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Major maintenance shutdown at Zellstoff Celgar underway

It takes approximately 36 hours to shut down the mill process.
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The annual Major Maintenance Shutdown at Zellstoff Celgar began on Saturday, May 27 when they stopped feeding wood chips to the digester.

It takes approximately 36 hours to shut down the mill process, so the majority of maintenance in most areas of the mill did not officially begin until Monday.

Some areas of the mill such as the recovery boiler take even longer to shut down, so maintenance in those areas were not expected to start until late Monday or Tuesday.

The annual shutdown is required to allow inspection of the major pieces of production equipment and repair any deficiencies found. This will help ensure the mill is in good order to run reliably for the next 12 months, until the next scheduled maintenance shutdown.

A lot of the work is preventative in nature much like doing regular maintenance on our vehicles.

There are approximately 2,000 maintenance tasks scheduled for this year’s shutdown.

Once the maintenance work in all areas has been completed Zellstoff Celgar will begin the start-up procedure using detailed safety and operational check sheets.

It generally takes about 1.5 days to bring the mill back up to full running rates. The expected date to begin startup is June 11.

Scope of the shutdown

As with all maintenance shutdowns, there is a “Critical Path” job that has the longest duration of work and sets the schedule for all of the other work. The Critical Path job for this shutdown is the inspection and repair of the digester. Crews will build scaffolding inside the 200-foot-tall digester to inspect the inside shell from top to bottom.

The digester uses chemicals, heat and pressure to cook wood chips and convert them to pulp. Of all the process equipment used at Zellstoff Celgar, the digester is one of the most expensive with a replacement value of $200 million.

This reliable piece of equipment on average costs Zellstoff Celgar less than one per cent of its value in maintenance each year. To put that in perspective, that would be the equivalent of paying only $300 in annual maintenance cost on a $30,000 vehicle that is 25 years old and you drove it non-stop 365 days a year.

Another major maintenance job for this shutdown is the inspection and repair of the recovery boiler. The recovery boiler will also have a new condensate collection tank installed. The tank was manufactured for Zellstoff Celgar in Maple Ridge, and travelled to the mill in two separate pieces which will be assembled once lifted into the recovery boiler building.

A capital project that will be completed in this year’s shutdown is the replacing of the 1993 primary surface condenser which has carbon steel components and is showing some signs of corrosion. Its function is to cool vapours, creating a vacuum that pulls these vapours through our evaporation process.

The new surface condenser that will be installed will be larger; measuring 11.5 metres long by 3.6 metres in diameter (37.8 feet by 11.7 feet) and is constructed entirely of stainless steel.

Zellstoff Celgar will be using a 500-tonne crane to perform the lift of this vessel that weight 50,000 kg (110,000 lbs). This is one of the largest cranes they have ever had onsite and will reach 190 feet in the air.

During last year’s shutdown numerous repairs were required to our 18-foot diameter by 40-foot tall flash tank which resulted in a significant delay in the start-up.

This is the vessel where cooking liquor extracted from the digester is flashed before being returned to the evaporation system.

The tank will be entirely replaced this year with a new, more efficient and much smaller TubeFlash measuring just 10 feet by 26 feet.

Investment and economic impact

An annual shutdown in a pulp mill is an expensive undertaking. Specialized parts and equipment are purchased, and the corrosive nature of the pulping process requires corrosion-resistant materials that are quite often more expensive.

To access many areas of the mill Zellstoff Celgar has to build elaborate scaffolds. They also have the expense of approximately 1,100 additional contractors, temporary employees and equipment specialists brought in from across the continent. Many of them will be staying in the local hotels, eating in local restaurants and purchasing or renting equipment from local businesses.

The estimated total expenditure for this outage are approximately $20 million. A significant amount of material and services will be procured from local businesses and contractors.

The positive impact on the local economy is in excess of $1 million.

Environment

Celgar uses this opportunity to inspect and repair their environmental-control equipment including precipitators and effluent-treatment systems.

They take a great deal of care and time while they are taking the mill down and starting back up to prevent odour or upsets.

However, this can sometimes occur depending on atmospheric conditions during certain stages of the process and would be temporary.

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Primary surface condenser. (Zellstoff Celgar)