The Challenge of Underground Mine “Dewatering”
If you are an owner, operator or user of Electric Submersible pumps in Mine Dewatering and currently experience multiple seal failures within one year of start-up and installation… Please read on. Additionally, if you are a fellow professional in the field that wishes to share observations and constructive comments then please feel free to respond to this post.
Most customers who I meet spend large amounts of time constantly changing seals and/or repairing and rewinding motors as a knock on result of an initial seal failure. The fact is that a majority of the failures that occur in electric submersibles are attributable primarily to seal failures.
Ask your maintenance team this one questions:
How many submersible pumps have we repaired in the past 2 years?
I would make a sportsman’s bet with you that nearly all of those pumps have been pulled from their installation because of performance concerns related to the seals. If that was your new vehicle, would you accept having to hand it back to the dealer once, twice or three times a year for a full strip down of the engine, transmission and chassis? Some of these pumps cost more than your average family car, so why do we accept failure on this scale?
Is it the fault of the seal? In most cases the answer is no. It is simply the wrong seal for the application.
After traveling to various sites I’ve noticed that most owners are more focused on keeping the process running while the multi-tasked maintenance foreman does his best to keep up with never ending pump failures. Here is prime example:
I recently visited an underground mine where the population of electric submersible “Dewatering” pumps numbered close to 80 pumps. Up to the first 6 months of this year (2017) the mine had spent close to $600k on pump repairs and replacements. This was a pretty typical application pumping runoff sump water and slimes from level to level via 4” piping laid overhead along the ramps. The mine superintendent advised me that he received great service from his local pump supplier and qualified that by adding that: “Everytime a pump breaks down they bring us a new or refurbished pump.” Pardon me for asking but isn’t that just buying into a model that rewards failure? Much of this culture is driven by the desire to keep the mines dewatered and de-slimed at almost any cost and I totally get that. However the deeper question is: Why do these pumps keep failing and is there a more reliable pump solution that will allow me to spend $600k where it is really adding value to my company?
Does this look familiar? This is a typical submersible dewatering pump return blocked up with dry slimes.
The video link below will partially explain why most dewatering pumps fail in de-sliming services.
Quite simply put you are asking an unmonitored and unattended pump, designed to pump water with no more than 1 to 2% solids, to pump a 30% cw (Concentration by Weight) slurry that consists of highly abrasive media suspended in clay and other abrasive substrates. The Hydraulic Institute would categorize this as Class 2 or Class 3 slurry. The majority of pumps in service underground are light to medium duty dewatering pumps and not slurry pumps and once the water level is drawn down they find themselves immersed in the settled solids. These clog the basket strainers resulting in dry running and overheating of the motors. The dry running will certainly kill the mechanical seal and the subsequent overheating will kill the motor if not fitted with thermal protection.
So what is the solution? It is here that I should offer you a Hevvy/Toyo Pump solution but unfortunately it is not that straightforward. Providing a high head, dry running slurry pump that can handle the solids up to 75% cw is the easy part; we face and meet that challenge on a daily basis.
The challenge is to pump the much heavier solids through existing piping infrastructure that was originally designed to carry water and light slurries. Friction losses increase, pumping pressure increases, wear increases, power increases; all of which the pump can be designed to overcome.
A balance has to be struck whereby the consistency and SG is altered by producing a more homogenized and lighter mix of water with solids. By utilizing the correct design of agitated submersible slurry pumps it is possible to create a mix that can be readily pumped through the existing pipeline without the need to upgrade the line. If done properly, this can totally eradicate the need for “mucking out” with the UG mine front end loaders thus realizing another saving. The longer term trade-off is replacement of piping periodically. This all sounds simple, and it is, but a commercially viable compromise has to be made whereby the cost of installing a submersible slurry pump provides maintenance and process benefits as well as lower operational costs…..BUT ABOVE ALL a reduction in the amount of unnecessary time entering the sump areas which present many safety hazards.
So back to the the constant failure of seals. If the pumps are not fitted with a suitable slurry seal then you cannot reasonably expect them to last a long period of time in a slurry application. You need to assume that if it’s going into an underground or any open pit sump that it will see abrasive particles and slurries at some time during its life and that is where you ask if the seal is capable of handling slurry.
I would invite you to contact our experts at Hevvy/Toyo Pumps. We will conduct a complete audit of your pumps and demonstrate where it makes sense to utilize slurry submersibles. We offer comprehensive no hassle Try and Buy programs to prove the integrity of our pumps in your system. We will perform hydraulic design calculations for your existing pipework to ensure that your performance and system curves intersect at or as close to best efficiency point (BEP). Our network of regional sales and service managers as well as extensive distribution coverage ensures that you will always receive prompt, professional and courteous advice.
To discuss the right Hevvy Pump Solution for your sumps please contact us at: firstname.lastname@example.org