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Alternative Combustible Fuels


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I was just wondering if there was a realistic alternative to fossil fuels. Why aren't there power stations running on wood, maize, sugar (cane, beet) etc.

Why don't they just dry and burn the stuff, rather than trying to process/convert/refine it first (turning it into oil or alcohol). Obviously that would create its own technical problems (eliminating ash, cleaning etc) but seems a simpler solution than the intermediate processing. What fuels might be suitable? Ceareals/grains? Bananas? Coconuts? Peanuts? Ok, so I'm thinking "foodstuffs" but they obviously do have high calorofic values. Are there any non-foodstoff options? Bamboo? Hay?

What would be the feasability of burning waste plastics + paper, rather than trying to recycle it. It seems idiotic that we burn nice "clean" oil, but the idea of burning plastic sounds so environmentally unfriendly..

Presumably the answer is, that they are much more expensive than coal, oil, gas, but do these fuels simply have the advantage of the massive existing dedicated infrastructure and economies of scale? In any event, will growing fuels be feasible in the distant future (100 to 500 years) when we really have finally exhausted the attainable fossil fuels?

I've been wondering about this for years. There seem to be people on this forum who know stuff about stuff, so hopefully someone can enlighten me.

BTW, here in Germany, the powers that be are just starting to realise that the "Energiewende" i.e. changing to energy from renewable/sustainable resources, is going to get kind of expensive. Squeal squeal. Why didn't someone mention that sooner?

Edited by BigPig
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The simple answer is that none of your options has a calorific value anywhere near oil or gas (per litre), and is much harder to transport. So if you throw enough wood into a power station, you can burn it to make energy, but gathering that wood and transporting it is an enormous undertaking. In contrast, digging a hole in the ground and getting coal out is pretty simple.

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Some calorific values for comparison (kJ/g)

Diesel 44

Coal Anthracxite 27~32

Coal Lignite 15

Wood 15~22

Peat 6~15

Ethanol 30

Sugar 17

Peanut kernels 37

Bananas 1~2

I appreciate the concerns about the transport and the volumes being less manageable, plus I might have to reduce the world's poulation to a tenth of its current size to have enough arable land available, but peanuts still look like a possible future fuel source to me. I've given up on the idea of bananas though. Unfortunately peanuts cost 65c per 200g at Lidl = €3.25 per kg while house coal is around €2.25 for 10kg so it would be up to10 times as expensive.

http://en.wikipedia.org/wiki/Heat_of_combustion

http://en.wikipedia.org/wiki/Energies_per_unit_mass

http://en.wikipedia.org/wiki/Food_energy

http://www.peanutsusa.org.uk/MainMenu/Nutrition-health/Peanut-Nutritional-Values

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I was just wondering if there was a realistic alternative to fossil fuels. Why aren't there power stations running on wood, maize, sugar (cane, beet) etc.

There are power plants around the world that do run on "biomass" - renewable solid fuels, such as wood, etc. Indeed, there are plans to convert some UK power plants to be biomass compatible. In general, however, there are difficulties in getting enough biomass to support large scale energy production.

A 200 hectare coal mine facility can produce about 10 million tonnes of coal per year. A 200 hectare field growing a high-yield crop such as sugar cane, can produce about 1000 tonnes of biomass per year. In other words, replacing one coal mine would require about 5 million hectares of sugar cane (allowing for the lower energy content of sugar cane compared to coal).

The sheer density of coal and other fossil fuel reserves is huge. This makes extraction very cheap and very easy, compared to biomass cultivation and harvesting - it also allows extraction rates vastly higher than are possible with conventional biomass production.

The reason for conversion to ethanol, etc. is for use in vehicles. Power plants can be made to burn anything. Vehicles, however a requirement for liquid fuels (or possible gas, but this is much less desirable) which produce no solid ash.

What would be the feasability of burning waste plastics + paper, rather than trying to recycle it. It seems idiotic that we burn nice "clean" oil, but the idea of burning plastic sounds so environmentally unfriendly..

This is done at a number of sites. The UK has some (for example Sheffield energy recovery facility), and there are several in Switzerland and other European countries. These provide a source of energy, while mitigating the problem of waste disposal. There are pollution issues with older incinerator designs, but modern plants such as the one linked, have advanced "scrubbers" which extract all relevant pollutants from the exhaust gas stream. The difficulty with this sort of plant, however, is that with increased availability and lower cost of recycling, they increasingly find it difficult to obtain enough fuel.

Presumably the answer is, that they are much more expensive than coal, oil, gas, but do these fuels simply have the advantage of the massive existing dedicated infrastructure and economies of scale? In any event, will growing fuels be feasible in the distant future (100 to 500 years) when we really have finally exhausted the attainable fossil fuels?

Growing fuels, at least in the conventional sense, would not supply energy consumption like is used today. The problem is that conventional plant growth is a very inefficient use of land and sunlight. Typically, a high-yield fuel crop only converts about 0.3% of the sunlight into usable energy (once harvesting and maintenance are taken into account). By contrast, modern solar PV panels can achieve around 20%, with solar concentrating systems exceeding 30%. PV also has the advantage of producing primary electricity, which mitigates the need for fuel processing and energy conversion - which are expensive and lossy steps.

There has been a lot of talk about unconventional plant growth (e.g. algae) which are potentially much more efficient at capturing energy than land plants. I'm not aware that these are anywhere remotely practical given the current state of technology.

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Giving up land to grow fuels is madness. In contrast PV can be deployed on roof tops so need not take up any land. Wind turbines only use a small area of land relative to their output.

For example a 3MW wind turbine will require an area around the base of about 400m2. That turbine operating at 25% capacity will produce about 6600 MWH per year. To produce that amount of electricity in a biomass power station you would need about 4000 tonnes of wood (plus the fuel to harvest and deliver it). Eveen with the fastest growing coppice species you would need about 75 hectares.

So to produce the same amount of electricity biomass needs about 1800 times more land than the wind turbine.

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The sad thing is Drax (coal powered) is being converted to burn woodchip. Imported from Canada where they mine trees in a totally unsustainable way. Why is that any better than burning coal? If you burn old growth forest - trees that have taken up to 1000 years to grow it is no more carbon free than coal that took the same amount of time to grow but was then buried for 250 million years.

Woodchip - rip down the trees and shove them through a chipper and ship the result to Drax

Coal - rip up the mountains and shove them through a crusher and ship them to Drax

The only difference is the government subsidy to avoid CO2 targets. It does not stop the CO2.

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