升温方式对中试鼓泡流化床气化过程的影响

Effect of heating style on gasification process of pilot scale bubble fluidized bed

为了研究中试鼓泡流化床升温过程特性,试验以木屑为原料,处理量50kg/h的自供热中试鼓泡流化床为反应装置,采取3种不同的升温方式进行空气气化试验研究。升温过程分别采用木屑、木屑与木炭混合、木炭为加热原料,针对气化前期系统升温过程中的气化温度、焦油含量、气体品质及最小流化速度进行了研究。结果表明:采用纯木炭的升温方式效果较为理想;气化主反应区温度控制在900℃以上,温度及升温速率的提高有利于减少焦油生成量,实测焦油含量为1.15g/m3;空气气化时热值可达6.9MJ/m3;最小流化速度受床料粒径和升温速率影响。该试验可为自供热中试流化床试验平台的升温方式提供一种设备简单,操作方便、快捷,经济性好的新方法。

In order to study the heat process characteristics of pilot scale bubbing fluidized bed, by using the self heating pilot scale bubbling fluidized bed reactor of 50 kg/h in capacity, with sawdust as raw material, the experimental study on air gasification were conducted. At present, the externally heating for the fluidized bed startup was widely used in bench scale experiment. It had the advantages of rapidly raising of temperature, accurate control, etc., but the equipment was complex and difficult for maintenance, and was higher energy cost, especially, the externally heating was quite different with that for practical utilization. It is not helpful for find out the reaction characteristics so that the guiding for practical utilization was weakened. For solving the problem, using the pilot scale fluidized bed reactor as experimental device which is self heated, continuously fed and operated, air gasification experiment study on 3 temperature raising modes were conducted. Three temperature raising modes, which were sawdust combustion heating, sawdust/charcoal mixture combustion heating and charcoal combustion heating, were adopted respectively. The influence of different temperature raising ways on gasification temperature, tar content, the minimum fluidization velocity and gas quality in the process of gasification has been studied. The results showed that the heating effect of charcoal combustion was more ideal, and its heat value of charcoal was up to 32 MJ/kg, thus the heat released was much larger than that of sawdust. It provided more heat for bed heating process. In the preheating process, the warming up process was faster in the first hour, along with the increase of bed height, the heat storage in the bed material was also increased, and the heating rate was steady. It took 2.5 h for the gasification reactor to reach the reaction temperature. Due to the complexity for adding bed material and charcoal in the reactor, the optimization on the feeding device and the relevant measures will be the next step of work. The gasification reaction temperature could be controlled above 900℃, the higher temperature and heating rate favor the reduction of tar content, tar content at the gas outlet was about 1.15 g /m3. Due to the charcoal combustion providing more heat to the bed materials and the raising of temperature in the reactor, which was better than the other two heating modes. Increasing the temperatureT2and the heating rate would benefit the reduction of tar content in the producer gas, thus, the heating with charcoal combustion could reduce the tar content in the producer gas and relief the gas purification process, meanwhile, the heating mode of charcoal combustion provided more heat for the gasification reactor in the preheating process and enhance the gasification intensity, which benefited the gasification reaction. The heat value of the producer gas was up to 6.9 MJ/m3,the producer gas quality was better than those of the other two heating modes; the bed temperature was also different in different heating modes. In the thermal experiment, the bed temperature had obvious influence on the minimum fluidization velocity, and it was different even in the same heating mode. The results showed that the minimum fluidization velocity tended to be influenced externally. The minimum fluidization velocity was affected by bed material particle size and heating rate, the minimum fluidization velocity was increased along with the increasing of the bed material particle size. The heating rate was fast, the small minimum fluidization velocity was low, and vice versus. This experiment can be self heating pilot fluidized bed experimental platform heating mode provides a new method of simple equipment, fast operation, good economy.