Odor emission management in a feather treatment plant
Lahti, Karoliina (2024)
2024
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
2024-04-08
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202403132832
https://urn.fi/URN:NBN:fi:tuni-202403132832
Tiivistelmä
Gas emissions from the process industry vary depending on the treatment methods, equipment and raw materials used in the process. The rendering process generates malodorous and harmful gases that need to be controlled. The formation of odorous gases is often prevented at the process stage or controlled by removing odorous compounds from the process off-gas by various chemical, physical, and biological techniques. The purpose of the off-gas treatment is to avoid the release of emissions harmful to human health and the environment into the surrounding air.
The objective of the thesis was to determine which regulations and emission limit values govern the odorous emissions from the treatment of animal by-products, and which off-gas treatment methods are suitable for this sector. The odorous compounds generated by the feather treatment process of Honkajoki Ltd, an animal by-products processing plant, were characterized. In addition, the operation of an existing off-gas treatment process, including a chemical scrubber and a biofilter, was optimized to minimize odor emissions by improving the removal efficiencies of hydrogen sulfide and ammonia. The topic is relevant with the update of the new BAT document, which defines the best available techniques for gas collection and treatment and at the same time sets emission levels for environmental permits for plants operating in EU Member States. The new document will require factories to review their emission levels and re-evaluate the adequacy of their gas treatment systems.
Among the 32 compounds identified from feather processing, the most significant odorous compounds were hydrogen sulfide, ammonia, and methyl mercaptan, due to their high concentrations of 12.9−55.8 mg/Nm3 and low odor thresholds. The characterization of the process off-gas showed that most of the ammonia is formed during the drying of the feather material and most of the hydrogen sulfide is formed during hydrolysis. The removal efficiency of the plant's chemical scrubber for hydrogen sulfide reached a maximum of 74 %, while the removal efficiency for ammonia remained between 90−100 % throughout the entire study. The hydrogen sulfide removal efficiency of the biofilter was close to 80 % at its highest but decreased to less than 20 % in the short term. The characterization of the biofilter bed material indicated that too low pH was responsible for the decrease in H2S removal efficiency in the biofilter.
The results of this work show that the current treatment system, when operating normally, is adequate for the BAT limit values that will be established. It is recommended that the bed material of the biofilter is limed in order to improve its functioning. Possible increases in production volumes in the future could cause the capacity of the off-gas treatment system to be exceeded, so based on the literature, the off-gas treatment could be improved, e.g., using a supplemental treatment such as a bioscrubber, which is particularly suitable method for hydrogen sulfide.
The objective of the thesis was to determine which regulations and emission limit values govern the odorous emissions from the treatment of animal by-products, and which off-gas treatment methods are suitable for this sector. The odorous compounds generated by the feather treatment process of Honkajoki Ltd, an animal by-products processing plant, were characterized. In addition, the operation of an existing off-gas treatment process, including a chemical scrubber and a biofilter, was optimized to minimize odor emissions by improving the removal efficiencies of hydrogen sulfide and ammonia. The topic is relevant with the update of the new BAT document, which defines the best available techniques for gas collection and treatment and at the same time sets emission levels for environmental permits for plants operating in EU Member States. The new document will require factories to review their emission levels and re-evaluate the adequacy of their gas treatment systems.
Among the 32 compounds identified from feather processing, the most significant odorous compounds were hydrogen sulfide, ammonia, and methyl mercaptan, due to their high concentrations of 12.9−55.8 mg/Nm3 and low odor thresholds. The characterization of the process off-gas showed that most of the ammonia is formed during the drying of the feather material and most of the hydrogen sulfide is formed during hydrolysis. The removal efficiency of the plant's chemical scrubber for hydrogen sulfide reached a maximum of 74 %, while the removal efficiency for ammonia remained between 90−100 % throughout the entire study. The hydrogen sulfide removal efficiency of the biofilter was close to 80 % at its highest but decreased to less than 20 % in the short term. The characterization of the biofilter bed material indicated that too low pH was responsible for the decrease in H2S removal efficiency in the biofilter.
The results of this work show that the current treatment system, when operating normally, is adequate for the BAT limit values that will be established. It is recommended that the bed material of the biofilter is limed in order to improve its functioning. Possible increases in production volumes in the future could cause the capacity of the off-gas treatment system to be exceeded, so based on the literature, the off-gas treatment could be improved, e.g., using a supplemental treatment such as a bioscrubber, which is particularly suitable method for hydrogen sulfide.