The objective of this project was to develop a robust, efficient, and compact syngas-cleaning system that would complement small-scale countercurrent, or updraft, gasifier technology. These gasifiers feature high efficiency and simple operation that would be beneficial for service as a waste-to-energy converter (WEC) at deployed military forward operating bases (FOBs), but are currently handicapped by the relatively high loading of condensable organics, tars, in the fuel gas.

This project was divided into the following four tasks: 

Task 1 – Tar-Cracking Reactor Optimization

Determine the catalyst bed configuration and operating conditions for the catalytic treatment of tars produced by the countercurrent gasification of a FOB waste stream.

Task 2 – Prototype System Performance Testing

Measure the sustained syngas-cleaning performance and heat recovery efficiency for the cleanup system using a prototype gasifier and cleanup system.

Task 3 – Integrated System Performance Testing

Integrate a diesel generator with the prototype system, conduct syngas cofiring tests to determine the overall conversion efficiency for the concept, and identify operational impacts to the military’s fleet of tactical generators.

Task 4 – WEC Design Analysis

Perform a design analysis of a deployable WEC using the findings from Tasks 1–3, and make a determination regarding whether the concept could meet the evaluation criteria.

Conceptual diagram showing the core concept of countercurrent gasification coupled with thermal catalytic tar cracking.

Results showed that the concept of using a countercurrent gasifier coupled with a catalytic tar-reforming stage can be a viable route to meet the performance targets established for FOBs—overall WEC operating efficiency of 50%, physical size constrained to a single 8-ft by 8-ft by 20-ft International Standards Organization transport container, and simple operation and minimal maintenance requirements. Data analysis from the prototype testing showed that the concept could exceed the conversion efficiency target of 50% with relatively straightforward improvements to sensible heat recovery from the clean syngas leaving the tar reformer. The analysis also showed the value of incorporating an integrated waste dryer using heat from the electric generator exhaust stream or other low-quality heat source. With relatively dry waste, the WEC’s net conversion efficiency could exceed 60%, and at the scale of a Force Provider base camp, the net WEC electrical generating potential would be approximately 10% of the entire base’s generation capacity. Over an 8-hour processing shift, a WEC under these conditions would displace approximately 100 gallons of diesel fuel.

In addition to the potential for high energy conversion, this project also substantiated the operational benefits associated with countercurrent gasification. The prototype produced a clean syngas that will minimize the frequency and severity of routine maintenance, and after passing through the system, the processed waste was fully converted to inert ash, thereby achieving the volume reduction and sanitized ash goals. The steps identified for system operation appear to be suitable for automatic control and would conceivably only require significant user oversight at start-up and incremental fuel loadings. The operator burden is estimated to be approximately 1 hour per 8 hours of waste processing.