Air operated diaphragm pumps are used with filter presses to pump sludge from the bottom of the sludge holding tank into the filter press. These pumps are ideal because they can handle the slurry which is generally about the consistency of a milkshake.
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The diaphragm pump usually starts out slowly and gradually ramps up. Once the pump starts to slow back down, (30-60 seconds between thrusts), it is usually an indicator that the filter press is full. At this point, the feed pump should be turned off and the valves on the filter press closed as the operator prepares to operate the air-blow-down process.
The diaphragm pump can be manually turned up or an Automatic Pump Control system may be added. This starts the pump at 25 psi, then moves up to 50, 75 and finally 100 psi which is standard operating pressure for the pump.
Met-Chem provides diaphragm pumps in the following sizes: 1”, 1.5”, 2” and 3”. The material of construction ranges from cast iron, aluminum, polypro or stainless steel.
With the purchase of a new Met-Chem filter press, Met-Chem can mount your air operated diaphragm pump to the legs of your filter press. This option also includes a flex hose that connects the outlet of the diaphragm pump to the center feed pipe, an air filter, a regulator, and an oiler. We can also provide a mounted diaphragm pump for your existing press.
Automatic Filter Press Pump Control SystemThe Met-Chem Automatic Pump Control System is used in conjunction with an air operated diaphragm pump to automatically increase the feed pump pressure at predetermined intervals during the filter press filling cycle. If the pump runs at a higher initial pressure, the filter cake will become a packed layer of solids on the filter cloth. This will restrict the flow of the slurry thereby creating a very dense coating of the filter cake. This can cause the cloths to blind off and not allow further filtration. Starting at a lower feed pressure allows a soft layer of slurry particles to be deposited on the filter cloth. This initial layer becomes the filtering media which will enhance the filterability of the incoming slurry.
The automatic pump control system automatically and gradually increases the feed pressure in four stages during the filling cycle. These stages are adjustable to suit your slurry and solids concentration. However, it is commonly set at increments of 25 psi. (25, 50, 75, 100). By monitoring the feed pump flow sensor, during the final pressure stage, the operator will be able to determine the cycle completion.
The Automatic Pump Control System also incorporates a low hydraulic pressure safety shut down the device. If there is not enough hydraulic clamping pressure present, the system will completely shut down, eliminating any possible leaking from between the filter plates.
The pump control system allows your filter press to run at its optimum efficiency creating dryer filter cakes, reducing disposal costs, reducing operator time and increasing the life of your filter cloths and feed pumps.
This system can be incorporated with a new filter press from Met-Chem, a used unit or even your own existing press.
Spare Parts KitMet-Chem is pleased to offer our spare parts kit which includes our 5 piece center feed pipe assembly, a head, tail, and 2 intermediate filter press cloths, and 100 foot of gasketing material. These are essential items for the operation of the filter press. A cracked pipe, ripped cloth, or torn gasket can happen anytime and having these items in your stock will ensure you will be back up and running in no time.
Center Feed and Manifold Filter Press UpgradesA center feed pipe assembly on a filter press should be able to last many years the same way any other type of plumbing will. However, if the material of the center feed pipe assembly is not strong enough to handle the corrosiveness of the solution running through the press then the center feed pipe assembly can corrode.
For cases of corrosive material or high temperatures, Met-Chem is pleased to offer upgrades from our standard center feed pipe and manifold. We are able to upgrade to CPVC, Carbon Steel, 304 or 316SS Stainless Steel, and Titanium. Met-Chem can also provide additional manifold upgrades such as automatic valves
The center feed pipe is what connects the filter press to the product that needs to be filtered. The center feed pipe assembly consists of five different parts. The first part is the lock nut which fastens on the center feed pipe and connects to the outside of the press. The pipe, which is the second part, goes through the head of the filter and all the way through the head plate of the filter press. The third part of the center feed pipe assembly is a gasket which ensures the assembly is watertight. Next, is the clip nut seat which fastens the assembly to the head plate. This part of the assembly will always stay in place unless you are replacing the assembly or one of its parts. The final part, the cloth clip nut, will be removed often as it is screwed into the cloth clip nut seat after the head cloth is put on the head plate. The cloth clip nut needs to be tightened in order to keep the cloth in place. Met-Chem provides a tool to make this process easier. The Met-Chem Spanner Wrench is a specially designed tool that can be used to loosen and tighten the cloth clip nut when changing the head cloth on a filter press. This tool can be very helpful as the cloth clip, but it has a design that requires a unique tool to tighten and loosen it.
Longer Legs and Filter Press Sludge Disposal ChuteMet-Chem can provide longer legs and a disposal chute on your new filter press. This is especially useful if you are releasing the sludge from the press into a sludge bag or a drum. The chute will direct the sludge directly into your container. If you plan to use a sludge disposal bag, we can add hooks to the chute so that the sludge bag can be hung from the frame of the press.
For some larger presses, we can build a catwalk along with the disposal chute in order to accommodate a roll-off container.
Sludge DumpsterSludge Dumpsters are used directly under the filter press to catch the sludge that is released from the filter press during cleaning. The dumpster is on casters for easy mobility. They are also equipped with forklift slats for convenient use with a tow motor. The operator can move the dumpster to a roll-off container with the forklift and then pull the release pin for easy emptying. The dumpster can then be snapped back to the upright position and put back under the filter press.
Backer Plate for Smaller Filter Press BatchesIf you produce varying size batches of wastewater and subsequently less sludge, or if the overall volume of waste that is generated at your facility has been reduced, you can still utilize your existing filter press. With the purchase of a backer plate, you can alter the holding capacity of your press to meet your individual batch needs.
A backer plate provides support to the tail plate so that it can be moved anywhere in the plate pack in order to isolate the chambers between the feed end and the tail plate. If you try to use the tail plate in a different position in the plate pack without the backer plate, you run the risk of damaging the chamber of the tail plate.
There are different kinds of backing plates. Some are made of plastic and look much like a standard plate; we prefer to use ~3/8” thick flat stock steel and cut an outline of a plate. This is clearly visible when placed in the stack so that all around know that the filter press is not at full capacity. This steel backing plate is then painted with the same two-part epoxy coating as the frame of the filter press.
Filter Press Plate ShiftersThe start-up and installation options are available with all Met-Chem waste treatment equipment. We can provide full support as you get your system up and running. We have installation technicians and technical representatives that we can send to your facility to make sure the system is running as it should based on the engineering and design.
Our services include but are not limited to:
All units and systems are complete with manuals and support. However, if you need someone to come to your facility, we will be happy to quote you on that as well.
Learn more about our Start-Up Assistance and Installation
Recessed chamber and membrane plate filter presses are gaining more popularity in the coalfields. The systems are used to dewater fine refuse that would traditionally be pumped to a thickener and eventually to an impoundment or settling pond. Instead, the dry cake produced by the filter press can be backfilled into the pit. This is important as coal operators are finding it more difficult to permit new impoundments.
A prime example of this new approach to refuse dewatering are the filter presses installed at the Bishop prep plant, which sits on the border of Tazewell County, Va., and McDowell County, W.Va., (See Coal Age, January , p. 32). With the help of Taggart Global (now Forge), Southern Coal constructed the new $60 million state-of-the-art prep plant in . The mine plan called for reject from the plant to be backfilled into the pit, and the centerpiece for this strategy was recessed-plate filter presses provided by McLanahan that dewater the reject. The prep plant began operating in January , and so far everything has been running according to plan.
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The alternative technology for dewatering fines is a belt press. Belt presses are less expensive to purchase, but they have higher operating costs. They use chemicals and require a full-time technician. They achieve about 10% less dryness than the filter press.
The coal industry has been testing recessed plate and membrane plate filter press technology for about four or five years and there has been a bit of a learning curve. Tragically, an incident last year at a different installation manufactured by a different vendor claimed the life of an engineer and injured another coal worker. The technology, however, continues to improve, and the Bishop installation is a testament to those advances. Taking what they learned from Bishop, McLanahan and Forge are already looking at how to improve future installations.
Dewatering With a Filter Press
The Bishop prep plant uses two McLanahan filter presses aligned end-to-end with a single conveyor underneath both machines. The filter cake drops onto the conveyor belt and it’s transported to a hopper, where it is batch loaded into trucks. The system produces roughly 20 tons of filter cake per cycle. “If they run both presses they can produce about 100 to 120 tons per hour [tph],” said Cory Jenson, general manager of McLanahan’s environmental division, which makes the filter presses. “Currently, they only need to produce about 60 tph.”
The system is an overhead beam filter press, which has a high production capacity and allows better access for maintenance. “Rather than pulling the plates open in groups of 10 and 20 where they may only be open a couple of inches, we open them with a chain carousel between the overhead I-beams,” Jenson said. “They open one-by-one, 30 in. apart, at high rate of speed. There is a lot of movement and a lot of space for the cake to drop.”
The filter press can be operated with two types of plates: recessed chamber or membrane. Bishop is using recessed chamber plates. “A recessed plate uses fluid pressure for the dewatering process,” Jenson said. “Nothing on the plates move. Slurry is pumped in at a high pressure. As more solids enter, water is forced out.”
The membrane filter will produce a drier cake, but there are trade-offs. The membrane acts as a diaphragm on the side of each plate. The chambers are filled with slurry, and then the diaphragm squeezes the cakes. The trade-off, Jenson explained, is that the membrane flexes with every cycle. “There is a limited life cycle of maybe 30,000 to 60,000 cycles before the membranes will have to be replaced.”
Forge specified the McLanahan filter presses for this installation, and the presses met the capacity that was expected. Forge commissioned and operated the plant for the first six months before turning it over to Southern Coal. The startup went well, Jenson explained. “The first cycle surprised everyone with the dryness of the cake,” Jenson said. “We had some problems with the pumps. That has been resolved and they have been producing cake at the dryness and volume that they specified.”
A lot of thought was put into this installation considering the characteristics of the coal and the refuse and the desired quality of the cake, explained Pat Borreggine, vice president procurement, Forge Group North America. “There was testing that figured into the selection of the cloth,” Borreggine said. “We bought the better cloth, which is critical as far as longevity and operations of the plate frames. We had anticipated, or were given the expected moistures for the cake, and we exceeded that by an additional 5%. That allowed us to reduce the cycle times and pressures.” Lessening the cycle times decreases the wear and tear on the machine.
The Development Curve
Believing that the technology could benefit coal operators, McLanahan has been working with these machines in the field for a while. Their first unit at Sunrise Coal was a recess chamber machine purchased from an Italian company. “After that installation, McLanahan worked with a second Italian company before deciding to pursue our own design that we could support ourselves with local parts and service.”
McLanahan now has five of these machines operating with more starting this year in other applications (aggregates and industrial minerals). The units at Bishop are the first two operating in coal. “Six additional McLanahan presses are due to be coming online in coal applications in the next six months,” Jenson said. “Anywhere that chemical or handling costs, permitting or compaction is an issue, we are seeing lots of interest.”
Mine operators have been fairly vocal about the headaches associated with permitting and permitting an impoundment or extending the permit for an impoundment. The filter press offers a closed-loop solution. The cake simply needs to be dry enough to meet compaction requirements.
After working with these systems, McLanahan discovered how it could improve the system using standardized local parts.
Probably the biggest selling point about the McLanhan filter presses is that they are easy to install, integrate and operate, and they provide an efficient, cost-effective operation. The company’s Smart Hydraulic system controls operating pressures and positions for fast, precise opening and closing. With pressures of 225 psi to 870 psi (16 to 60 b), the press can dewater even the most difficult sludge, including those with a high clay content. The PLC-controlled press has many available cake thicknesses or membrane plates for the driest possible cake.
Ultimately, it depends on the specification for the dryness of the filter cake. “Membrane has a higher up-front cost with higher operating costs,” Jenson said. “But, if the cake needs to be drier that’s the best technology commercially available. If a recessed chamber dries to 75% solids, the membrane might dewater to 78%-79% solids; it’s typically only three or four points better, but if that’s what a mine needs to meet specifications as far as compaction, then that’s the determining factor,” he said.
Cloth selection is also important. “Different cloths have different surface tensions depending on the material it contacts,” Jenson said. “One cloth may have less friction or be less electrically attractive. Different weaves have different properties. There are a number of ways to improve cake release, but we never had to use paddles at Bishop.”
McLanahan has made some improvements based on the performance at Bishop. “The main changes were switching from four hydraulic cylinders to one main hydraulic cylinder,” Jenson said. “It reduced the horsepower and reduced the number of valves. For automation, we no longer have to synchronize the cylinders. We kept four tensioned shafts. We kept the advantages of the old design, simplified it and used less parts and horsepower.”
The latest design has reduced the horsepower by one-third. “All of the torsional valves balancing the flow between the four cylinders require a lot of head and horsepower,” Jenson said. “By going with a single cylinder we cut out all of those valves and we no longer have to worry about synchronizing it and maintaining alignment. We were able to simplify everything, use less horsepower. Of course, we have a couple of new pump vendors as well.”
Operating the System at Bishop
At the time Forge was commissioning the filter press at Bishop, a freak accident occurred with a filter press at Patriot Coal’s Blue Creek prep plant. During February , an engineer was killed at the facility when he was struck by one of the hydraulic cylinders on a plate-type filter press from another vendor. A hydraulic cylinder catastrophically failed while the press was in operation, according to the Mine Safety and Health Administration (MSHA). The victim was positioned near the hydraulic cylinders, troubleshooting the operation of the filter press, when the accident occurred. A second employee received non-life threatening injuries.
“Obviously, this raised some serious concerns and we looked at what happened,” said Borreggine. “Blue Creek was also operating two plate-and-frame presses. For whatever reason, they chose to put the operator controls between the two units. The operators panels at Bishop are on the outside of the units, and they are perpendicular to the hydraulic cylinders that operate the presses.”
Borreggine said the key to keeping the machines running is keeping the cake off of the cloth or the panels, and they did not encounter any issues with the cake sticking. A sticking cake can cause issues with cloth tearing or possibly cracking the plates. “The McLanahan machine performed as it was supposed to,” Borreggine said. “It performed very well.”
The Blue Creek prep plant purchased the plate-and-frame press and Taggart installed it. “With this installation, we were involved with the purchasing and we were able to select the plate-and-frame press we wanted to install,” Borreggine said. “We have a great relationship with McLanahan and felt that they, from a technical and service standpoint, had the best plate-and-frame press.”
During startup, there was not much of a learning curve, Borreggine explained. Maintenance, he added, is also fairly simple. “One thing we did not have to deal with at Bishop was clay,” Borreggine said. “If we would have high-clay application, you would need a blow-back system or an automated spray wash system. We did not have those because this is what we call a ‘clean’ refuse dewatering system because it did not have a lot of clays.”
From the time Taggart (Forge) commissioned and operated the system, it has been nothing but standard maintenance — no issues, Borreggine explained. The Southern Coal team took over and it has been smooth sailing so far.
In the future, Borreggine thinks more prep plants will adopt this technique. “They would have to do some due diligence,” Borreggine said. “What are they doing as far as tonnage and coal quality. It is good to minimize chemical consumption. As they become more popular, I think McLanahan will make these units better, more user-friendly, and more cost –effective.”
Forge is looking at installing another facility considering plate-and-frame presses in U.S. coal. They currently operate belt presses. Because conditions are changing and they need more capacity, they are going to add a plate-and-frame press.
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