Monitoring of Ammonia in Biomass Combustion Flue Gas Using a Zeolite-Based Capacitive Sensor

Area of Science:

• Environmental Science
• Chemical Engineering
• Materials Science

Background:

• Biomass combustion systems produce significant particulate matter, hydrocarbons (HCs), and nitrogen oxides (NOx) emissions.
• Legal regulations mandate emission reduction for medium-sized plants (≈100 kW) using selective catalytic reduction (SCR) systems.
• Efficient ammonia (NH3) dosing is critical for SCR system performance, requiring selective sensors.

Purpose of the Study:

• To develop and evaluate a capacitive ammonia (NH3) sensor for real-time monitoring in biomass combustion flue gas.
• To assess the sensor's sensitivity, selectivity, and long-term stability under operational conditions.
• To validate sensor performance against established measurement techniques like FTIR spectroscopy.

Main Methods:

• Fabrication of a capacitive NH3 sensor utilizing a zeolite functional film.
• Laboratory testing of sensor performance with controlled gas mixtures (NH3, H2O, NOx).
• In-situ application and validation of the sensor in flue gas from a wood-burning stove and biogenic residue combustion plants with ammonia injection.

Main Results:

• The zeolite-based capacitive sensor demonstrated high sensitivity and selectivity to ammonia, with minimal cross-interference from water (H2O) and NOx.
• Excellent agreement was observed between NH3 concentrations measured by the developed sensor and a Fourier-transform infrared (FTIR) spectrometer.
• Preliminary investigations indicated promising long-term stability and potential resistance to poisoning effects from sulfur dioxide (SO2) and hydrogen chloride (HCl).

Conclusions:

• The developed capacitive NH3 sensor shows significant potential for accurate and reliable ammonia monitoring in biomass combustion flue gas.
• This sensor technology can facilitate efficient ammonia dosing for SCR systems, contributing to reduced NOx emissions.
• Further research on long-term stability and resistance to flue gas contaminants is warranted for commercial application.