Large Rotary Feeder (Continued)
The RDG 1800 x 1000-21-10,5 feeder has an imposing overall height of 3 000 mm (see photo below). The 1 800 mm diameter x 1 000 mm moving cellular wheel has a speed of 10.5 rpm and a volume of 1 143 dm3. The rotary feeder, including the scraper element, is driven by a geared motor with an installed rating of 15 kW. Both the housing of the feeder and the cellular wheel itself are fitted with replaceable wearing plates. Access to the cellular wheel and the scraper element is obtained through appropriate inspection openings so that the scraper blades can be readjusted without any difficulty. The feeder is heated and is protected by scavenging air from the ingress of dust and from blockages at the outer edges. At the client’s request the rotary feeder with scraper was mounted on a travelling device designed specifically for the individual situation so that it could be moved out to the side for repairs or to carry out regular inspections. The equipment supplied by KREISEL included installation of a shut-off slide under the travelling device. This is intended to protect the rotary feeder from high temperatures if there is an emergency and at the same time to serve as an inspection slide.
The rotary feeder with scraper at the Chelm cement works was commissioned in the presence of members of staff from KREISEL over the period from 27th April to 1st May. The new feeder demonstrably eliminated the high heat losses at the kiln plant caused by the false air. The resulting heat savings alone meant that the capital investment made by the operator had paid for itself after approx. one year. At the same time the noise nuisance associated with the ingress of false air was substantially reduced. The measures carried out relieved the load on the existing hot air fan and the exhaust gas fan, which opened up a significant reserve capacity for raising the kiln output. This means that the new feeder is making an indirect contribution to lowering the CO2 emissions. The new feeder has been watched critically since it was commissioned and its operating characteristics have been optimized. During the practical testing in collaboration with the operator there are plans for balance measurements so that the improvements that have been achieved in the kiln plant can be better evaluated and quantified.
The rotary feeder with scraper was developed in collaboration with the Chelm cement works in Poland with assistance from the Federal German Environment Foundation. It is entering the market just at the time when the need for efficient material feeders with particularly tight seals has risen to an exceptionally high level in the cement industry due to the increased use of vertical roller mills both for producing raw meal and for grinding cement and granulated blastfurnace slag. There is also a wide variety of possible uses for the new feeder in other industries and for handling particularly difficult secondary materials, such as sewage sludge.
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Large Rotary Feeder
Use of a large rotary feeder with positive mechanical scraper for the cellular wheel chambers at the Chelm Cement Works in Poland
First published in
CEMENT INTERNATIONAL
Issue No.: 2/2008, pp. 35–38
One long-standing unsolved problem is how moist, abrasive materials that have a tendency to form coatings can be metered reliably into the air system of a vertical roller mill under high negative pressure or into a fast-running impact rotor drier in the interconnected preheater of a semi-wet process cement kiln plant. KREISEL GmbH & Co. KG from Krauschwitz, Germany, is a medium-sized company that will celebrate its 100th anniversary in 2012. With financial support from the Federal German Environment Foundation it has developed a large rotary feeder with a positive scraper for the cellular wheel chambers for the particularly difficult application of feeding the raw material into a kiln plant at the Chelm Cement Works in Poland (see photo below). This feeder has been operating successfully since May 2007. The Chelm cement works, situated at Poland’s eastern border, has for many decades used the wet process for its kilns because it has to process very moist chalk and marl deposits. However, during the course of privatization that started in 1990 – the cement works now belongs to Cemex – it acquired a modern semi-wet process kiln line. The kiln line is equipped with a calciner and three preheater stages, operating with an interlinked gas system with an impact rotor drier that not only comminutes the raw material mix at gas temperatures between 500 and 600 °C but at the same time also dries the raw material. It is supplied continuously with the two main components, namely chalk and marl, by the new rotary feeder with scraper at system-dependent negative pressures of up to 5 000 Pa. The chalk component is particularly liable to form coatings and has a feed moisture content that can be as high as 24 %. The feeder, which was fitted with a triple flap feed gate, had to be removed from the plant after only a short time in operation due to the disruptive formation of coating. This meant that high levels of false air and loss of heat and output had to be accepted for years during the operation of the kiln plant. The kiln plant supplied by FLSmidth was a 4.75 m diameter x 74 m rotary kiln with a planned output of 4 500 t/d and a guaranteed specific heat consumption of 925 kcal/kg clinker.
This has to be capable of supplying an hourly mass flow of about 400 t to the impact rotor drier and at the same time has to fulfil the important function of sealing the gas regime against negative pressures of up to 5 000 Pa.
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