Process Instruments (UK) Ltd

Process Instruments (UK) Ltd

- Chlorine Analyzers

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Chlorine analyzers from Pi are used in many applications requiring the measurement and control of online residual chlorine levels in water. The HaloSense range is suitable for total or free residual chlorine monitoring or control applications in potable water, seawater, process water, swimming pool water, waste water, food washing, paper and pulp, etc.

The following are available in the HaloSense range;

  • Online free and total chlorine analyzers 0-2 ppm, 0-5 ppm, 0-10 ppm, 0-20 ppm
  • Online residual chlorine in seawater analyzers (free or total bromine) 0-2 ppm, 0-5 ppm, 0-10 ppm, 0-20 ppm
  • Online zero chlorine (designed to measure the absence of free chlorine) 0-2 ppm, 0-5 ppm, 0-10 ppm for applications such as post activated carbon and pre-RO monitoring.

The HaloSense range of controllers/transmitters means that you get exactly what you need and nothing that you don’t. From a low cost no-frills chlorine dosing controller (CRONOS) to a highly sophisticated color display, remote access controller (CRIUS) – and all with the same great sensors! The CRATOS HaloSense is now available with up to 12 sensor inputs, significantly reducing the cost per point. Chlorine dosing control is now simpler and cheaper than ever! All three analyzers can have multiple sensor and multiple sensor types, saving money on the requirement for one sensor and one transmitter per measurement.

The membraned amperometric sensors are enhanced with a third, reference electrode which eliminates zero drift. (NB. These chlorine sensors are often known as polarographic sensors although this is a misuse of the wordpolarographic). Its unique design means that pH compensation is not usually required at all, completely eliminating reagents.

The sensors used by the HaloSense analyzers are largely pH independent meaning that the measurements are bufferless and reagentless. They are amperometric sensors and show remarkable sensitivity and stability. For those making a free chlorine measurement at high pH (>pH 8.5) on variable pH water it is possible to provide pH compensation from either a pH sensor connected to the transmitter or from an external pH meter.

The sensors work by separating the electrodes that perform the measurement from the sample, by a membrane. This membrane allows the free residual chlorine (HOCl and OCl-) or the total residual chlorine (HOCl and OCl- plus chloramines) through the membrane. Inside the sensor the dissolved chlorine meets the electrolyte which is at a low pH. This converts the majority of the OCl- to HOCl. The HOCl is reduced at the gold working electrode and the current generated is proportional to the chlorine present, and the instrument gives a reading in ppm or mg/l.

This technique is the most advanced method of continuous chlorine measurement and has many benefits to the user including a very stable online measurement and better dosing control.

The HaloSense range is bufferless and reagent free, meaning that is has a low total cost of ownership and with maintenance intervals at 3 or even 6 months. HaloSense is fast becoming the instrument of choice for the engineer who wants the best instrument at the best price.

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  • Low purchase cost
  • Low cost of ownership
  • Reduced pH dependency (largely pH independent)
  • Stable and reliable
  • Bufferless
  • Reagentless

Many water companies want to measure free chlorine residuals without the need for chemical buffers traditionally associated with such measurements. Acetate and phosphate buffers are expensive and environmentally unfriendly. Buffer delivery systems are maintenance intensive and have fairly costly consumables and there are health and safety considerations in the handling of the acids and high disposal costs if the acid treated water is unable to be fed back into the water supply.

Amperometric cells and most polarographic probes only respond to hypochlorous acid, (HOCl). HOCl dissociates into hypochlorite (OCl-) in a pH dependent manner. This is why most chlorine monitors need acid buffers in most applications. The typical pH of water measured on a water treatment works may range from 7 to 9.2. Chemical buffering reduces the pH to between 5 and 6 and ensures that the majority of the residual chlorine is present as HOCl (see graph below).

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  • Continuous online monitoring for chlorine in any water
  • Water treatment plant residual chlorine dosing control
  • Secondary chlorination free chlorine dosing control
  • Distribution monitoring
  • Cooling tower monitoring and control
  • Pasteurizer dosing control
  • Seawater chlorination control
  • Bromine monitoring in seawater
  • Food washing
  • Chloramination control

Anywhere you have a requirement to measure residual free or total chlorine is a suitable application for the HaloSense chlorine monitor. The HaloSense chlorine monitor range is particularly suited to working in sites where reliability and ease of use are most important.

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