Deep Dewatering Solution for Quarries in South Wales
Cornelly Quarry is one of the deepest quarries in Wales, producing over 1 million tonnes of limestone a year.
With an expected final depth of -75m AOD, its location in an area of relatively high rainfall, and nearby to the Merthyr Mawr and Kenfig sand-dune SACs (Special Area of Conservation sites), the quarry’s WMP (Water Management Plan) and planning conditions are very rigorous indeed.
Looking ahead, quarry owner Tarmac saw the need for a future-proofed dewatering system that would extend to a total head of nearly 150m and be sufficient for an increased flow rate of up to 130 litres/second.
Furthermore, due to the planned deepening of the quarry base, the ability to relocate the pump from the existing basal sump to temporary sumps is necessary to provide continual dewatering whilst the extraction work proceeds.
Obviously, with the deepening of the quarry floor, the increase in both head height and flow rate was a particular challenge with such a large quarry. The traditional quarry dewatering approach offered the choice of installing a larger pump than initially required or replacing the pump at intervals for the next size up. Neither option appealed from a long-term value point of view, nor did inefficient consumption of energy fit well with Tarmac’s sustainability strategy to reduce CO2 by 45% per ton of product produced.
Tarmac are rightly proud of being at the forefront of implementing new, lower CO2 methods, so were open to looking at innovative dewatering ideas, if these could be backed up by technical experience.
With this quarry being so deep, Atlantic Pumps drew on the mine dewatering experience of Intrax Global to help design the best solution for Tarmac Cornelly.
A bespoke rig was engineered by Atlantic Pumps at their Derbyshire works. It consists of a buffer tank, fed by two 75kW soft-start Audex Submersible pumps mounted on a pontoon. This tank then feeds a pair of 12” diameter 220kW high-head centrifugal pumps in a duty standby arrangement. Each centrifugal pump has a capacity for 150l/s, making them an efficient and safe choice for the forecasted increase in flow rates.
The skid that holds the tank and twin pumps is constructed so that the weight is evenly distributed when lifted by the four hooks. This means it can be safely moved around the site multiple times to allow for blasting, sump re-siting, and other quarry operational changes over the years.
Intrax Global’s South American partner All Pumps have installed this type of flexible and extendable pumping system many times for dewatering mineral mines in South America.
The modular concept of this design uses standardised pumps and parts for the main workhorse, keeping initial investment and parts replacement at a lower cost.
Variable speed drives (VSD), controlled by a PID (proportional integral derivative) keep the two stages of pumping in continual balance. Sonic level indicators in the lagoon and buffer tank feed live data to the PID which then keeps the feeder and main pumps operating near their BEP (best efficiency point). This removes the wasteful high energy consumption when the pump is running too fast or cycling through multiple starts and stops. The motors are driven by LV power which is transformed down from the quarry’s HV supply and generally run at around 35hz.
In addition to enabling precise control of energy use, the stability and regulation of the PID controller is ideally suited to helping Tarmac manage the water levels in the quarry and the surrounding environment. Keeping groundwater levels in the neighbouring area within their natural range is a core part of their water management plan.
Excess water is recycled on-site for process use wherever possible, helping to meet the company’s sustainability target of reducing water consumption 25% per ton of product by 2030.
The duty standby arrangement ensures a spread of working hours between the two pumps and allows for maintenance without interruption to operations.
Live monitoring of the pump’s operational conditions such as amperage and flow rate feeds into the extensive water monitoring and reporting system that enables Cornelly Quarry’s WMP. Among this data stream is an alert if the first mechanical seal in a submersible pump should fail, giving protection against water damage. The Senteos remote monitoring system is able to send text or email alerts to nominated staff if specific events occur or pre-set parameters are reached.
A new 12” pipeline was also installed to transfer the quarry water to the upper settlement lagoon where the water is processed before discharge into a number of locations, depending on environmental conditions. Several monitoring stations around the quarry feedback measurements of bedrock and surface water levels, allowing for proactive dewatering control and pre-planned contingency action.
Tarmac’s investment in this innovative dewatering system has given them greater control of site water management, reduced energy consumption and provided a flexible system that is expected to pay back for itself again and again.
By being an early adopter of this mining-derived dewatering concept and its’ inter-connected, smart control system, Tarmac CRH has yet again demonstrated its commitment to leading on sustainability.