Electrostatic precipitators (ESP) have long been the preferred equipment for dedusting the large volume of gases produced during industrial processes. However, an ESP’s dust collection efficiency depends on the dust’s electrical resistivity – if it’s too high the ESP’s performance is dramatically reduced. To overcome this problem, FLSmidth designed the COROMAX® pulse system. Now in its fourth generation, the compact COROMAX reduces ESP dust outlet emissions by 50 percent and cuts power consumption by up to 30 percent in high resistivity dust applications.
As air pollution control regulations get tougher, minerals and other heavy industries have to find new and better ways to reduce their particulate emissions. Electrostatic precipitators are the most popular method used to control dust emissions. Conditions such as low humidity, very fine dust particles, high hydrocarbon levels and high resistivity can make the dust difficult to collect, which severely impedes the ESP’s operational efficiency.
In an ESP, airborne dust is designed to flow between rows of electrodes and collecting plates. A high voltage transformer is connected to the electrodes. When a high voltage current is applied, electrons charge the dust with electrical energy, which causes the dust to move to the collecting plates. The collecting efficiency depends on various factors, such as the size of dust particles, the high voltage peak value and its mean value. If dust resistivity is high, the maximum obtainable voltage level in the precipitator is limited to the level where back corona occurs. Back corona is a phenomenon where positive ions in the dust layer on the collecting plates are released back into the air, which eliminates the charge on the dust particles. Without this charge, the dust particles can’t be removed from the gas stream. This leads to higher dust emissions and increased power consumption.
Increase of ESP efficiency
When dust emissions exceed permitted levels, ESP efficiency must be improved. One solution is to build a larger precipitator. This option takes up more space, requires a plant shutdown – and it’s expensive. A more effective solution is to replace the traditional DC power supply with an FLSmidth® COROMAX® pulse system. This not only keeps plant downtime to a minimum during installation, it also dramatically reduces power consumption by almost 30 percent and emissions by half.
Independent mean and peak voltage control
The first FLSmidth COROMAX pulse system was delivered in 1985. An important advance in dust emission technology, the COROMAX pulse system superimposes an extremely narrow high voltage pulse (up to 80 kV) lasting 75 microseconds, on to a base voltage of up to 60 kV. This creates a total peak or pulse voltage of approximately 135 kV, almost double the voltage of a normal DC supply.
Another unique benefit of the COROMAX pulse system power supply is that the voltage and the current can be controlled independently. In a normal DC power supply, they can’t. If dust resistivity is high, voltage can only reach a certain level before back corona occurs – and this level is far below what’s necessary for efficient precipitation.
With the COROMAX pulse system, it’s easy to carry out precise voltage adjustments to match the level of dust resistivity. The peak voltage is significantly higher and has a shorter interval than the peak created with a DC power supply. Because the current is only released in short, intense pulses, the ESP does not experience back corona, which impedes efficiency. In addition, the charge is fully utilised in the precipitation process and not partially wasted as with conventional DC supplies. Therefore power consumption is reduced. During plant operation, changes in the raw material composition, dust recirculation, particle size, temperature, humidity, dust load and resistivity require adjustments to the base voltage, pulse voltage and current. Because the COROMAX pulse system gives operators the flexibility to alter the voltage and current to suit present operating conditions, the dust collection process remains stable.
More value for your money
For either ESP upgrades or new installations for high dust resistivity applications, the COROMAX pulse system improves performance. For existing ESPs, a COROMAX retrofit can improve ESP performance without the need to increase the ESP’s size. And for new installations, a smaller ESP can be installed, which means lower installation costs.
Power consumption savings
Increasing the performance of your new or existing air pollution control equipment with a COROMAX pulse system not only saves money. It also reduces the length of time your plant is out of commission.
Small, versatile and efficient, COROMAX pulse system is a smart way to capture high resistivity dust and avoid back corona. Easily installed on the roof of the ESP, COROMAX pulse system takes up little space, reduces plant power consumption and cuts dust emissions. Thisis great news for the industry and for the environment.
We’ve recently installed and retrofitted COROMAX pulse systems for:
- TATA Steel, India (awarded in 2010)
- ArcelorMittal Galati, Romania
- Usiminas Cosipa, Brazil
- China Steel, Taiwan
- BlueScope Steel, Australia
- POSCO, South Korea
- CSA Sepetiba, Brazil
CONTACT: Karsten S. Poulsen