As stated above the chlorine production of an electrochlorination package is achieved by means of varying the DC current supplied to the electrolysers. The productive capacity is directly proportional to the DC current with a turn down ratio of 10:1, i.e. 10% – 100% output of an electrolyser stream.
By this means the weight of hypochlorite produced varies, the mass balance remains constant, and the concentration of the product in the carrier stream varies.
The DC current control therefore permits a variable weight to be produced in a stable mass balance.
Mass balance through an ECP is required for three main reasons.
- To maintain the designed electrolyte flow through the Electrolysers.
- It enables the continuous operation of the Electrolyser assemblies which is beneficial to their operation and longevity. (Anode coating loss is exacerbated by frequent energising and de-energising)
- Permits maintenance of the appropriate velocity through the dosing system pipe work that prevents precipitation of the insoluble hydroxide electrolysis by-products.
Important Note
An ECP supplier will generally quote a turn down ratio of 10:1 for design productive capacity as stated above through varying the Transformer Rectifier DC current output. This strictly means that the concentration of NaOCl produced can be varied from 10% to 100%. The system mass balance however remains constant in most cases to maintain the required velocities in the dosing lines and retain all ancillary plant at its operating design conditions.
An example of how confusion can arise is where, for example, when 10 main seawater pumps are to be dosed with NaOCl and the 10:1 turn down ratio is considered appropriate for running any combination of pumps from 1-10. This is not the case as the dosing diffusers for the individual pumps are unlikely to be able to accept the full mass balance of the ECP. Where this 10:1 ratio of process seawater pumps is required this must be considered at the onset of the project and appropriate design incorporated in the ECP control and distribution system. (See appendix 2 for a sample calculation)
