Electrostatic Precipitators

Summary

This presentation introduces electrostatic precipitators (ESPs) and their role in air pollution control. It explains how ESPs remove particles from gas streams by charging them and collecting them on grounded plates. The video covers the three common types of ESPs: dry negative Corona, wet negative Corona, and wet positive Corona, as well as their components, operating conditions, and causes of performance issues. It also discusses particle resistivity, performance monitoring, and how electrical data can indicate potential problems with ESPs, emphasizing safety and compliance during field inspections.

Takeaways

• 🔌 Electrostatic precipitators (ESPs) remove particles from gas streams by charging them and depositing them on grounded collection plates.
• ⚡ There are three common types of ESPs: dry negative corona, wet negative corona, and wet positive corona.
• 📊 Dry negative corona ESPs are the most common and are highly efficient, with collection efficiencies greater than 99%.
• ⚙️ The design of ESPs includes discharge electrodes, collection plates, gas distribution plates, and wrappers that help with cleaning.
• 🌡️ Particle resistivity plays a crucial role in the deposition and removal of particles from the collection plates, with moderate resistivity being ideal.
• 🚿 Wet negative corona ESPs are suitable for handling liquid particles or solids with low resistivity, often using water to wash particles from the plates.
• 🛠️ Proper operation of ESPs depends on maintaining optimal voltage, current, sparking rate, and wrapping cycle for maximum efficiency.
• ❌ Decreased performance in ESPs can result from issues such as misalignment, component failure, or shifts in particle resistivity.
• 🧑‍🔧 Field inspections and monitoring are important for assessing compliance, identifying issues, and ensuring efficient performance of ESP systems.
• ⚠️ Safety considerations, including risks of electrical shock, explosive hazards, and hot surfaces, must always be observed during ESP operations.

Q & A

What is the primary purpose of electrostatic precipitators (ESPs)?

The primary purpose of ESPs is to remove particles from a gas stream by charging them either positively or negatively and causing them to be deposited on grounded collection plates. They are used for air pollution control with collection efficiencies greater than 99%.

What are the three common types of electrostatic precipitators?

The three common types of electrostatic precipitators are dry negative corona ESP, wet negative corona ESP, and wet positive corona ESP.

How does a dry negative corona ESP work?

In a dry negative corona ESP, a high negative DC voltage is applied to discharge electrodes, creating a corona. This ionizes gas molecules, which then charge particles in the gas stream. Negatively charged particles are attracted to the grounded collection plates where they are deposited and removed.

What is particle resistivity and why is it important in ESP operation?

Particle resistivity is the ability of a particle to resist conducting electrical charge. It is important because it affects the deposition and removal of particles from collection plates. Particles with moderate resistivity are ideal because they conduct away some charge without inhibiting the deposition of other particles.

What happens if particles have very high or very low resistivity?

If particles have very high resistivity, they retain their charge, making it difficult to deposit more particles and remove them from the plate. If particles have very low resistivity, they quickly lose their charge and may be repelled back into the gas stream, reducing collection efficiency.

How can resistivity be controlled in an ESP?

Resistivity can be controlled by conditioning the particles. Methods include adding moisture to the gas stream, reducing temperature, or adding conditioning agents like SO3 or ammonia to form a conductive layer on the particle surface.

What is the purpose of the 'wrappers' in an ESP?

Wrappers are used to clean the collection plates, discharge electrodes, and gas distribution plates in an ESP. They do this either through mechanical impact or vibrations to remove accumulated particles.

What distinguishes wet negative corona ESPs from dry ESPs?

Wet negative corona ESPs are used in applications where liquid particles must be controlled or when particles have undesirable electrical or physical properties such as low resistivity. The collection surfaces are kept wet, often with recirculated water, to prevent particles from drying and hardening.

What are the safety considerations when working with electrostatic precipitators?

Safety considerations include the risk of electrical shock, explosive hazards, and hot surfaces. Personnel should never enter the inside of an ESP due to these dangers. Strict OSHA regulations, including confined space entry protocols (OSHA rule 29 CFR 1910.146), must be followed.

How can changes in the electrical data indicate issues in an ESP field?

Shifts in voltage, current, and sparking rates in a single field can indicate mechanical or electrical problems. For instance, a decrease in voltage with an increase in current and sparking rate may indicate misalignment, while a low sparking rate with high current suggests a short in the field.