Product category:
Air handling: Dust + Fume extraction
News Release from: Donaldson Membranes | Subject: Tetratex 6255
Edited by the Processingtalk Editorial
Team on 20 June 2006
Tetratex filter on cement plant works
better
Decreased kiln emissions follow installation of baghouse filters equipped with filter bags manufactured from Tetratex 6255 ultra high efficiency ePTFE membrane with woven glass fabric
The Secil plant of Maceira-Liz has experienced decreased kiln emissions following the replacement of electrostatic filters with baghouse filters equipped with filter bags manufactured from Donaldson Membranes Tetratex 6255 Tetratex ultra high efficiency ePTFE membrane with woven glass fabric Secil Cement Company is the second largest cement manufacturer in Portugal and boasts a production capacity of around four million tons of cement per year, mainly for the Portuguese market
This article was originally published on Processingtalk on 11 Mar 2008 at 8.00am (UK)
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With a market share in Portugal of some 37%, Secil cement is produced at three plants - Maceira-Liz, Secil-Outao, and Cibra-Pataias.
With a strong local presence, growth in other countries also contributes to the worldwide development of Secil.
The company's international expansion began in 2000, with the acquisition of the Societe des Ciments de Gabes in Tunisia, which owns a cement plant with an annual capacity of more than one million tons and has a market share in Tunisia of approximately 17%.
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This global expansion has continued in Angola, through the Secil Lobito, and with the most recent Secil deal - an important financial investment at Ciment de Sibline SAL, located south of Beirut, in the Lebanon.
Secil manufactures and markets grey and white cement and operates a customer service and cement distribution for the Portuguese market.
Maceira-Liz plant has two kilns, with an actual production capacity of 1400 t/d each.
The kilns started up in 1968 and 1970, supplied by Fives Lille, with a production capacity of 900 t/d.
The coolers were manufactured by Fuller and the cyclone tower by Humbolt.
Two major changes were carried out at Maceira-Liz in order to increase production capacity and optimise the process.
A new Fuller Cooler and a new double cyclone 1 in 1984-86, and in 1998/99 a cyclone tower supplied by PSP.
Further changes took place in 2000.
Originally, dedusting in the kilns was carried out by electrostatic filters.
Secil decided to have a baghouse filter built instead, made up of six compartments containing 480 bags each.
The filter was designed to operate with compartments off-line to allow easy access for the maintenance staff and enabling the Secil Plant lines numbers 5 and 6 to work continuously all year round.
The kiln of lines numbers 5 and 6 operates by a combined system, with short breaks in direct system mode, during which the temperature of the gases entering the filter increases significantly.
In June and September 2000, baghouse filters manufactured by Redecam were installed, with the filter bags for the filters supplied by Testori using the recommended media Tetratex 6255.
Tetratex ultra high efficiency ePTFE membrane has woven glass fabric suitable for continuous service at temperatures of up to 260C.
Tetratex ePTFE membranes are used in many parts of the cement process, giving improved airflow throughput, which translates into increased production rates.
Tetratex 6255 was suitable for this application due to its requirements for lower pressure compressed air and less frequent cleaning due to its exceptional dust cake release properties, whilst giving near zero particle emissions, increased bag life and lower maintenance costs.
After the start up of the filter in 2000, the emission was around 4 to 6 mg/Nm3, with a pressure drop or around 50-60 mmH2O, and these values were maintained until the end of 2002.
Following these positive results from the first set of bags, Secil decided to maintain the quality of media by continuing to use Tetratex 6255, with modifications to the filterbags designed to increase resistance to abrasion damage.
The new bags were supplied during Spring 2004 to equip the filter which receives the fumes from kiln Number 5 and were the first replacement set after the original supply, which successfully exceeded the 3-year warranty.
The full replacement ended in May 2004 on kiln 5 and June 2004 on kiln 6.
A total of 2,880 filterbags were manufactured from Tetratex 6255, with properties as follows.
* Filtering surface: 5,900m2.
* Gas flow: 220,000 Nm3/h.
* Temperature: 125C, peaks of 260-280C per 15 mins/day.
* Filtration speed: 0.85m/minute.
* Pressure drop with a compartment off-line: 84mm/H2O.
* Dust concentration (entry): 70mg/Nm3.
Performance of the filter media continues to fulfil requirements.
Augusto Miragaia, Clinker and Cement Production Manager at Secil Plant Company, said: "The aim of the replacement of electrostatic filters by bag filters was to decrease the dust emissions and also to increase the reliability of the dedusting system of gases from the kiln.
These two goals were achieved in full.
Regarding the bag performance, the emission values agreed on the contract were 8 mg/Nm3.
We obtained between 4 and 6 mg/Nm3.
We managed to keep these values constant during the first 2.5 years of functioning.
With some partial replacements of bags it was possible to maintain a controlled emission under 25 mg/Nm3 until 3.5 years of functioning.
During the last 6 months we have proceeded with the full replacement of the bags.
As the filter is divided into sectors and its dimensions allow the normal functioning of the kiln with one sector out of work, the bag replacement may take place without affecting the normal functioning of the facilities.
The experience acquired showed us that the wear of the bags occurred mainly at the base.
The new bags installed are also Tetratex 6255, but have a reinforcement of 200 mm at the base.
With this modification we hope to increase substantially the duration of the new set of bags just installed.
Another important factor is the bag cleaning system which takes into account the differential pressure, which allows us to avoid excessive compressed air consumption and to reduce the wear of the bags caused by excessive cleaning.
The working pressure is between 50 and 70 mmH2O.
In global terms, we can say that the performance of the bag and filters is excellent.".
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