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.