VALORIZATION OF SOLID DIGESTATE THROUGH AUTOTHERMAL HYDROTHERMAL LIQUEFACTION

该项目探索了解决日益增长的湿废物问题的新方法，从农场生产的动物粪便到食品行业加工水果和蔬菜的废水。湿废物通常比固体废物含有更多的水分，阻碍了垃圾在垃圾填埋场的正常运输和储存或焚烧处理。取而代之的是，通常采用生物工艺来处理湿废物，但这些工艺速度慢，往往会留下大量需要特殊处理的固体残留物。该项目探索水热液化(HTL)过程，这是一种高温、高压过程，将氧气溶解到湿废物中，将这些废物转化为液体燃料，而不需要外部能源驱动该过程。通过将废物转化为液体燃料，该过程既消除了废物，又产生了有价值的产品。如果成功，该项目将提供新的方法来扩大HTL工艺，使其可用于更普遍的用途，从而加强国家的能源安全，同时减少农业和其他食品行业的废物数量。该项目还将培训博士后研究人员研究生，通过使用由首席研究员指导的分层指导方法，有效地指导他们自己的学生在未来的工程工作中。该项目的目标是通过直接耦合自热操作来强化热液液化(HTL)。这一操作将克服向该过程提供能量的热传递瓶颈，并允许扩大到商业用途。爱荷华州立大学之前的研究表明，通过向反应堆中引入少量空气，快速热解炉可以进行自热操作。与传统的(非氧化)热解相比，氧气的增加使产量增加了三倍，而生物油生产的损失最小。这项研究提出了一种类似的HTL反应器的自热操作，通过部分氧化一些低值水相液化产物来为该过程提供热焓。假设氧将优先溶解在HTL产品的水相组分中，在那里它很容易与溶解的有机物反应。相比之下，更有价值的生物原料油，悬浮在水相组分中的乳状液，接触到的溶解氧要少得多，不会发生实质性的氧化。该项目的方法是开发一种热量计高温气相沉积反应器，它将允许在高温气相沉积过程中测定动物粪便厌氧消化固体沼气的能量流动和产品组成。在惰性和氧化环境下的实验将确定液化的热能可由价值较低的液化产物的部分氧化提供的程度。除了大气条件下溶解固体的湿式氧化外，有机化合物在高温、高压水环境中的氧化研究很少。如果成功，这项研究将有助于修复美国每年产生的大约565兆克的湿垃圾。此外，这项工作中实施的科学和工程原则将作为HTL过程强化处理一系列湿废物所需的基础研究，这些湿废物包括农业残渣、食品废物、市政固体废物、污水污泥和动物粪便。一个正式的博士后研究人员和研究生指导结构，加上对幼儿园到12年级学生的有效接触，将有助于在这些工程实践中激励和培训未来的研究人员。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project explores new ways to address the growing problem of wet wastes ranging from animal manure produced on farms, to wastewater from processing fruits and vegetables in the food industry. Wet wastes usually contain more water than solid material wastes, preventing the normal transport and storage at landfills or treatment by burning. Instead, biological processes are often employed to treat wet wastes, but these processes are slow and often leave a significant solid residue requiring special disposal. This project explores the hydrothermal liquefaction (HTL) process, a high-temperate, high-pressure process that dissolves oxygen into the wet wastes, to convert this waste into liquid fuel without requiring external energy sources to drive the process. By turning waste into liquid fuel, the process both eliminates the waste and generates a valuable product. If successful, this project will provide new ways to scale up HTL processes to make them available for more common use, thereby strengthening the Nation’s energy security while reducing the amount of waste from agriculture and other food industries. This project will also train postdoctoral researchers graduate students to effectively mentor their own students in future engineering efforts through the use of a tiered mentoring approach guided by the lead investigator.This goal of this project is to intensify hydrothermal liquefaction (HTL) through directly coupled autothermal operation. This operation will overcome the heat transfer bottleneck of providing energy to the process and allow for scale-up to commercial use. Previous research at Iowa State University demonstrated autothermal operation of a fast pyrolyzer by admitting a small amount of air to the reactor. This increase in oxygen achieved a three-fold increase in throughput compared to conventional (non-oxidative) pyrolysis with minimal loss in bio-oil production. This study proposes a similar autothermal operation of an HTL reactor, providing the enthalpy for the process through partial oxidation of some of the low value aqueous phase products of liquefaction. It is hypothesized that oxygen will preferentially dissolve in the aqueous fraction of HTL products where it will readily react with dissolved organics. In contrast, the more valuable biocrude, an emulsion suspended in the aqueous fraction with far less exposure to the dissolved oxygen, will not substantially oxidize. The approach to this project is to develop a calorimetric HTL reactor that will allow energy flows as well as product composition to be determined during HTL of solid digestate from anaerobic digestion of animal manure. Experiments under both inert and oxidative environments will determine the extent that the enthalpy for liquefaction can be provided by partial oxidation of the less valuable products of liquefaction. The oxidation of organic compounds in high temperature, high pressure aqueous environments has been little studied outside wet oxidation of dissolved solids at atmospheric conditions. If successful, this research will help remediate the approximately 565 teragrams of wet waste generated annually in the United States. Additionally, the scientific and engineering principles implemented in this work will serve as foundational research required for the process intensification of HTL for a range of wet wastes including agricultural residue, food wastes, municipality solid wastes, sewage sludge, and animal manure. A formal postdoctoral researcher and graduate student mentoring structure, combined with effective outreach to kindergarten through twelfth grade students, will help inspire new and train future researchers in these engineering practices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.