August 2014 Labnotes

Researchers Use Waste Slag to Create Energy and Cut Emissions

Slag is a molten mixture of process waste ashes from the power and metallurgical industries. In gasification, slag is made from mineral impurities that remain after a carbon feedstock such as coal has been gasified. In metal refining, slag contains impurities removed from a metal while it is refined. Jinichiro Nakano sums it up succinctly: "Slag is basically waste that is vastly landfilled in many countries. The U.S. is no exception." He and fellow scientist James Bennett have found a way to make slag more valuable. They discovered that by mixing two particular types of slag at a unique ratio they can generate energy and fuels.

The Asia-Pacific Partnership on Clean Development and Climate targets reductions of 1.27 million tons of CO2 emissions per year among Australia, Canada, China, India, Japan, South Korea, and the United States. If practiced successfully, Nakano and Bennett’s method could reduce the CO2 emissions from a single steel plant that produces 7,680 tons of steel per day by 0.6 million tons per year without compromising the plant’s rate of production. This means that the Asia-Pacific Partnership on Clean Development’s goal would be surpassed if just a few plants practiced the method.

One of the slags is a byproduct of a metallurgical process that is rich in calcium oxide. The other slag contains high levels of vanadium (III) oxide generated during gasification using petroleum coke-based carbon feedstocks. When the two slags, molten at discharge, are mixed together in the presence of carbon dioxide (CO2), the resulting chemical reactions give off an incredible amount of heat—enough to turn a turbine and generate electricity. Simultaneously, the same chemical reactions turn CO2 into carbon monoxide (CO), which "can be combusted with oxygen for additional power generation," explains Bennett, "or it can be used as a raw material for producing chemicals such as synthetic petroleum." More value exists in CO because it allows you to do things that CO2 doesn’t."

Use of waste slags for CO2 reduction and fuel gas production

Hydrogen gas, which is useful in chemical manufacturing and industrial applications including fuel cells, can be economically made from water using the same method. Nakano and Bennett describe the reactions that yield these products in an article recently published in the International Journal of Hydrogen Energy.

Most importantly, by mixing the two slags Nakano and Bennett have the potential to reduce the quantity of CO2 entering the atmosphere by converting it into CO, which can be used in a power plant as fuel or in the chemical industry, reducing the amount of carbon needed in these processes. "That’s the real objective of this work," says Bennett, "to reduce our CO2 emissions."

Contact:  James Bennett, 541-967-5983; and Jinichiro Nakano, 541-918-4413

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