Intro
When choosing an air cleaning system for industrial enterprises a frequently asked question is, which type of filter is more preferable: a bag filter or an electrostatic precipitator. Both options have their advantages and disadvantages, which depend on the specific operating conditions, the type and amount of suspended particles in the purified air and the requirements for air purification.
The M HEAVY TECHNOLOGY team has helped reduce emissions of harmful substances into the atmosphere to acceptable standards at more than 100 metallurgical, mining and power generating enterprises of Ukraine and Europe. In each specific case the choice of dust catching equipment is individually calculated by specialists.
In this article we will provide insight of the main characteristics and features of each type of filter and help you make a conscious choice in favor of the most effective solution for your task.
What Is an ESP and How Does It Work?
“An electrostatic precipitator is a device for cleaning process gases or aspiration air of solid or liquid particles, the operating principle of which is based on the use of an electrostatic charge.
An electrostatic precipitator is is a housing that reliably protects a system of metal plates between which electrodes are located. These components create a difference of potentials, in the range of several kilovolts to tens of kilovolts. Dirty air passes through the space between the plates of the corona and collection electrodes, and dust particles and other small pollutants get an electric charge under the influence of ions of the electric field. Charged particles are attracted to the plates by the electric field and settle on them, and it makes it possible to clear the air of pollutants. Dust that accumulates on the plates is rapped into bins located under the filter housing.
Electrostatic precipitator design.
The electrostatic precipitator consists of the following key elements:
✔️ The sealed housing protects the internal components and prevents emissions of contaminated gases into the atmosphere.
✔️ Ionizer. A system of electrodes that creates a high-voltage electric field and charges dust particles with ions.
✔️ Dust catching section. Collection electrodes, which have an opposite charge and attract the dust particles, charged in the ionizer.
✔️ Cleaning system for collecting electrodes. A mechanism for removing particles, accumulated on the electrodes. It bincludes rapping devices or flushing systems. Rapping is performed by means of hammers or vibrators attached to the electrodes.
The electrostatic precipitator system also includes:
✔️ A high voltage source. It is an electrical system that supplies high voltage to the ionizer and collection electrodes. It typically consists of transformers and rectifiers.
✔️ Input and output pipe sockets. They are pipe sockets for feeding contaminated gases into the electrostatic precipitator and for output of purified gas.
✔️ Control system. It consists of electronic and automatic devices that control operation of the electrostatic precipitator, the voltage and the cleaning process of the electrodes.
Pros of ESP
The main advantages of using electrostatic precipitators are:
1. High cleaning efficiency.
Electrostatic precipitators are capable of removing fine particles with an efficiency of up to 99%, which is especially important for metallurgical industry, where flue gas emissions often contain fine dust particles.
2. High productivity.
An electric filter can clean large volumes of air with a high degree of pollution, providing reliable cleaning for various types of industries, such as thermal power plants and metallurgical units.
3. Energy efficiency.
Despite the need of application of high-voltage equipment, electrostatic precipitators can be called energy-efficient due to the possibility of using fans of lower power unlike other cleaning methods. It is due to the aerodynamic resistance of electrostatic precipitators (300 … 500 Pa) in comparison to bag filters (1500 … 2500 Pa).
4. Long service life.
Electrostatic precipitators are highly wear-resistant and durable and have operating efficiently over a long period of time.
5. Ability to work at high temperatures.
Metallurgical industry and thermal power plants are often a source of high-temperature gas emissions, and electrostatic precipitators are able to operate under these conditions without loss of efficiency.
6. Ability to work with pollutants.
Electrostatic precipitators can effectively capture both solid particles and liquid droplets, making them a versatile solution for various types of emissions in metallurgical industry.
7. Modular design.
Ability to scale and adapt the design of electrostatic precipitators to specific production needs allows for efficient solutions of cleaning problems at enterprises of various sizes.
The use of electrostatic precipitators in metallurgy not only helps to ensure a cleaner production, but also to reduce the environmental impact, which is important both for compliance with legislation and for maintaining the sustainable development of enterprises.
Cons of ESP
Despite all the variety of advantages electrostatic filters have a number of disadvantages as well, which are:
1. High equipment and installation costs.
Installation of electrostatic precipitators requires significant initial investments, which include the cost of the equipment itself, installation and connection to a high-voltage system.
2. The need for a constant source of electrical power.
Operation of electric filters requires the presence of a high voltage direct current power supply unit.
The power supply unit includes a step-up transformer, a semiconductor rectifier, a voltage regulator and a control panel. The voltage regulator maintains the voltage at the maximum pre-breakdown level. The breakdown voltage, which depends on many factors and primarily on the size and parameters of the dust and gas flow, fluctuates within significant limits. Therefore, the efficiency of the electrostatic precipitator largely depends on the regulator.
3. Dependence on dust level.
At high concentrations of fine particles the efficiency of electrostatic precipitators may decrease.
In addition to particle size electrical resistivity is also important for effective dust catching.
There are three groups electrical resistivity:
1) low-resistance dusts – electrical resistivity is below 104 Ohm*cm. When settling dust particles instantly give up their charge and can be carried away again by the flow if their adhesive properties are low;
2) well-seperating dusts with resistivity from 104 to 1010 Ohm*cm.
The rate of their discharge is such that it allows for formation of sediment on the electrodes, which is rapped into the bin;3) high-ohmic dusts — the resistivity is higher than 1010-1011 Ohm*cm. The difficulty of capturing dust of this group in an electrostatic precipitator is caused by formation of the so-called “reverse” corona in the microcracks of the deposited layer. The breakdown voltage, the charge of the particles, and the efficiency of catching accordingly are sharply reduced in this case.
Application of ESPs.
Electrostatic precipitators are used for cleaning gases with temperatures up to 2500C with acceptable vacuum inside the housing of up to 0.5 kPa.
Due to high degree of purification electrostatic precipitators find application in almost all branches of industry: metallurgical, chemical, power generating, cement industry and others.
What Are Baghouse Dust Filters and How Do They Work?
A bag filter is a device for cleaning air or gases of solid particles, which uses a porous material, most often fabric or non-woven fabric to trap contaminants.
The principle of operation of a bag filter is based on mechanical filtration. Dusty air or gas passes through a porous material that retains solid particles on its surface or in its thickness, and clean air or gas passes through the filter and is discharged outside.
Main components of a bag filter:
✔️ Housing: usually metal or plastic, containing filter elements and providing for the system tightness.
✔️ Filter bags: porous bags made of fabric or non-woven material that serve as filter elements.
✔️ Air ducts: help direct air or gas through the filter.
✔️ Cleaning mechanism: for removing contaminants from the surface of the bags (usually carried out by vibration, compressed air supply or mechanical rapping).
Pros of a Bag Filter.
The main advantages of bag filters are:
▪️ Cost effectiveness.
Bag filters are a cost-effective solution due to their relatively low installation costs.
▪️ Easy installation
▪️ High degree of purification
▪️ Ability to work under high temperatures and in conditions of high concentrations of contaminants.
Cons of Bag Filter.
Despite numerous advantages the use of bag filters has several disadvantages:
Need of regular maintenance and replacement of filter elements.
The frequency of filter bag replacement and maintenance requirements can result in high operating costs, especially under heavy use conditions. Filter cleaning procedures can be labor intensive and have special requirement to remove dust, such as compressed air supply for bag regeneration systems or backwash systems, as well as process shutdowns, which can cause downtime and reduced productivity.
Temperature and chemical resistance limitations.
Although bag filters can operate at high temperatures, there are limitations to the maximum temperature at which the filter material can function effectively. Besides, some aggressive chemicals can damage the filter materials, constraining their use in certain conditions.
Large-size equipment.
Bag filters can need significant floor space, especially in larger installations. This can be a problem for space-constrained facilities or for retrofits of existing dedusting and air-cleaning systems.
Pressure losses.
Air passing through bag filters causes pressure drops, which require additional energy to maintain the required air flow. This can lead to increased energy consumption of the draft equipment and associated costs.
Limited service life of filter elements.
Filter bags have a limited service life and wear out over time, especially when exposed to abrasive particles and aggressive chemicals. This leads to the need for regular replacement of filter elements, which increases operating costs.
Environmental aspects of recycling.
Worn filter bags require disposal, which can be an environmental issue, especially if they contain harmful substances or pollutants.
Ultimately, bag filters have a number of disadvantages that must be taken into account when choosing an air purification system for a specific production process.
Application of Bag Filters.
Bag filters are widely used in various industries to clean emissions and ventilation air of dust, smoke, aerosols and other particles.
Bag filters can remove dust particles smaller than 1 micron, so they are the main dust-catching equipment at enterprises of:
- ferrous and non-ferrous metallurgy,
- cement industry,
- chemical industry,
- production of building materials,
- food Industry,
- at power plants, etc.
What Are the Didifferences Between Electrostatic Precipitators and Industrial Baghouse Filters?
| Parameters | Electrostatic precipitator | Bag filter | |
| Separation efficiency | % | High 99 | High 99,9 |
| Outlet dust content | micron | Less than 50 | Less than 20 |
| Size of trapped particles | micron | 0,5 | 0,01 |
| Energy consumption | Low | High | |
| Installation cost | High | Low | |
| Operation complexity | Periodic cleaning of electrodes | Regular bag cleaning and replacement | |
What to choose: an ESP or a Bag Filter? Find Out the Best Solution With Our Experts
M HEAVY TECHNOLOGY Advice on Choosing a Filtration Technology.
M HEAVY TECHNOLOGY has completed a number of successful projects for the construction and revamping of industrial gas, air cleaning systems and dedusting systems. To achieve maximum results and the lowest emissions into the atmosphere the company’s specialists use a comprehensive approach and select an individual solution for each individual enterprise.
What to choose in Your Case? Find Out the Best Solution With Our Experts.
CONCLUSION
To sum up all above, we can confidently say that comparing two advanced dust removal technologies is incorrect. Both filters are equally good and each of them will be the best for a specific case.
The choice between a bag and an electrostatic precipitator depends on the specific needs of the plant, which include air purity requirements, economic aspects as well as available resources for maintenance and operation and gas properties and composition.
