Monitoring ammonia slip from large-scale selective catalytic reduction (SCR) systems in combined heat and power generation applications with field effect gas sensors
<p>Following tightened regulations, selective catalytic reduction (SCR) of nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub></span>) by ammonia (NH<span class="inline-formula"><sub>3</sub></span>)...
| मुख्य लेखकों: | , |
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| स्वरूप: | लेख |
| भाषा: | English |
| प्रकाशित: |
Copernicus Publications
2023-10-01
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| श्रृंखला: | Journal of Sensors and Sensor Systems |
| ऑनलाइन पहुंच: | https://jsss.copernicus.org/articles/12/235/2023/jsss-12-235-2023.pdf |
| सारांश: | <p>Following tightened regulations, selective catalytic reduction (SCR) of nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub></span>) by ammonia (NH<span class="inline-formula"><sub>3</sub></span>) has over
the last couple of decades found wider adoption as a means of reducing
NO<span class="inline-formula"><sub><i>x</i></sub></span> emissions from e.g. power production and district heating plants. As in the SCR process NH<span class="inline-formula"><sub>3</sub></span> injected into the flue gas reacts
with and reduces NO<span class="inline-formula"><sub><i>x</i></sub></span> to nitrogen (N<span class="inline-formula"><sub>2</sub></span>) and water (H<span class="inline-formula"><sub>2</sub></span>O) on the
surface of a specific catalyst, the NH<span class="inline-formula"><sub>3</sub></span> injection has to be dynamically adjusted to match both instant and long-term variations in flue gas nitrogen
oxide concentration in order to minimize NO<span class="inline-formula"><sub><i>x</i></sub></span> and NH<span class="inline-formula"><sub>3</sub></span> emissions. One possibility of realizing such NH<span class="inline-formula"><sub>3</sub></span> dosing control would be the real-time monitoring and feedback of downstream flue gas NO<span class="inline-formula"><sub><i>x</i></sub></span> and
NH<span class="inline-formula"><sub>3</sub></span> concentrations to the NH<span class="inline-formula"><sub>3</sub></span> injection control unit. In this
study the sensing characteristics and performance of SiC-based Metal Oxide Semiconductor Field
Effect Transistor (MOSFET)
sensors with a structurally tailored gas-sensitive gate contact of iridium
(Ir) for in situ NH<span class="inline-formula"><sub>3</sub></span> monitoring downstream from the SCR catalyst in a
combined heat and power (CHP) plant have therefore been investigated and
evaluated.</p>
<p>The sensor's NH<span class="inline-formula"><sub>3</sub></span> sensitivity and selectivity as well as the
cross-sensitivity to common flue gas components – oxygen (O<span class="inline-formula"><sub>2</sub></span>), water
vapour (H<span class="inline-formula"><sub>2</sub></span>O), nitric oxide (NO), nitrogen dioxide (NO<span class="inline-formula"><sub>2</sub></span>), carbon
monoxide (CO), and a model hydrocarbon, ethene (C<span class="inline-formula"><sub>2</sub></span>H<span class="inline-formula"><sub>4</sub></span>) – were
thereby investigated for relevant concentration ranges under controlled
conditions in the laboratory. While, at the prescribed sensor operation
temperature of 300 <span class="inline-formula"><sup>∘</sup></span>C, the influence of H<span class="inline-formula"><sub>2</sub></span>O, CO, and
C<span class="inline-formula"><sub>2</sub></span>H<span class="inline-formula"><sub>4</sub></span> on the sensor's NH<span class="inline-formula"><sub>3</sub></span> concentration reading could be
regarded as practically insignificant, a moderate cross-sensitivity was observed between
NH<span class="inline-formula"><sub>3</sub></span> and NO<span class="inline-formula"><sub>2</sub></span> and, to a lesser extent, between NH<span class="inline-formula"><sub>3</sub></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M30" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5c3774ab0600a2f03e83f0e636ae5ed2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jsss-12-235-2023-ie00001.svg" width="8pt" height="14pt" src="jsss-12-235-2023-ie00001.png"/></svg:svg></span></span> NO and NH<span class="inline-formula"><sub>3</sub></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M32" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5ea72e5fcd9e8768af40707a0416eed7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jsss-12-235-2023-ie00002.svg" width="8pt" height="14pt" src="jsss-12-235-2023-ie00002.png"/></svg:svg></span></span> O<span class="inline-formula"><sub>2</sub></span>. As the NO<span class="inline-formula"><sub><i>x</i></sub></span> concentration downstream from the
SCR catalyst under normal SCR and power plant operation is expected to be
considerably smaller than the NH<span class="inline-formula"><sub>3</sub></span> concentration whenever any
appreciable ammonia slip occurs, the observed NH<span class="inline-formula"><sub>3</sub></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M37" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f77694ccc584f068782523cf5fd7b6a6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jsss-12-235-2023-ie00003.svg" width="8pt" height="14pt" src="jsss-12-235-2023-ie00003.png"/></svg:svg></span></span> NO<span class="inline-formula"><sub><i>x</i></sub></span>
cross-sensitivities may, however, be of less practical significance for
ammonia monitoring in real flue gases downstream from the SCR catalyst.
Furthermore, if required, the small influence of O<span class="inline-formula"><sub>2</sub></span> concentration
variations on the sensor reading may also be compensated for by utilizing
the signal from a commercially available oxygen sensor. Judging from in situ measurements performed in a combined heat and power plant, the structurally tailored Ir gate field effect sensors also exhibit good NH<span class="inline-formula"><sub>3</sub></span> sensitivity over the relevant 0–40 ppm range when directly exposed to real flue gases, offering an accuracy of <span class="inline-formula">±</span>3 ppm as well as low sensor signal drift, the latter most likely to further improve with regular zero-point calibration and thereby make the Ir gate MOSFET ammonia sensor a promising alternative for cost-efficient real-time ammonia slip monitoring or SCR system control in heat and/or power production plants.</p> |
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| आईएसएसएन: | 2194-8771 2194-878X |