User manual
2920 1475 00
29
Instruction book
Open system
An open system is a pass-through system, or a circulating system
with a cooling tower. In the latter case, the composition of the
water that enters the cooler must be considered, and not the
composition of the make-up water. Due to the evaporative effect
in the cooling tower, much higher concentrations of ions can
be obtained in the circulating water than in the make-up water.
2.5.2 Cooling water parameters
The Rysnar stability index (RSI)
The Rysnar Index (RSI) is a parameter for predicting whether
water will tend to dissolve or precipitate calcium carbonate.
The adhesion of scaling depositions and their effect are different
on different materials, but the equilibrium of the water (scaling
or corrosive) is only determined by its actual pH value and by
the saturation pH value (pH
s
).
The saturation pH value is determined by the relationship
between the calcium hardness, the total alkalinity, the total solids
concentration and the temperature.
The Rysnar Index is calculated as follows :
RSI = 2*pH
s
- pH
where pH = measured pH (at room temperature) of
water sample
pH
s
= pH at saturation
The pH
s
is calculated by using :
pH
s
= (9.3 + A + B) - (C + D)
A : depends on the total solids concentration
(mg/l).
B : depends on the highest cooling water
temperature (°C),
For GA/GR units take T = 75°C
C : depends on the calcium hardness
(ppm CaCO
3
).
D : depends on the HCO
3
-
concentration or
M-alkalinity (mval/l).
The values from A, B, C and D are found in the
table below.
Total dissolved solids Temperature Ca-hardness M-Alkalinity
(mg/l) A (°C) B (ppm CaCO
3
) C (mval/l) D
50 - 300 0.1 0 - 1 2.6 10 - 11 0.6 0.20 - 0.22 1.0
400 - 1000 0.2 2 - 6 2.5 12 - 13 0.7 0.24 - 0.26 1.1
7 - 9 2.4 14 - 17 0.8 0.28 - 0.34 1.2
10 - 13 2.3 18 - 22 0.9 0.36 - 0.44 1.3
14 - 17 2.2 23 - 27 1.0 0.46 - 0.54 1.4
18 - 21 2.1 28 - 34 1.1 0.56 - 0.70 1.5
22 - 27 2.0 35 - 43 1.2 0.72 - 0.88 1.6
28 - 31 1.9 44 - 55 1.3 0.90 - 1.10 1.7
32 - 37 1.8 56 - 69 1.4 1.12 - 1.38 1.8
38 - 44 1.7 70 - 87 1.5 1.40 - 1.76 1.9
45 - 50 1.6 88 - 110 1.6 1.78 - 2.20 2.0
51 - 56 1.5 111 - 138 1.7 2.22 - 2.78 2.1
57 - 63 1.4 138 - 174 1.8 2.80 - 3.54 2.2
64 - 71 1.3 175 - 220 1.9 3.54 - 4.40 2.3
72 - 80 1.2 230 - 270 2.0 4.6 - 5.4 2.4
280 - 340 2.1 5.6 - 7.0 2.5
350 - 430 2.2 7.2 - 8.8 2.6
440 - 550 2.3 9.0 - 11.0 2.7
560 - 690 2.4 11.2 - 13.8 2.8
700 - 870 2.5 14.0 - 17.6 2.9
880 - 1000 2.6 17.8 - 20.0 3.0