Study On Combustion Mechanism Of Ultra-low Calorific Gas In Module Porous Media With Annular Seam Regenerative Heat Transfer Type

In order to improve the unreasonable energy structure and the resulting ecological pollution problems,it has a great significance to develop the technology of value porous media combustion with ultra-low calorific gas in a high efficient and low pollution way.In the utilization of ultra-low calorific value gas,porous medium combustion has become one of the key research directions in combustion technology because of its unique advantages.It is of great theoretical and engineering significance for developing new type burners to study and master the influence of internal modular arrangement structure of porous media on Combustion Characteristics and its internal combustion mechanism.In this paper,a modular porous media structure with both axial and radial apertures changing was developed,and an annular space outside the combustion chamber was designed for intensified preheating.Meanwhile,the heat adaptability,combustion intensity range and pollutant emission of ultra-low calorific value gas combustion were experimentally and numerically studied,respectively.The research results provide experimental and theoretical guidance for the development of new burners suitable for ultra-low calorific value combustion and the realization of efficient and clean combustion.The main research contents and achievements are as follows:The effects of different structures on preheating time of homogeneous and gradual porous media were studied,and the effect of preheating temperature on the combustion of ultra-low calorific value gas was also revealed.It is found that preheating temperature plays an important role in stable combustion of ultra-low calorific value gas.In detail,the gradual structure can better promote the heat return and combustion than the uniform structure.Thus,the effects of calorific value and preheating temperature on CO emission from combustion products were obtained.In this paper,the experimental platform of low calorific value gas combustion in the annular slot regenerative modular porous media was built.The modular porous media structure was designed with both axial and radial aperture changes,and an annular space was arranged outside the combustion room to strengthen preheating and heat storage.In this experiment,the effects of different modular porous media structure on the adaptability of ultra-low calorific value gas,combustion intensity range and CO emission of combustion products,as well as the effects of adding metal fiber into the inner and outer cylinder circumferential slots on combustion characteristics were studied in detail.It is found that different modular structures in porous media can change their adaptability to calorific value.The results show that the modular structure can make the combustion of gas with lower calorific value stable and the addition metal fiber in the annulus can promote the combustion and flame stability of ultra-low calorific value gas.At the same time,the influence of modular structure on CO emission from combustion products was studied.The influence of different arrangement of porous media on CO emission was obtained.The optimization of modular layout structure can reduce CO content in combustion products,which is more conducive to the control of pollutant emissions.The mechanism of reducing pollutant emissions by changing the modular structure of porous media is revealed.In order to reduce the CO production,an experimental study of reducing CO content by introducing water vapor was carried out,which was succeed by introducing the water vapor entering the burner and being pyrolyzed to produce OH-.It is found that the temperature of combustion chamber changes little after adding water vapor,but the content of CO in combustion products decreases.This paper analyzes the mechanism of reducing pollutant emission by introducing water vapor,and provides a solution and research direction for reducing pollutant emission in ultra-low calorific value gas combustion.In this paper,the numerical model of ultra-low calorific value gas combustion in modular porous media is established,and the effects of different ignition positions,different preheating temperatures,different combinations of structures and metal filling in the annulus on combustion characteristics of porous media were also carefully studied by numerical simulatio.The results showed that ignition in the exit side was better than in the inlet side.When the preheating temperature was low,the combustion was unstable,which means that preheating temperature is an important factor to the stable combustion of ultra-low calorific value gas.In addition,filling metal fibers in the annular gap between the inner and outer cylinders can strengthen the preheating of premixed gases,which also increased the overall temperature of the combustor and slow the flame propagation downstream,and then leading to a more stable combustion.Through comparative analysis,the effect of gradual change and modular structure on combustion stability and regeneration was better than that of uniform structure.Compared with gradual change structure,the downstream temperature of modular structure was lower,which shows that modular structure has better effect on heat return.The combustion mechanism of ultra-low calorific value gas in annular regenerative modular porous medium burner was studied through numerical methods.Through numerical study of three typical modular structures,the adaptability of different modular porous media to calorific value,the range of combustion intensity and the rule of pollutant emission were summarized when realizing stable combustion of ultra-low calorific value gas.The results showed that different layout structures had different calorific adaptability to ultra-low calorific value gas,and the corresponding combustion intensity limits were also different.In detail,the structure with larger pore size along the flow direction has better combustion characteristics and lower pollutant emission than the structure with smaller pore size along the flow direction,which is because of the radiation heat transfer.Meanwhile,the research on pollutant emission showed that with the increasing gas calorific value,CO emission decreases with combustion chamber temperature increasing,and a reasonable modular structure can improve its calorific value adaptability,stable combustion limit range and CO emission.Finally,the influences of modular structure on calorific value adaptability,combustion intensity limit and pollutant emissions were revealed preliminarily,which confirmed different modular structures can optimize the combustion characteristics of ultra-low calorific value gas,and then a better modular structure scheme was proposed.