Tuesday, September 09, 2014

Reclaiming the land

Major oilsands players are making strides in dealing with troublesome bitumen tailings. This article appears in the September 2014 issue of Oilweek; chart from here.

By Peter McKenzie-Brown
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 chart shows 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.”

Post a Comment