A lab-scale biomass fast pyrolysis system was designed and constructed based on an auger reactor concept. The design features two intermeshing augers that mix biomass with a heated bulk solid material that serves as a heat transfer medium. A literature review, engineering design process, and shake-down testing procedure was included as part of the system development.

A response surface methodology was carried out by performing 30 experiments based on a four factor, five level central composite design to evaluate and optimize the system. The factors investigated were: (1) heat carrier inlet temperature, (2) heat carrier mass feed rate, (3) rotational speed of the reactor augers, and (4) volumetric flow rate of nitrogen used as a carrier gas. Red oak (Quercus Rubra L.) was used as the biomass feedstock, and S-280 cast steel shot was used as a heat carrier. Gravimetric methods were used to determine the mass yields of the fast pyrolysis products. Linear regression methods were used to develop statistically significant quadratic models to estimate and investigate the bio-oil and biochar yield. The optimal conditions that were found to maximize bio-oil yield and minimize biochar yield are high nitrogen flow rates (3.5 sL/min), high heat carrier temperatures (625yC), high auger speeds (63 RPM) and high heat carrier feed rates (18 kg/hr).

The produced bio-oil, biochar and gas samples were subjected to multiple analytical tests to characterize the physical properties and chemical composition. These included determination of bio-oil moisture content, solid particulate matter, water insoluble content, higher heating value, viscosity, total acid number, proximate and ultimate analyses and GC/MS characterization. Statistically significant linear regression models were developed to predict the yield of gaseous carbon monoxide, the hydrogen content, moisture content and water-insoluble content of the bio-oil, and the vapor reaction temperature at the reactor outlet. A significant result is that with increasing bio-oil yield, the oxygen to carbon ratio and the hydrogen to carbon ratio of the wet bio-oil both decrease, largely due to a reduction in water content.

The auger type reactor is currently less researched than other systems, and the results from this study suggest the design is well suited for fast pyrolysis processing. The reactor as designed and operated is able to achieve high liquid yields (greater than 70%-wt.), and produces bio-oil and biochar products that are physically and chemically similar to products from other fast pyrolysis reactors.