System Integration & Control Systems Design

Hybrid Automation supplies control for fertiliser plant in Zimbabwe

December 2017 System Integration & Control Systems Design

Grow Agriculture is a significant industry player, manufacturing and distributing fertilisers and chemicals in Zimbabwe. Its client base includes the largest sugar estates, tobacco merchants, brewers and independent grain farmers in that country. Earlier this year the company purchased a new fertiliser blending plant for its Harare operation. The new facility is a batch blending system, whereby multiple fertiliser ingredients can be blended together with DDP micronutrients to formulate a range of different fertiliser products.

The batch blending system allows for an increase in the pace and number of products that can be produced while delivering more accurate production tolerances, thereby increasing efficiencies in the supply chain. The blending machine was built in South Africa and the automation and control was undertaken by Hybrid Automation.

The system includes five bulk weigh hoppers for major ingredients, three micro weigh hoppers for micronutrient ingredients, one dosing pump for liquid product, a conveyor to transport the ingredients, as well as bucket elevators to transfer product in and out of the paddle blender which blends the different ingredients. The paddle blender is the first of its type in Zimbabwe and can blend granular product, along with powdered micronutrients sourced from the USA, in a single process. This results in an extremely precise blended product that delivers better value to the Grow Agriculture client base.

The discharge of product from the hoppers is controlled by a combination of pneumatic gates and auger screw systems. The process and control of the system is managed by a Siemens ET200SP CPU and Flintec analog digitisers provide signals from load cells that are strategically mounted on the weigh hoppers. The Flintec device transfers data to the PLC via Profinet, and this data is then used to calibrate the weigh hoppers and determine the loss in weight when dosing product.

The motors for the micro hoppers and the bucket elevators are controlled by Siemens V20 variable speed drives (VSDs) required to operate at different speeds. Siemens soft starters control the conveyor and blender motors, to allow these motors to operate at a reduced load and torque in the power train and current surge of the motor at start-up.

The control and operation of the system is conducted by a Siemens KTP1200 touch screen, for a recipe-driven batching system process. This allows Grow to create recipes for different blends, and also allows it to select recipes for the system to run. A recipe can contain different ingredients from multiple weigh hoppers. When a recipe is selected and the process is started, product is dosed in a sequence onto a conveyor and then moved into the bucket elevator which transfers the ingredients into the paddle mixer, where the blend will be mixed and then discharged into a holding bin.

“The overall project was a tremendous success and was commissioned effortlessly in Zimbabwe. The client is very happy with the end results,” concludes Sachin Singh of Hybrid Automation.

For more information contact Sachin Singh, Hybrid Automation, +27 (0)31 573 2795,,


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