Rudersdorfer Zement GmbH in Germany placed an order in 1996 to modernize its grate cooler in its clinker production lines 3 and 4. Humboldt Wedag ZAB GmbH/Dessau was awarded the contract.

A heat savings of 134 kJ/kg clinker (32 kcal/kg) per kiln line had been originally guaranteed and 335 kJ/kg clinker (80 kcal/kg) was achieved for kiln line 3 and 234 kJ/kg clinker (56 kcal/kg) for kiln line 4, according to Rudersdorder Zement. The upgrade project was completed in June 1997.

The current consumption of the cooling air fans could be reduced by 18.3% and 8.7%, respectively. The conversion of the thrust-type grate coolers was essentially concentrated upon the first six plate rows. By the installation of seven Omega grate plates per row, the energy exchange between clinker and recuperation air was improved, according to plant employees.

Moreover, an improved design minimized the inflow of false air. The volume of recuperation air and the related required fan capacities could be reduced. As a result, the reduced fuel and energy consumption cuts down the operating costs considerably.

At about the same time, another plant-Southdown's Victorville, Calif. facility-was entering into the task of modernizing its entire kiln No. 2. Humbolt Wedag Inc. was awarded the job in July 1996. Among the upgrades to the line was a modern cooler configuration.

In 1984, KHD Humboldt Wedag supplied the original 2,400-tpd plant to Southdown with a 4-stage preheater, a calciner with tertiary split air duct withdrawn from the kilnhood without a dust settling chamber, 4.2- % 57-meter rotary kiln, and a second-generation grate cooler.

The recent upgrade modifications to the pyroprocessing line include the replacement and enlargement of all four cyclone stages. The top cyclones (Stage 1) were completely replaced. On Stages 2, 3, and 4, only the cyclone cones were retained. The upper part of the existing calciner was enlarged and an additional compact mixing chamber installed. With this, the clinker volume and the retention time were increased.

All new cyclone sections were fitted to the existing structure. The tertiary air duct was modified with a new cylindrical dust settling chamber. The tertiary air is now withdrawn from the front of the kiln hood.

The I.D. fan wheel was replaced; the kiln drive was modified; and new burners were installed on both of Southdown's kiln lines. The recuperation area of the clinker cooler was completely modified to a modern Pyrostep cooler with one static step grate followed by omega grate plates.

The Pyrostep has several cooling zones (see Figure 1), which differ in design and method of aeration. In the first four zones, each row is individually supplied with a variable volume of cooling air.

Zone I comprises a stationary step grate with horizontal air outlets in the plates. The individual rows are aerated in several transverse sections with a pulsating and individually adjustable stream of air.

Zone II is a reciprocating grate section equipped with omega plates for aeration in rows. These plates have small pockets in which the clinker accumulates, thus allowing for a widespread and uniform flow of air through the layer of clinker. The lip of the omega plate also is cooled with air to extend the service life. A wear-resistant external telescopic seal makes it possible to supply cooling air to the moving rows via rigid pipes.

Zone III comprises a stationary step grate similar to Zone I.

Zone IV also is equipped with omega plates similar to Zone II. The length of this zone depends on the process requirements and the capacity of the pyroprocess system.

Zone V is aerated by chambers and can be equipped with standard or omega plates. The specific cooling air distributed to each plate is calculated to prevent inrushes of air causing clinker to whirl up in fountains. The gaps between the plates are narrowed to reduce clinker trickling.

If a plant has a small cooler unit, as the one at Victorville does, Zone II is followed directly by Zone V with chamber aeration (see Figure 2).

The plant pyro system at Victorville was shut down in June 1997 and the kiln/preheater system restarted after being down for two months. By September 1997 the guaranteed production figure of 3,300 tpd was already regularly being exceeded to 3,600 tpd, which is now the established daily capacity for the kiln.

This article was adapted from information provided by KHD Humboldt Wedag.