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Cenovus's blowdown boiler process reduces water usage, costs
When Cenovus Energy Inc.’s technical team first proposed running waste water from its steam generators at its Foster Creek oilsands operations through a second boiler without treatment to increase the amount of water it was recycling, colleagues promptly organized a pool as to how long it would take before solids in the water plugged the tubes.
The results convinced the skeptics. Over a period of 166 days in 2007, a pilot project using a 50-million-British-thermal-unit-per-hour boiler—smaller than the boilers typically used to generate steam—generated more than 59,000 cubic metres of steam and produced nearly 150,000 barrels of bitumen using only untreated water. Following the pilot, Cenovus ran a successful commercial test for 100 days in late 2010 and early 2011 using a larger, standard 175-million-British-thermal-unit-per-hour boiler.
The boilers were inspected at the end of each testing stage and showed no significant wear, despite the higher component of solids, proving that a boiler could generate steam using untreated waste water, in contrast to standard industry belief.
“We wanted to recycle as much water as we reasonably could and to exceed the regulations, going beyond compliance,” says Mark Bilozir, director, technology development, at Cenovus. Under the company’s patented blowdown boiler process, up to 90 per cent of the original input water can now be converted to steam.
In a typical steam assisted gravity drainage operation, a steam generator converts about 80 per cent of the water it receives into steam, with the remaining 20 per cent usually disposed of due to the concentration of solids left behind in the water. “We could take that water out of our normal operations and spend a lot of money and chemicals and equipment and treat it so that it is back down to spec and run it again,” he says. “But it’s a lot more economical and simpler if we can just figure out how to go from one boiler right into another, and find out what the problems are and just solve the problems rather than just treating everything.”
To accomplish that, those involved in the project had to go “off-spec” from what was considered normal boiler operation, something that Bilozir acknowledges caused a lot of debate within the operation. “We took a calculated risk and some people were thinking there is no way this could work, but we had good reason and solid evidence to say we think we could do this,” he says.
A major benefit of the blowdown boiler process is a 50 per cent reduction in the demand for makeup water, which means that the company draws less water from natural saline aquifers, according to Bilozir. As a result, only two to five per cent of the original feedwater is disposed of in saltwater aquifers compared with the 20 per cent had the water not been run through the blowdown boiler.
The process also reduces capital and field costs. If Cenovus can get more steam from the same amount of water, fewer water wells will be needed to provide water and less water will have to be disposed of, he says.
“This is about as close as you can get [to a win-win] because we don’t add any chemicals or do further treating,” he says. “We just get more steam with less energy and less water required from the environment.”
The water treatment plant, the largest single capital cost, can be a little smaller, resulting in an estimated saving of $100 million because now it will have to handle less than 10 per cent of the blowdown water compared to the previous 20 per cent. “We sort of joke that we run giant water treatment plants and produce a little bit of oil to pay for it,” says Susan Sun, senior staff, water treatment engineer.
Based on the company’s evaluation, the Cenovus-patented process will reduce operating costs by 15 cents per barrel, says Sun. For a 100,000-barrel-per-day operation, that would amount to about $15,000 per day. “It can improve the water recycling ratio above 90 per cent without using energy-intensive technologies like other people are using in the industry.”
Additional benefits include reductions in natural gas requirements, CO2 emissions, the waste disposal stream and the surface footprint due to the reduction in the makeup and water disposal systems, as well as the smaller water treatment plant.
“This was tremendous work by Susan and we had a guy who is very well versed—Mike Wasylyk, a long-time boiler guy—[also] behind it,” says Bilozir. “There are a lot of good people who did a lot of good work on this.
“Cenovus spends a lot of time making its plant more efficient, using less water and making the whole project smaller any way that it can,” he says. “It’s a big area of research for us.”
The blowdown boiler process will be used in future expansion phases at its Foster Creek and Christina Lake in situ oilsands projects, as well as at future developments at Narrows Lake and Telephone Lake, says Sun. At Foster Creek, one of Phases F, G and H will be run off water from the two other phases, says Bilozir.
The blowdown boiler process could potentially be licensed by other oilsands operators who have shown interest in it. While Cenovus sees its patented process as a competitive advantage, it would be open to discussing the idea of licensing, though “the terms have to be defined,” he says.