Continuously operating filtration plants for solid-liquid separation: Unique technology enables continuous operation without supplementary equipment
In May, BHS-Sonthofen delivered its one-thousandth rotary pressure filter since the establishment of the Filtration Technology division; the filter plant was supplied to an Asian manufacturer of cellulose derivatives. Thanks to decades of continual development, these filters are today rated for operating pressures of up to 7 bar (g) and temperatures of up to 160°C.
Prior to this, BHS-Sonthofen had already set a new record at the end of 2011 with the delivery of five RPF X 20 rotary pressure filters to a customer in China: in terms of throughput, they are the world“s largest rotary pressure filters, capable of filtering a suspension volume of 225 m³ per hour. With the new filters, which have a filter area of 9 m² each, BHS is the only manufacturer to offer rotary pressure filters with an atmospheric output of this magnitude.
BHS-Sonthofen has been manufacturing this unique filter system since 1954. This patented filter was developed in Munich in the early 1950s by chief engineer Erich Fest sen. and brought to Sonthofen by the inventor“s son, Dr. Erich Fest, where it formed the basis for the new Filtration Division. At that time, the filter was rated for a maximum operating pressure of 3 bar (g) and temperatures of up to 120°C.
Alongside the other company divisions at the time – Construction Machines and Gear Technology – Filtration Technology quickly became established as the third main pillar of BHS in Sonthofen. Thanks to their robust design, some of the rotary pressure filters from the 1960s are still in service at various chemical companies.
The unique feature of the filters is that filtration and further treatment of the filter cake take place under pressure, whereas the cake is discharged into the atmosphere from the non-pressurized discharge zone. This enables continuous operation without the use of supplementary equipment. This development led to a technological leap in the filtration technology of the day.
Over the years, BHS has continued to develop the rotary pressure filter, including a complete revision at the end of the 1990s. Detailed design calculations, modern design procedures for mechanical systems (FEA) and process engineering (CFD), new manufacturing technologies and innovative materials – especially in the area of sealing – have made it possible to extend the use of these filters to operating pressures of up to 7 bar (g) and temperatures of up to 160°C. The series is patented under the name of „Rotary filter plant“.
These are mechanically engineered for demanding applications: the systems supplied to the Asian customer mentioned above have a drum diameter of 1.8 m and an active length of 2 m and must therefore withstand high loads. BHS-Sonthofen uses state-of-the-art calculation and production methods. The result is high-tech mechanical engineering: each of the 35 t filter systems incorporates approximately 20 t of stainless steel.
Furthermore, new technologies for the drive system and drum bearings enable low-maintenance operation of these plants.
The current generation of filters is marketed worldwide by BHS-Sonthofen under the product name „Rotary pressure filter“ with the type designation RPF, and is available in sizes ranging from P01 (filter area: 0.18 m2) to X 20 (filter area: 8.8 m2). The machines today enjoy worldwide recognition as state-of-the-art products. With these filters, BHS has opened up new, future-oriented fields of application, for example in the production of cellulose derivatives and plastic intermediates, as well as for demanding processes in the beverage industry and for the filtering of starch.
In parallel with the ongoing technical development, BHS has also continually expanded its expertise in cake filtration over a period of more than 50 years. The wealth of knowledge and experience amassed in this time is also utilized by BHS for other products, such as belt, candle and pressure plate filters – and increasingly for filter plants.
Annex 1: BHS rotary pressure filters
Rotary pressure filters can be used for nearly all filterable suspensions. As high-performance filters, they are excellent for the precise separation of products that are difficult to filter. They also represent well-proven solutions in complex production processes for which other filter methods are not suitable.
The filter drum rotates at infinitely variable speed in the pressure-sealed housing. The surface of the drum consists of filter cells connected to the control head via drainage pipes. During filtration, the solids are retained on the filter medium, forming a filter cake that has a uniform structure and density.
The working zones of the filter are divided by separating elements that are pressed onto the drum pneumatically. This creates individual pressure-tight chambers that enable further treatment of the filter cake. In this way, the suspension, washing agents and filtrates are precisely separated from each other. Cross-contamination between the treatment stages is prevented by hermetically isolating the various process stages and separating the individual filtrates.
Depending on the design, the filter allows numerous processing steps after the main solid-liquid separation process. These include single- or multi-stage cake washing, counter-current or re-flux-washing, reslurrying, solvent exchange, steaming or extraction. Since all process steps are carried out in isolated chambers within the filter, the filtrates are discharged entirely separately from each other.
Next, the filter cake can be dewatered and, if desired, dried thermally. This typically happens during blow-drying and can be performed using air, nitrogen or other gases.
The cake is discharged into the atmosphere from the non-pressurized discharge zone. Release from the filter medium is made by a pneumatic backblow or assisted by a mechanical scraper if necessary. This unique atmospheric product discharge method is patented. The filter cloth is cleaned in the downstream single- or multi-stage rinsing chamber.
The filter is available with a CENTER DRIVE or TWIN DRIVE, which makes sure that the drum is centered in relation to the housing and thus compensates for lateral forces and radial movements of the drumTogether with a suitable bearing arrangement this ensures the tightness of the system.
Thanks to their enclosed design, BHS rotary pressure filters are suitable for many applications, especially filtration of volatile or hazardous substances, as well as for sterile processes that require special precautionary measures for reasons of toxicity, workplace hygiene or sterility.
Unlike nutsches and many centrifuges, BHS rotary pressure filters operate continuously. This eliminates the need to invest in additional systems for homogenization of the product stream and further treatment. Moreover, there are no costs for supplementary equipment such as discharge gates because the discharge zone is non-pressurized.
Annex 2: Applications in the chemical industry
Dyes and pigments
Dyes and pigments such as phthalocyanine, pearlescent or silicate pigments and aniline or anthraquinone dyes are usually difficult to filter. However, when the cake is thin, rotary pressure filters offer high throughput rates, good elution and excellent residual moisture values for these substances too.
Pharmaceuticals and antibiotics
Pharmaceuticals and antibiotics, such as synthetic or semi-synthetic antibiotics and antibiotic salts as well as herbal active ingredients and extracts, are separated in enclosed rotary pressure filters meeting GMP requirements.
Plastics
Fine-grained and coarse-grained polymers and crystals, polyolefins, aromatic acids, acrylic or melamin resins are optimally separated, washed and dewatered using high-performance filters with throughput rates of up to 100 t/h.
Agrochemicals
The rotary pressure filter meets strict workplace hygiene standards for toxic products such as insecticides, fungicides, molluscicides or herbicides.
Foodstuffs
Rotary pressure filters gently process cooking fat, stearins, amino acids, synthetic proteins, lecithins, starch, plant extracts, coffee or vitamins in compliance with food industry standards and without contaminating the product.
Cellulose products
With rotary pressure filters, even products that are difficult to process can be filtered, washed and dewatered in a precisely specified temperature range without gelling. Such products include methylcellulose or microcellulose, CMC and cellulose derivatives.
Inorganic and organic chemicals
Inorganic and organic chemicals such as vulcanization additives, sodium hydrosulfite, carbonates, phenyls, amines, paraffins, urea adducts or raw materials for detergents can be processed in rotary pressure filters.
About BHS-Sonthofen GmbH
BHS-Sonthofen develops and manufactures machines and plants for mixing, crushing, recycling and filtration applications in the field of mechanical process engineering. The company focuses on customized solutions tailored to the specific requirements of individual industries.
For over 50 years, BHS has manufactured a wide range of filtration plants for solid-liquid separation in batch and continuous processes. These plants are used on a daily basis by over 1000 customers for highly diverse applications and are regarded as innovative, state-of-the-art solutions. A common feature of all BHS filters is that they work with a comparatively thin cake.
Well-known customers in the construction and building materials, mining, chemicals, pharmaceuticals and food processing industries as well as the environmental and waste management sectors and other major industries have been relying on machines and plants from BHS-Sonthofen for many decades.
BHS-Sonthofen GmbH has been an independent group of companies since 1996. Its history stretches back to an iron-smelting works founded 400 years ago on the site of the present-day company premises. Today, BHS-Sonthofen is a mid-sized global player with over 300 employees, 210 of whom work in Sonthofen. The group of companies is headquartered in Sonthofen, Germany, and has subsidiaries in the US, China and India.
For more information, visit www.bhs-sonthofen.de.
Kontakt:
BHS-Sonthofen GmbH
Roland Schmid
An der Eisenschmelze 47
D-87527 Sonthofen, Germany
+49 8321 6099-231
press@bhs-sonthofen.de
http://www.bhs-sonthofen.de
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