Quenching the Thirst for Water in Qatar
MRS Ltd water-recirculation system solves water shortage problem for QPMC in Doha
In the extreme heat of the Qatar desert, water is a particularly valuable commodity and is in very short supply. So, when Qatar Primary Materials Company (QPMC) required considerable quantities of the precious liquid for a newly completed sand-washing plant at a site near Doha, capital city of the state of Qatar, they faced a significant problem.
In conditions where the ambient daytime temperature can reach 50°C, the company needed to secure a continuous supply of around 500,000 gallons of clean water per day in order to produce high-quality washed building sand. At an early stage in the plant development, thought was given as to how to recycle water brought in by tankers, but knowing that additional quantities would be required time and time again, QPMC quickly realized that a more permanent, economical and reliable solution would be needed to satisfy the site’s ongoing water requirements and to avoid the considerable cost of purchasing and transporting supplies on a daily basis.
As development of the site progressed, QPMC contacted Len McGarry, managing director and geotechnical consultant of UK-based Moisture Reduction Systems Co. Ltd (MRS), to draw upon his 50 years’ experience in the provision of solutions to water-related problems. Having assessed the situation, he recommended a cost-effective and simple solution involving the installation of one of MRS’s unique and patented abstraction/recirculation vacuum-assisted pumping systems.
The system supplied to QPMC consists of a total of six 100mm large air handling Selwood 7.5kW electrically driven vacuum pumps operating in two separate set-ups, each comprising two duty pumps and one standby pump. In addition, both pump set-ups incorporate a pair of manifolds each equipped with four take-off points. These are connected to special filter-wrapped perforated drainage pipes laid in a spiral arrangement beneath the washed sand stockpiles.
Using design criteria and calculations to suit the prevailing D10 sieve sizes, the system ensures that no fines are removed during the pumping process and only clean water is discharged from the two pump set-ups, ready for constant recirculation back to the washing plant for subsequent reuse.
To ensure that virtually all process water draining down through each of the 1,000-tonne washed sand stockpiles is captured and returned to the wash plant, heavy-duty impervious membranes have been installed underneath the filter-wrapped perforated drainage pipes beneath each of the stockpiles. According to MRS, this has made it possible for approximately 90% of the initial wash water to be returned to the plant on a continuous basis, while around 3% of the water is taken up by evaporation. This means the final washed sand product has a moisture content of around 7%.
A spokesperson for QPMC said: ‘The MRS system performs well even in the high ambient temperatures, allowing us to either load directly from live stockpiles or transport material to stock areas very soon after production. Moreover, our plant floor remains clear and dry, which benefits both transport vehicles and our loader operators.
‘The reduced moisture content is also a bonus for concrete producing companies, as it allows them to add a greater volume of ice during batching without affecting the water : cement ratio, thereby giving the concrete a longer life before its temperature rises, rendering it unsuitable for use.
‘With a significant reduction in our water costs, this has given us an edge in a very tight and competitive market. In every respect, we are very happy with the new system.’
As a result of the considerable benefits being delivered by the QPMC installation in Qatar and several independent third party recommendations, MRS say they have secured a number of similar projects around the world, with contracts now completed, ongoing or due to be installed in Saudi Arabia, Tunisia, Dubai, South Africa, Australia, New Zealand, the US and Hong Kong.
These are in addition to many other installations already completed throughout the UK, Ireland and Europe for major sand-processing companies, all of whom are said to be benefiting, and profiting, from the energy cost savings, improved handling characteristics and environmental advantages of the MRS Ltd system and service offering.