The production of bio-ethanol is much the same as the brewing of alcohol. Particular crops are fermented an the resulting alcohol is distilled. Producing bio-ethanol requires the development of farming and transport within the city, using the canal for shipping and growing crops in Wollaton Park. Thus the bio-ethanol prompts the creation of new infrastructure in Nottingham and supports the growth of it by providing fuel.
Crops used for Bio-Ethanol
By using a variety of crops a better harvest is assured and planting/harvesting can be staggered though the year. Barley, wheat and sugarbeet can all be fermented as well as eaten. Even after the fermentation process the solid material is edible, often used as animal feed.
Producing bio-ethanol is very similar to the process for home-brewing. First crops are processed to convert starch into sugar, then they are ground and mixed with water in a process called mashing. This dissolves the sugars into the water so that yeast can be added. This mixture is then fermented without access to oxygen. The yeast converts sugar into alcohol and CO2. To convert this low strength alcohol into higher content bio-ethanol requires distillation. The solution is evaporated up a distillation column with the alcohol boiling off sooner than the water. These fumes are then condensed through a water cooled coil. The distillation will be repeated 3 times to get the concentration up to 95%abv. The last 5% of water is filtered out through salt.
Neccessary Equipment
Distillation Column Model
A distillation column and condensing tube was assembled, from acrylic tubing and metal pipe, to better illustrate the process through which bio-ethanol is created. Weak alcohol is first evaporated up the vertical column, with alcohol boiling off faster than water does. The alcohol gases are then condensed back to a liquid with the aid of water cooling.
Bio-Ethanol Production Stages
Through the analysis of the bio-ethanol production process, the need for a series of spaces has become clear. Crops need to be unloaded from the canal, barley needs to be malted, grain must be milled then mashed, the mixture needs to be fermented requiring room for several fermentors, a distillery building needs to provide boiling temperatures and a distillation column must lead from this building to a filtration area. Taking the needs of the post-oil community into account, the workers in the bio-ethanol plant will require recreation space. It is possible that the bio-ethanol produced can be watered back down and served as conventional drinking alcohol.
Using Waste Products to Grow Algae
With warmed water being released into the canal, algae and weed would grow around the output. Exploiting this, a set of algae beds can be set up, letting warm water fall down through the levels as the CO2 produced by the fermentors and biomass boiler is pumped up. This results in warm, carbon rich water ideal for algae growth. The algae can be used a food for human or animal consumption or as a fertiliser.
In order to heat and cool the different parts of the process, a siphon draws water up from the canal and circulates it through the site. The drop in water level over the lock-gate pumps the water without the need for a power source. The water drawn up is first used for cooling, then it is heated by a biomass boiler and used for heating buildings and processes. The warm water is then returned to the canal.
Siphon Model
A model was built to illustrate this process, with water being drawn up by a siphon from a high reservoir and circulated up and down, before being released at an ultimately lower down point. Once the siphon is brought to pressure by having the air sucked out of it, creating a vacuum, it does not require any energy to continue to run.
Temperature Regulation within the Malthouse
Using the kind of hinge found on greenhouse windows, the temperature inside the malthouse can be regulated by a louvred wall to prevent the enzymes in the barley denaturing.
Moving Grain through the Malthouse
In order to produce enough bio-ethanol to support the community, the malthouse has to release 2.5 tonnes of crops per day. Taking that it takes barley approximately 10 days to malt, the malthouse is required to hold 25 tonnes of grain at any one time. A series of conveyor belts could be assembled to move the grain through the building.
Required Quantities and Process Calculations
Using the land available at Wollaton Park, 260 people can be supported in terms of food and fuel. If the average UK consumption of gasoline is 9.5 barrels per capita per anum, then the 260 people living onsite would require 2470 barrels of bio-ethanol per year. This converts to approximately 400,000 litres of alcohol fuel at 100%abv.
Soaked in Water
It takes around 2 1/2 weeks for a 10,000 litre fermentor to complete its process. At 21/2 weeks you can fit in 20 fermentation cycles a year. 20 cycles of a 10,000 litre fermentor produces 200,000 litres of low strength alcohol (10%abv). 20 fermentation tanks would be able to produce 4,000,000 litres of 10%abv alcohol per year, equivalent to the required 400,000 litres of pure alcohol fuel required. A yield of 0.4 litres of bio-ethanol (100%abv) is expected for every kilogram of crop used. Hence 4 litres of 10%abv beer per kg. A 10,000 litre fermentor would require 2,500kg worth of crops to fill.
Barley sprouts, then is killed off by being dried out.
The distillation of the beer (10%abv) is powered by biomass boilers. A domestic biomass boiler has on average 30 kilowatts of power. It takes 2.6 MegaJoules of energy to evaporate 1kg of water from an initial temperature of 20째C. Hence for 10,000 litres of beer, 26,000 MJ is required. This is equivalent to 7,200 KilowattHours. Taking that the distillery will be running for 12 hours a day, the boilers will require a power output of 600kw. This is equal to the power of 20 domestic biomass boilers.
Barley
5 boilers will be used to distill the beer into pure bio-ethanol. Hence, each boiler is 120kw. A 120kw boiler will evaporate 166L of water per hour. Alcohol has a lower boiling point than water, it evaporates at 78.5째C instead of 100째C. This means that 467L of alcohol can be evaporated per hour. The average of water and alcohol results in 316L of evaporation per hour per boiler.
Malting barley involves soaking it in water and allowing it to begin growing, In these first stages of growth, maltase is produced; an enzyme that converts starch to sugar. Barley produces more malt that it requires itself so it is an ideal crop to use, providing the enzymes needed for other crops. As it malts, barley heats up and requires cooling to prevent the enzymes denaturing. Natural ventilation can prevent this overheating. Although not relevant to the production of bio-ethanol, malting is what provides a lot of flavour within beer brewing. Nottingham has a long history of malthouses, with many being built within the sandstone cliffs.
Assuming 21/2 weeks to ferment and 20 fermentation tanks, a tank is emptied and refilled practically every day. This means that every day the malthouse has to produce 2,500kg of processed crops. With barley taking 10 days to malt, the malthouse has to hold at least 25 tonnes of crop.
The biomass boilers are fuelled by woodchips. Burning dry oak at 100% efficiency releases 14MJ of energy per kg. At 25% moisture the average wood fuel releases 12MJ per kg.
Dried
A 120kw boiler uses 430MJ of energy per hour, or 5,100MJ per 12 hour day. The 5 stills will use just over 25,000MJ of energy every day. 2,100kg of woodchips will meet this requirement. So 2.1 tonnes of timber consumed per day. Timber grown in forestry conditions is usually 1 tonne per m3, hence 2 tonnes of timber used per day.
To distill the bio-ethanol up to full strength a biomass boiler evaporates the solution from a boiling pot. The boiler is composed of a brick-lined fire pit with a hopper feeding it woodchip fuel. The still would be built on 2 levels, with service access to both the fire pit and the boiling pots.