The “gravel plant in a container”
With its new container-mobile processing concept GRAVEX, SBM Mineral Processing is combining the great advantages of stationary technology regarding sustainability, product quality, and availability with the excellent flexibility of mobile systems. Recently, a specifically configured plant of the modular GRAVEX technology came on stream in the Tyrolean Kühtai. Within an uninterrupted production line, a mobile concrete mixing plant EUROMIX 3300 SPACE is – regardless of the weather conditions - supplied with high-quality washed aggregates coming from pre-crushed primary material accruing directly on site.
In the Tyrolean Kühtai high up the Inntal at about 2,000 m above sea level and 30 km to the west of Innsbruck, the Tyrolean Hydropower Group AG (TIWAG) will until 2026 significantly expand the capacity of its existing power plant group Sellrain-Silz (currently: 531 million kWh p.a.). Apart from the new Kühtai reservoir with a useful capacity of about 31 million m³ which is fed by an also newly built diversion tunnel more than 25 km long and a total of six water catchments, the project as well comprises the underground pumped-storage plant Kühtai 2 which connects the existing high reservoir Finstertal (useful capacity 60 million m³) to the new Kühtai reservoir. The new lake reservoir alone will provide an extra of 216 million kWh electricity per year coming from natural inflow; and due to the pumped-storage power plant, existing energy can be stored for later use, and fluctuations of other renewable energies such as wind or sun can be flexibly balanced.
The main contract section including the 510 m long and 113 m high natural stone dam was conceded to a consortium of the Austrian companies Swietelsky, Jäger and Bodner. Since springtime 2021, the consortium ARGE SKW Kühtai with its central construction site infrastructure has been working parallelly on tunnel driving and lining, mass movements, and dam construction directly above the existing power plant Kühtai
In total, more than 240,000 m³ concrete have been estimated for the whole project of building the water and access tunnels and the power generating house situated in an about 80,000 m³ large cavern. All this concrete will be produced on site, the aggregates come from the excavated tunnel material respectively the material accruing above ground, a granodiorite gneiss with an extremely high abrasiveness and refractivity index. In the light of the remoteness of the construction site, there are really no alternatives to this course of action. Supplying the site with concrete aggregates from the nearest delivery plants alone would require considerably more than 18,000 additional lorry journeys causing the corresponding CO2 discharge; and in view of the altitude difference of 1,400 m, supply shortages and total breakdowns would be inevitable in the Tyrolean winter.
For this reason, the whole concrete production based on pre-crushed material lies with the German-Austrian enterprise Mobile Beton Konzepte GmbH (mbk). As one of the leading service providers in the German-speaking countries and the adjoining Eastern and South-eastern European regions, the enterprise with its headquarters in Munich and a subsidiary in Röthelstein, Austria, has been undertaking the concrete supply on large-scale construction projects for tunnel construction, generating plant construction, structuring engineering, or civil engineering on client orders since 2009. In addition to the precisely coordinated provision of the required concrete qualities based upon the suitable concrete-technological concepts, mbk upon request also provides raw material coordination or project-specific circle-flow solutions to use accruing materials or to facilitate their sustainable recovery in surrounding regions. According to the company, 60 internal and about 250 external employees of subcontractors produce about 800,000 m³ concrete and about 800,000 tons construction aggregates per year.
For concrete production, the mbk Management and its Partner Hans Peter Haid fully rely on the supermobile and easily moveable pant technology made by SBM Mineral Processing. Currently, the mbk mixing plant fleet comprises a total of 18 EUROMIX plants with hourly outputs from 80 to 145 m³ hardened concrete; the trailer-mobile units and hoppers respectively aggregate silos offer flexible capacities due to their modular design; they can be deployed in short-term construction sites as well as long construction projects lasting several months or even seasons; and they ensure on-site production of premium-quality concrete with documented daily production peaks coming to more than 2,000 m³.
In Kühtai too, mbk brought the SBM technology up to the mountains. Since April 2021, a concrete mixing plant EUROMIX 2000 (105 m³/h) operating on the TIWAG construction site has already delivered 45,000 m³ concrete until October. In view of the future challenges the team of mbk Technical Manager Peter Schreiner is carrying out major upgrades: A new plant EUROMIX 3300 SPACE will produce concrete for the first time in combination with the innovative container-mobile processing, washing, and separating system GRAVEX from SBM Mineral Processing. After centralised material feeding with 0/22 primary material, several washing and screening units as well as an integrated crusher produce a total of five final grain sizes and store them ready-for-processing in eight insulated overhead hoppers with a capacity of 200 m³ each, meaning 2,500 tons in total. All components are designed in container-suitable dimensions, and thanks to the space-saving vertical installation over several levels with bucket elevators and feeding and distributing conveyors, the whole semi-stationary plant can be installed quickly and safely in an only 250 m² large concrete foundation
It is amazingly easy to adapt the modular GRAVEX concept to precisely meet the specific requirements of construction site and products. In Kühtai, the fine grain size 0/4 is the essential part of the about 30 “standard concrete mixes” that are - like all other aggregates - constantly quality-assured in the affiliated TIQU test laboratory (a 100-% TIWAG subsidiary). To that effect, half of the storage volume is reserved for the sands that are elaborately classified by two heavy-duty wet-screening units before the filler is removed by a final dewatering screen with a hydrocyclone to f3.
To integrate the production screens positioned some 30 m above the silo chambers into the container design that is so important for easy transport, simple crane erection, and the safe static construction of the whole plant, SBM’s elliptical vibrating screens with digital drive synchronisation are used for the first time. Thanks to the horizontally mounted screening decks (dimensions 1,500 x 4,000 mm each) both the primary 2-deck screen (separation 22/4 mm, feed capacity: 120 t/h) and the secondary 2.5-deck screen (16/8/4 mm; 80 t/h) are only 2.25 m high, meaning that they remain below the standard inside dimensions of containers of 2.38 m. Due to the separate frequency converter control of the two unbalance motors, various different elliptical movements can be infinitely set to precisely adjust screening capacity and performance to material and output.
To ensure constant availability of the 0/4 sands even in times of unexpectedly high demands or when the primary material shows quality fluctuations, the GRAVEX system in Kühtai is also equipped with a vertical impact crusher SBM V8. With a feed material size of 4/22, the wear-resistant 132-kW unit can process the stored grain size material 4/8/16/22 to top-quality 0/4 sands that once again pass through filler removal in a cycle.
The whole GRAVEX process including feeding the container-mobile overhead hoppers of the plant EUROMIX 3300 SPACE (4 x 100 m³) which are used as an additional production buffer is controlled fully automatically and monitored in the central mbk control room minimising the workforce requirements in Kühtai. Per shift, one mixing plant supervisor, one site manager, and one service technician for the regular maintenance of the entire system are calculated.
“Here at 2,000 m altitude, we are extremely exposed to the weather conditions; and at the same time, we must closely coordinate our logistics and production concerning space and organisation with the other trades,” explains mbk Technical Manager Peter Schleinzer. This regards on the one hand aggregate deliveries coming directly to the mobile primary crushers “just-in-time” and without large interim storage. On the other hand, this especially applies to supplying the concrete workers in the tunnels and in the underground power generating house, as well as the tubbing segment production set up directly on the large-scale construction site Kühtai. “Even under the most adverse external conditions possible we must reliably provide shotcrete, structural concrete, and tubbing segment concrete whenever it is required at weatherproof installation points or in production.” By contract, production may only come to a halt if temperatures fall below – 20 ° C, wind speeds exceed 200 km/h, and snow loads reach 7 m. “The new GRAVEX system allows weatherproof production and storage of high-quality grain sizes; additionally, its hourly output of some 120 t/h and the connected silo volume of totally 1,600 m³ offer sufficient buffer capacity for our EUROMIX 3300 SPACE that is configured for 100 m³/h concrete,” summarises Peter Schleinzer the grand expectations set on this technology.
“Actually, the GRAVEX premiere has become a real acid test,“ says SBM Managing Director Erwin Schneller who accompanied the installation in Kühtai. The GRAVEX concept was developed in less than 3 years, and with the already considered integration of upstream crushing stages the SBM engineers chose an overly broad approach to the “gravel plant in a container”. “We see the application fields of GRAVEX especially where higher quantities of primary materials are processed directly on site, ensuring better quality and having less impact of and influence on the environment than would be possible by using a track-mounted technology,“ outlines Erwin Schneller the new SBM concept, which also allows a significant reduction of environment emissions such as dust or noise.
With set-up and moving times of two to three months, GRAVEX is aimed at long-term projects lasting about 12 months or longer – meaning mainly large-scale construction sites in tunnelling or power plant construction. A big advantage of GRAVEX is the fact that the plant can be moved and put into operation again almost without any loss in value. Another issue is the extraction sector, e.g. exploiting the remains present in existing plants with overaged stationary technology or exploiting smaller, limited deposits meeting an economically interesting demand for high-quality raw materials – with or without connected temporary processing of construction material. “In both cases we rely on the great benefits of the modular container design which we know from our many years of experience with container-mobile concrete mixing plants. Many of our customers in this field keep 10- to 20-year-old plants that can be adapted to new requirements or upgraded to the latest technological standards with little effort. The first SBM mixing plant in Kühtai, a EUROMIX plant of the first generation, which was deployed temporarily until the new concrete and GRAVEX combination was finished, is already more than 20 years old.”