(74h) Gasification of Coal/Plastic Mixtures: Fundamental Studies in a Laminar Entrained-Flow Reactor

While literature reports various instances of plastic co-gasification with biomass/coal in fluidized bed gasifiers, research in coal and plastic gasification in entrained flow gasifier (EFG) is limited. Entrained flow gasification is of great interest considering its elevated temperature, flexibility of feedstocks fed, high efficiency, low cost of operation, low carbon emissions, and large-scale commercial applicability. EFG operates with liquid or slurries containing small solid particles at high pressure (3-8 MPa) and typically uses pure oxygen to partially oxidize the feedstock. Compared to other gasification types, it maximizes the carbon conversion rate, lowers methane content (enabling detachment of H₂ from hydrocarbon molecules), promotes atomization of slurries to increase the heat transfer rate, and typically runs in a slagging mode, i.e., at high temperature where the ash becomes molten.

To foster a circular economy, there is interest in the co-gasification of granulated plastics and pulverized coal in a pressurized, oxygen-blown, entrained-flow system. For this blended mixture, It is unclear how the introduction of plastics will affect coal conversion and the associated production of CO and CO₂. Relative to coal, plastics have a much higher volatile content (essentially 100%), and the volatiles are released at lower temperatures. With the addition of volatiles in the oxygen-rich portion of the burner, there is a question of whether oxygen that would otherwise be available for coal burnout will be consumed by the plastics volatiles (competitive oxidation).

To answer the research question, the University of Utah has lab-scale facilities to help understand the fundamentals of co-gasification, including a high-temperature laminar entrained-flow reactor (LEFR) and thermogravimetric analyzers, as well as analytical equipment including gas analyzers, an analyzer for total carbon and sulfur, and scanning electron microscopes. The experimental setup involved precise temperature control, plastic concentration, particle size, and residence time within the LEFR. Samples were prepared, loaded, and subjected to carbon conversion and syngas composition analysis. Findings revealed nuanced effects of temperature, plastic concentration, particle size, and residence time on coal-based carbon conversion and CO/CO₂ ratio. Elevated temperature, smaller particle size, and longer residence time enhanced carbon conversion, while plastic concentration notably increased the CO/CO₂ ratio. This research underscores the significance of temperature, plastic concentration, particle size, and residence time in shaping carbon conversion and syngas composition. The findings provide valuable insights into optimizing gasification parameters and pave the way for future investigations.