07.10.2008 | Autor / Editor: DEMAG Cranes & Components / Marcel Dröttboom
The Austrian Gmundner Zement Produktions- und Handels GmbH company has improved the efficiency of its raw material storage operation by means of an automatic crane solution.
By investing in an automatic crane solution for its raw material storage system, Gmundner Zement Produktions- und Handels GmbH aimed at achieving a lasting improvement in the storage and retrieval operations in an older building. In co-operation with Demag Cranes & Components, an installation was implemented with a connection to the storage management system. Scanners were used for continuous detection of the filling levels in the individual storage boxes.
The construction of a cement factory began in the municipality of Gmunden 100 years ago. The plant, originally planned to supply material for the manufacture of fibre-cement board, was continuously extended. Two quarries in the immediate vicinity were mined to extract the raw materials. The company, which belongs to the Rohrdorfer construction materials group, today has an annual production capacity of more than 700000 t. Various types of cement are supplied to medium size customers within a radius of some 200 km.
Following the decision to make the investment, the specifications for the new crane installation were clearly defined:
A major step towards achieving a rapid return on the investment was already taken by taking the old crane system out of service. The two old cranes in the raw materials bay had caused an enormous amount of maintenance and repair work and were hardly able to cope with the amount of material that had to be handled, which had increased by more than 65% in just two years.
The raw materials bay is 180 m long, 17.9 m wide and the last extension dates back to 1966. Gmundner Zement extracts the basic materials for the cement ingredients to be stored from two quarries. The materials are delivered by conveyor belts and by rail. Approximately 850 m2 of the storage area is occupied by clinker – as an intermediate product from the furnace. In an area measuring almost twice the size, the company stores Thiodur clinker, a material used in the production of sulphate-resisting cements. Other additives such as anhydrite and FGD gypsum are stored in further compartments.
The clinker is brought in from the furnace on conveyor belts. The other materials are delivered by truck or rail and placed in three manual and two automatic zones.
When the truck are automatically unloaded, the truck driver takes a card at the weighing station and the storage management computer releases the storage location. When the barriers have closed, the system gives the crane the command to clear the tipping area. If the material is delivered by rail, it is stored under manual control. When trucks are loaded direct, e.g. for direct sales of clinker, the crane is also controlled in manual mode, either from the cabin or by radio.
Already at the tender stage, the cement producer attached great importance to the maximum possible availability of the installation. The storage area for normal clinker features four chutes, into which the material slides before it is transported to the cement mills by conveyor belt. Besides the storage and retrieval operations, the crane is also responsible for delivering the additives as needed. The Thiodur clinker is produced during five two-week periods in Gmunden every year. No intermediate silo is available for this material, the mills are supplied by the crane from the raw materials bay “just in time”. A standstill in the storage operation would have immediate consequences for the production process.
The new double-girder overhead travelling crane has a load capacity of 11 t and was designed to fit the crane runway in the raw materials bay exactly. In order not to increase the pressure of the individual wheels on the runway, the travel units were fitted with eight travel wheels and single-sided guide rollers. Speeds of up to 55 m/min for the lifting motion, 120 m/min for long travel and 60 m/min for the cross-travel motion ensure that the material is handled efficiently. To protect it against the harsh operating conditions, the crane electrical equipment is installed inside a container with an air-conditioning unit on the crane girders.
A further highlight includes continuous detection of the material in stock. For this purpose, Demag Cranes & Components installed a scanner on the crane that measures the height contours of the stored material every time the crane passes over it. The information is transmitted by radio to the facility director, which uses it to calculate and provide a visual representation of the fill levels in the individual compartments.
Data transfer also includes reporting and control of the quantity of material that has been picked up. The clamshell grab has a capacity of up to 4 m3. A crane weighing device determines the weight of the load that has been picked up and sends the information to the facility director. The crane receives information from the facility director on the quantities to be retrieved – for example to ensure a specific blend ratio for the additives. A wireless LAN access point was installed in the weighing cabin outside the bay. From here, there is an Ethernet connection to the facility director. The crane control system is in constant dialogue with another radio link. When the raw materials store was converted to fully automatic operation, all of the entrances to the bay had to be secured. The signals such as access functions and light barrier status messages are transmitted via a separate secure radio link.
Before the new crane was delivered, the runway rails that exhibited strong wear from decades of operation had to be replaced. The rails were gradually replaced while the installation was in operation. For this purpose, sections of the crane runway were only blocked off during the day shift. When it had been completely fitted, the runway was surveyed by Demag service engineers. When a new conductor line had been installed, the older lattice-girder crane was scrapped and the second old crane was parked at the back of the bay.
Gmundner Zement recognised the benefits of using refuse derived fuels for heating purposes at an early date. Since the early 1980s, the company has been incinerating shredded used tyres to warm up the furnace, combustible waste fluids were used later. An installation for making use of plastic refuse was subsequently put into service. As already in the used tyre store, Gmundner Zement also relies on Demag crane systems for this operation.
The already shredded material is delivered by truck. When the delivery has been registered in the system, the storage management computer raises the barrier at one of the tipping positions; this area remains blocked for the crane while the delivery is unloaded. The 7 t automatic crane then has to clear the tipping position. With its 5 m3 grab, it picks up the delivered material and stores it as specified by the system. A grid pattern was defined for sorting the plastics in the 1500 m3 bunker.
At a speed of 25 m/min with a full grab and 40 m/min for partial loads, the double-girder overhead travelling crane lifts the fuel to a gallery at a height of nine metres to serve the feed bunker. From here, the necessary quantities of shredded plastic are blown into the incinerators. In normal operation, some 3000 kg are incinerated per hour, although the feed system is rated for double the capacity.
In retrospect, Gmundner Zement is satisfied with the crane investment. The hardware of the raw materials crane has passed the usual tests of daily operation and the materials handling goals have been met in full. Integration of the installation into the company’s shipping system has also been completed with all of the defined interfaces.
Demag Cranes & Components GmbH
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