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Tian Y.,Chinese Academy of Agricultural Sciences | Tian Y.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | Wang R.,Chinese Academy of Agricultural Sciences | Wang R.,China Agricultural University
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

Thermokinetics analysis can test the relationship between physical and chemical properties of material and temperature through controlling heating rate. Through thermokinetics analysis, we can study the combustion, pyrolysis and gasification reaction kinetics of biomass, decide the reaction kinetics model and calculate the reaction kinetics parameters, such as activation energy and pre-exponential factor. In the article, we chose 6 kinds of biomass raw materials, including corn straw, wheat straw, cotton stalk, pine sawdust, peanut shell, and residue of sweet sorghum. The thermal gravity analysis (TG) experiments were carried out, and 8 loss curves were obtained under non-isothermal conditions at linear heating rate of 5, 10, 20 and 30 ℃/min. The 99.99% nitrogen continuously passed and the temperature rose from room temperature to 600℃. The initial sample weight was always within the range of 3-4 mg. The method of different heating rates was applied to non-isothermal data. The Friedman method and the Flynn-Wall-Ozawa method were used for the estimation of the activation energy, and the Malek method was used for the decision of the reaction kinetics model, which were defined as the sample of the pre-exponential factor and the conversion function, respectively. The results showed that the pyrolysis process of biomass included 3 main stages: drying and preheating stage, volatile matter evaporation stage and carbonization stage. The higher the total moisture in biomass, the greater the mass loss rate for the sample at the first stage. Volatile matter evaporation stage was the most important stage in the pyrolysis process, in which the mass loss rate of the sample increased rapidly with the increase of the temperature. The carbonization stage was mainly the continued pyrolysis of lignin, and carbon and ash were the final products. In the whole range of conversion rate, the activation energy of biomass was not a fixed value, and it would increase gradually with the increase of conversion rate. Due to the influence of the particle size, the buoyancy and the non homogeneous phase, in the range of conversion rate <0.2, and >0.8, the TG curve was difficult to meet the requirements of the temperature at different heating rates under the same conversion rate. In the volatile matter evaporation stage, the activation energies obtained by Friedman method and Flynn-Wall-Ozawa method were almost the same and hardly changed with the conversion rate. The pyrolysis activation energy of the biomass ranged from 144.61 to 167.34 kJ/mol, and the correlation coefficient was almost between 0.99 and 1.00. This shows that the calculation method of the activation energy is reliable in this paper. Among biomass raw materials, corn straw and wheat straw belonged to gramineous crops, whose activation energy was high, 167.34 and 167.20 kJ/mol respectively; lignification degree of cotton stalk, pine sawdust and peanut shell was higher, whose activation energy was lower, 154.06, 147.29 and 146.91 kJ/mol respectively; residue of sweet sorghum was processed by biochemical process, whose activation energy was the lowest, 144.61 kJ/mol. The reaction kinetics models of the biomass conformed the Avrami-Erofeev function. This shows that because the composition and structure of different biomass materials are basically the same, the reaction kinetics models are basically the same. But, there were some differences in the reaction orders. The reaction order of corn stalk and peanut shell was 3; the reaction order of wheat straw, cotton stalk and residue of sweet sorghum was 2; and the reaction order of pine sawdust was 1.5. The pre-exponential factor of the biomass ranged from 26.66 to 33.97 s-1. Our results show that biomass pyrolysis is an extremely complex multi-step process, which has different activation energy and reaction kinetics model in different temperature range. This is important theoretical basis for the optimization of process conditions and engineering amplification of biomass pyrolysis process. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved. Source


Fu C.G.,China Agricultural University | Fu C.G.,Chinese Academy of Agricultural Sciences | Fu C.G.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | Ma S.B.,Nanyang Normal University | And 5 more authors.
Advanced Materials Research | Year: 2014

Ignition temperature is an important parameter in fuel combustion characteristics research. In this paper, tradition ignition temperature determination methods and their application limitations were discussed by analyzing the DTA curve. All discussions were demonstrated in sweet sorghum fermentation residue particles combustion test. As commonly-used methods were totally established with no consideration of thermal analyzing, the calculating value error were obvious. Taking account detected time tk (uV>0) and delay time(Δtd) in DTG (derivative thermogravimetry)-DTA (differential thermal analyses) profile, DTG-DTA delay time method was established in this paper. The calculated values comparison has been performed between new method and TG-DTG dividing point method, the latter was recognized as the most accurate method. It was showed that new method has almost the same ignition temperature to that of TG-DTG dividing point method. While new method needs only half workloads of TG-DTG diving point method. The physical conception of new method is clear and corresponded ignition temperature is accurate. Therefore, new method is suitable for biomass ignition temperature determination. © (2014) Trans Tech Publications, Switzerland. Source


Tian Y.,Chinese Academy of Agricultural Sciences | Tian Y.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | Xu Y.,Chinese Academy of Agricultural Sciences | Xu Y.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | And 8 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

To understand the effects of different storage conditions on physicochemical properties of crop straw, this paper has studied 3 kinds of straw pretreated methods which specifically are the whole plant, baling and crushing, together with 3 storage methods of pretreated straw i.e. stored in the open air, under the covering condition and under the sealed condition with tarpaulin for a period of 5 months. The results show that average of total moisture content of crushed stalks reaches 19.16%, which is respectively 15.71% and 15.34% higher than whole plant and baling straw. Due to the influence of environmental humidity and their own physical and chemical effects, total moisture contents of straw stored in the open air and under the sealed condition are higher than that stored under the covering condition; for the same pile of straw, total moisture content in each layer has the same change, but there are significant differences between the values. Straw temperature changes with the external environment; all are closely related to moisture content, average daily temperature does not change significantly, and the range is only between 3.24 and 3.71℃. The maximum storage temperatures are 40.8, 35.4 and 44.7℃, respectively, when whole plant stalks are stored in the open air, under the covering and sealed condition; the above data for baling straw are 32.7, 30.3 and 35.8℃, respectively; and crushed stalks are 40.5, 39.3 and 43.7℃, respectively. So, the bale of straw is easy safe storage, and when the whole plant and crushing straw are stored for a long time, it should keep the environment ventilated. The calorific value is negatively correlated with total moisture content, the calorific value based on dry basis is higher than that based on receive basis. When the group is on dry basis, the calorific values of whole plant and baling straw are similar, with the average reaching 14 000 kJ/kg, and the calorific value of crushed straw is lower, around 13 000 kJ/kg. When the group is on receive basis, the calorific value presents downward trend over time, showing more obvious decline in February and a negative correlation with the total moisture change. Taking the whole plant stalks as the example, the calorific value is reduced by 1512, 1608 and 1612 kJ/kg respectively from January to May when straw is stored in open air, under the covering and sealed condition; the average calorific value of sealed storage is the lowest, only 11 547 kJ/kg. On the whole, the total moisture and volatile of crushed straw are higher than whole plant and baling straw, and the ash content is lower than them; the total moisture and volatile of sealed storage are higher than stored in the open air and covered storage, and the ash content is lower than them. Therefore, crushed straw is not conducive to energy use, and bale of straw is easier storage than the whole plant, but its cost is higher; sealed storage is not recommended, and because the parameter indices change inconsistently when straw is stored in the open air and under the covering condition, the latter two methods require further study. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved. Source


Fu C.,Chinese Academy of Agricultural Sciences | Fu C.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | Fu C.,China Agricultural University | Tian Y.,Chinese Academy of Agricultural Sciences | And 7 more authors.
Taiyangneng Xuebao/Acta Energiae Solaris Sinica | Year: 2016

The combustion characteristic test and the NOx(CO)emission tests were carried out to explore the feasibility of the fermentation residue of the sweet sorghum stalk as biomass fuel. While the TG-DTG-DTA technology had been utilized to test the characteristics in different heating rate with air and nitrogen condition,and the unburnt pollutions tests were experimented on the fire test platform in the Key Laboratory of Energy Resource Utilization from Agricultural Residues,Ministry of Agriculture. The tests showed that volatile combustion occupies a large part of the fermentation residue's whole combustion stage. Under the heating rate 40 ℃/min in air atmosphere,the best combustion efficiency happened,where the volatile release characteristic index and comprehensive combustion characteristics are the biggest in the all heating rate circumstances. when the air ration between 1.7 and 2.2,the maximum NOx emission is 348.4 mg/m3. When the excessive air ratio below 1.95 and 1.72,the NOx emission under 300 and 200 mg/m3 respectively. © 2016, Editorial Board of Acta Energiae Solaris Sinica. All right reserved. Source


Tian Y.,Chinese Academy of Agricultural Sciences | Tian Y.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | Fu C.,Chinese Academy of Agricultural Sciences | Fu C.,Key Laboratory of Energy Resource Utilization from Agricultural Residues | And 10 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2014

Crop residues are important biological resources that can be used as sources of renewable energy, feed and other industries. After crushing crop straws into particles, belt conveyor is a common transportation way of the straw particles for production process. However, the quantity of mass transferred straw with belt conveyor was affected by various factors, whose influencing mechanisms are not clear so far.. In this study, corn straw was used as an experimental material to determine the mass transfer rules of the physical factors (total moisture and bulk density) and belt conveyor factors (conveying inclination and belt speed) with belt conveyor. For comparison, wheat and sweet sorghum straws were also experimented. The results showed that the mass transfer rate and bulk density of corn straw increased almost linearly along with the increase of total moisture.On the contrary, the dry mass transfer rate decreased linearly. As the bulk density of particle increased with total moisture, the rate of change in mass transfer rate decreased oppositely. In addition, particle size has a vital effect on the mass transfer rate and the fluidization angle of conveyor belt. Decreasing the particle size resulted in an increase of the mass transfer rate, the angle of conveyor belt, and the bulk density in the corn straw experiment. Furthermore, there is a critical belt speed point when conveyor inclination from 25-35°. Once the belt speed surpasses this speed point, an obviously rate of change will be present in the mass transfer rate curve. For the corn straw, the critical belt speed point was 1.6 m/s. Wheat straw and sweet sorghum straw were tested to verify the transfer rules with the same testing methods. The correlation between the mass transfer rate with conveying belt inclination in corn straw is different from that in wheat straw, whose correlation was linear dependence. But the results from straw of sweet sorghum test was similar to that of corn straw. The experimental results lead to the conclusion that the same type bio-structure straw has the same mass transfer law. To the corn and sweet sorghum straw, the conveying inclination should less than 32° and 35.5°, the belt speed should exceed 1.6 m/s and 1.8 m/s respectively. In the mass transfer process stage, critical fluidization angle is an important physical parameter, which has important influences on mass transfer rate. In this paper, the computed correlation function has been shown that fluidization angle equal to the weighed linear relations of the accumulated angle of move, which corresponding to every particle size range. The theoretically calculated results had a good agreement with the experimental results. Above all, this paper provided the research methods for other agriculture residues' mass transfer rate with belt conveyor. Source

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