Study On Thermo-Physical And Combustion Characteristics Of Biomass Mixed Pellets

As the fourth-largest energy resources of world's primary energy consumption, Biomass energy is the only renewable energy that can be stored and transported. Biomass energy will occupy a very important role in mankind's future energy system. It's a form of solar energy which is stored in Biological bodies on basis of the chemical energy. With biomass as a carrier, it comes from plant photosynthesis directly or indirectly. It's renewable and stable. Compared with wind power, solar energy, it's rarely constrained by natural factors, and it also can be processed into conventional fuels of solid, liquid and gaseous.Energy and environmental issues have become the focus of world attention when the human society entered the 21st century. Although coal, natural gas and oil are still the main sources of fuels, developing and utilizing of new clean renewable energy sources have become a very important and pressing issue with the increasing depletion of fossil energy and increasingly serious environmental problems. China is a large agricultural country and biomass resources are very rich. Utilization of biomass resources has still great developing potential. Therefore, adequate and reasonable developing and using biomass energy are of critical importance to ease the energy crisis of our country, preventing environmental degradation and enhancing national energy security and other aspects.World powers began to research and utilize biomass energy as early as 30 years in the 20th century. In many developed countries such as Europe, America and Japan, molding and combustion equipment of biomass have realized industrialization. Although molding and combustion equipments of biomass in these countries have many advantages such as reasonable processing, high degree of specialization, good degree of automation, high thermal efficiency, low-smoke pollution and so on, it is not suitable for our country to import it in which they have many disadvantages such as high price, single variety of fuels, easy slagging, high power consumption and so on compared to my country. We must also realize that the use and research of biomass energy are not deep enough in the current, and there is still a certain gap with developed countries. Especially, study of Biomass Briquette need to go a long way. Therefore, there is no available theory for practical application. Taking simple substance briquette of corn stalks as an example, there is a serious cinder problem in during of combustion, which makes higher requirements to molding and combustion equipment. Simple substance briquette of wood chips has been at high prices, and there is also a cinder problem in using, so it is difficult to promote the use of it in reality. Although ash melting point of simple substance briquette of rice husks is very high, there are problems of difficulties in forming and lower heat release in reality.This paper is exactly aimed at easy slagging of simple substance briquette, high prices and difficult molding problems on the basis of a large number of domestic and foreign documens. Reasonable mixed corn stalks, rice husks and wood chips as raw biomass materials through the scientific method. The author mainly focuses on the slagging characteristics, compression molding and combustion characteristics. The purpose of this paper is to get some more systematic and regular conclusions for biomass briquette applying to industrial production, which would provide some valuable guidance.The main contents of this paper include:1)Slagging characteristics research. In this paper, biomass materials of different components are made to mix and form. In order to product ash, the author used furnace to simulate the combustion process of biomass pellet fuel mixture in the boiler. By using Ash Fusion Tester to analyze the ash slag.Using whether softening temperature or the difficult degree of ash, simple substance briquette of corn stalks and wood chips slag severely, but rice husks doesn't slag. Ash fusion temperature was higher than cinder temperature when evaluating with CRC(about 100-150℃). Experimental results show that there a marked increase of ash melting point with the increasing amount of rice husk. Slag can not be formed with 75% corn stalks - 25% rice husks and 80% wood chips -20% corn stalks. It means that mix of different kinds of simple substance briquette solves the slagging problem and this enable to meet the normal using requirements of the combustion equipment. Finally, the author provided two mixing ratios of biomass after comprehensive research and analysis. That is 75% corn stalks - 25% rice husks and 57% wood chips -43% corn stalks.2)Design of Orthogonal Experiment. In this paper, the author uses corn stalks, rice husks and wood chips which were produced in northeast as the main object of study, and then thermoformed after mixing. The forming effect of biomass mixture is the basis of studying the fuel various aspects of characteristics of the fuel. The pressure and temperature of molding are two important factors in the forming tests. The author used Combination of binary quadratic regression orthogonal design method of Optimal Design and Analysis of Test to optimize the design of the test. Under the research and analysis of the molding experiment, the author obtains the orthogonal combination of the regression equation of forming density, heating temperature and molding pressure. And then he carries out the analysis of variance and significance test of the regression equation of the test indicators. The results show that the test is feasible.3)Hot forming research. Forming pressure is the most basic conditions of the biomass mixture dense forming. Study shows that the relationship between forming pressure and forming density is similar to a quadratic function. If the pressure is too small, it will result in difficulties to form or forming density be very small. When the pressure reaches a certain value, the pressure increased while the increase of density is not obvious. The mixture of corn stalks and rice husk can achieve forming close, surface smooth and density moderate when the molding pressure values of the corn stalks and rice husk is within 16 to 48MPa, regression equation isρ= ?7. 63×10?7 (p?32)2+0.0012(p?32)+0.6817,and for Sawdust and rice husk mixture is within 24 to 48MPa, regression equation isρ= ?5 .08×10?7 (p?32)2+0.0011(p?32)+0.6291,Temperature and density of molding have a linear relationship. Comparing with the molding pressure, the impact of molding temperature to molding density is much smaller. The author sums up by experiment that we can get ideal result of the mixture 75% corn stalk and 25% rice hull when pressure values within 16 to 48MPa and molding temperature within the scope of 160 to 200 degrees, regression equation isρ= 0. 001T+0.991. While for mixture 57% sawdust and 43% rice husk, the pressure value is within 16 to 48MPa and molding temperature within above 180 degree, regression equation isρ= 0 .0017T+0.7782. The role of molding pressure to the molding density is greater than that of molding temperature within the scope of the test settings value.4)Combustion characteristic test. The author carries out a TGA Test of programmed temperature method under the conditions of pure oxygen of the mixed sample, and then he finishes out the data of quality, temperature and time. Then he obtains the combustion characteristic parameters of mixed biomass particle by thermal gravimetric curves (TG) and derivative thermal gravimetric curves (DTG). Combustion process is divided into three phases based on the characteristic parameters: stage of Fuel desiccation, stage of precipitation and combustion of volatile constituents and stage of coke combustion. The second stage is the most important of all. We find that there are many advantages of mixed particles of biomass fuels by comparing combustion characteristic parameters of Biomass briquette and traditional coal. It can not only reduce the requirement of temperature of the boiler material, but also improve the efficiency of industrial boilers. This can reduce the operation and maintenance costs of dust desulphurization equipment.5)Combustion Kinetics. The author carries out the combustion dynamics analysis and the corresponding kinetic model of combustion. Through the combustion kinetics of the formula, draw the curve of. The combustion process is divided into two stages through Curve equation. And then calculate the specific values of initiation and termination combustion temperature, activation energy and frequency factor of every stage. Under different experimental conditions, the result shows that the combustion process of biomass includes the volatile combustion stage and the coke burning stage. Increasing molding pressure can improve the reaction rate, but delay the ignition point temperature, so that the combustion characteristic of volatile components is more obvious. Increasing heating rate of speed can also improve the reaction rate, but delay the ignition point temperature . Rising molding temperature can increase the ignition temperature, but the combustion reaction slow down. Reduction of rice husk mixed content, ignition temperature of the mixed grains becomes lower and the reaction becomes faster. The combustion characteristic of Volatile constituents is very obvious. The relationship of model parameters and combustion characteristics value made activation energy reflects the rate of combustion reaction clearly. When the activation energy and frequency factor are reduced, the combustion reaction and the combustion temperature accelerate. On the contrary, no exceptionThis paper further study the slagging properties, hot forming and combustion characteristics of biomass fuels, and provided a theoretical basis for the future development of molding equipment. At the same time, it also has a guiding significance of biomass fuel boiler designing optimization and industrialization.