脱灰预处理对水稻秸秆物化性/水蒸气气化反应特性的影响

在固定床反应器中研究了水洗、不同浓度酸洗预处理对水稻秸秆物化性/水蒸气气化反应特性的影响。结果表明,水洗处理后稻秆中的钾、钠脱除率分别为90.5%和82.1%,酸洗处理后稻秆中的钾脱除率达到99.2%,而钠脱除率随酸种类略有差异,在84.6%~92.3%;酸洗并未改变稻秆中主要组分含量,但破坏了稻秆微观物理结构。比较不同浓度酸洗后稻秆的孔容、孔径分布、BET比表面积发现,各指标的排列顺序均为水洗稻秆>3%硫酸洗后稻秆>原稻秆>7%硫酸洗后稻秆>10%硫酸洗后稻秆;各种预处理酸的浓度均为3%时,硫酸洗后稻秆的孔容、孔径分布、BET比表面积最大,而磷酸洗后稻秆各指标则最小。水蒸气气化结果表明,钾、钠及丰富的孔径结构均能促进H₂的生成,且钾、钠对气化过程的作用明显强于孔径结构对气化过程的影响。水洗稻秆气化产气中H₂、CO₂的瞬时释放浓度高于酸洗稻秆;CO、CH₄则相反。4种酸的浓度为3%时,稻秆气化中H₂、CO₂瞬时释放浓度与稻秆孔径分布呈正相关性;CO、CH₄瞬时释放浓度则与稻秆孔径分布呈负相关性。4种酸浓度为3%时,孔径越丰富,气化速率越快。脱灰预处理虽降低了稻秆气化氢气产率,但提高了气化气体热值。

Influence of deashing pretreatments on physicochemical properties and steam gasification reaction characteristics of rice straw

The influences of water-leaching and different concentration acid-leaching pretreatments on physicochemical properties and steam gasification reaction characteristics of rice straw (RS) were investigated in a laboratory fixed-bed reactor. The results show that after water-leaching, the potassium and sodium in RS are removed by 90.5% and 82.1%, respectively, and after acid-leaching, the removal of potassium from RS reaches to 99.2%, and the removal efficiency of sodium with acids is between 84.6% and 92.3%. Acid leaching does not change the main component content of RS, but destroys the microscopic structures of RS. The order of different concentration acid-treated RSs with respect to the three indexes including pore volume, pore diameter distribution and specific surface area is: all water-leached RS > 3% sulfuric acid-treated RS > raw RS > 7% sulfuric acid-treated RS > 10% sulfuric acid-treated RS. As the concentration of various pretreatment acids is 3%, the sulfuric acid-treated RS has the largest values of the three indexes and the phosphoric acid-treated RS has the smallest values of the three indexes. The steam gasification results show that potassium, sodium and abundant pore structure all can promote hydrogen generation, and the effects of potassium and sodium on gasification process are significantly stronger than pore structure. The H₂ and CO₂ instantaneous release concentration for water-leached RS is higher than that for acid-treated RS during gasification; however, it is contrary to CO and CH₄. When the four acids concentration is 3%, there is a positive correlation between H₂ and CO₂ instantaneous release concentration and the pore diameter distribution; and there is a negative correlation between CO and CH₄ instantaneous release concentration and the pore diameter distribution. The more abundant the pore, the faster the gasification rate. Though deashing pretreatment decreases the H₂ production, it increases the calorific value of gasification gas.