Use of Pyrolysis Processing for Trash to Supply Gas (TtSG)

Technologies that reduce logistical needs will be a key component of long term space missions. For this reason, NASA has recently begun a Logistic Reduction and Repurposing (LRR) project. This project involves four hardware oriented tasks: 1) conversion of logistical items to useable products using Heat Melt Compactor (HMC) processing; 2) conversion of trash to supply gas (TtSG) in order to make propellants (e.g., CH4, H2) from solid waste products; 3) use of an Advanced Clothing System (ACS) to reduce mass, volume, and flammability; 4) use of Logistics-to-Living (L2L) technologies to repurpose launch packaging containers. The current paper addresses TtSG technologies, in general, and pyrolysis processing in particular. The overall goal of TtSG is to develop methods to convert trash and other solid waste materials to valuable products (e.g., propellants) plus materials that can benefit the life support system (e.g., oxygen, water). The production of propellants could be especially important, as it would reduce the need to launch fuel to locations beyond earth orbit. In addition, since over 5 kg per day of trash is produced for a crew of 4, there is significant logistical leverage to be gained by this conversion process. Recently, several TtSG processes were evaluated by NASA in laboratory testing using simulated waste streams, including a High Fidelity Waste Simulant (HFWS). In the project that is the subject of the current paper, two-stage pyrolysis processing of the HFWS was studied over a range of conditions, in order to examine the effects of cracking temperature, residence time, gas atmosphere, sample size, etc. For all of these experiments, relatively high yields (0.5 to 10 wt. %) of individual gas products (CO2, CO, CH4, C2H4, C2H2, and H2) were observed, with the total gas yields ranging from ~30 to 45 wt. %. The largest yield was generally a liquid product (~40 to 50 wt. %) that was assumed to be mainly water (based on condensates produced from similar two-stage pyrolysis experiments), while modest amounts of a char product (~10 to 15 wt. %) were formed.