The Heart of the Matter

FROM THE SEPTEMBER ISSUE: Increasing efficiency by taking advantage of the latest pump designs and technology.
By Matt Thompson | August 14, 2019

George Gregorowicz, seal division manager at ProFlow Pumping Solutions, has seen his share of leaky pumps. “I have been at plants where a leaking seal has flooded an area,” he says. “I’ve been down in the Permian Basin and seen hundreds and hundreds of gallons of oil laying in a field. Then you have remediation issues there and it has to be cleaned up.”

Having spent more than 40 years in the seal business, he’s become familiar not only with the mechanical seals used on pumps in many ethanol plants, but a type of pump designed to be leak-proof: the canned motor pump.

“What we’re finding is, especially a lot of [ethanol plants] located up in cold country, use a lot of centrifugal pumps for tank unloading and tank transfer, and cold weather has an effect on those seals up in those areas,” Gregorowicz says. “So canned motor pumps will eliminate a lot of headaches in terms of emissions and motor alignment.” A typical O-ring in mechanical seals can handle temperatures down to -15 degrees Fahrenheit, he says, but temperatures in some parts of the Midwest hit -40.

Canned motor pumps—also called hermetically sealed pumps—are leak-proof because they are completely self-contained. The pump and the motor operate as one unit, and the fluid being pumped is sealed inside. Canned motor pumps are also free of mechanical seals. Failure of those seals is often the cause of leaks. “The weak link in most of these pumps will be the mechanical seal,” Gregorowicz says.

The lack of mechanical seals removes other costs, as well. “Typically, you’re running a lot of double-seal, so you’re running probably a seal support system with a barrier fluid, so you eliminate all of that,” Gregorowicz says. “I sell these to refineries where the seal support system is $15,000 to $20,000.”

Canned motor pumps are commonly used in the biodiesel industry, but aren’t as widely used in ethanol. “Typically, a canned motor pump is going to be more money than a centrifugal pump, so dollars and cents do all the talking,” he says. The pumps excel in 190- and 200-proof applications, feed water, hot oil and corn oil, according to Gregorowicz.
Canned motor pumps offer an environmental advantage, too. Emissions requirements are becoming more stringent, and “it’s going to be very hard to hit those emissions requirements with seal pumps,” Gregorowicz says.

He cites a refiner in Indianapolis that switched from traditional pumps, which operated at 1,075 PSI, to canned motor pumps to accomodate its caustic. “Single sealed would work, but when a single seal leaked at 1,000 PSI, it had a tendency of spraying,” he says. “So they tried double-sealed. They would go through three or four seals a year at $10,000 to $12,000 a seal. We put in a canned motor pump—drop-in replacement, no piping modifications, nothing—and that pump’s now been running for about 2.5 years. It pays for itself. The pump was $70,000, $80,000.”

The challenges of working with ethanol present the perfect opportunity for the canned motor pump, Gregorowicz says. “Ethanol is some of the toughest stuff to seal. When it’s hot, it’s sticky. It’s abrasive. It changes when it gets too hot, and it changes when it gets too cold.”

A Step Up
Ethanol plants can also take advantage of pump technology in their dosing systems, says Jared Gabel, product manager at Grundfos Pumps. He says by coupling a dosing pump with a stepper motor, plants can realize several advantages, including gaining better control over expensive chemicals used in the processes. “A stepper motor is really advantageous because it can be very accurately controlled in terms of the speed at which it turns and then the rotational angle,” he says. “That translates into some more features and benefits and things that we can start to realize from a capabilities perspective and how we can build technologies around a chemical feed pump.” He adds that stepper motors are ideal on pumps that feed antiscalant or biocides into cooling towers.

One of the advantages stepper motors offer is the turndown ratio. Because the turndown ratio is so high, Gabel says the same pump can be used in several applications within the plant. “It’s not too cumbersome for them to maintain that piece of equipment ongoing with one style of pump that can handle several different applications because we have such a large turndown ratio,” he says.

Colin Cummings, direct sales manager at Grundfos, agrees. “Because of the stepper motor and the turndown ratio that we have within these pumps, I can actually size one pump for all of their applications, rather than having a specific pump for each application.” That feature is the one ethanol plants tend to like the most, he adds.

But there are other benefits, including how the pumps operate at low speeds. “If you were running a pump at its furthest turndown, so its slowest speed, and it’s microstepping at that low, you basically won’t know that that pump’s running,” he says. Because the pump has minimal vibration, it results in lower maintenance costs throughout the system and increased safety, Gabel adds. “If it’s a smooth discharge into the line instead of a quick one that you would get from a conventional type of solenoid pump, then you can start reducing the vibrations that are happening on the system, which will allow that pipework to last longer and not break as easily.”

Gabel says sensors can also be added to the pumps, which can help fine-tune operation automatically. “We can take a sensor, measure something, and then we can do something with that signal in terms of the speed of the motor, whether or not we need to slow it down or speed it up to maintain a set point to continue dosing at an accurate, reliable feed rate,” Gabel says. That automated adjustment on Grundfos pumps is called AutoFlowAdapt.

AutoFlowAdapt allows plant personnel to set the pumps to alert the engineers when they sense an increase in pressure, which may indicate a maintenance issue, such as plugged injection quills. “The pump is rated for 232 PSI, but I want the pump to tell me when the pumps sees 100 PSI because I know my injection quills for this process line may be starting to plug, or build up a little bit, so I need to have a maintenance guy go out there and do a little bit of preventative maintenance on the injection quill to clean it,” Cummings says. “That’s one of the features that you can use the pump to prevent things downstream.”

The pumps with sensors are also useful in preventing vapor lock and loss of prime, Gabel says. “If a pump is in standby, it’ll move the diaphragm to shake the bubbles up to the top and then be able to keep the pump primed, basically. So that really is a way that most plants have been switching to this type of technology, because they don’t want to have to go reprime the pump and that requires a manual operation. When a pump can stay primed and the sensor’s in there looking at that, that directly relates to savings in time and money for the plant.”

Cummings agrees. “The No. 1 reason, probably, why our pump gets inserted into an existing application would be a degassing situation,” he says. “If you’re looking at a bleach pump, bleach chemical usually degasses pretty easily, and they’ve run into vapor locking with the pump that they have, so we’ll go in there and try to offer our solution.”

Gabel says plants may also be able to remove unnecessary pieces of equipment by using digital dosing pumps with sensors. “Because of the stepper motor, we’re drawing in chemical fast, but then we’re pushing out very slowly. So we can start to reduce unnecessary pieces of equipment also in the plant, like a mixer or a variable frequency drive for example, which does take some energy, and because they do have motors, that would directly reduce that need to buy that piece of equipment.”

The Right Tool for the Job
While the stepper motors for digital dosing pumps come with advantages, there are factors to consider. “They are basically small computers, so they don’t directly have an explosion-proof rating,” Gabel says. “It’s good to be aware of the technical specifications around equipment, especially these types of metering pumps, and their enclosure ratings.” He adds that Grundfos has installed the pumps in explosion-proof enclosures. “It’s not that it’s a deal breaker, it just takes another step,” he says. “If you really want that control that a smart digital stepper motor type of pump would offer, there are ways to get it in the application with an enclosure.”

Gregorowicz says canned motor pumps aren’t typically recommended for slurry applications in ethanol plants, although there are some models designed to pump slurries. “They do have a slurry version that has a seal that seals off that bearing end, then they have to use some type of lubricant to be injected into the bearing area,” he says. “A lot of plants may not be set up for that.”

As plants explore different cleaning chemicals and applications, material compatibility becomes important for any type of pump. Gregorowicz says canned motor pumps can be fabricated out of nearly any material. “The metallurgy of the pump itself can be made in anything. It can be steel, it can be a high chrome alloy, stainless steel,” he says. “Most of the pumps that we sold are CD4MCu or some other duplex stainless.”

Gabel says compatibility is an important consideration for Grundfos as well. “Most metering pumps out in the market will be offered in several different kinds of plastic, PVC, PVDF, polypropylene and also stainless steel, so your high 3/16-inch stainless steel,” he says. “That is definitely something we consider and is a very important piece to selecting which model variant of pump to go with.”

Author: Matt Thompson
Associate Editor, Ethanol Producer Magazine
[email protected]