Cellulosic Ethanol

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Banana Waste

January 12, 2009

Periodically Vincent Corporation receives inquiries in regards to handling waste from banana plantations and processors.  These involve three kinds of waste:  banana peel, banana stems, and banana trunks.  The peel falls in two separate categories:  ripe banana and green banana.  

RIPE BANANA PEEL.  Recently inquiries have increased with the hope that the waste can be converted into valuable animal feed.  Vincent undertook tests seeking a practical process.  We found that banana peel (yellow, with some brown spots) was about 88% moisture.  When pressed, some press liquor was produced, measuring 7 Brix.  However the press cake was still a very humid 84% moisture.   This is too high to be converted into a dried animal feed.

Tests were conducted to determine if the use of a press aid would make the material pressable.  Lime, the old standby, as well as gypsum and alum, along with wood fiber, were added to the shredded peel.  None of these press aids worked.  The press cake still came out over 80% moisture.  If we cannot do better than that, a feedmill will never be justified.

GREEN BANANA PEEL.  One customer in Jamaica processes green bananas.  (Green bananas are very hard to peel; just try a batch.)  The challenge here was to shred the waste in order to reduce the volume being hauled to landfill.  Green banana peel has enzymes which make it very sticky and hard to handle.  This presented a challenge for our shredder; however, the comb style shredder proved a satisfactory solution.

BANANA STEMS.  When banana bunches are harvested, there is a stem about 18” long and 3” in diameter at the end of the bunch.  This stem is cut off in the packing plant.  One customer in Costa Rica used Vincent twin screw presses to dewater these stems.  After shredding, the stems released a great deal of moisture in the press.  However, like ripe peel, the press cake still had a high moisture content.  The concept was to dry this press cake in order to produce a woody fiber.  Unfortunately, the cost of the dryer operation exceeded the value of the dried product, and the operation folded.

The plantation where this operation was located took over the screw press.  Their intent was to eliminate a waste disposal problem and produce a press cake that was suitable for mulching.  Since the mulch did not need to be as dry as what the twin screw press was designed to produce, we recommended a much less expensive Series KP press for future installations.  Good mulch material was produced, but, in the end, the project was abandoned.  The mulch became a breeding ground for insects in the wet climate.

This mulch could be used as a feedstock for a paper mill.  After all, it is cellulose fiber.  It has the advantage of having a year-round supply (in contrast to making paper out of corn stalks or wheat straw).  Nevertheless the scale of operation does not appear to be sufficient to justify the investment in a paper mill.

BANANA TRUNKS.   A development project in Colombia involves shredding and pressing the trunks of banana plants.  The volume and size is much larger than banana stems.  However, the process would be the same.

ETHANOL.  The largest producer of alcohol in Ecuador uses banana waste.  Because of the Brix content, the material readily ferments.  That is cheaper than using corn syrup, but the volume is not there.

Issue 206


Cellulosic Ethanol

August 8, 2007

Cellulosic ethanol is very much in the news nowadays.

Cellulosic ethanol is ethanol made from plant biomass such as agricultural wastes and forest residues. Plant biomass is another term for the tissue of recently dead plants, or plants that grow and die annually. This is in contrast to plant matter that died eons ago and over time created our current supply of carbon fuels, namely coal and oil.

In February of this year, the US Department of Energy (DOE) selected six companies to construct demonstration "biorefineries" that will produce energy and fuels from biomass. The funding was set at US$ 385,000,000. A variety of biomass materials were addressed:

Abengoa Bioenergy is focusing on producing ethanol from corn stover. Corn stover, sometimes called forage or silage, is the cob, husk, stalk and stem of corn plants. Abengoa is likely to use a "steam explosion" process to pre-treat the stover prior to enzymatic hydrolysis. Sugars liberated in the process are fermented to produce ethanol.

Verenium is a company recently formed by the merger of Diversa and Celunol. Diversa is in the production of enzymes, while Celunol has their ethanol facility in Jennings, Louisiana. Verenium is focused on producing ethanol from sugar cane bagasse. Bagasse has the advantages of sugar content and a long growing season. Its agricultural base is especially strong in Brazil.

Metabolix is focused on genetically modified switch grass. Switch grass, also known as prairie grass, grows over much of the United States and northern Mexico. It has the advantages of growing with minimal cultivation, with multiple harvests per season.

Here in Florida, there is strong political support for producing cellulosic ethanol from citrus waste. Several projects have been announced. One disadvantage is the relatively short, 150 day, orange harvest season. More significantly, there are technical barriers to be overcome in processing the spent orange peel once it has been fermented to produce alcohol.

Currently Vincent presses are being used in five different, albeit minor, projects based on producing cellulosic ethanol from sweet sorghum. See a previous Pressing News, #181 Sweet Sorghum, for details.

Our presses suit several applications: extracting juice from biomass, dewatering between the stages of counter flow washing, and final pressing ahead of a dryer. Our expertise in the manufacture of vapor-tight screw presses is also important.

Vincent screw presses are in operation in a surprising number of cellulosic ethanol operations. All of these activities started with the renting small screw presses, for trials, testing, and pilot runs.

Issue 192

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

Custard Apples

January 8, 1997

This fall a testing program was undertaken which at first had exciting possibilities. We were contacted by a waste energy firm, Bartow Ethanol, in regards to pressing custard apples.

Custard apples are a fruit that looks somewhat like a green apple. The inside is almost entirely filled with large seeds, each growing from the core to the outer skin. The fruit is harvested in Australia for commercial purposes, and the sugar content is known to be satisfactory.

Another variety of this fruit grows wild on land on the southern shores of Lake Okeechobee here in Florida. The trees are on public lands and they serve some erosion control purposes.

The idea was to harvest these custard apples and press them to extract the juice. Because of the sugar content, it was felt that the juice could be fermented for the production of alcohol. One advantage was that the trees bear fruit at only three to five years of age.

A pilot plan called for harvesting the fruit with prison labor. A Vincent screw press, driven by a diesel engine, would be used in the field to squeeze the juice, thus minimizing transportation costs and solving the problem of press cake disposal.

Initial tests were conducted in Tampa. The fruit, shredded in an angle Disintegrator, was run through a screw press. The yield was approximately one gallon of press liquor per sixteen pounds of apples. The press liquor had a great deal of suspended solids; it looked like apple sauce. Nevertheless the separation achieved was quite adequate for preparing juice for the digester.

Tests included adding an enzyme to the fruit. Thirty five minutes after adding the enzyme the mass became pulpy and was readily pressed. The seeds came out whole (that is, not broken open) using this procedure.

Unfortunately it turned out that the Brix value (sugar content) of the juice never exceeded 4-1/2º, whereas the Australian variety runs 12º. The lower Florida content was not adequate or proper for fermentation, so the project has been abandoned.

Issue 54

Ethanol - Potato Waste

April 22, 1999

We recently visited an interesting ethanol plant in Idaho. It is one of two owned by the J. R. Simplot Company that uses potato peel waste as a raw material.

The potato peel is a zero value waste from nearby potato processing plants. These plants peel the potatoes as part of the production of french fries, instant potatoes and similar products. The resultant waste is hauled to the ethanol plant.

The first step at the ethanol plant is to shred the waste because it contains whole cull potatoes. The material contains a great deal of white starch that results from the peeling process. The material is processed with enzymes in order to liquify the starch and sugar. The flow, containing 12 to 15% total solids, is referred to as beer. It is pumped to a distillation tower. Alcohol is taken off the top of the tower, while stillage comes off the bottom.

The stillage consists of the remaining solids and water. The flow is 130 gpm with 5% solids. At the plant this is pumped to a Sharples centrifuge which separates the waste into filtrate and solids with 85% moisture content. Centrate is the name given to the filtered liquid; it is also called thin stillage. The solids from the centrifuge are trucked to nearby farms for use as a cattle feed.

The stillage is too thin to separate in a screw press. However, we feel that the Fiber Filter, feeding its sludge to a small KP-6 screw press, might achieve the same results as the centrifuge. Centrifuge maintenance costs are high, approaching the cost of a FF-12 Fiber Filter on an annual basis.

A more promising application is to use the FF-12 on the flow between the enzyme reactors and the distillation tower. This flow contains materials such as brown potato peel and stringy material referred to as vines or roots. They hinder the effectiveness of the distillation tower, so efforts have been made previously to filter them from the flow.

We hope to test a Fiber Filter at the plant later this year.

Issue 93


July 17, 2001

For several years Vincent Corporation has been testing various screw presses in ethanol plants.

In 1994 Pressing News #9 described a system that used corn stalk and a unique bacteria to produce ethanol. In 1995 Pressing News #26 described an NREL project where a Vincent press was used to extract cane juice, part of an effort to reclaim the lands left from phosphate strip mining. In 1997 Pressing News #54 reported a false start at producing ethanol from custard apples. More recently, in 1999, Pressing News #93 told how J. R. Simplot Company uses potato peel waste as a raw material for the production of ethanol.

All of this Vincent testing work has been aimed at penetrating the much larger market, ethanol production from corn and other grains. This ethanol is sold as an additive used in gasoline, producing gasahol. The leading firms in this government sponsored industry are ADM and Cargill, with a significant number of smaller firms, mostly farmer cooperatives, also operating facilities.

These ethanol plants share a common need to dewater the spent grain that remains at the end of the fermentation process. This fiber is dried and sold as animal feed. The industry would like to use screw presses for this dewatering. However limited success with Vetter, Stord, and even Vincent presses has led to the common use of centrifuges for dewatering spent grain. The high annual maintenance costs of centrifuges are cited as incentive to screw press designers.

In April 2001 a Vincent Twin Screw Press was tested in dewatering thin stillage. The results were better than achieved previously with our single screw Series VP, CP, and KP presses. However it was concluded that a press aid, such as cotton seed hulls, would have to be used in order to equal the performance achieved by centrifuges. In addition, a reversing starter, with an automatic timer, was required to keep the press screens operating at peak performance.

Press aids are commonly used by producers of apple and grape juice. For ethanol plants the roughage represented by the cotton seed hulls may improve the value of the feed and its drying characteristics. Yet clearly it remains to be seen if the industry will adapt to using these press aids.

Issue 119

Ethanol Process

January 15, 1994

There is an interesting end use intended for a VP-6 press recently delivered by Vincent Corporation. It will be used in Gainesville, Florida as part of a pilot plant to produce ethanol alcohol.

The process to be refined in the pilot plant involves using a genetically engineered and patented bacteria. This unique e-coli bacteria is capable of digesting C-5 sugars.

The raw material in the process is stover. This is nothing more than chopped corn stalks and corn husks. Stover contains the hemi-cellulose sugar molecular structure known as C-5.

The first step of the process is to release the C-5 sugars through hydrolysis. Hydrolysis simply involves tumbling the stover in a pressure vessel for half an hour with 150 psi steam.

In the pilot plant the hydrolyzed stover will be run through the Vincent press. This will separate out the C-5 hydrolysate, or press liquor, so that it can be placed in a fermentation vessel. The fermentation will produce a 4% ethanol solution which can subsequently be distilled into 200 proof alcohol.

The fermentation of C-5 is possible only with a special genetically engineered bacteria. This microbe was developed and patented by the University of Florida. Vincent's client, Bioenergy Inc., has been granted an exclusive license to use this bacteria.

Save your corn stalks!

Issue 9

Sweet Sorghum

December 5, 2006

It seems that every time there is an energy crunch, Vincent gets involved with a sweet sorghum project. The attraction is two-fold: sorghum is very easy to grow, and sorghum contains a high level of sugar.

Other plants, like corn, sugar beets, sugar cane, vegetables, and all fruits, also contain sugar. All of these can be used as part of ethanol, biogas, and other bioenergy schemes. So it is no surprise that, with this year's high energy costs, Vincent currently has projects underway involving sorghum, corn, beets, cane, banana, oranges, and onions.

This year's sorghum project involved testing a variety of Florida sorghums. The juice yield, along with the amount of dissolved sugar (Brix*), was measured. The effect of shredding, or not shredding, was studied. The benefit of using a Vincent Twin Screw press as a combination shredder and press was also evaluated.

Sorghum is a soft cane-like plant. It is fibrous, but not fibrous enough to cause problems with shredding or abrasive wear. This gives it an advantage over sugar cane. It is a little like water reeds, only thicker (3/4" diameter) and taller (8').

Most of the sorghums tested measured only 7º to 9º Brix. This was presumed to be lower than normal because of the maturity of the plants. The juice yields ranged from 66% to 79%. The project was focused on providing a sugar solution that could be used in the production of ethanol at Bartow Ethanol.

These sorghums, as harvested, measured 81% to 83% moisture content. The press cake ranged from 45% to 59% moisture content.

A search of our files revealed interesting reports and articles, all based on testing with Vincent screw presses:

Overall, these projects were technical successes in that they demonstrate that sorghum yields high Brix juice that is suitable for the production of ethanol. However, the projects all fail commercially because the price of fuel oil is not high enough for the projects to be justified. Nevertheless, it is comforting to know that alternative, renewable energy sources exist, should the day come when the availability of fossil fuels declines.

*Brix Definition: Dissolved solids divided by the sum of the dissolved solids plus water, multiplied by 100. Note that suspended solids do not enter into the equation.

Issue 181

UCO (Used Cooking Oil) to Biodiesel

February 5, 2015

Buster Biofuels is an interesting customer located in Escondido, California. The firm is developing advanced technology for the production of biodiesel fuel.

Currently the company is processing UCO – Used Cooking Oil – to recover clarified oil. This oil is being used to further develop their process for converting it into biodiesel. The key to this is the use of advanced enzymes which accelerate the chemical process required to convert the cooking oil into engine fuel.

Novazyme, the Danish company, is helping with the modified enzymes which are required for the process. In addition, a specialty enzyme development firm in Florida is contributing to the effort.

Used cooking oil is purchased from local restaurants and transported to the processing plant. This oil is first screened to remove plastic film, rags, big bones, and other large trash. Next it is filtered in a self cleaning filter. These use slotted wedgewire screens which are kept clear with a wiper mounted on a piston. The sludge pushed out by this piston goes to the Vincent screw press, and the filtered oil goes to heated clarification tanks.

The screw press being used is a rental CP-4 which they purchased after trials. It features a tapered shaft design which improves separation of oil from the sludge. The press liquor (oil) goes to the clarification tank system.

The plant is designed to produce 800,000 gallons/year of biodiesel from their UCO network. Actual production, using recovered waste oil purchased from others, will get the capacity up to 5,600,000 gallons/year.

Press cake is hauled by Miramar Greenery, where it is mixed with other organic waste to produce compost.

Vincent supplied newer screen designs for the press with a goal of reducing the fine contaminants which now come through the screen. This led to the selection of the optimal screen configuration.

Issue 271

Water Hyacinths

October 6, 1993

Vincent presses have encountered an interesting application at a sewage treatment plant in the city of San Diego. Facilities are currently being commissioned to use water hyacinths to both reduce BOD and generate methane fuel.

The concept was developed at Disney World in Florida about ten years ago. At the time funding was provided by the Gas Institute. Subsequently Black and Veatch, the Kansas City consulting engineers, have assumed leadership in promoting the process.

The cycle utilized calls for growing water hyacinths in ponds of waste water. This growth process reduces biological oxygen demand (BOD), a vital step in sewage treatment.

The next step is to harvest the hyacinths and press the liquid from the plants. It is in this pressing operation that the Vincent screw press is used. Typically the hyacinths are separated into 5% press cake and 95% press liquor.

The press cake has little value. It can conveniently be sent to landfill. Or, in sufficient quantity, it can be made into an animal feed. At the City of San Diego project the press cake will be placed in windrows where composting will occur.

The press liquor is key to the process. It will be pumped to tank-type digesters. In these tanks anaerobic digestion will occur, which results in the release of methane gas. This gas, very similar to natural gas, has significant energy value.

The equipment now in service at the City of San Diego is of a pilot plant scale. It is felt that different operating systems must be tested and refined before the water hyacinth process can be successfully commercialized.

Issue 7