I have just returned from a great month travelling in Far North Queensland, an area that is both very environmentally conscious and conservative. Bob Katter, a local MP is strongly pursuing an increase in ethanol production to improve the lot of cane growers, provide an economic boost and jobs while possibly protecting the environment. It is time for a look at biofuels from a technical perspective and as always politics and economics play the major role.
Biofuels include ethanol, biodiesel, biogas and wood, which in turn can replace or supplement petrol, diesel, natural gas and coal use. Ethanol is generally produced from products with high sugar content (sugar cane etc), high starch content (corn, potatoes, barley, wheat etc) or high cellulose. Biodiesel is made from vegetable oil, waste vegetable oil or animal fats. Biogas is produced from manure, sewerage and agricultural waste.
All three have the potential to offer fuel security with potential environmental gains. In the US and Brazil they have substantially reduced the need for imported fuels. In Brazil however there are issues with creating cropland by reducing rainforest area and in the US it can be argued that there is little, if any energy gain from producing ethanol from corn with current practices.
Ethanol is ethyl alcohol, or C2H5OH (or ethane with an OH group replacing a hydrogen atom). It is generally produced by fermenting sugar where
C6H12O6 → 2 C2H5OH+ 2 CO2
It is much the same process as making wine and then distilling the alcohol out. It requires heat and creates residue or by products as pure sugar is not the starting point. Pure ethanol burns to create energy with only carbon dioxide and water remaining. Ethanol is the alcohol in alcoholic drinks.
Starch is essentially long chains of sugar molecules and can be similarly fermented. Cellulose can be converted to sugars and fermented but is not yet done commercially. When it is, the economics and environmental concerns over ethanol production will benefit greatly. Ethanol can also be produced from fermenting algae and it may also be possible to create and store ethanol directly from living algae.
Sugar cane has the best yield of ethanol per acre of land used, has the best greenhouse savings and requires the least energy input. It produces about 8 times the energy input. That is for every unit of energy used to grow, transport, ferment and distil the sugar cane, 8 units of energy are created. Greenhouse Gas (GHG) savings (over petrol) are estimated at about 90%. Corn on the other hand only produces about 1.2 times the energy input and has up to 20%GHG savings currently. Research on increasing crop yields, energy input and GHG savings will improve the economics of each crop.
Brazil produces most of its ethanol from sugar cane, while US mostly uses corn. Australia has three ethanol production facilities (Feb 2014) with the largest at Nowra in NSW (Manildra plant) producing ethanol from waste starch – mostly wheat. The only plant using sugar by products is at Sarina, near Mackay in Qld with only about 15% of total production.
So why don’t we produce more ethanol?
The first issue is land use. Sugar cane is grown in the tropics (or sub tropical regions). Current land produces sugar for human consumption and at current oil prices is not economic for fuel (without subsidies). Producing more sugar for fuel will require land clearing, with its environmental consequences (including runoff into the Great Barrier Reef). With the cost difference, coal and CSG are the preferred energy sources (rather than ethanol) for plant and transport.
Energy from waste products is more viable as it is using products that would otherwise decay to GHGs. This includes grain crops, timber and other plant waste. Environmentally ethanol would also reduce air pollution, particularly with less particulates and nitrates. In Brazil, however, where sugar cane ethanol is most used, large increases in atmospheric formaldehydes and acetaldehydes have been measured! Additionally increases in ozone levels have been predicted.
The major problem with ethanol as a fuel is the perceived engine damage and running problems. The major one of these is that ethanol attracts water and is therefore hard to keep pure. This makes the transport of ethanol difficult and expensive. It can’t be shipped by pipeline for example.
Ethanol as fuel comes at various percentages of ethanol with ten percent ethanol E10 being standard in Australia. At this percentage water absorption is not a problem and modern engines are designed to handle this level. At higher levels eg E100 does create corrosion problems. Numerous car engines are designed to run on any ethanol blends these days.
The other major issue is starting in cold weather, anything under about 14 deg C. Engine design and additives are improving this problem. Ethanol engines designed to run in a diesel like mode are used in Sweden.
All things considered we probably should use more ethanol as a fuel in Australia and Bob is probably right that we should be producing it from excess sugar (rather than eating it!). Barley ethanol is another fuel to consider as it appears to provide a 50% reduction in GHGs to produce.
There are 12 Biodiesel plants in Australia, of which six have been mothballed or closed. Of the remaining six, five produce biodiesel from used cooking oil and tallow while the sixth produces a small amount from Canola oil. Palm oil has also been used.
Again biodiesel is seen as a renewable, clean burning fuel resource, and when made from waste this would appear to be the case. Other feedstocks are being developed including algae and various trees. The use of palm oil has the obvious problems of destroying rainforests. It is estimated to take about 100 years to become carbon dioxide neutral after destroying rain forest and planting new trees, notwithstanding horrendous habitat issues.
There are also some waste problems from biodiesel manufacture. Glycerin is one of these with large amounts produced. It can be purified to near 100% levels and used in the chemical industry (to some degree). Generally the glycerine is only about 50% pure and needs to be disposed of using anaerobic digestion. It can not be dumped due to its high methanol content.
Biodiesel can be added to petroleum sourced diesel at levels up to 5% without any notice.
Natural gas (methane or CH4) from biological origins is called biogas and is identical to the thermogenic gas derived from deep gas wells ( or coal gas). Biogas is generally derived from landfill sites, sewerage systems or specifically designed digester using animal waste. It is generally used to produce electricity at the source by burning it to run a turbine. Compressing gas for storage in small systems is not generally an option.
Numerous landfill areas are used to generate small amounts of electricity from the locally produced gas. In these areas dangerous levels of gas can build up and eventually explode or catch on fire. It is more sensible to use this gas profitably than let it escape into the atmosphere. Another issue from landfill gas is the presence of poisonous gases like hydrogen sulphide (rotten egg gas), which need to be managed.
Agricultural waste (from pigs and chooks in particular) can also be converted to gas using a digester. This can be used to run a generator at farm level.
Biogas is generally a way of solving a pollution problem rather than a mainstream energy source.
Wood burning is a major source of energy for developing countries and is still significant in developed countries as a heating fuel. Nothing beats a wood fire for feel good heat. Wood fires are highly polluting, even the modern controlled fire boxes. They produce fine particles and toxic gases including benzene, particularly when turned down (ie low oxygen levels). Particulates hang around in the low atmosphere for up to ten days after a fire and are a major health problem.
Once wood is burned to charcoal, noxious emissions are significantly less. However it is not recommended to burn charcoal indoors as it may produce enough carbon monoxide to be dangerous if there is not enough ventilation! Deaths have occurred from indoor charcoal burning.
Wood or biomass pellets are another fuel source with improved levels of pollution from regular wood. Home pellet burners still have the same particulate emission problem. Large scale burners can also control these emissions more effectively.
Wood is often seen as carbon neutral. It is estimated to have a carbon deficit of about 20 -25 years ( ie it takes that long to grow the carbon back).
All in all biofuels have their place, particularly in developing economies. A lot of work still needs to be done to effectively produce the fuels without the use of fossil fuels and with little waste. Land use issues will always be a problem.