| Energy is the foundation of survival and development of economy and society, the use and increasingly exhausted of fossil fuels and the environmental problems because of fossil fuels are two major challenges faced human in today society, the development and utilization of renewable energy have become an increasing concern. Biomass as an important and renewable new energy, its reserves is second only to coal, oil and natural gas,and development and utilization of Biomass has a great significance to the national energy strategy and environmental protection. But the content of alkali metal element of Biomass ash is relatively high, the complex physical and chemical reactions are occurring in the combustion process, produces low melting point eutectic compound, results in serious slagging, corrosion problems and affects the normal safe operation of combustion equipment, restrictions biomass scale use. About these, many scholars had study on different ways to alleviate slagging problem, Found that added in the biomass material with suitable additive is a viable option. Therefore, this study take rice straw, wheat straw and corn straw as raw materials, the major elements of straw ash are Al、Ca、Fe、Mg、P、Si and S,and make its corresponding oxide or salt as additives, such as Al2O3、Ca O、Fe2O3、Mg O、（NH4）H2PO4、Si O2、（NH4）2SO4. This paper studying on selection of additives、adding amount、the mechanism of slagging mitigation、the order of the effects of additives on the sintering strength index and the effects on combustion characteristics of biomass briquettes fuel.First, according to the requirements of experimental design, the additives are uniformly mixed with the raw materials and rapidly ashing in the muffle furnace, then analyzed the ash sample morphology, and test sintering strength index SII index of each ash sample in accordance with the Mohs hardness, finding the suitable additives and the add appropriate proportion. The results showed that: Ca O and Mg O are very effective additives, the corresponding gray ash are delicate, soft, not only to the effect of alleviating slagging is very satisfactory, and the add amount is relatively small, they are suitable as additives;（NH4）H2PO4, at n（K）: n（P） = 1: 1, the rice straw to the effect of alleviate slagging of the rice straw is obvious, but in other addition ratio, increase the degree of slagging, and to the other two straw the effect of alleviating slagging is not ideal; Al2O3 although can play a role to ease slagging, but the effect is not ideal.Secondly, analyze and study the mechanism of alleviating slagging of additives from three aspects. First, predict the effect of every element on the migration of K element in straw ash by using the thermodynamic equilibrium,and analyze the mechanism of alleviateing slagging of various additives in combustion of straw, although thermodynamic equilibrium prediction has various constraints, but the balance calculation for the migration tendency of alkali metal element in straw burning ash provides a valuable guidance; Second, according to the special point on the graph of sintering intensity index point, analyze the corresponding ash samples by using SEM-EDX, study ash microstructure and the main elements of ash; third, make XRD analysis to the representative ash samples, test the phase of ash, get the mechanism of remission slagging.Then, make the orthogonal experiment based on the single factor tests, analyze the result by using the range method, get the effect order of each single factor additive on sinter strength Index. The order of rice straw were ranked as follows: Mg O>Fe2O3>Ca O>（NH4）2SO4>（NH4）H2PO4> Si O2>Al2O3, the order of corn stalks were ranked as follows:（NH4）H2PO4>Mg O>Ca O>Al2O3>（NH4）2SO4>Fe2O3.Finally, study the effect of additives on briquette combustion characteristics. The raw materials and additives were added in different proportions and mixed uniformly, briquetting, then make combustion test, study the situation changes of combustion speed at three different time frame. The results show that: in the straw briquette combustion process, the additive inhibite combust in the first stage, play a catalytic role in the second phase,and have no significant effect in the third stage. |
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