The U.S. Department of Defense (DoD) has a strong interest and focused need to reduce the logistics tail associated with forward operations. Activities associated with mission sustainment at forward operating bases (FOBs) and combat outposts (COPs) present significant challenges with respect to fuel and water supply, and waste footprint management. Waste to energy conversion (WEC) systems present a promising option for managing waste burdens while providing supplemental energy/heat. While a number of gasification and pyrolysis-based WEC systems are currently under evaluation by DoD, no system has been demonstrated to meet PM Force Sustainment Systems’ (PM FSS) desire for a compact (8’x8’x20’), efficient (50% net chemical energy recovery), and robust (field-worthy, minimal operator interface) WEC system.

The overall objective of this project was to design, fabricate, and characterize a downdraft gasification system capable of reliably and efficiently converting shredded (single-stage), co-mingled (paper, food, plastic, and wood) waste into a clean-burning syngas suitable for use in either a spark ignition or diesel cycle generator set.

This project focused on the development of a flow optimized downdraft gasifier. IST’s stratified downdraft gasifier served as a baseline against which to develop enhancements. The six primary tasks to the research and development effort, all executed in an iterative fashion until program completion, were to (1) define needs, (2) characterize material flow, (3) model air flow, (4) design and fabricate the gasifier modifications, (5) experiment, and (6) analyze and evaluate results.

Through this project, a containerized gasification system capable of processing shredded mixed waste streams has been conceived. The system will feature a preprocessing system that represents a significant departure from the one utilized for a pellet-fed gasification system. To select the final configuration, flow simulations were completed to model secondary air penetration within the system. The shredded waste gasifier was also demonstrated in a laboratory environment to achieve bulk solids flow without stagnation due to bridging or arching. This was achieved with both paper/cardboard and food/plastic/paper/cardboard feedstock. Finally, a scaled-up diverging downdraft gasifier capable of processing three tons of mixed waste per day was designed.

The anticipated advantages of the new downdraft configuration are a reduced system weight and a reduced system cost. Additional benefits of using WEC systems for FOBs include:

• Dramatic reduction of the footprint and logistics burden associated with waste management.
• Generation of electricity from co-mingled waste.
• High thermal efficiency to reduce dependency on liquid fuel for on-site field uses.
• Deployable and compact to minimize logistics transportation support and on-site field set-up.
• Reliability with minimal operator and soldier interface, and minimal field system maintenance.