Dredging World News Blog

Dredge Pumping Systems Improve with VFD Motor Controls

Posted by Elizabeth Kaiser on Wed, Nov 09, 2011 @ 08:11 AM

Submitted by Dave Stoltenberg, Dredge Rental Specialist, SRS Crisafulli

Pumps and Systems MagazinePumps and Systems recently published an article by Christopher Jaszczolt titled “VFDs Improve Motor and Pump Control”.   The article discussed current applications of variable frequency driven (VFD) motor controls as an excellent method to improve on mechanical control methods.  VFD control systems have gained market share and visibility in the past decade as an excellent motor control methodology with the added benefit of energy conservation.  By implementing VFD controls on dredge pumps, dredges become much more usable with the typical slower processing speeds of dewatering systems. 

Jaszczolt says:  ”Preferably, some of the pumps can be shut down when demand is low, and the system can be designed so that the water pressure can be maintained by a single pump during periods of low demand. Properly designed lead-lag systems will improve the efficiency, performance and longevity of the pumping system.

Jaszczolt also tells us:  “Like a PLC—advanced VFDs can be programmed, monitored and maintained with PC-based software. Unlike a PLC, this software is generally provided free by the VFD supplier. VFD programming and monitoring software is also easier to use than similar software for PLCs because the software is for a single application specific rather than general purpose.

VFDs have been used to control pumps for many years. However, advanced pump-specific VFDs now allow users to improve motor/pump control and protection without the need for inefficient mechanical devices or costly PLCs.

 

Christopher Jaszczolt is an application engineer with the Drives and Motion Division of Yaskawa America, Inc., in Waukegan, Ill. He has a BSEE from Northern Illinois University and five years’ experience applying variable frequency drives in industrial applications.

Read Christopher Jaszczolt’s complete article online at:  VFDs Improve Motor & Pump Control

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Topics: Dredges, crisafulli, dredge, dredging, dredging system, dredging and pumps

Proactive Dredging: A Little Now or a Lot Later

Posted by Elizabeth Kaiser on Wed, Oct 19, 2011 @ 08:10 AM

By Isaiah Helm, Applications Engineer, SRS Crisafulli

 

If public works departments had a list of fun things to do, dredging sediment out of holding ponds would not be on it.  It’s like cleaning the shower in your bathroom.  Whether you make it a frequent quick job or an occasional laborious task, time and effort must be set aside to maintain a fixture that is as critical as it is uninteresting.  This is the scenario that played out for Georgia’s Cobb County-Marietta Water Authority (CCMWA) during the summer and fall of 2010, as reported in Public Works Magazine

CCMWA had two water treatment plants and a 25 million gallon reservoir in need of upgrade to meet the EPA’s Stage 2 Disinfectant and Disinfection Byproduct Rule of 2006.  During the upgrade, one plant would be running, one shut down.  The reservoir had to be at full capacity to do this.  Unfortunately, it hadn’t been dredged since 1978 and was half full of sludge.  

 proactive dredging resized 600The reservoir was restored to its original 14-foot depth
within six months.  (Photo Credit:  Public Works Magazine)

Timing of all the different upgrade stages coupled with the EPA deadline meant the reservoir had to be cleaned out in six months.  (The dredging had originally been scheduled to take place 2013-2014.) 

In other words, the CCMWA had to make up over 30 years of maintenance in 6 months (that would be one nasty shower!).  The result: increased scale, decreased competition, and ultimately an increased cost.  The amount of dewatering equipment doubled.  Four mobile belt presses and four recessed chamber presses were used.  Fifty trucks made four 45-mile round trips per day.  Bidding on the project was limited to the few large contractors who were even capable of completing the project.  There were five bidders and all five of them listed the same two companies as their subcontractors.  Total cost to dredge the reservoir and perform maintenance on the banks and sluice gates totaled just over $4 million.

The World Dredging Mining & Construction Journal [1] contains a version of the article authored by Steve Gibbs.  It goes on to discuss some observations from the project:

One of the lessons learned by CCMWA is the need for regular dredging of the reservoir.  One benefit of regular dredging is economics – greater capacity in the reservoir reduces the amount of pumping necessary to bring water from the Chattahoochee, thus saving electrical costs.  Also, doing a smaller dredging project every five years or so will eliminate the need to do a massive project such as the one just completed.

A deeper, cleaner reservoir will allow suspended solids to settle out better, which will enhance treatment efficiency.  The reservoir will also have ample capacity while the treatment plants are in their construction phase.

“This (the reservoir dredging project) will decrease the potential for water quality problems or process issues at our treatment plants,” said Ginn (CCMWA process engineer). “It’s a very good proactive preventive maintenance step.”

There you have it.  Proactive dredging of sludge-collecting ponds really does make life easier in the end.  It also increases the options:

  • Put out a request for bids on that smaller dredging project every five years

  • Contract with a dredging company to clean out the pond every five years

  • Rent dredging and dewatering equipment directly and eliminate the middleman

  • Purchase an automated or remote dredging and dewatering system and have it permanently installed for complete self-sufficiency

At least it’s something to think about while you’re cleaning your shower tonight.

 

[1] World Dredging Mining & Construction Journal, “Proper Planning for a Perfect Project” (Volume 46, Nos. 11/12, Page 16)

 

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Topics: Dredges, crisafulli, dredge, dredging, srs crisafulli, dredging abrasive materials, lagoon dredges, dredging system, dredging and pumps, dredging equipment rentals, rotomite sd110, lagoon, rotomite 6000c, Hydraulic dredging, rotomite 6000

Ask a FLUMP Expert. Seven ways to Secure your Traverse System

Posted by Elizabeth Kaiser on Thu, Jul 28, 2011 @ 08:07 AM

The propulsion and traverse systems are critically important to the operation of an unmanned, cabled dredge. The FLUMP, SRS Crisafulli's unmanned dredge, propels itself along a traverse cable connected to lateral cables at opposite sides of the lagoon, configured at 90 degrees to the traverse cable.

The FLUMP's drive system is onboard.  SRS Crisafulli's FLUMP Specialist, Senior Applications Engineer Eric Lillberg, explains seven ways to secure the lateral traverse cables to land, on opposite sides of the lagoon.

The standard method is to drive three 48" long stakes into a triangular steel base plate on each of the four corners of the lagoon or pond.  From the four corners, wire rope winches are connected to each lateral cable, each of which is connected in turn to the traverse cable that runs the length of the lagoon.  The corner winches can exert 2,000 lbs. of tension into the cable system. 

Normally, this method provides more than adequate results, depending on the length of the traverse cable.

traverse 1 resized 600

Even at 700 lbs. of tension, however, a base plate can be pulled out of soft ground, which leads us to Method #2, a daisy chain setup with multiple stakes connected by chains or cables.

Method #3:  In more permanent installations the use of concrete bollard posts is an economical solution. 

 Traverse   2

 

Method #4: A motorized trolley system mounted on a steel rail structure. A rail structure with a motorized trolley system is the preferred method for permanent installations.  The rail structure adds cost to the system, but can result in a substantial reduction in ongoing operator cost thereby improving the overall return on investment (ROI) from the dredging system.  Traverse 3 resized 600

 

Method #5:  When the lagoon is surrounded by hard packed or rocky terrain, other methods have been utilized, including large concrete blocks, about 32" x 32" x 64" and weighing approximately 5700 lbs.  Depending on the lay of the land, it may take some jockeying to prevent the blocks from sliding, once tension is applied.

 Traverse 4 resized 600

 

Method #6:  We have drilled holes in existing rock and concrete structures to set anchors. 

Method #7:  A not so common, but equally effective approach is to use two motor vehicles, one on each side of the lagoon.  Skilled drivers move the two vehicles in perfect parallel, enabling the system to work with no adjustment to the traverse system. Traverse 5 resized 600

 

No matter what the method, a taut cable is essential to effective unmanned dredging.

Read more about SRS Crisafulli's Cable Traverse System.

Click here to ask us a question.  Mention Eric's article.

Topics: lagoon dredges, dredging system, flump, agriculture