Processing blended coal in a non-recovery oven yields more than coke
April 2013 - Something old, something new; with less coal borrowed, an idea grew. Researchers at Purdue University Calumet, Hammond, Ind., are making the old method of coke production (with a non-recovery oven and imported metallurgical coal) into something new. By using lower-ranked blended coal from the Indiana/Illinois Basin, coke producers can decrease the cost of “borrowed” coal while maintaining the same quality coke needed for steel-making. Furthering the idea of reduced cost, the Purdue team also has altered the coke-making process to produce ancillary products such as fuel, fertilizer and electricity.
Close to home
According to the university’s website, 22 percent of American steel is produced in Indiana, which requires 8 million tons of coal annually for coke production. However, “with the advent of the coal strength reactive parameter, the steel industry has stopped using Indiana coal for production of steel in the state,” says Robert Kramer, Ph.D., director of the Purdue Calumet Energy and Reliability Center, Hammond, Ind. The CSR parameter is used to measure the quality of coal used in coking.
“As blast furnaces became very large, the CSR parameter became more important and, as a consequence, a lot of steelmaking companies moved away from lower-rank coal towards pure metallurgical coal, which also added to the cost,” says Kramer.
According to Kramer, Indiana coal has a lower cost per ton and because of its lighter density and proximity to Indiana steelmakers, transportation costs also would decrease. By optimizing this lower-rank coal to the correct temperature, controlling other factors and blending it with standard metallurgical coal, Kramer and his team have created a type of coke that has the same properties as coke created with higher-ranked coals.
Additionally, “it allows us to add some new value to the coke-making process, help the steelmaking industry and do some very intriguing and interesting research on new processes that can add value,” says Kramer.
An added bonus
With this research, Kramer hopes to not only use Indiana coal for coke production but also gain additional value from the more cost-effective process. “We’ve come up with a way of selectively harvesting different value products based on the operation of a conventional [non-recovery] plant,” he says.
Coal is carbonized into coke by baking it in a properly heated oven, burning off its impurities. In a non-recovery plant, the slag and other byproducts are combusted within the oven, supplying the heat needed for the coke-making process. Researchers particularly are interested in using these byproducts in meaningful ways and harvesting gas from the process.
“We have a total of five different value streams depending on the particular temperature at which we’re extracting that pyrolysis gas from the oven,” says Kramer. Some of the gas may be used for a gas turbine in conventional electric generation, while a separation process creates fertilizer and bulk hydrogen. “We’re also extracting some gas to be used in the Fischer Tropsch process to produce liquid transportation fuel,” he says. “Then, of course, we’re also looking at processes that may allow us to use that gas inside the steel plant.
“So we’re extracting a pyrolysis gas under these conditions with certain coal blends that allow us to add value to the entire coke-making process,” he continues. “In a typical coal gasification plant that’s being used to produce, for example liquid transportation fuels, roughly 70 percent of the cost of the plant is the cost of the gasifier. But in reality, a coke oven is actually a coal gasifier that operates in a bit of a different situation.”
Kramer explains that coke ovens have been used for many years, therefore the technology is known and the cost already is justified, “so the business and the technical risk are reduced dramatically by having this process. I think the industry is looking at non-recovery ovens for the future,” says Kramer.
Kramer says the process provides a new direction and approach for future coke production that optimizes value. “We think this can be a perfect way of developing some advanced processes for the clean and economical use of the coal in the future.” MM