Collection efficiency is the primary consideration of ESP design. The collection efficiency and/or the collection area of an ESP can be estimated using several equations. These equations give a theoretical estimate of the overall collection efficiency of the unit operating under ideal conditions. Unfortunately, a number of operating parameters can adversely affect the collection efficiency of the precipitator. A discussion of collectionefficiency equations and operating parameters affecting collection-efficiency equations follows.
Particle-Migration Velocity
Before determining the collection area and the collection efficiency, the designer must estimate or measure (if possible) the particle-migration velocity. This is the speed at which a particle, once charged, migrates toward the grounded collection electrode. Variables affecting particle velocity are particle size, the strength of the electric field, and the viscosity of the gas. How readily the charged particles move to the collection electrode is denoted by the symbol, w, called the particle-migration velocity, or drift velocity. The migration-velocity parameter represents the collectability of the particle within the confines of a specific ESP. The migration velocity is expressed in Equation
Before determining the collection area and the collection efficiency, the designer must estimate or measure (if possible) the particle-migration velocity. This is the speed at which a particle, once charged, migrates toward the grounded collection electrode. Variables affecting particle velocity are particle size, the strength of the electric field, and the viscosity of the gas. How readily the charged particles move to the collection electrode is denoted by the symbol, w, called the particle-migration velocity, or drift velocity. The migration-velocity parameter represents the collectability of the particle within the confines of a specific ESP. The migration velocity is expressed in Equation
equation 1
migration velocity depends on the voltage strength of both the charging and collection fields. Therefore, the precipitator must be designed using the maximum electric field voltage for maximum collection efficiency. The migration velocity also depends on particle size; larger particles are collected more easily than smaller ones.
Particle-migration velocity can also be determined by Equation
equation 2
jThe particle-migration velocity can be calculated using either Equations 1 or 2, depending on the information available on the particle size and electric field strength. However, most ESPs are designed using a particle-migration velocity based on field experience rather than theory. Typical particle migration velocity rates, such as those listed in Table
Typical effective particle-migration velocity rates for various applications
Typical effective particle-migration velocity rates for various applications
0 comments:
Post a Comment