As facilities perform 7-day sorbent trap sampling, many operators, especially those newer to the industry, have had to learn through trial and error. It’s common for teams to reach out to industry experts like us for guidance as they work to optimize their sampling practices.
One of the most frequently asked questions is: “What sampling parameters should I use to ensure successful long-term runs?”
While the best settings can vary based on your specific source conditions, like high moisture, elevated SO₂ or SO₃ levels, or particulate matter, there are a few universal best practices that can help you avoid common issues and generate reliable data. Whether you’re sampling at a power plant, cement kiln, or any other industrial source, the following tips can set you up for success:
1. Start the Pumps Before Inserting the Probe
Start your sampling pumps a few seconds before inserting the probe into the flue gas. This prevents the initial surge of flow, when the pump briefly pulls harder than your set rate, from drawing excess moisture or particulate into the trap. That quick surge might seem minor, but it can lead to skewed results or trap damage.
2. Keep the Probe Horizontal After Sampling
Once sampling is complete, never raise the tip of the probe above a horizontal position. Holding the probe vertically can cause any moisture that made it into the trap to flow directly into the carbon section of your sorbent trap. That moisture is likely to contain high levels of mercury, and if it drains into the sorbent trap carbon, it can lead to artificially high readings.
3. Analyze the Front Plug Separately
Analyzing the front plug independently provides valuable insights into your sampling run. Although this plug can trap oxidized vapor-phase mercury, it typically captures very little. If you find a significant mercury load here, it’s usually a red flag, often indicating problems like moisture or particulate entrainment during sampling.
4. Ensure Sufficient Mercury Capture (≥ 20ng Total)
Capturing at least 20ng of mercury helps to safeguard your results. Why? Because small sampling or analytical errors are less likely to influence the outcome when the total capture is higher. For instance, a 1-2 ng mercury background level can significantly impact a 10ng capture but will have minimal effect on a 100ng capture.
5. Maintain a Clean Sampling and Analysis Environment
Cleanliness counts. Always use fresh paper, foil, soda, and carbon each day. change your gloves before handling the sorbent traps, especially after calibrations, to avoid cross-contamination. Even trace amounts of mercury can affect your samples, even if transferred unknowingly.
6. Prioritize Quality Control Throughout the Sampling Process
Good data starts with good practices. Routine system checks help prevent small issues from turning into major data problems:
- Inspect probe ferrules and O-rings regularly. Look for wear, ridges, or cuts that could compromise seal integrity and cause leaks.
- Always perform leak checks with the probe heated. Some leaks only become apparent at operating temperatures.
- Once sampling begins, monitor vacuum levels periodically to catch potential trap plugging or system blockages before they affect results.
Additional Long-Term Sampling Best Practices
In addition to the basics, here are some field-tested tips from our experts to help ensure your long-term sorbent trap sampling is accurate and reliable:
- Acid Gas Management: Sources with more than 150ppm of SO₂ or SO₃ can lead to spike loss or breakthrough. In these cases, use an acid gas scrubber section on your sorbent traps to protect data quality.
- High Moisture Precautions: High moisture levels can compromise sampling, so keep your probe temperature at a minimum of 325°F-360°F to avoid condensation issues.
- High Temperature Events at Cement Plants: During raw mill off conditions, cement plant stacks may exceed 400°F. This can lead to breakthrough or spike loss. To mitigate this, use an air-cooled probe and run cooling air continuously during high-temp periods.
- Flow Rate Selection by Industry and Load:
- Power Plants: Use a sampling profile based on the current stack load. For example:
- Startup: 200ccm
- Low Load: 250ccm
- Mid Load: 325ccm
- Full Load: 400ccm
- Cement Plants: Select a flow rate between 150ccm and 300ccm, depending on the sampling system manufacturer.
- Power Plants: Use a sampling profile based on the current stack load. For example:
Final Thoughts
While no two sampling locations are the same, following these simple suggestions will significantly reduce the risk of biased or inaccurate data. Long-term sorbent trap sampling doesn’t have to be complicated. With the right practices in place, you can maintain the simplicity of sorbent trap systems while achieving dependable, high-quality results.
Need help analyzing your traps?
Ohio Lumex has a full-service analytical laboratory that offers expert sorbent trap analysis and support to ensure your data is accurate and defensible. Our specialists assist with diagnosing any problems with your results and provide guidance if you need a few pointers. We also offer industry-leading turnaround times, including expedited options such as same-day, one-day, or two-day services for mercury (Hg) sorbent traps. Contact us today to learn more or to send your traps for analysis.
