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Wilson D.M.,Iowa State University | Dalluge D.L.,Iowa State University | Rover M.,Center for Sustainable Environmental Technologies | Heaton E.A.,Iowa State University | And 2 more authors.
Bioenergy Research | Year: 2013

Although upgrading bio-oil from fast pyrolysis of biomass is an attractive pathway for biofuel production, nitrogen (N) and mineral matter carried over from the feedstock to the bio-oil represents a serious contaminant in the process. Reducing the N and ash content of biomass feedstocks would improve process reliability and reduce production costs of pyrolytic biofuels. This study investigated: (1) How does switchgrass harvest date influence the yield, N concentration ([N]), and ash concentration of biomass and fast pyrolysis products? and (2) Is there a predictive relationship between [N] of switchgrass biomass and [N] of fast pyrolysis products? Switchgrass from five harvest dates and varying [N] from central Iowa were pyrolyzed using a free-fall reactor. Harvestable biomass peaked in August (8. 6 Mg ha-1), dropping significantly by November (6. 7 Mg ha-1, P = 0. 0027). Production of bio-oil per unit area mirrored that of harvested biomass at each harvest date; however, bio-oil yield per unit dry biomass increased from 46. 6 % to 56. 7 % during the season (P = 0. 0018). Allowing switchgrass to senesce lowered biomass [N] dramatically, by as much as 68 % from June to November (P < 0. 0001). Concurrently, bio-oil [N] declined from 0. 51 % in June to 0. 17 % by November (P < 0. 0001). Significant reductions in ash concentration were also observed in biomass and char. Finally, we show for the first time that the [N] of switchgrass biomass is a strong predictor of the [N] of bio-oil, char, and non-condensable gas with R2 values of 0. 89, 0. 94, and 0. 88, respectively. © 2012 Springer Science+Business Media, LLC.

Brown J.N.,Iowa State University | Brown J.N.,Avello Bioenergy Inc. | Brown R.C.,Iowa State University | Brown R.C.,Center for Sustainable Environmental Technologies
Bioresource Technology | Year: 2012

A 1. kg/h auger reactor utilizing mechanical mixing of steel shot heat carrier was used to pyrolyze red oak wood biomass. Response surface methodology was employed using a circumscribed central composite design of experiments to optimize the system. Factors investigated were: heat carrier inlet temperature and mass flow rate, rotational speed of screws in the reactor, and volumetric flow rate of sweep gas. Conditions for maximum bio-oil and minimum char yields were high flow rate of sweep gas (3.5. standard. L/min), high heat carrier temperature (∼600. °C), high auger speeds (63. RPM) and high heat carrier mass flow rates (18. kg/h). Regression models for bio-oil and char yields are described including identification of a novel interaction effect between heat carrier mass flow rate and auger speed. Results suggest that auger reactors, which are rarely described in literature, are well suited for bio-oil production. The reactor achieved liquid yields greater than 73. wt.%. © 2011 Elsevier Ltd.

Ellens C.J.,Iowa State University | Ellens C.J.,Avello Bioenergy Inc. | Brown R.C.,Iowa State University | Brown R.C.,Center for Sustainable Environmental Technologies
Bioresource Technology | Year: 2012

A central composite design of experiments was performed to optimize a free-fall reactor for the production of bio-oil from red oak biomass. The effects of four experimental variables including heater set-point temperature, biomass particle size, sweep gas flow rate and biomass feed rate were studied. Heater set-point temperature ranged from 450 to 650. °C, average biomass particle size from 200 to 600. μm, sweep gas flow rate from 1 to 5. sL/min and biomass feed rate from 1 to 2. kg/h. Optimal operating conditions yielding over 70. wt.% bio-oil were identified at a heater set-point temperature of 575. °C, while feeding red oak biomass sized less than 300. μm at 2. kg/h into the 0.021. m diameter, 1.8. m tall reactor. Sweep gas flow rate did not have significant effect on bio-oil yield over the range tested. © 2011 Elsevier Ltd.

Pollard A.S.,Iowa State University | Pollard A.S.,Avello Bioenergy Inc. | Rover M.R.,Center for Sustainable Environmental Technologies | Brown R.C.,Iowa State University | Brown R.C.,Center for Sustainable Environmental Technologies
Journal of Analytical and Applied Pyrolysis | Year: 2012

Bio-oil from fast pyrolysis of biomass consists of hundreds of compounds with a wide range of molecular weights. These include both volatile and non-volatile compounds and viscous oligomers, which complicates recovery of the liquid product from vapors and aerosols generated during pyrolysis. We have developed a bio-oil recovery system that overcomes the fouling problems that commonly occur in conventional condensers, allowing recovery of stage fractions (SF) of bio-oil with distinctive chemical and physical properties. The concept has been evaluated in an 8 kg/h process development unit (PDU) consisting of a fluidized bed pyrolyzer, hot cyclones, and a series of condensers and electrostatic precipitators (ESPs) that recover five stage fractions. Red oak was pyrolyzed in the PDU and the resulting stage fractions of bio-oil analyzed for moisture, modified acid number (MAN), water insoluble content, solids content, higher heating value (HHV), kinematic viscosity and chemical composition. © 2011 Elsevier B.V. All rights reserved.

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