Domtar’s Plymouth mill is located in Plymouth, North Carolina, and has the capacity to produce 390,000 ADMT (air dry metric tonnes) per year of softwood fluff pulp known for its excellent absorbency and sheet properties. The pulp is used in the production of adult incontinence products, baby diapers and absorbent hygiene products.
Last year, the mill improved its hog fuel boiler so it can produce more steam while burning less biomass (typically bark), which 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. After the project, the boiler is producing 15 percent more steam per ton of biomass.
Lower Daily Water Consumption
The Plymouth Mill has taken another step toward a more sustainable future thanks to the success of a recent resource conservation project. Just one year after the installation of a cooling tower and new heat exchangers, the mill’s closed-loop system for heating process water has exceeded expectations by dramatically reducing daily water consumption and fuel costs. Last May, the team installed a cooling tower and two large heat exchangers to reclaim waste heat from the mill and use it to reduce steam consumption. While the resource conservation project was originally expected to eliminate the use of about 11 million gallons of river water per day, Operations Manager David Council says the system is performing better than expected, saving approximately 18 million gallons of water per day
Before the team installed the new equipment, the mill used water from the nearby Roanoke River to cool mill processes. The mill returned the water to the river in the same condition, only slightly warmer
With the addition of the cooling tower and heat exchangers, the mill now has a closed-loop system that reclaims heat from the mill’s evaporation equipment and transfers it to process water. The reclaimed heat reduces the mill’s steam load, which means it burns less fuel in the boilers to make steam.
“Our water use reductions are exceeding our expectations thanks to the new cooling tower and heat exchangers,” Council says of the resource conservation project. “We are more than achieving our goal, and our water use is now among the lowest of Domtar’s mills.”
More Efficient Heating
Council says the resource conservation project is also exceeding the mill’s expectations with regard to heating process water. Before installing the new heat exchangers, the team expected the system to heat water to 85 degrees Fahrenheit. Instead, Council says the heat exchangers are warming it to 97 degrees, and they are confident they can reach 100 degrees soon.
Why is this so important? Many processes across the mill operate at temperatures at or above 140 degrees. Before the new closed-loop system was operating, the mill burned fuels like biomass or natural gas to make steam that was used to heat the river water to process temperatures. The colder the river water, the more fuel required to reach process temperatures.
“In the winter, the river water can be as cold as 45 degrees,” Council says. “It takes a lot of heat to bring it up to temperature. Today, the heat exchangers use waste heat from the mill to achieve a portion of this heating requirement, reducing the need for inefficient and costly heat sources.”
A More Sustainable Future
Plymouth Mill Manager Everick Spence says the resource conservation project is creating efficiencies that will ensure the Plymouth Mill has a strong and sustainable future.
“This resource conservation project has played an important role in helping achieve our strategic vision of becoming a highly efficient mill,” he says. “I look forward to continuing to realize and build on these benefits to ensure our mill continues to be a great place to work for many years to come.”