News from Schwing Bioset

Joe Lundell Retires from Schwing Bioset, Inc.


Posted by Kelly Kramer, November 1, 2016


The Schwing Bioset team would like to congratulate Joe Lundell on his retirement.

Please join us in extending best wishes to Joe Lundell, who retired from Schwing Bioset, Inc. at the end of October. Joe has been a valuable member of the team for over 10 years and he will be missed by his Schwing Bioset friends and colleagues.

Joe's attention to detail, while keeping the broader picture in mind, has been invaluable. His willingness to put in extra time to help us meet goals has demonstrated a commitment to excellence that we have appreciated.

Joe's retirement is our loss, but well-deserved for him. He will surely enjoy his extra time out on the golf course. We wish Mr. and Mrs. Lundell well as they enjoy Joe's retirement together.

To contact our to office or accounting department, call us at (715) 247-3433 or visit us here


(Joe is pictured at his retirement party with Schwing Bioset President, Tom Anderson).

Schwing Bioset Retirement



Tags: Announcements, Events

Replacing Failing Filter Press Yields Huge Improvements


Schwing Bioset Application Report 22, Seneca Water

Written by Larry Trojak, Trojak Communications

Version also published in WE&T Magazine, October 2016 Issue


When the Seneca (S.C.) Water Treatment Plant embarked on a recent expansion project, its overall goals were fairly straightforward: eliminate the use of chlorine in purification, relocate its new chemical treatment process, and upgrade the alum sludge dewatering operation. On that last point, plant officials opted to replace an outdated and difficult to maintain batch filter press with a different technology altogether — a fully-automated screw press — to handle its dewatering needs. In doing so, they not only eliminated an ongoing maintenance headache, they also dramatically improved the efficiency of their dewatering operations as well as their overall residuals management operation.


Water for Sale

Built on a hill overlooking Lake Keowee, the Seneca Water Treatment Plant is a 20 million gallon per day (MGD) facility located in Seneca, South Carolina, that serves more than 39,000 residents in and around Oconee County in the far northwestern part of the state. According to Steve Fletcher, the lake is owned by Duke Power Company, which allows the City to draw raw water for municipal purposes.

“As part of the agreement with Duke Power, we take in and treat the lake water, then, once purified, wholesale it to area communities,” he said. “That 20 MGD number is our peak permitted flow — our actual volumes vary, but are generally in the seven to 10 MGD range.”

Storage facilities for the treated and purified water currently consist of three ground storage clear wells and eight elevated tanks with a total capacity of 6.5 million gallons.

Seneca Water Screw Press


Risk Management

Until this latest expansion, water disinfection was done using chlorination which, while effective, was seen as a serious potential hazard, said Fletcher.

“When this plant was first built in 1968, there was literally one house in the immediate area,” he said. “However, the lake’s popularity has attracted large-scale development — both residential and commercial — and today the area immediately around the water plant is dense with some very nice homes. Should one of our three one-ton cylinders of chlorine gas have ruptured, it could have seriously affected people for a mile around the plant. We didn’t want to risk that any longer and decided that generating our own sodium hypochlorite was a much safer alternative.”

In addition to the change in chemical process, the expansion also resulted in a brand new operations building which houses not only the offices and administrative staff for the plant, but also includes a new laboratory facility and a common area that will be made available to city residents for meetings and other functions.

“This project really grew as we went along, as did the price tag which went from $3 million to $10 million.” Said Fletcher. “But we knew that, as long as we were making changes, we might as well make all the improvements we’ve talked about wanting for a long time.  Right now this is one of the most functional — and beautiful — water treatment plants around.”


Residuals Shortcomings             

Treatment of alum sludge at Seneca Water, the by-product of using aluminum sulfate as a coagulant, has a storied history. When the plant was originally built in 1968 there was no treatment effort at all; sludge was simply returned to the lake. The advent of clean water regulations changed all that and Seneca Water was soon recovering and disposing of its sludge in an area landfill. To dewater the material, Fletcher said the plant officials in about 1990 opted for use of a plate and frame filter press.

“Once installed, that press remained in place up to the recent upgrade and eventually became one of the main motivations behind a re-tooling of the sludge process,” he said. “I’m sure that, in its day, it was a solid performer. In recent years, however, it had become such a headache to maintain that it was a full-time job just keeping it operational. In addition, it ran as a batch process which meant it had to stop after every batch of dewatered sludge it created. We knew there were better solutions available out there and we started looking at them.”

It’s worth noting that the overall configuration of the alum sludge plant was sorely lacking as well. At the time, sludge was collected in the backwash holding basin, sent to a vertical turbine transfer pump, then routed up to a thickener.

“Unfortunately, that thickener was on the top of a hill on the other side of the plant,” said Fletcher. “Hardly the most efficient layout. Once thickened, sludge came back down the hill into a diaphragm pump and into the filter press. The transfer pumps were not only costly to run and almost always in need of rebuilding, they weren’t really designed to pump sludge so they were continually stopping up. All those things collectively got us thinking about ways to improve the overall biosolids process — starting with the press.”


Trials and Errors

After a fairly lengthy process of demos and trials, Seneca Water, working through their consulting engineer, chose a screw press from Schwing Bioset, Inc. Fletcher said the unit best met established criteria which were focused on cost versus performance.

“We looked at a number of manufacturers and a number of different technologies and knew that the Schwing Bioset unit would best meet our needs,” he said. “Our old press was taking in sludge with 4% to 5% solids and dewatering it to about 24% solids, so we were hoping for at least that. However, many of the presses we tested were giving us product in the 16% to 17% range — we definitely didn’t need a step backward. The team from Schwing Bioset brought their demo unit online and almost immediately we were getting dewatered sludge in the 28% to 32% range. Equally important, however, was the fact that the screw press was fully-automated rather than a batch-process design. That meant we no longer needed to have a man assigned to the press six hours a day, every day, as we’d done in the past.”

With Seneca Water committed to the Schwing Bioset screw press, additional changes were made to the alum sludge processing line, including the addition of a Model 300 large bubble mixer from Pulsed Hydraulics, Inc. (Oroville, Wash.).

“In the past, we’d had problems with the sludge settling and stagnating in some of the lower parts of the holding basin,” said Tommy Clayton, a Class A operator at the Seneca plant. “This PHi bubble mixer keeps the sludge moving and further increases production through the Schwing Bioset screw press. It has very low energy demands, has no other moving parts and runs off a compressor which we need for the press as well. The two are a perfect fit.”

Seneca Dewawtering Screw Press


Pressing Issues

The increase in production with the screw press in place was immediate and substantial. Because of the batch nature of the former plate and frame press, Seneca Water was forced to process sludge continuously all year long. According to Fletcher, that has changed with the addition of the Schwing Bioset unit.

“Now, with the continuous dewatering process we can have material being collected in the basins and, when ready, can get caught up in just two to three weeks. There really is no comparison between the two presses, but it’s safe to say that we can probably do close to two tons of alum sludge a day with the Bioset press while the old press took two days to do just a ton.”

Those old production figures were affected by both the cleaning process and by maintenance-related downtime. The plate and frame press, said Fletcher, had to be washed down after every batch — a process that could take as long as three hours. By comparison, the Bioset screw press has a self-cleaning function in which the screen gets sprayed — while the unit is in operation — cleaning it off.

“That means continuous production and no lost time, which is huge” said Fletcher. “We are saving no less than six hours a day in manpower alone just by nature of not having to have a man on the filter press handling the batch process, cleaning it and so on. However, without a doubt, we are benefiting most by finally having a press that is reliable — we are no longer having to constantly work to keep that unit operational. We simply start up the Schwing Bioset unit and it runs all day long.”


Working Together 

Once dewatered, Seneca’s sludge is collected and sent to an area wastewater treatment plant where it is mixed with that facility’s dewatered biosolids and trucked to a landfill in a collaborative city/county effort.

“There are so many facets of our operation that have been improved with this latest expansion,” said Fletcher. “We are much more efficient now, our process is better and far more reliable, and the risk of danger from chemical exposure has been eliminated. That’s a very nice turnaround for us and a benefit to the Seneca community as a whole. We couldn’t be happier with the way things turned out.”


 Download Our Brochures    or Application Reports  

Read More Schwing Bioset  News and Blog Articles



Tags: Water Treatment, Screw Press, Dewatering, Water Plants

Schwing Bioset Wraps Up 2016 WEFTEC and MINExpo Tradeshows


Posted by Kelly Kramer

The Schwing Bioset team has now wrapped up our two largest trade show displays of the year, WEFTEC and MINExpo. Thank you to everyone who stopped by one of our booths, enjoyed breakfast in our booth, or sent one of your contacts our way. We were able to meet with friends and customers, new and old, to discuss existing and potential projects.  We were also excited to debut our huge FSP 1102 dewatering screw press and our new pumps, the Smartec Sludge Pump and the KSP 315 mining pump (see photos below).

If we weren't able to connect at one of the shows and you'd like more information about Schwing Bioset or our products, please feel free to contact us with questions or download our brochures and application reports.

We hope to see you at one of our upcoming shows! 


Schwing Bioset WEFTEC 2016 Screw Press


Schwing Bioset WEFTEC 2016 Smartec Sludge Pump


Schwing Bioset MINExpo Mining Pump


 Download Our Brochures    or Application Reports 

Read More Schwing Bioset  News and Blog Articles



Tags: Events, WEFTEC, Mining Pumps, Screw Press, Mining Shows, Smartec Pump

NuReSys Technology for Struvite Recovery to be Built in Braunschweig/Germany


WEFTEC is the perfect place to learn more about our Struvite and Phosphorus Recovery technology. Stop by the Schwing Bioset booth (Hall C, booth 1828) and talk with our Schwing Bioset and NuReSys representatives.

If we won't see you at WEFTEC, you can learn more in the press release below, by visiting our Struvite Recovery webpage, or by contacting one of our regional reps.


PRESS RELEASE  09/24/2016


NuReSys technology for struvite recovery to be built in Braunschweig/Germany.

NuReSys is proud to announce that the Municipality of Braunschweig, assisted by PFI Planungsgemeinschaft GbR regarding unbiased evaluation of the different offers, has awarded its future phosphorus recovery plant to the combination Bremer-Pro-Aqua and NuReSys. The requirements of the tender were quite challenging and therefore the solution offered had to be versatile and flexible. The flow can vary from 8 to 25m³/h and the PO4-P levels between 300 and 800 ppm. The combination offered a tailor made solution which not only takes into account the phosphate recovery but also any post and preceding processes. Dipl. Ing. Thomas Meyer from Bremer-Pro-Aqua says: "We had a first collaboration with NuReSys when back in 2006 we built a phosphorus recovery plant in Altentreptow. This was an industrial plant in the dairy sector. Also this time the collaboration with NuReSys was correct and we felt very much on the same wavelength.”

Visit us at Weftec 2016 New Orleans (26-28 Sept.)  -  Booth 1828 Hall C,  SCHWING BIOSET


Struvite Recovery               Struvite Recovery


NuReSys Nutrient Recovery Technology



Read More Schwing Bioset  News and Blog Articles

 Download Our Brochures    or Application Reports



Tags: Struvite Recovery, Nutrient Recovery

Recover Phosphorus from Waste Stream for Beneficial Reuse


Posted by Kelly Kramer

At wastewater plants utilizing anaerobic digestion, Struvite commonly forms and creates issues with pipes clogging and equipment being damaged as a result of scaling.  Additionally, tanks can accumulate Struvite, which requires periodic removal and creates an additional expense to plant operations.

Schwing Bioset Struvite Recovery Bio-Stru Product

Schwing Bioset’s Nutrient recovery system recovers Ortho Phosphate and Ammonia Nitrogen from wastewater while offering great benefits to the treatment plant, not only by significantly reducing phosphorus in the waste stream, but also preventing unwanted scaling and accumulations, and creating a valuable end product.  The phosphorus forms a stable Struvite crystal that can be marketed and sold for beneficial reuse, thus keeping excess phosphorus out of the local waterways and helping close the phosphorus recycling loop. 

The article, "The Six Natural Resources Most Drained by Our 7 Billion People," posted on The Guardian, discusses phosphorus and provides a resourceful link to learn more about this essential nutrient and it's role in food production.

To learn more about how Schwing Bioset can help your plant with Nutrient Management, visit our website, call us at (715) 247-3433, or email us at


Nutrient Management Air Stripper Schwing Bioset 


Download Our Nutrient Recovery Brochure



Tags: Beneficial Reuse, Struvite Recovery, Nutrient Recovery, Phosphorus Removal

Schwing Bioset, Inc. is Exhibiting at MINExpo 2016


Schwing Bioset, Inc. is excited to be exhibiting at the 2016 MINExpo Event in Las Vegas on September 26 - 28.  

Please be sure to stop by our booth (#4258) while you're on the exhibit floor. We will be displaying our NEW KSP 315XL - SSL, which is the largest pump we manufacture. This pump uses the most modern technology in Positive Displacement Piston Pumps with our proprietary “Synchro Flow System” to minimize line pulsation and is capable of up to 230 m3/hr and 150 Bar of material pressure. 

Schwing Bioset Team members attending the show include our President, Tom Anderson, as well as Erik Weisser, Dan Anderson, and Paul Katka from our Engineering, Service, and Spare Parts departments. Our rep dealers will also be present. If you'd like to meet with one of our team members, please email us and we'll put you in touch with the appropriate person. Visit the conference website to view the event details and exhibition map:

As a recognized leader in the Mining Industry, Schwing Bioset, Inc. (SBI) provides Mining Pumps designed for paste, thickened tailings, slimes, and any other high solids slurries pumping application. Delivering dependable service day after day in underground and surface operations,  our pumps are known to stand up to the harshest of site conditions, proven by the many years of reliable operation in surface and underground mines around the world. We also offer high quality paste plant equipment including twin shaft batch mixers and specialized design services. 

Schwing Bioset is your one stop solution for mining projects and also offers fluidized bed drying technologies for internal and surface moisture removal and size reduction for a variety of coals, potash, salts, etc., and sliding frame storage bins for wet coal storage, paste, ash, biomass, wood waste, and sludge. We also maintain a significant spare parts inventory at our Wisconsin headquarters to ensure quick turnaround for customer requests.

Read about our Mining Pumps and other products hereand then stop by booth 4258 to learn more!

We hope to see you at MINExpo 2016!



  Read More Schwing Bioset  News and Blog Articles


Tags: Events, Mining, Expos

Schwing Bioset, Inc. is Exhibiting at WEFTEC 2016


Schwing Bioset, Inc. is excited to be exhibiting at the 2016 WEFTEC Event in New Orleans on September 24 - 28.  

Please be sure to stop by our booth (#1828) while you're on the exhibit floor. We will be displaying our 1102 model screw press, which is one of the largest screw presses we manufacture, as well as our newest piston pump, the Smartec Sludge Pump System.   

The SBI team members attending the show include Executives, Managers, and Regional Sales Managers. If you'd like to meet with one of our team members, please email us and we'll put you in touch with the appropriate person.

Visit the conference website to view the event details and exhibition map: Here is the Schwing Bioset listing for the show.

For more than 30 years, Schwing Bioset, Inc. has been helping wastewater treatment plants, mines, and power generation customers by engineering solids handling solutions. Schwing Bioset’s custom-engineered solutions can be found in hundreds of wastewater treatments plants in North America, as well as mines, and tunnels around the world.

Our products include, among others, sludge, industrial, and tunnel piston pumps, screw presses, nutrient removal and management, sliding frame and push floor silos, fluid bed drying products, Bioset process for Class AA Biosolids, container wagons, and soil conditioners. We also offers spare parts and equipment maintenance services and training. 

Read about our Nutrient Removal and Struvite Harvesting, Dewatering Equipment, Smartec Pumps, Bioset Process and Class 'A' Biosolids, and other products hereand then stop by booth 1828 to learn more!

We hope to see you at WEFTEC 2016!

Smartec Sludge Pump          Screw_Press_NEW.jpg


  Read More Schwing Bioset  News and Blog Articles




Tags: Events, WEFTEC, Expos

Southerly Sets The Standard with Sludge Disposal Efforts


Schwing Bioset Application Report 14, Columbus, Ohio

Written by Larry Trojak, Trojak Communications

Version also published in WE&T Magazine (click to view)


Pumps and sliding frames allow options for effective disposal of cake from Columbus, Ohio, operation.

Wastewater treatment plants can distinguish themselves in any number of ways: by the volumes they can handle, by the number of industry awards they have earned, by the manner in which they handle an interruption in “business-as-usual”, and so on. They can also do so by demonstrating a creative, effective and successful effort to use or dispose of the biosolids they generate. Given those criteria alone, the Southerly Wastewater Treatment Plant could likely be seen as one of the premier WWTPs in operation today. Just coming off a five-year, $350 million expansion which nearly tripled its peak capacity from 114 mgd to about 330 mgd (built-in contingencies for further expansion can take the plant as high as 550 mgd), the plant services the majority of the greater Columbus area. State-of-the-art in every regard, Southerly is poised to build upon an already impressive reputation that has won them numerous National Association of Clean Water Agencies (NACWA) awards for plant and employee performance.


But it is also its innovative sludge disposal program that separates Southerly from super-plant wannabes. Using a quartet of heavy-duty pumps and a number of sliding frame components (all from Schwing Bioset, Inc. [SBI] Somerset, WI) cake can either be routed directly for incineration or sent to a pair of storage silos. Once in the silos, the material is readily available for truck-loading and transport, either to an already-successful composting operation run by the department or directly to the landfill.  Options, it seems, are the hallmark of this successful operation. 

Change They Can Use

Built in 1967, the Southerly WWTP is one of two plants serving the Columbus metropolitan area (the other being the nearby Jackson Pike WWTP). The current plant expansion which so dramatically increased overall capacity, also increased volumes in the solids handling area. New centrifuges, installed a number of years in advance of that expansion, handle that increase nicely, according to Jeff Hall, Assistant Plant Manager.

“That upgrade was implemented both to replace aging equipment, as in the case of the centrifuges, and to add functionality to other areas like the transportation of solids,” he says. In the past, primary solids were gravity thickened while older centrifuges thickened the waste activated sludge (WAS). The new units now thicken both the primary solids and the WAS. This new approach boosts the solids content of the resulting dewatered cake to about 20-25%, a nice improvement over the 17-21% solids content with the older system.”

Additional changes brought about in that initial upgrade included installation of new cake pumps, a pair of storage silos, and sliding frames at two points in the solids handling process. 


The Route To Disposal

Getting cake to the point where disposal options are available is a function of Southerly’s pumps and silos. As material exits the centrifuges, it is routed to any of four Schwing KSP 45V(HD)L-SFMS pumps which direct it to the appropriate area. Where that is, varies greatly according to need.

“Even though incineration is the most efficient method of disposal, we still try to keep the compost operation fed with as much as it needs, since that is the better use of the product,” says Carmon “Skip” Allen, Solids Supervisor 2. “Obviously that can vary from day to day. The balance of the material—we can do anywhere from 5.5 tons up to 9 tons an hour—is then sent for incineration. But we know at all times what is going to the silos for storage and what’s getting burned.”

The sludge pumps at Southerly are designed to generate a force sufficient to move cake the long distances needed for either incineration or storage. He says it is easily 300 feet to the multi-hearth incinerators (which have operating temps of 1400°F), and about 400 feet to the storage silos. Equipped with Schwing Bioset’s Sludge Flow Measuring System, the pumps are able to measure to within +/-5% the amount of sludge that is pumped to the incinerator. This simplifies their USEPA reporting requirements for their incinerator operations.

“Material headed to the silos, however, has an additional challenge to overcome,” says Allen. “Once there, the cake has to go straight up another 100 feet to enter the top of the structures, so the force needed to do that is really pretty impressive. I don’t think any regular equipment would be up to a task like that; these are definitely the right pumps for the job.”

Giving it the Slip

Despite maximum operating pressures of 1,100 psi for each pump, those extended distances at Southerly prompted Schwing Bioset to make accommodations to help move the sludge along. To do so, they added a “slip ring,” or pipeline lubrication system. Schwing Bioset’s unique design includes a 360 degree annular groove that evenly injects a thin film of water around the entire annulus of the pipe that separates viscous and sticky materials from the inner wall of the pipeline. The end result is a reduction in friction loss in the pipeline, and lower—in some cases better than 50% less—pipeline operating pressures.

Additional benefits include a savings in energy by reducing the demand on each pump and hydraulic unit, and, because of the reduction in pipeline friction, an increase in wear part life. While other systems try to address the friction issue through the use of as many as four drilled ports which inject more fluid, this offsets a percentage of the gains made by the centrifuges. Still other designs mix polymer with the water to help reduce pressure which, while effective, adds both up-front and perpetual costs to the operation.

Tom Thomas, Maintenance Supervisor 2 at Southerly, says the reduction in friction has also shown benefits in wear part life for the pumps—a fact that is borne out in similar results at Jackson Pike. “We run these pumps round the clock and, even with that 24/7 operation, parts such as the pumping rams, poppet valve discs and seats are getting six months of wear. That’s about 4,000 hours of wear part life, which is outstanding given what they’re being asked to pump.”

Silo Efficiency

As mentioned, the SBI sliding frame silos offer a storage option for cake headed either to the landfill for disposal or to the compost site. Prior to their installation, Southerly relied upon a smaller holding vessel known as “the pit,” a belt-fed, hopper-equipped component that used a series of screws to feed a truck sitting under the discharge chute. City officials say the new silos are larger (providing about 75% more capacity) as well as far more efficient, thereby reducing truck loading times from 45 minutes with “the pit,” down to only five minutes. This was an important criterion when selecting equipment.

Because the City pays a contractor to haul the biosolids, reducing loading times lowers overall hauling costs—the trucks now spend more time hauling and less time waiting to be loaded. The net result is more trucks loaded per day (and a lower cost to do so.) In addition, because of that added storage capability, the composting operation now has the option of drawing material solely from Jackson Pike, if necessary. "Anytime you can reuse something rather than just burying it or burning it, you are making a positive impact," says Assistant Plant Manager Jeff Hall.

“Today, we are reusing about one-third of the solids we handle through the composting operation,” says Hall. “That’s obviously good from an economic standpoint, since we are generating revenue from a product that was once simply discarded. However, it is also a plus from an environmental perspective."

The concept of the sliding frame silo is simple, yet very effective. Hydraulic cylinders move an elliptical frame across the silo floor. The frame’s action not only breaks any bridging that can occur over the extraction screw, it also pushes and pulls material towards the silo extraction screws for discharge into trucks.

Allen says the sliding frame silos were a nice addition to the operation. “Each silo holds better than 1,500 tons of cake, so even if one of the incinerators went down and there was an interruption in the trucking operation, we’d still have a nice short-term storage option while things get back up again. It’s really all about flexibility and these silos afford us that.”

Due to the sheer size of the silos, they are each equipped with three extraction screw conveyors at the bottom which allows the trailers to be evenly loaded without having to be jockeyed back and forth.

The silos also include an odor and splash control shroud that pulls fumes directly off the trailer, thereby minimizing the need for odor control in the truck loading building. In addition, it helps reduce the chance of material splatter during load-out, and confines any such instances to the area immediately adjacent to the trailer, which makes periodic cleanup of the area much easier.

Allen adds that they also use SBI sliding frames on hoppers in advance of the pumps which feed the incinerator. Doing so provides a wide spot in the process line enabling them to maintain steady incinerator operations for several hours in the event of any upset condition with the centrifuges.

Sibling Growth

Southerly WWTP’s growth is being mirrored in the expansion of its sister plant, Jackson Pike WWTP, located a mere seven miles from Southerly’s facility. That plant also installed SBI equipment for similar end uses, but because its capacities are less, scaled down the size of that equipment. So today, Jackson Pike uses a quartet of KSP 25 V(HD)L pumps, rather than the 45s in use at Southerly and powers them with a 100hp power pack compared to its 150hp counterpart. The silos, though smaller in height, are of the same design and offer the same performance benefits as Southerly’s. Once the expansion at Jackson Pike is complete, the two plants will effectively meet all of Columbus’s wastewater treatment needs for decades to come. For Skip Allen, seeing construction at Southerly come to an end after nearly six years is a welcome relief.

“We are all really happy about the changes that have taken place here; there’s no doubt about that. But it feels like we will now finally be able to get back into the treatment plant business. With construction done, we have a big headache behind us, we have a great operation in place, and we’re doing good things for the residents of Columbus. That’s not a bad place to be.”



To download the entire #14 application report for Columbus, Ohio, click here.

To learn more about Schwing Bioset, our products and engineering, or this project specifically, please call 715-247-3433, email, view our website, or find us on social media.


 Download Our Brochures    or Application Reports

Read More Schwing Bioset  News and Blog Articles


Tags: Biosolids, Wastewater Treatment, Municipal Pumps, Sliding Frame Silos, Truck Loading

Material Classification in Drying Operations


Written by Joe Scholl, July 18, 2016

The word “classify” has different meanings, depending on the context in which the word is used. In bulk solids handling applications, it is generally taken to mean the separation of one type of material from others, even though the materials may be substantially similar.  For example, a material is discharged from a drying operation and is then sent to a screening operation to remove over-sized (“overs”) or under-sized (“unders”) material from the “on-spec” material of a desirable particle size or particle size distribution (“PSD”).  With respect to the various bulk solids drying technologies available, only a fluidized bed operation can be used as means to classify overs and unders from the on-spec material to some degree and without a further screening or separation operation.

Material Classification Fluid Bed Drying

(Here is an example of different classifications, from left to right are unders, on-spec, and overs).

Examples of the most prevalent drying technologies available today include spray and/or flash, heated or hollow flight, belt, rotary drum, and fluidized bed dryers.  While each of these technologies has applicability in various drying applications, some provide no material classification whatsoever, with others providing a small extent of classification, and others providing even more material classification.  Certainly, there are many different equipment configurations that can be developed for any given application that can influence the material classification effect.  However, as will be discussed in the following, only a fluid bed operation can specifically be designed and/or operated to achieve material classification within the drying operation itself. 

In spray drying, a solution of suspended or dissolved solids is sprayed into a drying chamber that receives hot drying gas (“gas” because it may be air, nitrogen, carbon dioxide, or some other heated gas suitable for the application).  As the sprayed liquid droplets contact the hot gas, the water evaporates, leaving a residual solid behind.  The velocity of the drying gas (typically in counter-current flow to the solids) is controlled such that the dried residual solids fall via gravity to the bottom of the drying chamber.  The solids may be collected and discharged intermittently or continuously from the unit.  As there is some gas movement that is counter-current to the solids flow, it is possible that some very small particles (“fines”) are removed from the drying vessel and collected in exhaust gas dust removal equipment.  While, technically, this is a small degree of classification, it is more the consequence of a gas flowing in opposition to the direction of the dried solids and, with the gas velocity intentionally set at low values, the object of the unit operation is more to conserve mass from being removed from the vessel to exhaust gas de-dusting equipment and maintain the highest rate of solids flow toward the bottom of the unit operation for further processing.  In other words, the unit is not designed to provide classification to any significant degree.  Rather, it is designed to minimize classification of material within the vessel.  In some configurations, the spray drying vessel directly feeds a fluid bed dryer unit operation to complete the drying process. 

Flash drying is similar to spray drying in the sense that a solution of suspended or dissolved solids is sprayed into the drying vessel, where it also contacts a hot drying gas.  However, in this case, the hot gas and spray/residual solids are typically arranged to be in co-current fashion.  In this manner, the hot gas acts not only as the drying media, but also the pneumatic transport mechanism by which the dried material is removed from the drying vessel.  The product is then recouped via dust removal equipment (cyclone, bag filter, etc.).  In this case, it can also be seen that the technology is not a means by which a portion of the material is segregated or classified from the balance of material.

Heated or hollow flight drying technologies utilize one or more (typically two) screw conveyor-like shafts and flights that are fabricated such that there are internal spaces within the shafts/flights for the movement of a heated thermal transfer fluid (hot water, thermal oil, steam, etc.).  With this particular drying technology, the wet material is introduced into the drying operation and the movement of the heated flights move, turn, mix, and (via direct contact with the heated flights in a conductive energy transfer fashion) dry the material.  Typically, heated flight drying technology does not use a “sweep” gas (a gas passed through the internal volume of the dryer to prevent high moisture vapor content in the vessel and, therefore, to prevent internal moisture condensation), or uses very little sweep gas for this same purpose.  As such, there is little, if any, material removed from the main bulk of the product to downstream dust removal equipment.  Therefore, the unit has little or no material classification ability (and is not designed to do so).

In belt drying, the wet material to be dried is deposited on to a moving belt.  The belt may be arranged in a single-, double- or even greater number of “passes” within the dryer unit in a serpentine fashion.  The belt typically is of a mesh or perforated design such that the hot drying gas may pass through the belt and material residing on the belt.  The gas flow may be co-current, counter-current, or some other arrangement (passes through the wet material vertically/perpendicularly).  In all configurations, the drying gas is meant only to impart the drying energy necessary and is not meant to carry smaller particles away from the unit with it.  As such, it can also be seen that belt drying operations do not present an opportunity for material classification within the drying operation itself.  In fact, fines generated during the drying process may pass through the belt perforations and wind up accumulating in the bottom of the dryer requiring periodic removal.

With rotary or drum drying, a heated drying gas is introduced into a rotating shell (the “drum”) that is equipped with internal vanes or flights.  The material is fed to the dryer and is “lifted” within the vessel by the internal flights.  As the drum rotates, the internal flights reach a point where the material falls off the flight and drops via gravity toward the bottom of the dryer vessel in a “curtain-like” shower of falling material.  As the material falls, it directly contacts the hot drying gas, thereby receiving the necessary drying energy.  The material and drying gas are typically in counter-current flow to each other, although it is possible to have a co-current arrangement as well.  Since the material is falling through a moving gas stream, smaller particles (“fines”) of sufficiently-small size may be entrained in the drying gas stream and be removed from the drying vessel in a process known as “elutriation” (the separation of small particles from the main bulk of larger-sized material and exhausted with the gas).  This “dust” is then removed from the exhaust gas stream via downstream dust-recovery equipment.  While this is a form of material classification, it is not generally the intent in a rotary drum drying application to do so.  It is merely the consequence of the smaller particles being captured by the moving exhaust stream, with the movement (velocity) of the gas stream within the vessel more designed for providing the necessary gas mass rate to (a) effect proper heat transfer for the drying operation and (b) have sufficient moisture-carrying capacity for the moisture removed from the product such that internal condensing conditions are avoided.  In this sense, it can be seen that, while a rotary drum unit can achieve some small degree of material classification, this is not the intent of the operation and the unit operation is not specifically designed to classify material.

With fluidized bed drying, however, it is possible to exert a significant influence on the classifying effect via the selection of a fluidizing velocity that will result in classification of smaller particles (“unders,” “fines,” “dust,” etc.).  Additionally, design features can be incorporated into the fluid bed dryer unit that can also assist in the separation of larger-sized particles from the main bulk of material (i.e. “overs” separation/classification).  In this sense, the fluid bed dryer operation can act as a triple-deck screener (separating unders, overs, and on-size material into three distinct material streams), while concurrently acting as a drying operation.  To further illustrate this point, one should consider the act of material fluidization itself. 

In fluidization operations, a fluidizing gas (heated in the case of a drying operation) enters the dryer through its lower “plenum” section.  The gas then passes through a gas distributor to evenly-distribute the fluidizing gas over the entire fluidized area.  The fluidizing gas then passes through the bulk solids, exerting “drag force” on the surface of the particles and, with proper velocity selection, suspending the particle in a “cushion” of gas, thereby fluidizing the material.  Were all of the particles of the exact same size, shape, density (or particle specific gravity), etc., no particles would be removed from the others, nor elutriated or classified from the main bulk of material.  This, however, is almost never the case, as the vast majority of applications involve materials having distinct particle size distributions, shapes, etc. (i.e. all particles do not have the exact same fluidizing characteristics).  Therefore, at a constant fluidizing velocity, the “right-sized” particles will be suspended and the “fines”/“unders” will necessarily be classified from the balance of material, since the fluidizing velocity being used is higher than the necessary “transport” velocity of the fines/unders.  Therefore, they will be removed from the dryer unit with the exhaust gas for recovery in downstream dust-recovery equipment.  Should the fluidizing velocity be increased from the previous velocity, particles that were previously too large to be elutriated are now elutriated, establishing a new larger “cut point” particle size for classification.  In general, the lower the fluidizing velocity, the smaller the cut-point particle size, and vice-versa.  As such, the fluidizing velocity can be adjusted to directly-affect the size of particle removed (classified/elutriated).

As discussed above, at a given fluidizing velocity, the “on-size” material is properly fluidized and the fines classified from the bulk of material.  However, it is also likely that the particle size distribution of the material is such that there are particles larger than those that would be suspended by the set fluidizing velocity.  These “overs” may not fluidize as well as the on-size material and drop toward the top of the gas distributor.  As Schwing Bioset utilizes a “directional flow” gas distributor design, these larger particles are essentially “pushed” toward the discharge end of the unit, with the gas distributor acting as a transport mechanism for these larger particles.  When these larger-sized particles reach the discharge end of the unit, they may be discharged via an “underflow” arrangement, which may constitute a separate discharge stream from the dryer unit and may be kept separate from the main bulk of material discharged, thereby establishing a distinct “overs” stream from the unit.  With the on-size material discharged from the dryer via a second discharge point (typically on “overflow” weir), one can see that there are now three distinct material streams from the dryer unit – the “unders” elutriated with the exhaust gas stream, the “overs” discharged via a separate underflow discharge point, and the “on-size” material stream discharged from the overflow weir. 

With proper fluidization velocity selection and system design, it can be seen that a fluidized bed unit operation can be designed and operated such that, while acting predominately as a drying operation, can also be used to exert influence on the material such that it can be classified into two (or more) material streams.  In this respect, it can be seen that only a fluidized bed drying operation, relative to other drying technologies, can also “double” as a means by which material classification may be achieved, potentially eliminating further downstream screening steps or, at a minimum, reducing the design requirements of such downstream processing equipment.

To learn more about material classifying and our Fluid Bed Technology, please contact a Schwing Bioset Regional Sales Manager by calling 715-247-3433, email us, and/or visit our website here.


 Download Our Brochures    or Application Reports

Read More Schwing Bioset  News and Blog Articles


Tags: Fluid Bed Drying, Material Handling, Fluid Bed Dryer, Bulk Solids Handling, Material Classification, Solids Drying

City of Edmonton's WWTP Truck Loading Tribulations


Written by Joshua DiValentino, June 27, 2016

The City of Edmonton’s Gold Bar WWTP saw cake storage and transfer to truck loading as a bottleneck in their plant. Current operations included storage of mechanically dewatered sludge in a Schwing Bioset push floor bunker installed in 1999. From there it was pumped to a composting operation where the product is distributed for beneficial use.  Area growth led to biosolids volumes exceeding composter capacity and a screw conveyor bypass was installed from the storage bunker to divert excess biosolids to truck loading for land application.  As biosolids production grew, it became increasingly clear this conveyor bypass was not a long-term solution, as it would take 45 minutes to load a truck.

Edmonton installed a new piston pump in the existing storage bunker to transfer biosolids to two new, 250 cubic yard capacity sliding frame truck loading silos. The silos are capable of storing enough volume of biosolids to seamlessly support plant process flow.  Each has three drop points to load two different styles of trailers, and hanging pendant controls, so the driver does not need to leave his cab during loading operations.

The plant can now easily handle the increased biosolids production and is able to load trailers in less than 15 minutes without requiring repositioning. The system improved process efficiency while minimizing O&M costs, providing more operational uptime for this 24-hour facility.

The Schwing Bioset, Inc. Field Services Team supports start-up and long term parts/maintenance of these systems. To see video of the Sliding Frame System in action or learn more about it, contact a Schwing Bioset Regional Sales Manager, call 715.247.3433, email, and/or visit our Sliding Frame Silos webpage.

Schwing Bioset Sliding Frame Silos    Schwing Bioset Sliding Frame Silos


 Download Our Brochures    or Application Reports




Read More Schwing Bioset  News and Blog Articles



Tags: Biosolids Handling, Sliding Frame Silos, Biosolids Storage