Designing of the dryer section of nutritional yeast production plant – Industrial sector review – Part 2

Designing of the dryer section of nutritional yeast production plant – Industrial sector review – Part 2

Review of alternative processes

This section details the research carried out into main equipment variants that can be used to carry out the process.

Drying is the final unit operation in the manufacture of protein supplement. The Choice of the dryer to be used in the design depends on many factors, of which the most influencing are:

The type of feed (liquids, liquid suspensions, high solid density cakes), the moisture content to be removed from the feed, the load, the size and shape of the end product, heat sensitivity, loss in activity,  effect on viability and nutritional value (Endo,
2009).

Product Requirements

The required product out of the dryer is finely divided powdered nutritional yeast with the production rate of 9,090 kg/day. It is a form of protein supplements which can be used directly (by pressing) into vitamin tablets, as an ingredient in cheese substitute
and it can also be consumed as protein supplement powder to prevent vitamin deficiency or increase strength. The product has to be of superior quality as for direct human consumption with most particles of equal size (fine) and optimum density and moisture
content (Endo, 2009).

The drying time, also known as residence time shall be low (few seconds) and a high outlet temperature such that it does not damage the proteins. The enzymatic activity of the yeast has to be inactivated during the drying as this can cause fermentation in
stomach of the consumer. The total residual moisture in the product powder shall be about 8% (optimum).

Choice of dryer: Batch dryer

A wide range dryer designs are available that can be used to dry the product cream out of the separators. Batch dryers e.g. tray and tunnel dryers are normally used where the relatively small scale production is required, that is the duty of the dryer is
not high. It uses direct heating method (high thermal efficiency), but it cannot produce finely divided product and is therefore do not meet our product requirements. Furthermore the direct heating method is not recommended as it has the tendency to damage
the proteins.

The amount of water need to be evaporated from the incoming cream is calculated as 1555 kg/hr. This is such as to produce the required amount of powdered yeast with optimum moisture content of 8%. This is a high evaporation rate for any batch dryer (Coulson,
1991) and therefore continues dryer is to be used in the process.

Continued in part 3

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Posted by Ahmed Tariq on Feb 21 2012. Filed under Sci-Tech. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry