Combustion Simulation And Experimental Research On Housed-hold Biomass Gasification Stove

Currently, as the environment and energy crisis is becoming even more aggravating, It is an important task for human being to explore and utilize the renewable energy. Biomass recourse as one of the renewable energy, various related technology have being developed. Biomass thermal pyrolysis gasification technology, as one of the most important Energy conversion technologies, is getting more and more attention. However, the present gasification stoves in the market have lots of problems, such as the complex structure, tough operation, tar problem, and so on. Rural China areas can provide abundant biomass materials for Household Biomass Gasification Stove, and stoves are very suitable for rural area for its advantages with simple structure, economic and practical, operational. Biomass energy utilization will dramatically promote rural energy saving and environmental protection.In this subject, it did some experiments combined with CFD simulation analysis for a new type of up-down-draft stove. The stove structure integrates updraft and down-draft fixed-bed gasifier and takes the advantages of them, which is developed for the hope of overcoming the defects and problems existing in the application of current stoves in the market. The preliminary research in this subject provides some basic performance parameters to further improvement and points the way to further design and investigation.In the experiment, as the gasification agent air mass flow injected increased, the oxygen layer thickness in gasifying chamber increased, the stove temperature became higher, gasification intensity increased, and also thermal power increased. While the stove was working in low power conditions, the performance of the gasification stove was steady which can be used of continuous heating for rural user energy daily required. Contrarily, while the stove power was larger than a level, the performance was unsteady which could only provide intermittent heating. So there is a problem to be resolved next.The study was also made a research on different coefficient of excess air cases. When the coefficient of excess air was in the range of 1.2 to 1.3, the mixture fuel gas combustion flame was steady, and left less combustible ingredients and pollutions in smoke emissions. However the result also showed that temperature of the smoke exiting from outlet was higher and the heat exchange in the furnace was insufficient. So there is still room to make some changes in stove geometrical structure to further improve the heat exchange effect.In the subject, it employed the software STAR-CD to have CFD flow and combustion simulation. In the calculation, some simplifications and assumptions were necessary, and it chose the appropriate turbulence flow and combustion model and heat radiation model. The parameters including velocity, the temperature and concentration were predicted, the results showed that: when just flow were calculated, biomass syngas were converged at the circle premixing plenum and mixed, then the premixed gas were into the furnace through the hole located in the inner plenum wall, where the turbulent kinetic energy was much more powerful and the premixing process took well for their combustion in the furnace; when combustion occurred, the firing flame happened almost in the central area of furnace, forming the high temperature area, where there is also the product species high concentration area. As a result of the resistance of the upper water space wall, the flame was forced to the round in the furnace, so the unburnt gas could burn again, and then the temperature rose and the product species concentration increased. In conclusion, the prediction had a good agreement with the experimental results, so the simulation models used in the paper was generally reasonable.According to the issue mentioned above, the present furnace volume was small, the gas couldn't burn completely, heat exchange was not wall, and it was difficult to perform at high power for a long time, so works had to be done to improve the stove geometrical structure in the simulation model, as decreased the holes to 6 or elevated the furnace up to 200mm. Then the calculations were made in the same CFD method and models to have a simulation for new improved structure. It shows that for the holes decreased, the inject velocity increased, turbulent kinetic energy enhanced, the premixing process took well; in the 200mm furnace, absolutely the volume increased, and the retention time was prolonged, then the combustion and heat exchange took well, the unburnt fuel concentration in the emission decreased. The predictions showed that the improved structure enhances heat exchange between smoke and coolant, which decreases dramatically the outlet smoke temperature and also reduces pollutants in emissions.Briefly speaking, it provides a new practical method to improve the structure of the next generation product for house-hold biomass gasification stove by means of this experiment research combined simulation prediction. The results obtained here can be very useful for further investigations and applications.