Air Pollution Control Technologies: Electrostatic Precipitators (ESP)
Air pollution control (APC) systems are crucial for minimising SPM and gaseous pollutants from industrial processes, thus protecting the environment and human health. Among these devices, Electrostatic Precipitators (ESP) stand out due to their high efficiency low-pressure drop, and comparatively reduced maintenance compared to other types of dust collectors. Techflow Enterprises Private Limited (TEPL) a leading OEM in air pollution control solutions, specializes in the design, manufacture, and supply of state-of-the-art ESPs, ensuring cleaner air for a sustainable future, particularly in the coal (imported and indigenous) and biomass-fired boilers and thermic fluid heaters.
Principle of Operation
The operation of an Electrostatic Precipitator is based on the principle of electrostatic force. It involves charging the particulate matter in the gas stream and then collecting these charged particles on ground collecting plates by electrostatic forces. Here’s a step-by-step breakdown of the process:
- Ionization: As the flue gas enters the ESP, it passes through a region where high-voltage discharge electrodes emit corona (negatively charged electrons) and also ionised the flue gases.
- Charging: The dust particles (SPM) thus get negatively charged by ions and electrons particles acquire a negative or positive charge. Once negatively charged, the dust particles then start moving towards collecting electrodes which are at earth potential under the effect of electrostatic forces.
- Collection: The charged particles are then attracted to collecting plates and then ultimately hand over their charges to collecting plates forming a layer of dust cake.
- Cleaning: Periodically, the collected particles in the dust cake are removed from the plates by rapping or vibrating the collecting plates causing the particles to fall into hoppers for dust disposal.
The following parts referred to as ESP internals responsible for the proper functioning of an ESP
- Discharge Electrodes: Emitting electrons/Corona to charge the dust particles. Typically made from high-quality, corrosion-resistant materials like stainless steel or high Chromium Carbon Steel. These electrodes may be spiralised wires at various levels over the height of the electrodes, rigid mast type, rigid pipe and spike type hung from the emitting frame with more than one level, if necessary.
- Collecting Plates: These plates are usually manufactured from cold rolled cold annealed (CRCA) carbon steel as per IS 513, Grade D with thickness ranging between 1.2 to 1.5mm. Since it is made in one piece (top to bottom), to increase the rigidity of the electrodes
- Rapping System: This is required for shearing the dust cake from collection plates as well as for removing the dust particles from the spikes of discharge electrodes at pre-determined and adjustable frequencies. Rappers can be of several types, like MIGI (Electromagnetic Gravity impact) or Tumbling Hammer Type (TH)
- Gas Distribution System: Ensure uniform gas velocity across the cross-section (between 0.4m/sec to 1.2m sec) of the ESP. It is usually made from 2.5 to 3.0mm carbon steel plates with a circular hole of 8-inch diameter punched-in plates. The configuration of punching holes on the GD screen is determined by CFD analysis. There are 2 GD screens at the inlet and one screen at the outlet of the ESP. The GD screens at the inlet are also provided with MIGI/TH-type rappers.
- High-Voltage Power Supply: Provides the necessary electric field. This system includes high Voltage Transformers (DC) with rectifiers (T/R Set) designed to deliver stable and adjustable DC voltage and current to the individual field of the ESP T/R unit is hermetically sealed without a conservator and b The rectifier is a full-wave bridge type. Each T/R set is provided with a microprocessor-based semi-pulse controller. The power supply to the primary side of the T/R set is single-phase AC under normal conditions. However, with very fine specks of dust, we sometimes provide a 3-phase T/R set.
There are two types of ESPs
- Dry horizontal plate type (Collecting) ESP with 1,2,3,4 and more no of Fields.
- Wet ESPs: Designed for removing Tar and acid Mist from Coke oven gas, Producer gas in Steel Plants and also from Copper, Aluminium and Zinc Smelters. These are cylindrical types with only one field and Efficiency below 98%
Electrostatic precipitators (ESP) – 1
Electrostatic precipitators (ESP) – 2
TECHFLOW at present involved in the design and manufacturing of dry horizontal plate-type ESP for Emission control.
Comparative Analysis
When compared to other air pollution control devices like bag filters, Wet Scrubbers, and cyclones, Electrostatic Precipitators offer several advantages:
- Capable of achieving over 99% removal efficiency with particle sizes less than 10 microns.
However, to achieve efficiency less than 20mgm/nm3 (present-day emission standard), the cost of ESP will be higher (due to more nos of Fields) compared to bag filters.
- ESP pressure drop is 25mmwg as against 150mmwg for bag filter,80mmwg for wet scrubber and 40mmwg against multi cyclones. Thus, ID fan power consumption will be lowest in the case of ESP
- Dust disposal in case of ESP and bag filter will be dry discharge like screw conveyor or pneumatic conveying system. In the case of wet scrubber handling of slurry disposal will be a problem.
- Dust resistivity plays a big role in case ESP sizing, thus ESP sizing will depend on the type of coal/fuel used apart from gas volume, dust burden and operating temperature whereas bag filter efficiency does not depend on coal/fuel type.
- Operating temperature plays a big role in the case of the selection of bag material and is restricted up to 200 degrees C, whereas in the case of ESP, for temperatures above 250 degrees C, we can offer hot ESP with lesser efficiency.
- Maintenance cost is much less in ESP compared to bag filters where you need to change 100% of bags after every 2 years
- Thus, with ESP you have to incur high capex with low maintenance as against bag filter, where capex will be less but running maintenance cost will be much higher
Case Study: Overcoming Major Challenges
Techflow ESP 3D Section view
Input parameters
Type and Capacity of Boiler: AFBC,20TPH
Flow: 51000m3/hr
Fuel: Imported coal /Rice Husk/ other Biomass
Moisture content in Flue Gas(v/v): 25%
Operating temp: 180degc
Inlet dust Burden: 28gm/nm3
Outlet emission: 50mgm/nm3
ESP Efficiency: 99.82%
ESP Design
No of fields: 4
Field lengths: 3.5m
Field Height: 7.0m
No of GPs: 10,400mm width
No of CE: 308 [500mm width, Inverted ‘C’ Profile]
No of DE: 280 (Pipe & Spike)
Rapping System: Tumbling Hammer
No of T/R Sets: 4 Nos, 110KV (Peak) / 200Ma (mean)
Outlook for ESPs in Pollution Control
The future of ESPs in air pollution control for boilers and thermic fluid heaters is promising, with advancements in technology and stricter environmental regulations driving their adoption. Techflow is at the forefront of this evolution, continuously innovating to enhance the efficiency and reliability of ESPs, have a look at Techflow’s ESPs in Pollution control.
Emerging trends include:
- Integration with IoT: Utilizing smart sensors and data analytics for real-time monitoring and optimization by installing an opacity meter in the stack for continuous emission monitoring in-house and also by the local pollution control board. installation of ESP management system (EPMS)
- Hybrid Systems: Combining ESPs with other pollution control devices, Like wet scrubber/MDC, for enhanced performance. This is particularly useful in applications with varying dust loads.
- Regulatory Compliance: As emission norms become stricter, ESPs will play a crucial role in helping industries meet these standards efficiently.
Conclusion
Electrostatic Precipitators are a cornerstone in the realm of air pollution control, and Techflow Enterprises Private Limited stands as a leader in this field. With their expertise and commitment to innovation, Techflow ensures that industries can meet environmental standards while maintaining operational efficiency. As the demand for cleaner air continues to rise, Techflow’s ESP will play a vital role in safeguarding our environment for future generations.
For more information on Techflow’s cutting-edge ESP solutions, visit our website Techflow Enterprises Private Limited
Techflow ESP – 2D
Author:
Mr Monil Parikh
Managing Director
Techflow Enterprises Pvt. Ltd.
