EXECUTIVE SUMMARY
4.3 CONVERSION TECHNOLOGY OPTIONS .1 Direct Combustion
4.3.7 Fuel Ethanol
BIOMASS IN THE ENERGY CYCLE
In a more advanced development, a laboratory scale process is being evaluated to produce hydrogen from wet biomass by gasifying in supercritical water. The University of Hawaii is studying hydrogen production from a marine derived biomass as feedstock.
BIOMASS IN THE ENERGY CYCLE
TABLE 4.10 Capital Costs : Ethanol Production from Biomass
* Includes raw material costs
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BIOMASS IN THE ENERGY CYCLE
Companies in the US are claiming to be building demonstration plants as a prelude to the commercialisation phase. Organisations at the forefront in this area include Iogen and StakeTech in Canada (steam explosion route) and the National Renewable Energy Laboratory (enzyme hydrolysis and fermentation), the Tennessee Valley Authority (dilute and concentrated acid hydrolysis) and Arkenol in the US.
Stake Tech have three pilot plants processing waste paper at capacities between 0.5 and 6 tonnes an hour in Canada and the US, and in France they have a 30 cubic meter facility to trial enzyme production and fermentation.
They also claim to have demonstrated single stage hydrolysis and fermentation.
The TVA has tested its dilute and concentrated acid hydrolysis process on hardwood at 2 dry tonnes a day and 6 dry tonnes an hour respectively. TVA are in the process of scaling up a new concentrated acid process with acid recovery and recycle, which they say they have demonstrated at laboratory scale. The fermentation step uses yeasts in these processes.
Arkenol are developing a concentrated sulphuric acid process and their first two commercial scale plants due to start up over the next two years. The first project will be a combined grain/cellulosic plant in Texas producing 13% of its ethanol from cellulose initially, increasing to 55% over 5 years.
The second will be a plant utilising waste heat from a 148.5 MW cogeneration plant. The Arkenol process is a 2-stage acid hydrolysis system in which the acid and sugars are separated by ion exchange. The acid is recycled and a yeast will convert both glucose and xylose to ethanol.
No information was received from Iogen on their process.
The National Renewable Energy Laboratory is developing a single stage sacharification and fermentation process using enzymes. A first generation demonstration project is presently under construction near Denver, with the participation of AMOCO. The project, due for start-up this year will have a capacity of 1 tonne a day lignocellulose feed and utilise state of the art technology blocks as developed to date by NREL. Further work is being carried out on a lab and pilot scale on the pretreatment and single stage hexose and pentose fermentation systems. The program has the objective of achieving a production cost of ethanol of US$1.00 a gallon using the present technology system and US$0.70 a gallon by the year 2000.
The yields of ethanol for the various technologies are shown below The large differences between the TVA and other technologies are mainly due to pentose conversion.
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B I O M A S S I N T H E E N E R G Y C Y C L E
N R E L 372 litres a tonne dry wood A R K E N O L 363 S T A K E T E C H 320 T V A cone acid 240 dilute acid 205 A two million litre a year lignocellulose to ethanol demonstration plant using a Zymomonas process under development at the University of N S W , is at the design stage in a feasibility study presently being conducted by Gorton Timber of Grafton, N e w South Wales, Australia.
The Australian non profit company APACE Research has developed a combined ethanol recovery/waste treatment process. The developers indicate that the process is energy self-sufficient and lower cost than conventional technology, and is being included in the demonstration plant design.
No details of the technology or capital and operating costs were made \ available in time for a thorough evaluation.
Process development work is focussed on :
* facilitating hydrolysis through pretreatment of the biomass by size reduction and/or extracting the cellulose and hemicellulose, or making it more accessible to enzymes or acid hydrolysis through steam explosion;
* improved acid or enzyme hydrolysis through lower temperatures, less product degradation, faster reaction times and acid or enzyme recovery and recycle;
* improved fermentation processes through faster fermentation, simultaneous hydrolysis and fermentation, and the genetic engineering of enzymes and yeasts that will increase yields by allowing the fermentation of pentose sugars.
4.3.8 Vegetable Oils and E s t e r s
Vegetable oils and their methyl or ethyl esters have been used as diesel engine fuels both in their crude form and fully refined state. They have been used neat and in a range of blends as they are fully miscible in all proportions with diesei.
The technologies for extracting vegetable oils and their esterification are mature.
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BIOMASS IN THE ENERGY CYCLE
The original process for extracting oil for vegetable seeds was by expeller The process is used on both a large and small scale. The oil can be squeezed out of the seeds leaving a 5-7% oil in the residual meal. This meal is suitable for pigs and chickens and may be suitable as a partial diet for cattle. The crude oil produced is suitable both for use as a fuel and for esterification.
Almost all modem world plants now produce vegetable oil on a large scale by solvent extraction. The oil is then filtered and is suitable in this crude form as a liquid fuel.
Low glycerol content is a prerequisite for any biodiesel process because traces of the chemical can clog injection nozzles during combustion. Austria has been the first to set a national biodiesel standard with a maximum of 0.25% and 0.03% for total and free glycerol, respectively. In 1993, these limits will be tightened to 0.24% and 0,02%. A similar proposal is currently being reviewed in Germany. US companies are informally following Austria's lead.
A process developed by Vogel & Noot GmbH of Austria using a potassium hydroxide catalysed process meets these standards. Other processes are lowering glycerine content by more closely controlling the phase separation step. Oelmuhle Connemann GmbH of Germany plans to use a centrifuge in a 60,000 tonnes a year plant, which will come onstream in 1994.
Meanwhile, Sofiporteol SA's Compiegne plant uses a patented process called Esterfip, developed by the Institute Francais du Petrole.
Typical capacities for an esterification plant are between 8,000 and 60,000 tonnes a year with plans for 100,000 tonnes a year methylated vegetable oil facility under consideration.
Vogel & Noot claim to have built five esterification plants. Three of them have a capacity of 1,000 tonnes oil a year, one of 15,000 tonnes oil a year and one of 30,000 tonnes oil a year, with its start up scheduled for early 1994.
More than 200,000 tonnes a year of esterified vegetable oil production capacity has been installed in Europe, with a further 500,000 tonnes a year planned by 1995. The largest producer is the Novamont subsidiary of Italy's Ferruzi-Montedison Group, which has just started up a 60,000 tonnes a year plant at Livorno. A second 100,000 tonnes a year biodiesel plant is planned.
By 1994, Interchem Industries plans to market between 30 and 60 million gallon of biodiesel in the US. The company has contracted Proctor &
Gamble's Industrial Chemicals Div. to produce 15 million gallons a year of biodiesel at its plants in Massachusetts and California.
B I O M A S S I N T H E E N E R G Y C Y C L E
Both the extraction of vegetable oils and the esterification of vegetable oils can be done on farm at any scale using simple technology. The raw material may be seed which is contaminated or otherwise unfit for human consumption.
The esterification process can also be used to convert waste oils, e.g.
cooking oils, into a useful fuel.
At the very low technology end, CSIRO and A N U in Australia have combined to produce a processing unit for $200 which will extract oil from coconuts. A commercial prototype has been built.
Cost data for large and small scale plant is given in Table 4.11.
4.3.9 A n a e r o b i c Digestion
Anaerobic digestion is the breakdown of organic material to methane and ; carbon dioxide by bacteria in the absence of air.
The process can be applied to a wide range of raw materials including sewage sludge, animal wastes and wastes from abattoirs, industrial and food processing wastes and municipal solid waste. Plants can be built on a large or small scale.
The evolution of technologies for anaerobic digestion began with digesting low solid sewage sludges ( 5 % solids), through animal waste slurries (15%
solids) and then on to municipal solid wastes in landfill sites ( + 5 0 % solids) and in specially designed reactors ( 3 5 % solids). All of these applications, except the very last perhaps, are commercially demonstrated and well established over many hundreds of projects, with technologies being offered that have been developed in Europe, Japan and the U S .
Digestion can occur in three temperature ranges: ambient; 37-40°C (mesophilic); or at around 55 °C (thermophilic). This temperature affects the rate at which the digestion process occurs, but not its conversion efficiency, Generally 2 5 - 4 5 % of the feed solids are destroyed, producing 0.5m3 of biogas (50-80% methane, 3 0 - 5 0 % carbon dioxide depending on the feed type) for every kg of C O D converted. Some designs operating at the higher temperatures can consume 20 - 3 0 % of the gas generated to maintain the required temperature regimes.
Some wastes, particularly industrial wastes, require nutrients to be added, usually nitrogen and phosphorous, to support the digestion process.
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TABLE 4.11 Cost Data : Vegetable Oil and Esteriflcation Technologies
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B I O M A S S I N T H E E N E R G Y C Y C L E
Both the extraction of vegetable oils and the esterification of vegetable oils can be done on farm at any scale using simple technology. The raw material may be seed which is contaminated or otherwise unfit for human consumption.
The esterification process can also be used to convert waste oils, e.g.
cooking oils, into a useful fuel.
At the very low technology end, CSIRO and ANU in Australia have combined to produce a processing unit for $200 which will extract oil from coconuts. A commercial prototype has been built.
Cost data for large and small scale plant is given in Table 4.11.