【作者】 莫乾赐；

【导师】 卢苇；

【作者基本信息】 广西大学 ， 化学工程， 2022， 博士

【摘要】 “碳达峰·碳中和”已成为全球发展目标,我国化工生产过程中存在着大量能源消耗、浪费的现象,尤其是制糖企业,大多存在因设备老旧,技术更新慢,运行效率低以及大量的余（废）热不能充分利用的现象,不利于企业、行业乃至社会的可持续发展。而制糖过程中能量消耗最为显著的环节在锅炉和煮糖工段。基于此背景,本文展开了糖厂锅炉和煮糖工段能量分析和能效提升的研究,基于糖厂锅炉能效测试数据分析了锅炉的能效现状、影响因素及节能减排潜力,确定其关键因素对能效的影响程度,揭示不同煮糖真空度对煮糖能效的影响规律,并依据锅炉和工段煮糖能效分析结果提出相应的改进措施。主要研究内容如下:（1）以广西南部多家制糖企业196台样品锅炉的能效测试结果数据为研究对象进行能量分析。分析结果表明:锅炉平均热效率为85.95%,最低的仅为76.22%,其中有46.84%的蔗渣锅炉达不到标准规定的限定值。工业锅炉的热效率明显比电站锅炉的热效率低;设备服役周期长、容量及运行参数低以及设计不合理是效率偏低主要原因。热损失主要由排烟和碳未完全燃烧产生,损失值分别为10%和2%,水分的热损失占了前者的近25%,影响较大。基于136台进行详细测试的蔗渣锅炉能效测试数据进行更为深入的（火用）分析,结果表明,平均（火用）效率为29.77%,不可逆性约占60%。热量（火用）损失主要是排烟和碳未完全燃烧的热量（火用）,分别占8.32%和1.55%,其余不超过0.5%。对热效率的影响因素研究发现,烟气温度、低位发热量、含水率、飞灰的碳含量有较明显的影响趋势。应用灰色关联分析发现,燃料收到基低位发热量对锅炉效率影响最大,烟气CO含量影响最低。节能减排潜力分析表明,CO₂排放量平均为131.54 kg·GJ^-1,121台3.82 MPa的样品锅炉能效不达标者经改造后能效可达目标值,每年的蔗渣消耗以及CO₂、SO₂、NO_x和烟尘排放量可分别减少568 kt、522 kt、0.38 kt、0.87 kt和17.69 kt,其节能减排潜力巨大。进一步以一台180 t·h^-1的蔗渣锅炉为样品,分析其在设计工况下不同部件的（火用）效率和损失,结果表明,整体（火用）效率只有29.61%,而不可逆性（火用）损失高达64.01%,其主要集中在炉膛和水冷壁,分别为46.14%和11.10%,主要原因是燃烧过程中的化学反应不可逆性及传热温差过大。（2）以广西区内某糖厂典型的三系煮糖系统为研究对象,对不同真空度下的煮糖工况进行能量和（火用）分析,当真空罐真空度分别提高10.1%和8.6%时,消耗的乏汽量分别减少11.8%和13.4%,蔗渣打包率平均提高约1.5%。在真空压力相同的工况下,加热蒸汽温度较高的工况需要多消耗12.5%的能量。分析结果表明,提高煮糖时罐内的真空度是节能降耗的有效途径。（3）基于136台进行详细测试的蔗渣样品锅炉和一台蒸发量为85t·h^-1的典型蔗渣锅炉测试结果进行了蔗渣含水率、过量空气系数和入炉空气氧浓度参数对热效率影响程度的模拟分析。结果表明:蔗渣样品锅炉的含水率从60%降低至20%,平均热效率则由84.61%提升至87.75%;干蔗渣消耗量随含水率的升高呈近似线性的上升趋势,其平均值由72.04 kg·GJ^-1增加至76.21 kg·GJ^-1,平均每增加1%的含水率,干蔗渣就多消耗0.10 kg·GJ^-1;随着空气过量系数增大,热效率降低,两者间呈近似线性的关系,空气过量系数由1增加至2.5时,蔗渣样品锅炉平均热效率由89.16%降低至80.80%;而热效率随入炉空气氧浓度的增高而增高,氧浓度由21%增加至55%时,蔗渣样品锅炉平均热效率则由86.36%增加至91.75%。另外,氧的体积浓度在21%～30%之间时热效率增长较快。（4）基于锅炉和煮糖工段能量分析的结果,在烟气干燥的基础上,结合Rillieux原理,提出并分析了利用提升温度后的蒸发汁汽与烟气联合加热的新型蔗渣干燥系统。以一台85 t·h^-1蒸发量的典型蔗渣锅炉为样本,对以乏汽和五效蒸发系统各效汁汽为干燥器的加热源的对象进行研究,研究结果表明,按蒸发系统效数的次序排列,各效蒸发对锅炉分别有3.3%、3.90%、4.79%、5.53%、6.26%和6.88%的热效率提升效果。其中,加热源为三效抽汽的系统可为典型锅炉的燃料增加可利用能量430 k J·kg^-1,效率可由原来的84.5%提升至90.03%,每年节省约160 t标煤。接着应用ANSYS软件分别在有、无三次风的工况下对一台60 t·h^-1的样品锅炉进行分析,结果发现,增加三次风后效果更佳,锅炉改造后燃尽率和热效率分别提高约1.4%和2.98%。最后,基于应用富氧燃烧技术和提高真空度分别有利于提高锅炉和煮糖工段能效的研究结果,结合热流逸效应的气体分离和抽真空特性,分别提出热流逸式的富氧空气制备系统和煮糖抽真空系统并对其进行能量分析。以一台蒸发量85 t·h^-1的典型锅炉为研究对象,在入炉空气氧浓度由21%升至30%时,排烟损失由8.64%降到7.00%,而基于热流逸式富氧空气制备系统的锅炉富氧燃烧装置将使其热效率提高5%;在蒸汽产量一定时,节约蔗渣2230 kg·h^-1,节约能耗4828 k W。节省的能耗远多于系统需要的最高能耗（83.44 k W）。而以7000 TCD糖厂为分析对象,设计的热流逸式新型抽真空系统,需要消耗的低品位热量总量为596.78 k W。若其提高的真空度使煮糖时能利用后一效的汁汽加热,将节省更高品质的蒸汽约7.27 k W。从用能角度看该方法可直接利用糖厂余（废）热等低品位热能驱动,能有效实现能量的综合利用,到达提升效率的目标。更多还原

【Abstract】 "Carbon peak·carbon neutral"has become a global development goals,there are a lot of energy consumption in the process of chemical production in our country,the phenomenon of waste,especially the sugar industry,mostly exists because of its old equipment,technology update slow,low efficiency and large amount of（waste）cannot make full use of the phenomenon,is not conducive to the sustainable development of enterprise,industry and even the society.The most significant energy consumption in the process of sugar production is in the boiler and sugar boiling section.Based on this background,this paper carried out the research on energy analysis and energy efficiency improvement of boiler and sugar boiling section in sugar factory.Based on the performance test data of boiler in sugar factory,the energy efficiency status,influencing factors and energy saving and emission reduction potential of boiler were analyzed,to confirm the influence degree of the key factors of energy efficiency,and reveals the influence of different boiling sugar vacuity on the boiling sugar efficiency,in view of the boiler and boiling sugar section the results of the analysis of energy efficiency improvement measures are proposed.The main research contents are as follows:（1）The performance test data of 196 sample boilers from several sugar manufacturing enterprises in southern Guangxi were used for energy analysis.The results show that the average thermal efficiency of the boiler is85.95%,the lowest is only 76.22%,and 46.84%of bagasse boilers can not reach the limit value specified in the standard.The efficiency of industrial boiler is obviously lower than that of utility boiler.Long service cycle,low capacity and operation parameters and unreasonable design are the main reasons for low efficiency.The heat loss is mainly caused by flue gases exhaust and incomplete combustion of carbon,and the loss value is 10%and 2%respectively.The heat loss of water accounts for nearly 25%of the former,which has great influence.Further exergy analysis was carried out based on the performance test data of 136bagasse boilers that were tested in detail.The results showed that the average exergic efficiency was 29.77%and irreversibility accounted for about 60%.The exergy loss of heat is mainly the exergy of flue gases exhaust and incomplete combustion of carbon,accounting for 8.32%and 1.55%respectively,and the rest is not more than 0.5%.It is found that flue gas temperature,low calorific value,water content and carbon content of fly ash have obvious influence trend.The grey correlation analysis shows that the low calorific value of fuel has the greatest influence on boiler efficiency,and the CO content of flue gas has the lowest influence.The analysis of energy saving and emission reduction potential shows that the average CO₂ emission is 131.54 kg·GJ^-1.121 sample boilers with 3.82MPa energy efficiency that are not up to the standard can reach the target value after modification.The annual bagasse consumption,CO₂,SO₂,NO_x and dust emissions could be reduced by 568 kt,522 kt,0.38 kt,0.87 kt and 17.69 kt,respectively.Taking a 180 t·h^-1 bagasse boiler as a sample,the exergic efficiency and loss of different components were analyzed under design conditions.The results showed that overall exergic efficiency was only 29.61%,while irreversible exergic loss was as high as 64.01%,mainly concentrated in furnace and water wall,which were 46.14%and 11.10%respectively.The main reasons are the irreversibility of chemical reaction and large temperature difference of heat transfer.（2）Taking the typical three-stage boiling scheme of a sugar factory in Guangxi as the research object,energy and exergy analysis was carried out on the sugar boiling conditions with different vacuum pressure.When the vacuum pressure of vacuum pan was increased by 10.1%and 8.6%,the amount of steam consumed was decreased by 11.8%and 13.4%,respectively,and bagasse-packing rate was increased by 1.5%on average.Under the condition of the same vacuum pressure,heating steam at higher temperature requires 12.5%more energy consumption.The results show that increasing the vacuum pressure is an effective way to save energy and reduce consumption.（3）Based on 136 sample bagasse boilers and a typical bagasse boiler with evaporation capacity of 85 t·h^-1,the effects of bagasse moisture content,excess air coefficient and oxygen concentration on efficiency were simulated and analyzed.The results show that the moisture content of bagasse sample boiler decreases from 60%to 20%,and the average thermal efficiency increases from84.61%to 87.75%.The consumption of bagasse increased linearly with the increase of moisture content,and its average value increased from 72.04 kg·GJ^-1to 76.21 kg·GJ^-1.With an average increase of 1%moisture content,the consumption of bagasse increased by 0.10 kg·GJ^-1.With the increase of air excess coefficient,the thermal efficiency decreases,and the relationship between them is almost linear.When the air excess coefficient increases from 1 to 2.5,the average thermal efficiency of the former decreases from 89.16%to80.80%.When the oxygen concentration increases from 21%to 55%,the average thermal efficiency increases from 86.36%to 91.75%.In addition,the thermal efficiency increases faster when the volume concentration of oxygen is between21%and 30%.（4）Based on the energy analysis results of boiler and sugar-boiling section,a new bagasse drying system was proposed and analyzed in combination with flue gas drying and Rillieux principle.A typical bagasse boiler with evaporation capacity of 85 t·h^-1 was taken as a sample.The results show that,in order of efficiency,it has the potential to improve the thermal efficiency of boiler by 3.3%,3.90%,4.79%,5.53%,6.26%and 6.88%respectively.Among them,the system with third-effect bleed vapor as heating source can increase available energy 430k J·kg^-1 for typical boiler fuel,increase efficiency from 84.5%to 90.03%,and save about 160 t standard coal per year.Then,a sample boiler of 60 t·h^-1 is analyzed by ANSYS software under the condition of having and without third wind respectively,the results found that the effect was better after the third wind.At the same time,the burnout rate and thermal efficiency of the boiler are increased by 1.4%and 2.98%respectively after the modification.Finally,based on the application and research results that the application of oxygen-rich combustion technology and the improvement of vacuum pressure are conducive to improving the energy efficiency of sugar boiling section respectively,combined with the characteristics of gas separation and vacuum extraction of thermal transpiration effect,the thermal transpiration effect oxygen-rich air preparation system and sugar boiling vacuum system are proposed and their energy analysis is carried out.Taking a typical boiler with evaporation capacity of 85 t·h^-1 as the research object,when the oxygen concentration in the furnace increases from 21%to 30%,the flue gases exhaust loss decreases from 8.64%to 7.00%,and the boiler oxygen-rich combustion device based on heat flow escape oxygen-rich air preparation system will increase its thermal efficiency by 5%.When steam production is constant,2230 kg·h^-1 of bagasse and 4828 k W of energy can be saved.The energy savings far exceed the maximum power consumption required by the system（83.44 k W）.Taking 7000 TCD sugar factory as the analysis object,the new thermal transpiration effect vacuum system is designed,and the total amount of low grade heat consumed is 596.78 k W.If the improved vacuum pressure makes it possible to use bleed vapor in the post-effect evaporator for heating massecuite when boiling sugar,it will save about 7.27 k W of higher quality steam.From the perspective of energy use,the method can be driven directly by low grade heat energy such as waste heat of sugar factory,which can effectively realize comprehensive utilization of energy and achieve the goal of improving efficiency.更多还原