Research About Synergistic Effect Duirng Co-pyrolysis Of Biomass And Coal

Energy is the material basis for survival and development of human society. Biomass andcoal are both the integral parts of China’s energy resources. They have many similar properties.It is an efficient way to use biomass and coal by means of co-pyrolysis and co-gasificationaccording to China energy situation. It could alleviate the energy crisis, improve environmentalconditions and increase the utilaization of biomass resources. Studies about co-pyrolysischaracteristics and synergistic effect could provide theoretical base for the co-use of biomassand coal efficiently. In this paper, rice husk and lignite were taken as represent of biomass andcoal respectively. Several methods were used to analysis the co-pyrolysis characteristics andthe synergistic effect. The main contents and results are summarized as follows:1. The thermal gravimetric (TG) analysis was used to analysis the mono-pyrolysis andco-pyrplysis. Rresults showed that the main pyrolysis stages of rice husk and lignitemono-pyrolysis have overlapping part, which showed the possibility of synergistic effectduring co-pyrolysis. Co-pyrolysis mass lost was large when co-pyrolysis happened under themixed ratio of rice husk to lignite was2:8. It suggested that the synergistic effect was moreobvious under this condition. Heating rate has a certain impact on the pyrolysis process. Itincreases the interaction time of the rice husk and lignite during co-pyrolysis with slow heatingrate, which could make the synergistic effect obviously. The endo-exothermic status duringpyrolysis was analyzed through TG-DSC methods. Results showed that the co-pyrolysis DSCcurve could not get from the rice husk and lignite mono-pyrolysis. There needed moreheat-absorption at high temperature during co-pyrolysis.2. Three kind of kinetic analysis methods were used to analysis the co-pyrolysis. Theywere Coats-Redfern integration method, Kissinger differential method and DAEM (DistributedActivation Energy Model). Comparison of three mothods, it found the DAEM is the mostsuitable method to analyze the co-pyrolysis kinetic characteristic. Generally, the activation energy shows an elevated-smooth-elevated tendency with the conversion rate of raw materialsincreasing under DAEM method. The average activation energy of rice husk is about180kJ/mol, lignite is about290kJ/mol, and the co-pyrolysis of rice husk and lignite with differentmixed ratio is about180-190kJ/mol, which far less than the lignite.3. Products of slow co-pyrolysis process of rice husk and lignite were analyzed by gaschromatography and the TG-IR. The mechanism of co-pyrolysis process was investigatedaccording to the mechanism analysis of biomass and coal mono-pyrolysis reported in theliteratures. Studies have shown that the total gas product of slow co-pyrolysis process of ricehusk and lignite was more than biomass and coal mono-pyrolysis. And gas product componentchanged a little during co-pyrolysis. Heating rate also has a certain impact on the product ofco-pyrolysis. By the mechanism of co-pyrolysis process, the synergy of biomass and coalduring co-pyrolysis process is because some elements oxide in biomass, such as SiO2, couldrestrain the process of coal bond into coke; thus it contributes to the further decomposition ofcoal. In addition, the biomass produces H2earlier than coal during co-pyrolysis, and thecondensation reaction of coal at high temperature is inhibited by H2; so the prolysis of coal ispromoted.4. The gas products of rice husk and lignite during fast co-pyrolysis process wereinvestigated by tube furnace and gas chromatography. In addition, the fast co-pyrolysis ofbiomass and coal with adding water was studied, also the effect of adding water amount on theco-pyrolysis gas products. Results showed that the gas products yield increased during fastco-pyrolysis compared to fast mono-pyrolysised, however, the increasing degree was notsignificant. After adding water, the gas products yields of rice husk and lignite fastmono-pyrolysis have not increased obviously. However, the gas products yields during fastco-pyrolysis increased much after adding water. With the amount of adding water increasingthe gas products yield increased, too. The gas products yield increased most when it added60%water to the weight of material. Then the gas products yield did not increase with addingmore water. Besides, the amount of adding water has effect on gas product content in certain degree. However, the mixed ratio of rice husk and lignite has larger effect on the gas productcontent than the amount of adding water.