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.

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 DIN EN IEC 60079-0 necessitate an assessment of the entire heated line, including electrostatic discharge risks. Safe operation can be ensured by employing authentic conductive jacket materials that are properly grounded through potential equalization.
Another key consideration is cut-to-length technology for heated sample lines. Since selecting the precise length is often tricky, lines are typically ordered longer than necessary. However, excessive length introduces multiple drawbacks, including:
Given that heated sample lines often represent the highest energy demand within the system, effective insulation is crucial for maintaining the required holding temperature while minimizing energy loss. Innovations such as the PSG Plus Extruded ATEX 180 heated cables have demonstrated energy savings of up to 25 % compared to conventional alternatives while providing the benefits of a robust outer jacket for industrial applications.

3. Gas Conditioning Systems

Gas conditioning constitutes the final step before analysis after sample extraction via the Gas Sampling Probe and transportation through the Heated Sample Line. While the placement of the gas sampling probe and heated sample line is often dictated by plant layout and ATEX/IECEx requirements, conditioning and analyzer systems can frequently be housed within an analyzer shelter or container, providing a controlled and safe environment. When such an installation is not feasible, all sample conditioning components, including the Sample Gas Cooler or Dryer and the Sample Gas Pump, must comply with hazardous area classifications, alongside the analyzer itself. Certified solutions, such as the PSG Process Cooler BCR ATEX, have been specifically designed and third-party approved for safe operation. These systems offer configurations with one, two, or even up to four gas paths, providing flexibility and reliability in gas conditioning applications.
In specific applications, an alternative to conventional compressor- or thermoelectric-based sample gas drying methods is using a Nafion Dryer, such as those developed by PermaPure. Traditional drying techniques, including condensate coolers, adsorption dryers, and permeation dryers, often alter the composition of the sample gas by either precipitating certain components along with condensate, adsorbing them into water, or enabling their permeation. In contrast, Nafion® membrane-based drying relies on a selective water transport mechanism, preserving the integrity of the sample gas composition. A thorough evaluation of relevant process parameters is required to assess the feasibility of Nafion technology for a given application. The primary advantage of this technology in hazardous environments lies in its inherent safety: as it operates solely with instrument air and does not incorporate electrical components, the risks associated with ignition sources are effectively mitigated.

Conclusion

Optimizing gas sampling and conditioning in hazardous areas requires carefully selecting components that comply with stringent regulatory standards. Ensuring proper integration between the gas sampling probe, heated sample line, and gas conditioning system is essential for achieving reliable, accurate, and safe measurement results. Innovations in heating technologies, self-cleaning functionalities, and energy-efficient designs continue to advance the field, improving both system performance and sustainability.