Spirit of permanent improvementAutomated sinter plant operation
Each year, the sinter plants produce 6.3 million tonnes of sinter. The ore mixture is further mixed with coke breeze and limestone, after which the total mixture is baked. The sintering process runs in two identical, fully automated plants monitored from one central control room.
PLC units control these plants so that they operate regularly and to the optimum. This creates regularity in the process, in the quality of the sinter product and in the operation of the dedusting installations.
The slightest defect in this huge automated chain can cause an outage in the entire line. The challenge for the production and maintenance people is to prevent such defects:
Recording monitored process data
- Preventive and predictive electrical and mechanical maintenance gives us a very dependable installation.
- Thoroughly studying malfunctions and defects creates a spirit of permanent improvement.
- Using the most modern PLC technology.
- Close cooperation between the different maintenance and production sections of sinter plants and the raw materials department.
- Troubleshooting and permanent improvement.
By analogy with the blast furnace, the sinter plants have a complete process monitoring system including process data visualisation. These data are transferred regularly (e.g. once a minute) to the regional process computer, where they are recorded and used as a calculating basis for derived process magnitudes. There are some 500 monitoring points per sinter plant.
The time data are also transferred to the user centre as long-term history. This enables reporting and statistical process studies.
Monitoring burn-through point
The central baking fan generates a uniform underpressure in the wind boxes under the top run of the chain. Fresh air from the surroundings is fed into the charge above the combustion zone. The air is preheated when passing through the zone with the newly formed sinter. The combustion gases are conveyed away through the charge thereby taking the underlying mixture layer up to ignition temperature.
This heat exchanging system means that, once the combustion in the upper layer is well under way, it moves on downwards while the sinter conveyor gradually advances and tips off the newly formed sinter at the end of the chain.
The baking process is monitored based on the temperature trend of the exiting flue gases as measured in the wind boxes. The chain speed is varied, either automatically or by the operator, in such a way that the combustion zone reaches the strand in the penultimate wind box. This point is called the burn-through point. It corresponds with the maximum temperature, which can be observed on the temperature graph.
Based on measurement point recording, it becomes possible to facilitate monitoring the burn-through point and to report it graphically from the regional process computer. Properly monitoring the charging of the chain with mixture (cleanliness of strike-off plate, cleaning dosing roller, incline position) and good ignition make it possible to lay the burn-through point more uniformly. This makes sintering more regularly, benefiting both sinter quality and fuel consumption.
Annually, the sinter plants produce 6.5 million tonnes of net sinter with a fuel consumption of 60 kg coke or anthracite per tonne of net sinter. So a small fuel saving (typically -1 kg/tonne of sinter) always represents a significant saving in energy and cost.
By way of illustration, the example below shows a good and a less good distribution of the burn-through point.