Electrostatic precipitators
Magnetic-impulse-gravity rapper
Also known as MIGI rapper, MIGI, American-style rapper, top rapper.
A magnetic-impulse-gravity (MIGI) rapper uses an electromagnet to lift a steel plunger and then release it, letting the plunger fall under gravity onto an anvil rod that conducts the impact down into the collecting-electrode frame. It is the dominant rapper design in American-style ESPs from suppliers including B&W, Mitsubishi Heavy Industries, Hamon Research-Cottrell, and Siemens / KC Cottrell legacy designs.
Operation
A MIGI rapper is normally mounted on the ESP penthouse above the plate stack. Plunger lift, drop height and firing frequency are programmed in the rapper-controller PLC, with each rapper firing in sequence across the field. Compared with tumbling-hammer designs, the MIGI rapper offers individual plate targeting and easy tuning of impact intensity, but at the cost of greater electrical infrastructure and a more complex top-of-ESP layout.
Where sonic horns complement MIGI rappers
MIGI rappers excel at the top of the plate but lose impact transmission towards the bottom. Sonic horns installed on the penthouse cover the upper plate volume and discharge electrodes; horns mounted at the hopper wall cover the bottom region. The combination defends against both back-corona and hopper bridging that MIGI rapping alone leaves vulnerable.
Related terms
Related terms
- ESP rapperAn ESP rapper is the mechanical hammer or magnetic impulse device used to dislodge accumulated dust from ESP plates and discharge electrodes. Sonic horns complement and partly replace this duty.
- Tumbling-hammer rapperA tumbling-hammer rapper uses a rotating shaft and weighted hammers that strike anvils on the ESP plate frame. It is the dominant rapper design in European-style ESPs.
- Electrostatic precipitatorAn ESP removes particulate from flue gas by charging dust and collecting it on plate electrodes. Sonic horns are widely used to dislodge ash from plates and to keep hoppers from bridging.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.