Fat Fractionation by Distillation
Tuohi, Eetu (2020)
Åbo Akademi
2020
Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe202002206012
https://urn.fi/URN:NBN:fi-fe202002206012
Tiivistelmä
The demand for renewable fuels and chemicals is growing, but at the same time, discussion about the use of edible raw materials in the production has intensified. Waste-based fats and oils are cheaper and their consumption is generally more acceptable than edible feedstock’s. They are, however, more challenging to process as their composition and availability varies substantially. Waste-based fats and oils may contain, for example, solid particles, chlorides and volatile organic compounds (VOCs). The literature part of this thesis reviews some of the edible and non-edible feedstocks, suitable pre-processing methods and distillation techniques for the fat and oil feedstocks.
The applied part of the thesis studies the separation of free fatty acids (FFA) and glycerides by distillation from a waste-based fat feedstock. As a result, two distillation concepts were developed and simulated in Aspen Plus. The constructed base case feed had a feed FFA content of 65%. The distillation column bottom temperature of the concepts was kept below 260 °C in order to avoid the possible thermal decomposition of the fat feedstock. The first concept included a side-stream distillation column with 6 separation stages. The FFA fraction was taken out as a side-stream, the light fraction, including water, VOCs and organochlorides, was drawn as an overhead stream while the glyceride fraction was drawn from the bottom. FFA recovery via the side-stream was 86.2% of the feed’s FFA in the base case simulation. The FFA purity of the side-stream was over 99.99% and the glyceride purity of the bottom stream was 79.5%. 400 kg of steam was injected to the column in order to bring the bottom temperature below 260 °C. The turndown ratio of the column geometry, for this concept, was excellent as the column could be operated with varying feed FFA content between 90 wt.% and 20 wt.%.
The second concept included a pre-flash drum before a simple distillation column with 3 separation stages. The light fraction was separated in the flash drum, the FFA fraction was taken out as an overhead stream while the glycerides were obtained as a bottom stream. The same level of FFA recovery to the overhead stream was achieved with the pre-flash concept as with the side-stream concept. Compared to the side-stream concept, glyceride fraction purity was about the same, but the FFA fraction purity was slightly worse for the pre-flash concept. The energy input requirment of the pre-flash concept was, however, 0.7 MW less than for the side-stream concept due to more effective heat integration. The turndown ratio of the pre-flash concept was worse than the side stream column concept’s because jet flooding occurred at high feed FFA contents (90% or more) while the bottom temperature rose over 260 °C at low feed FFA content (50% or less). For both concepts, modified Sulzer-Nutter BDH valve trays were chosen as column internals as they resulted in the best performance with respect to column diameter and pressure drop under the deep vacuum conditions used. Lower pressure drop and column diameter are obtainable with structured packings, but these were not selected due to uncertain fouling characteristics of fat feedstock.
The applied part of the thesis studies the separation of free fatty acids (FFA) and glycerides by distillation from a waste-based fat feedstock. As a result, two distillation concepts were developed and simulated in Aspen Plus. The constructed base case feed had a feed FFA content of 65%. The distillation column bottom temperature of the concepts was kept below 260 °C in order to avoid the possible thermal decomposition of the fat feedstock. The first concept included a side-stream distillation column with 6 separation stages. The FFA fraction was taken out as a side-stream, the light fraction, including water, VOCs and organochlorides, was drawn as an overhead stream while the glyceride fraction was drawn from the bottom. FFA recovery via the side-stream was 86.2% of the feed’s FFA in the base case simulation. The FFA purity of the side-stream was over 99.99% and the glyceride purity of the bottom stream was 79.5%. 400 kg of steam was injected to the column in order to bring the bottom temperature below 260 °C. The turndown ratio of the column geometry, for this concept, was excellent as the column could be operated with varying feed FFA content between 90 wt.% and 20 wt.%.
The second concept included a pre-flash drum before a simple distillation column with 3 separation stages. The light fraction was separated in the flash drum, the FFA fraction was taken out as an overhead stream while the glycerides were obtained as a bottom stream. The same level of FFA recovery to the overhead stream was achieved with the pre-flash concept as with the side-stream concept. Compared to the side-stream concept, glyceride fraction purity was about the same, but the FFA fraction purity was slightly worse for the pre-flash concept. The energy input requirment of the pre-flash concept was, however, 0.7 MW less than for the side-stream concept due to more effective heat integration. The turndown ratio of the pre-flash concept was worse than the side stream column concept’s because jet flooding occurred at high feed FFA contents (90% or more) while the bottom temperature rose over 260 °C at low feed FFA content (50% or less). For both concepts, modified Sulzer-Nutter BDH valve trays were chosen as column internals as they resulted in the best performance with respect to column diameter and pressure drop under the deep vacuum conditions used. Lower pressure drop and column diameter are obtainable with structured packings, but these were not selected due to uncertain fouling characteristics of fat feedstock.