Deep Oxidation of Nitrogen Oxides by Ozone in Wet Flue Gas Scrubbers : Pilot-scale experimental study
Nest, Niklas Sebastian (2022)
2022
Ympäristö- ja energiatekniikan DI-ohjelma - Programme in Environmental and Energy Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2022-04-26
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202203122493
https://urn.fi/URN:NBN:fi:tuni-202203122493
Tiivistelmä
The formation of NOX emissions is a problem that occurs in all combustion processes. NOX emissions contribute to photochemical smog, acid rain and tropospheric ozone. Ozone and NOX together with particulate matter are the most important air pollutants globally. Air pollution is also recognised as the most significant environmental threat to human health. With increasingly strict emission limits new technologies are explored for NOX emission reduction.
The objective of this Master’s thesis is to study the role of deep oxidation of nitrogen oxides with ozone in wet flue gas scrubbers for NOX reduction at combustion units in power production and industry. The deep oxidation of NOX by ozone was explored by studying the recent scientific literature on the subject to recognise the main factors that affect the oxidation process. An experimental study was conducted at a pilot-scale ozone scrubber installation with an oxidation reactor and a wet packed bed flue gas scrubber. The objectives of the experimental study were to find the most efficient molar ratio for NOX removal in terms of achieved NOX reduction and the resultant HNO3 and O3 slip, to study how temperature and residence time affect the deep oxidation process, and to study the relevance of liquid to gas flow ratio in the scrubber for the absorption of NOX and HNO3.
Temperature, residence time and O3/NO molar ratio were recognised as the main factors that affect the oxidation process. An optimal O3 /NO molar ratio was found for ozone injection in the experimental study to receive the highest possible NOX reduction before ozone slip could be observed in the flue gas. The results of the experimental study found that the most efficient oxidation temperature is at the lower end of the temperature range 60 – 90 ◦ C. This result is in line with results in previous studies. The residence time was observed to have a minor positive correlation with higher oxidation efficiency. The shortest residence times correlated with higher HNO3 slip after the scrubber. Significant amounts of HNO3 slip after the scrubber were observed in most measurements.
Ozone scrubbers are an economically viable alternative to SCR catalysts for NOX reduction for combustion units where the higher investment cost of an SCR catalyst is not outweighed by the operation costs of an ozone scrubber. This thesis presents a theoretical outline for ozone scrubber design. Further studies should still be conducted to optimize the process. The formation of HNO3 in the wet scrubbing process of nitrogen oxides should be studied to learn to minimise its formation and to better understand the chemistry of the process.
The objective of this Master’s thesis is to study the role of deep oxidation of nitrogen oxides with ozone in wet flue gas scrubbers for NOX reduction at combustion units in power production and industry. The deep oxidation of NOX by ozone was explored by studying the recent scientific literature on the subject to recognise the main factors that affect the oxidation process. An experimental study was conducted at a pilot-scale ozone scrubber installation with an oxidation reactor and a wet packed bed flue gas scrubber. The objectives of the experimental study were to find the most efficient molar ratio for NOX removal in terms of achieved NOX reduction and the resultant HNO3 and O3 slip, to study how temperature and residence time affect the deep oxidation process, and to study the relevance of liquid to gas flow ratio in the scrubber for the absorption of NOX and HNO3.
Temperature, residence time and O3/NO molar ratio were recognised as the main factors that affect the oxidation process. An optimal O3 /NO molar ratio was found for ozone injection in the experimental study to receive the highest possible NOX reduction before ozone slip could be observed in the flue gas. The results of the experimental study found that the most efficient oxidation temperature is at the lower end of the temperature range 60 – 90 ◦ C. This result is in line with results in previous studies. The residence time was observed to have a minor positive correlation with higher oxidation efficiency. The shortest residence times correlated with higher HNO3 slip after the scrubber. Significant amounts of HNO3 slip after the scrubber were observed in most measurements.
Ozone scrubbers are an economically viable alternative to SCR catalysts for NOX reduction for combustion units where the higher investment cost of an SCR catalyst is not outweighed by the operation costs of an ozone scrubber. This thesis presents a theoretical outline for ozone scrubber design. Further studies should still be conducted to optimize the process. The formation of HNO3 in the wet scrubbing process of nitrogen oxides should be studied to learn to minimise its formation and to better understand the chemistry of the process.