基于生物质活性炭可控构建下太阳能干燥除湿回热运行特性研究

In this project, the hot and humid air flow derived from the solar drying system was treated by solid desiccant in order to realize the dehumidification and heat recovery. The double benefits of recovering the heat energy and protecting the environment would be attained. The dehumidification and heat recovery in solar drying system were investigated by means of theoretical analysis, numerical simulation, material characterization and experimental process. Firstly, Agricultural by-products such as tobacco stems and walnut shells were proved to be promising raw materials for the preparation of biomass-based activated carbons because they were widely available and low-cost. The pore structures, surface oxygen functional groups, and active components of the biomass-based activated carbons were characterized systematically and scientifically at different preparation conditions. The relationship between the preparation conditions and these characteristics of the biomass-based activated carbons was quantified. The water adsorption capacity and regeneration temperature of these adsorbents were also optimized at different preparation conditions. The novel biomass-based activated carbons with big adsorption capacity and low regeneration temperature were obtained and its preparation method was identified. Secondly, the fixed bed filled with the biomass-based activated carbons was used to study the dehumidification and heat recovery characteristic in solar drying system theoretically and experimentally. The characteristic parameters of the adsorbent, the structural parameters of the fixed bed and the operation parameters were analyzed in terms of the humidification efficiency of the fixed bed. And the operational characteristics was investigated systematically under the various parameters and operation conditions. Finally, the water adsorption mechanism onto the biomass-based activated carbons was proposed under the hot and humid atmosphere of the solar drying system. The target of this project coincides with the requirements of utilizing the energy-saving technology and renewable energy in our country. These research results will lay a theoretical foundation and methodology of the dehumidification and heat recovery in solar drying system.

基于固体除湿方式对太阳能干燥后的湿热气流进行除湿回热，可实现热量回收和环境保护的双重效益。本项目拟建立材料制备表征分析、实验测试、数值模拟与理论分析相结合的研究方法，选用成本低廉、来源广泛的农林废弃物烟杆、核桃壳等为原料，分析制备过程与生物质活性炭孔结构、表面含氧官能团、活性组分之间的影响规律，获得循环吸附量大且再生温度较低的生物质活性炭可控构建方法；建立生物质活性炭固定床除湿回热系统和传热传质理论模型，深入分析吸附剂物性参数、固定床结构参数和运行参数对生物质活性炭固定床除湿回热效率的影响规律并进行实验验证，阐明多参数变工况条件下生物质活性炭固定床除湿回热运行特性，揭示基于太阳能干燥湿热气氛条件下生物质活性炭水蒸气吸附作用机理。项目符合当前国家积极发展节能技术和可再生能源的要求，为太阳能干燥系统高效除湿回热的实用化发展提供理论依据和方法。

本项目以实现太阳能干燥系统高效除湿回热为目标，完善了生物质活性炭制备、表征及吸脱附性能测试平台，以生物质资源——核桃壳、烟杆和咖啡壳为原料，采用物理活化法、化学活化法、物理化学联合活化法研制了适宜水蒸气吸附的生物质活性炭，通过亲水性盐负载和十二烷基苯磺酸钠改性两种手段，进一步提升了生物质活性炭的水蒸气吸附能力，利用现代分析测试技术对生物质活性炭的孔结构特性、表观形貌特征、表面官能团和热解特性进行了分析测试表征，分析制备过程与生物质活性炭孔结构、表面含氧官能团、活性组分之间的影响规律，获得了循环吸附量大、再生温度较低且稳定性较高的生物质活性炭可控构建方法。建立了以Do-Do水蒸气吸脱附等温理论模型为基础的有限简化模型，获得了水蒸气在生物质活性炭上的吸附平衡、吸附热力学和吸附动力学基础数据，结合现代分析测试表征方法探究了生物质活性炭孔结构特性、表面官能团、活性组分在水蒸气吸附过程中的变化特征，提出特定太阳能干燥湿热气氛下水蒸气在生物质活性炭上的吸附作用机理：在较低的相对压力下，水蒸气分子首先吸附在活性炭表面吸附中心、含氧官能团及其他吸附中心位点，这些活性位点诱导水分子移动，并在活性位点和水分子之间形成氢键，进而在生物质活性炭中发生水蒸气吸附行为。随着相对压力的增加，水分子继续进入生物质活性炭中并被吸附在先前已吸附在活性位点上的水分子上形成水分子簇，生物质活性炭的水蒸气吸附速率也随之增加，累积吸附量增加越快。当水分子簇大小达到一定程度时，水分子簇进入微孔形成微孔填充，直到水蒸气吸附饱和。建立了生物质活性炭固定床吸附除湿回热系统和传热传质理论模型，深入分析吸附除湿过程运行参数对生物质活性炭固定床除湿回热效率的影响规律并进行实验验证，阐明多参数变工况条件下生物质活性炭固定床除湿回热运行特性。研究成果为太阳能干燥系统高效除湿回热的实用化发展提供理论依据和方法。