02 Aug

Chemical Injection process: Sodium hypochlorite

We look at the chemical injection process of injecting sodium hypochlorite into sea water, in a variety of settings.

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use.

In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials.

At Litre Meter, we’ve always concentrated on the more challenging margins of metering, typically at low flows and/or high pressure. For this application note, Litre Meter offers one solution to this application 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. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. 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 on the last page assists in the selection of the best technology.

Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All seals within the meter are fully compatible with Sodium Hypochlorite. PVC is not available currently for the VFF.

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.

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.