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Air Pollution Monitor and Control
News Release from: Donaldson Membranes | Subject: Elementis Chromium
Edited by the Processingtalk Editorial
Team on 11 March 2008
Tetratex Media for new Elementis
Chromium filters
The Donaldson Membranes Tetratex ePTFE membrane filter media is helping Elementis Chromium meet stringent legislation on emissions at its Eaglescliffe plant in Stockton-on-Tees, UK
As an international market-leader in chromium chemicals, with production facilities in the UK and USA, Elementis is the only manufacturer providing such a complete range of chromium products These are used in a diverse range of applications including: leather tanning, metal finishing and pigment intermediates
This article was originally published on Processingtalk on 10 Mar 2008 at 8.00am (UK)
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The company is committed to protecting the environment and the health and safety of its employees, as well as the wider public.
Their focus is on operational excellence and producing cost-effective, first class products.
Therefore it is imperative that all equipment employed within their production process is of premium quality, offering the highest performance.
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To meet Environmental Agency requirements, exhaust stack emissions are continually monitored and Elementis is rigorous in its adherence to permitted levels, along with the programmed maintenance of all processes and equipment employed.
When the bags in their Pulse-Jet type filter (which dedusts Chromic Oxide Rotary Kiln No.5) were due for replacement, Donaldson Membranes, expert provider of filtration solutions, were consulted.
The bag filter on Kiln 5 had operated with the previous set of Tetratex filter bags satisfactorily without any problems for approximately six years.
However, recommendations had been provided by the OEM concerned that such filter bags should be considered for a change every five years.
Given this information, Elementis took the proactive step of changing the bags despite operations at that time being acceptable.
"With continuous on-line monitoring of stack emissions and routine maintenance checks, any issues with the unit would have been apparent, and on an annual basis we remove the filter lids to check for any signs of leaking filter elements, which we would then replace" said Manufacturing Engineer, Keith Greenwood: "However we prefer to stay one step ahead with our maintenance, so we proceeded with the replacement ahead of any problems developing, using material offering the most advanced technology".
In order to verify the continued suitability of their media, Donaldson Membranes carried out a thorough investigation of the process and gas conditions.
The exhaust stream from Kiln 5 contains chromium oxide dust, oxides of sulphur (SO2, SO3), oxides of nitrogen (NOx), ammonia and ammonium sulphate fume, in a gas stream at a temperature of between 260-280C.
The gas cleaning system provides for removal of all kiln exhaust dust in a bag filter from which the recovered dust is returned mechanically to the kiln feed system.
The filter bags are protected against over-temperature by means of an air bleed control system which ensures the inlet temperature to the bag filter never exceeds the limit of the media.
The cleaned gas stream is subject to Environment Agency operating discharge limits as specified in the operating licence and as such, is subject to continuous on-line monitoring.
For this process, it is imperative that material used in the manufacture of the filter bags is capable of the highest levels of emission control.
Once the operating conditions had been confirmed, Donaldson Membranes again recommended their Tetratex Ultra High Efficiency #6255 Woven Glass fabric.
Donaldson Membranes high performance filter media offers excellent dust cake release, low pressure drop, higher air flow and high collection efficiency, making Tetratex an the best choice for filtration and other applications.
The key difference that Tetratex ePTFE membrane filter media provides over conventional non-membrane media is its non-reliance on a filter cake.
Non-membrane media will often allow the passing of quantities of fine particles not only into but also beyond the media.
This is especially so on start-up when the media is new.
Conventional media only truly start to filter efficiently when a suitably dense filter cake has formed on the filter surface.
Whilst this can sometimes provide the necessary performance, the reliance on a filter cake and the readiness of fine particles to penetrate into the open surface structure of the media often limits the ability of non-membrane media to perform consistently over extended periods of operation.
Additionally, capability to recover from process upsets can be limited.
Tetratex ePTFE membrane media has no such reliance on cake formation and the membrane prevents the penetration of particles into and beyond the backing fabric.
Additionally, the PTFE surface provides exceptional dust release on cleaning and as such operating differential pressures can be expected to be much lower and altogether more consistent over time.
Donaldson Membranes worked on the Elementis project with partner Tyne Tees Filtration, a specialist manufacturer of filter bags who are dedicated to process optimisation and environmental protection.
Between them, Tyne Tees and Donaldson Membranes were able to draw upon their combined extensive experience of production and application knowledge for the expert manufacture and installation of 594 off filter bags made from Tetratex Ultra High Efficiency #6255 Woven Glass 745 g/m2 fabric.
The final product is working as well as anticipated and Elementis Chromium is very pleased with the results to date.
Mr Greenwood said: "Donaldson Membranes media is both effective and affordable, and we are confident that the fabric supplied will enable us to maintain our excellent record of reliability and commitment to Health and Safety and the environment.
At the same time we can continue to offer products to our customers which have been manufactured to the highest standards, whilst keeping our running costs down.
We are again expecting the filter bags to last at least five years in process operation, during which time we will also benefit from the ability of Tetratex filter media to reduce maintenance and energy costs".
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