面向生物甲烷过程的生成焓估算新思路与极限能耗的应用

Biomass converts to biomethane effectively has three strategic significances of energy saving, emission reduction and resource. In this project, we will calculate the theoretical energy consumption of straw’s fermentation process to optimize its technology. With the help of theoretical analysis, the key of the theoretical energy consumption determination is the estimation of the enthalpy of formation of straw, biogas slurry and biogas residue. The enthalpy of formation of straw and biogas residue are calculated via a reasonable thermodynamic cycle, whose key problem is the estimation of the enthalpy of formation of solid residue that from the combustion of straw and the gasification or pyrolysis of biogas residue. Activity coefficient of organic matter in biogas slurry is estimated to make the estimation accuracy of the enthalpy of formation of biogas slurry highest. Owing to straw contains polymer and its components can not be determined, the enthalpy of formation estimation of straw can not select the discrete component method used in the construction of the relation between the enthalpy of formation of biogas slurry/biogas residue and component. Thus, the distribution function of straw’s composition with molecular weight as variable is obtained by Gel Permeation Chromatography, then a general accurate estimation model between the enthalpy of formation of different straws and composition is built based on the continuous thermodynamics. Because of the predictability advantage of thermodynamics, the potential of energy saving can be pointed out and the technology optimization of straw’s fermentation process can be instructed by comparison the actual energy consumption with the theoretical energy consumption.

低劣生物质高效转化制生物甲烷兼具节能、减排、资源化的三重战略意义。本项目以低劣生物质中秸秆为研究对象，以获得极限能耗来优化发酵过程工艺为目标，根据理论分析可知，计算极限能耗的关键在于秸秆、沼液、沼渣生成焓的估算。本项目通过建立合理的热力学循环来计算秸秆、沼渣生成焓，其关键在于秸秆燃烧过程及沼渣气化或热解过程产生的固渣生成焓的估算；通过估算沼液中有机质等活度系数以使沼液生成焓估算精度更高；因秸秆内含聚合物，组份无法确定，因此无法像建立沼液和沼渣生成焓与组成的关系式那样用离散组份法。本项目基于连续热力学方法，通过凝胶渗透色谱/体积排阻色谱得出以分子量为自变量的秸秆组成的分布函数，最终建立不同类型的秸秆生成焓与组成相关联的通用精确估算模型；利用热力学具有可预测性的优势，通过极限能耗与实际能耗对比，指出发酵过程节能的潜力，指导发酵过程工艺的优化，为生物甲烷中的秸秆发酵过程的设计开发提供理论基础。

本项目以生物甲烷过程为研究背景，开展相关理论模型和实验研究。（1）将火灾领域的物质燃烧释放的热量计算模型延伸到生物质领域并加以修正，从理论上提出一种生物质高位热值简单估算模型，与文献中最新的15个模型相比，其形式简单且精度最高。通过上述估算模型最终建立了不同类型的生物质生成焓与组成相关联的通用精确估算模型；（2）提出了一个新概念——每还原度化学有效能，基于此建立了生物质化学有效能的简单估算模型，通过78种生物质计算发现每还原度化学有效能可视为常数，故我们提出的估算模型不仅形式简单、精度高，关键在于其具有理论意义。通过化学有效能估算模型计算获得生物甲烷过程极限能耗，指出发酵过程的节能潜力；（3）探索了生物甲烷过程产物沼渣的资源化利用途径，成功地将沼渣一步法制备出比表面积1297m2/g、孔容0.96cm3/g和亚甲基蓝最大吸附值476mg/g的活性炭，提出了利用沼渣制备的活性炭来提高生物质发酵过程产气率这样的生物甲烷过程系统内部循环新思路；（4）对于生物质高位热值的量热装置氧弹量热仪，将其扩大为燃烧法合成材料的新技术之一，该技术大大缩短反应时间且产物纯度高、形貌好。上述研究完成了项目立项时所设定的研究内容和目标。