Pulp mill 'right-sizes' a motor and saves $28,000 a year
|At the Neucel pulp mill at Port Alice, a BC Hydro assessment led to huge annual savings from one pump.|
Neucel's 1960's-era fan pump was just too big for the job
No one wants to be responsible for building an industrial system that underperforms. But when equipment is oversized, energy efficiency can drop — and costs rise.
That was the case for Neucel, a specialty pulp manufacturer in Port Alice. Neucel produces several varieties of dissolving pulp, primarily destined for the textiles market. With the help of 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 delivers too much power, forcing you to constantly drive with your foot on the brake 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
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," recalls Brennan. "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 Power Smart, 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 the equivalent of 73 B.C. homes.
Re-engineering for modern efficiency
|Neucel energy manager Chris Brennan estimates that pulp mills typically use 30 to 40 per cent of their end-use energy on pumping.|
Upsizing pump sizes was "just the culture of the time'
Brennan says he's not sure why the motor was so oversized 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."
Brennan estimates that pulp mills typically use 30 to 40 per cent 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."