Humans have an incredibly extensive waste problem. Currently, most of that waste is sent to landfills where it takes up space for thousands of years, leaching harmful chemicals and gases into the soil and atmosphere. Alternatively, we send it to incinerators which burn it for energy, but which release harmful greenhouse gases (GHGs) and toxic by-products in the process. A large proportion of our plastic waste ends up in the ocean, where it strangles and poisons fish, seabirds and marine mammals. What if I told you that there was a way to get rid of almost any type of waste in one machine, that the machine would release no harmful chemicals or GHGs, and that the process would produce useful by-products and excess energy that could be sold back to the grid? Such a machine exists right now; the plasma waste converter (PWC).
While incinerators are able to extract about 15% of the potential energy from rubbish, PWCs can extract an incredible 80% using a process called ‘gasification’. Plasma is ionised gas, meaning that it contains roughly equal numbers of positively charged ions and negatively charged electrons. One way you can make plasma is by creating an arc of electricity between two rods, then passing a gas like argon through it. This set-up is known as a plasma torch and can heat gases to a higher temperature than the surface of the sun. The crucial difference between using a plasma torch and using an incinerator is that in PWCs, combustion doesn’t take place. That means no smoke, no GHGs and no ash. The plasma breaks down the bonds between atoms, separating them into very simple forms. Despite the extremely high temperatures, it would be wrong to say that the waste is being ‘burned’; rather it is being decomposed at an accelerated rate.
One of the products of gasification is, you guessed it, gas. This energy-rich gas, known as syngas, is largely made up of hydrogen and carbon monoxide. Syngas mainly comes from the gasification of organic matter. As the gas expands, it turns a gas turbine, generating electricity. The high temperature of the gas can also be used to evaporate water, generating steam to turn another turbine. The syngas itself can then be burned for fuel or scrubbed with water and released safely. All of this energy production and revenue is coming from rubbish. We are talking about the plastics that are decimating marine life. Metals, fabrics, wood, even toxic or hazardous waste from industrial run-off or medical facilities. This is stuff we need to get rid of and by getting rid of it like this, we can also take some of the stress off an already strained energy production sector.
The solid by-product of gasification is called ‘slag’. Slag is produced mainly from inorganic materials like metals. It can be used in construction to bulk up concrete and tarmac. The molten slag also pools at the bottom of the chamber and helps to maintain the temperature, reducing the energy consumption. The real magic happens when you pass compressed air through molten slag to create a material known as ‘rock wool’. Rock wool is currently made by drilling into rock, melting it down and spinning it. Made in this way, it is sold at one US dollar per pound, but when it’s made of rubbish, it can be sold at just 10 cent per pound.
Rock wool can be used in many ways. As an insulation material, it is twice as efficient as fibreglass and could significantly decrease heating and air conditioning bills. Surprisingly, you can also hydroponically grow plants from seed in rock wool. Perhaps its most amazing use is that it can clean up oil spills. Rock wool is lighter than water and extremely absorbent. This means that if you spread it out over the surface of an oil spill, it will float and absorb all the oil. The rock wool can then be collected with relative ease. Slag and rock wool are two more saleable products that can increase the economic viability of plasma waste conversion.
PWCs are currently being built all around the world. Some plants are already so efficient that they need to take rubbish out of landfills to use as feedstock. There is even a mobile plasma torch on the back of a truck in the US which can be jammed straight into landfills, which act as makeshift gasification chambers. The need to reduce GHG emissions and simultaneously fix our massive waste problem has generated huge interest in PWCs in recent years. Landfills have only one way to make money; they charge you a ‘tipping fee’ for getting rid of your waste. Since PWCs can generate revenue from both energy production and by-products, they can make their tipping fees much more competitive.
PWCs are a relatively new technology. The cost of building and operating one is still much higher than that of some of its competitors including landfills and incinerators. There has not yet been standardisation of the design and thus the huge and complex machinery must be custom-built every time. The energy needed to power it is also very high, especially compared to incineration, which requires only a match. PWCs are extremely efficient long-term; unfortunately, short-term profits dictate much of what happens in society.
Fossil fuels are becoming more and more scarce and their price is constantly being driven up by various international climate change initiatives. With thousands of landfills already full and the global population expected to exceed 10 billion by 2050, rubbish will not be scarce for a very long time. This really is a win win win win win. One machine can get rid of harmful waste, cut GHG emissions, produce fuel, energy and construction materials and clean up oil spills all while making a profit. An investment in plasma waste converters is not only economically sound, but it is also an investment in the future of our planet.
By Adam Boland – Science Writer
