System components HM-1400 TRX

Sampling system

The sampling system consists of a sampling probe and a sampling line. Both components are heated to 180 °C. With flue gas temperatures < 200 °C, the sampling tube must also be in heated tube design to prevent faulty measurements (lower findings for the mercury concentration measurement due to the absorption properties of HgCl₂).

Gas patch switchover

The sample gas is extracted condensate-free from the exhaust stack with approx. 100 Nl/h and fed via a three-way ball valve to the thermocatalytic reactor. The path switchover is also heated and is operated as component of the measuring device by means of the device control. You can select between sample gas connection, reference connection or zero gas connection.

Thermocatalytic reactor

The total mercury analysis measures not only the elementary metallic mercury that is stored freely in the sample gas or deposited in the materials, but also measures the chemically bonded mercury that is found in the flue gas. The ionic mercury must also be converted into elementary, atomic mercury so that the detector can acquire and evaluate the total mercury. The thermocatalytic reactor carries out this function at a preset operating temperature.

Gas drying

Before the mercury content is determined, the now created sample gas containing Hg⁰ is dried while flowing through a Peltier cooler. At the same time the system pressure and the measured gas temperature are continuously recorded.

Prefilter

Before the prepared and dried sample gas flows through the photometer, it passes through an additional filter with hygroscopic effect to eliminate even lower residual humidity components. This is important first for recording the gas volume flow in dry form and, second, pollution and deposits are avoided in the photometer and the maintenance-free service life increased.

2-beam UV photometer

The sample gas enters the measuring cuvette and is then routed over a selective filter in which the mercury is absorbed. The sample gas thus freed from the mercury then flows through the reference cuvette. The advantage of this cuvette switching is that the entire gas matrix flows through both the measuring cuvette and the reference cuvette and most of the mercury is selectively filtered out before it reaches the reference cuvette. This principle of differential measurement means that the measurement is less sensitive to spectrometric interference components than the single-beam photometer that has only one cuvette. With the cuvette switching of the two-beam device this cross sensitivity for SO₂, for example, only becomes effective after 1000 mg/m?. The measured signal from the photometer is taken over by the internal PLC.

Gas volume flow generation

When the sample gas volume flow leaves the 2-beam UV photometer, it passes through the vacuum pump which generates the gas flow. The volume flow of approx. 100 Nl/h is set manually with the fine regulating valve. The system pressure and sample gas temperature parameters are measured after the gas drying at the photometer, where the mercury is also measured, and are used ultimately to convert the gas volume flow to standard conditions. The mercury concentration as result of a measurement is output as 4 to 20 mA current signal to match the set measuring range of 0 to X µg/Nm³ (dry).

Optional:

• Larger measuring range with dilution device
• Side-mounted cooling device
• Integrated system to generate reference gas
• Heated sample pipe 0.6 m, 1.0 m, 1.5 m