Rotary lobe compressor cuts costs

Problem

Personnel at the Town of Huntington (N.Y.) Wastewater Treatment Plant were troubled by the energy requirements of three 125 hp blowers powering aerators with variable-frequency drives in the two 1.5-million-gallon sequencing batch reactors. Supervisor John Pavlik looked at various blower manufacturer proposals.

 

Solution

G.A. Fleet Associates in Harrison, N.Y., suggested a side-by-side test with one of the older blowers and a Delta Hybrid rotary lobe compressor made in Germany by Aerzener Maschinenfabrik GmbH and distributed by Aerzen USA. The belt-driven unit combines the packaging principles of Aerzen rotary lobe blowers with screw compressor technologies for volume flows of 400 to 2,000 cfm. Low-pressure (3 to 5 psi) units use a 3+3 twisted rotor (supercharger) profile, while a 3+4 compressor rotor profile is used for higher pressures (up to 22 psi). The compressor is matched to the required pressure range for optimum efficiency.

 

Result

Four times per day, staff took readings and checked blower temperatures and pressures. “For the first few days, we questioned if we were monitoring the meters correctly because the numbers shocked us,” says Pavlik. “They showed a 28 to 29 percent kW reduction, a 30 percent peak demand reduction, and a 45-degree temperature difference between the two units. Replacing the three original blowers will save us $56,000 to $58,000 in electricity per year, not including labor and materials.” 610/517-0758; www.aerzenusa.com.

 

Combined heat and power saves money

Problem

In 2007, the City of Oceanside, Calif., looked for a partner to build, own, and operate a biogas-fired cogeneration plant at the San Luis Rey Water Reclamation Facility.

 

Solution

CHP Clean Energy won the bid with the BioSpark system that conditions biogas before it enters the prime mover. A 30- by 55-foot building replaced the methane flares and houses the combined heat and power system. Engineers chose a modified Guascor reciprocating engine. The electrical interconnect is in the CHP structure. The gas treatment system’s scalable technology focused on removing moisture, hydrogen sulfide, and siloxanes.

 

Result

The system enabled operators to maintain the reciprocating engine on a schedule consistent with a natural gas cogeneration facility. The city, participating in a power purchase agreement for the delivery of discounted electricity and heat, expects savings of $350,000 to $500,000 annually. 978/621-0421; www.chpcleanenergy.com.

 

Dissolved oxygen probe improves control

Problem

Operators at the Bristol-Myers Squibb plant in East Syracuse, N.Y., manually measured dissolved oxygen in the aeration tanks because the treatment process operates at 112 degrees F, and the maximum operating temperature for online DO monitors is 105 degrees F. Without a way to constantly measure DO, the aeration blowers ran more than was necessary.

 

Solution

Hach Company engineers recommended the LDO sensors to provide continuous DO readings. When combined with automated variable-frequency drives, the sensors can control aeration blowers on a closed control loop in direct response to DO measurements. The units use 99 percent accurate luminescent technology and operate in water at 122 degrees F. They require no calibration for a year and almost no maintenance.

 

Result

The upgrade enabled the plant to use almost 75 percent less power and recoup the cost of sensors in less than a year. 800/227-4224; www.hach.com.

 

Heat exchangers stop clogging and baking

Problem

Holes in three tube-in-tube heat exchangers at the Stanely Street Wastewater Treatment Plant in Niagara City, Ont., affected the heating of sludge with hot water. Heat exchanger replacements would have to fit through a 5-foot-square hatch in the roof, then be rolled down a long, winding corridor.

 

Solution

The facility bought rectangular-channeled heat exchangers from DDI Heat Exchangers to handle viscous material. The nonblock design has 3-inch gaps to prevent sludge blockage and no spacers for both liquids. The 3-feet-per-second flow prevents baking, while creating more turbulence for better heat transfer.

Although the units have a small footprint, their larger circumference reduces the need for macerators. A full door makes it easy to clean them every few years. DDI added a hoist bar to the exchangers for lowering them down the hatch with a crane, and rollers for maneuvering them into position.

 

Result

The heat exchangers are operating as specified. 514/696-7961; www.ddi-heatexchangers.com.

 

Air bearing turbo blowers use less power

Problem

The 3 mgd Festus/Crystal City Sewage Treatment Plant in Festus, Mo., spent $42,000 in five years to fix three 100 hp positive displacement blowers.

 

Solution

Engineers from HSI Blowers recommended replacing the existing blowers with two HSI 75 hp high-speed turbo units producing 1,300 cfm/7.5 psi. The pre-engineered systems include compressor, motor, variable-speed motor starter, pressure relief valve, expansion joint, and control cabinet.

Impellers at both ends of a common shaft counterbalance and eliminate axial thrust load, stress, and twisting. Individually layered air bearings support the shaft. As the shaft rotates, the bearings float friction free on a film of air. The compact, lightweight unit requires no special foundation support or overhead cranes to access.

 

Result

The units use 40 percent less power than the original blowers, enabling the plant to receive an energy rebate from its electric provider and realize a payback in two to three years. 713/947-1623; www.hsiblowers.com.

 

Peristaltic pumps increase energy efficiency

Problem

To comply with a U.S. EPA consent order, the City of Nashua, N.H., built a 60 mgd wet-weather treatment facility to receive overflows from its 50 mgd wastewater treatment plant. The new facility needed hose pumps to dose sodium hypochlorite tube pumps to meter sodium bisulfate.

 

Solution

The engineering consultant selected two LPP-D peristaltic hose pumps and four LPP-M peristaltic tube pumps from Flowrox. A single bearing-mounted roller in the hose pumps presses the hose once per 360-degree cycle, producing the maximum flow per revolution. The roller, mounted on a crankshaft, creates eccentric rotation to eliminate friction and lower energy consumption.

The flow rate of the tube pumps is unaffected by discharge pressure variations. Positive displacement of the tube bore with zero slip provides the same output volume on every cycle. The compression point of the tube acts as a self-cleaning check valve, providing a clear flow path with no possibility for vapor lock.

 

Result

After two years of constant operation, the pumps continue to run with no downtime. 410/636-2250; www.flowrox.com.

 

Rotary lobe pump cuts rebuilds

Problem

Three operators at the Wyoming Valley Sanitary Authority in Wilkes-Barre, Pa., spent three days per quarter rebuilding three progressive cavity sludge pumps. Annual maintenance for each pump cost $24,000 to $32,000. The authority needed a way to save money and reduce labor.

 

Solution

The authority installed an SL133 500 rpm rotary lobe pump from LobePro on a trial basis. Handling 665 gpm/125 psi, the compact, positive displacement unit pumped sludge with greater than 3 percent solids. As fluid enters the suction side of the pump, it fills the cavities between the lobes, then travels around the casing and is forced out the discharge port. Because of the operation design, the pump rarely ragged and could be run dry for a time without damage.

 

Result

Operators inspected the pump monthly. After four months, they reported no change in performance or wear and installed the pump permanently. It ran continuously for 15 months before the first rebuild, costing less than $4,000. “We’re getting four to five times the service life over the screw pump,” says superintendent Mike Jacobs. “And our lead mechanic can rebuild the pump in three hours because he can replace the four-wing lobes, seals, and wear plates without removing the piping or pump.” 888/997-7867; www.lobepro.com.

 

Biological activity enhancer aids digestion

Problem

The 5.5 mgd Landis Sewerage Authority in Vineland, N.J., struggled to increase methane gas production in the anaerobic digesters to maximize performance and energy savings. The combined heat and power unit ran at 32 percent electrical efficiency and 53 percent thermal efficiency.

 

Solution

By adding BAE, a natural digestion-enhancing peat extract from Prodex, a JSH company, the authority increased its average daily methane production by more than 28 percent from the previous year. The liquid biostimulant enhances BOD and TSS removal, improves sludge settling, eliminates FOG, and reduces solids handling.

 

Result

The authority increased methane gas production by 28 percent and boosted the generator’s performance from 85 percent capacity to maximum design capacity of 95 to 98 percent, realizing a yearly savings of $78,739 with a reduced loan payback period of 5.4 months. The U.S. EPA honored the authority with its Energy Star CHP Award. 856-234-4540; www.prodexproducts.com.

 

Speed reducers boost reliability

Problem

Outdated speed reducers on settling tank collector drives at the City of Los Angeles (Calif.) Department of Public Works Bureau of Sanitation experienced high-speed pinion failures and other related problems.

 

Solution

The utility replaced six of the drives with Cyclo Bevel Buddybox speed reducers from Sumitomo. The shaft-mounted, right-angle units have cycloidal speed reduction input and spiral bevel gearbox output. The compact, modular design provides high-torque density with multiple-output speed and torque combinations. The Taper-Grip bushing, a keyless device integrated into the reducer, provides self-aligning, backlash-free torque transmission to the driven shaft. The utility also purchased a self-aligning NEMA C-face adapter to replace the existing motor scoop arrangement.

 

Result

The utility will replace the remaining drives with speed reducers in the next phase of their retrofit. 800/762-9256; www.smcyclo.com.