Graham Corporation Technical Article: Vacuum System Deodorizers

Vacuum System Deodorizers

August 2023

Greetings!

This article is going to provide an overview of vacuum systems in the service of edible oil deodorizing towers. "Edible oils" is a general term to describe cooking oils that are used to fry and bake foods. This discussion highlight how these systems are laid out and how they function. Deodorizing is an important process in the production of edible oils like vegetable oils and nut oils. It is vital to remove fatty acids and other volatile components so that they do not negatively affect the smell, color, and taste of the final products. This can only be achieved under a deep vacuum and that vacuum is usually generated using a steam ejector vacuum system.

The unwanted fatty acids and other volatile components are removed from the process using stripping steam in a deodorizing vacuum column. This is done at an elevated temperature around 450ºF – 470ºF and under a vacuum of 1.0 - 5.0 mmHgA in most instances. If the process was not at a deep vacuum, a hotter temperature would be needed to vaporize and strip out the fatty acids and volatiles. This hotter temperature would however degrade the oil, ruining the final produce, making a reliable vacuum system instrumental to a successful operation.

Traditional Four-Stage System

In order to achieve a pressure in the 1.0-5.0 mmHgA range, a four-stage ejector system is normally selected. This includes two large booster ejectors on the front end followed by a larger first intercondenser. Downstream of the large first intercondenser is a set of smaller ejectors and condensers. A condenser cannot be supplied between the first two booster ejectors because tower supplied cooling water is not cold enough to condense steam at very deep vacuum making a water condenser not possible. Some designs do utilized a chilled water source, making a condenser in that location viable.

Use of a Hybrid System

A liquid ring vacuum pump is sometimes used in place of or in parallel with the last two ejectors in the system. This is what is known as a hybrid system configuration. A liquid ring vacuum pump may be selected to reduce the steam consumption and/or cooling water demands of the vacuum system. Liquid ring pumps can be installed at grade level, where ejectors and condensers need to be installed at elevation. This can reduce the amount of equipment that needs to be installed up on a structure. These features can make a hybrid design attractive, especially for revamped designs were utilities and structures are already in place.

Liquid Ring Pump

Vertical Condenser Design

The most common condenser design for deodorizer systems is vertical tube-side condensing. This condenser layout has the condensers installed vertically with the cooling water on the outside of the tubes and the process condensing on the inside of the tubes. This orientation is chosen for the condensers as it allows the process to run down the inside of the tube, which allows for easy cleaning. The fatty acids in the process will solidify on the tubes as they condense out. A spray header with a full cone pattern is then installed in the top bonnet of the condenser tubeside and positioned so that a cleaning agent can be sprayed on all the inside of the tubes. A water and caustic solution is then sprayed continually on the tubes so that fouling never builds up to a point where it would disrupt the process.

Graham EcoFreeze Design Option

One of the drawbacks of a traditional four-stage ejector configuration for this service is that the larger booster ejectors on the front end of the system use a considerable amount of motive steam. A special design for this service uses a pair of chilled ammonia freeze condensers on the front end of the system to capture nearly all of the stripping steam and fatty acids coming over from the deodorizing tower. This allows the downstream vacuum system to be sized for a much smaller load and results in a substantial reduction in steam consumption. This greatly reduces the overall operating cost of the deodorizer vacuum system, however this does come at a cost. An EcoFreeze design requires an ammonia chilling skid, additional valving, piping, and controls which increases operating complexity and the initial capital costs.

Given the importance of the ejector vacuum system in successful deodorizer operation, understanding how systems are configured and how they are laid out is very useful. Graham has a long history of supplying these systems and a deep understanding of how ejector systems operate in this application. Please feel free to reach out to Graham for support with any existing system or to consult with on any new planned installation.