废气自循环利用生物质炭化装备设计与性能研究

为有效解决现阶段生物质炭化设备存在的炭产率低、炭品质差、余气不能循环利用而污染环境、副产物不能有效分离等问题,设计并研制了一套废气自循环生物质炭化装备,对其炭化炉主体、加热系统、焦油回收装置、余气循环装置、温度压力监控系统分别进行了详细设计和参数确定,并以炭化炉主体和焦油回收装置为加热和冷却对象,采用有限元方法对其进行传热性能研究,最后对其进行了炭化试验研究。结果表明:生物质炭化装备能够满足制炭、副产物回收、废气循环利用、工艺参数精确控制等要求;炉体门框上部温度分布不均,其余炉体内部温度分布均匀,温度梯度平缓,可对生物质进行均匀加热;焦油回收装置在三级冷却水进口流速分别为0.045、0.03、0.015 m/s时,冷却温降分别为:271、111、61℃,烟气温度从500℃降温到50℃,冷却效果显著,并可对挥发分中的焦油和木醋液进行分离;影响炭产率、热值、能源得率的因素顺序为:炭化终温保温时间升温速率。炭产率与能源得率呈正相关,而两者又与热值成负相关。炭化条件在升温速率3℃/min、炭化终温450℃、保温时间3 h工况下较好,在此条件下的炭得率为54.2%,热值为25 767 k J/kg,能源得率为84.8%。

Design and performance of waste gas self-circulation biomass carbonization equipment

In the current, due to the shortage of energy, greenhouse effect and serious pollution of ecological environment, the development and utilization of biomass energy can meet the objective law of sustainable development, promote the adjustment of energy structure in China, reduce dependence on fossil energy, and increase the renewable energy utilization ratio. It can help to alleviate various ecological environmental pollution and damage caused by the current fossil energy use, and establish the clean renewable energy system. And it can be conducive to broaden the human energy utilization scope, alleviate the pressure of energy shortage and improve life quality of the people. Compared with biomass gasification and oil production, biomass carbonization has the advantages of low cost, low equipment requirement and is used widely. Except for being used as fuel, it can also be used to improve the soil adsorption of heavy metal, pesticides, pollutants, and so on, reduce greenhouse gas emissions and improve the water quality. Biomass pyrolysis technology has made some progress, but it still remains in the technology level of charcoal preparation in traditional kiln, and it has disadvantages of low carbon rate, poor quality, high labor intensity, poor working environment, serious environmental pollution, low efficiency and long period, so biomass carbonization is not applied in large area. In order to effectively solve the problems of the present biomass carbonization equipment of carbon preparation, such as low carbon yield, poor quality of the carbon, the surplus gas to pollute the environment, the by-products being not effectively separated, a set of biomass carbonization equipment with exhaust gas self-circulation is designed and manufactured. Carbonization furnace body, heating system, tar recovery device, gas circulation device, and temperature and pressure monitoring system are designed in detail and the parameters are set. The finite element method is used to study the heat transfer performance of the carbonization furnace body and tar recovery device. In the end, the carbonization test is carried out. The results show that the biomass carbonization equipment can meet the demand of carbon preparation, by-product recovery, waste recycling, precise control of process parameters for the furnace door frame. The upper temperature distribution is uneven, the internal temperature distribution of the furnace body is uniform and the temperature gradient of biomass can be smooth. The flow rates at the 3 cooling water inlets of the tar recovery device are 0.045, 0.03 and 0.015 m/s, respectively, and the temperature decline during the cooling is 271, 111 and 61 ℃, respectively. The temperature of flue gas cools from 500 to 50 ℃. The cooling effect is obvious, and volatile of tar can be separated from wood vinegar liquid. The influence order of the factors of carbon yield, calorific value and energy yield is as follows: Carbonization temperature > holding time > heating rate. The carbon yield has positive correlation with the energy yield, and both have negative correlation with the heat value. Considering comprehensively, the best carbonization conditions are the heating rate of 3 ℃/min, the carbonization temperature of 450 ℃ and the holding time of 3 h.