Studies of the Flash Carbonization Process. 2. Violent Ignition Behavior of Pressurized Packed Beds of Biomass: A Factorial Study

The Flash Carbonization (FC) process is a novel procedure by which biomass is converted to biocarbon (i.e., charcoal) quickly and efficiently. To begin this process, a canister containing a packed bed of feedstock is placed within a pressure vessel, compressed air is used to charge the system to an initial pressure of 1-2 MPa, and a flash fire is ignited at the bottom of the bed. After about two minutes, air is delivered to the top of the bed and the biomass is converted to a high-yield biocarbon. In lab-scale tests, some fuels have been observed to ignite violently, resulting in a sudden drastic pressure rise ((delta)P (almost equal) 1 MPa within 2-3 s). Because this event could be potentially hazardous, a study of this phenomenon was undertaken in preparation for a scale-up of the FC process to a commercial-sized demonstration reactor. The influence of initial pressure, feed moisture content, and ignition heater power were examined following a 2^3 full factorial experimental design approach. The combined effect of initial pressure and feed moisture content was found to influence the violence of the combustion phenomenon. Additionally, the continued propagation of the initial violent combustion was found to be limited by heat and mass transfer constraints and not by the complete exhaustion of the fuel or oxidizer initially present in the system.