Sasol Nitro Calcium Ammonium Nitrate Plant, Secunda, South Africa
Key Data
Energy and chemical company Sasol Nitro is constructing a new calcium ammonium nitrate (CAN) production plant at its existing chemical complex in Secunda, South Africa. The plant will produce 400,000t of CAN fertiliser granules (27%N).
Construction of the plant started in May 2010 and is scheduled for completion and commissioning in August 2011. The total cost of the project is estimated to be approximately C$96m.
Sasol Nitro CAN plant contractors
In March 2010, Sasol Nitro awarded the engineering, procurement and construction management (EPCM) contract for the erection of the plant to SNC-Lavalin.
The project is being executed in collaboration SNC-Lavalin's local subsidiary in South Africa.
The company made a conceptual study for the project in 2008. The EPCM and basic engineering phase started in October 2009 before the award of the contract.
Plant design and construction
The Sasol Nitro CAN plant design is based on SNC-Lavalin technology for the production of CAN fertiliser grade. The granulation circuit will consist of a fluidised drum granulator (FDG), elevator, main screen, oversize hammer crusher, recycling dosing conveyor of final product, a roller crusher and small screen for the seeds.
The granulator will consist of a horizontally aligned cylindrical granulating drum, fitted internally with anti-clogging lifters.
The drum will rotate about its axis in a conventional manner, but differs from the conventional drum granulator by having an internal fluidised bed. It will comprise a flat, slightly inclined, perforated plate through which fluidising air is blown.
Feedstock and technology
Sasol Nitro's CAN plant will use ammonium nitrate at 85%, dolomite as filler and other utilities such as steam and cooling water as raw materials.
The CAN will be produced with a mixture of pure melted ammonium nitrate and dolomite. The production process will involve three steps:
- concentration of the ammonium nitrate solution
- granulation
- cooling and conditioning of the final product.
The concentration will be done in vertical evaporators. The concentrated melt will then be mixed with the filler and sent to a fluidised bed granulator designed by SNC-Lavalin's fertiliser division, which is based in Brussels, Belgium. The granulated product will finally be screened, cooled, coated and stored.
SNC-Lavalin process technology
In SNC-Lavalin technology, the 85% ammonium nitrate solution will be pumped to an evaporator working under vacuum. The resulting 90% ammonium nitrate solution will be pumped to a falling film evaporator (air-swept type) where it is concentrated to 98.5-99.5% melt. It will then flow to the remelt tank (homogeniser) where fines and dolomite are added and mixed. The remelt tank will be agitated and heated-up with internal coils to assist the melting of the fines. The solution will then be pumped to the FDG.
Seed material, which is recycle off-size, is fed to the granulator and subjected to the size enlargement and cooling. The process occurs in a progressively cyclical sequence.
The lifters raise the seed material to the upper part of the drum, where it falls onto the surface of the fluidised table and cooled. The product is sprayed with the feed melt in the lower part of the drum.
The coated granule is lifted back to the fluidised bed where the new surface layer solidifies by cooling or the evaporation of its moisture content. The same cycle is repeated to achieve the desired grain size. Product granules are sent to the fluidised bed coolers. The cooled product is then passed to a coating drum and finally sent to the storage unit.
The main advantage of the process is the simple granulator operation. The granule size can be modified by varying the air flow and the residence time in the granulator. The process has high granulation efficiency.
Due to the nature of granulation, Mg(NO3)2 can be added to the ammonium nitrate to stabilise it and reduce caking and dust formation during storage and transport due to thermal cycling.
