| Biomass, which is kind of environmental friendly renewable energy, is believed to have broad application prospects. In the absence of oxygen and medium temperature (about500℃), biomass can be converted into pyrolysis gas and bio-char, and then pyrolysis gas changes into bio-oil and non-condensable gas by fast condensation. It is well known that the yield and composition of the bio-oil collected can be affected significantly by the performance of condenser, and then the quality of the oil is also influenced. As direct-fired energy generation is the most economical technology route for bio-oil at present. Based on this back ground, bio-oil’s physicochemical characteristics, evaporation combustion characteristic, atomization characteristics are investigated, and the pyrolysis vapor’s characteristic is also investigated in the meantime. The chemical models of bio-oil and pyrolysis vapor are built. In addition, experimental research and numerical simulation are conducted to study pyrolysis vapor’s condensation characteristics and bio-oil’s combustion characteristics.Bio-oil’s elemental analysis, biochemical analysis, basic physical parameters analysis (moisture content, calorific value, viscosity, surface tension, specific heat and density, etc.) were finished and the measure methods were introduced and concluded in this thesis. The relationship between the moisture content and calorific value were expounded in detail. Meanwhile, the viscosity and surface tension of the bio-oil and low carbon alcohol mix system variation with temperature were discussed. Then, the chemical composition and thermodynamics characteristics of the non-condensable gas were analyzed and calculated. The results indicated that: bio-oil’s C content is much lower compared with petroleum oil, while its0content is much higher. In addition, the bio-oil almost do not have N and S content. The moisture content of the bio-oil is around30%; rice-husk’bio-oil’s dry base calorific value is about23.4MJ/kg. The viscosity of the bio-oil and low carbon alcohol mix system decrease with the rising temperature, and finally become stable. The surface tension of the bio-oil was decreased with the increasing temperature. The viscosity and surface tension of the bio-oil and low carbon alcohol mix system decrease with the addition of more alcohol. The non-condensable gas are mainly CO, CO2, N2, H2and CH4, several important physical parameters (means density, molecular weight, calorific value and specific heat capacity) of the non-condensable gas can be calculated based on the results above.The evaporation and combustion characteristics of bio-oil were studied by thermal analysis, and the dynamic analysis was done. The results showed that the evaporation process of the bio-oil was divided into two stages:volatilization of low boiling point materials and macromolecular cracking, the combustion process of bio-oil were divided into three stages:volatilization of low boiling point materials, macromolecules pyrolysis and coke burning. First-order reaction model and three dimensional sphere shrinkage model fitted better on the evaporation and combustion of bio-oil at low temperature, and three dimensional spherical diffusion model region fitted better on the evaporation and combustion of bio-oil in high temperature. In the low temperature area, the evaporation activation energy of bio-oil was in50-65kJ/mol band, activation energy of combustion was in40-50kJ/mol band, it showed that combustion was easier than evaporation in this area. Coke combustion activation energy of weightlessness was87.55kJ/mol, activation energy of combustion was106.62kJ/mol.The spray characteristics of bio-oil were investigated by high-speed camera and MATLAB. When the temperature of bio-oil was35℃, the atomization angle increases at the beginning, and then decreases with the increase of the rotational speed, and the maximum is47.10°. With the increase of jet distance, the Sauter Mean Diameter of the bio-oil droplets increased firstly, then decreased, and increased again slowly, and the number of spray droplets decreased firstly, then increased. The condensation and combustion effect of atomized droplets is the best at35℃,300r/min.A spray combustion device was built, and the atomization combustion of bio-oil was done. The ignition temperature of bio-oil was high, so the spray droplets of bio-oil could be ignited when the combustion chamber was preheated up to about250℃and existed naked flame. The combustion could be stable in10minute. With complete combustion of bio-oil, the emission of CO was lower than80ppm, and the emission of NO was lower than100ppm. Both of them were met the boiler flue gas emission standards. The temperature of combustion device was increased by increasing the amount of bio-oil and air, increasing the inner diameter of the combustion device, and reducing the heat loss rate of combustion outdoor wall. The maximum temperature of combustion debvice was higher than1400K.Four chemical models with five compounds for condensable gas were built by a gas chromatography mass spectrometry (GC-MS) and a thermal analyzer (TG-DSC) of bio-oil. By comparing the elemental composition, moisture content and TG-DSC curves of bio-oil and its models, it was shown that the chemical composition of model with the smallest error were methanol, eater, ethanol, furfural and phenol, and its mass percentage were27.10,44.96,16.24,4.40and7.30, respectively. Chemical model with four compounds for non-condensable gas was built by a gas chromatography of the non-condensable gas, the chemical composition of it were CO, CH4, CO2and N2, and the mass percentage of model were32.16,4.44,38.58and24.81, respectively. By analyzing the gas-liquid mass ratio of pyrolysis liquefaction experiment, the chemical model of condensable gas and non-condensable gas were integrated, and the chemical model with nine compounds was built.Aspen Plus was used to simulate the condensation process of pyrolysis gas at700kg/h and450℃. The simulation results indicated that the mass flow of spray liquid was9107kg/h, the mass flow of cooling water was6522.8kg/h, and the outlet temperature of bio-oil was40℃. In this condition, the parameters of the tubular heat exchanger were that the heat transfer area was20.50m2, the total heat duty was192.4kW, and the total heat transfer coefficient was850.0J/(s-m2-K).A fractional condensation device was built. The thermostatic glycerin was used for contact condensation in the first stage, and the liquid nitrogen was used for indirect condensation in the second stage. The results showed that when the glycerin temperature was110℃, the quality of bio-oil which was collected in the second stage was the best. The quality of this bio-oil was the highest dry base heat value (28.90MJ/kg), the lowest water yield (9.3%) and the lowest acetic acid yield (0.368%). This condensing device can not only improve the quality of bio-oil, but also the primary separation was carried out on the water and acetic acid.Three-dimensional numerical simulation was performed to the combustion system by FLUENT and the results were similar to thermal analysis. The bio-oil combustion process could be divided into three stages. At first stage, the small molecules evaporated. At second stage, bio-oil burned and macromolecules cracked into char and small molecules, and then the small molecules burned in the combustor. At third stage, the char burned. In the second half of the combustion chamber, when the mass flow of air was constant, with the increase of the bio-oil mass flow, the combustor temperature increased firstly, then decreased. Meanwhile, the content of O2decreased, the content of CO2increased, the content of CO increased rapidly, and the content of NO changed little. Meanwhile, when the mass flow of bio-oil was constant and the excess air coefficient increased from0.8to1.4, the temperature of combustor was decreased slightly. This model could be used to simulate the combustion of bio-oil. |
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