As the world is evolving, the pollution rate is also going higher. Harmful rays are destroying our environment and the protective ozone layer. That’s why global air emission limits and regulations have become stricter than ever. A lot of companies are struggling to meet the legal requirements. Business owners are looking for a way to reduce their industrial emissions and save the environment from pollutants.
In order to find a cheap and effective filtration method, the hot gas filtration method was discovered. Here I will tell you what filtration is, what is hot gas filtration, why it is widespread, and the types of filters used in this process. So keep reading the article to find all things you should know about hot gas filtration.
What is filtration?
Before getting to know hot gas filtration, let’s first find out what is the meaning of filtration. Filtration is the simple process of passing the liquid or gas through a substance to remove other solids, toxins, and pollutants. As we go further, filtration has many applications and methods to filter numerous substances.
There are many types of filtration. The substance you want to filter, the particle size of the substance, and the ambient conditions significantly affect the method you would choose to filter the certain product.
What is hot gas filtration?
Hot gas filtration is the process of removing particulate matter, toxins, and pollutants from hot gas streams, often at temperatures above 150°C. This technology is essential for ensuring cleaner emissions and protecting downstream equipment such as heat exchangers, gas turbines, and catalytic units from damage caused by particulates. Hot gas filtration systems can be used across various industrial processes, including waste incineration, power generation, and chemical processing.
Methods:
There are various methods to remove unwanted particles from the gas. This includes:
- Brownian motion method
- Electrostatic method
- Locking effect
- Inertial method
- Sieving effect
Brownian motion
The Brownian motion method is actually the diffusion method. In Brownian motion, the particles within the gas stream and atoms on a molecular level collide, which causes particles’ constant movement. This random movement of particles allows contaminants or toxic particles to strike the system’s filter media, resulting in the filtered gas stream. This method is mainly used to filter fine particles.
Electrostatic method
In the electrostatic method, electrostatic filters are used in the filtration system. These filters attract the charged particles which pass by them. The particles are filtered based on their electronic charge and will be removed from the gas. This method is best suited to filtering fine particles.
Locking affect
The locking effect, as the name suggests, filters the gas by trapping or locking contaminants in the filter. In this method, the filter’s geometry traps the particles to purify the gas. This method is used to filter larger particles.
Inertial
The inertial method is also used to filter larger particles. Particles get trapped and locked into the filter due to the momentum flow of the gas.
Sieve affect
The sieve effect is used to filter out the larger particles. Particles larger than the filter aperture are get trapped on the surface of the filter, creating a filter cake.
How did hot gas filtration become the first choice of industrialists?
In the early 1970s, hot gas filtration was first used for the cleaning of flue gas at the incineration of low-level contaminated radioactive wastes produced from nuclear power generation. Because of its success, this technology is now widely used, and people find it very reliable.
Later in the 1980s and 1990s, the introduction of advanced coal-based power generation techniques significantly affected the hot gas filter system’s development and filter media. Nowadays, the whole world greatly relies on hot gas filtration to clean waste products, and various hot gas filters are already applied in multiple industries worldwide.
High-Temperature Operation
Hot gas filtration operates at high temperatures, often exceeding 150°C, which can be problematic for conventional filters. Standard filtration systems may degrade at such high temperatures, making it essential to use advanced materials that can withstand extreme conditions. Ceramic filters and metal filters are commonly used in these systems due to their high-temperature resistance and mechanical stability.
What are hot gas filters?
The filters applied in hot gas filtration system to process the gas produced in various industries are called hot gas filters. These filters are the main components of the hot gas filtration system that deal with particulate matter and other pollutants.
Hot gas filters have shown excellent filtration performance over the years. These filter media provide highly efficient separation of contaminants; they can filter particles of even sub-micron size. Companies concerned about pollution and want to reduce harmful emissions can take benefit from hot gas filter media. The hot gas filtration system can help industrialists conserve the environment and effectively eliminate harmful waste and by-products.
Previously, the hot gas filtration system could filter the gases at temperatures between 150°C to 500°C. But nowadays, with the introduction of ceramic filters, you can filter gases up to 850°C. Mainly only ceramic or metal filters are installed in a hot gas filtration system because of high temperature and mechanical stability needs. Metal and ceramic are rigid and self-supporting materials and can work best at higher temperatures.
Advantages of hot gas filters
Hot had filters can be efficiently used in many industrial processes. They can be used in downstream equipment to protect following things from erosion, fouling, and pollution.
- Catalyst units
- Turbines
- Heat exchangers
- Scrubbers
Moreover, the high temperature in hot gas filtration system can prevent unwanted condensation or sublimation reactions of gases.
In general, hot gas filtration is becoming popular day by day because:
- The process is simple, and you can further intensify and simplify the process.
- Provide better energy efficiency
- Improve the product quality
- Lower the emission level of contaminants.
Hot gas filtration offers numerous advantages, including:
- Improved Energy Efficiency: By removing particulates and pollutants, these systems help optimize heat recovery and power generation.
- Pollution Control: Hot gas filtration reduces emissions, ensuring industries comply with environmental regulations.
- Equipment Protection: By filtering out harmful particulates, hot gas filtration systems help protect expensive equipment such as catalysts, turbines, and heat exchangers from damage due to erosion or fouling.
- Cost-Effective: Hot gas filtration reduces maintenance costs by protecting downstream equipment and improving the operational efficiency of industrial processes.
What kind of filters are commonly available in the market?
Depending on the application, different filter types are used to ensure optimal performance. The most common filter types include ceramic filters, ceramic filter candles, sintered metal filters, and catalytically active filters. Each type offers unique advantages tailored to specific industrial needs.
The most commonly used hot gas filters for hot gas filtration systems are:
- PTFE on glass bag filter
- Ceramic filter
- High-temperature cartridge filter
Ceramic filters are the most widely used hot gas filters because they offer higher temperature resistance. Moreover, the ceramic is much more robust and improved than its older 20 years old version. They came in various lengths and diameters to suit every hot gas filtration system type.
On the other side, the hot gas cartridge filter does not offer higher temperature resistance. But it has a pleated filter design to provide a larger surface area. Usually, both bag and ceramic filters are used in clinical waste incineration.
Types of filters used in hot gas filtration
As the industries are evolving, ceramic filters and ceramic filter candles are the most commonly used hot gas filters in hot gas filtration systems. The other filters have very limited use in very few industries.
Ceramic filters
With the introduction of ceramic filters in the market, conventional bag filters are now used only for very high-temperature hot gas filtration.
Ceramic filters are composed of inorganically bound ceramic fibers. These filters are self-supporting and do not need a supporting cage to work correctly.
Ceramic filters are chemically inert and can withstand the temperature of up to 900°C. Because of their inert nature, they can easily withstand chemical environments.
Ceramic filters can also be cleaned easily, just like other methods used to clean bag or cartridge filter media. Both compressed air and reverse air can be used to clean the filters. However, the pulse jet cleaning method is the best method to date because of its better cleaning efficiency. You can also use cold cleaning gas for cleaning ceramic filters.
Ceramic filter candles
Ceramic filters are known as “candles” because of their solid tube-like shape. They can endure higher temperatures than the simple ceramic filter elements. They can easily withstand temperatures above 1000°C. Ceramic filter candles have high burst resistance, better thermal shock resistance, high permeability, high filtration efficiency, and better corrosion resistance.
Ceramic filter candles do not just remove contaminants, but they can also recover valuable products from the following applications:
- Halogenated hydrocarbons
- Petrochemicals processing
- Catalyst activation
- Fluid catalytic cracking
The structure of ceramic candles or fibrous ceramic candles allows them to be a suitable substrate for catalyst coating. That’s why they can perform catalytic reduction to some extent. They can also carry out other reactions to remove gaseous pollutants like NOx and dioxin.
Sintered Metal Filters
Sintered metal filters, made from metal fibers or powders, offer high-temperature resistance and chemical stability, making them ideal for processing high-temperature gases and chemically aggressive environments. Key advantages of sintered metal filters include:
- High Temperature and Chemical Resistance: Sintered metal filters can withstand temperatures ranging from 500°C to 850°C, suitable for high-temperature gas filtration and aggressive chemical environments.
- Superior Mechanical Strength: These filters provide high mechanical strength, enabling them to handle high-pressure and high-flow conditions.
- Efficient Filtration: Sintered metal filters effectively remove both large and fine particles, making them suitable for industries requiring precise particle separation.
Sintered metal filters are commonly used in industries like petrochemicals, metallurgy, and waste incineration, where high-temperature and high-corrosion resistance is crucial.
Catalytically Active Filters
Catalytically active filters combine filtration with catalytic reactions, allowing them to remove both particulate matter and gaseous pollutants like NOx and dioxins. The benefits of catalytically active filters include:
- Dual Functionality: These filters not only capture particulate matter but also reduce gaseous pollutants, making them versatile for industrial processes that need to address both particulate and gas emissions.
- High Temperature Suitability: Catalytically active filters operate effectively at high temperatures, ensuring stable performance in demanding conditions.
- Widespread Application: These filters are widely used in industries such as waste incineration, petrochemical processing, and chemical treatment that require a comprehensive solution for removing both particulates and harmful gases.
Catalytically active filters are ideal for industries that deal with both solid and gaseous pollutants, offering a combined solution for effective air pollution control.
How does hot gas filtration work?
The hot gas filtration system has two compartments. One is ‘dirty,’ and the other is ‘clean.’ The filtration units pass the flue gas through the hollow ceramic filters and capture the small contaminants and other impurities.
As you know, there are two compartments, dirty and clean. The flue gas first enters the dirty side, and the contaminated particles are captured in the filter element of this side. The clean air passes through the filter element, gets stored on the clean side, and then goes out of the stack.
Lastly, the built-up waste on the filters can be cleaned with the reverse pulse method using compressed air. All of the built-up waste will go to the collecting bin.
Why ceramic filters are the most preferred ones?
Ceramic filters have numerous advantages, which make them the first choice of most industrialists. Here are some benefits of ceramic that you need to know to learn more about hot gas filtration.
- Ceramic filters can withstand high temperatures of up to 1000°C. This temperature is much higher compared to conventional bag filters, which can endure only 140°C to 180°C.
- Ceramic is non-flammable.
- Ceramic filters are resistant to acids and alkalis.
- Ceramic filters provide the most efficient temperature for almost all processes, including scrubbing.
- Hot gas filtration system reaction towers or cyclones are not needed in ceramic filters.
- Thanks to ceramic filters, industrialists can achieve the lowest possible emission levels and reliable performance.
Uses of hot gas filtration system
Hot gas filtration system is a widely used filtration system in almost every industry. Its most notable uses are in the following industries:
- In incineration
- In cremation
- In gasification and pyrolysis
- In biomass combustion
- In nuclear waste processing
- In mineral processing and smelting
- In coal drying
- In the oil and gas industries
- For waste-to-energy conversion
- In foundry processes
- In cement production
When Should You Choose Hot Filtration Over Cold Filtration?
Hot filtration is typically used when filtering gases or liquids at high temperatures, particularly when contaminants are sensitive to temperature or need to be removed while the substance is still in a heated state. Cold filtration, on the other hand, is employed when the substance is cooler or when heat might affect the filtration medium or process. The key difference lies in the temperature tolerance and nature of the contaminants being filtered.
What Is the Difference Between Hot Gas Bypass and Hot Gas Reheat?
Hot gas bypass refers to the process where a portion of the gas is diverted around the filtration system to prevent overheating or damage to equipment. It is commonly used to control gas flow and temperature. Hot gas reheat, however, involves reheating the gas after it passes through the filtration system, often used in processes that require temperature consistency post-filtration, such as in energy recovery or industrial processes.
How Does Hot Filtration Differ from Gravity Filtration?
Hot filtration involves filtering substances at elevated temperatures, which is crucial for handling gases or liquids that are hot or volatile. Gravity filtration, however, is based on the natural force of gravity to pull liquid or gas through a filter, typically used in colder, non-volatile conditions. Hot filtration is more suited for industrial processes where the filtering medium must withstand high temperatures, whereas gravity filtration works well for simpler, lower-temperature filtration needs.
Conclusion
The hot gas filtration system is the reliable and most efficient method of purifying the gas and lowering the waste emission levels. We have covered everything you should know about hot gas filtration. So if you are trying to find a sound flue gas filtration system, then read our guide and make wise decisions.