Alternative Pyrolyzer Design: Auger Reactor

Center for Sustainable Environmental Technologies

Alternative Pyrolyzer Design: Auger Reactor

This project aims to explore a viable alternative to fluidized bed reactors for bio-oil production via the thermochemical process fast pyrolysis. This conversion method decomposes lignocellulosic biomass in the presence of heat to produce a mixture of organic vapors, bio-char and combustible gas. When quickly cooled, the vapors are condensed into a liquid bio-oil which is a suitable feedstock for further refining into an array of biorenewable products. Fast pyrolysis reactions typically occur in the absence of Oxygen at atmospheric pressure and a temperature of approximately 500°C (932°F).

Fluidized bed reactors have been proven at a commercial scale, and are the most common design used for fast pyrolysis processing. Though they are well understood, provide high biomass throughputs and bio-oil yield, their operation relies on a large volumetric flow of an inert gas such as Nitrogen that must be heated and compressed. Other reactor designs may offer certain advantages such as the reduction or elimination of carrier gas, but they have not been as thoroughly investigated. The auger type of pyrolyzer has been identified as especially appealing for its potential to reduce operating costs associated with bio-oil production. This design may also be well suited for small, portable pyrolysis systems in a highly distributed or decentralized biomass processing scheme. After a thorough research and design process, a lab scale auger reactor system has been developed at Iowa State University. The completed alternative reactor system is shown below.

Figure 1. Auger reactor system
Figure 2. Auger detail

The operating principle of this design is that biomass is continuously pyrolyzed by being brought into direct contact with a bulk solid heat transfer medium referred to as a “heat carrier.” The heat carrier material, such as sand or steel shot, is heated independently before being metered into the reactor. On a gravimetric basis, thermodynamic calculations suggest a heat carrier feed rate 20 times the biomass feed rate. Two intermeshing, co-rotating 1” augers quickly combine biomass and heat carrier in a shallow bed to effectively carry out the pyrolysis reactions. This mechanical mixing process, though not well understood, appears to be the essence of this alternative pyrolyzer design. Volatile vapors and aerosols exit at various ports, while char is transported axially through the 20” long reactor section and stored in a canister with the heat carrier. A detail of the stainless steel augers is depicted below.

Video: Mixing Behavior of sand and corn stover biomass

The 1.0 kg/hr reactor system has been extensively tested for proof-of-concept regarding bio-oil and bio-char production with promising results. A data acquisition system monitors and record system temperatures, pressures, flow rates and electrical power input. The non-condensable gas stream is analyzed in-situ using a mirco-GC. Initial experimentation using corn stover as a feedstock included relating process parameters such as auger speed, biomass and heat carrier feed rates to product distribution. With initial parameters understood, an experimental procedure based on a 4 factor 5 level central composite design is currently being performed with red oak biomass.

Presentation:

Brown, J.N., et al. "Development and demonstration of a lab-scale auger reactor for bio-oil production." Poster presentation. 2008 Biobased Industry Outlook Conference, Ames, Iowa. September 7-10, 2008.

Principal Investigators:

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

Research By:

Jared Brown, Iowa State University, jnbrown@iastate.edu

Participating and/or Sponsoring Organizations:

ConocoPhillips