About 70 years ago, the filter press (invented in the UK a century ago) gained a foothold in industrial liquid handling applications in the United States. Through its design and operation, the filter press is used as a tool in the separation process, that is, solids must be removed from the liquid stream. When the liquid containing solids passes through the filter press, the separated sludge can be easily removed and processed. The cleaned liquid can then be transferred to the next stage of the production process or recycled back to the filter press for further processing.
In this role, the performance of filter presses in industrial applications is admirable, but recently, enterprising consumable manufacturers (some of which must be produced under hygienic/sanitary operating conditions) have discovered that filter presses can be further optimized for operation . This article will introduce three markets and applications where filter presses can shine: one is traditional, the other is to reimagine its production process, and the other is to operate reliably under extreme conditions. In addition, this article will focus on pump technology-Positive Displacement (PD) Pneumatic Double Diaphragm (AODD)-regardless of industry or application, this technology can be used with filter presses.
Industrial water and wastewater are applications where the filter press has proven its value from the beginning. This is an application that needs to separate a large amount of solids and liquids every day. Due to its method of operation, the filter press is very suitable for this application. When the solid-containing slurry is pumped into the press, the two chambers are filled, which helps to form a thick cake. When the chamber is full, the pressure inside the system increases so that when the chamber reaches its capacity, the liquid is filtered out with the help of compressed air or water flow. This dewatering leaves a solid sludge or sludge cake that can be processed.
For operators of water/wastewater treatment plants, one advantage of this cake making process is that there is no need to process a large amount of wet mud. As a result, the water flow and a small amount of cake are neutralized, thereby reducing treatment costs.
In order to operate normally, the filter press needs good filtration and constant system pressure so that the flakes forming the pulp cake will not be destroyed. This means that pressures of up to 100 pounds per square inch (7 bar) are usually required. The filter press process in water/wastewater treatment also requires the use of various types of auxiliary liquids. In many cases, these liquids (including abrasive lime milk and various alkaline substances) cannot be released into the environment. This requires a reliable leak-free pumping technology compatible with various liquid types.
At least everyone has seen a description of the maple syrup manufacturing process: a series of barrels connected by plastic pipes are hung from the knocked maple trees, allowing their juice to flow into the barrels. When enough juice has been collected, boil the juice over and over again until it reaches what can be called a pancake-like maple syrup. This is a labor-intensive process that takes hundreds of years.
In the past two to three years, the production of maple syrup has been completely mechanized and modernized. Many manufacturers now use reverse osmosis production processes to reduce the time and cost of making maple syrup. Enter the filter press-or as the syrup manufacturer calls it, the syrup press. In today's process, the sap is passed through a filter press in the so-called evaporation stage, rather than boiled repeatedly to make a syrup. When evaporation occurs, the sap is separated into a viscous syrupy solution, which is removed along with the watery by-products. In order to start the production process, at the beginning of the production process, a pump is used to transport the raw juice to the filter press.
Some industrial production processes require components that need to be separated under extremely cold operating conditions to make finished products. In some cases, this requires the use of liquids (such as ethanol) that have been cooled to temperatures as low as -40 F (-40 C). It is at the beginning of these types of processes that the pump is used to push the mixture of raw material and supercooled ethanol through the filter press.
Since many of these processes are also used to produce goods for human consumption, they must be produced under the strict support of sanitary/hygienic manufacturing regulations. This means that the pump must not only be able to withstand extremely low temperatures, but also must meet the requirements of the US Food and Drug Administration (FDA) and the European Restriction of Hazardous Substances (RoHS) directive. Specifically, the RoHS 3 regulation lists the highest possible levels (less than 1,000 parts per million) of substances such as lead, mercury, and cadmium in finished consumer products.
In addition, because ethanol is classified as an explosive substance, pumps used to produce goods that require it during the manufacturing process must be certified in accordance with the ATEX category II guidelines, which govern in environments characterized by gas, steam, or air Use of / potentially explosive dust mixture.
For those who wish to optimize the operation of filter presses, no matter what industry or product, AODD pumps can provide a variety of operating advantages, including dry running capability, compatibility with liquids of different viscosities and pressures, good controllability and The inherent leak-free design has no gaskets or seals. AODD pumps also have no drives, rotating parts or rotating shaft seals.
Other PD pump technologies have been used in conjunction with filter presses, but may have flaws that prevent them from being the best choice:
Due to its simple design and method of operation, AODD pumps can be operated in filter press applications. A pair of diaphragms connected by a diaphragm rod work together to pass the liquid through the pump. When one side of the pump is in suction mode, the other side is in discharge mode. When the diaphragm moves inward, it creates suction. This suction force causes the balls on the check valve to approach each other.
In this case, the top ball will close the valve, and the bottom ball will move away from the valve, opening a path that allows liquid to enter the pump chamber. As the diaphragm moves outward, the discharge movement causes the balls to move away from each other. In this case, the top valve is open and the bottom valve is closed.
This allows the liquid to leave the chamber and drain through the top port. This process alternates between the two chambers to form a continuous cycle. The pump diaphragm is driven by compressed air, which is oriented left and right by the movement of the main air valve.
The result is that the pumping process maintains a consistent volume at a flow rate of 200 gallons per minute (gpm) (757 L/min) or higher, even if the liquid viscosity and delivery pressure are different. Start-up involves connecting the compressed air hose to the air distribution system (ADS) of the pump and turning it on. AODD pumps require a smaller footprint, which allows them to be used in a more compact operating area.
Many AODD pump manufacturers now also produce sanitary/sanitary pumps, which can be used to produce consumables or work environments that require ATEX grade pumps. This further expands the operating range of AODD pumps that can be used in conjunction with filter presses.
Facts have proved that the filter press is reliable in many industrial applications that require the separation of solids and liquids, but its application range does not stop there. Manufacturers of consumer products (some of which are manufactured in extreme environments) have discovered that filter presses can become an integral part of their manufacturing operations if used with appropriate pump technology (such as AODD pumps), which helps Optimize many key operating industries.
Paul McGarry is the sales manager for PSG, a manufacturer of All-Flo and AODD pumps. You can contact him at paul.mcgarry@psgdover.com. For more information, please visit www.all-flo.com or www.psgdover.com.