To a large degree
because of its agricultural roots, Alberta’s concern about the soil goes far
back.
The province’s first
efforts to conserve its soil date back to the 1932 “Noxious Weed Act.” In 1935
came “The Control of Drifting Soil Act” in response to Depression-era drought,
which damaged agriculture throughout North America’s Great Interior Basin. That
act mandated that the occupier of the land was responsible for preventing soil
drifting. It was adequate for the time, when the province was poor and there
was little industry. After the Second World War, however, rural municipalities
began seeking a broader definition of soil conservation, and in 1962 the
province replaced the legislation from the Dirty Thirties with the Soil
Conservation Act.
That changed
fundamentally in 1973, according to Bruce Patterson, who played many roles
within Alberta Environment. In that year the province made environmental and
reclamation planning part of every major industrial application. “You start the
reclamation plan the moment you identify the land and make a decision what you’re
going to do on it,” he says. “Identify what the issues are and how you’re going
to deal with them. That was the important issue at that time.”
For
oil sands projects, reclamation meant digging up the overburden, which had gone
into an industrial dump, and using it to cover up the clean sand being dumped
into mined-out oil sands deposits at Suncor and, later, Syncrude. In the
decades since, a lot of science and spending has gone into reclamation, and
tailings ponds have become an important issue in the oil sands picture.
The chartshows
that, although the money invested in reclamation has borne fruit, development
and land disturbance is outpacing reclamation by orders of magnitude. Certified
reclamation – the industry’s Holy Grail – is mostly a faint hope. In early
2008, a reclamation certificate was issued to Syncrude Canada for 104 hectares
of reclaimed land that was then returned to the province. To put that in
perspective, certified reclamation amounts to about one thousandth of total disturbance
by oil sands mining.
Although nearly 4,000
hectares of land and 1,200 hectares of ponds and wetlands have been reclaimed,
but not certified, the amount of land now covered by tailings ponds is daunting
– more than 170 square kilometres. Calculating how to reclaim these ponds –
lakes, in many cases – has become a head-scratching challenge for the industry.
The goal in the end to turn these disturbed areas back into forests and
wetlands. So far the two pioneering operators, Suncor and Syncrude, have done the
bulk of the reclamation work.
Syncrude’s
Centrifuge: According to Syncrude spokesman Leithan Slade,
“The challenge right now is what we call fluid fines – water containing finer
clays and silts.” Fines are in effect land that needs to be reclaimed. Since
those tails are in no hurry to exit the water they are suspended in, tailings
ponds grow bigger and bigger, and the industry’s reclamation problems mount.
Slade says Syncrude now
has plans to “apply three main technologies to transform them into a
reclamation material.” The first is removing water from the tailings pond;
second, adding a water treatment material – “a bit like flocculants used in water
treatment plants. Then we will basically use centrifuges to spin out” the fluid
fines.
Once it’s completed –
sometime next year, possibly in the first half – this remarkable, $1.9 billion
new plant will feature 18 parallel centrifuges. Each centrifuge will be about nine
metres long and two metres high, and look like a long, steel tube, and will
spin at approximately 1,700 revolutions per minute – only half the speed of
many home clothes driers spinning at full speed.
The workforce on the
project peaked last year at 1,800 craft workers, making it one of Canada’s
largest construction projects; and there are still 1,200 workers on site. But
what is the purpose of the plant? It will produce a clay-based tailings cake
which will be held in storage for use in reclamation. After 12 to 18 months, “that
material will become strong enough for use as a reclamation material. It first needs
to go through one freeze cycle” – a polite way of describing Fort McMurray’s
bitter winter. “Probably all 18 centrifuges will not be operational at once,”
according to Slade. “Some may need to be kept in reserve for maintenance in the
centrifuge plant. Also, we need to be able to manage the amount of tailings cake
being produced.”
Asked about whether
this technology will be shared through the Canadian Oil Sands Innovation
Alliance, he says “We actually started a pilot project to test the viability of
the technology in 2007. This is technology we would share through COSIA, but we
developed it before COSIA was created.”
Don Klym is not quite
so taken with COSIA as newcomers are, however. An agricultural engineer and
soils scientist by training, he spent a lengthy career at Suncor – managing the
environmental group from 1986 to 1992, then regulatory affairs until he retired
a decade ago. Asked about COSIA he says, “There was always a sharing. It’s just
different organizations in different decades. I recall quite a number of
committees where we would sit with Syncrude. Then there were government/industry
groups. Later on, public stakeholders got involved.”
Syncrude will soon use centrifuge
technology, but at present uses CT or Consolidated Tailings. Simply put, this
means the plant mixes its coarse tailings with its fluid fines. “You typically
use a different type of chemical to cause the combined material to be
non-segregating,” according to COSIA’s Alan Fair. “When you deposit it out into
a reclamation area, you don’t want all the fines to run away. Typically gypsum
is what they use.” As Syncrude’s centrifuge illustrates, the most important
problem with tails is to remove water (“dewater”) before using them for land
reclamation. Shell is also conducting field pilots using centrifuge technology,
Fair says. They are “looking at Syncrude’s use of centrifuge technology, but
also looking at different, larger centrifuges as well. So, others are trying to
optimize or improve that technology.”
Suncor’s
TRO:
Today, of course, the oilsands industry is so big it has created COSIA as the
coordinator of technology sharing and research efforts, and Alan Fair is
director of its tailings EPA – an acronym for “environmental priority area.” Before
joining the organization, he spent 32 years at Syncrude – his last eight years in
research and development. “I retired from Syncrude in order to start the Oil
Sands Tailings Consortium which was then integrated into COSIA to become the
Tailings EPA. By background I’m a geotechnical engineer, so I definitely know
the tailings thing. I worked on it off and on for thirty-odd years at Syncrude.”
To stress how important
the tailings file has become, he offers a few statistics: Last year alone, alliance
members invested about $80 million in environmental research and development – a
number which illustrates that “significant dollars are being spent by the
companies to develop these technologies. That’s strictly R&D. So, there’s
considerably more money being spent in commercially implementing these
technologies, for example. We’ve got a substantive project portfolio on the go
now – about 48 projects that various companies are working on.”
“All de-watering
technologies to some degree rely on gravity,” according to Fair, “and they also
rely on some form of polymer.” These chemicals bind to clay particles, with
each polymer becoming a complex molecule connected to many clay particles. Once
a molecule has taken on its load of clay, it will settle more quickly. That, he
says is the first step. From that point on there are only a few ways to separate
solids from the water. “You can use thermal energy – heat it up and boil it off
– or mechanical energy,” which is what centrifuges do.
“You can also use
evaporation, like what naturally occurs, and that is what thin-lift drying does.
In that particular technology you add the polymer or the flocculent and then
spread the resulting slurry in very thin layers, typically 23 centimetres
thick. And, by doing that you create a large surface area that’s exposed to the
atmosphere.”
Given that Fort
McMurray is surrounded by wetlands, at first it seems surprising that these
layers will dry out if left to themselves, but the environment is dry and the
moisture does evaporate from the reclaimed material. “Granted, it only occurs about
five or six months of the year,” says Fair. “In the winter months there’s very
little evaporation. It’s a seasonal effort to dry them with evaporative forces.”
Suncor’s most important
contribution in this field is Tails Reduction Operations, a patented technology.
According to Suncor, TRO has enabled the company to cancel plans for five
additional tailings ponds at existing operations. An in the years ahead, the
company expects it to play a role in reducing tailings ponds at its present
mine site from eight to two, and reduce the land area covered by ponds by 80%. “Although
people don’t generally understand it this way, in reality it’s their overall
tailings management system,” says Alan Fair. “It’s essentially thin-lift
drying.”
When he begins describing
the process of using thickening technology, he quickly gives a sense of the
scale of these operations. The vessels the industry uses for tailings
reclamation are big and essentially horizontal. “In diameter, they’re about 90
metres, even as big as 100 metres. So, they’re large vessels. The aspect ratio,
height to diameter, it’s usually four to five times bigger in diameter than it
is in height. So, if it’s 100 metres in diameter, it might be 20 metres in
height.” By contrast, vessels used to clarify process water for reuse are more
vertical in shape – only twice as wide as they are tall, say.
How do they work? By
adding the flocculent to the vessel, “you create an environment where the solid
particles will settle from the bottom of the vessel and of course the water
rises to the top.” Inside the vessel “you use a number of rakes within the
thickener that slowly go round and round. These rakes are sections of a picket
fence. They create a path for the water to move upwards in the thickener
vessel.” Canadian Natural, Shell and
Imperial Oil also use thickener technology for treating fluid fine tails, but
each has a different approach.
Shell’s
AFD:
Shell’s version of this technology carries the Atmospheric Fines Drying patent.
It is another technology aimed at accelerating the pace of tailings reclamation,
developed for tailings from the Shell-led Athabasca Oil Sands Project (AOSP),
which includes participation by Chevron and Marathon. Like the Syncrude and
Suncor projects, AOSP is a fully-integrated project – that is, it begins with
an oilsands mine, extracts the bitumen, and upgrades it into commercial
products.
According to Shell VP
John Abbott,[2]
the original test of Atmospheric Fines Drying involved pumping mature fine
tailings from the tailings pond into a large barge, which transferred them to a
drying area which covered 75 acres. The mature fine tailings were then mixed
with flocculants – chemical thickeners like the ones Alan Fair described – and
spread the concoction on a sloped surface, allowing the sun and gravity to
extract the water from the grayish goop. The released water was reused for
bitumen extraction, and the deposits of particles further dried to make sure
they were strong enough to use in reclamation, and the treated slurry delivered
250,000 tonnes of soil useable for land reclamation.
By combining it with non-segregated
tailings, the system can create a fine-tails mixture which contains 40-45% solids
and has the consistency of motor oil. “Then they pump it to the disposal site,”
says Fair, “and often add another chemical or even spike it with additional
fines to create slurry. Canadian Natural does much the same, but they have an
added piece. They treat all of their tailings with CO2. The carbon
dioxide changes the pH of the slurry, making it more basic so the particles,
the fine clays they drop out. They precipitate out more easily in a basic
environment than in a neutral or acidic environment.”
Imperial Oil does much
the same thing, he adds, but with a difference. “They’re looking to place their
material in mined-out areas, so they can put it in much thicker deposits.
Otherwise, they’re also relying on a non-segregating tailings thickener
technology.”
