When considering the grinding process from an electro-physical perspective, grinding capacity can be improved by reducing the loss of mechanical energy in the comminution process, a process carried out by ECOFOR through its electro-neutraliser. Operational results from applications in ball mills and roller presses have not only show increased cement grinding capacity but also a reduction in specific electrical power consumption.
Just over two decades ago, Russia-based ECOFOR Co proposed a novel method to reduce specific power consumption in the cement grinding process: the ECOFOR (EF) grinding device. This technology prevents the electrisation of comminuted material and enables cement producers to increase mill capacity at the same level of electric power consumption. The grindability of the clinker improves while the aggregates of the smallest cement particles are also destroyed. Without the use of this technology, part of the elastic energy that is present during deformation of the material is used in the electrisation of the material. The use of the device enables this component of total energy used to intensify grinding.
Initially, the EF grinding device was used for ball mills with open and closed grinding systems. Its use resulted in a reduction of specific power consumption of 3kWh/t of cement. However, since 2000 EF technology has also been used on roller presses.
Roller press application
After switching on the EF device on the roller press (see Figure 1), the grindability of the electro-neutralised material starts to improve.
The transient process of reducing the pressure of the rollers and the power consumed by their motors begins. A 10-12 per cent reduction in power without loss of capacity of the roller press occurs after 15 minutes (see Figure 2).
The amplitude of the oscillations also decreases, thereby reducing the risk of roller vibration. Meanwhile, the quality of the semi-product remains unchanged.
This transient process of power change is characteristic in the absence of an automatic pressure control system of rollers. In this case, the EF device is used either to reduce power consumption or increase the capacity of the roller press by at least 10 per cent by manually returning the pressure and power to the former level.
Roller presses, working together with dynamic or static separators, are equipped by a modern automatic pressure control system. In these cases, with the EF device, the pressure and the power of the roller will automatically be returned to the former level. Power consumption and semi-product quality do not change, but the capacity of the roller press increases by at least 10 per cent. To meet the requirements set by the ball mill capacity, the dynamic separator rotor speed of the roller press increases by 2-5 per cent. After that, the specific surface area of the separated semi-product improves by 200-500cm2 /g, which offers potential for the further intensification of grinding.
Increase of V-separator efficiency
If a V-separator is used, the EF device will be connected to this separator in parallel with the roller press. As a result, the electrostatic component of the adhesion force is neutralised and separator efficiency improves. Without the EF device, the electrisation of crushed material would cause the adhesion of small particles to large particles. With the use of the EF device, the return of particles sized 1-100 µm to the roller press is reduced (see Figure 3).
At the same time the output of such particles to the finish mill increases. The share of material returned for recrushing in the roller press reduces by 20 per cent. The coordination of the capacity of the roller press and fresh feed to the ball mill results in a reduction in the speed of the separating airflow and/or a 7-10 per cent decrease in the roller speed. Due to this, the quality of the separated semi-product is also further improved. This improvement of the fractional composition of the separated semi-product after a dynamic or static separator is the key reason for improving the quality of the cement at the outlet of the dynamic separator of the ball mill. When the EF device is used only for the roller press and its separator, this leads to a six per cent increase in the entire grinding system’s capacity.
Combined grinding systems
Initially, the intensification method using the EF device was developed separately for roller presses and separators. Later on, for the intensification of the combined grinding systems, EF devices were simultaneously used not only for roller presses but for ball mills as well. The tests on combined systems did not exclude the use of grinding aids. Generally EF devices increased the capacity of such systems by 7-11 per cent. Combined grinding systems are most often used in the Turkish cement industry. The results of some tests are presented in Table 1.
Over the past three years, together with CET MAKINA Cimento, eight combined grinding systems in Turkey have been equipped with 20 EF devices. The system has proven to reduce specific power consumption by at least 3 kWh/t of cement, thereby reducing manufacturing costs. The EF device can be applied to any roller press, either new or existing, stand-alone or as part of a combined grinding system.