Quarry control helps maintain river levels
Hanson Aggregates are using ABB drives to pump water from their limestone quarry near Frome, Somerset, which produces 3 million tonnes a year from work levels up to 90m below the water table.
Water was previously pumped to a discharge channel but, as part the planning permission to extend the quarry, Hanson proposed using the water to increase river levels and maintain the region’s ecological balance, particularly during dry periods. To ensure the scheme’s success, a sump was built in the quarry floor creating a 7m deep reservoir.
The Whatley Pumping Scheme relies on a 335kW pump to augment the river and two 250kW levelling pumps. The reservoir is also used to provide high-pressure water from a 55kW pump that is primarily used for washing stone in the quarry.
To control the pumps Hanson worked closely with ABB’s local distributor, South West Industrial Drive Centre (SWIDC), to find a solution. As the pumps are on a level some 30m below the sur-rounding land, SWIDC decided to fit four variable-speed drives in a 32ft container. A 55kW drive is used to control the high-pressure pump while three larger drives are used for the augmentation and levelling pumps.
SWIDC supplied an ABB ultrasonic level controller to sense the reservoir water level, and the augmentation water is also tested for turbidity using an ABB controller. If turbidity exceeds an agreed minimum, a proportional-and-integral (PI) controller operated by the 355kW drive automatically stops the pumps for 30min to allow the water to settle. Two ABB flowmeters monitor the exact flow rates of water.
If the water level in the reservoir exceeds 7.2m, the two PI-controlled 250kW levelling pumps are used to maintain the level. If the water level continues to rise, however, the 250kW drive reduces the first pump to 80% output before starting the second pump. It then increases the speed of both pumps in tandem to control the water level. Water is then discharged through a common main into the river.
The drives are programmed to stop pumping if the reservoir level falls below 6m.
