Statement by Domtar released this past week:
Through a combination of capital investments and continuous improvement projects, our Plymouth Mill is building a sustainable future by increasing energy and resource efficiency. In fact, the mill recently completed two more important initiatives to reduce fuel and water consumption, in turn reducing its bottom-line costs and contributing to our corporate sustainability goals.
Our efforts to optimize and improve the operational efficiency of our pulp business are part of a strategic plan to grow into a world-class supplier with strong, long-term customer partnerships and a sustainable future.
Greater Energy Efficiency
With an eye toward a more sustainable future, the mill improved its hog fuel boiler so it can produce more steam while burning less biomass (typically bark), known in the industry as hog fuel. This is particularly important because the mill has to purchase biomass from a third party to supplement its own biomass so it has enough hog fuel to produce the steam needed to power mill processes.
“We essentially modified the hog fuel boiler’s air system for better combustion,” says Bracky Bickerstaff, project manager for Plymouth Mill’s optimization program. “Now it’s burning biomass more efficiently, which allows us to produce more steam from the same amount of fuel.”
The hog fuel boiler upgrades have already made a big difference. The boiler is producing 15 percent more steam per ton of biomass, which equates to significant cost savings for the mill because now it can purchase less biomass from outside vendors. Bickerstaff says the efficiency improvement comes from better heat transfer. The upgraded boiler captures more heat to boil water to produce steam and loses less heat to venting.
Lower Water Requirements
Another step on the path toward a more sustainable future is the installation of a cooling tower and two large heat exchangers that reclaim waste heat and use it to make steam from existing process water. Capturing all that heat and water from various mill processes required the mill to install more than one mile of large-diameter pipe.
Ken Hardison, Plymouth Mill’s optimization program process engineer, says that before the new equipment was installed, the mill used water from the nearby river to cool mill processes. This water was then returned to the river in the same condition but slightly warmer than when it came into the mill.
“With the addition of the cooling tower and heat exchangers, we now have a closed loop,” Hardison says. “This eliminates the use of about 11 million gallons of river water per day. The new heat exchangers allow us to reclaim heat from the mill and transfer it to the process water. The reclaimed heat reduces the mill’s steam load, which means we burn less biomass in the boiler. Any residual heat is simply exhausted out the cooling tower.”
A More Sustainable Future
These latest projects are delivering the benefits the team expected to keep Plymouth Mill on its path to a more sustainable future.
“These projects would not be possible without hard work and collaboration with our employees and union partners to ensure the Plymouth Mill has a strong and sustainable future,” says Plymouth Mill Manager Everick Spence. “We have a strategic plan and vision for becoming a highly efficient mill. These projects are playing an important role in achieving that goal while inspiring confidence in our employees and the local community that we are committed to making the mill a good place to work for many years to come.”
TAPPI
http://www.tappi.org/