Recently I was asked for support at an open pit mine that was having trouble dewatering. The main challenge in short was that the inflow from springs and rainfall was exceeding their capacity to pump water from the pit floor and this was affecting mining operations.
The first step was to tour the mine to get an overview of the application. I also wanted to have a look at how they were currently handling the issue. During the tour, the mine operations team commented that they had doubled up on pumps with almost no increase in flow rate.
On the pit floor, there were two large, diesel driven, self-priming horizontal pumps drawing from a large sump located only inches below the pump skids. The two pumps were operating in parallel at max rpm, pumping into a single pipeline that went vertically straight up the pit wall and terminating at a holding pond. After seeing the pump configuration I was confident that I fully understood why doubling the pumps had not yielded a doubling of flow rates, but the question for me now was:
“How can I relay this so that the mine operations staff also understand the issue?”
Returning to the mine office, we sat down and drew out a system curve for their application. We then accessed a copy of the pump curve for their pit pumps operating at maximum rpm and overlaid both single and twin pumps on the system curve. The drawing below is similar to the one that we created.
The drawing we created clearly illustrated a system issue not a pump issue. The solution to the problem would be to somehow flatten out the system curve and thereby maximize the potential of the second pump. The drawing below illustrates this point:
The shape of a system curve, however, is based on dynamic resistance (typically referred to as friction). Since we wanted to change the shape we needed to alter the system friction. Friction for this application was simply a function of pipe diameter and length. As many of you know, piping is a difficult problem to solve. With this particular project, changing the length of the piping was absolutely off the table so our next option was to look at increasing the pipe sizing. Unfortunately for this customer, with limited availability to larger pipes, we had to keep searching for another alternative. After further discussion, a new solution was proposed, designed and employed. The customer installed a second independent pipeline for the second pump. As soon as this was implemented, a true doubling of flow rate was finally achieved.
Spending time working with pump curves and a sheet of paper can save hours, days and weeks of expensive trial and error. Thankfully this customer understood that reaching out and asking for help was his best option and we understood that the best way to help them was to create a system curve and help them to understand how pumps in parallel operated.
The Hevvy application team has curves, paper, and is always available to help! Please reach out if you have any questions or challenges that you are having difficulty solving. We offer support via phone, email, site audits and on site training sessions!
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