Manufactured sand as an alternative to river sands

• 
• 30th December 2009
• Quarrying
 

Much of the sand supplied to the market in the Kaliyal region of India has traditionally been dredged from rivers. With growing pressure to reduce the environmental impact of such activities and ever increasing legislation operators are now looking at alternative methods of production for the sand products required to meet the requirements of the planned infrastructure developments in the region.

One such company is Poabs Granite Products who have been operating in the quarrying sector since 1986. The company have recently installed a new 100tph sand washing plant from CDE's Asian office with its headquarters in Kolkata. The plant was required by Poabs Granite in order to allow them to meet the growing demand for a manufactured sand product for use in concrete manufacture.

Poabs previously operated an extensive crushing operation in Kaliyal and while this brought the stone size down to a manufactured sand specification the problem lay in the high percentage of material passing 150 micron. There are stringent limits set on the volume of material in this range that is permitted in concrete sand and this required that Poabs adapt their existing system to allow for the production of material which would allow the efficient production of a concrete sand product.

Using their previous system, the excessive fines content in the manufactured sand product meant that a large volume of water was required if the product was to be used to manufacture concrete. This essentially ensured that Poabs were not able to manufacture this product as it was not commercially viable. The costs of production were so high that the concrete sand product was not able to be sold to the local market.

The introduction of an Evowash sand washing plant from CDE has eliminated this barrier to market and allows Poabs to produce in-spec concrete sand at a price which has resulted in the company enjoying significant demand for the product. The Evowash system is built around the philosophy that through proper testing of the feed material in the first instance accompanied by details of the final product specification required by the customer it is possible to ensure the production of high quality sand products which meet the target specification.

"CDE has become a name synonymous with world class sand washing systems across the world. The Evowash system is an industry leader in terms of both fines recovery and the production of high quality, high value material" explains Manish Bhartia, Managing Director of CDE Asia. "As a company we pride ourselves on the design of an individually tailored solution for every customer. The installation with Poabs is proof that the system delivers the results required and we are looking forward to further introduction of the system throughout the Indian construction industry in the months and years to come."

The Evowash system is a compact design incorporating a specialised rubber lined hydrocyclone, a high frequency dewatering screen and a recirculating slurry pump into a single system. The washed sand product is discharged at approximately 12% moisture content which is significantly less than other sand washing systems available. This offers significant advantages for the customer as it means that the material is ready for market straight from the belts.

"With other sand washing plants operators are required to allow the sand product to dry out before it can be sold on due to the fact that the typical moisture content of the material is up around the 25% to 30% mark" explains Manish Bhartia. "By producing a washed sand product that consistently shows a moisture content of significantly less that 12% we are allowing operators to generate revenue from their material much more quickly than has previously been the case. In addition to this, the specification of the sand product allows operators to secure the maximum commercial price per ton for their material."

Environmental awareness

The unwanted fines are carried off from the Evowash system with the cyclone overflow. On many systems this waste material is simply sent to on site ponds or lagoons. The build up of material in these ponds adds additional costs to the operation of the plant as these need cleaned regularly resulting in plant downtime and lost production. In their discussions with CDE about the introduction of a new sand washing system, Poabs Granite made it very clear from the start that they were keen to look into the introduction of a primary stage water treatment system with the plant.

In addition to being aware of the costs of regularly cleaning out on site ponds the company were also very keen to ensure that the environmental impact of the new plant was reduced as far as possible."We are very aware of our responsibility to minimise the environmental impact of our operations" says Joseph Jacob, a Director of Poabs Granite, and the person responsible for specifying the CDE Evowash system. "We had visited some of their previous installations in the UK and The Middle East and understood the significant advantages that the introduction of a water treatment system would bring."

CDE were able to meet the requirements of Poabs Granite in this instance through the introduction of their AquaCycle thickener system. This system has been been tried and tested on many of the CDE installations throughout Ireland, the UK, Europe and The Middle East as well as on many of the company's iron ore washing plants in India and offers operators a means of significantly reducing both the volume of water required as part of the sand washing operation and the volume of waste material generated by the plant.

The AquaCycle model specified in this instance is the A400 which is capable of treating 400m3 per hour of slurried fines from the Evowash plant. The introduction of the system reduces the volume of fresh water required to feed the washing plant by 80% - 90% - the specific figures for the Poabs plant show an 85% reduction. As the slurried material enters the thickener tank a small amount of polymer flocculent is added. This forces the fines within the slurry to bind together and fall to the bottom of the AquaCycle tank. A set of rakes at the bottom of the tank feedback information on the sludge density to the plc control panel and provide a trigger for discharging the sludge to storage. Meanwhile, the clean water overflows the top of the AquaCycle tank before being sent to an AquaStore water recycling system where it is recirculated to the washing plant.

Retrofit to minimise plant installation time

Another key factor behind the specification of the CDE plant by Poabs lay with the capability for the plant to be retrofitted to Poabs existing operation with minimal impact on production. "Time is money" explains Joseph Jacob of Poabs. "The whole installation of the CDE system on our site was completed with minimal impact on production time."

This is achieved through the pre-assembly of a large part of the plant at the CDE Asia manufacturing facility in Kolkata prior to it arriving on site. "We are fully aware of the need to keep our customers up and running for as close to 100% of the time as possible" says Manish Bhartia. "It is because of this that we have developed a very well planned installation and commissioning program that minimises the impact that our presence on site has on overall production levels."

Increasing coverage

Following the successful installation with Poabs Granite, CDE are looking forward to the development of further sand washing installations throughout India in the coming months. "The Evowash and AquaCycle combination is tried and tested throughout the world" comments Manish Bhartia. "The results being achieved by this plant will allow us to further develop our coverage in India as we seek to allow sand producers to ensure the highest quality products which can command the highest commercial value."

With their previous system Poabs Granite were not only producing a sand product with a fines content that provided a barrier to their chosen market but were also losing a substantial quantity of good quality sand in their waste product. The CDE system has addressed both these issues increasing both the volume and the quality of the final sand product. "The CDE plant has allowed us to consistently and economically achieve an in-spec washed manufactured sand" says Joseph Jacob of Poabs Granite. "This has transformed our production and allowed us opportunities to further develop our business."

You can view further project case studies from CDE on their web site at www.cdeglobal.com/downloads.html and can contact the company in India at enquiry@cdeasia.com. You can also view many project videos at www.youtube.com/cdeirelandtv and download many project images at www.flickr.com/cdeimages.

For further information on this or any other project in India contact CDE Asia at +91 33 3028 2080 or for worldwide enquiries at +44 28 8676 7900 or info@cdeglobal.com

Associated Links

• Hub-4 Profile of CDE Ireland (Peter Craven)
• CDE Ireland (Peter Craven) Company Website