Evoqua WALLACE & TIERNAN DEOX/2000, Инструкция по эксплуатации

Страница: 35 / 86

W3T331759 / WT.050.585.003.UE.IM.1014 31
MICRO/2000® AND DEOX/2000® MODULE
Iodine is used as the “biasing reagent” because it is less likely (and
slower to react with organic oxidant demand, making determination of
residuals more reliable than a hypochlorite (chlorine) biased measurement.
Because iodine is not stable in solution (i.e., is volatized and reacts
readily), Potassium iodate solution is reacted with potassium iodide (KI)
and releases iodine as used. This conversion reaction takes place in the
long length of “reaction” tubing where the mixed reagents react before
entering the water sample.
The analyser measuring process is as follows:
A continuous sample is delivered to the analyser. A flushing Y-strainer
divides the sample into two streams—the larger bypass stream
continuously flushes the Y-strainer strainer element and the smaller
stream, about 500 ml/min, flows into the analyser. Most of the flow into
the analyser is again bypassed, but a small portion is metered from this
flow by a peristaltic metering pump. The reagents, Potassium Iodate in
pH4 buffer and potassium iodide in distilled water, are also metered by
the same pump. As the reagents are discharged from the pump, they are
combined and reacted in a length of tubing referred to as the reaction
tubing. The reacted reagents are then mixed with the sample inlet to the
metering pump and the “Biased” sample then enters the analyser cell. A
three- electrode “probe” is immersed in the sample in the cell. A rotating
impeller stirs the sample and maintains a constant sample velocity across
the electrode surfaces. It also agitates the grit used to clean deposits from
the electrodes, improving the stability of calibration. The three-electrode
amperometric cell produces a signal (electrical current) proportional to
the oxidant (iodine) concentration in the cell.
3.2.1.3 Sample flow adjustment
Before starting the sample pump or otherwise starting sample flow, check that
the bypass control valve on the bypass leg of the Y-strainer, at the analyser, is
open and that the sample flow control valve to the inlet of the analyser is closed.
CAUTION: To prevent possible equipment damage, apply up to a maximum
of 0.3 bar (5 psi) water pressure to the analyser sample input. The tubing
in the analyser metering pump cannot withstand more than 5 psi pressure.
If pressure in excess of 0.3 bar (5 psi) is applied to the analyser input, fluid
may be sprayed from the analyser metering pump inlet.
CAUTION: Pressures in Excess of 0.3 bar (5 psi) will cause the the
tubing passing through the peristaltic pump to expand resulting in an
increase in flow and hence a change in the dilution ratio. Ideally the flow
to the drain should not be any more than a constant drip.