During August 2012, 18 SAIMC members from Chingola together with five members from Kitwe & Mufulira travelled to Lusaka to visit the Lafarge chemical plant. The entourage was led by Jones Kalela, Leo Chikasa and Victor Kameli.
The plant tour was hosted by plant chairman Andrew Sikwese who welcomed SAIMC members along with students from Lusaka Technical College. This was followed by a safety induction from the plant manager, before we went onto the plant in groups of eight.
Process cycle
Raw material and preparation
Limestone, hauled by 35-ton trucks from an open pit 9 km from the plant is crushed and then transported on conveyor belts to a storage shed. In the storage a stacker, a reclaimer machine blends lime stone rock as well as phylite and coal in respective sheds. Raw cement is made of a mixture of limestone with phyrite, mined next to old Chilanga, plus bauxite which is outsourced. The raw mixture is moved on conveyors through weigh feeders into a ball mill of 151 t/hr capacity which grinds the material into powder. Pulverised material called kiln feed is dried by excess heat from the kiln.
Burning and chemical reaction
In the pre-heater tower, powdered kiln feed is heated to 950°C. The pre-heater has a coal fired burner to de-carbonate the material. At the bottom of the tower, material enters the rotary kiln where the main coal fired burner heats it to 1450°C. Powdered kiln feed is heated close to melting point to form a material called clinker which is then cooled quickly before final grinding into cement.
Cement grinding
Cooled clinker is moved into the cement mill where it is mixed with gypsum through weigh feeders and then crushed into cement. Two types of cement are made – SupaSet and Mphamvu – by varying the proportions of clinker and gypsum. The mill is driven by a 5 MW motor and grinds cement at 140 t/hr. The plant silo holds 10 000 tons of cement which is packed into 50 kg bags for transport by rail and trucks. More than 3000 tons are dispatched every day.
The entire cement process from crushing to shipping is monitored and controlled through a computerised control room. The control philosophy is a Siemens PCS7 scada with a separate server room.
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