Smart Biosludge Atomization for Waste-to-Energy Conversion

We introduce a novel "smart atomization" system to immediately accommodate and mitigate dynamically varying viscosity in a biosludge atomizer. Direct spray injection of a highly concentrated biosludge into a boiler could provide a new means of efficiently extracting energy from human or animal waste. Critical to this process, however, is an atomization system that maintains consistent droplet size production for combustion despite widely varying viscosities. High viscosity leads to a restrictive biosludge pressure drop and decreased atomization quality. CFD simulations are used to model biosludge atomization in a steam-assisted twin-fluid atomizer. To improve robustness, we transform the biosludge atomizer into a smart atomization system by adding two simultaneous, yet independent, PID controllers. The first PID controller adjusts the biosludge feed to maintain a constant pressure drop in the biosludge annulus. The second PID controller adjusts the steam feed to maintain constant droplet sizes, thereby compensating for the phase momentum ratio. We demonstrate the efficacy of the smart atomization system in maintaining consistent droplet sizes for a 100-fold increase in biosludge viscosity. To do so, however, the biosludge throughput is dramatically reduced, pointing to the need for a variable-geometry atomizer design.