Types of Demister Mists

The precise removal of mist from gas or steam streams is crucial as improper handling can lead to wastage of raw materials, product quality impairment, equipment damage, and environmental hazards. Demister mists act as separators to enhance upstream processing by eliminating heavy droplets from the vicinity of vapor outlets.

Demister mists can be categorized according to the type of design, applications, and function as follows:

Design: The wire mesh demister design comprises a thick layer of wire mesh composed of stainless steel or other alloys. The mesh's open spaces capture mist droplets, while the vapor fills the spaces to go through, leaving behind only the mist. The fiber demister employs finer strands of fiber to form a dense blanket or mat that captures the mist droplets more efficiently than wire demisters. Bucket-type demisters comprise a chamber with a sloped floor that resembles a bucket. The vapor with mist enters the chamber, and the mist gets trapped at the bottom, while the clean vapor escapes through the top.
Function: A coalescing demister captures the mist droplets and then merges them into larger droplets (coalescing). This happens due to the influence of the demisting element's surface tension. In many demisting applications, this phase precedes the actual separation phase. A gravity demister lies at rest and depends on gravity to eliminate mists. It does not require any specific equipment or instruments. While gravity demisters can be helpful in specific settings, most demisters require some active separation method.
Application: Air demisters are primarily used to reduce humidity levels in expansive air handling units, dehumidify tunnels, and air conditioning systems, among others. Vapor demisters, on the other hand, are employed to treat waste water, process oill, and separate hydrocarbons, amongst other applications.

Specifications and maintenance of demister mist

Specifications

Material

Common demister materials include stainless steel, polypropylene, carbon steel, copper, and ceramics. When choosing the material, factors such as temperature, pressure, acidity, and alkalinity of the gas must be considered to ensure that the material can withstand working conditions. For example, stainless steel is widely used in harsh chemical processes because of its high corrosion resistance.
Structure

Demisters often have structural features, such as trays and barrels, which are commonly used in industrial oil refining processes. The tray will take the liquid to the next unit, while the barrel will store the liquid for further processing.
Apparatus

Some industrial demisters need to be fitted with other equipment, such as repos, reactors, rags, and cranes. A repos refers to a demister used as a separator. Reactors are used for chemical reactions, and rags are about membrane technology and filter units. The rags are combined with a demister in the refinery to filter oil products into motor oils, while a crane refers to the handling equipment that moves the demister around the workshop.

Maintenance

Clean the filter

Cleaning the filter should be the first step in maintaining the demister, as this will help remove debris and dust from the gas.
Check the connections

Inspect the connections of the demister to ensure that there are no loose or leaking parts. This will ensure that there are no leakage problems in the gas passing through the connection.
Check for corrosion

Inspect the demister for corrosion damage. Users should repair or replace the corroded parts in a timely manner to prevent further expansion of the corrosion.
Check the operation of the fan

If the demister equipped with a fan, the user should check the fan's operation. Ensure that the fan is operating normally and is not making any unusual noises.
Lubricate moving parts

The moving parts of the demister should be lubricated regularly to ensure smooth operation and to avoid them becoming stuck or worn out faster.

Industry applications of demister mists

Demister mists can be used in a number of industries, from oil and gas to chemical processing to making power. Here are some typical applications of demister mists in different industries.

Oil and gas: Mist eliminators are usually used in the oil and gas industry to separate hydrocarbon mist from gas streams. For instance, in the refinery sector, they are installed in the top of crude distillation columns, refinery unit overhead lines, and fractionation column funnels. The purpose is to recover valuable products and protect downstream equipment.
Chemical and petrochemical: Demister mists find broad applications in the chemical and processing industry as well. They are used in reactors, scrubbers, separators, and distillation units to eliminate liquid droplets from gas streams, such as process solvents, chemical reagents, and mineral oils.
Power generation: Power plants that utilize fossil fuels or biomass usually install demister mists in their flue gas treatment systems. This way, fine ash particles and water vapor can be eliminated, keeping the environment clean and meeting emission standards.
Pharmaceuticals: In the pharmaceutical industry, mist eliminators can be used to protect clean rooms and sterile manufacturing processes. They help remove microbial growth, culture media, and contaminants to ensure product quality and compliance with regulations.
Food and beverage: Demister mists can be used in food and beverage processing to separate oil mist, flavoring agents, fermentation liquids, and other liquids from the air. They help improve workplace safety and product purity.
Metallurgy and mining: Demister mists are used in metallurgy and mining to separate oil mist and coolant mist from smelting, mineral processing, and cutting operations. They help prevent equipment fouling and maintain product recovery efficiency.
Aerospace and aviation: These industries often make use of mist eliminators in their gas filtration systems to separate oil mist, coolant mist, combustion gas, and other contaminants. This helps protect expensive aero-engines and ensures their proper functioning.

To sum up, no matter what the industry is, the demister mist plays a key role in improving the quality of the working environment, protecting equipment, reducing product loss, and preventing pollution. It has become an indispensable device in many industrial production processes.

How to choose demister mist

Several factors should be considered when choosing the demister for the equipment.

Identify the Source of Mist

Understanding the root of the mist can help one know the right equipment to purchase. Industrial mist is usually produced during the machining process due to air saturation. This can lead to product cooling, employee health risks, and fire hazards. Other sources of mist in manufacturing environments may include condensate vaporization, liquid aerosolization, humidification, and hazardous materials.
Identify the Type of Mist

mits can be classified into different types based on its size and composition. Mist with small droplets, often found in chemical and pharmaceutical manufacturing, may require a different demister than industrial mist.

Some common types of mist include:
- Oil Mist: This includes lubricant oils, hydraulic oils, and cutting oils used in industrial machining processes. An Oil mist separator helps to filter oil from the mist.
- Water Mist: It can come from machining processes involving water-based cutting fluids or moisture from the environment. A demister in a cooling tower helps to filter water mist.
- Psyhical Mist: This is moisture from the environment that results condensation or fog. This occurs when the difference between the air temperature and dew point is very low. The demisters used in humidification systems help to eliminate physical mist.
- Chemical Mist: This includes aerosols from chemical processes, which may pose significant health and safety hazards.
Consider the Demister Design

Demisters come in various designs to filter various types of mist. Some common demister designs include:

An air vortex mist eliminator applies centrifugal force to separate liquid particles from gas streams. It has a cylindrical body with an inlet and outlet. When the fluid enters the unit, the whirling motion inside occurs. The heavier liquids move to the perimeter and drop back to the collecting pot or drain.

An electrostatic mist eliminator uses electrical forces to remove liquid droplets from gas streams. The gas flow enters the unit and passes through a powerful electric field. This field charges the liquid droplets, making them behave like opposites. They get attracted to each other and then get separated and drained off.

Demister mist Q & A

Q: What is a demister in a column?

A: A demister in a column is a mist eliminator installed at the top of a processing column. It works by capturing and removing residual liquid from vapor that escapes after mixing different chemical compounds in a column. Without a demister in a column, one could find oneself repeating the same process or wasting time on the same chemical compound over and over again.

Q: What is the purpose of a demister?

A: The main purpose of a demister is to separate vapor from liquid or mist in the gas processing industry. The demister will capture water, other liquids, or droplets and pass dry gas through.

Q: Where should demisters be installed?

A: Demisters should always be installed in their ideal location. This means they should be placed where there is a high probability of mist formation. Some of the ideal spots one can consider are: upstream of cooling coils, within condensation vessels, after gas-liquid separator, between heat exchangers, and in filter units.

Q: How do demisters work?

A: Demisters work through coalescence. When the mist-laden gas comes into the demister, it passes through an inlet, and then the gas streams expand to occupy a large volume in the demister chamber. The pressure drops, and the gas stream slows down. As a result, the droplets in the gas stream will not have sufficient momentum to keep moving along with the gas stream. They will fall out and be captured into the demister chamber.