An Improved Pyrolyzer for Solid Waste Resource Recovery in Space

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The overall objective of this study was to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process a maximum of about 0.5 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600 °C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N₂ purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000-1100 °C. The tars are cracked into carbon and additional gases. Most of the deposited carbon is subsequently gasified by oxygenated volatiles (CO₂, H₂O) from the first stage. In a final step, the temperature of the first stage can be raised and the purge gas switched from N₂ to CO₂ and/or O₂ in order to gasify the remaining char in the first stage and the remaining carbon deposits in the second stage. Alternatively, the char can be removed from the first stage and saved as a future source of CO₂ or partially gasified to make activated carbon. This paper describes several improvements that were made in the original (First Generation) prototype pyrolyzer including: 1) replacement of stainless steel flanges with machineable ceramic in order to reduce weight; 2) construction of a new sample holder in order to make sample insertion and removal easier and sample heat-up more uniform; 3) replacement of a stainless steel outer shell with a double-wall quartz cylinder in order to significantly reduce weight and heat losses. In addition, experimental results are included for wheat straw and chicken manure feedstocks, primarily from the First Generation prototype.