What is dredging?
Dredging removes sediment and sludge in liquid environments, usually water. The three main types of dredges are clam shell, cutter-suction, and horizontal auger. Clam shell or bucket dredges can be small excavators, or large cranes on a barge. Cutter-suction dredges are typically large ocean going vessels, that anchor themselves with a pillar and dredge in an arch before moving to the next area.
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We build horizontal auger dredges, which are the smallest of the dredge types. Our dredges are run on a cable system, or with a propulsion system. They resemble a household vacuum cleaner, with a wide cutterhead, that you push forward and pull backwards as they remove one layer of sediment per pass.
How do dredges work?
Each style of dredge works in a unique way and has it's strengths and weaknesses.
The clam shell dredges drop their bucket into the material and then extract what they collect and dump it onto a barge or land, before repeating the process. Clam shell dredges can work in almost any environment, and to any depth. It's the slowest process, from a cubic yards per hour measurement, for the size of the unit, but they can't get clogged, so they're able to operate in harsh environments, like harbors, which can have lots of debris. If you have a project requiring removing material 40' below the surface, or are worried about what's under the water, a clam shell dredge may be the best choice.
Cutter-suction dredges are generally large barges. The cutter is designed to extract compact material, and many are used near ocean shore lines to remove abrasive sand and clear erosion sedimentation. With the large size and aggressive cutting, many cutter-suction dredges use one or multiple pillars to anchor themselves into the ground before dredging in an arch in front of them. After they've cleared the arch, they move forward and clean another arch. Cutter-suction dredges are great for large projects and excel at dealing with compact material.
Auger dredges mix the sediment with water with their cutterhead, and pump the slurries to the surface of lagoons, ponds, lakes, waterways, and canals. The material is then pumped through floating and land-based pipe to a disposal/spoil site. The compact size of the unmanned dredges, and cable systems they use, mean they're ideal for dredging lagoons with linings, which would be damaged by a clam shell, or the posts and aggressive cutter of the cutter-suction dredges. We can add wheels and a cage to our auger, so the cutterhead rests on top of a liner, and won't cut into it, even if you're dredging directly on the bottom of your lagoon.
What is a horizontal auger dredge?
Horizontal hydraulic auger dredges have a horizontally positioned cutterhead (auger) that rotates to combine sediments and water thus creating a slurry.
What are the Benefits of Horizontal Auger Dredges?
- Ease of movement and use
- Transportability
- Productivity
- Turbidity
- Cost
Benefits of Horizontal Hydraulic dredges explained
1. Ease of movement and use
Horizonal dredges are nimble and easily maneuvered in various sized and shaped bodies of water. Operators point the dredge where they want to cut, lower the cutterhead, and move forward. This simple system can be quickly taught to an employee/operator.
2. Transportability of hydraulic dredges
Crisafulli dredges can be carried on standard step-deck or flatbed trailer. Dredges are delivered fully assembled on a truck or partially assembled when delivered in a shipping container.
3. Productivity of hydraulic dredges
Horizonal auger dredges are productive at moving liquids and solids. Productivity is measured as the percentage of solids relative to the mixture being extracted and pumped. The production of solids is measured in Cubic Yards per hour or Cubic Meters per hour. Depending on the type of materials, it is typical to extract up to a 25% or more of solids content. The rate of extraction is measured in Gallons per Minute (GPM) or Cubic Meters per Hour (m3/h) of slurry or sludge. Crisafulli dredges are matched to meet the output demands of dewatering devices such as dewatering bags, geo-tubes, drying beds, clarifiers, belt presses, filter presses, screens, centrifuges, and tanks. Depending on output demands, Crisafulli dredge output can be adjusted from 200 GPM to 2,500 GPM, which equals 45.4 m3/h to 567.8 m3/h.
4. Turbidity and hydraulic dredges
By design, horizontal auger dredges capture dredged material by sucking the dredged material into a shroud where it is directed into the pump’s suction mouth. The shrouding of material enables horizontal auger dredges to suck up dredged materials while dredging.
5. Cost of hydraulic dredges
Small horizontal auger dredges are priced for as little as $125,000 for a new unit, while the largest horizontal auger dredges are less than $600,000.
What are the basic components of hydraulic dredge?
Basic components of hydraulic dredges include a cutterhead (auger), pump, floatation system or platform, engine or motor, operational controls, and discharge.
What is the process of hydraulic dredging?
During hydraulic dredging, the engine (diesel or electric powered), transfers power to the cutterhead and pump by means of hydraulic motors and high-pressure hoses. Then the cutterhead creates a slurry from the sediment. The centrifugal pump (mounted directly behind the cutterhead) draws the slurry into a discharge piping system. From there, the pump pushes the slurry through a floating discharge pipe to the surface and then to the discharge/spoil site.
What size dredge do I need?
To determine the best dredge to fulfil project requirements, consider these questions:
- 1. What are the dimensions of dredging area (L, W, D)?
- 2. What is amount of material to be extracted?
- 3. What is depth of the material to be extracted?
- 4. Is the material compacted or not?
- 5. Is the material free flowing?
- 6. What is the specific gravity (weight relative to size) of the material?
- 7. What is the maximum distance from dredge to the discharge/spoil site?
- 8. What is the vertical lift from the dredge to the discharge site (elevation change)?
- 9. What is the particle size in the material to be dredged?
- 10. Are there any flow requirements?
Who is SRS Crisafulli?
SRS Crisafulli, Inc. is a Montana USA-based manufacturing and engineering company founded in with customers throughout the United States and around the world. SRS Crisafulli, Inc. manufactures hydraulic auger dredges, power take off (PTO) powered trailer pumps, smaller submersible pumps, power units, floating pumps, and floating platforms. See Crisafulli pumps and dredges.
What dredges does SRS Crisafulli manufacture?
Crisafulli manufactures standard and custom hydraulic dredges. Crisafulli dredges are available in manned Rotomite or unmanned FLUMP with electric motor or diesel engine models. Four models of Rotomite (manned) dredges and many configurations of FLUMP (unmanned) dredges are available. SRS Crisafulli customizes standard dredges to meet customer’s specifications.
Rotomite manned dredges
Rotomite dredges are nimble, self-propelled, and steerable with superior maneuverability. Rotomite dredges are easy to operate and provide maximum versatility for a wide range of applications. Operators can dredge various sizes and/or shaped ponds, lagoons, or lakes without external support vessels or draglines. The Rotomite can also be operated with a cabling system.
The Rotomite ’s 275 HP engine, coupled with a Crisafulli sludge pump is capable of extracting up to 2,500 gal/min (567.8 m3/h) of mixture. The fuel tanks are sized to provide up to 10 hours of continuous operation. The hydraulically powered propulsion and steering system provide both thrust and steering which is unique in the dredging world. The system provides adequate force to enable the horizontal auger on the cutterhead to engage, cut, and dislodge settled solids.
The standard models are diesel and hydraulically powered. Electric configurations are available by special order. Four Rotomite models are available: Rotomite CD, Rotomite , Rotomite , and Rotomite SD-110.
FLUMP unmanned dredges
Dredge operators control FLUMP dredges remotely which reduces their exposure to potentially hazardous materials. FLUMP dredges are designed and built for dependable service in harsh environments. FLUMP unmanned dredges are portable, cabled, and remote controlled with an optional Pivoting Traverse System available.
FLUMP stands for “Floating Lagoon Pumper”. FLUMP dredges are popular with customers for cleaning settling ponds and extracting sludge, sediment, biosolids or residuals from lagoons. FLUMPS are compact and work in small ponds and/or lagoons where other conventional dredges are too large. Its structural steel framework and lightweight construction make it durable and easy to transport.
There are many configurations for the standard FLUMP. Various models available depending customer’s requirements.
How can dredging productivity be increased and reduce dredging time?
Every pass is a productive forward pass with the Pivoting Traverse System, available on new FLUMPS. With the Pivoting Traverse System, operators dredge forward then rotate the dredge at 180 degrees and dredge forward again. The Pivoting Traverse System makes dredging faster.
Dredge Rentals
Many domestic and Canadian customers rent Crisafulli dredges and then buy them. Click here to see available rental dredges.
Mine tailings and hydraulic dredging
The safe dredging of tailing ponds ensures that they are performing adequately. Dredging also allows for the recycling of the tailings to produce additional minerals. The Crisafulli liner protection system enables operators to dredge lined lagoons without fear of damaging the geomembrane liner.
Mine resource recovery with hydraulic dredging
Waste streams and tailing ponds are becoming more valuable due to increasing prices of various precious metals. From Clays to Gold, Crisafulli dredges help improve profitability. Most tailings ponds contain very fine solids with potentially valuable materials trapped within the sediment. The cutterhead effectively slurries the solids to be re-processed. This process enables the mining industry to recover more of the valuable and historically lost minerals. The dredging process enables mines to keep their ponds in service, while eliminating the need for dry ponds.
Mine Environmental Remediation with Hydraulic Dredging
As waste material accumulates in retention ponds, the available storage space declines. This creates the potential for hazardous waste spills. To prevent spills during high water events, operators need to clean their ponds and maintain containment capacity. Crisafulli dredges work well in a corrosive environment without any disruption of the mine operation.
Mine Retention Pond Waste Removal
Both active and abandoned mine sites are potentially hazardous as waste products can leach or spill into the environment. Hazardous pollutants are usually held in a lined lagoon. Crisafulli dredges effectively remove, for proper disposal, these contaminated substrates, without damaging the geomembrane liner.
Hi, I’m looking at re configuring the dredge I recently brought, it’s been well made by someone in the South Island previous to who I brought it from.
It runs a swimjoy pump on a 9 hp honda engine.
For more dredge hosesinformation, please contact us. We will provide professional answers.
( my mistake it’s a gx 140 5.5 hp running a p180 equivalent pump.) Suction hose is 3 meters.
It’s clear from the great help I need to classify and build a wider box. Will and thank those who have generously contributed personally.
I have 17 riffles 50mm x 250mm, with classification this may help keep the boxes open and stop clogging? (Insert some technical term here)
Mixing in expanded mesh may also help clearing and capture?
I’m chasing flood gold so is flaky and light. Maximum size to date is .3gm
I. Working my permit near Kumara, West Coast.
Problems, tends to block up the pipe unless running at 3/4 or above, resulting in jetting out over the box.
It’s got a 5 inch suction pipe on it which is probably over sized for the pump.
The box is 250mm wide by mm long. It runs riffles and collects lots of rocks etc. It has about 100mm deep of water when running going through the box and the end of the box is submerged… the force of water going out seems to not cause any back pressure.
I tend to have better recovery with my hand sluice box.
Improvements, I am looking at or have done.
I put a grate on the nozzle to reduce the size of rock going through and blockages but it just means less production and more arm and hand work.
Would periodically stopping dredging and running full throttle to clear the suction hose upset the sluice bed if not picking up gravel?
When things open up again, I want to set up a classifying mesh or punch plate in the box, this will have a wave at the start to deflect any jetting due to blocked up suction hose.
Does anyone have experience with gold hog Matt’s or dream Matt in a dredge? I guess they would reduce the concentrates but imagine the rocks rolling would unsettle the bed holding the gold.
If I run it over 3/4 throttle I am concerned the light flood gold will float away.
Pros of the unit is the portability and width, can break down and carry into tight gorges…
Classification is probably the most urgent , with a longer and heavier dampening mat, in future will re engineer a wider box. It wouldnt take much to lift the box and engine.
If any one has some suggestions or input that will help that would be great.
New users can’t put up more than 1 photo sorry.
Hey J.A
A couple of really important questions first-
Is the dredge powered by a powerjet or suction nozzle? If powerjet is it single or twin jets?
Does the dredge have a flare, or crash box or just straight into the sluice?
How long is the dredge hose?
Approx how high is the head of the box above the water when it is running?
What is the inlet and outlet size of your pump? Do you know how many Litres per minute and its head pressure are?
Does the sluice have a rubber dampener at the head of the sluice?
Looking at you sluice its way undersized for a 5 inch. For fine gold recovery as Dave Mccraken said you need to reduce the turbulence in the box and classify, classify and classify.
In order to get fine gold recovery on a box most people talk about the the importance of the sluice (which is very important) but thats only half the story. What you need for good fine gold recovery is get your self a well designed flare and rubber dampner
A flare allows the water to slow and for heavies to drop out of and ride the bottom of the flare so when they hit the sluice they go blip straight into the top of or head of the sluice .
A flare will also allow you to reduce the height of the column of water that is lifted above the water thereby increasing efficiency which translates into to increased suction.
A well designed flare will also allow greater extraction of the energy of the high pressure jets of water that create the venturi effect if your running a powerjet.- Translation- Greater efficiency= more suction
As for a rubber dampner- this creates a low pressure zone at the head of the sluice which causes heavies to fall out. Its other function is to break the surface tension of the water so any gold particles riding on top of the water (Similar when your panning fine gold in a pan and you see the gold floating on the water) drop out into the sluice.
Do yourself a favor- I repeat do not run Gold hog mats in a dredge. Biggest waste of money. Been there done that, and done back to back testing. Gold hog mats work well as cleanup mats or in environments that you can control a lot of variable like sluice pitch, water column height, classification, water velocity etc. Dredges run deep water with varying flows of water as material goes up the nozzle especially as you go up in dredge size. The ability to modify pitch on a dredge is limited.
For fine gold recovery in a sluice you really want to be running a over/under setup. The idea behind this is classified material is removed from sluice and treated in a lower turbulence environment.
As for Keenes 3 stage as alluded to above by another user- This is a form of an over/under. Works very well.They are alot heavier so you need to have the proper flotation. they also require a bit of playing around to get pitch right and know how to use the choke in them and ensure you have enough water flowing through the box.
Alot of people will say they tend to load up in the bottom stage. They are actually designed to do this as it acts as a giant fluid bed( but thats another story)
Another really good way to get really fine gold is running a sump setup but that starts getting up there in complexity and cost.
Once you come back with those answers to those questions above I can give you more specifics
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