Pulp Mill ‘Right-Sizes’ One Motor, Saves 800 MWH/Year
That was the case for Neucel, a specialty pulp manufacturer in Port Alice, British Columbia. Neucel produces several varieties of dissolving pulp, primarily destined for the textiles market. With the help of electrical utility BC Hydro, they assessed the fan pump that feeds pulp slurry to the wet end of their pulp machine – and discovered a big opportunity.
“There’s a gate valve on the discharge side of the fan pump, which the operator would manually open and close to control the flow coming off the pump,” says Chris Brennan, Neucel’s energy manager. “This pump was originally installed in the 1960s, and it was just so oversized, they basically always operated with the valve 80 to 90 percent closed.”
Brennan equates the situation to having an accelerator on your car that’s too powerful, and driving with your foot on the brake all the time to rein it in. “The pump would operate at one speed – 900 rpm,” says Brennan. “So no matter what, it’s putting out a certain amount of pressure and then they’d control that pressure and flow with the valve.”
Pump efficiency study targets opportunities
Brennan says the pump efficiency study assessed various metrics such as the amps going to the motor, and the flow through the pump. “Most importantly, we looked at the pressure drop: the pressure before the pump, the pressure after the pump, and then the pressure after that gate valve. You could see there was just a huge pressure drop across the system – it went from 25 psi down to 8 psi.”
The excess pressure was dissipated as heat and vibration, increasing maintenance costs. “It caused a lot of stress,” says Brennan. “There’s a drive shaft between the electric motor and the pump and at least once a year they were snapping that shaft. It’s a solid piece of metal and it was just snapping.”
With 100% project funding from BC Hydro’s Power Smart program, Neucel downsized its 200 hp pump motor to a 150 hp model, and added a variable frequency drive (VFD). That single fix is now saving the company a whopping 800 MWh of electricity per year, estimated at BC Hydro’s blended industrial rates to be approximately $28,000 annually. Says Brennan, “Now the pump’s only turning at 500 rpm instead of 900, and we can keep the valve fully open all the time. The VFD allows a slow-down and that’s what saves a lot of energy.” The system now uses 75 percent less energy than before, saving enough electricity to power 73 B.C. homes.
Re-engineering for modern efficiency
Brennan says he’s not sure why the motor was so over-sized for the job, but his experience with the project has left him keen to examine every pumping system in the plant. “The more I’m getting into this job, the more I’m hearing historical stories. Usually an engineer would oversize their design by, say,15 percent. And then he’d go to the pump supplier who doesn’t want to sell you something that he’s going to have to worry about, so he upsizes it another 15 percent. It was just the culture of the time – oversize it and then throttle the valve. But, in this case it was so large that they had to throttle the valve until it was almost closed.”
“Pulp mills typically use 30-40% of their end-use energy on pumping. So when those pumps are oversized and throttled, or when you have a mill that’s older and less automated, it just speaks opportunity.”
Efficiency and reliability go hand in hand
· Pump systems account for up to 60% of the total electrical energy usage in many industrial facilities.
· 58% of a pump’s life cycle cost is energy cost.
· Pumps are frequently oversized and operate far from their best efficiency point.
· Inefficient pump systems are less reliable and require more frequent maintenance.
· By optimizing the pump system, 30 – 50% of the annual energy consumption can be saved.
Nina Winham is a principal with New Climate Strategies. For more information on optimizing pump systems visit www.bchydro.com/pumps.
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