Energy Efficiency Evaluation Of Biomass And Coal For Low Temperature Co-pyrolysis Based On ASPEN+PLUS

At present,coal still occupies a dominant position in China's energy structure,supporting the development of our country's economy.However,the low utilization efficiency of coal resources,especially low-rank coal,not only causes waste of resources but also pollutes the environment.China's energy consumption is huge,accounting for 23.2% of the whole world,and energy consumption growth accounts for 33.6% of the world.It has ranked first in global energy growth for 17 consecutive years.The high demand for energy has made renewable energy and the role of clean and efficient use of fossil energy increasingly prominent.Therefore,the biomass is copyrolysis with coal,and the co-pyrolysis process is simulated using Aspen Plus.It can not only effectively utilize renewable biomass energy,save coal resources,but also analyze the energy consumption and energy conversion of complex pyrolysis processes.This is beneficial to improve the energy efficiency of the system while cleaning and efficient use of biomass and coal energy.In this study,a total of six samples of rice straw and lignite with a mass ratio of 0%,10%,20%,30%,40%,and 100% were subjected to co-pyrolysis experiments to investigate how the ratio of rice straw influences the distribution of pyrolysis products.Using the Aspen Plus chemical process simulation software to establish a biomass and coal co-pyrolysis process model,and the co-pyrolysis process was divided into three units: drying,pyrolysis and separation.And Combining the experimental yield data,the complex pyrolysis process was black boxed by Aspen Plus software,the reaction heat was calculated,and then the energy balance and energy conversion efficiency of the system were calculated according to the thermodynamic principle.According to the energy conversion analysis results of the co-pyrolysis system,the sensitivity analysis of the key operational variables affecting the overall performance of the system,such as the lignite moisture content,the rice straw ratio,the pyrolysis final temperature and the semi-coke combustion ratio,is explored to investigate the effects of these four operational variables on system energy consumption and energy efficiency.The results obtained under the conditions of this study are as follows:(1)When the rice straw ratio is 20%,the deviation between the experimental value of the tar yield and the theoretical value reaches the maximum,which is 10.64%,and the yield of the tar is 12.06%.(2)After the end of pyrolysis,tar,semi-coke,and pyrolysis gas respectively took away 20.77%,40.06%,and 13.64% of the total input energy of the system.The pyrolysis unit is the main energy consumption unit of the system,accounting for 55.39% of the total energy consumption of the system.The energy consumption of the drying unit is mainly caused by the evaporation of the raw material moisture,accounting for 82.56% of the energy consumption of the drying unit.(3)Sensitivity analysis showed that for every 5% increase in water content of lignite,the energy consumption of drying units increased by 19.27%(416.88 MJ/h).When the ratio of rice straw is 20%,the energy consumption of the co-pyrolysis unit is the largest,and the increase of system energy efficiency is also the largest,which is 6.04% higher than that of lignite alone.This shows that the addition of rice straw is beneficial to improve the energy utilization efficiency of the system.The energy consumption of the system increases with the increase of the final temperature of pyrolysis.The final temperature of pyrolysis is 510 °C,which not only improves the yield of tar,but also reduces the energy consumption of the pyrolysis process.When the proportion of semicoke combustion is 22.55%,it can meet the total energy demand of the drying process and pyrolysis process.The energy efficiency of the system increased from 74.48% to 81.62%,an increase of 17.64% over the same period of last year.(4)The energy efficiency of lignite alone pyrolysis is 70.24%,and the energy utilization efficiency of the system under the ratio of 20% is 74.48%.If the sensible heat of steam and gas is recovered,the energy efficiency of the system is 78.03%.(5)The universality evaluation of the model indicates that the model can be universally applied to the quantitative analysis of energy conversion in coal pyrolysis process and biomass and coal co-pyrolysis process.