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Home » Electrostatic Precipitators » Glossary

Glossary

General
ESP
Bagfilter
General Terms
gas Formless state of matter completely occupying any space.  Air is a gas.
gas volume or volumetric flow rate

Usually expressed as quantity of air per unit of time.
A Prefix meaning the Actual gas conditions within the duct or vessel (including moisture content).
N Prefix meaning the "Normal" gas conditions which is the actual gas volume recalculated at 0?C and 101.325kPa.
dry (d) Flue gas volume expressed as a hypothetical value, where the water vapour in the gas is removed.
wet Flue gas volume including moisture.  Assume gas is wet unless stated otherwise.
Am3/hr or m3/hr

Actual cubic metres of gas per hour.
Am3/s or m3/s Actual cubic metres of gas per second.
Nm3/h

Flue gas volume expressed at "N" conditions.
Nm3/h dry Flue gas volume expressed at "N" conditions with water vapour removed.
kg mol Volume of permanent gases is 22.4136 m3 at 0?C, one atmosphere.
Pa Pascal ? unit of pressure.
kPa Kilopascal ? unit of pressure.  Note, in most calculations pressure is expressed in absolute terms i.e. kPa + 101.325.
WC (water column)
WG (water gauge)		 Unit of pressure, usually related to mm or inches.  In calculations WC + 760mm for metric or WC in inches Hg + 29.92 for imperial.
°C Degrees Celsius.  Note, in most calculations temperature is expressed in absolute terms (Kelvin), i.e. ?K = ?C + 273.
density The ratio of the mass of a specimen of a substance to the volume of the specimen.
Dust Concentration The weight of dust contained in a unit of gas.  The temperature and pressure of the gas must be specified, examples below.
g/Nm3 (mg/Nm3)

Weight of dust in a cubic metre of air at "N" conditions.

mg/Nm3 (dry)

 Weight of dust in a cubic metre of air at "N" conditions expressed as a dry condition.  Commonly used by EPA for outlet emission values.
particulate

Dust particles.
fume

Very fine particulate.
collection efficiency The weight of dust collected per unit time divided by the weight of dust entering the dust collector during the same unit time expressed in percentage.
hygroscopic particulate

Particulate that readily absorbs moisture.
incandescent particulate Particulate that is still alight or readily flames upon contact with oxygen, e.g. fly ash from wood fired boilers.
casing

Enveloping structure:

For rectangular configuration ? roof, sides, ends, hoppers and/or bottoms, gas inlet, gas outlet;

For cylindrical configurations ? gas inlet, gas outlet, hoppers and/or bottom, head, barrel shell.
 
Electrostatic Precipitator Terms
Collecting System The grounded portion of the precipitator to which the charged particles are driven and to which they adhere:

a) Collecting Surfaces ? The individual elements which make up the collecting system and which collectively provide the total area of the precipitator for the deposition of dust particles.

b) Collecting Surface Rapper ? A device for imparting vibration or shock to the collecting surface to dislodge the deposited particles or dust.

c) Collecting Surface Area - The total flat projected area of collecting surface exposed to the active electrostatic field (length x height x 2 x number of gas passages).
High Voltage System All parts of the precipitator which are maintained at a high potential:

a) High Voltage Structure ? The structural elements necessary to support the discharge electrodes in their relation to the collecting surfaces.

b) Discharge Electrode ? The part which is installed in the high voltage system to perform the function of ionizing the gas and/or creating the electric field.

c) Discharge Electrode Rapper ? A device for imparting vibration or shock to the discharge electrodes in order to dislodge dust accumulation.

d) High Voltage System Support Insulators ? A device to support physically and isolate electrically the high voltage system.

e) Rapper Insulators ? A device to isolate electrically, yet transmit mechanically, forces necessary to create vibration or shock in the high voltage system.
Electrical

a) Transformer-Rectifier ? A unit comprising a transformer for stepping up normal service voltages to voltages in the kilovolt range, and a rectifier operating at high voltage to convert AC to unidirectional current.

b) Primary Current ? Current in the transformer primary as measured by an AC ammeter.

c) Precipitator Current ? The rectified or unidirectional average current to the precipitator measured by a milliammeter in the ground leg of the rectifier.

d) Precipitator Voltage ? The average DC voltage between the high voltage system and grounded side of the precipitator.

e) Primary Voltage ? The voltage as indicated by an AC voltmeter across the primary of the transformer.

f) Spark ? A discharge from the high voltage system to the grounded system, self-extinguishing and of short duration.

g) Arc ? A discharge of substantial magnitude from the high voltage system to the grounded system, of relatively long duration and not tending to be immediately self-extinguishing.
Operational

a) Precipitator Gas Velocity ? A figure obtained by dividing the volume rate of gas flow through the precipitator by the effective cross-sectional area of the precipitator.

b) Treatment Time ? A figure, in seconds, obtained by dividing the effective in length in feet of a precipitator by the precipitator gas velocity figure calculated above.
Effective Precipitator Dimensions

a) Effective Length ? Total length of collecting surface measured in the direction of gas flow.

b) Effective Height ? Total height of collecting surface (as) measured from top to bottom.

c) Effective Width ? Total number of gas passages multiplied by centre to centre spacing of the collecting surfaces.

d) Effective Cross-Sectional Area ? Effective width times effective height.
Construction

a) Gas Passage ? Formed by two adjacent rows of collecting surfaces.

b) Chamber ? A gas-tight longitudinal subdivision of a precipitator a precipitator without any internal dividing wall is a single chamber unit a precipitator with a single internal dividing wall is a two chamber unit, etc.).
Bagfilter Terms

Fabric Filter, Bag Filter, Baghouse

 A box containing fabric material as a filtration medium

Reverse Air or Reverse Flow

 A fabric filter where a compartment is isolated and low pressure air passes through the fabric in the reverse direction to normal air flow.

Reverse Jet or Reverse Pulse

 A fabric filter where a shot of high pressure compressed air passes through the fabric of one row of bags in the reverse direction to normal air flow.

Shaker

 A fabric filter where a compartment is isolated and the bags of that compartment are shaken by mechanical means.

Particulate

 Dust particles.

Fume

 Very fine particulate.

Tube Sheet

 Metal sheet to which bags or other collection media are attached.

Bag

 Material formed into a shape usually cylindrical, open at one end and capped at the other end.
Cage Structure for support of the bag to prevent collapse under normal air flow conditions.
Diaphragm Valve Pneumatically operated valve connected between the filter air header and the blow pipe.
Pilot Valve Small electrically operated unloading valve to operate the diaphragm valve.
Blow Pipe Pipe running over the top of a row of bags with outlet holes over the centre of each open bag top.
Air Header Manifold for connection of all the diaphragm valves serving the filter.
Snap Cuff Metal band at the open end of a bag for snap fitting into the tube sheet.
Cell

Isolatable section of a filter system.
Module Transportable filter box.  May be an isolatable section of a filter system.
Filtration Velocity Commonly expressed in terms of m/min or mVelocity of air through the filter medium.  /sec or (m3/min)/m2.
Air to Cloth Ratio As for Filtration Velocity.  Commonly used in imperial system e.g. ratio = 5:1, based on acfm/sq ft.
Demand Cleaning Cleaning cycle is initiated upon pressure differential across filter medium.
Timed Cleaning Cleaning by set time periods only
Forward Pressure Pressure differential across the filter medium as a result of normal air flow.
Reverse Pulse Pressure

Pressure generated by reverse thrust of air.
Hygroscopic Particulate Particulate that readily absorbs moisture.
Incandescent Particulate Particulate that is still alight or readily flames upon contact with oxygen, e.g. fly ash from wood fired boilers.
Ceramic Element Filter medium manufactured from ceramic based materials.
Metallic Element Filter medium manufactured from metallic fibres or powders.


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