Liquid filtration is a process used in many industries to separate liquid and solid materials. Manufacturing, chemical, and pharmaceutical industries are just a few of the areas where this type of filtration equipment and filter presses are needed. What are the key elements of a filter press? What types are there? We've put together all the important information in one place!
Liquid filtration
The liquid filtration process separates the liquid from the dry material. This is done by passing the liquid through a filter medium, on which the solids are trapped. The filtered liquid is called the filtrate, the pressure difference is called the filter resistance, and the residual material is called the sludge cake.
The first step in the filtration process is to load the material into the filtering machine. For this, either gravity or the force of a pump is relied upon. Depending on the type of filtration, this may be followed by pre-pressing, post-pressing (where the membrane sheet is expanded with air or water and this compresses the sludge cake), blowdown (where the remaining filtrate is removed from the filter paper bundles) and draining.
Two main processes are distinguished: static (chamber) filtration and dynamic (membrane) filtration.
Here is what you need to know about how chamber filter pressing and membrane filter pressing work!
Types of filter presses
Based on the operating mechanism, two types of filter presses are distinguished: chamber filter presses and membrane filter presses. Let's find out what you need to know about them.
The chamber filter press
The chamber filter press is very efficient in separating liquid and solid phases. Its main components are the filter plate bundles. These are filter cloth-coated filter plates that, depending on their permeability, pass or retain larger-sized materials. What passes through is removed by the filter and what is retained in the chamber is the sludge.
There are several types of filter presses working on this principle: the chamber volume, the filter surface, the pressure of the hydraulic cylinder, etc. There are, for example, sidebar-plate and overhead-plate filter presses, the former being used when there is little solid material and the latter when there is a high load, and it may be necessary to have easy access to the filter cloths during maintenance.
The membrane filter press
A membrane filter press is a device in which the membrane plate plays the main role. It is bounded by flexible plastic on the side facing the chambers, creating a hollow space which, when filled with a high-pressure medium such as water, increases the volume of the sheets, compressing the sludge sheet.
The dewatered material is pumped into the chamber, passes through a filter screen that traps the solids, and the water is discharged from the system. A water or air pump, which is part of the system, can be used to achieve further water loss by compressing the membrane sheets.
The membrane filter press consists of a head plate (which contains the sludge inlet and filtrate outlet), an end plate (which contact to the hydraulic power cylinder by the pressure plate), and the sole-bar (which support the filter plates with the filter cloth and the pressure plate).
A huge advantage of this type of filter press is that it can be used to achieve the lowest dry solids content. Short cycle times are expected, which means that dewatering can be very efficient.
The main components of the filter press: are the filter sheet and the filter cloth
In the complex process of liquid filtration, two elements fundamentally determine the quality of the filtration: the filter sheet and the filter cloth.
The function of the filter plate is to retain the filtrate and to help the filtrate escape. In choosing the right one, chemical resistance, pressure differential, support of the filter cloth, drainage capacity, and handling must also be considered. Typical sizes range from 400 mm x 400 mm to 2000 mm x 2000 mm.
Depending on whether the filter press is chambered or membrane filter press, a different filter sheet is required. Chambered filter sheets are single-component and can withstand pressures up to 50 bar and higher temperatures. Diaphragm filter valves can be of several types: for example, some can operate without damaging the diaphragm, even when empty or at very low levels.
The filter cloth performs the function of filtration. The type to be used will depend on the elements to be filtered, i.e. what will form the sludge cake. The material is usually a woven textile such as industrial textile, polypropylene, polyester, or cotton. Essential properties include fibre-structure, fibre thickness, weave, density, breathability.
In what areas is liquid filtration used?
In many areas, liquid filtration is an important part of the process. If we talk about manufacturing, coolants, lubricants, and oils are the most filtered. In the pharmaceutical, food, and chemical industries, process fluids are the most filtered. The same filtration processes are used for filtering water from lakes, wells, rivers, heat exchange systems, heating systems, condensate, thermal water, and irrigation water.
Liquid filtration and sludge dewatering also play an important role in the wastewater treatment process. The residual material left over from the treatment of wastewater is called sludge, which must be disposed of because of its pollutant content. The first step is dewatering, which is carried out using filter presses. The resulting material is reduced in volume and is easier to handle and transport.
Makrofilt manufactures complete filtration systems to order for all levels of industry. We provide our customers with high-quality solutions and professional and accurate equipment to make this process efficient.
Looking for more information on filtration systems? Contact us and we will help you find the most efficient solution!
