Case Studies

Pumps

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Solving costly clogging issues

Problem: Household items clogged the pump impellers in the Inkster (Mich.) lift station every 28 hours and, in some cases, within 10 minutes of reinstallation. During downtime, sewage was diverted to a retention pond, then vacuumed and transported to the treatment plant. The city considered decommissioning the station and just using the retention pond. While searching for a long-term solution, officials tried several options that included a mix flush valve system. It didn’t work.

Solution: A proposal from Crane Pumps & Systems suggested installing three Barnes 4SHVB 10 hp vortex solids handling pumps. The city accepted them on a 60-day trial. The recessed vortex impellers handle 3-inch spherical solids and stringy solids, even at low-flow, high-head operation. Pumpout vanes protect the mechanical seal. Inverter duty-rated motors and steep performance curves make the pumps suitable for variable-speed operation. The pump shaft, all fasteners, and the large lifting bail are stainless steel. The external coating is corrosion resistant.

Result: The city purchased the pumps, which have not clogged in 10 months. Maintenance is minimal. 937/778-8947; www.cranepumps.com.

Double disc pump reduces maintenance

Problem: Failures of the two progressive cavity pumps at the East End Wastewater Treatment Plant in Portland, Maine, was costing the city $28,000 annually in repairs, not including labor for dismantling and assembling the pumps four times per year. The pumps, one operating and one on standby, transferred thickened primary sludge at 4 to 8 percent solids for 8 to 10 hours per day. The Portland Water District needed a way to reduce the frequent high maintenance costs.

Solution: Penn Valley Pump conducted a one-year trial with its 6-inch Model 6DDSX76 double disc pump. The self-priming unit pumps 500 gpm, handles 2-inch solids, and runs dry without damage. Its seal-less design has no stuffing box, mechanical seals, check valves, or fouling problems. After six months of running the pump exclusively, it was torn down and inspected. Penn Valley found no visible signs of wear. The process was repeated six months later with identical results. During the trial, the pump required no maintenance or repair. The district then purchased the unit.

Result: The pump has operated without maintenance or parts replacement. Compared with the progressive cavity units, the district saved more than $70,000 in repair costs over four years. The payback period was 15 months. 800/311-3311; www.pennvalleypump.com.

Pump sharply reduces maintenance time

Problem: The multiple progressing cavity sludge pumps failed frequently at the Thames Water plant in Dorking, United Kingdom. Operators worked for two-and-a-half days to disconnect the pumps and replace the rotor, stator, and connecting rod assembly. “We needed a way to improve efficiency and reduce downtime,” says sewage operator Gavin Parker. “It took four hours to de-rag these pumps and eight hours to disassemble them for maintenance.”

Solution: Thames Water installed the EZstrip sewage pump from NOV Monoflo. The pump’s split coupling and detachable feed chamber give direct access to the coupling rod area. Operators strip, maintain, and replace pumping elements and drive train items without disconnecting the pump and without any dismantling space. The pump also fits easily into the same space as the previous pump.

Result: “We’ve reduced our maintenance time from hours to minutes,” says Parker. “Pump disassembly now takes 30 minutes, saving $562.50 in labor costs. Our de-rag time is down to 15 minutes, saving us $273.75.” Compared with traditional progressing cavity pumps, the EZstrip pump will deliver more than $16,700 in savings over its life. 281/200-1200; www.ezstrip.com.

Eddy-current drives handle over-voltage

Problem: The St. Joseph (Mo.) Water Protection system is near a power station on the Missouri River, and the line output experiences occasional fluctuations. The wastewater treatment plant had 15 variable-frequency drives, but most were not functioning. “We had multiple 18-month-old 300 hp VFDs quit on us because they didn’t have a fail-safe to address over-voltage,” says superintendent Don Gilpin. “Then we had to explain to the Missouri Department of Natural Resources why we were bypassing wastewater treatment for a week. We needed a more reliable and economical answer.”

Solution: The city purchased six Dynamatic eddy-current drives from Drive Source International. The units have a flange-mounted fixed-speed AC motor and an air-cooled, adjustable-speed magnetic clutch or eddy-current coupling. The magnetic field determines the torque transmitted from the input rotor to the output rotor. A controller varying the clutch current allows it to transmit only enough torque to operate at the desired speed. Transmitting torque at variable speeds produces a smooth response that eliminates shock and loading.

Result: With no high-voltage electronics in front of the motors, over-voltage is no longer a problem. “We did an annual cost and reliability evaluation of our different pump and air-handling drives,” says Gilpin. “The cost of maintaining the eddy-current drives is $40 a year for brushes. Every two to three years, we soapstone the contacts to clean them, and that’s it. We would have spent millions replacing the VFDs.” 800/548-2169; www.drivesourceusa.com.

Mono-port impeller eliminates pump clogging

Problem: The City of Rancho Santa Fe, Calif., battled blockages caused by disposable wipes that prevented its Smith & Loveless underground Custom Series pump station from operating at full capacity. The station had two 4C2A 4-inch non-clog flooded-suction rotating assemblies at 20 hp handling 500 gpm at 85 feet of total dynamic head. “We pulled each pump at least once a week,” says collection systems manager Rick Russell. Russell thought the wipes built up in the pumps when the station’s variable-frequency drives ramped down to low speed during the night. A closer look showed that the wipes were building up inside the impellers and binding the pumps. “We tried various ramp speeds and RPM ranges to level out the station, but they never made much difference,” he says.

Solution: Smith & Loveless technicians recommended retrofitting the X-PELLER, a single-port impeller designed for high-trash volumes and low-flow conditions. The unit expels high volumes of stringy material, rags and other trashy items.

Result: “We haven’t pulled a clogged pump since we changed the impeller six months ago,” says Russell. “It was a simple, effective solution.” 913/888-5201; www.smithandloveless.com.

Cake pump system offers compact solution

Problem: The Harpers Ferry & Bolivar (W.Va.) Public Service District Waste Water Treatment Plant used drying beds and open-air dewatering before disposing of the cake in a landfill. To meet new regulations, the district needed a more compact, efficient system.

Solution: The district selected a cake pump system from seepex Inc. that included a BN 30-6LT progressive cavity pump feeding 2,200 gpm at 720 psi to a belt press. A lime-feed system enables operators to create Class A biosolids. Dewatered cake at 16 to 20 percent solids falls into the hopper of a BTI 17-12 progressive cavity pump. A load cell system turns on the pump, which shuts off when the belt stops feeding the hopper. The dry-run protection system includes a Telkonet SmartEnergy control unit that turns off the pump if it reaches the set point temperature. The thermal motor protection device shuts off the pump if the motor temperature reaches unsafe levels. A discharge pressure ring protects the discharge piping against failure from over-pressure. A custom control panel monitors the sensors and shows the load cell weight level, shutoff button, cake output temperature, lime-feed signal, and various fault signals for the sensors.

Result: “The pumps are running without issue, and the control system is easy to adjust and monitor,” says plant supervisor Jimmy Williams. 937/864-7150; www.seepex.com.

Centrifugal pumps purify wastewater

Problem: NieuWater wanted to add a pure-water plant to its wastewater treatment facility in Emmen, The Netherlands, to process effluent into ultrapure water for the Netherlands Mineral Oil (NAM) Co. The company injected steam into wells to liquidize and extract heavy, viscous oil in Schoonebeek Field. The water needed to be ultrapure. Finding the proper purification technology was crucial to the success of the project.

Solution: NieuWater selected advanced technology reverse osmosis (RO) pumping equipment from SPX Flow Technology. The package included more than 60 frequency-regulated, vertical set-up centrifugal RO Johnson pumps. They draw effluent through five layers of dual-pass RO membranes in 20-foot-long housings. The purification surface area is 200,000 square feet. An anti-scaling medium prevents membrane fouling, but should contamination occur and increase resistance, the pumps continue to run at the same capacity. Pipe forces have little effect on pump calibration. Proper calibration prevents unnecessary loads and vibrations, reduces maintenance, and extends service life to 25 years. The water then passes through an electrodeionization unit to remove the last mineral ions. The combination of membrane filtration and ion exchange uses an electrical current to regenerate the resin.

Result: The plant went online last autumn, pumping 2.6 mgd of ultrapure water four miles to storage tanks at the NAM site. 800/252-5200; www.spxft.com.



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