Mist is not just something in the air on a rainy day. Mist, which is a danger to your health is formed in chemical and other manufacturing processes. When it comes to health and safety, imagine mist as the suspension of chemicals and combustible liquids in lingering the air. It will settle in wherever it lands, corrode machinery and cars, and possibly cause irreversible health concerns.
Responsible companies will invest heavily in capital equipment and internals to abate harmful mist and remove mist from the gaseous phase. Typically, this investment will come in the form of mist eliminations. When crossing this path, it is wise to choose a company that specializes in mist elimination.
The need to separate mist droplets from the gas stream in industrial chemical processes is one of the most common occurrences in unit operation. This is achieved by using mist eliminators or demisters. A mist eliminator, also known as a demister, should meet the needs of the customer both technically and commercially, therefore you need to know what you as the client want to achieve.
A properly designed and installed mist eliminator can reduce carry over, recover valuable product, increase capacity, and substantially minimize downtime. Mist eliminators are designed to address these issues and assist with production, by improving emissions and product loss which will protect downstream equipment.
Mist eliminators are commonly found either in vertical towers or in stages in a horizontal scrubber or in cooling towers. They can be engineered for an existing or new scrubber vessel and are custom made to fit the vessel. The mist eliminators can be cleaned and reused if they are able to be removed, handled, and re-installed without damage.
Several factors will be taken into consideration when designing a mist eliminator such as, the chemical process conditions, pressure, temperature, the application, gas flow, liquid flow rates and inlet droplets. The location where the mist eliminator will be inserted into the vessel is also important as well as understanding the design and the knowledge of the other internals.
Droplet consideration is essential in the technical design. Mist, which is formed of entrained liquid droplets or contaminants can form in many different sizes depending on how they are generated, therefore, to properly design a mist eliminator, you must know if it will be a FOG (submicron particles) or a mist will be generated.
Once you have identified the type of mist and depending on the droplet size, different types of mist eliminators will be appropriate for the chemical process. Mesh type mist eliminators for example, are very efficient with smaller droplet sizes at lower velocities, while fiber bed filters serve for submicron particles such as FOG as these particles will not attach to a filament that is used to make a mesh type mist eliminator.
Mist that consist of droplets that are larger than submicron will be addressed by mist eliminators that are composed of various media configurations. Materials will include woven metals or plastics such as, polypropylene. For a mist eliminator to remove liquid droplets from a gas stream, the mist must contact the surface of the mist eliminator. Mist Elimination pads work by coalescing smaller liquid droplets by obstructing their path. They then stick to the mist elimination pad while the clean gas passes around the mist eliminator pad.
If you choose a company that specializes in mist elimination, you may save yourself some headache. Not all companies have the same expertise and that may cause problems. A company that knows your process and works closely with you should be able to design a properly functioning mist eliminator. If you do not have a mist eliminator that is designed with all the considerations, once it is installed, you may not notice when it is having problems until it is underperforming. At this point, there may be product loss, entrainment, pressure drop, and equipment damage. These are all known as process inefficiencies. All of this will lead to premature shutdowns to address the issues.