| Source
newsletter fall 2002 |
|
 |
Quick Payback for Papermaker
Reclaiming usable raw materials from
its wastewater, Stora Enso reduced the amount of solids released
to the sewer and justified a $134,000 project.
Stora
Enso Duluth Paper Mill, formerly Lake Superior Paper Industries,
makes supercalendered paper—high-gloss paper used in
advertising inserts, catalogs and magazines. On average, the
Duluth plant released 45,000 pounds of total suspended solids
(TSS) to the sewer per day. The solids released were mostly
fiber, clay and other fillers.
“We were wasting raw materials
and losing money in treatment and material costs,” said
Diane Gobin, environmental supervisor at the Duluth plant.
Stora Enso needed to reclaim these
solids. MnTAP intern Tim Bauer, a chemical engineering
student at the University of Minnesota-Duluth, worked with
company staff to review the plant’s processes and identify
ways to reduce the TSS released to the sewer.
The intern identified the top contributors
of TSS at the plant. The top two were 1) solids in the water
squeezed out of the paper in the paper machine press section,
and 2) the reject pulp stream from the paper machine cleaners—cleaners
used to remove contaminants from the pulp leaving the paper
machine. Solids released from the press water alone cost Stora
Enso about $66,000 per year for wastewater treatment.
The $134,000 Solution
With the help of plant employees, the intern looked at installing
a system to reclaim fiber, clay and other fillers. Based on
his findings the company undertook a $134,000 capital investment
project.
The project involved reclaiming wastewater
from the press section of the paper machine. The press water
was re-routed through an existing gravity strainer to remove
unwanted debris. The contaminant-free press water is then
returned to the papermaking system. And, the fiber and fillers
reclaimed from the wastewater are incorporated back into the
papermaking process.
Working with an equipment supplier, the
intern found that adjusting pressure differentials and increasing
dilution-water pressure in the paper machine cleaners would
maximize efficiency.
The $730,000
Savings
Before starting projects with a big capital investment, Stora
Enso uses a capital planning process to evaluate them. But,
according to Gobin, “Just looking at the savings from
the amount of solids recovered proved this project was worthwhile.”
Within eight months, overall TSS levels
dropped 45 percent by reclaiming approximately 18,000 pounds
of raw materials from its wastewater daily. This saved about
$2,000 per day, or $730,000 per year in raw material and waste
treatment costs. Looking only at these savings, the project
paid for itself in just over two months.
Gobin said, “Having the intern
take the time to put together the numbers was a huge help
to show management that this would be money well spent.”
|
