How to make dirty coal clean for $1.2 B
By Bruce Johnstone, The Leader-Post
Much has been written about SaskPower’s $1.24-billion integrated carbon capture and storage project at Boundary Dam power station’s Unit 3 near Estevan:
The Boundary Dam Unit 3 project is the world’s first commercial-scale, post-combustion, clean-coal power project. It will reduce carbon dioxide emissions at Unit 3 by 90 per cent or one million tonnes a year, equivalent to taking 250,000 vehicles off the road for a year. It will capture and compress one million tonnes of CO2 and transport it 60 kilometres to an enhanced oil recovery project in Weyburn.
But how exactly does CCS technology work? How does SaskPower propose to clean up flue gases from the combustion of lignite coal to remove CO2, as well as sulphur dioxide, nitrous oxides and particulate matter such as flyash?
Not only that, but how does SaskPower hope to turn these contaminants and waste products into revenue streams? In so doing, Sask-Power hopes to make clean coal pay for itself, and perhaps become a profit centre for the Crown corporation.
On a recent tour of the carbon capture project site, the Leader-Post, along with other media outlets and delegates at the SaskPower Carbon Capture and Storage Information and Planning Symposium held in Regina last week, got a close-up look.
The carbon capture project involves a number of proprietary technologies that are closely guarded secrets – so secret reporters couldn’t photograph inside the massive carbon capture building that is connected to the province’s largest power plant.
Mike Zeleny, SaskPower’s project manager for carbon capture transition to operations, conducted the tour of the carbon capture building, while Corwyn Bruce, associate manager of carbon capture and storage initiatives, conducted the tour of the Unit 3 power island project.
Coal is mined about 13 km east of the plant and stored at the Boundary Dam power station, with about 500,000 tonnes on site and another 175,000 tonnes nearby.
“Boundary Dam has about a 40-to 50-day supply of coal reserves,” said Zeleny, who is the former plant manager of Boundary Dam power station, the largest in SaskPower’s fleet, with about 766 megawatts of generating capacity.
“The plant burns about 14,000 metric tonnes of coal per day, so a pile like that won’t last very long,” Zeleny added, pointing to the mountain of black lignite coal stockpiled behind the power station.
That coal is pulverized and burned at about 1,370 C in boilers to produce steam for the power station’s turbines, which turn generators that produce about six billion kilowatt hours of electricity – roughly one-third of the province’s electricity supply. But the combustion also produces millions of tonnes of CO2 – Unit 3 alone produces 1.1 million tonnes per year.
Bruce said the Unit 3 power island, which was built in 1969, is undergoing a top-to-bottom refurbishment, including a new carbon capture-ready turbine built by Hitachi. The new Unit 3 will have a rated capacity of about 160 MW, “but when it’s in (carbon) capture mode it will be about 147.4 MW gross,” Bruce said.
“Eleven MW of that gets used within the power plant, 15 MW gets used to compress CO2 and 12.4 MW is used for running the auxiliaries in the capture plant.”
When the parasitic loss of power from the carbon capture process is added, the net output of Unit 3 will be 110 to 115 MW.
The flue gas produced from the combustion of coal will be piped through ductwork to the carbon capture facility for cooling and processing into CO2 and SO2.
“The flue gas comes from Unit 3. It enters a flue gas cooler because you have to cool it off before it enters the SO2 absorber, so the amine can do its absorption work. The flue gas passes through the SO2 absorber, then comes out the top, then a big fan sucks the flue gas all the way from the SO2 absorber then blows it into the bottom of the CO2 absorber,” Zeleny said.
“The SO2 is removed and we transform it into sulphuric acid,” by adding air, a catalyst and water to the sulphur dioxide, Zeleny said. “We’re going to sell that sulphuric acid on the market and make a bit of money on the byproduct.”
About 60 tonnes a day – about one and a half truck loads – of sulphuric acid will be produced.
“We’re removing all of the SO2 as well – 100 per cent of it – so that’s a good thing for the environment,” Zeleny said.
Zeleny added the two absorbers are separated by thick walls of concrete and lined with 70,000 ceramic tiles to prevent contamination of the amine solvent and degradation of the concrete. Heat exchangers are used to heat the amine solvent before it goes into the CO2 and SO2 reclaim-ers, and reduce overall energy consumption by reusing the heat.
“It’s one of the largest – if not the largest – heat exchangers in the world,” Zele-ny said.
The CO2 stripper – a huge stainless steel vessel weighing 400 tonnes – will take the heated amine solution from the heat exchangers and drive off the CO2.
“The CO2 comes out at low pressure – less than 50 PSI – but it’s wet, and so it comes out of pipe and heads over to the compressor building,” Zeleny said.
The thermal reclaimers use distillation technology to capture, clean and reclaim the amine solvent to be reused in the CO2 and SO2 capture process.
“Part of the (carbon capture process) is making sure you’re maintaining the amine in an effective form. As you add flue gas, you’re going to contaminate the amine over time, and so there are various purification and filtration units that will take out any flyash or filter out impurities in the CO2 and SO2 amine,” Zeleny said.
After the CO2 is captured, it is compressed to eliminate moisture and turn the carbon dioxide into a dense liquid state, where it is transported through a pipeline more than 60 km to the Cenovus Energy enhanced oil recovery project at Weyburn. The CO2 is then injected about 1.5 km underground into the oil-bearing formation where it increases reservoir pressure and acts as a solvent to push the oil to the production wells.
The CO2 can also be stored at the nearby Acquistore project operated by the Petroleum Technology Research Centre, where the CO2 is placed in a deep geological storage in a saline sandstone formation. At 3.4 km deep, it’s the deepest well drilled in Saskatchewan.
Zeleny said the capture project is about 80 per cent complete, while the power island project is between 30 to 50 per cent. With more than 1,000 workers involved in the project, the project is on schedule for commercial operation starting April 1, 2014.