Research On Energy Analysis And Energy Efficiency Improvement Of Boiler And Crystallization Units In The Cane Sugar Factory

"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.