Even before its commissioning, the new lime kiln at SCA's Östrand pulp mill is attracting a lot of interest. It is the first in the world to substitute fuel oil for wood powder, which is eco-friendly and cheaper.
The SCA Östrand pulp mill in Timrå, 390 kilometers north of Stockholm, is a major producer of totally chlorine free bleached sulfate kraft pulp. About half the mill’s output is used for the SCA Group’s own needs to manufacture publication paper and hygiene products, and the rest is sold to external customers. The Östrand mill also produces CTMP (chemical thermo-mechanical pulp) for hygiene, packaging and other products.
Partly out of environmental considerations and partly with an eye to the mill’s future capacity needs, SCA Östrand decided to install a large new lime kiln to replace the two existing oil-fired ones.
Lime kilns play an important part in the chemical recovery process at sulfate pulp mills. They convert lime sludge, a waste product from the process that consists mainly of calcium carbonate, into calcium oxide that is reused in the pulp production process.
The construction of Östrand’s new lime kiln, one of the largest in Europe, started in 2010. By early autumn of 2011 the machines were in place. If the fi rst tests meet the objective – 24/7 operation without downtime due to the machine – production proper will start.
“The equipment isn’t exactly rocket science,” says Håkan Wänglund, project manager. “The challenge is rather that we will run the lime kiln on pulverized fuel pellets instead of the fuel oil that all other lime kilns use.”
In fact, the Östrand lime kiln is the fi rst one globally to run entirely on wood powder. So what was the reason for choosing this solution?
“First of all, using fuel oil isn’t environmentally friendly,” Wänglund says. “On top of that, oil prices are high and we have no control over them. Now we’ll reduce our yearly fuel oil consumption by 17,000 cubic meters. We’ll save a lot of money, but we’ll also reduce our carbon footprint by 80 percent.
What’s more, the wood powder that will be used is part of an SCA business loop. The fuel pellets that Östrand uses to grind to wood powder are made from sawdust from SCA’s sawmills in Sundsvall and elsewhere. The sawdust is made into fuel pellets by SCA’s plant in Härnösand, 39 kilometers west-northwest of Timrå. The same trucks that bring sawdust to the pellet mill, brings pellets back
to the pulpmill, thus avoiding empty runs.
“Everybody wins, as does the environment,” Wänglund says.
Besides the considerable environmental gains, the other main reason for installing the new lime kiln is that Östrand’s existing two lime kilns are hitting their capacity ceiling. There is simply no capacity left to grow the operation to the significantly increased output levels that the pulp mill plans for the future. This problem is solved with the new lime kiln, which has capacity well beyond current needs.
“When the new lime kiln is in place, the pulp mill can increase its production by 10,000 metric tonnes a year,” Wänglund says. “Looking to the future, the lime kiln has the capacity to match the need for a production of 800,000 tonnes of craft pulp, almost twice the present production.”
Having one high-capacity lime kiln instead of two smaller ones aligns with another long-term SCA objective – to rely on one machine per process phase and still increase output.
There is yet another loop in the system, one that Wänglund says is quite uncommon. “The sulfate process produces odorous gases,” he says. “These will be collected and routed back to the burner in a canal system. Not only does this reduce the smell, but the gas is rich in energy, which we’ll recover.”
The project has caused a stir in the industry. This is not surprising, since all kraft pulp mills want to improve their sustainability as well as reduce their fuel oil consumption.
“A lot of our colleagues around the world have contacted us to learn more about what we’re doing,” Wänglund says.
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TEXT Ulf Wiman
ILLUSTRATION: KJELL THORSSON
Source Shape 4/11