four steps: adsorption, indirect adsorbent bed heating, vacuum desorption and cooling. A nonequilibrium, nonisothermal mathematical model of the VTSA process is developed and solved using the numerical method of lines. Exemplary simulation results are presented for the system: 2-propanol–activated carbon Sorbonorit 4. The effect of desorption temperature, pressure and purge gas use on 2-propanol desorption efficiency is investigated.     

Isothermal composite adsorbent. Part I: Thermal characterisation

Adsorption and desorption are respectively exo and endothermic phenomena leading to significant temperature changes in adsorption columns. Enhanced efficiency of a sorption process could be obtained under isothermal conditions, either for gas storage, purification or separation applications. The heat transfer within the adsorbent beds can be managed in situ, using thermal energy storage material: a phase change materials (PCM) for example. The thermal behaviour of a mixture of activated carbon and PCM during CO₂ adsorption has been studied. The thermal characteristics of the involved materials have been determined and experiments carried out to highlight the positive effect of the PCM to reduce the CO₂ adsorption heat effects on an activated carbon bed. Calorimetry was the technique used for all the thermal characterisations. It appears that the heat effects induced by CO₂ adsorption are reduced by the presence of the PCM together with the adsorbent. The endothermic effect of fusion balances the heat effect of adsorption and significantly reduces the temperature changes.     

The effect of microwave regenerated adsorbent bed on the performance of an adsorption heat pump

The heat transfer problem of an adsorption heat pump during the regeneration of adsorbent bed was investigated numerically. A numerical analysis of the heat and mass transfer in an adsorbent bed during an adsorption heat pump cycle, achieved with both conventional and microwave heating, was successfully simulated. The influence of the microwave heating on the performance criteria of an adsorption heat pump was investigated. The distributions of temperature, pressure and adsorbate concentration of adsorbent bed through the radius of the bed were analyzed. The Clausius–Clapeyron diagram was constructed for both cases. The period of the cycle was improved by about 20% with the microwave regeneration, since the period of the isobaric desorption process for a microwave heated cycle was enhanced by 51% relative to the period of the isobaric desorption process for a conventional heated cycle. The COP for the microwave heated cycle was improved by 61% according to the conventional heated cycle.