Technical note

How high can cycles of concentration go? Start with LSI

Cycles of concentration are capped by scaling tendency, not pumping capacity. What GB/T 50050-2017 requires, and why removing scale-forming ions changes the ceiling.

A common misconception

"If I raise the cycles of concentration, blowdown drops and I save water." The direction is right — but the cycles of concentration are not a free choice. They are capped by the scaling tendency of the water, and that tendency can be calculated.

1. What the standard says

In China this is not a matter of experience; GB/T 50050-2017 (Code for design of industrial circulating cooling water treatment) is explicit:

• Clause 3.1.11: cycles of concentration shall not be less than 3.0;
• Clause 3.1.10: where calcium hardness plus total alkalinity exceeds 1,100 mg/L (as CaCO₃), or RSI is below 3.3, treatment measures shall be taken;
• Clause 4.0.1(2): side-stream treatment shall be provided.

Read together, the ceiling on cycles of concentration is set by calcium hardness + total alkalinity and by LSI/RSI — not by pumping capacity.

2. Why dosing cannot push it up

Inhibitor dosing keeps scale-forming ions in solution: crystal growth is distorted and dispersed so that scale does not form on heat transfer surfaces. But the ions remain in the water. Every step up in cycles of concentration raises calcium and alkalinity proportionally; once the LSI limit is passed, the heat exchangers start to foul — usually seen as rising approach temperature and higher energy consumption.

That is why chemical programmes keep a safety margin and rarely go higher. It is not a lack of skill; it is the mechanism.

3. Why electrochemical treatment can

JT-ECT works on the side-stream and removes the scale-forming components: calcium and magnesium deposit on the cathode (a 316L plate stack) and leave the system with blowdown.

The key point is that calcium hardness and total alkalinity fall together, in equal amounts — and these are the dominant positive terms in the LSI equation. Because they drop together, LSI does not run away as cycles increase, so cycles can be raised towards the LSI limit and blowdown falls accordingly.

4. How high? It must be recalculated for your water

We will not give a number that is meant to fit every plant. The real limit depends on:

1. Make-up water: calcium hardness, total alkalinity, chloride, TDS and pH;
2. System heat load and circulating water temperature rise;
3. Dosing history and the condition of existing deposits;
4. Side-stream capacity and operating strategy (continuous or intermittent).

Send us the make-up water analysis and we will recalculate the mass balance and LSI, and issue a report stating the cycles your system can hold, the blowdown reduction, and the assumptions behind both.

5. Next step

If you already have a make-up water report, four numbers are enough: calcium hardness, total alkalinity, chloride and TDS. If not, tell us the water source type (municipal / groundwater / surface / reclaimed) and cooling tower rated flow, and we will give a first assessment before arranging sampling.