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Home >> Electrostatic Precipitators >> Glossary

Glossary of Terms used in ESPs      

Glossary

The following is a glossary of terminology used in electrostatic precipitators. It may be of assistance when discussing your issues with our technicians and engineers.

Electrostatic Precipitator Terminology


Collecting System The grounded (or earthed) 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 or Discharge 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.

h) Current density - The ratio of the transformer rectifier name plate secondary current to the collecting surface area. Normally reported in micro Amps per square metre (µA/m2)


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.

c) Migration Velocity - A figure, in centimetres per second, which is the average rate at which charged dust moves towards the collecting surface


Effective Precipitator Dimensions

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

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

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

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

e) Specific Collecting Area (SCA) - The ratio of the Collecting Surface Area (m2) to the actual gas volume (Am2/s). Normally reported in seconds per metre (s/m).


Construction

a) Gas Passage - The vertical chamber formed by two adjacent rows of collecting surfaces.

b) Chamber - A gas-tight longitudinal subdivision of a precipitator.  (An ESP without any internal dividing wall is a single chamber unit, whereas an ESP with a single internal dividing wall is a two chamber unit, etc.).

c) Sneakage Plates - Strips of steel used to prevent gas containing dust from flowing around the charged area of the ESP (i.e. between the collecting plates).


Parameters

gas Formless state of matter completely occupying any space.  Air is a gas.
Gas volume or
Volumetric flow rate
Usually expressed as quantity of gas 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.
acfm Actual cubic feet per minute.
scfm Standard cubic feet per minute is the volumetric flow rate of a gas corrected to "standardized" conditions of temperature and pressure. However, great care must be taken, as the "standard" conditions vary between definitions and should therefore always be checked. Worldwide, the "standard" condition for pressure is variously defined as an absolute pressure of 101.325 pascals, but the "standard" temperature is varies between definitions: 68°F, 60°F, 0°C, 15°C, 20°C or 25°C.
Pressure Pressure is the ratio of force to the area over which that force is distributed.
Pa Pascal - standard international (SI) unit of pressure equal to one Newton per square metre.  Can be followed by (a) = absolute pressure, or (g) = gauge pressure (pressure relative to atmosphere).
1 Pa = 10-3 kPa = 10-5 bar = 9.869210−6 atmospheres (atm) = 1.45037710−4 psi
kPa 1 Kilopascal = 1,000 Pa.  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.
Temperature Degrees Celsius.  Note, in most calculations temperature is expressed in absolute terms (Kelvin), i.e. °K = °C + 273.15
°C Degrees Celsius.  Note, in most calculations temperature is expressed in absolute terms (Kelvin), i.e. °K = °C + 273.15
Density The ratio of the mass of a specimen of a substance to the volume of the specimen.
kg/m3 The standard measure of density.  Also expressed as g/L and lb/ft3
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 gas at "N" conditions.
mg/Nm3 (dry) Weight of dust in a cubic metre of gas 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.
 


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