INM MTL 130-0202 Rev 4
1
1
INTRODUCTION
The KK650 measures hydrogen in the ranges 0 to 5% or 0 to 10% (depending on the model),
and also chlorine in the range 0 to 100%, when these gases are mixed with air. It is designed
specifically for the chlor-alkali industry. Chlorine is usually manufactured by the electrolysis
of brine (sodium chloride) or potassium chloride. This process also produces hydrogen and
a small quantity is found in the chlorine stream. Larger quantities can indicate failure of a
mercury cell, diaphragm or membrane and lead to potentially fatal explosive mixtures of
hydrogen and chlorine!
The complete analyser comprises two separate parts, the sensor/reactor and the control/
display electronics, which are linked by multi-core cables.
1.1
The katharometer sensor
This comprises two thermal conductivity measurement sensors and a sealed reference sensor.
These are mounted together in one encapsulated assembly, which ensures that the sample gas
comes into contact only with materials that are chemically inert. The katharometer assembly is
mounted on a PVC panel along with its associated temperature controlled reactor.
1.2
The control/display electronics
These are housed in a separate IP66 enclosure containing the supply and signal processing
for the katharometer, along with the power supply and controller for the reactor. Hydrogen
and chlorine concentrations are displayed together with the reactor temperature and status.
Analogue outputs and volt-free contacts are also provided, depending on the options chosen –
see specification.
1.3
How it works
First, the thermal conductivity of the plant sample, as delivered, is measured. Next the sample
is passed through a heated reactor tube where the hydrogen is reacted with the excess of
chlorine (the hydrogen reacts preferentially with the chlorine and not with the oxygen within
the sample). This mixture, now comprising chlorine, air and hydrogen chloride, is passed
through the second sensor. The difference in thermal conductivity between the first and second
measurement is a direct function of the hydrogen content, which the instrument calculates.
A measurement of thermal conductivity can only be used to interpret concentration where the
change of only one component affects the sample’s thermal conductivity, but measuring the
hydrogen content in the way that we do means that the thermal conductivity measurement of
the chlorine, hydrogen and air mix can be corrected for hydrogen content. This then enables the
chlorine to air ratio to be calculated and hence the chlorine concentration.
The KK650 relies on the hydrogen reacting with chlorine or oxygen in order to measure it,
consequently it is not able to measure hydrogen in any other type of gas mixture, e.g. hydrogen
in nitrogen. However, other analysers are available for this type of duty.
Thermal conductivity measurements are not affected to a great extent by pressure fluctuations
of a few centimetres (or inches) W.G. For optimum accuracy the process gas sample should be
flowed at 350ml/min. (100ml/min = 0.212cuft/hr).
Katharometer
Assembly
Temperature
Controlled
Reactor
(725°C/1337°F)
WARNING
These parts run HOT
in normal operation
Quartz Reaction Tube
Outline of
heat shield
Connectors are ¼“ double ferrule in PFA
All interconnecting pipework is in PFA
Sample in
Sample out
