Design and Implementation of a PID-Controlled Small-Scale Electric Torrefaction System for Biomass Processing

Overview

Torrefaction is the mild thermal decomposition of biomass in an inert environment. Torrefied biomass can prove revolutionary by providing cleaner fuel and a profitable, environmentally sustainable solution for dealing with agricultural waste. Unfortunately, small-scale torrefaction kilns, which are the next step to widespread adoption, face major issues with energy efficiency and precise, affordable temperature control. The goal of this project was to design and validate a prototype of a PID-controlled thermal reactor capable of regulating temperature and demonstrating the control principles required for torrefaction systems. A stainless steel reactor was constructed and controlled using an Arduino-based PI controller. The system was tested under three conditions: no biomass, 0.5 g biomass, and 1 g biomass. Temperature response and electrical power consumption were recorded during ramp-up and one-hour residence periods. The controller reached 100 degrees Celsius with temperature regulation that had less than 10% overshoot and a steady-state accuracy of approximately ±1 °C. The system demonstrated an average thermal efficiency of approximately 35% and required roughly 3.8 kJ of electrical energy per gram of biomass processed. Increased biomass loading produced greater temperature fluctuations due to increased thermal inertia, resulting in slower system response. Scaling analysis suggests that a larger reactor capable of reaching torrefaction temperatures of 200–300 °C would produce an energy return of 10 kJ per gram of biomass. Overall, additional studies that include more biomass, better heating elements, and different kiln designs can optimize the thermal efficiency and expand to uses to other forms of carbon capturing.

Competition history

• CSEF 2026 Environmental Engineering (Track 2) (Junior Division) · Entry J-12-12

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