顶部点火上吸式固定床中农业废弃物气化特性分析

Gasification property of agriculture wastes in an updraft fixed bed gasifier with top-lit ignition

为了了解在固定床气化炉中生物质的气化特性和炉内温度演变规律,该研究采用顶部点火上吸式(top-lit up draft,简称TLUD)固定床气化炉研究了农业废弃物的气化行为,重点考察了不同空气流量下炉内温度分布、燃气成分和热值的变化规律,探讨了生物质气化过程机理。结果表明,气化过程明显分为2个阶段,即挥发份的析出和焦炭的缓慢气化。整个气化过程中燃气的热值可稳定维持在3MJ/m3以上,温度场的演变过程与波传递具有相似性,花生壳和稻壳的最佳空气当量比分别为0.31和0.35,且其燃气中焦油含量很低,分别为0.25、0.49g/m3。该研究为TLUD固定床气化炉的设计和运行提供了有益的参考。

The gasification behavior of agriculture waste was investigated using a Top-lit Up Draft （TLUD） fixed-bed gasifier system which consists of four subsystems （gasifier reaction system, temperature monitor system, tar sampling system, and gas measurement system）, in an attempt to find out the influence of air flow on the gasifier’s temperature distribution, gas component, and heating value, and discuss the gasification mechanism of biomass. In the study, peanut shells and rice husks were chosen as experiment material. The reactor is made from Ф219 mm×6 mm stainless steel pipe with length of 800 mm. After the reactor filled up with sample materials （about3.5 kg）, a certain amount of air （range from2.5 m3 /h to 4.0 m3 /h） was pumped in at the bottom, and the sample was lit at the top. The temperature was then tested by a temperature monitoring system, and the gas product was detected by a Gasboard-3100P-type multi-component portable infrared gas analyzer （Quartet Photoelectric Technology Co., Ltd. Wuhan, China）, and the tar was collected by a tar sampling system. From the results of the investigation, the gasification process lasted about 100 min, and was divided into two stages. First, the main reaction was biomass drying, volatile releasing, and char gasification, and the main gas products were CO2 , CO, H2, and CH 4 . About 50 min later, it went into the second stage, and the oxidization of solid char residue played a major role in the gasifier with a large amount of CO production. Throughout the whole reaction, the heating value of gas products was a minimum of3 MJ/m3 , and the evolution of the gasfier temperature profile was very similar with that of wave propagation. During the first stage of gasification, the maximum temperature of the gasifier was 730℃; when it switched into the second stage, the main reaction occurred at the bottom, and the max temperature would rise up to 1000℃. The airflow rate can be converted to the Air/Fuel equivalence ratio （ER）, the most important aspect of gasifier operation. ER had great influence on biomass gasification property, and higher ER was favorable for the enhancing of gas yield, however, it had different effects on the releasing of flammable gas （CO and H2 ）. The optimum gasfication condition was achieved when ER is 0.31 and 0.35 for peanut shell and rice husk, respectively, and the tar content of gas is very low （as low as 0.25g/m3 and 0.49g/m3 , respectively）. This study would be helpful to the design and operation of TLUD fixed-bed gasifiers.