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Pumps and sumps

The following is an interview with Dan Adams, technical representative with ITT Flygt. Based at the company’s Sudbury branch, Dan serves the needs of the mining industry across northeastern Ontario. ITT Flygt is based in Sweden and has operations in 130 countries. The Canadian operation consists of 14 branches and a head office in Montreal.

SMSJ: Pump technology and dewatering play an important role in underground mining operations. Is the importance of pumping fully appreciated?

Dan Adams: As we all know, there’s water underground. It comes in through seepage and it’s used in drilling to flush cuttings away from the bit. Water is a problem because you have to get rid of it. If it’s not disposed of, it can prevent the passage of equipment. It can damage machinery, hydraulic equipment, motors and supplies left on the ground. It’s a huge expense.

SMSJ: How important are sump design and maintenance?

DA: As the water comes back off the face and runs down the drift to the sumps, it picks up coarse material. If the sumps aren’t cleaned out, the life cycle of the pump is compromised. If good maintenance is done, the pump will last longer and costs can be controlled. Ideally, the dirty water is first collected in a dirty water sump. It builds up and the water decants into a secondary, or clean water sump. As long as the dirty water sump is cleaned out periodically, the clean water sump will stay clean.

SMSJ: How are the sumps cleaned out?

DA: They’re mainly cleaned out by a loader. The operator will go in with a bucket, scoop up the slime and dump it in an area of the mine where there’s no further development or production planned. It can get pretty thick. I’ve seen sumps that you can actually walk on.

SMSJ: How diligent are the mines about cleaning out the sumps?

DA: There’s no money in it for them. It does damage to the loaders. Nobody likes to put their scoop in there. You’ll get the odd foreman who has his mind set on keeping the sumps clean, but that only lasts for a couple of weeks until he’s got a production target to meet. Loaders are supposed to be hauling ore, not cleaning out sumps. It’s not that hard to do, but they have to figure out where they’re going to dump the slimes. Typically, you don’t see a dirty water sump and a clean water sump. Typically, there’s one sump with a pump at the back. They hope the loader is going to come by and clean it out, but it rarely happens. They’d sooner pay for the cost of repairing the pump before they go in and muck it out.

SMSJ: Are mine pumps getting better?

DA: Yes, pumps are getting better. Our mine pump has been completely redesigned the last couple of years. We’ve seen the life cycle go from between four and six months, to a couple of years. We have installations out there where we haven’t touched the pump. It’s come back for maintenance and all of the components are pretty much like new.

SMSJ: What are some of the improvements that have been made?

DA: One thing is the material inside the pump. It used to be a high chrome cast with a rubber diffuser. Now, all the components are high chrome, so there’s better wear resistance and increased longevity. Pumps today are also designed so the impeller can be easily adjusted to regain pressure after a bit of wear. The motor has better insulation on it, so the pumps will run dry for a longer period of time before they fail. We’ve also improved the design to keep granular material away from the face of the seal so it lasts longer.

SMSJ: Do you assist the mines in choosing the right pump for an application?

DA: Our customer will tell us they need a pump to move water 1,000 feet away and 200 feet up. We’re given the design criteria – the size of pipe, any power restrictions and the size of the sump. We plug all that into a software program that tells us what pump to use for the application. We can also provide advice if we think they’re undersizing the pipe, or if we think of a better alternative for the sump layout. It’s awfully easy to blame the pump, but nine times out of 10, it’s not the pump. It’s the pipe, it’s where the pump is sitting or how it’s mounted, or the material it’s pumping is not what they said it was going to be.

SMSJ: Are there any alternatives to using a loader to clean out sumps?

DA: You can pump out the slimes, but that means adding more water, so you end up with a larger volume of material to move. You can move water to surface by pumping it from sump to sump to sump, or you can pump it to the main dewatering system at the shaft. If you don’t deal with the slimes in the sumps, you have to deal with it somewhere else, and those high-pressure pumps used in the main dewatering systems are very unforgiving. Most of them can’t take any grit or they’ll tear themselves to pieces. Some mines have moved toward dirty water systems that pump all the crud and water. These pumps are two to three times the cost. Now, you’ve moved the problem to surface.

SMSJ: How is it dealt with on surface?

DA: You can run it into the back 40, but there are limitations from the Ministry of the Environment on what you can do with it and where it can go. If it’s just mixed with mine tailings, that’s fine. Vale Inco has thousands of acres, but smaller operations don’t have that capacity. They’ll have a series of holding ponds. They’ll pump into one all year, let the slimes settle and then they’ll switch over to the next one. After the slimes settle, they get a permit from the Ministry and pump the water off the top during the very narrow windows in the spring and fall when watercourses are at their maximum flow and they are able to get maximum dilution. So, one way or another, you have to deal with the slimes.

SMSJ: You probably get some pumps back in pretty rough shape.

DA: If backfill seeps out and gets into the sumps, you not only have slimes, but you now have concrete in the mix. We’ve had pumps come back that are full of concrete. It’s literally a block of concrete inside of a working pump. In between the motor housing and the outer casing, it’s a solid block.

SMSJ: What’s new in pumping?

DA: One thing I’ve been promoting is what we call the Flygt automatic pump controller, the FPC100. It’s an electronic device that manages and monitors the pump. It sits in the control package that the pump is connected to and replaces the level regulators or float switches that sit inside the sump. The level regulators can get hung up on the slimes or they get damaged by a scoop coming in to clean out the sump. That could cause the pump to run continuously and fail. The FPC100 monitors what the pump is doing, so it’s not dependent on external sensors and it knows when the pump runs out of water. We sold more than 100 units last year and, this year, we’ve incorporated it into a standard control package used by both Vale Inco and Xstrata.

SMSJ: Do you do any customization of pumps to address specific needs of the mining companies in Northern Ontario?

DA:  Yes. We customize a pump for Vale Inco to better withstand the high acidity of the water at North Mine. Typical mine water in Ontario is anywhere between a pH of 4 and 7. At North Mine, it’s as low as 2.3. We put stainless steel impellers in it and the entire body and discharge connection is cast iron. The alternative would be to go to all stainless steel, which would be three times the cost. High acidity just eats away a conventional pump. Ultimately, it will completely dissolve it.

SMSJ: Do you see any trends in pump design or dewatering technology? What will we see in the future?

DA: We will probably see fewer sumps and more powerful pumps for moving water higher and longer distances. More mines are going to higher and higher heads. Pumps will have to adapt for that, but still be able to handle the cuttings and fines.

 

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