CRYSTALLISATION PLANT FOR AMBATOVY PROJECT UNDERWAY

 

VWS Envig is currently completing a turnkey project for the Ambatovy Project in Madagascar. The large nickel project includes the design and construction of an ammonium sulphate processing plant.

Once operational, Ambatovy will mine, prepare and pump ore via a pipeline from the open pit mine site, located approximately 80 kilometres east of the country's capital, Antananarivo, to the processing facility and refinery adjacent to the Port of Toamasina on the country's east coast. The thickened slurry will then undergo a number of processes to extract nickel and cobalt.

According to Gerhard Vosloo, Deputy Project Manager, Design and Build Projects, VWS Envig, one of the main objectives of the Ambatovy project is to limit the impact on Madagascar's unique environment.

"One of VWS Envig's core philosophies is ensuring that our plants have a minimal effect on the surrounding environment, something that can clearly be seen in our use of the most appropriate technologies and processes. For this project, our plant will be treating one of the by-products of this mining process in order to recover ammonium sulphate, a valuable, saleable, high grade fertilizer that can be used for agriculture," says Vosloo.

The plant utilises crystallisation technology, developed by VWS Envig sister company, HPD Technology. The company is a global specialist in supplying crystallisation and evaporation solutions to metals processing projects.

"HPD Technology has tremendous expertise and experience in designing these kinds of plants. We consulted them throughout the design process and, once complete, they validated the design," says Vosloo.

A model of the Ambatovy crystallisation plant

The crystallisation process, using evaporation, occurs over three stages. The entire process is energy efficient with the initial energy input of low pressure steam, 43 tons per hour, used in the first phase, while the resulting vapour powers the subsequent stages. In the third stage, this vapour is condensed with a surface condenser and non-condensable gas is released into the atmosphere.

"The crystals are produced in each of the three phases of the process and settle towards the bottom of the vessel," notes Vosloo. "They are then extracted using slurry pumps and strained through sieve bends. The remaining crystals are separated using centrifuges, and are then sent to a rotary kiln to remove excess water."

Only crystals of a certain size are required and over- and undersized crystals are removed and fed back into the process. The plant's output of final product grade crystals is 25,6 tons per hour.

As a turnkey project, VWS Envig was also responsible for the design of the plant. Due to its location, the plant was designed to cater for cyclone conditions with cyclone season extending from January to March.

"Essentially during a cyclone, the plant will shut down and go into safe mode with only the critical systems operating. The plant is also robust in design to ensure that there is no risk of failure or downtime. Even though the ammonium sulphate plant is peripheral to the mining process itself, it is critical and a shut down means a stop in the entire process. We therefore included redundant systems for the pumps and vessels."

Vosloo notes that to meet the challenge of the plant's location, most of the equipment is being pre-manufactured by sub-contractors in South Africa with some equipment manufactured at VWS Envig's premises in Isando.

"All items are being manufactured with modularisation in mind because it makes it easier from a logistical point of view. We have extensive experience in designing and building treatment plants throughout Africa and are capable of overcoming the challenges that remote locations or limited resources present."

The construction phase of the project is divided into two stages. The first, currently being completed, is a storage facility with a 6600 ton capacity where the dry crystals will be stockpiled. The second stage, the crystallisation plant, with piping and vessels to be manufactured in 316L stainless steel, is expected to be to be commissioned by end 2010.

Vosloo concludes that through the use of its experience in Africa, international resources and specialist technologies, VWS Envig is delivering an efficient, economical solution that meets the needs of the Ambatovy project.

For more information, please contact us:

Gerhard Vosloo
Deputy Project Manager - Design & Build Projects
VWS Envig
Tel.: +27 (0) 11 663 3600
Fax: +27 (0) 11 608 4772
Email