PMV travelled to Ras Al Khaimah to visit the largest quarry in the Middle East, where quarry dumpers, excavators and crushers are daily fare. But despite the harsh environment, a ‘green solution’ will transform the quarry, saving money and lowering emissions.
By any measure, the quarry in Ras Al Khaimah is visually impressive, a giant cauldron hollowed out of the mountain, with a steady stream of quarry dumpers carrying material down its twisting roads.
Equally impressive is the quarry’s impact on the construction industry of the GCC, and further afield. Owned by the ruler of Ras Al Khaimah, His Highness Sheikh Saud Bin Saqr al Qasimi, the quarry produces 65 million tonnes of limestone aggregate annually, making it one of the three largest quarries in the world, and the largest in the Middle East.
The aggregate is used in construction in the UAE, Bahrain, Qatar, and further afield. Recently it signed a contract to provide 11 million tonnes limestone annually to India, to be used in steel factories for purifying the steel, a process requiring high quality limestone, and the stone quarried here is amongst the purest in the world.
As expected, the quarry has significant numbers of machinery and vehicles: giant Terex quarry dumpers, Komatsu PC800SE hydraulic excavators, as well as Caterpillar wheel loaders, motor graders and bulldozers.
Yet the real work in shaping the quarry is done by dynamite, and each day the quarry is closed at lunchtime to blast apart the virgin material. Yet change is in the air, and the quarry is undergoing a slow process of transformation, which will see the lumbering mining trucks replaced by a huge system of conveyor belts.
At the very bottom of the hill, almost inside the quarry itself, is Quarry & Mining. Touting itself as a ‘German company’, Q&M is the agent for Stiebel gear drive units and GKM screening units for the GCC, and is the agent for Kleemann crushers in UAE and in Saudi Arabia.
It also has a manufacturing capability, specialising in the design, production and installations of conveyors for bulk material handling, and has won high profile contracts including the design and construction contract for the conveyor system at Knauf’s nearby $100 million gypsum plant. More recently they signed a contract with Etihad Rail to provide bulk-material handling facilities at the railway stations.
General manager Moritz Kerler is on a mission to bring the most modern techniques to this quarry, and other quarries in the region.
In the UAE, many quarries make extensive use of quarry dumpers to carry the blasted material down the hill to the primary crushers. Mining trucks are an extremely expensive solution, says Kerler, with a high purchase price, and signficant operating and maintenance costs, as well as being heavy emitters of pollution.
A further inefficiency is introduced by the fact that the primary crusher removes a good deal of waste material, which can be used in the quarry for building of roads, rather than being transported by truck to the crushing site and there discarded.
Meanwhile in Europe, the trend is to use mobile primary crushers that move progressively with the blasting face. A number of mobile primary crushers have been sold to quarries in Fujairah, says Kerler, but it is still relatively uncommon in the Middle East.
Q&M is yet to implement the use of mobile primary crushers at the RAK quarry, but instead they are installing huge static primary crushers halfway up the mountain, close to the blasting face.
On the northern slope of the quarry are two giant static primary crushers, buried in the mountain, with a combined capacity of 2500 tonnes per hour. A second set of stationary primary crushers will soon be built on the southern side of the quarry.
The second piece to the puzzle is a system of conveyor belts, carrying the pre-crushed material down the mountain to the secondary crushers. A kilometre-long section of belt has already been installed from the primary crushers, and carries pre-crushed material down the mountain to the secondary crushers, with the conveyor capable of carrying up to 4500 tonnes per hour.
4500 t/h is an enormous quantity of material, and if the conveyors were not braked the material would travel down the mountain reaching massive speeds of 30-40 metres per second (110-140km/h), destroying both the conveyor system and anything in its path.
The solution is a series of braking stations, controlling the speed of the conveyor down to 2.2-2.8 metres per second.
Stiebel gear motors are used for the braking, effectively functioning as dynamos, and the braking energy is converted into electricity, which is fed back into the quarry’s operations, reducing its reliance on the national infrastructure, as well as reducing its monthly power bill.
Capturing electricity from the braking of conveyor belts in quarries is a technology that was pioneered in Switzerland and Austria, with material transported down from high in the Alps.
In the Middle East there are a number of factors that further complicate the implementation of any engineering solution. Here, ambient temperatures are high, and the heat means that it is a much dustier environment; in addition the maintenance people and operators are far less skilled.
Quarry & Mining is the first to introduce the technology here, and Kerler says many people – both here and in Europe – advised against it.
“We were the first company in the Middle East to implement such a project. Everyone thought
it would be risky or dangerous,” he explains.
With the extreme volume of rock, Kerler says that there has to be rigorous controls, planning – as is done in the nuclear power industry – for every possible scenario or problem.
“We have to control the system, because if you’re bringing down on one belt 4500 tonnes an hour, it’s an unbelievable quantity, and if the breaking system stops working it will run at 30-40 metres a second and it will destroy everything,” says Kerler.
“In the system we have facilities which are covering all the eventualities – this we did with a very sophisticated PLC controller. There is a lot of brainwork and a lot of safety [built in].”
Soon, Quarry and Mining will have built 9.2 kilometres of conveyors in the quarry, bringing down the pre-crushed material along three separate belts, and the total power generated will be 2.2MW per hour – equivalent to a small power plant.
And as the quarry develops, the conveyers can be extended. With the system in place, ordinary trucks can be used to transport the crushed material from the secondary crushers, rather than the extensive use of the more-expensive mining trucks.
“The crusher system was implemented five years ago and was a big success. There they have seen how much money they can save,” says Kerler.
He explains that the cost of a conveyor system is dramatically cheaper than using quarry dumpers, only 40% of the cost, with an ROI of three years.
However one obstacle to the widespread implementation of conveyor systems in the quarries of the UAE is that licenses are often only granted for two-three years before they are renewed, discouraging investment, although in practice companies often operate quarries for long stretches of time.
And unlike a conveyor system, mining trucks can be easily moved to a new quarry – or sold – if the owner desires. And though the conveyor system can be resited, it would be at considerable effort and expense.
While the conveyor system is expected to introduce considerable cost savings for the quarry, Kerler sees it as a step towards introducing best practice into the quarry. “The final solution will be to go even further up, with conveyors, and then implement what we feel is the best solution n – as is also done in the rest of the world by the very big quarries – they then go mobile.”
