Understanding and controlling approach temperature is critical to the effective operation of dry scrubbing systems. In our latest technical paper, Direct Measurement of Approach Temperature in a Spray Dry Absorber, we explore how real-time dewpoint measurement can provide a more accurate and practical method for identifying true acid condensation onset in-duct.
Traditionally, approach temperature has been referenced to the Approach to Adiabatic Saturation Temperature (AAST), a value that is extremely difficult to measure directly in an operating system. Recent research and field data suggest that acid dewpoint, defined as the temperature at which condensation first begins, offers a more actionable and measurable parameter for process control.
To evaluate this approach, Ohio Lumex conducted a multi-week site demonstration using the Ei4200 Dewpoint Monitor installed between the spray dry absorber (SDA) reactor and the baghouse. The instrument operated reliably under real plant conditions, providing continuous in-situ dewpoint measurement.
By analyzing the relationship between sensor temperature and delta current, we were able to project the true onset of acid condensation at extremely low detection levels.
The curve above illustrates how projected onset dewpoint can be calculated using the minimum detectable delta current (0.01 μA). Based on both single-cycle and multi-day data analysis, projected acid onset dewpoints were identified at approximately 211–217°F, while the reactor outlet temperature remained steady at 265°F.
This gap between reactor outlet temperature and onset dewpoint represents an opportunity.
Further analysis demonstrated that dewpoint is influenced by SOâ‚‚ load, hydrated lime feed rate, and cooling water rate. Reducing the differential between outlet temperature and acid onset dewpoint has the potential to:
- Improve hydrate utilization
- Increase SOâ‚‚ removal efficiency
- Optimize water usage
- Minimize corrosion risk
Supporting literature suggests that reducing the temperature differential by as little as 10 K could yield measurable improvements in system performance.
For facilities operating spray dry absorbers, direct dewpoint measurement offers a practical path toward improving efficiency while maintaining operational reliability. Rather than relying on difficult-to-measure theoretical values, operators can use real-time dewpoint data to make informed process decisions.
Interested in learning how this applies to your system? Contact our team to discuss your application.
