Slurry pump alternative meets demands of ultra-fines recovery system

By |  November 21, 2016

Jimmy Smith noticed something was wrong with the ultra-fines recovery system at Short Mountain Silica. Eventually, Smith pinpointed a two-month-old pump as the problem. The operation disassembled the pump three months into its use, confirming Smith’s suspicion.

“We noticed the impeller was almost completely gone,” says Smith, quality control manager at the operation in Mooresburg, Tennessee.

Short Mountain’s minus 400-mesh silica had eaten away at the metal. The operation could have replaced the existing pump with another of the same model, Smith says, but Short Mountain, which operates a plate and frame filter press, likely would have encountered the same predicament in another three months or so.

Instead, Smith sought a longer-lasting solution.

“We decided we were going to need a high-pressure pump,” Smith says. So Smith turned to Paschal Associates, which presented a Schurco Slurry pump as a solution.

“In [Short Mountain’s] application, a pump has to generate a lot of pressure to force water through mud,” says Tom O’Brien, sales engineer at Paschal Associates. “A pump in a typical application might develop, in worst cases, 100 lbs. of pressure. Typically, though, when pumping slurries it may be 45 to 65 lbs. of pressure – and a lot of times less than that.”

In Short Mountain’s case, a pump providing 185 lbs. of pressure is now being utilized.

“Short Mountain’s process is a batching process,” O’Brien says. “The plate press is filled up with mud by this pump, and the pump pushes mud into the press, and, thereby, water out of the press.”

Devising a system

Short Mountain Silica’s 4-in. x 3-in. x 20-in. high-head slurry pump delivers higher pressures because of a unique impeller geometry, according to Schurco Slurry, the pump manufacturer. Photo courtesy of Jimmy Smith

Short Mountain Silica’s 4-in. x 3-in. x 20-in. high-head slurry pump delivers higher pressures because of a unique impeller geometry, according to Schurco Slurry, the pump manufacturer. Photo courtesy of Jimmy Smith

The pump is one key component in Short Mountain’s ultra-fines recovery system, which was constructed in three phases to eliminate the costly task of digging the operation’s waste stream from three settling ponds.

Cyclones and a dewatering screen were added in the first phase of the project several years ago. That equipment captures about 90 percent of the operation’s plus-325-mesh material, O’Brien says, reducing the amount of solids reporting to settling ponds.

“You pull out some of the solids mechanically so you don’t have to dig it out afterward,” O’Brien says.

A second phase of the ultra-fines recovery system’s development involved adding a clarifier to achieve solid/liquid separation.

“We’re separating the mud from the water right there,” O’Brien says. “The clean water goes back into the water system and is reduced. This is a means mining operations have to recycle clean water so they’re not constantly pulling water from the environment.”

The mud pumped out of the clarifier is then pumped to a filter press, the third stage, where it is dewatered. But the pump breakdown Short Mountain experienced at that stage made the entire system less efficient.

That is, until the Schurco H Series 4-in. x 3-in. x 20-in. high-head slurry pump was presented as a solution. According to Schurco, H Series filter press feed pumps deliver higher pressures because of a unique impeller geometry. The H Series impellers have very large outside diameters relative to their suction and discharge sizes. This translates into higher pressures at lower speeds, says Will Pierce, Schurco’s vice president of engineering.

The pumps turn slower to achieve the duty point, reducing particle velocities and wear rates, Pierce adds.

“Speed kills in slurry pumps,” he says.

Key features

Another feature of the H Series pumps are low-flow gland seals. Filter presses are dewatering equipment by design, Pierce says. But shaft seals in slurry pumps typically require injection of a significant amount of freshwater to adequately seal the pump.

Schurco’s low-flow gland seal reduces the amount of water required to seal the pump and eliminates the need for mechanical seals. According to Pierce, this feature increases the mean time between failure on the pump seals.

“[Short Mountain’s] pump might start off at 200 gallons per minute,” O’Brien says. “After the flow rate into that press goes down to a predetermined point – maybe 25 gallons per minute – that press fills up and continuously decays the volume pumped in. When that pump quits pumping, the press starts to open one plate at a time, dumping the mud that was dewatered.”

Such an application puts high demands on a pump, O’Brien adds.

“When it starts pumping mud into the cavity, it’s high volume and low pressure,” he says. “During the cycle, it becomes low volume, high pressure – up to 185 lbs. of pressure. That’s very aggressive.”

The pump and the system as a whole have surpassed Smith’s expectations.

“We’ve been really impressed,” he says. “The fines recovery system has operated really well. We’ve been efficient, and experienced very little downtime in the plant. We can use their pumps in every part of the system.”

One improvement Short Mountain has experienced with the new pump is parts availability. Because the operation previously used an overseas-made pump, parts weren’t readily available. Schurco’s location in Jacksonville, Fla., provides faster parts solutions, Smith says.

Smith also came up with a unique solution of his own in the event of a pump breakdown.

“We like to keep two of everything here because we can’t be shut down,” he says. “So I do have a backup pump. If we ever need to, we’ll switch it out and then fix the other one.”

After three months of use, Short Mountain took the pump apart for an inspection – just as it did previously with the system’s original pump. The operation found virtually no pump wear.

“Now, we’re going on the sixth month,” Smith says. “It hasn’t slowed down any.”


Water regulation challenges

Most aggregate producers are experts at crushing and screening rock. They aren’t, however, experts at recovering fines.

But, given the current trajectory of the regulatory environment, producers will likely be forced to become more familiar with recovering fines and making more efficient use of existing ponds.

“Water rights are forcing companies to get into water recovery,” says Tom O’Brien, sales engineer at Paschal Associates. “The whole industry is going to become more familiar with this because of environmental regulations. Plus, economically it is cheaper to handle waste fines with equipment than it is to dig waste fines out of a pond.”

A number of producers are currently exploring the capital investment cost associated with a fines recovery system, O’Brien adds. But most producers aren’t as familiar with fines recovery as they are with other areas of production.

“Recently, I gave a talk on fines recovery,” he says. “The audience I typically get is varied, from a company president, to owners, to operators. The one common theme is that their level of awareness is always pretty low. They are mostly going on rumors, speculation and, frankly, over the years there have been manufacturers of equipment that have taken advantage of the fact that we are immature to fines recovery.”

Producers should take it upon themselves to become experts in this area, O’Brien argues, because the regulatory environment surrounding water is likely to become even more burdensome.

“Everybody assumes when you go to a permitted greenfield site you’ll likely need to have some means of controlling water and water recirculating,” he says. “But it’s going to be more difficult to permit ponds. We have seen quite a change.”

Kevin Yanik

About the Author:

Kevin Yanik is the editor-in-chief of Pit & Quarry magazine. Yanik can be reached at 216-706-3724 or kyanik@northcoastmedia.net.

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