Dosing regimes typically comprise a combination of continuous and shock dosing of the seawater system.
Continuous Dosing is a low level dosing regime that satisfies the chlorine demand of the treated seawater leaving a low level residual of free chlorine at the system outfall. Dependent on geographical location this can be anywhere between 1-5 mg/l with a residual of approximately 0.1 – 0.5 mg/l.
Shock Dosing is at a frequency and duration determined by the seawater analysis wherein the level of hypochlorite dosing is periodically increased, typically 2 – 3 times the continuous dosing level. There are changing schools of thought as to the effectiveness and necessity of Shock Dosing however it has been understood to better control marine micro fouling, shock dosing for example for 20 minutes every 6 hours..
EICS’s will typically propose suspension of continuous dosing during a shock dosing period however it could equally be cumulative, it is important that the consensus on this is agreed between client and EICS.
As will be shown in the later calculation examples the continuous dosing demand is by far the greatest factor in determining the product concentration required and as such, unless taken into account at the design stage, will determine that the shock dosing regime which will always be at a similar ratio to the continuous dosing, i.e. halve the continuous dosing regime and the shock dosing regime will inherently halve in a mass balanced electrochlorination system.
Typically an electrochlorination package will vary its productivity by means of varying the DC current supplied to the Electrolysers, generally at a ratio of 10:1, this is explored further in 2d Note below as it there are other factors that can lead to confusion.
