By: Edmonton Journal
It looks like a giant waterbed, covering an area the size of four football fields and surrounded by a chest-high concrete perimeter wall.
As Donald Trump might say, it’s huge! And like the wackadoodle U.S. presidential candidate, this massive vessel, constructed next to West Fraser Timber’s Slave Lake Pulp mill, is also full of gas. In this case, biogas.
Technically, the big waterbed is known as an anaerobic digester. It’s a reactor in which micro-organisms called methanogens — the same kind of bacteria found in our stomachs — break down organic waste in the mill’s effluent, in the absence of oxygen, to produce methane.
None of this is visible to the naked eye, of course. All the biological magic happens in the about nine-metres deep, geotextile-lined basin that sits beneath the big waterbed’s multi-layered, flexible white geomembrane cover. Inside the basin, 13 days worth of effluent from the mill cycles through on a 24/7 basis, slowly but steadily.
Surprisingly, the cover is easily strong enough to handle the weight of a group of visitors, including yours truly. So at the invitation of Shannon Fehr, Slave Lake Pulp’s smart-as-a-whip engineering superintendent, who oversaw the $40-million project to turn the mill’s waste into a source of green energy, we step gingerly on to the surface.
Like a waterbed, it rolls like a wave under my feet. A puddle on the cover’s surface follows me as I walk. I imagine myself plunging through the cover and dying a horrible death, my body eaten by an army of little bugs. Fortunately, that doesn’t happen.
Fehr suggests we form a line and walk in unison, so we can use our collective body weight to push a bulging gas bubble just beneath the cover’s surface to the digester’s perimeter, where it can be collected and piped to the towering biogas scrubbers next door.
Inside the towering scrubbers, which are among the largest tanks of their kind in the world, hydrogen sulphide and excess moisture are removed from the biogas, and the methane that comes out the bottom is piped back to a power plant next to the mill.
Once there, the biogas is fed into a trio of three-megawatt, Austrian-made, dual-fuel GE Jenbacher engine generators, which supply between 3.5 MW and 4.5 MW of power to the mill, or about 10 per cent of its total requirements.
Not only does it reduce the mill’s reliance on coal-fired power, it represents a new revenue stream for West Fraser as it sells power into the grid while it aims to monetize its rising stockpile of carbon credits. It’s all a marvel of bio-engineering and part of West Fraser’s push into the brave new world of green energy.
None of this was easy or cheap, of course. Besides West Fraser’s $25-million commitment to the project, the Slave Lake mill received $5 million from Alberta’s Climate Change and Emissions Management Corp., and $10 million from the Canada Eco-Trust and Clean Air Fund.
It took two construction seasons to build the anaerobic digester, install the biogas scrubbers and the three gensets, while looking at several options along the way. In all, the management team at Slave Lake Pulp — led by general manager Tony McWhannel — looked at seven digesters, four scrubbing technologies and six different engine types before settling on a final design.
Some were flops. A much-hyped, high-speed, “technically sophisticated” digester brought in from Europe “struggled to work” properly on-site. If it was shut off, it couldn’t be easily restarted, says McWhannel.
“On an effluent treatment system it has microbiology and that’s what billions of these little bugs are eating. So if you shut off their food they go dormant, they’ll stay dormant for hours. So that’s why our digester has this 13-day retention time built into it,” he explains. “With our digester, it operates in a very stable way. There’s no fuss, it just runs.”
Finding the right scrubbers was also a challenge. A crew from Thailand was first hired to build them. But the liners wouldn’t hold water and had to be demolished. Eventually, the mill turned to Edmonton-based ZCL Composites, a maker of environmentally friendly fibreglass storage tanks. The next problem: how to move ZCL’s massive tanks to the mill site.
“It took 1,000 kilometres on the roads to get them here because of their size. They had to go around the Westlock highway and up to Peace River, then over to Red Earth and finally down the highway to here. We had to use two 350-tonne cranes to pick and set them in place,” says Fehr.
Although McWhannel’s team are rightly proud of the leadership role they’re playing in the nascent world of green energy, he’s keenly aware that the pulp industry is highly competitive, and his mill will ultimately be judged on how much profit it generates. As Canada’s mills face rising costs tied to carbon emissions policies, mills elsewhere don’t.
“We’ve been forced to do the right things for many years due to Alberta’s SGER (Specified Gas Emitters Regulations). But if you look at the forest industry, about 100,000 jobs have been lost over the last 15 years across Canada, and a lot of mills have closed simply because they couldn’t compete without capital investment,” he says.
“Ontario is a good example. Power prices have doubled or quadrupled in some regions as well as the carbon taxes (cap-and-trade system) coming in, so they just can’t compete against the Chinese, the Indians, the Indonesians or South Americans, who don’t have the same kind of regulations to deal with.”
By: Edmonton Journal