利用场效应气体传感器监测热电联产应用中大规模选择性催化还原(SCR)系统的氨泄漏

IF 0.8 Q4 INSTRUMENTS & INSTRUMENTATION Journal of Sensors and Sensor Systems Pub Date : 2023-10-05 DOI:10.5194/jsss-12-235-2023
Lida Khajavizadeh, Mike Andersson
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引用次数: 0

摘要

摘要随着法规的收紧,在过去的几十年里,氨(NH3)选择性催化还原(SCR)氮氧化物(NOx)作为减少电力生产和区域供热厂等氮氧化物排放的一种手段被广泛采用。由于在SCR过程中,注入烟气中的NH3与特定催化剂表面的氮氧化物(N2)和水(H2O)发生反应并将NOx还原为氮氧化物,因此必须动态调整NH3的注入,以匹配烟气中氮氧化物浓度的即时和长期变化,从而最大限度地减少NOx和NH3的排放。实现这种NH3加药控制的一种可能是将下游烟气NOx和NH3浓度实时监测并反馈给NH3注入控制单元。因此,在本研究中,研究和评估了基于sic的金属氧化物半导体场效应晶体管(MOSFET)传感器的传感特性和性能,该传感器具有结构定制的气敏栅极触点铱(Ir),用于现场监测热电联产(CHP)电厂SCR催化剂下游的NH3。因此,在实验室受控条件下,研究了传感器对NH3的灵敏度和选择性以及对常见烟气组分——氧气(O2)、水蒸气(H2O)、一氧化氮(NO)、二氧化氮(NO2)、一氧化碳(CO)和模型碳氢化合物乙烯(C2H4)——的交叉灵敏度。在300°C的规定传感器工作温度下,H2O、CO和C2H4对传感器NH3浓度读数的影响几乎可以忽略不计,NH3和NO2之间有中等程度的交叉敏感性,NH3 / NO和NH3 / O2之间的交叉敏感性较小。由于在SCR和电厂正常运行情况下,SCR催化剂下游的NOx浓度预计在任何明显的氨滑发生时都要远远小于NH3浓度,因此所观察到的NH3 / NOx交叉灵敏度对于SCR催化剂下游实际烟气中的氨监测可能没有太大的实际意义。此外,如果需要,O2浓度变化对传感器读数的小影响也可以通过利用市售氧传感器的信号来补偿。从热电联产电厂进行的现场测量判断,当直接暴露于真实烟气时,结构量身定制的Ir门场效应传感器在相关的0-40 ppm范围内也表现出良好的NH3灵敏度,提供±3 ppm的精度以及低传感器信号漂移。后者最有可能通过定期零点校准进一步改进,从而使Ir栅极MOSFET氨传感器成为热电厂和/或发电厂中具有成本效益的实时氨滑监测或可控硅系统控制的有希望的替代方案。
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Monitoring ammonia slip from large-scale selective catalytic reduction (SCR) systems in combined heat and power generation applications with field effect gas sensors
Abstract. Following tightened regulations, selective catalytic reduction (SCR) of nitrogen oxides (NOx) by ammonia (NH3) has over the last couple of decades found wider adoption as a means of reducing NOx emissions from e.g. power production and district heating plants. As in the SCR process NH3 injected into the flue gas reacts with and reduces NOx to nitrogen (N2) and water (H2O) on the surface of a specific catalyst, the NH3 injection has to be dynamically adjusted to match both instant and long-term variations in flue gas nitrogen oxide concentration in order to minimize NOx and NH3 emissions. One possibility of realizing such NH3 dosing control would be the real-time monitoring and feedback of downstream flue gas NOx and NH3 concentrations to the NH3 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 NH3 monitoring downstream from the SCR catalyst in a combined heat and power (CHP) plant have therefore been investigated and evaluated. The sensor's NH3 sensitivity and selectivity as well as the cross-sensitivity to common flue gas components – oxygen (O2), water vapour (H2O), nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), and a model hydrocarbon, ethene (C2H4) – were thereby investigated for relevant concentration ranges under controlled conditions in the laboratory. While, at the prescribed sensor operation temperature of 300 ∘C, the influence of H2O, CO, and C2H4 on the sensor's NH3 concentration reading could be regarded as practically insignificant, a moderate cross-sensitivity was observed between NH3 and NO2 and, to a lesser extent, between NH3 / NO and NH3 / O2. As the NOx concentration downstream from the SCR catalyst under normal SCR and power plant operation is expected to be considerably smaller than the NH3 concentration whenever any appreciable ammonia slip occurs, the observed NH3 / NOx 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 O2 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 NH3 sensitivity over the relevant 0–40 ppm range when directly exposed to real flue gases, offering an accuracy of ±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.
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来源期刊
Journal of Sensors and Sensor Systems
Journal of Sensors and Sensor Systems INSTRUMENTS & INSTRUMENTATION-
CiteScore
2.30
自引率
10.00%
发文量
26
审稿时长
23 weeks
期刊介绍: Journal of Sensors and Sensor Systems (JSSS) is an international open-access journal dedicated to science, application, and advancement of sensors and sensors as part of measurement systems. The emphasis is on sensor principles and phenomena, measuring systems, sensor technologies, and applications. The goal of JSSS is to provide a platform for scientists and professionals in academia – as well as for developers, engineers, and users – to discuss new developments and advancements in sensors and sensor systems.
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