Cellulosic Ethanol 2

August 3, 2012

Cellulosic ethanol is ethanol made from agricultural waste like corn stalks, switch grass, sugar cane bagasse, and even tree materials.  (The "trees" application is very difficult, the least perfected technology.)  The process Vincent is interested in involves pre-treating the waste with heat and enzymes in order to convert it into fermentable sugars.  Ethanol is made in the fermentation step. 

There are two things that can go into our screw presses in the process of making cellulosic ethanol.  One is material produced by STEX - Steam Explosion.  That is fiber that has been put into a pressure chamber with steam and then blown out to atmosphere.  Sometimes they add water to wash it, usually in a counterflow system.  Regardless, the fiber presses reasonably well.

The second application is much more challenging.  After pre-treating the agricultural waste, they ferment it to make alcohol.  The residue after fermentation is sometimes called stillage.  This fiber and water can be impossible to dewater in a screw press, or it can dewater reasonably well.  It depends on the pretreatment, which involves a combination of grinding, heating, and enzyme reaction.  It seems that if in the pretreatment they grind the agricultural waste into dust ("mill it into flour"), then it is like spent grain from a whiskey distillery: it does not dewater in a screw press.  But they like to do that because it gives them the most gallons of ethanol per ton of agricultural waste, a prime DOE specification.

On the other hand, if they are less aggressive in the pretreatment, the residue waste is like spent grain from a beer brewery.  The particles are relatively large, almost like cracked corn.  The ethanol yield is not as high, but that waste stillage dewaters reasonably well in a screw press.

What to do with the press cake separated from the stillage is a challenge.  The Abengoa project in Hugoton calls for it to be burned as a biofuel.  Because of the high moisture content, a fluidized bed boiler is required.  At the other end of the scale, these same solids from their Salamanca demonstration plant (now closed) were landfilled.  The material is not suitable as an animal feed.

Vincent has rented and sold presses to a large number of firms attempting to develop cellulosic ethanol technology.  This includes:
Verenium (owned by British Petroleum, but their Jennings, Louisiana facility is now closed),

  • Abengoa in York, Nebraska,
  • Poet in Scotland, South Dakota,
  • NREL in Golden, Colorado,
  • Edeniq in Goshen, California,
  • Fiberight in Lawrenceville, Virginia,
  • Lignol Innovations in British Colombia,
  • Mascoma in New York,
  • Trillium Fiber Fuels in New York,
  • GeoSyn Fuels in Golden, Colorado,
  • Cobalt Technologies in California (butanol),
  • Menon International in California,
  • The Georgia Institute of Technology, and
  • ADM in Decatur, Illinois
  • DONG – INBICON Biomass Refinery, Kalundborg, Denmark

Many of the screw presses sold were made of 316 stainless, although we are not aware of chlorides being present.  The specification may have been a carryover from wet corn milling operations.

The ADM pilot plant is now in start-up.  It uses three presses in a counterflow wash system, with a fourth press being used to dewater the final stillage.  The facility runs on corn stover.  It can do either thermal chemical pretreatment or STEX (steam explosion).

One operation of great current interest is with Blue Sugars (formerly KL Energy).  They are using various Vincent presses on STEX material.  Their focus is on using sugarcane bagasse as a feedstock.  They are headquartered on the business development center adjacent to South Dakota State University in Rapid City, SD; their ethanol plant is in Wyoming.  Petrobras of Brazil has a strong interest in the firm. 

Currently there two one-hundred million dollar projects under way, both enabled by Federal government guarantees.  One is in Hugoton, Kansas, being built by the Spanish company, Abengoa.  The other, known as the Liberty project in Emmetsburg, Iowa, is being done by Poet.  Unfortunately, neither project is apt to use screw press technology.

Issue 248