Thursday, August 25, 2011

Garbage Incineration.

Municipal waste being incinerated.  Courtesy Wikipedia.
So,

It would seem that there is some kerfuffle in the Greater Toronto Area.  The ground has been broken on a garbage incinerator project, and the locals are certainly worked up about it.  While I will not pretend to be an expert on the subject, I do know some pertinent science that I am sure you, my monocled, Brandy-swirling readers would love to hear about.

I will freely admit that at first, burning garbage seems like a bad idea.  After all, many of us have thrown things onto a fire and seen the evolution of black pillars of foul-smelling smoke.  This, however, is far different from what goes on in a garbage incinerator.  You see, inside an incinerator, it is much easier to get up to high temperatures in an enclosed space than in an open fire pit.  Those of you who have used a chimney to ignite charcoal (or "cookin' biochar", as I am certain no one calls it) may be familiar with this effect.  The objective here is to achieve total combustion, where all carbon [or fuel, the garbage] is fully converted to carbon dioxide ["is fully oxidised"].  This is far better for our air than the results of impure combusion, which include much higher amounts of ash, soot [what I assume to be aerosolised/dispersed ash, really], and harmful products like carbon monoxide.  Fire pits see impure combustion when "smoky".  The combustion above appears to be very pure, by comparison.

The structure and synthesis of polystyrene. Wikipedia.

I will also admit that, in many cases, garbage incineration is often accompanied by the abandonment of recycling plastics.  They are necessary to fuel the blaze, and are included with the garbage.  This, too, sounds like a nightmare to the environmentalist.  I agree that in a perfect world, all plastic would be recycled forever.  Sadly, this is either not the case, or not possible.  Some classes of plastics would be easy to recycle.  Styrofoam, polymerized styrene [or "polystyrene"] is an example.  This is easily dissolved in the solvent acetone.  Acetone also has a very, very low boiling point.  It would be very easy to dissolve all those meat trays and packing chips, then boil off the solvent to have relatively unscathed polystyrene to reuse.  Unfortunately, as with other classes of plastics (water bottles, especially), this is not the case.  The manufacturing process for these types of plastics is inexpensive enough that the recycled product is too expensive for anyone to purchase.

The other challenge facing plastic recycling is the nature of the substance.  As can be seen above, plastics [polymers] are very long chains of some individual molecule [the monomer].  The recycling process must heat plastic so that it can be reformed.  Heating damages the bonds of the polymer, causing the plastic to degrade.  In fact, the reason that one rarely sees 100% recycled plastic products is that the structural integrity of recycled plastic is compromised, and it must be blended with new plastic so that the product may serve its purpose.  For the record, recycled metal does not share this problem, and I think it a fabulous idea, given the environmental costs of smelting metal.  Metal is also easily recovered in the incineration process.

A garbage incinerator in Vienna.  Source.

"Now see here!" You may demand.  "Won't this contribute to global warming?  Spewing out all that carbon dioxide?!"  This is an excellent point, and I am glad that you [might have] raised it.  It is true that greenhouse gas emissions will be added to with garbage incineration, however, it is much better than other emissions associated with dumps.  You may have seen torches burning outside of buried garbage dumps.  I know that I have near Carp, Ontario.  The reason for this is the venting of methane, a common byproduct of garbage disposal.  A methane leak is far, far worse than the leaking of carbon dioxide into the atmosphere.  The reason can be explained with very simple physical chemistry and math (you may skip the next paragraph if you are truly averse to it, though I find it interesting).

The surface of the Earth is heated by the Sun.  As can be seen in math here, the light that an object emits depends on its temperature.  The very hot Sun emits all colours of the rainbow, but the Earth is by comparison only lukewarm.  Objects at that temperature emit infrared (IR) radiation (this is how night and thermal cameras work).  Normally, a substantial amount of heat from the Earth is converted into IR and is lost to space.  Molecules, however, will absorb IR and begin to vibrate, blocking the exit of the heat into space.  This is the cause of the greenhouse effect.  Now, not all molecules are created equally.  The amount of IR that a molecule can absorb depends on how many ways that molecule can vibrate, known as vibrational modes.  The number of vibrational modes of a molecule depend only on the number of atoms.  Carbon dioxide has three atoms, and linear molecules follow the formula 3N-5, meaning it has 4 modes of vibration.  Non-linear molecules have 3N-6 vibrational modes, giving methane, a 5 atom species, 9 modes of vibration (or something like that).  Other math which I do not wish to get into demonstrates that this makes methane 21 times worse to have in the atmosphere than carbon dioxide.

We must also consider the issue of storage.  Many municipalities are running out of space for garbage, and it is much easier to bury the remaining ash of an incinerator than it is for the immense volume it started as.  Also, while most modern dumps are more or less sealed, leaks of contaminants are not impossible.  Many contaminants released by the incineration process can be captured before discharge into the air, meaning that, in my opinion, it is likely safer to incinerate garbage than it is to simply bury it.
Power transmission lines, because I discuss it below, and this certainly is a large block of text.  Source.

I must also discuss the issue of power.  Conventional dumps may use the methane generated by the garbage to spin a turbine and generate power, which seems like a fantastic idea.  Energy from our waste. However, garbage incineration offers a much higher amount of energy to us.  The fire from the incinerator can be used to generate steam from a boiler.  This would spin a turbine in exactly the same way as nuclear, coal and natural gas power plants do, but from a power source we are currently wasting. In a twist on this idea, a company called Plasco has found that heating and exposure to a plasma torch can produce refined syngas (mentioned previously in my biofuels post), which can then be used to make various other products and fuels.  It is also worth noting that steam-generating applications can route waste heat to nearby schools and hospitals to heat hot water, boosting the overall efficiency of the process.

With this in mind, I feel that garbage incineration is beneficial, and ultimately an opportunity.  It would lead to safer disposal of our waste, which is inherently invaluable.  Further, it represents an untapped energy source which could ease strain on our grid, and provide baseline electricity generation which most renewable fuels cannot (as the sun does not always shine, nor does the wind always blow).  I think that, if done properly, widespread incineration efforts would lead to a better tomorrow.

NM
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