International Dredging Review

International Dredging Review

RIGHT TO LEFT: John Rankin Floquip general manager; John Melvin technical sales specialist SNF Environmental; Kirk Thomas mining director SNF Holding Company; and Mike Chancey business development manager and director SNF Environmental in front of one of the trailers.


Close up of the dry polymer PSU system.

Dewatering operations at dredging sites use polymers to clarify water so the water can be returned to the source and regulatory requirements. Projects generally choose liquid polymers over powder polymers because they are more economical on temporary project sites.

Powders require a larger infrastructure to store and operate at a higher cost than their emulsion polymer counterparts.

As an alternative SNF Environmental subsidiary of SNF Holding Co. has patented technology that vastly improves the ability to use dry polymers economically on dredging projects.

“In the past of those two forms the emulsion (liquid) was much easier to work with on project sites. You add water mix them together in a tank and in 15 to 20 minutes it’s ready. It can sit outside; it doesn’t need to be stored in a building” Mike Chancy business development manager for SNF Holding Co. and director of SNF Environmental said.

On project sites powder polymers must stay dry so they need secure storage. Also the dry powder and water needs to be agitated for up to an hour before it is fully activated so much larger tanks are needed on-site Chancey said.

But aside from its dry storage requirements dry polymers are really more economical as a raw material than emulsion polymers. Emulsion polymers are only approximately one third polymer whereas the powders are 100 percent Chancey said.

With a dry polymer the mixture is 100 percent polymer with no byproducts. With a cheaper storage and operation structure it could be more economical than emulsion polymers. It was under that principal that SNF Environmental developed a modular mobile system the PSU™ (polymer slicing unit) that contains and mixes the dry powder polymers on project sites in a trailer rather than requiring large application tanks and a building for storage of the equipment and polymer.

Chancey said SNF leases the equipment as part of its turnkey polymer operation. The company typically works with dewatering companies to train their operators to work the automated system. SNF developed extensive software that automates much of the process. The system receives density and fl ow signals which measure the amount of solids going through the system. It has a pump that runs on a variable frequency drive so it’s always adjusting the polymer and dosage rate to keep the performance where it needs to be for that site.

Chancey said to achieve that peak performance intricate analyses pre-operation will choose the right polymers from hundreds that SNF manufactures for the dredging industry.

Polymers work by electric charges which attract unwanted particles and remove them from the water. Everything has a charge including microscopic particles and a polymer with an opposite charge either anionic or cationic is added to water and attracts either the positive or negative targeted sediment.

The dry polymer fed to the PSU™ consists of extremely high molecular weight long-chain molecules. These polymers are composed of several types of low molecular weight (LMW) organic molecules called “monomers” which add to each other in end-to-end fashion forming chains several hundred-thousand monomers in length.

Use of a nonionic (no charge) monomer alone gives rise to a nonionic polymer. There are also several LMW charged monomer molecules which can be incorporated along with the nonionic monomer into each polymer chain to give the chain either negative (“anionic”) or positive (“cationic”) charge.

The amount of charge on each chain is carefully controlled as different sediments require different charge types and charge levels. Thus a polymer termed 10 percent charge (anionic or cationic) is composed of a number of chains with one charged monomer for every nine uncharged monomers. If there is one charged monomer for each two nonionic monomers this would be a 33 percent-charged polymer. The molecular weight or length of the polymer chains is also carefully controlled as different applications (e.g. clarifi cation; geotextile tube plate and frame belt fi lter press centrifuge etc.) will require different polymer molecular weights.

“The more exact we get the chemistry the cleaner and more effi cient the polymer will be and projects will use less” Chancey said.

SNF Holding Co. produces more than 1000 different polymers for many different industries including mining oil sands agriculture hydraulic fracturing (fracking) and work with municipalities. The mobile PSU system was first implemented in the oil sands industry where the technology is widely used. There SNF has continued to advance the technology allowing them to provide larger and larger systems.

Two-hundred employees work in SNF’s Floquip division which engineers the PSU systems.

“In the dredging industry the use of this newer technology will allow us to use dry polymers for dredging projects where it could not have been considered in the past and it will save companies money. Dry polymers are much more cost-effective to use now that we have the right equipment that meets the modular portable demand of the dredging industry” Chancey said.