Sodium Hypochlorite Measurement - LITRE METER

Litre Meter is renowned as the leading flow meter experts having 40 years of experience in supplying mass, water and chemical injection flowmeters across the globe. The company has been supplying businesses worldwide with a large selection of durable, industry-standard flowmeters. Our bespoke range of customizable flowmeters can be adjusted to suit to almost any flow application.

Sodium Hypochlorite

Sodium hypochlorite is a green/yellow liquid containing the smell of chlorine. Previously, it was used as a bleaching agent, later it was discovered to be effective in controlling wound infections. Consequently, sodium hypochlorite is commonly known as household bleach. It displays broad spectrum anti-microbial activity and is extensively used in healthcare facilities in a wide range of settings. This liquid is diluted in water depending on its anticipated usage.

Injection of sodium hypochlorite into sea water is common in the chemical injection arena. In addition, sea water can restrain dissolved oxygen, solids and bacteria and these can affect an oil reservoirs life. Hypochlorite can be used a bactericide whilst filters take care of the solids. Before diluted in the sea water, hypo is hostile in nature. Therefore, it requires some specialized devices in terms of wetted materials.

Litre Meter has been manufacturing flowmeters since 1975 and we have always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note, Litre Meter illustrates two solutions based on <20% solution.

Sodium Hypochlorite Flowmeters - Applications and Rates - VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance.

Litre Meter recommends Titanium for the body and chamber with carbon graphite for the actual rotary piston for sodium hypochlorite. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.

Applications for flow-rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved. The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 - 270 L/min max. Higher flow-rate meters are available to special order. The table at the end of this article assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters - Applications and Rates - Pelton Wheel

The company has started manufacturing the Pelton Wheel turbine in 1975. These wheels are made with some stainless steel components together with a plastic rotor, Elastomer seals and sapphire bearings.

The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal. The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O-ring and PFA rotor. The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non-pulsing flows.

Compatible Materials

Litre Meter recommends only a selected group of tested materials due to the nature of Sodium Hypochlorite. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

•    PVC, Hastelloy and titanium
•    The PVC design can be used up to 15 bar pressure maximum. Hastelloy (UNS N10276) up to 1035 bar.
•    For the ultimate select titanium (UNS R50400) designed for 1380 bar (20,000psi, 20 ksi)

These materials are used to make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM and the other materials include FFKM and PTFE. All seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity.

With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.

Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.