Scalable Efficient Microwave Conversion of Waste to Carbon-Rich Fuel
Abstract
The University of Colorado is submitting a proposal to investigate generation of microwave power for a scalable and/or modular and efficient conversion of waste to carbon-rich fuel. The intended applications are for reducing impact of troops on the move and for recycling waste in military bases, as well as industrial, commercial and residential waste management. Currently, either no waste recycling is used as a choice to reduce weight, or in some cases waste is incinerated with syngas as a by-product, in volumes that are relatively large, on the order of 30 cubic meters (leaving ash that is then buried). However, when waste with carbon content is subjected to volume power densities on the order of 0.25 watts per cubic centimeter at GHz frequencies, it can convert to highly caloric fuel with gas bi-products that can either be pumped out or used to continue the coking process, depending on the available power. The coke and gas can be contained for use as energy sources, leaving little or no trace. For an efficient microwave-based waste management process, a well-controlled uniform RF electric field volume density is needed. The proposed investigation focuses on developing an active microwave cavity which is capable of scaling in terms of waste mass and volume power density, while maintaining electric field uniformity adaptively within the waste volume. Over-moded microwave cavities are scalable in size and can be excited with multiple sources for volumetric power combining. For lower power levels, solid-state power circuit and spatial combining is proposed, while for larger power levels and volumes, magnetron volumetric combining is investigated. Adaptive field uniformity within a variable waste volume is proposed through frequency modulation and load stirring, adaptive source phasing, time-domain pulse shaping and cavity wall (boundary condition) design. In the first phase of this research, we propose to demonstrate a portable lower-power solid-state cavity and theoretically investigate power and volume scaling. An efficiency study for scalable microwave waste management is performed. For an efficient process, a well-controlled uniform RF field should be maintained in a non-uniform and time-variable material. We are developing a 2.45-GHz active microwave cavity with solid-state (GaN) spatially power combined sources for lower volumes. In the energy balance calculations, the input energy into the system consists of the waste chemical energy and the DC electrical energy used to obtain the RF power with an efficiency that can reach 70 percent for kilowatt power levels. The efficiency of RF power conversion to heat in the waste mass is calculated from full-wave simulations for typical waste mixtures and ranges from 10 to 90 percent depending on the material and cavity filling. The output energy estimates are collected from various pyrolysis process descriptions with the total energy being that of the solid fuel (35MJ/kg) and oil caloric values, e.g. 40MJ/kg for plastics and about 10-15MJ/kg for nonplastics. A byproduct is flue gas which can be converted to Syngas. The total worse-case carbon footprint balance will be studied and calculations as a function of type of waste mixture and overall time of exposure to high microwave power densities will be performed and supported by experimental investigations using smaller volume cavities with solid-state power amplifiers.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 01, 2019
- Source ID
- W911NF1810073
Entities
People
- Zoya Popovic
Organizations
- Army Contracting Command
- Defense Advanced Research Projects Agency
- University of Colorado Boulder