Another post arising from our recent talk on remanufacturing. (See also: Motorcycle upcycle.)
Imagine a car that’s reached the end of its life. It’s been in a scrapyard for a good while, and everything of use has been stripped off it. Viable components go on to serve in other vehicles, and some of the more valuable materials such as copper or aluminium are specifically targeted for salvage.
After a few months, what we’re left with is a car body that’s mostly steel. There are some other, low-value oddments such as plastics, glass, fabric, paint… but by weight, it’s mostly steel. That’s a recyclable commodity: it has sufficient value to be worth collecting, and melting down. In fact, old cars are a much better source of metal for new cars than iron ore is. So far so good: we scrap our old cars, as required by the European Union’s End of Life Vehicles Directive (2000/53/EC) and the majority of the materials are destined to be used again (a 95% reuse or recovery target from January 1st 2015).
Consider this, though: the melting point of steel is around 1370°C, and we have to put a lot of energy into our steel to raise it to that temperature. This is unavoidable; the specific heat capacity of steel is 420J/kg/°C at room temperature, and increases to 720J/kg/°C as we near the melting point. This equates to approximately 375KWh to melt a tonne of steel, if starting at room temperature. Of course, no real-world machinery is 100% efficient, and in practice foundries use between 500 and 800 KWh to raise a tonne of steel to its melting point.
What spoils our fun is sustainability: specifically anthropogenic climate change. The amount of carbon dioxide associated with energy usage in known; Defra publish Conversion Factors regularly, associating a range of activities with greenhouse gas emissions. If we assume that we’re using UK grid electricity to power our arc furnace, and we use figures from Defra, that’s 0.44528 kg CO2e per KWh… which means that our 500 to 800 KWh process is going to cause the emission of 223 – 356 kg CO2 (or equivalent). Remember, that’s not to produce a new car… that’s just to melt a tonne of steel. It is to be hoped that while the steel is nice and hot we pour it into new castings, or send it through a slab mill and then roll it into sheet, etc… but whatever we do with it, all we’ve ‘paid for’ with our 223 – 356 kg CO2e is the melting process itself – nothing to do with reverse logistics (collection of the end-of-life product) or downstream activity such as manufacturing, quality control or distribution.
If we are to have any hope of meeting the terms of the Kyoto Protocol (an international environmental treaty aimed at the reduction of greenhouse gas emissions, to limit anthropogenic climate change) then we simply can’t afford to deal with metal objects at the end-of-life by raising them to their melting point every few years. Our dwindling national allowances of emissions are going to be required to meet more fundamental needs, such as agriculture.
But if we can’t melt products down, what can we do with them?
We can reuse them. Not in the sense that everybody will end up driving a used car, but some things can be made to serve again, in a new capacity or with a new owner. Eventually, though, things wear out, or become obsolete. There will always be an end to the useful life of products.
The calculations relating to steel, above, tell us that simply declaring that we can recycle is not the answer. It’s better than dumping unwanted products in a hole in the ground, but it’s not efficient. Consider all the skill, energy, effort and care invested in the creation of a product: do you really want to just smash it apart, identify each fragment by material type, and melt them again? Is identifying the chemical constituents of a product and separating them out the best we can do? (Not that all compounds are separable…) Reverting an end-of-life product to its most basic state means we salvage the material, but probably squander most of the skill, energy, effort and care that went into it… making society poorer over time.
The image of Hewlett-Packard cartridges illustrates the problem: they are fed into a machine that chops them up, into fragments that can be sifted to eliminate contaminants. The fragments can then be reduced to granules, becoming the feedstock for a new injection moulding process.
It’s better than nothing… but it’s a long way from perfect. Again, recycling is energy-intensive – and keep in mind that most thermoplastic recycling involves some degradation; the second time around, plastics are typically relegated to an alternative usage. A major problem here is phase separation, where a mixed plastic feedstock tends to separate out, leaving us with distinct ‘interfaces’ between materials within a moulded component, creating weak points. This limits the value of reclaimed plastics, and limits their application. (‘Plastic lumber’ makes great decking and park benches, but you can’t attempt fine moulding with reclaimed material.)
For centuries, now, most supply chains have been configured on the assumption that wealth creation begins with extractive industries such as mining. (Of course, some feedstocks are grown, rather than dug out of the ground…) We’ve known for generations that extraction couldn’t go on forever; there is only so much iron, oil, and whatnot in the ground.
For a time, it seemed that ‘mining’ our waste streams held the answer. There are useful materials to be had, and it would be a terrible waste to simply push them into a hole and forget about them… but recycling isn’t always easy, and it doesn’t come ‘free’. We need to think of recycling as a last-ditch attempt at damage limitation… not as a ‘green’ outcome, or a success.