AIR MONITORING
PROBE SAMPLING IN HAZARDOUS AREAS UNDER EXTREME CONDITIONS
Introduction
Thanks to extensive research and industry discussions, the importance of innovative, state-of-the-art probe sampling solutions in emission monitoring is well established. Numerous studies indicate that nearly 80% of continuous extractive gas measurement issues originate from the probe sampling system. This underscores the necessity for harmonizing integration between the probe sampling system and the analyzer to ensure reliable and consistent measurement results.
From a technical standpoint, designing an optimal sample gas system is challenging, and even minor details significantly influence performance. The complexity increases further when measurements are conducted in hazardous and explosive environments, which demand a careful selection of components. This article provides an overview of the key elements of a sample handling system and the specific requirements for equipment in hazardous areas, covering gas extraction via the gas sampling probe, transportation using a heated sample line, and conditioning through the sample gas cooler or sample gas dryer.
1. The Gas Sampling Probe
The gas sampling probe serves as the primary sampling point and acts as the gateway to the entire gas analysis system. Efficient filtration of sample gases is crucial for smooth system operation. While various gas sampling probes are available for use in safe areas, the options for ATEX-certified probes capable of maintaining holding temperatures of 150°C or even 180°C remain limited.
Most available probes are controlled to maintain a temperature of 180°C to reach those temperatures. To prevent overheating, ATEX regulations mandate temperature limiters to prevent exceeding temperature class ratings. Products such as the PSG Process Probe incorporate built-in limiter functions, simplifying installation and compliance.
Another critical factor in operating a gas sampling probe in hazardous areas is minimizing human presence for maintenance. Various strategies exist to reduce maintenance efforts, including optimizing filter surface area to prolong operational life. Therefore, PSG uses the largest active filter surface in the market, reducing the maintenance demand to a minimum. If the dust concentration is even higher, different back purging options are available that enable self-cleaning of the probe and its filter element.
Especially when measuring toxic gases (that can even arise as incomplete combustion), it is essential that the sample gas stream can be completely shut off. In such cases, an integrated shut-off valve positioned directly at the entry point of the Gas Sampling Probe is required. While this requirement may seem straightforward, its technical implementation is complex: the solution must ensure that no cold spots form, as these could lead to condensation. Therefore, the shut-off valve must be integrated into the electrical heating system of the gas sampling probe.
PSG Process Probe 180 PSG Extruded ATEX/IECEx 180 14 | AET MAY 2025 |
ENVIROTECH-ONLINE.COM
2. Heated Sample Lines for Gas Transportation
Following primary gas extraction via the gas sampling probe, another essential task is the transportation of sample gas to the sample conditioning or analyzer system. Maintaining temperatures between 150°C and 180°C (or even 200°C in some cases) is crucial to prevent acid dewpoint condensation. Ensuring that interfaces remain free of cold spots is also essential to prevent condensation and its potential impact on the gas composition.
Like Gas Sampling Probes, high-temperature heating technologies for Heated Sample Lines are limited. Safety remains the top priority in emission and process measurement, and regulatory requirements for ATEX/IECEx-approved heated lines have evolved. While past regulations focused primarily on the approval of the electrical heating cable, current standards like the
Standard Flex Line
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