ESP – Dust Controlling Equipment

Electrostatic Precipitator (ESP) is used to remove particulate/dust from the exhaust emission of many processing industries such as power plant (usually coal based), boiler (usually coal based), cement manufacturing, metal refining or smelting.

The fundamental principle to operate an ESP is that the dusty gas is passed through an electric field where the dust particles receive electrical charges. There are series of vertical parallel plates, called collecting electrode (CE), at ground potential and a series of discharging electrodes positioned midway between CEs. The discharge electrodes render electrons, generally referred corona discharge, which migrate under the influence of electric field into the inter electrode space. The gas-borne particles that pass through the inter electrode space receive an electric charge and then move under the influence of electric field towards collecting electrode. The charge subsequently leaks away to the ground. The collecting electrodes are mechanically hammered with certain interval to remove the deposited material.

The first use of corona (electric charge) to remove particles from an aerosol was by Hohlfeld in 1824. However, it was not commercialized until almost a century later. In 1907 Dr. Frederick G. Cottrell, a Professor of Chemistry at the University of California, Berkley, applied for a patent on a device for charging particles and then collecting them through electrostatic attraction — the first electrostatic precipitator.

Figure 1: Components of a typical ESP

The effectiveness of the dust removal depends upon operating conditions such as dust size, concentration, composition and distribution plus gas composition, temperature, volume and flow distribution.

Important Components
• Gas inlet nozzle
• Gas distribution (GD) screen
• Collecting electrode (CE) system
• CE rapping device
• Discharge electrode (DE) system
• DE rapping device
• Hopper
• Insulator heating
• High voltage transformer
• High tension (HT) set

ESP sizing and design
Deutsch formula is the base of ESP sizing. The efficiency describing equation of Deutsch is:

n = 1 – e-(AW/Q)
where,
A= Collecting surface area
W= Dust migration velocity (usually 7 to 12 cm/s)
Q= Gas flow through ESP

Assumptions for ESP sizing
• Design process parameters should be valid
• Gas flow should be uniform throughout the ESP cross- sectional area
• No fugitive/cold air entry to activate re-entrainment of dust
• Maintaining stable electric power supply
• Heated insulation to avoid dust build-up due to moisture condensation
• No frequent start/stop of the sequence

Usual problems encountered by ESP users

Any trouble to ESP means high dust emission. The common problems that are usually encountered by ESP users are
• High dust re-entrainment
• Sparking
• Back corona

Figure 2: An ESP at place (collected from internet)

Conclusion
The ESP should be handled with care as there is danger of high voltage electric field. It may explode due to mis-operation (e.g. allowing high CO formation). Only skilled operators should deal with operation and maintenance job of ESP. The OEM (original equipment manufacturer) provided sequence/instructions for ESP operation as well as maintenance shouldn’t be bypassed or violated.
 

 

To cite this article, please use following information:

(use the given format or any standard citation format)

Mohiuddin, M., ESP – Dust Controlling Equipment, ChE Thoughts 1 (1), 10-11, 2011.

 

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