Deodorizer design and upgrade
Conceptually, there are usually two types of technologies involved in
the design and construction of deodorizers: columns with trays, in which
different type of internal devices (special steam lift pumps, steam
bubbling rings, etc.) are used in the tray to inject the stripping
steam, and columns with packings. Here, mostly structured packings are
used, due to its low-pressure drop of vapor phase and optimal gas-liquid
contact (Shahidi, 2005). Both stripping column designs attempt to
provide the best contact between the vapor phase and the liquid phase by
creating a large contact surface, together with an optimal stripping
steam distribution. Moreover, existing deodorizers have individual
advantages. Tray columns can provide a certain holding period at the
deodorization temperature for effective heat bleaching. However, the
tray column still has certain defects. For example, the only one-time
contact between oil and steam results in the usage of large amounts of
direct steam and therefore low deodorization efficiency to remove FFA
and flavor substances. Furthermore, the long time deodorization results
in higher amounts of TFA. Certainly, the stripping efficiency can be
improved by incorporating a packed column filled with structured
packing, in which the contact surface between steam and oil is largely
improved. Such a column has been designed by Alfa Laval (SoftColumn™)
and is widely used in industrial vegetable oil refining in recent years.
Besides the continuous need for more efficient processes, new
developments in deodorization technology are also driven by the
increased attention to the nutritional quality of vegetable oil. As a
result, De Smet developed the DUAL TEMP©deodorizer (De Greyt et al, 1999). This deodorizer consists of several
trays. In the first tray, the incoming oil is heated with high-pressure
steam or a thermal fluid to a moderate temperature (e.g. 230°C), after
which it passes through the first deodorizing trays. In these trays,
deacidification and deodorization takes place under mild conditions
(moderate temperature/moderate stripping). After the first tray, the oil
passes to a second heating tray, in which the oil is heated to a final
and higher temperature (250°C). In the last tray, final stripping and
heat bleaching occurs. Only low amounts of TFA were generated because
the time at high temperature is restricted.
Therefore, in order to obtain a final oil product with good nutritional
and standard physicochemical qualities, a dual columns with dual
temperatures (DCDT) deodorizer was for the first time proposed, designed
and upgraded in this study. Negative temperature effects (geometrical
cis-trans isomerization) can be maximally minimized by the use of DCDT
deodorizers. The DCDT deodorizer was designed to operate at different
temperatures to reach the best compromise between required residence
time for deodorization and heat bleaching (at a low temperature) in a
tray column and final stripping at a higher temperature (for a short
period) in a packed column. The process flow was presented above.