High Voltage ESP

PEAK performance from your ESPs with ModuPower® MPX

High-frequency switch mode power supply


Electrostatic precipitators (ESPs) are expected to run at ever-lower emission limits. That means there is no margin for error in maintenance and operations. With our comprehensive knowledge and expertise in ESP power supplies, controls and hardware, we make ESP processes work to optimum effect – whatever the challenge.

Simple in concept, difficult in reality

ESP operation is very straightforward in principle. Particles to be removed from the gas stream are charged by a series of high-voltage electric discharge electrodes to produce negatively charged ions (corona discharge) that charge the particles in the flue gas, providing the driving force for moving particles to the collecting plates. Next, plates stationed parallel and on each side of the gas stream are grounded to attract and accumulate the negatively charged particles in cake-like layers on the plate surface. Finally, the particulate matter is removed from the plates by mechanical rappers, causing the material to fall into collection hoppers out of which it is disposed or recycled. The ESP removal efficiency is highly dependent on the voltage differential between the discharge electrode (Eo) and the collection plate (Ep). The typical ESP operates at a voltage in the range of 30 kV to 100 kV.

There are several upgrade alternatives available to plant owners who need to increase the particulate removal capacity of an ESP, or to boost the performance of an otherwise underperforming unit. End users can increase collecting surface area, improve flow distribution entering the ESP, or upgrade/replace the collection plates or discharge electrodes. Each of these options requires extensive physical changes to each stage of the ESP and necessitates an extended unit outage at significant cost.

The old type power supply system for an ESP consists of the transformer-rectifier (TR) set, current-limiting reactor (CLR), and silicone-controlled rectifier (SCR) that produce the high voltage power source for the discharge electrodes. The TR set is a high voltage transformer and rectifier that converts single-phase AC power to single-phase DC power with approximately 30-40% ripple in the output voltage waveform due to the 50/60 Hz operating frequency. The CLR provides current limiting during transient overload (sparking) conditions. The SCR regulates the voltage into the TR set to adjust the output voltage and current to the ESP. Separate conventional power systems are used on each ESP stage (sometimes each lane in a field) in order to optimize individual field performance.

Anatomy of the ModuPower™ SMPS

Often a less intrusive, quicker, and more cost-effective solution for improving ESP performance can be realized by replacing a conventional power supply system with a high-frequency switch-mode power supply (SMPS) that converts 50/60 Hz power to low ripple DC with output waveform ripple below 3 percent. The reduced ripple in the output voltage allows the SMPS to produce a higher average output voltage (Eo), which in turn produces higher collection efficiency. The typical voltage output from the SMPS, usually determined by the ESP plate spacing, discharge electrode type, and particle resistivity, ranges from 50 kV to 120 kV with improved spark handling. The SMPS also has a faster spark and arc response time—microseconds instead of milliseconds—that reduces power dissipated in sparks and arcs, as well as wear on power feed components and ESP internals.

An SMPS upgrade has two principal benefits, which are dependent on how the unit is operated:

The first benefit is an improvement in ESP collection efficiency when less particulate emission is desired. This is made possible because the SMPS puts more power (increased Eo) into the ESP, resulting in higher collection efficiency.

The second benefit can be realized by plant owners who desire a unit in which less ESP auxiliary power is used in order to either improve unit heat rate or increase sellable power to the grid. In this option, the SMPS replaces the inefficient conventional power systems used on an ESP that is operating with acceptable collection efficiency by limiting the power output to that of the TR and CLR it replaces. The SMPS operates at greater than 90% power efficiency compared to the TR, which generally operates at less than 60%. For the same power input into the ESP (and the same ESP collection efficiency), a ModuPower SMPS can reduce auxiliary power use by 30-40%.