February 8, 2009 – Vol.13 No.47
FROM WASTE TO RESOURCE WITH PLASMA.
by Bruce Mulliken, Green Energy News
In a perfect world everything that is built or manufactured would be designed from the beginning to be reused or recycled at its end of life. Every bit of plastic, metal, glass, paper, silicon, stone and cement would find another use or be rejuvenated to become a new raw material and be the basis for yet another product.
As we know the world is not a perfect place and we’re not as smart as we think we are. Our products are so complex and ever-changing that to include reuse or recycle in every part or component is far beyond our capabilities. Instead, we recycle some but throw much away. Our landfills are our manmade mountains that are getting bigger by the day because our waste disposal options are few.
But our trash can be a source of energy. Much of what we throw away is made of hydrogen, carbon and oxygen, the same elements that make up the fuels we burn.
Some of what we toss aside will eventually decay underground and create methane, a potent greenhouse gas. Where methane concentration is high enough we can capture it in a network of pipes to use as fuel for internal combustion engines that will generate electricity. Sure the engines will make carbon dioxide, but overall, greenhouse gases will be reduced since CO2 has far less planet-warming potential than methane (more than 20 times less.)
We can also burn our trash directly in waste-to-energy plants. Burning waste creates thermal energy for steam that can be used for heating or generating electricity. But burning waste also creates pollutants such as fly ash. Conventional waste-to-energy is probably not the optimum solution to our waste disposal problems.
For five years or so, another waste solution has been attracting attention: plasma gasification. The technology, quite different from plasma television technology, basically is comprised of a plasma torch confined to a chamber in which municipal solid waste (MSW) is fed. The torch is similar to a plasma torch used for cutting steel: An inert gas, sometimes air, is blown over an electric arc to make a kind of “flame.”
Temperatures in the plasma flame can approach those of the Sun. A few feet away the flame front can reach 9000 F (5000 C). Anything that gets in its way has its molecules dissociated to its elemental parts. Anything can include our daily trash: garbage, paper, plastic, old tires, even eventually the computer display with which you are reading this now.
The result of this high temperature incineration is a synthesis gas made of hydrogen, carbon monoxide and a few trace elements. That which isn’t incinerated becomes a glasslike slag that can be used in construction materials.
The synthesis gas can be used to make hydrocarbon fuels or it can be used directly as a fuel for internal combustion engine generators to make electricity. Power generated can energize the plasma gasifier itself with additional electricity sold to the grid. The more efficient the electric power generation process using the syngas, the more electricity is generated and sold, thus more revenues for the plasma gasification operator and the smaller the carbon footprint.
Fuel cells are more energy efficient than internal combustion engines, and at least one plasma gasification developer, Waste2Tricity of the UK, is planning to package alkaline fuel cells with its gasification technology. The company has recently signed a supply agreement with AFC Energy PLC for low-cost new generation fuel cells which will be mated to Waste2Tricity equipment.
The company currently is in the early stages of efforts with a number of strategic partners to proceed with its first 50,000 metric ton (55,000 US ton) per year pilot plant that represents Stage One of its development program: combining plasma gasification with internal combustion engines to generate electricity.
Stage Two will incorporate the fuel cells potentially increasing the net output of electricity by a minimum of 60 percent over the engine system to generate electricity.
Looking into the future, plasma could solve the world’s waste disposal problems by creating a 24/7, 365 day-per-year source of energy with fewer carbon emissions than burying our waste underground.
And no longer would we be building mountains of trash on expensive land.
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