Working Together for a Cleaner Environment 1

Considered one of the giants of the Russian building material industry, the Company produces more than 2.5 million tonnes of cement a year. Its unique source of raw materials has helped them to become a leader among Russia’s wet cement manufacturers.

With the world cement industry committed to reducing environmental emissions, the Company has made continual efforts to embrace operational methods which are not only economical, but that also minimise the impact of their operations on the environment.

After in-depth technical consultation, the Cement company placed the order for their new kiln dedusting bag filter systems utilising filter bags manufactured from Tetratex ePTFE membrane filter media.

Prior to installation, the filterbag manufacturer analyse the mechanical, physical and chemical processing conditions of the filter system to guarantee that the new filter is produced according to individual requirements, ensuring successful operation and increased filter element life.

When recommending a filter media, their specialist team takes into consideration various criteria, such as procedural data, operating efficiency, requested operating durability and required emissions. Using state-of-the-art production techniques, they manufacture filters with outstanding airflow characteristics, long service life and emission levels far below mandatory limit values.

Following a full technical evaluation, four bespoke bag filter systems were designed, manufactured and installed incorporating the very latest filter media and pulse-jet cleaning technology.

Specification for Each Bag Filter – 4 off Filters

Gas Volume	460,000 Am³/Hr
Dust Loading	Typically 22g/Nm³
Gas Temperature	Operating 180-230^oC
Filtration Air-to-Cloth Ratio	1.03 m³/m²/min
Bag Size	165mm nom dia x 6000mm long
No. of Bags	2400 off
Filter Cloth Area (total)	7465m²
Cleaning (offline or on-line)	Pulse-Jet, Off-line
Bag Support Cages	20 Wire, Stainless Steel
Warranted Particulate Emissions	<20mg/Nm³
Filter Media Employed	Tetratex #6255 Ultra High Efficiency Woven Glass

The filter was to be fitted with 2400 off tubular filter bags mounted on stainless steel support cages. All such dedusting applications require the filter bags to be cleaned to ensure operating pressure drop and gas flow are maintained at satisfactory levels. In the case of the filter installed at the cement plant, dust building up on the surface of the bags is removed by means of a controlled jet of compressed air which is periodically blown down the centre of each bag.

Engineered components ensure this jet provides an accurately formed “pulse” or “wave” of air which not only momentarily reverses the flow of air through the filter media, but also dislodges the cake build-up as it moves vertically down each bag. The frequency of cleaning is determined by a PLC which monitors the operating pressure drop, constantly maintaining the system at an acceptable level.

Factors Influencing Pressure Drop and Frequency / Pressure of Cleaning:

Dust loading

Humidity

Efficiency and condition of the cleaning system

Design of bag and cage

Inlet configuration

Can velocity (spacing between filter bags)

Filter velocity (Air-to-Cloth Ratio)

Condition of filter media

Particle size and shape

Agglomerative nature of dust

Type of filter media employed

To ensure the required high level performance was successfully achieved on this project, Donaldson Membranes Tetratex Ultra High Efficiency #6255 Woven Glass fabric was selected, with the filter bags themselves being manufactured to the required design and specification to provide optimum performance and lifetime.

Tetratex Ultra High Efficiency #6255 Woven Glass filter media has been widely used throughout the world on cement kiln dedusting applications. The fabric comprises a woven glass substrate laminated with a Tetratex ePTFE membrane. Emissions to atmosphere can be warranted to near-zero levels with expected bag lives for kiln dedusting reaching upwards of six years.

The key differentiation 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 (being laminated to the filter surface as it is) prevents the penetration of particulate into and beyond the backing fabric. Additionally, the smooth 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.

Filter bags constructed from Tetratex ePTFE membrane media are used in many parts of the cement manufacturing process including kilns, clinker coolers, raw and finish mills and fuel mills.

Of course, no two applications are ever the same. If optimum performance is to be achieved, it is vital that all factors related to the process are considered. Donaldson Membranes’ engineers have the necessary product and technical application experience to offer sound advice on the required selection from their full range of membranes and their respective backing fabrics, the combination of which is designed to provide specific physical and filtration characteristics.

The four membrane families; Tetratex Release, Tetratex EXTREME, Tetratex High Efficiency and Tetratex Ultra High Efficiency are all available with an extensive range of backing fabrics to meet a wide variety of thermal and chemical demands, whether that be for operation in pulse-jet, reverse-air or shaker filters. These high performance Tetratex laminates can all supply superior dust cake release, low pressure drop, high air flow and high particulate collection efficiency.

Donaldson Membranes Sales Manager, Wolfgang Drong, said: “Performance figures achieved from the filters to date are well within regulatory limits as well as those laid down in the comprehensive warranty that was provided at the time of supply. All parties involved in this project are very pleased with the results to date”.