Sand production - wet or dry?

Wet?

Washing is widely accepted to be the most efficient way of producing high quality sands for use in a variety of applications ranging from sands for use in concrete to specialist applications such as golf and silica sands.

This is because of limitations with traditional dry screening processes particularly in regard to the ability of these systems to effectively and consistently remove minus 75 micron material.

CDE Global have built a reputation on the delivery of efficient sand washing plants throughout the world over the last two decades and have been working in the Gulf for almost 10 years.

During this time we have completed many sand washing installations including two 1200 tonne per hour plants in Qatar. There are numerous other CDE washing plants in operation in many other regions of the Gulf and North Africa including KSA, Oman, Bahrain, Tunisia and Morocco.

Our entry into the Gulf came as the result of the demand for high quality washed sands in the region. This resulted in the two large 1200 tonne per hour projects in Qatar initially and since then there have been many other installations with capacities more in line with every day requirements – between 50 and 150 tonnes per hour.

Over the years CDE has developed a project list full of examples of replacing inefficient traditional sand washing plants such as bucket wheels and screw classifiers with the hydrocyclone based Evowash system.

Old sand washing technology has a number of issues, not least the loss of significant quantities of quality fines to the settling ponds or water treatment phase. In an effort to ensure effective removal of the minus 75 micron fraction these inefficient systems take a lot of commercial quality sand with them which has a negative impact on the profitability of the operation.

Operators using inefficient sand washing plants are taking a hit on two fronts. Not only is the final value of their sand product compromised by the presence of larger quantities of minus 75 micron material than is ideally the case but operational costs are also increased as a result of the requirement to clean out settling ponds regularly in an effort to recover the good material that has been lost.

There are various design features on the Evowash plant that prevent this problem from arising with the choice of hydrocyclone technology being one of the key factors. Hydrocyclones offer the most efficient means of delivering the required cut point thus ensuring a sand product that meets the desired specification. The effect of being able to guarantee a sand specification is to maximise the commercial value of the material and thus the profitability of the operation.

Investing in low cost, old technology is a false economy as the return on investment takes much longer than is the case when our washing system is specified.

Water recycling

The ability to offer operators water recycling equipment to accompany the sand washing plant has also been a key factor in the success that we have enjoyed in the Gulf.

Given the climate in the region and a scarcity of water when compared to the North European markets where CDE originally established a reputation the specification of the Aquacycle thickeners and GHT filter presses that we offer was very frequent as business grew.

You could say that Gulf operators led the way for the global washing industry in relation to the specification of water recycling equipment. We would now include our thickeners and filter presses on 80% of all global washing projects whereas as recently as five years ago this figure would only have been around 20%.

The scarcity of water in the Gulf was a major factor here and made the CDE water recycling and sludge management system a ‘must have’ rather than a ‘like to have’ as it was seen in some other territories. Environmental concerns and subsequent legislation in this area has driven demand for water recycling systems but there is also a growing realisation that their introduction does actually offer a more efficient way of operating.

When you factor in the costs of managing large settling ponds, the additional space required to accommodate the operation and the potential health and safety risks, water recycling systems offer operators a way to ensure a much more efficient and easily managed washing plant.

Dry?

Just as the introduction of effective water recycling systems was a response to the unique climate of the Gulf region we then introduced new air classification technology.

The introduction of our Sirocco air classification system was a move inspired by the need to offer a solution to operators not able to consider a washing plant due to water supply issues. Even with full closed circuit water recycling reducing the volume of fresh wash water required to around 5% of the total volume some operators are simply not able to ensure supply of the volumes needed to operate a wash plant.

The question that arises from this decision is how does it fit in with the previous assertion that dry screening of material is not as efficient a process as washing?

Well, although a dry process, the Sirocco air classification system is far removed from the traditional dry screening process which has been problematic for those seeking to produce high quality sand.

The key success of washing using our Evowash system is the capability to efficiently remove the minus 75 micron material. We prefer to describe the Sirocco as a dry wash system – or washing without the water as it is able to achieve the same results as washing in terms of minus 75 micron fines removal.

Previous to the introduction of the Sirocco air classifier to the Gulf operators wishing to produce quality washed sands were unable to do so because of a lack of water availability. With the introduction of Sirocco the option exists for these same operators to achieve the higher specification sand products that will allow them to diversify into new sectors of the construction market.

We have several Sirocco units operating in KSA and Oman which are producing concrete sands to the same specification as those being produced by our Evowash sand washing plant. With each new Sirocco unit comes a growing acceptance of the technology and a realisation that this dry wash system is a viable alternative to a washing plant.

An additional feature of the Sirocco system that has made it attractive to operators is the small amount of space required to accommodate the system. We offer the Sirocco as a stand alone unit or as part of a turnkey package. The turnkey option includes a feed system, the Sirocco air classification unit, two stockpile conveyors – one for the sand product and one for the fines – and a dust suppression system.

The fines product from the Sirocco is not a waste material but has a number of applications including its use in the manufacture of ceramic tile adhesives and grouts. This provides additional revenue for operators from what many consider to be a waste material.

The Sirocco system is available in a variety of configurations from 50 tonnes per hour to 800 tonnes per hour in a single unit. This differentiates the Sirocco from other air classification systems on the market which offer single units at 150 tonnes per hour and multiples of this system should larger capacities be required.

Our washing plants are customised to the specific requirements of each project and our Sirocco units are built according to the same principles.  The specification of the right system needs to take account of the individual characteristics of the feed material, with the level of fines being the critical factor. Other systems take a ‘one size fits all’ approach which compromises final product quality.

The future

The introduction of the Evowash and Sirocco units reflects the approach we take to all the regions in which we operate. We will continue to respond to the specific requirements of the Gulf region and all of the other territories we are working in or aspire to work in as we seek to continue to offer operators the most efficient sand processing systems available.