Page 49 - Hub-4 Magazine Issue 74

Hillhead 2022
Preview
Fine Sand Cleaning
The water that has washed the aggregates up until this point in the process along with the sand is collected in the sump of the FM 120 C-2G Sand Plant. This plant consists of a collection tank, centrifugal slurry pumps, separators and a 12x5 high frequency dewatering screen. The slurry is pumped to the primary separator for an initial wash. The underflow discharges onto the dewatering screen where it receives a further rinse. Any fine sand which passes through the screen is collected in the sump and pumped to the secondary separator for a final wash. Two washes of the material at the SAPA site was necessary due to the high percentage passing 63-micron in the feed.
After this double wash process the two in spec grades of sand are dewatered on the high frequency dewatering screen, which reduces residual water content in the final product to 10-15%. The water from both separators containing the minus 63-micron material is collected in a ground sump and pumped into the deep cone thickener tank—where the water management process begins.
Aquaclear Water Management
The waste water is pumped into a deep cone thickener with flocculent added along the way, thanks to the flocculent dosing unit present within the central control room. Within the deep cone thickener, the waste particles of silt and clay combine to create a larger heavier particle that sinks towards the base of the cone. The flocculent dramatically speeds this process up and allows the clean water to weir over the top of the deep cone into a collection tank, where it is recycled back into the wash plant.
The slurry that has been collected at the bottom of the deep cone
thickener is pumped into a buffer tank, where it is stored until enough volume is gathered. At this point it is transferred into a filterpress.
The filterpress is used to recover the last remaining water within the silt and clay. A total of 150 plates are used on this side beam filterpress, that has a working pressure of 16 bar (232 psi). Each plate is covered in a nylon filter cloth, which when filled with sludge under pressure, forces the remaining water to be removed from the sludge. This water is then recycled back into the wash plant to be used for washing aggregates and sand once again.
After the water has been squeezed from the sludge, bomb doors below the filterpress open and the hydraulic ram begins to decompress. The slurry cakes are then rapidly discharged into the bay below the filterpress. Particularly sticky cakes are removed with a pneumatic plate shaker that ensures all the plates are ready for the next cycle. The cakes below can then be re-used for several applications, such as lining for ponds.
In this case SAPA opted for an automatic cloth wash system so that the lifespan of the filter cloths could be extended while optimum performance is ensured. This system cleans each cloth individually using a high-pressure water jet. Johnston Patterson, Product & Applications Manager at Terex Washing Systems explained that, “This water management system recycles 95% of the water used for this application. SAPA only needs a small tank of water to top up the system every so often. This has a hugely positive impact on the environment and has financial benefits.”
The result for SAPA is the sustainable production of usable and saleable sand and aggregate product from C&D and excavation waste. This also has the environmental benefit of being diverted from landfill. Additionally, the water
management products recycles the dirty water from the process and returns a clean water back to the process
again for use.
Johnston Patterson explained that, “the customer is very pleased to have a solution in place to
recycle their C&D and excavation waste. The working relationship between Terex Washing
Systems and SAPA has played a huge part in achieving a high level of performance for this plant.”
To learn more about Terex Washing Systems or how they can assist you in your wash recycling needs, please contact tws.sales@terex.com or visit www.terex.com/washing
www.hub-4.com May-June 22 - Issue 74
| p49 |