What Is a Coalescing Filter & How Does It Work?
The presence of water vapor, sulfur, ethane, methane, carbon dioxide (CO2), and other impurities in industrial process fluids and products necessitates the use of precision filtration systems for quality control of the final products. A coalescer is an industrial device used for this purpose.
What Is a Coalescing Filter
A coalescer or coalescing filter is a device used to separate fluid mixtures into individual pieces using the principle of coalescence. Coalescence is a process whereby fluid molecules agglomerate (come together) to form a larger whole. Coalescing filters can separate particulate components of mixtures at comparable efficiencies as particulate filters.
What Does a Coalescing Filter Do?
Coalescence can be used to separate the components of homogenous or heterogeneous mixtures and emulsions. There are several types of coalescing filters which are employed in several industries, including Oil & Gas and chemical plants.
Common types include the gas coalescer, oil coalescer, fuel coalescer, and condensate coalescer which can be used for water-gas, gasoil, and fuel-gas separation.
How Does a Coalescer Work?
A coalescing filter (or simply coalescer) is a filtration system consisting of several baffle walls or screens. A stream of fluid to be separated (e.g., a gas-water mixture) is applied to the filter and the baffles screen out the various components by trapping them in different sections. Thus, the components of interest can be recovered in pure form, while the contaminants are drained away for purification or disposal.
The screening mechanism works based on the physical properties of the component substances e.g., molecular weight and density. In water-oil separation, the baffle walls in the coalescing filter divert the heavier oil molecules in one direction to a drain point, while the water vapor molecules diffuse through the filter element to coalesce and be drained out of the system gravitationally.
Similarly, in gas-water separation, ‘wet gas’ (gas stream containing water droplets) is fed into the coalescer inlet, diffuses through the filter element, and exits via an outlet port as dehydrated gas. The denser water molecules coalesce and fall to the bottom of the tank for drainage.
Electrostatic & Mechanical Coalescers
There are two main types of coalescing systems based on the mode of operation.
Electrostatic Coalescers
Induces droplet coalescence in fluid mixtures using an AC or DC current, or both. Electrostatic coalescers work by passing an electric charge through the fluid which destabilizes the emulsion and increases the size of the molecules, causing them to fall in collection tank for drainage.
Typically, AC currents in the 50 – 60 Hz range is used for this purpose. The generated electric field causes forces of attraction between the fluid molecules causing them to come together to form heavier molecules. Electrostatic coalescers are widely used for separating water-fuel emulsions in offshore oil and gas production facilities.
Mechanical Coalescers
Do not utilize electrostatic charges; employ a series of filter elements or barriers for separation. Mechanical coalescers can be used in oil refineries to separate water vapor from hydrocarbon condensate by coalescing the water molecules into larger particles which are then drained out of the system.
The purity of the final products post-separation is dependent on the selectivity of the filter element. Common materials used for manufacturing filter elements are borosilicate microfibers and membrane technology.
Industrial Applications
Coalescers are employed for a wide range of applications in the oil and gas and chemical industries.
Downstream Operations
In downstream oil and gas, coalescers are used for product refining. At natural gas refineries, filter elements can be used to de-humify natural gas to ensure product purity before marketing the product.
Gas-oil coalescer systems can purify natural gas by removing several natural liquids and condensate. Furthermore, coalescing filters are actively used to prevent corrosion in oil and gas downstream assets such as compressors, amine/glycol absorbers, turbines, and membrane filtration systems by removing contaminants such as water vapor and sulfur with efficiencies up to 99.98%.
Coalescing filters can be used to recover lube oil from a compressor when installed at its outlet. Fluids fed into the compressor inlet may include aerosols, particulate matter, dissolved hydrocarbon liquids, and slugs and are extracted by a filter element located upstream of the compressor.
Petrochemical Industries
Liquid-liquid coalescers can be used for phase removal of water vapor, amine solutions, and sulfur from petrochemical feedstock prior to storage. Removal of contaminants ensures product purity and prevents corrosion of industrial equipment.
Advantages of Using Coalescers
Microfiltration using coalescers ensures product purity up to 95%. It also consumes much less power than other industrial filtration methods and is eco-friendly.