Alternative​ Sources for Fuel: Rubbish

As most people have noticed, there is finally some awakening relating to climate change and the need to switch from fossil fuels, not that politicians are exactly accepting such trends, and indeed they seem to have heads firmly buried in the sand. The difficulty is there are no easy solutions, and as I remarked in a previous post, we need multiple solutions.

So what to do? I got into the matter after the first “energy crisis” in the 1970s. I worked for the New Zealand national chemistry laboratory, and I was given the task of looking at biofuels. My first consideration was that because biomass varies so much, oil would always be cheaper than anything else, and the problem was ultimately so big, one needed to start by solving two problems. My concept was that a good place to start was with municipal rubbish: they pay you to take it away, and they pay a lot. Which leads to the question, how can you handle rubbish and get something back from it? The following is restricted to municipal rubbish. Commercial waste is different because it is usually one rather awkward thing that has specific disposal issues. For example, demolition waste that is basically concrete rubble is useless for recovering energy.

The simplest way is to burn it. You can take it as is, burn it, use the heat in part to recover electricity, and dump the resultant ash, which will include metal oxides, and maybe even metals. The drawback is you should take the glass out first because it can make a slag that blocks air inlets and messes with the combustion. If you are going to do that, you might as well take out the cans as well because they can be recycled. The other drawback is the problem of noxious fumes, etc. These can be caught, or the generators can be separated out first. There are a number of such plants operating throughout the world so they work, and could be considered a base case. There have also been quite satisfactory means of separating the components of municipal refuse, and there is plenty of operational experience, so having to separate is not a big issue. Citizens can also separate, although their accuracy and cooperativeness is an issue.

There are three other technologies that have similarities, in that they basically involve pyrolysis. Simple pyrolysis of waste gives an awful mix, although pyrolysis of waste plastics is a potential source of fuel. Polystyrene gives styrene, which if hydrogenated gives ethylbenzene, a very high-octane petrol. Pyrolysis of polyethylene gives a very good diesel, but pvc and polyurethanes give noxious fumes. Pyrolysis always leaves carbon, which can either be burned or buried to fix carbon. (The charcoal generator is a sort of wood pyrolysis system.)

The next step up is the gasifier. In this, the pyrolysis is carried out by extreme heat, usually generated by burning some of it in air, or oxygen. The most spectacular option I ever saw was the “Purox” system that used oxygen to maintain the heat by burning the char that got to the bottom. It took everything and ended up with a slag that could be used as road fill. I went to see the plant, but it was down for maintenance. I was a little suspicious at the time because nobody was working on it, which is not what you expect for maintenance. Its product was supposed to be synthesis gas. Other plants tended to use air to burn waste to provide the heat, but the problem with this is that the produced gas is full of nitrogen, which means it is a low-quality gas.

The route that took my interest was high-pressure liquefaction, using hydrogen to upgrade the product. I saw a small bench-top unit working, and the product looked impressive. It was supposed to be upgraded to a 35 t/d pilot plant, to take up all of a small city’s rubbish, but the company decided not to proceed, largely because suddenly OPEC lost its cohesion and the price of oil dropped like a stone. Which is why biofuels will never stand up in their own right: it is always cheaper to pump oil from the ground than make it, and it is always cheaper to refine it in a large refinery than in a small-scale plant. This may seem to have engineering difficulties, but this process is essentially the same as the Bergius process that helped keep the German synthetic fuels going in WW II. The process works.

So where does that leave us? I still think municipal waste is a good way to start an attack on climate change, except what some places seem to be doing is shipping their wastes to dump somewhere else, like Africa. The point is, it is possible to make hydrocarbon fuels, and the vehicles that are being sold now will need to be fuelled for a number of years. The current feedstock prices for a Municipal Waste processing plant is about MINUS $100/t. Coupled with a tax on oil, that could lead to money being made. The technologies are there on the bench scale, we need more non-fossil fuel, and we badly need to get rid of rubbish. So why don’t we do something? Because our neo-liberal economics says, let the market decide. But the market cannot recognise long-term options. That is our problem with climate change. The market sets prices, but that is ALL it does, and it does not care if civilization eradicates itself in five years time. The market is an economic form of evolution, and evolution leads to massive extinction events, when life forms are unsuitable for changing situations. The dinosaurs were just too big to support themselves when food supplies became too difficult to obtain by a rather abrupt climate change. Our coming climate change won’t be as abrupt nor as devastating, but it will not be pleasant either. And it won’t be avoided by the market because the market, through the fact that fossil fuels are the cheapest, is the CAUSE of what is coming. But that needs its own post.