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Precipitator installation at Northern Pulp nears completion

June 06 2015

New Glasgow News

Carol Dunn
Published on June 05, 2015

 

ABERCROMBIE POINT – A crane lifts materials 10 storeys up in the air to deliver the goods to workers waiting high atop the new precipitator unit.

Telehandlers zip along moving other supplies, sparks fly as welders work on the ducts, and trucks line up, waiting for their turn to dump loads of wood chips.

Work has not slowed down at Northern Pulp, even though pulp production has ceased while the mill is shut down for its annual maintenance. The site is busier than ever as installation of a new recovery boiler precipitator is in the final stages.

Two hundred workers – electricians, boilermakers, sheet metal workers, millrights, industrial mechanics, steamfitters, pipefitters and general labourers – work in shifts around the clock to install the precipitator.

“Work is being done at an accelerated pace – that’s why there are so many on site – we want to get it back up and running,” said project manager Hugh MacDougall, adding that it’s the largest single project the mill has undertaken in his 26 years working there.

The precipitator has 14 major sections, and all but three are now installed, he said.

The familiar plume is missing on this bright, sunny day – gone from the sky over Pictou Harbour since May 30 when the shut down began. The mill won’t resume production again until the $22-million precipitator is installed, which will help the mill meet present, as well as future Canada-wide, environmental standards.

Staff at Northern Pulp are confident that the installation, which began in June 2014, will be complete and the mill will return to production by the end of this month. “The project is slightly behind in completion, however Lorneville Mechanical and its subcontractors have been very successful in recovering time lost,” said communications manager Kathy Cloutier.

Once the new unit is up and running, MacDougall explains that the ash-filled gas stream, or dirty gas, will enter the precipitator and the particles of ash will be charged with static electricity, causing them to attach to big steel collection plates. Periodically, these plates are tapped, the collected ash drops and is then collected in a slurry tank and put back into the process.

“It’s a benefit to the community and a benefit to the mill,” said MacDougall, noting that the air emissions from the stacks will be cleaner once it’s fully commissioned. However, he said what is being spent on the project will not be offset by the savings achieved from the chemical recovery.

The clean gas then carries on and is released through the stacks.

“What comes out of the stacks is mostly vapour,” he said. “The stuff we’re addressing came out of the main boiler and went through the old precipitator.”

MacDougall said the old unit was “beyond its useful life.” While it was meeting all regulations when it was first installed, over time wear and tear has made it less efficient and production has increased beyond what it was designed for.

Once the new precipitator begins functioning, Pictou County residents will still see the plume coming from the stacks, but it will be a white, fluffy cloud, which is made up of steam.

“You will still see a slight plume, but it won’t have the tail – the dark greyish tail – that’s been the source of controversy,” said Cloutier.

High particle emissions and Northern Pulp’s inability in the past to meet provincial standards received national media coverage last summer when a group called Clean the Pictou County Pulp Mill voiced its concerns over social media sites and held events that drew the public’s attention to the mill’s emissions.

 

What goes into making kraft pulp

 

The Northern Pulp mill makes kraft pulp, which is used to make tissue paper, paper towel, toilet paper, writing paper and photocopy paper.

The process involves converting wood into wood pulp consisting of cellulose fibres. The process entails treatment of wood chips with a mixture of sodium hydroxide and sodium sulfide, known as white liquor, that break the bonds that links lignin to the cellulose.

The wood chips are cooked under high pressure and temperature similar to a pressure cooker at home. Then they’re impregnated with the white liquor and screened. The result is brown stock, which is bleached. The whitened pulp is then dried (90 per cent of the water is removed) and then converted to 625-pound bales, wrapped, tied and sent to customers.

The kraft process was developed in 1879, and was first used in a mill in Sweden in 1890.

The invention of the recovery boiler took place in the early 1930s, enabling the recovery and reuse of the inorganic pulping chemicals so that a kraft mill is a nearly closed cycle with respect to inorganic chemicals.

Source: Northern Pulp, referenced from: Biermann, Christopher J. (1993). Essentials of Pulping and Papermaking. San Diego: Academic Press, Inc.

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