Investigation of Energy Harvest from the Thermal Decomposition of Munitions Wastewater

Fabrication processes in munitions plants produce an Ammonium Nitrate (AN) laden wastewater stream that needs to be disposed of in accordance with regulatory guidelines. This stream is composed of oxygen-rich nitrates, and carbon- and hydrogen- containing compounds, and therefore offers an opportunity to repurpose it as a nitrogen based monofuel for energy harvest. The thermal decomposition of small batches of the wastewater and control samples of comparable compositions at pressures from 0.1 to 10 MPa are explored in this work. The energy and emissions released from the decomposition of the samples are measured using a Differential Scanning Calorimeter (DSC), and a Fourier-Transform Infrared (FTIR) Spectrometer respectively. Experimental results are compared with the theoretically determined energy contents and ideal decomposition products to evaluate the “quality” of decomposition, and profiles and quantities of heat flow and emissions are used to elucidate major modes of sample decomposition. This investigation demonstrated that higher pressures improve energy release and reduce the amounts of harmful NO_x emissions. The decomposition enthalpy of the wastewater improved from 0.2 MJ/kg at 0.1 MPa to 1.8 MJ/kg at 10 MPa. Similarly, while NO and NO₂ emissions accounted for 6.5% and 2.5% of sample nitrogen, respectively, at 0.1 MPa, they accounted for only 0.7% and 0.08% the sample nitrogen at 10 MPa.