Mist Extractor Design, Specifications and Applications in Natural Gas Processing Plants

A demister, a mist eliminator or entrainment separator, is a device used in process plants to remove liquid droplets or mist from a gas stream. This is important in many industrial processes where it is necessary to separate a gas from a liquid or to prevent the escape of liquid droplets from a process vessel or column.

In a demister, the gas stream is passed through a bed of material such as wire mesh, corrugated plates or vanes. The liquid droplets in the gas stream collide with the surfaces of the material and coalesce to form larger droplets which then fall to the bottom of the demister and are removed. The gas stream, now free of liquid droplets, can then be further processed or released into the atmosphere.

Demisters are commonly used in a variety of process industries such as petrochemicals, oil and gas, pharmaceuticals, food and beverage, and wastewater treatment.

Demisters are critical in natural gas processing plants as they help remove liquid droplets and mist from the gas stream, which could cause significant problems in downstream processes or equipment. Here are some of the reasons why demisters are important in natural gas processing:

Protecting equipment: Liquid droplets and mist in the gas stream can cause corrosion, hydrate formation, slugging and erosion in pipes, valves, compressors, and other equipment, leading to significant maintenance and repair costs. Demisters help prevent this by removing the liquid droplets from the gas stream before it reaches the downstream equipment.

Ensuring product quality: Some natural gas products, such as liquefied petroleum gas (LPG), require high purity levels. Liquid droplets and mist can contaminate the gas stream and compromise product quality. Demisters help remove these contaminants, ensuring that the final product meets the required specifications.

Safety: Liquid droplets and mist in the gas stream can also pose a safety hazard if they accumulate in low-lying areas of the plant or cause fires and explosions. Demisters help prevent this by removing the liquid droplets before they can cause any harm.

Regulatory compliance: Natural gas processing plants must comply with environmental regulations, which often include limits on emissions of certain contaminants. Demisters can help ensure compliance by removing liquid droplets and mist, which could contain harmful pollutants.

Designing a mist eliminator for a natural gas processing plant involves several considerations, including the size of the plant, the amount of natural gas processing, the type of mist present, and the desired efficiency of mist removal. Here are some general steps to guide you through the process:

Determine the type of mist: The first step in designing a mist eliminator is to determine the type of mist that needs to be removed. There are various types of mist, including liquid droplets, solid particles, and a combination of both. The mist eliminator design will depend on the type of mist present.

Determine the flow rate: The next step is to determine the flow rate of the natural gas that needs to be treated. This will help you determine the size of the mist eliminator required.

Determine the efficiency required: The efficiency of mist elimination is expressed as the percentage of mist removed from the gas stream. The higher the efficiency required, the more complex the mist eliminator design will be.

Choose the mist eliminator type: There are various types of mist eliminators available, including mesh pads, vane-type separators, and cyclone separators. The selection of the mist eliminator will depend on the type of mist present, the flow rate, and the required efficiency.

Determine the size and configuration: Once you have chosen the mist eliminator type, you need to determine the size and configuration of the mist eliminator required. This will depend on the flow rate and the efficiency required.

Consider other factors: When designing a mist eliminator, there are several other factors to consider, including pressure drop, material selection, maintenance requirements, and operating conditions.

Design and optimize: After considering all the factors, you can proceed with the design and optimization of the mist eliminator.

Testing and validation: Once the design is complete, it is essential to test and validate the mist eliminator's performance to ensure that it meets the required efficiency and performance specifications.