DURAG HM-1400 TRX 2 User manual

Operating manual
HM-1400 TRX 2
Total Mercury Analyser
GmbH • Kollaustraße 105 • 22453 Hamburg • Germany • www.durag.com
Before starting any work please read the operating
manual!
Article no.:
4 019 962

Version: 10016370-31-07 Previous version: 10016370-30-05
Production date: 20/07/2020
Document scope: 94
Operating manual Total mercury analyser HM‑1400TRX 2
DURAG GmbH
Kollaustraße 105
22453 Hamburg
Germany
Telephone:
Fax:
Email:
Internet:
[phone] – 0
[phone]
[email protected]
www.durag.com
This manual...
●Generally relates to the entire equipment, even when individual program modules or (parts of)
devices were not purchased.
●Must not be reproduced or transferred in any manner, language or medium, electronic or mechan-
ical, without the express permission of DURAGGmbH. The same applies to parts of the manual.
●Relates to the current device design version at the time this documentation was updated (see page
2 above for production date);
●Contains illustrations which may differ from the actual appearance due to further technical develop-
ments or for reasons of clarity. Therefore, the existing illustrations do not make any claims for deliv-
ery of identical products.

Contents
HM-1400 TRX 2 3
Contents
1 Information on this manual 5
2 Safety 7
2.1 General safety information..................................................................................................7
2.2 Device-specific hazards ......................................................................................................7
2.2.1 Hazards due to electrical equipment...................................................................................7
2.2.2 Hazard due to hot, aggressive, explosive gases or to high pressure of gas to be measured
8
2.2.3 Hazards due to chemicals...................................................................................................8
2.2.4 Hazards due to hot surfaces .............................................................................................10
2.2.5 Hazards during transportation...........................................................................................10
2.3 Personnel, qualifications ...................................................................................................10
2.4 Description and location of safety equipment and emergency stop mechanisms ............11
2.5 Intended use .....................................................................................................................11
3 Product description 12
3.1 Designation of device components ...................................................................................13
4 Theoretical basis 15
4.1 Principle of operation ........................................................................................................15
4.2 Sampling system...............................................................................................................16
4.3 Thermocatalytic reactor ....................................................................................................17
4.4 Gas drier ...........................................................................................................................19
4.5 The Hg0 photometer .........................................................................................................19
4.6 Standardisation .................................................................................................................20
4.7 Gas transport ....................................................................................................................20
4.8 Speciation (optional) .........................................................................................................21
4.9 Dilution (optional) ..............................................................................................................21
4.10 Zero adjustment ................................................................................................................23
4.11 Leak test ...........................................................................................................................24
4.12 Internal reference gas generator.......................................................................................24
4.13 Back-purging.....................................................................................................................25
4.14 Control ..............................................................................................................................25
4.15 Checking for malfunctions.................................................................................................26
5 Installation, commissioning 27
5.1 Safety................................................................................................................................27
5.2 Preparation for installation ................................................................................................29
5.2.1 Instrument location............................................................................................................29
5.2.2 Installation location of the sampling probe........................................................................29
5.2.3 Electrical connection .........................................................................................................31
5.3 Installation sequence for the measurement system..........................................................32
5.4 Installation.........................................................................................................................33
5.4.1 Installing the sampling probe ............................................................................................33
5.4.2 Installation of the measurement instrument ......................................................................34
5.5 Connections ......................................................................................................................34
5.5.1 Sampling probe and sample gas line................................................................................34
5.5.2 Power supply ....................................................................................................................35

Contents
4HM-1400 TRX 2
5.5.3 Signal lines........................................................................................................................36
5.5.4 Exhaust gas .....................................................................................................................36
5.5.5 Condensate.......................................................................................................................36
5.6 Using the chemicals necessary for operation ...................................................................36
5.7 Commissioning with preset parameters............................................................................37
5.8 Preparation for operation phase .......................................................................................37
5.9 Measuring mode ...............................................................................................................38
5.10 Decommissioning, storage, disassembly..........................................................................38
5.10.1 Decommissioning..............................................................................................................38
5.10.2 Storage .............................................................................................................................38
5.10.3 Dismantling .......................................................................................................................39
5.10.4 Disposal ............................................................................................................................40
6 Operation 41
6.1 The terminal ......................................................................................................................41
6.2 Basic rules for operation ...................................................................................................42
6.3 Measured values and system structure menu ..................................................................44
6.4 System messages.............................................................................................................46
6.5 Password protection .........................................................................................................47
6.6 Main menu ........................................................................................................................48
6.6.1 "Control room signals" menu (11, …, 14) .........................................................................49
6.6.2 "Functions" Menu (21, …, 24)...........................................................................................49
6.6.2.1 "Start, adjustment" menu (211, …, 214) ...........................................................................50
6.6.2.2 "Reactor, pump, valves" Menu (221, …, 224)...................................................................51
6.6.2.3 "Optional" menu (231, …, 233) .........................................................................................53
6.6.2.4 "Validation" Menu (241, …, 246).......................................................................................54
6.6.3 "Settings" Menu (31, …, 34) .............................................................................................56
6.6.3.1 "User" menu (311…314)...................................................................................................57
6.6.3.2 "Language" menu (341, …, 347) ......................................................................................61
6.6.4 "Status" Menu (41, …, 46) ................................................................................................61
7 Verification of the measuring system 63
7.1 Connecting an external reference gas generator..............................................................63
7.2 Testing the HM-1400TRX2 with the external test gas generator TR-81 (optional) .........64
7.3 Adjusting the HM-1400TRX2 with the internal reference gas generator.........................67
8 Maintenance 70
8.1 Notes on cleaning .............................................................................................................71
9 Technical data 73
10 Dimensioned drawings 75
11 Messages/fault elimination 80
11.1 Monitored parameters and error messages in plain text...................................................80
11.2 Causes of errors and their rectification .............................................................................81
12 Parameter list (device parameters in delivered condition) 87
13 Index 93

1 | Information on this manual
HM-1400 TRX 2 5
1 Information on this manual
This manual is aimed at qualified
specialised personnel.
The manual is part of the product and must be stored in the im-
mediate vicinity of the place of operation such that it is access-
ible to the personnel at all times. The instructions on preventing
dangers and damage indicated in this manual must be followed.
The following symbols are used
Warning symbols Warning symbols (general)
Warning of electrical voltage
Warning of corrosive substances
Warning of toxic substances
Warning of hot surfaces
ESD-sensitive components
Signal words DANGER Risk leading to death or serious injury.
WARNING Risk that could potentially lead to death or serious
injury.
CAUTION Risk that could potentially lead to less serious or
minor injury.
ATTENTION Risk that could potentially lead to material or envir-
onmental damage.
Hazardous substance symbols Harmful to health
Harmful to the environment
Information symbols This symbol indicates potential material and environ-
mental damage

1 | Information on this manual
6HM-1400 TRX 2
This symbol indicates a notification or tip
This symbol indicates the required special tool and
the particular technical equipment.
Text [ nnn]
Text presented in this way indicates a link to addi-
tional information. The (final) number before the in-
dicates the page number where this information can
be found. In the PDF version of the manual, you can
click on the link to go to the required information.
Safety information is displayed particularly clearly in this manual
( example ):
WARNING Risk of injury due to incorrect spare parts.
Incorrect or faulty spare parts can cause malfunctions that can
lead to serious injuries.
▶Use only original spare parts from the manufacturer.
▶Purchase spare parts from authorised dealers or directly from
the manufacturer.

2 | Safety
HM-1400 TRX 2 7
2 Safety
2.1 General safety information
Only operate the product in perfect condition and in accordance
with the operating manual. Perceptible changes from normal op-
eration indicate functional impairments and should be taken seri-
ously.
Malfunction detection Look out for:
●Formation of smoke or unusual odours
●Unusual noises caused by and occurring during operation of
the device (e.g. including the fan)
●Unusual vibrations
●Unusually high surface-temperatures of system components
●Unexpected changes in power consumption
●Triggering of safety monitoring devices
●Unusual and significant fluctuations or shifts in the measure-
ment results
●Device warning and fault messages
Safety information As a general rule, the following safety information applies for the
described product:
●When preparing and performing work:
Follow the statutory regulations valid for the plant and the cor-
responding technical rules. Observe national safety and acci-
dent prevention regulations.
●Maintenance work and repairs not described in this manual
must not be performed without prior arrangement with the
manufacturer.
2.2 Device-specific hazards
The following section describes residual risks determined by the
risk assessment.
Follow the safety instructions listed here and the warning inform-
ation in the subsequent chapters of this manual in order to re-
duce health hazards and prevent dangerous situations.
The personnel assigned to carry out installation, commissioning
and maintenance must be thoroughly familiar with all potential
hazards and repair measures as set out in this manual.
2.2.1 Hazards due to electrical equipment
The device is operated with electric current. There is an immedi-
ate risk to life when touching parts carrying live voltage. Damage
to the insulation or individual components can present a risk to
life. Work on electrical systems must only be performed by spe-
cialised electricians. Before opening the housing or removing the

2 | Safety
8HM-1400 TRX 2
touch guard, disconnect the device. Check that there is no
voltage, and take measures to protect against unauthorised re-
activation.
Where there are extreme fluctuations of temperature and mois-
ture, condensation can cause moisture to build up within the
device. This can cause an electrical short circuit.
After transportation of the device, do not put it into operation until
the device, including its internal parts, has acclimatised to the
ambient temperature.
Only connect the HM‑1400TRX 2 to the supply voltage set out
on the type label.
Only switch on the operating voltage once installation is com-
plete. Only switch on the device once installation is complete.
This measuring system has been designed to ensure safe separ-
ation between primary and secondary electric circuits. Connec-
ted low voltages must therefore also be generated by safe separ-
ation.
Steps must be taken to protect the electronic components
against electrostatic discharge (ESD protection) for all work on
the open device. To prevent static charge of the human body,
use a device such as a personnel earthing system.
2.2.2 Hazard due to hot, aggressive, explosive gases or to
high pressure of gas to be measured
The HM‑1400TRX 2 is connected to the flue gas duct via the
sampling probe and the exhaust gas duct.
In the case of systems with a low hazard potential (ambient pres-
sure, low temperatures, no health hazard), mounting/removal
can be carried out during system operation or when replacing
connecting cables. The applicable provisions and safety regula-
tions for the system must be complied with and any necessary
and appropriate protective measures taken.
The HM‑1400TRX 2 is not suitable for use in explosive gas mix-
tures!
2.2.3 Hazards due to chemicals
Chemicals always pose particular risks and hazards. They
should therefore only be handled by appropriately trained per-
sonnel with the necessary care.

2 | Safety
HM-1400 TRX 2 9
WARNING Risk of chemical burns, risk of skin irritation
Corrosive chemicals such as potassium hydroxide are used in
the
HM‑1400TRX 2 to analyse the mercury concentration.
Maintenance work involves replacing these substances. Follow
the instructions on the containers and in the safety data sheets.
▶Wear appropriate protective equipment/clothing.
WARNING Risk of poisoning
With (elemental) mercury, there is a risk of inhaling the sub-
stance when breathing in.
When performing maintenance work, note the information in the
mercury safety data sheet.
▶Do not heat the iodine-activated carbon loaded with mercury
above 70°C. This prevents evaporation and the release of
mercury.
▶Wear appropriate protective equipment/clothing.
The technique for measuring the mercury concentration is to
pass the gas through an iodised activated carbon filter (between
the measurement and reference cell of the photometer). The
mercury contained in the gas being measured bonds to the car-
bon and is thus trapped in the filter.
A mercury chloride solution (HgCl2) is used for the Hgn+ gas gen-
erator integrated in the device.
Empty containers must always be replaced by full, fresh contain-
ers. Topping up empty containers is not permitted. In addition to
damage caused by spilled acidic solution in the device cabinet,
changes in the available mercury content in topped-up contain-
ers also occur.
Please note the information in the relevant safety data sheet.
If the HM‑1400TRX 2 also contains an optional speciation mod-
ule, a potassium hydroxide solution (KOH) will need to be
provided in an additional reservoir and replaced at regular inter-
vals. Please note the information in the relevant safety data
sheet.
Used chemicals that must be disposed of after a maximum of
6months as part of device maintenance:
●Contents of the selective filter (iodine-active carbon loaded
with mercury)
●Mercury chloride solution
●Any condensate collected
The company operating the measuring device is responsible for
the handling, transportation and, where necessary, disposal of
the chemicals. The German Ordinance on Hazardous Sub-
stances and the separate safety data sheets for all used chemic-
als must be observed here.

2 | Safety
10 HM-1400 TRX 2
The latest versions of the material safety data sheets included
with the chemicals are authoritative. All personnel who work with
these substances must be familiar with the contents of these
safety data sheets.
Take the necessary and appropriate protective measures as spe-
cified in the data sheets. Please also note any specified first-aid
measures.
2.2.4 Hazards due to hot surfaces
Some of the components used in the HM‑1400TRX 2, as well as
the sampling probe, sampling line, flange and flange piece ex-
ternal components, may be hot or may become hot during opera-
tion. There is a risk of burns. Observe the relevant warning sym-
bols on the device components!
2.2.5 Hazards during transportation
The HM‑1400TRX 2 is a heavy device. There are therefore risks
due to:
Suspended loads Loads may swing out and fall to the ground during lifting proced-
ures. This can lead to serious or even fatal injuries. Do not walk
underneath suspended loads, or into their swivel range. Put
down the load when you leave the work area.
Heavy weight When lifting or moving heavy loads, this can lead to back pain
and injury. Do not lift heavy loads without assistance. Use suit-
able lifting equipment or lifting tools.
2.3 Personnel, qualifications
The manual is intended for qualified specialised personnel:
Work on the HM‑1400TRX 2 must only be carried out by the fol-
lowing personnel:
●Specialised personnel are able to perform the work assigned
to them and identify hazards independently on the basis of
their technical training, knowledge and experience, as well as
their knowledge of the relevant provisions.
●With their professional training, knowledge and experience,
as well as their knowledge of the relevant standards and reg-
ulations, electricians are capable of properly carrying out work
on electrical systems and identifying potential hazards inde-
pendently. Electricians are specially trained for the working
environment in which they operate.

2 | Safety
HM-1400 TRX 2 11
2.4 Description and location of safety equipment
and emergency stop mechanisms
The operating company must incorporate safety measures for
the HM‑1400TRX 2 product into the safety plan for the overall
system. This also includes the setup and description of the safety
and emergency stop equipment, including information on the loc-
ation of the relevant emergency stop switches.
The customer must install a main switch in the mains supply line
that can be used to disconnect the measuring system from the
power supply.
2.5 Intended use
The HM‑1400TRX 2 described in this manual is used for the on-
going determination of the mercury concentration in the flue gas
from incineration plants and in process gases.
The device is expressly not permitted for use in potentially ex-
plosive areas.
The specifications set out in Section 9 Technical data [}73]
must be observed and complied with.
If the device is not used as intended, the protection provided by
the device may be impaired!

3 | Product description
12 HM-1400 TRX 2
3 Product description
The HM‑1400TRX 2 is an automatic measuring system certified
to EN15267. It is used for the ongoing analysis of all gaseous
mercury compounds in systems or process gases that are sub-
ject to compulsory monitoring.
A double-beam photometer is used to determine the concentra-
tion of atomic mercury Hg0. To determine the total mercury con-
tent Hgtotal, oxidised mercury Hgn+
is reduced to Hg0 beforehand. This is performed in a thermocata-
lytic reactor.
The HM‑1400TRX 2 has a connection point for an external gen-
erator in order to check the photometer and the overall device.
Control functions ●Leak test: The device checks the leak-tightness of the sys-
tem.
●Zero adjustment: The zero point of the device is adjusted at
regular intervals.
●Zero point measurement: The device carries out an automatic
zero point measurement.
●Connection point for external gas generator: Allows for the
connection of external gas generators in order to check the
photometer and the overall device.
Options (not compliant with
measuring mode in accordance
with EN 15267!)
●Reference point measurement: The device carries out an
automatic reference point measurement using the internal ref-
erence gas generator.
●Speciation: Determines the amounts of both Hg0 and Hgn+
(see Section 4.8 Speciation (optional) [}21])
●Dilution: For applications with a very high mercury concentra-
tion or an aggressive flue gas matrix (see Section 4.9 Dilution
(optional) [}21])
Variant examples
HM‑1400TRX 2 2EC-230-A1LFJ Total mercury analyser,
power supply 230/400V50Hz,
steel sheet safety cabinet, cable feed from above,
heated line fed in at the left-hand side
or from above for use within rooms,
built-in fan with inlet and outlet filter,
protection class IP54, ambient temperature +5…+40°C,
tested for suitability according to EN15267,
incl. internal HgCl2 test gas generator
HM‑1400TRX 2 2EC-230-A1LFT Total mercury analyser,
power supply 230/400V50Hz,
steel sheet safety cabinet, cable feed from above,
heated line fed in at the left-hand side
or from above for use within rooms,
built-in fan with inlet and outlet filter,
protection class IP54, ambient temperature +5…+40°C,
tested for suitability according to EN15267,
with speciation unit, incl. internal HgCl2 test gas generator
Table3.1: Examples of different variants

3 | Product description
HM-1400 TRX 2 13
3.1 Designation of device components
Fig.3.1: Overview of components, designation of measurement instrument parts
12 Hg0 adsorber (zero gas generation) F1 Residual current circuit breaker
13 Pre-filter for particles and aerosols F7 Fuse for reactor heating
14 Hg0 adsorber (photometer) Kl Terminals
15 Needle valve for volume flow adjustment LR Overload relay
16 Condensate barrier membrane M1 Sample gas cooler
21 HgCl2 solution reservoir (gas generator) M2 Fan
22 KOH solution reservoir
(speciation) ①
M3 Sample gas pump
A2 PLC (programmable logic controller) M4 Condensate pumps
A3 Control unit M5 Peristaltic pump for KOH solution ①
A5 Hg0 photometer M31 Peristaltic pump for HgCl2 solution
A6 Thermocatalytic reactor R Relay
A7 Safety temperature limiter for reactor S1 Switch
A31 Mass flow controller for gas generator Si Fuse(s)
A32 Mass flow controller for dilution ① T1 Power supply unit
A33 HgCl2 evaporator X10 Socket for external test gas generator

3 | Product description
14 HM-1400 TRX 2
B1 Thermostat fan M2 Y1 3-way valve (zero gas/sample gas)
B2 Differential pressure sensor Y2 Selection valve for reduction vessel A6.1/
A6.2
B3 Absolute pressure sensor Y11 Leak test/zero gas valve
B4 Level gauge for monitoring the
KOH solution (speciation) ①
Y30 Switchover valve for dilution ①
B5 Level gauge for monitoring the
HgCl2 solution (gas generator)
Y51 Valve for speciation ①
B6 Mass flow meter for HgCl2 solution Z5 Mains filter
B15 Temperature sensor for sample gas Lf Air filter
B31 Pressure sensor for dilution air inlet ① Option
Fig.3.2: Overview of components, designation of sampling probe
1Sampling probe housing cover 4Weld-in pipe with mounting flange
2Electric terminal box 5Sampling tube
3Adapter flange for heated sampling tube 6Sample gas line with two inner lines

4 | Theoretical basis
HM-1400 TRX 2 15
4 Theoretical basis
The HM‑1400TRX 2 is an extractive system for the continuous
measurement of total mercury in flue gases. It does not matter
whether the mercury occurs in elemental form Hg0 or as oxidised
Hgn+.
The flue gas is fed into the measuring device via a sample sys-
tem, where all mercury compounds are first converted into ele-
mental mercury and any interfering components are filtered out
of the flue gas. After the sample gas has been dried, the mercury
content is determined using UV absorption spectroscopy and
output as a standardised value following temperature and pres-
sure corrections.
The HM‑1400TRX 2 also contains the following modules for
monitoring the system:
●Zero point monitoring
●Reference point monitoring
●Linearity monitoring
●System leak-tightness monitoring
Variants of the device can also dilute the sample gas or determ-
ine the ratio of elemental mercury to total mercury.
4.1 Principle of operation
Sample probe Sample lineSample tube
Leak check
Speciation
Reactor box
HgCl2 Gasgenerator
Dillution / Gas generator Hg0, Hg+
Speciation
Sample
Inlet
Fig.4.1: Substance flow plan HM‑1400TRX 2
01 Gas inlet into stack ① Option
02 Test connection (test gas application) B2 Differential pressure sensor
04 Zero gas B3 Absolute pressure sensor

4 | Theoretical basis
16 HM-1400 TRX 2
05 Flue gas B4 Level gauge for monitoring the
KOH solution (speciation) ①
06 Condensate B5 Level gauge for monitoring the
HgCl2 solution (gas generator)
07 Instrument air B6 Mass flow meter for HgCl2 solution
12 Hg0 adsorber (zero gas generation) B15 Temperature sensor for the sample gas in
the photometer
13 Pre-filter for particles and aerosols B31 Pressure sensor for instrument air inlet
14 Hg0 adsorber (photometer) E11.1 Sample gas line (heated)
15 Needle valve for volume flow adjustment E11.2 Extension for the heated sample gas line ①
16 Condensate barrier membrane E12 Sampling probe
21 Reservoir (HgCl2 gas generator) E13 Sampling tube
22 KOH solution reservoir
(speciation) ①
M1 Sample gas cooler
23 Damping for mass flow meter M3 Sample gas pump
31 Pressure switch M4.1 Condensate pump
A5 Hg0 photometer M4.2 Condensate pump
A6 Thermocatalytic reactor M5 Peristaltic pump for KOH solution ①
A6.1 Reduction vessel1 M31 Peristaltic pump for HgCl2 solution
A6.2 Reduction vessel2 Y1 3-way valve (zero gas/sample gas)
A7 Safety temperature limiter Y2 Selection valve for reduction vessel A6.1/
A6.2
A31 Mass flow controller for gas generator Y11 Leak test/zero gas valve
A32 Mass flow controller for dilution ① Y30 Switchover valve for dilution
A33 HgCl2 evaporator Y51 Valve for speciation ①
4.2 Sampling system
The sample system consists of the sampling tube E13, the
sampling probe E12 and the sample gas line E11. The sampling
tube extracts the sample gas from a central position in the flue
gas duct and transports it into the sampling probe. A filter in the
sampling probe removes any dust. Once filtered, the gas then
moves through the sample gas line to the measuring system.
Unlike elemental mercury, many mercury compounds are not
volatile, and instead adhere to surfaces. They are only certain to
be in gas form at temperatures above 150°C.
The entire sampling path is heated, which means that the water
in the sample gas will not condense. Heating also prevents mer-
cury compounds from dissolving in condensation water or ad-
sorption on cold surfaces.
The sampling probe has a test gas connection. In order to test
the measuring system, defined test gases are injected into the
system via this inlet using a test gas generator.

4 | Theoretical basis
HM-1400 TRX 2 17
4.3 Thermocatalytic reactor
In the measuring system, the extracted flue gas passes through
the heated 3-way valve Y1 into the thermocatalytic reactor A6
(which consists of the 2 reduction vessels A6.1 and A6.2). In this
reactor, oxidised mercury is converted into elemental mercury
and interfering components of the flue gas are chemically ab-
sorbed, all at temperatures of around 300°C.
The sample gas reacts with the reactor filling as it flows through
the reactor. Acidic components of the sample gas such as nitro-
gen oxides (NOx), halogens, hydrogen halides (HCl, Cl2) and sul-
phur dioxide (SOx) are absorbed. Elemental mercury passes
through the reactor. Mercury compounds react with the reactor
filling and are converted to elemental mercury, which then also
leaves the reactor.
Due to the retention of the acidic gas components, the reactor
filling is slowly used up. There is only ever one reduction vessel
in use during measuring operation. This means that when the
first filling reaches the end of its service life, it is possible to
switch to the second filling with barely any interruption to mea-
suring operation. There is then sufficient time to replace the used
up reactor filling. Both reduction vessels A6.1 and A6.2 are dir-
ectly connected on the inlet side. Switching between vessels is
via the valve Y2 on the outlet side. This valve and the upstream
heated 3-way valve Y1 are shown in the figure below.
At the reactor outlet, the cleaned flue gas contains only ele-
mental mercury. This is not soluble in water and has a sufficiently
high vapour pressure. It remains in gas form even at temperat-
ures around freezing point. As a result, the sample gas can be
cooled to ambient temperature once it has left the reactor.

4 | Theoretical basis
18 HM-1400 TRX 2
2
456789 310
1
1 Reduction vessel (A6.1) 6 Evaporator (A33)
2 Reduction vessel (A6.2) 7 Sample gas line connection
3 Reactor housing 8 Connection for speciation ①
4 Supply lines to the
switchover valve (Y2)
9 Connection to the gas gener-
ator and
dilution if required ①
5 Zero gas/sample gas valve
(Y1)
10 Zero gas connection
① Option
Fig.4.2: Structure of the reactor housing
There is also the option of using the HM‑1400TRX 2 to measure
only the elemental mercury in the flue gas. In this case, the spe-
ciation valve Y51 is adjusted so that the flue gas is not fed
through the thermocatalytic reactor, but directly to the photo-
meter. There is therefore no conversion of bound mercury to ele-
mental mercury. Only the elemental mercury content is fed into
the photometer.
Because the flue gas does not pass through the reactor filling in
this case, the acidic components such as sulphur oxide, nitrogen
oxide or hydrogen halides need to be removed in another way.
To achieve this, a small quantity of potassium hydroxide solution
is added to the sample gas. The potassium hydroxide solution
reacts with and binds the acidic components of the gas.
The potassium hydroxide solution prevents contamination of the
gas-carrying lines and cross-sensitivity to sulphur dioxide.

4 | Theoretical basis
HM-1400 TRX 2 19
4.4 Gas drier
Flue gases often contain a high proportion of water. After wet
cleaning, this can be up to 40%. When the sample gas cools
down to approx. 3°C in the cooler M1, this causes excess water
to condense. The humidity level then remains constant at 0.7%.
The accumulating condensate is removed from the cooler using
two condensate pumps M4.x and is then transported to the
device’s condensation outlet.
If the speciation unit has been installed in the device, then the
excess potassium hydroxide solution will be removed from the
system together with the condensate.
Due to the low level of residual humidity, there is no possibility of
water getting into the photometer. In the event of a water break-
through, e.g. due to a defective cooler, the ingress of water is
prevented by means of a condensate blocking membrane (16).
Gaseous molecules can pass through this membrane, but liquid
water is blocked. This can cause the membrane to form a seal,
leading to the subsequent failure of the measuring instrument.
There is an upstream particle filter to protect the pores of the
condensate blocking membrane. This filter also prevents dust
getting into the photometer.
4.5 The Hg0 photometer
The mercury content of the flue gas is measured using the Hg0
photometer (A5). This involves using the properties of mercury to
absorb the UV light with a wavelength of 253.7nm. The attenu-
ation is described by the Beer-Lambert law, and is dependent
upon the path length through the irradiated gas and the concen-
tration of mercury in the gas. The path length in the photometer
is constant. The concentration of mercury in the sample gas can
therefore be determined from the attenuation of the light.
However, other substances also absorb light in this spectral
range, causing cross-sensitivities. If the attenuation of the signal
is measured from the same sample gas with and without mer-
cury, the cross-sensitivity can be compensated.
The photometer in the HM‑1400TRX 2 therefore has two cells, a
measurement cell and a reference cell. The sample gas first
flows through the measurement cell. It is then transported via a
selective mercury filter, after which it flows through the reference
cell with the mercury removed.

4 | Theoretical basis
20 HM-1400 TRX 2
Measuring cuvette
Reference cuvette
Gas outlet
Photo diodes
Gas inlet
UV-lamp
Diaphragm
Selective
Hg filter
Fig.4.3: Structure of the Hg0 photometer
The light in the photometer is generated by a mercury vapour
lamp. This process makes use of the physical effect that when
stimulated, elements emit precisely the same waves that they
absorb. The other wavelengths from the lamp are optically
filtered. The light is distributed evenly to the two cells.
Once the light has passed through the cells, the residual intensity
is measured using photodiodes. The ratio of the intensity of the
measurement cell to the intensity of the reference cell is used to
calculate the amount of mercury in the measurement cell.
This measurement method is used to determine the absolute
mercury content in the measurement cell. The value is independ-
ent of flow velocity, temperature or pressure.
4.6 Standardisation
The photometer itself supplies the raw concentration of mercury
inside the cell. This value relates to the operating conditions, i.e.
the cell temperature and the pressure within the cell. In order to
obtain comparable measured values, the raw concentrations
need to be converted to reference values. To this end, measure-
ments are taken of the cell temperature (B15) and the pressure
within the cells (B2). These values are used to convert the raw
value to standard conditions using the Ideal Gas Law.
The humidity of the gas is constant at around 0.7%, and has no
more influence once the device has been calibrated.
4.7 Gas transport
The sample gas pump M3 at the end of the gas path pumps the
gas through the measuring instrument. A needle valve (15) up-
stream from the sample gas pump slows down the gas flow to
approx. 100 l/h. The gas flow is measured at the device outlet via
a differential pressure gauge (B2) at a Venturi nozzle.
The gas flow measurement serves only to check the proper func-
tioning of the device. As the flow decreases, the t-90 time in-
creases. If the flow is too high, the cooler will be overloaded, and
it will no longer be possible to guarantee the drying of the gas.
The measurement process itself does not depend on the flow.