HEIDELBERG CEMENT’S LIXHE PLANT IN BELGIUM BENEFITS FROM DONALDSON MEMBRANES FILTRATION MEDIA 1

Donaldson Membranes was chosen as the supplier of filter media for bag filters as part of the overhaul of the dry process line at HeidelbergCement’s Lixhe plant.

HeidelbergCement, a world-leading producer of cement, concrete and building materials, shut down Lixhe’s wet process kiln and carried out a complete modernisation of the dry process production line in order to: increase capacity from 3400 tpd to 4200 tpd; maximise the use of the most profitable secondary fuels; and to meet environmental protection standards. This will enable the group to cover its clinker production needs in Benelux with 3 kilns only: Lixhe, Antoing and Maastricht.

The Lixhe cement works which belongs to the Heidelbergcement group is located close to the Belgian town of Liège, in an area bordering the Netherlands and Germany. The works had a clinker capacity of 1.6 million tons per year with one wet kiln line and a dry kiln line with preheater.

The dry process production line had a capacity of 3400 tons of clinker/day.

After preblending of the various components (2 marly limestones, fly ashes and clay) in a stockpile, the preblend with a moisture content of 15 % was dried in a rotary dryer and subsequently ground in a ball mill before being stored in the homo silos. The clinker was burnt in a rotary kiln (95 m. long; diameter 5.4 m.) equipped with a four stage preheater tower and a grate cooler. The kiln exhaust gases were dedusted in an electrofilter, the cooler gases in a gravel bed filter. The fuels were coal (88 %) and whole tires in the smoke chamber (12 %).

As part of the overhaul and in order to reduce dust emissions, two bag filters were erected for the dedusting of the kiln exhaust gases and of the cooler gases; NOx emissions have been decreased by the installation of a multistage combustion system on the preheater.

Previously kiln exhaust gases and part of the cooler exhaust gases used to dry raw materials in the rotary dryer were dedusted in an electrostatic precipitator. This electrostatic precipitator, with dust emissions of 50 mg/Nm3, was clearly not sufficient to accommodate the higher gas flow and to satisfy the more and more stringent environmental regulations. Therefore a new bag filter was necessary to operate as a kiln filter and Donaldson Membranes, worldwide manufacturers and suppliers of expanded PTFE membranes, films and laminates, were asked to provide a solution.

Donaldson Membrane’s recommendation was Tetratex #6255 with 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.

Tetratex ePTFE membranes are used in many parts of the cement process, giving improved airflow throughput, which translates into increased production rates. Tetratex ePTFE membranes have become a significant market player as the fabric and technology of choice in the replacement of electrostatic precipitators (ESP) with baghouse filters in the kiln de-dusting process.

The bag filter, supplied by Redecam, encompasses 7680 bags, height 4.5 meter; diameter 145mm, guaranteed for 5 years. It was manufactured in Tetratex #6255 Woven Glass fabric with Tetratex Ultra High Efficiency ePTFE membrane, suitable for continuous service at temperatures of up to 260⁰C. The bag filter was installed after the raw materials dryer in order to dedust kiln gases and part of the cooler gases when the dryer is in operation – and was built behind the casing of the electrostatic precipitator which has been retained as a settling chamber.

In order to protect the filter against high temperatures a conditioning tower has been added in the circuit to cool down the gases in case of lack of raw materials in the dryer

Bernard Boulangé, Project Director, at HeidelbergCement said: “Our choice of the bag filter technology was based on the excellent performances of a bag filter installed recently on the Antoing kiln which produced low dust emissions, no sensitivity to CO peaks or to modification in process conditions. At Lixhe the current operation is 120°C only but during transition phases it can increase drastically. The new bag filter has been in operation since July 2001 and the bags are still performing well. The emissions have been reduced drastically from 50 mg/Nm3 to below 3 mg/Nm3); the guaranteed pressure drop is 80 mm, although the actual pressure drop is somehow higher due to higher gas flow.

“In short, the new bag filter is a success and has provided a dramatic reduction of dust (and Hg ) emissions, and up to now lifetime guarantees of the bags have been maintained.

“Today the kiln is generally operated at a throughput between 4400 and 4600 tons/day (5-10% above nominal). The exit gases temperature may be regulated between 350°C and 420°C and the pressure drop of the system is as low as 340-370 mm WG. We have recently inspected the filter and all remains satisfactory.”

From an environmental point of view, the investment has considerably improved the previous situation; all emissions have been considerably reduced. Clearly, for applications employing fabric filter media, the best available control technology for the capture of fine and difficult particulate is recognised as ePTFE membranes.

Donaldson Membrane’s Tetratex® Microporous ePTFE membrane filter media has a proven track record as a very high efficiency, highly effective fabric filter media, with several different membrane types available to achieve, subject to various parameters, the desired performance: Tetratex Release, Tetratex, Tetratex High Efficiency and Tetratex Ultra High Efficiency. These high performance laminates supply superior dust cake release, low pressure drop, higher air flow, and high efficiency.