Filtrate

What Does Filtrate Mean?

Filtration is a process for separating out unwanted substances in the liquid or gas phases. The filtrate is any substance, liquid or gas, that has passed through a filter. What is left behind in the filter is termed the residue. In the corrosion control sector, filtration techniques are used to remove potentially corrosive contaminants in the aqueous or gaseous phases.

Corrosionpedia Explains Filtrate

Water filtration in water treatment

The removal of solids and particles from water by filtration is just one part of the much wider water treatment sector. Water purification for industrial use employs filtration as part of a four-step process that begins with water screening for large matter, followed by coagulation (flocculation) which draws together and out of the water system any smaller particles by getting them to stick together. They are removed either by skimming off (from the top) or drainage (from the bottom). Filtration is the third step where any remaining coagulated matter is removed as a residue. Different filter types may be used according to the narrowness of particle diameter targeted for removal. The final stage of water treatment is disinfection in a closed tank to remove any bacteria that may have survived the treatment process.

Water filtration is necessary in corrosion control in order to eliminate corrosive ions such as chloride, fluoride or sulfate. This is especially crucial for industrial processes that operate at high temperatures, where the combination of corrosive ions with elevated temperatures may rapidly accelerate corrosion reactions in water tanks or pipelines.

Gas/air filtration

Gas/air filtration is employed in several heavy and high-tech industry sectors to eliminate the presence of acidic, alkaline or oxidizing gases. The most important examples are sulfur dioxide (SO₂), sulfur trioxide (SO₃), hydrogen fluoride (HF) – each of which is acidic – and ammonia, which is alkaline. Ozone (O₃) is an example of an oxidizing gas. Key industries where gas/air filtration is used include the petrochemical sector, the pulp and paper industry, semiconductor production, steel-making, smelting and fertilizers. The ingress of these gases into different industrial settings can create corrosion problems in the electrical circuits found in industrial control rooms, server rooms, electricity substations and so on. Many of those corrosive gasses also have unpleasant odors that would be desirable to eliminate.

Corrosion of electronic process control equipment can result in disruptions in production leading to lower productivity and lower profitability, and can be expensive to fix. But it is possible to control and reduce the risk of corrosion by using air filtration, thereby improving indoor air quality and thus eliminating corrosion-inducing pollutants.

Typical applications include contaminants such hydrogen sulfide (H₂S) in pulp and paper mills where it emits from the wood pulping process and the sewage system and sulfur dioxide (SO₂) from the recovery boiler. H₂S is also a major emission from waste treatment plants, onshore and offshore oil wells and refineries.