Alternative Pyrolyzer Design: Free Fall Reactor

Center for Sustainable Environmental Technologies

Alternative Pyrolyzer Design: Free Fall Reactor

Figure 1: Removing Free-fall reactor char catch

The primary focus of this project is to research, develop and evaluate an alternative fast pyrolysis reactor design for the production of bio-oil.  The reactor being studied is a radiative free-fall reactor shown in Figure 1. 

Fast pyrolysis is a process that is predominantly performed in a fluidized bed reactor.  It is the thermal degradation of carbonaceous material in the absence of oxygen.  Though the fluidized bed reactor boasts high throughputs and bio-oil yields alternative designs seek to capitalize on its inefficiencies by minimizing the use of an inert carrier gas, simplifying the design and reducing the number of moving parts.

 

Figure 2: Process flow diagram

 

The free fall reactor is essentially a heated, upright pipe through which biomass is fed.  The reactor is externally heated to 500°C by ceramic radiative heaters.  Biomass is ground down to small particles using a mill and fed into the top of the reactor with a screw feeder (not shown).  The particles fall for 2m through the length of the pipe before they are completely pyrolyzed. Pyrolysis vapors and char exit the reactor at the bottom.  The char is collected in a canister and the vapors pass through a heated cyclone before entering a condenser system.  Here the vapors are quenched into bio-oil and the non-condensable gases exit to a vent and a micro GC for further analysis.  This process is shown in Figure 2.

Recent shakedown trials feeding corn stover biomass were used to determine reactor limitations and troubleshoot problems. The following parameters were varied:

Particle size (microns): 200, 300, 400, 500, 600
Feed rate (kg/hr): 1.0, 1.25, 1.50, 1.75, 2.0
Heater temperature (°C): 450 – 650
Nitrogen flow rate (SLPM): 0-5

Figure 3: Bio-oil yields from corn stover biomass


The liquid bio-oil yields from these shakedown trials are shown in Figure 3 as a function of the heater temperature.  Maximum bio-oil yields for the corn stover reached 50 %wt.   Liquid bio-oil yields can be as high as 70 %wt. when other sources of biomass with lower ash content are used.

Fast pyrolysis of corn stover biomass in a free-fall reactor configuration is a potential alternative to the fluidized bed reactor for the production of bio-oil.  Maximum bio-oil yields were found near 500°C while operating at 400°C resembles torrefaction and operating at temperatures much greater than 500°C is similar to gasification.  

Future work includes completing a set of 30 statistically designed experiments to determine the optimum operating conditions for maximum bio-oil yields.  A red oak biomass will be used as the feedstock.  Four parameters will be tested including: particle size, feed rate, heater temperature and nitrogen flow rate.

For further information and inquiries please contact those listed below:

Principal Investigators:

    Dr. Robert Brown, Iowa State University, rcbrown@iastate.edu
    Dr. Samuel Jones, Iowa State University, sjones@iastate.edu

Research by:
   
    Cody Ellens, Iowa State University, cdyllns@iastate.edu

Participating and/or Sponsoring Organizations:
   
    ConocoPhillips Company