Sodium Hypochlorite Bleach Tanks

What is sodium hypochlorite?  Known commonly as bleach, sodium hypochlorite is an ionic compound with unique properties that is regularly used in many industries. It is manufactured using chlorine gas and sodium hydroxide and is a pH-dependent alkaline solution. Concentrated bleach solutions have pH values greater than 11 and are considered corrosive and hazardous.

Sodium hypochlorite is the chemical compound known largely as bleach when dissolved in water. Pure anhydrous (without water) sodium hypochlorite is very unstable and subject to intense chemical, even explosive, reactions in the presence of heat, friction, or other chemicals and is not commonly utilized. A solution of sodium hypochlorite is a clear, yellow to green liquid with an immediately recognizable odour.

Molecularly, sodium hypochlorite is the combination of a sodium cation, Na+, and the anionic compound hypochlorite, ClO, from which the name sodium hypochlorite is derived: Na? + ClO = NaOCl.

What is sodium hypochlorite used for?

The chemical solution of sodium hypochlorite is used for its function as a whitening agent, an oxidizer, and as a sanitizing disinfectant. It sees heavy use in textiles, paper, detergents, petrochemical refining, and water/wastewater treatment industries. Plant matter such as cotton and wood fiber/pulp are processed with NaOCl to brighten or render the end product white.

TANK VENTING

The O2 gas formed from NaOCl decomposition presents a problem not only in the piping and usage of sodium hypochlorite but also in the storage of the chemical. If O2 gas production occurs under storage, the pressure buildup can occur presenting the safety concern of handling. Sodium Hypochlorite Bleach Tanks should have a venting system to allow the release of built-up oxygen gas and should receive regular maintenance/inspections to ensure the release of any accumulated pressure. A general recommendation for venting is to use vents of diameters at least double the inlet pipe diameter. The use of flexible joints in the pipework is recommended to accommodate for potential contraction

It is also recommended to use storage containers equipped with an outlet valve that allows for full draining of the sodium hypochlorite tank for maintenance and before refilling with fresh sodium hypochlorite. This flushing will prevent the buildup of nickel, cobalt, copper, iron and other suspended solids that contribute to the decomposition of NaOCl. Without regular flushing, these metals can accumulate in the container and can contribute to the very rapid decomposition of a sodium hypochlorite solution and subsequently the generation of oxygen gas.

Sodium Hypochlorite secondary containment

Sodium Hypochlorite Bleach Tank regulations require secondary containment measures in the event of catastrophic tank failure releasing bulk hazardous material. Good engineering practices direct containment areas should hold at least 110% the total volume of the tank or tanks being protected.

HDPE catchment basins are secondary containment measures applicable for smaller NaOCl storage tanks. Double-walled tanks are another secondary containment option for sodium hypochlorite solutions and make good selections when operational spaces may be limited for full tank and external containment measures.

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