| Biomass Molding Fuel(BMF)is the only substitute energy among various kinds of renewable energies,which could be stored for long time,be convenient for transportation,large scale production and utilization.Its application conforms to the energy development strategy of China.Required by the 13th Five-year plan for environment protection of Guangdong province,the coal boilers of 3.7 tons in total in steam capacity have to be modified to be fueled by biomass,the demand for biomass molding fuel is 2 million tons,yet the current industrial development of biomass molding fuel has the bottleneck problem of lack of natural forest sawdust.Eucalyptus is the most important fast growing tree species for wood and forest purpose in South China,it has the advantages of growing fast,higher density and higher heat value and etc.,is the fine biomass energy,and its planting area is around 1.1million hm~2,the tree are mainly using in paper making,fiber board production and etc.,the annual sawdust residues of eucalyptus amount to over 1.5 million.Due to the characteristics of higher growing stress,lower viscosity of the lignin of eucalyptus sawdust,the specific energy consumption for molding is higher while the hardness of the molded fuel is lower,thus it is difficult to be used directly and is abandoned at large quantity.Aimed at effectively utilizing the sawdust residues of eucalyptus for biomass molding fuel,the influence rule has been acquired first by systematically study on the key molding parameters of eucalyptus sawdust,and with natural forest-hard miscellaneous wood as reference,the molding difference between fast growing forest wood and natural forest wood has be analyzed;with above study as breakthrough point,hydrolysis lignin is added in order to improve the molding characteristics,and with lignin,which plays the role of adhesion in molding process,as study object,by analyzing the joint state between the terminal temperature and the melting temperature of glass state transformation within the thermal transformation temperature range,and the cracking and reduction of some functional groups before and after the thermal transformation,the lignin molding mechanism was explored further,this will provide theoretical basis for fast growing forest residues molding technology;based on above mentioned and with the help of response surface experiment design,the blending for molding experiment has been carried out by adding wood sawdust,corn stalk respectively,the response surface model(CCD)of relaxeddensity,specific energy consumption,Meyer hardness as set up,the interactive influence of temperature,moisture,pressure and etc.was analyzed,the results could be used as theoretical basis for large scale utilization of eucalyptus sawdust.The detail study contents as well as the drawn conclusions are as following:1.Set up biomass thermal molding device and determine the methods for measuring the indexes of molding fuel.The mould suitable for the experimental feedstock has been designed,integrating with the pressing equipment,the experimental methods have been designed;the technical parameters of molding were determined that were moisture,pressure,temperature and particle size,the determined characteristics indexes are specific energy consumption,relaxeddensity and Meyer hardness.2.The influence rule of molding parameters of eucalyptus sawdust on the characteristics indexes has been systematically studied.With the moisture of 12%,the pressure of 6000N,the temperature of 120?and particle size of 3 mm as basic parameters for molding,by monofactorial experiment,the influence rule of molding parameters on specific energy consumption,relaxeddensity and Meyer hardness has been investigated.Along with the increasing of temperature and the pressure,the relaxeddensity will increased,the relaxeddensity will first be increased and then be decreased along with the increase of the moisture,the loosen density is at the highest value when the moisture is 10%;the relaxeddensity will first be increased and then be decreased along with the increase of the particle size,and the highest value is at the particle size of 3 mm;the specific energy consumption is increased along with the increase of temperature and pressure,the specific energy consumption will be decreased if increasing the moisture,and be first decreased and then be increased along with the increase of particle size,which is the lowest at the particle size of 3 mm;the Meyer hardness will be increased along with the increase of temperature and pressure,and it will be first increased and then be decreased along with the increase of moisture,its highest value is at the moisture of 12%,the Meyer hardness will be fist increased and the be decreased along with the increase of particle size,which is highest at the particle size of 3 mm.Meanwhile,the acquired parameter range is used as basis for the design of blending for molding experiment.3.There exists obvious difference between the fast growing forest-eucalyptus sawdust and natural forest-hard miscellaneous wood on molding.Under the same molding condition,the comparison results on characteristics indexes are:the densities are similar,the specific energy consumption of eucalyptus sawdust is higher by 21.66%,its Meyer hardness is lower by 59.66%.Analyzing in the view of growing difference of two forest woods,it is considered that the growing stress of eucalyptus sawdust is higher than that of the natural forest sawdust.4.The "solid bridge" structure was found during the molding experiment of different particle sizes of eucalyptus sawdust,the adding quantity of 5%in weight is the ideal proposition.Adding 5%of eucalyptus sawdust of 5 mm in particle size in the eucalyptus sawdust of 1 mm will apparently increase the Meyer hardness of the molding fuel,which is increased from 11.56 N/mm~2 to 23.93 N/mm~2,the increase proportion is 107.11%,the SEM analysis shows that the"solid bridge" structure is formed by the crossing and twisting of the long fibers,and the short fibers fill fully in the gap of long fibers.5.The lignin has fine adhesion performance in the thermal transformation temperature range.With the thermal transformation temperature of lignin as key parameter,the adhesion mechanism of lignin has been studied systematically by adding hydrolysis lignin in eucalyptus sawdust.At first,the thermal transformation temperature of eucalyptus sawdust and hydrolysis lignin have been measured by DSC,the glass state transformation initial temperatures of eucalyptus sawdust and hydrolysis lignin are 72?and 84.4?respectively,while the terminal temperatures are 102?and 104.3?respectively,the melting temperatures are127.4?and 136.5?respectively,the SEM analysis shows that the hydrolysis lignin is in a state of melting and joint in the temperature range between the terminal temperature and the melting temperature of hydrolysis lignin glass state transformation(120~140?),the gap among the particles are small and the joint is close,that shows the lignin has fine adhesion performance;at last,the functional groups distribution and content of lignin before and after the thermal transformation have been analyzed by FTIR,it is found that the oxygen contained functional groups are cracking and reduced in the hydrolysis lignin added molding fuel,meanwhile,the–OH and C-H bonds are increased,this means that the inner joint force is strengthened,and further verify that the hydrolysis lignin could improve the molding effect.6.The adding of hydrolysis lignin may practically improve the molding effect.The influence rule of hydrolysis lignin on the molding of eucalyptus sawdust has been investigated.The influence rule of hydrolysis lignin adding quantity,moisture,temperature,pressure and particle size on the characteristic indexes of density,specific energy consumption and Meyer hardness has of been studied;the joint style between the particles in the molded pellet has been characterized by SEM,the result shows that the particles are queued in scale form and the stuff material is full between the gap of the particles when the adding quantity is 20%weight.7.Aimed at eucalyptus sawdust blending for molding,the(CCD)non-linear response surface design is adopted to obtain the technical parameters of molding.The blending of eucalyptus sawdust with hard miscellaneous wood sawdust and corn stalk respectively has been studied,by regression analysis on the experiment data,selecting the model of specific energy consumption,relaxeddensity and Meyer hardness as the secondary optimized model(Quadratic),the response surface equation was built.The interactive function of influential factors on the indexes has been analyzed and the molding model for blended feedstock as well as the optimized parameters were obtained.The verification result show that the difference between the experiment value and the predicted value is within 10%,the model could used as theoretical basis for technical parameter determination,optimization and prediction of the characteristic indexes for blending the eucalyptus sawdust with hard miscellaneous wood sawdust,corn stalk for molding. |
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