Power Plant Fueled By Nut Shells

sbszine writes "The Sydney Morning Herald is running an article about a green power plant that runs on the discarded shells of macadamia nuts. The power plant, located in Gympie, Queensland, is expected to reduce greenhouse gas emissions by around 9500 tonnes in its first year of operation."

Comments

Higher usable energy

[moscow]

According to ABC Queensland , Macadamia shells are actually prime material for electricity generation - they burn more cleanly than coal, and produce more energy.

Of course, natural decay of the shells would release the CO2 in any case.

Re:Reduction in Co2?

[zmooc]

Wrong. The only thing that matters in this context, is the percentage of CO2 in the atmosphere. While in the long term, burning plants would indeed not introduce any new CO2 into the biosystem. The only problem is that it is generally assumed it takes about 100 years for nature to create a balance between CO2-production ans CO2-consumption by plants. Just compare it to a closed system in a box with a plant and a device burning it's seeds; the plant will consume the CO2 a lot slower than the device can produce it so the CO2-level in the box will definately go up just like a sink will fill when the tap runs faster than the drain can put up with.

But in the long term it's always better to burn plants instead of oil since burning oil introduces new C into our biosystem while burning plants only raises the C-level in the atmosphere but not in the biosystem.

By the way, this only works if you assume each burned plant will be replaced by a equivalent plant. Burning more plants means the average age and therefore size of plants will decrease and therefore the amount of C these plants can hold will also decrease. And then even the space that's available for plants is declining.

Re:The article doesn't say...

[Thomas M Hughes]

My understanding is they had an existing facility that shells and cans macadamia nuts, and previously the shells were just being discarded as waste product. Someone had the bright idea to use the waste shells as fuel for a power plant. Basically, they just turned an expense (waste disposal) into a profit (electricity generation). And the facility only cost $3 million to create. All in all, I think this was an absolutely brilliant move.

Re:The article doesn't say...

[madbastd]

But does anyone know why they chose macadamia nuts? Seems a very strange choice.

Macadamia trees are a native plant in that part of Australia, and grow very well. There's a large macadamia nut industry there, which was throwing out huge amounts of nutshell.

Re:Reduction in Co2?

[famebait]

Just compare it to a closed system in a box with a plant and a device burning it's seeds; the plant will consume the CO2 a lot slower than the device can produce it

What makes you believe that? Are you assuming that the plant produces seeds at a diminishing rate, or that burning a seed releases more carbon than was put into building it? Because something doesn't add up here.

You are describing a closed system with a net production of carbon. If you have one of those you could be very rich indeed.

Just like a sink will fill when the tap runs faster than the drain can put up with.

That's not a closed system.

The only problem is that it is generally assumed it takes about 100 years for nature to create a balance between CO2-production ans CO2-consumption by plants.

That's a little out of context. Yes, if you completely cut down a forest, it takes a long time until there is once again the same amount of biomass contained on that area. But we're not _removing_ the ecosystem and waiting for it to return here, we're burning a nutshell in stead of allowing it to rot. The tree is still there, and it doesn't take a 100 years to replace a nutshell. If you burn a billion shells a year and produce a billion too, you have a net emission of zero. You're basically just extracting solar energy, the shells and the carbon are just carriers in the process.

There would be an minor initial 'cost' in that you're shortening the cycle a little, releasing the carbon more shortly after it's trapped compared to natural decomposition. So you get an initial emission over the first year or two after start up, as the 'cache' of decomposing shells releases its carbon at the same time as new shells are burnt immediately. But after they're gone you'll be running in balance. Or you could avoid that too by imitating nature and storing the shells a couple of years before burning them.

Re:Are you suggesting burning rubbish?

[ajs318]

Not true. Extreme heat destroys dioxins. They are often created by partial combustion {think bonfire}. What is basically going on in a fire is two processes. Pyrolysis is the fuel being decomposed into simpler chemicals, almost always incomplete fragments {sometimes even individual atoms} which will bond with whatever is nearest to hand {strictly speaking, nearest to valence electron?} as soon as they cool down enough. Pyrolysis consumes energy in breaking chemical bonds. Oxidation is the simpler chemicals reacting with oxygen. This gives out energy. Oxygen is chemically very horny and also will try very hard to avoid having to share with anything else. The pyrolysis products undergo some further decomposition as the oxygen atoms each try to grab something for themselves. Since the oxidation puts out more energy than the pyrolysis required, the fire stays alight. But you have to put some energy in {typically from a match} to start the pyrolysis, otherwise you would get spontaneous combustion.

Now, in a bonfire or badly-designed furnace, the pyrolysis products cool and recombine into literally goodness-knows-what and escape before they get a chance to combine with oxygen. This is where incineration can fail. Large lumps of fuel, and mixed fuels, all exacerbate the problems.

In a well-designed furnace, the fuel is finely-divided and the air supply forced {an unattended fire will tend to produce only as much energy as it needs to stay alight; this may mean partial combustion with great quantities of chemicals being released. A fan requires energy, but MOTN the energy gain from fetter combustion is greater than the consumption of the motor}. If the fuel is very heterogeneous, the pyrolysis phase of the reaction can be completed separately in by heating the fuel in an airless chamber {consuming energy} and the pyrolysis products burned later {releasing more energy than it took to do the pyrolysis}. By adjusting the temperature and pressure you can select whether the intermediate product is a gas, a light liquid like petrol or a heavy liquid like diesel fuel. This has the advantage that you know how long is the longest carbon chain in the fuel for the next stage, and there is no way that the products can contain sny longer carbon chains. The disadvantage is that it distributes the high-temperature processes, thereby creating more opportunities for heat leakage.

As for the "plastics" argument, it's a red herring. Upstream segregation could be used to separate plastic from the waste being used for energy recovery, if you were really concerned. But I can't see how it would not be better to extract energy from plastic that has already been used for something, than to use up energy burying that plastic in landfill and digging up more fossil fuel just to burn for energy. Over time, as fossil fuels became more expensive, plastics would begin to be made from plants anyway. Not to mention that lanfills also produce dioxins, albeit more slowly, and organic matter in landfill decays to CH4, which, molecule-for-molecule, is a better heat trap than CO2. The real problem is ignorance of the First Law of Thermodynamics. We've already had people bitching about CO2 emissions like they don't know where the carbon in a plant comes from, and if people can't appreciate the First Law as it applies to the tangible form of matter, how can we suppose they can appreciate it as applied to energy?

Of course, I'm with you about reduction. My ex's daughter was raised in reusable cotton nappies, so will be my niece at least while she is stopping with me. I avoid single-serving packs whenever possible. I wipe my nose on yesterday's T-shirt, and I put my sandwiches straight in my lunchbox without using a polybag {in the absence of a satisfactory explanation as to how wrapping food in plastic saves me from risking cancer by letting it touch plastic}. I don't use sanitary towels either, but only for The Reason That Does Not Count.

Re:Reduction in Co2?

[shokk]

Bullshit. Plants absorb quite a bit of carbon from the ground. That's a lot of old carbon that's released there. They estimate about 30% of the plant is old carbon.

http://www.sciencenet.org.uk/database/earth/natura lenvironment/e00077d.html