U-loop fermentor for bioethanol fermentation
Background
Oil prices are increasing steadily. In 2001 a barrel of oil cost about USD 10, and it now costs more than USD 100. Nobody knows the future but there is no sign that prices will decrease in the years to come as the demand is increasing heavily worldwide, particularly in China and India.
Interest in finding alternatives to fossil fuels is great on account of the high oil prices, and substitutes for petrol, e.g. ethanol, become more and more interesting.
A side benefit of the production of ethanol based on agricultural crops is that the CO2 balance is neutral and not CO2-generating in contrast to petrol burning. Popularly speaking, agricultural crops will not contribute to CO2 emissions as plants use as much CO2 in the photosynthesis in one season as is developed by ethanol combustion. In contrast to this, the CO2 consumption at the fossil fuel took place 65 million years ago and therefore contributes with the whole CO2 development by combustion today.
Ethanol combustion poses very little risk to the environment compared to petrol combustion, and at the same time ethanol can substitute for MTBE in petrol.
In the USA, a major wheat-growing country, ethanol production has risen markedly in recent years (concurrently with the rise in oil prices). In 2004 there were about one hundred ethanol production facilities, and new companies opened in 2005 in the US Corn Belt. In 2004 3.4 billion gallons of ethanol were produced in the US corresponding to 15.5 billion litres/year.
The consumption of petrol in Denmark amounted to about 2.8 billion litres in 2004.
Contrary to e.g. sugar cane-based ethanol production, wheat-based ethanol production requires an extra-expensive enzymatic process in order to transform the starch into free glucose, which can ferment and form ethanol.
Today the ethanol production price is higher than the petrol production price, but the price difference is smaller than ever. Today the refinery production price for petrol is about DKK 2.10 compared to a production price for ethanol of about DKK 2.60 (the price is based on wheat as raw material), all prices WITHOUT tax.
When planning an ethanol factory based on crops, the predominant factor is the production price. Other arguments such as CO2 neutrality, MTBE substitution etc. do not count as much if the production price is much higher than the production price for petrol.
The below table shows the production price for bioethanol. 
The raw material price is by far the most expensive unit cost, followed by the enzyme process, the fermentation and the distillation.
The raw material price for crops as e.g. sugar cane and wheat is determined by the world market, and the only way to influence these prices is to find other sugary and starchy raw materials which are cheaper per unit of glucose or starch.
The enzyme process can only be made cheaper by developing cheaper and better enzymes that can transform starch into glucose, but using raw materials containing glucose (i.e. without the enzyme process) is of course cheapest.
The unit operations fermenting and distillation are used in many industries within chemistry, food production and pharmaceutical production, and the traditional methods are well-known. Therefore new methods with lower unit costs (steam, consumption, better substance mixing and an optimal steering and regulation are interesting, too. The U-loop fermenting principle has these advantages, and it will be interesting to demonstrate this theoretically and practically in connection with the fermentation of sugary raw materials.
Agriculture is Thailand’s biggest trade. The main crop is rice, and the country is one of the world’s biggest exporters. In the northern part of the country they grow rice, vegetables, tobacco and fruits. In the southeast area you will find cassava, sugar canes, pineapples and rubber plantations. Thailand is the world's leading pineapple producer, accounting for 20% of the world’s total pineapple production.
Extract from the American Coalition for Ethanol (ACE)’s homepage http://www.ethanol.org
Ethanol production
US ethanol production is reaching unprecedented levels. In 2004 ethanol production reached 3.4 billion gallons, up from 2.81 billion gallons the previous year. The dramatic growth continues on the back of consumer demand, the banning of methyl tertiary butyl ether (MTBE) and the number of production facilities set to begin operations.
Currently, there are 83 ethanol production facilities in the US, primarily centred throughout the Corn Belt. Today, nearly half the ethanol plants in the US are farmer-owned cooperatives. In addition, of the 16 new facilities under construction in 2004 nearly all are owned by farmer investors.
With few exceptions US ethanol production is mainly corn-based. Ethanol can also be made from other products such as grain sorghum (milo), wheat, barley, sugar cane or beets, cheese whey and potatoes. Cellulosic feedstocks such as municipal waste or recycled products, rice hulls, bagasse (fibrous residue from sugar cane), small-diameter trees, wood chips and switch grass may also be used to produce ethanol, but these products are not yet utilised on a commercial scale.
Ethanol can be made by a dry-mill process or a wet-mill process. Most of the fuel ethanol in the US is made using the dry-mill method.
The major steps in the dry-mill process are:
1. Milling. The feedstock (corn, wheat, barley, etc.) passes through a hammer mill which grinds it into a fine powder called meal. The vast majority of ethanol in the US is produced from corn.
2. Liquefaction. The meal is mixed with water and alpha-amylase, then passed through cookers where the starch is liquefied. Heat is applied at this stage to enable liquefaction. Cookers with a high-temperature stage (120-150 degrees Celsius) and a lower- temperature holding period (95 degrees Celsius) are used. High temperatures reduce bacteria levels in the mash.
3. Saccharification. The mash from the cookers is cooled, and the secondary enzyme (gluco-amylase) is added to convert the liquefied starch to fermentable sugars (dextrose).
4. Fermentation. Yeast is added to the mash to ferment the sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash is allowed to flow through several fermentors until it is fully fermented and leaves the final tank. In a batch process, the mash stays in one fermentor for about 48 hours before the distillation process is started.
5. Distillation. The fermented mash, now called beer, contains about 10% alcohol plus all the non-fermentable solids from the corn and yeast cells. The mash is pumped to the continuous-flow, multi-column distillation system, where the alcohol is removed from the solids and the water. The alcohol leaves the top of the final column at about 96% strength, and the residue mash, called stillage, is transferred from the base of the column to the co-product processing area.
6. Dehydration. The alcohol from the top of the column passes through a dehydration system where the remaining water will be removed. Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous ethanol (pure, without water) and is approximately 200 proof.
7. Denaturing. Ethanol that will be used for fuel is denatured or made unfit for human consumption with a small amount (2-5%) of gasoline at the facility which produces the ethanol.
8. Co-products. There are two main co-products from the production of ethanol: distillers grain and carbon dioxide. Distillers grain, wet or dry, is a valuable livestock feed. Carbon dioxide is given off in great quantities during fermentation, and many ethanol plants collect, compress and sell it for use in other industries.
U-loop fermentation is a key to profitable bioethanol fermentation.