Sustainable development through continuous optimization
Lafarge operates one of Germany’s most modern cement plants in Wössingen (Fig. 1). With the changeover from the semi-dry (Lepol) process to the dry process, which was completed in 2009 after only 17 months, the products were improved, the emissions were significantly reduced and the fuel mix was optimized. ZKG INTERNATIONAL has talked to the plant manager, Lutz Weber, about his experience with operating the new plant (see webcode ZKG0M6RR). Continuous optimization and modernization is traditional at Wössingen. Over the years this has enabled it to maintain its competitiveness and improve it still further. An open door day was held in September 2010 on the 60th anniversary of the cement plant at Wössingen to which politicians, neighbours and customers were invited to see the current state of the plant for themselves. Thanks to the new production line with a 5-stage cyclone preheater with calciner and combustion chamber from A TEC (Fig. 2) the way is open for a successful future for the Lafarge plant at Wössingen.
The site at Wössingen has a long tradition. It started in the 1950s directly at Wössingen. The first kiln was a shaft kiln. The first Lepol kiln was built in 1961 and came into operation in 1962 with a capacity of 130000 t/a clinker. A second kiln was added in 1971. Lafarge then became involved in the Wössingen cement plant in 1976. Further milestones in the history of the plant were the change from oil to coal firing in 1980, the inaugu-ration of the new circular clinker store in 1989 and two years later the construction of the electrostatic precipitator for kiln I. 1994 saw the 100% takeover of the Wössingen cement plant by the Lafarge Group. The use of the first alternative fuel was authorized in 1995 and the works for chopping up used tyres was incorporated into the plant. In 1995–1998 the plant invested in extensive modernization measures and commissioned the central control room, the automatic laboratory and an electrostatic precipitator for kiln II. The electrical systems for fuel metering were also renovated. In 2005 the authorized alternative fuel rate in kiln II rose to 60%. Solid shredded waste was added as a new alternative fuel for kiln II in 2006. In 2007 the plant received approval for extensive modernization of its works, which was completed in 2009 at a capital cost of about €60 million.
The Wössingen plant obtains the limestone for cement production from the upper shelly limestone in the Lugenberg quarry (Fig. 3). Most of the limestone is extracted by blasting. The rock from the quarry is fed to a twin-shaft hammer crusher from FAM with a nominal capacity of 600 t/h that was installed in 2004. The rock is transported to a blending bed hall (MIAG) on a belt system that passes through an online analyzer from Gamma-Metrics. Two blending beds are formed by the chevron method, one with a high lime saturation factor and one with a low one. The required quality can then be achieved by mixing the material from the two beds. The stockpiling capacity is 600 t/h and the reclaiming capacity is 200 t/h.
The raw mill, an O&K mill from 1982 with a nominal capacity of 180 t/h (main drive 3300 kW), is supplied with limestone from the blending bed hall. The raw mill is dedusted by a bag filter from Redecam installed in 2009 (filter area 3299 m2, 6 m filter bags). There is also the option of taking limestone directly from the blending bed hall to the cement mill for composite cements. The raw mill had been set up for the Lepol kiln, so a new hot gas duct, among other things, was needed to adapt it to the modernized plant design. A new evaporative conditioning tower (nozzles from Caldyn, overall design by A TEC) (Fig. 1) was also installed. Four homogenizing silos are connected to the mill. The kiln feed is provided by Pfister metering units combined with Aumund bucket elevators.
The kiln for the modernized plant was taken from the old kiln line II. It is a converted Polysius kiln (3.8 m x 54 m, slope 3%). The first and last kiln segments and the tyres were renewed (Fig. 4). It is dedusted by the Redecam bag filter that is also used for dedusting the raw mill. The fans for the induced draught as well as for the kiln filter, the bypass filter and the cooler filter come from Ventilatorenfabrik Oelde.
Gas, heavy fuel oil, petroleum coke, solid shredded waste and animal meal can be burnt with the Unitherm M.A.S. main burner (Fig. 5). The fluff is delivered by lorry, stored, reclaimed automatically with an EBS system and then discharged directly into the main burner or the calciner by metering screws (Fig. 6). The shredded tyres are also metered directly into the calciner. The petroleum coke is metered to the main burner from the coal mill, an O&K mill (3rd generation classifier, 12 t/h). The new clinker cooler, an IKN pendulum reciprocating grate cooler, achieves better recuperation rates, among other things, and is dedusted by a Redecam electrostatic precipitator. The clinker is conveyed to the clinker silos (storage capacity 60000 t) by a new Aumund clinker transport system that was integrated into the old existing plant by Aumund. The new works is equipped with a bypass (10%) from A TEC with single-stage quenching that is dedusted by a bag filter (1787 m2 filter area, 6 m filter bags). The bypass dust is held in temporary storage in a silo and then either removed or fed to the cement mills. The POLAB system is used for monitoring the quality.
Three cement mills are fed from the clinker silos. These are two ball mills (Hirschmann O&K, 90 t/h, and Polysius/KHD, 45 t/h) and a birotator ball mill (MIAG/Christian Pfeiffer, 55 t/h). The cement silo capacity is 29000 t. The process control system from ABB was modernized for the first time in 1998, so it only needed fine-tuning before the conversion – which is typical of a brownfield project. All the cement at Wössingen is loaded in bulk in 24 h operation. The loading is fully automated.
